Download : DRIVER LASERJET 1005
Klik downloadnya, tunggu 5 detik, di pojok kanan atas, klik SKIP AD, maka akan terbuka halaman downloadnya.
Kamis, 10 Oktober 2013
Driver Printer Laserjet 1005 - 1008 For WIN 7 WIN 8
Printer ini memang cukup handal untuk kerja berat dan efisien terhadap pemakaian tinta, jadi cukup banyak digunakan di kantor, kampus dan sekolah. Bagi anda yang membutuhkan driver printer LASERJET 1005, dapat di download disini, semoga bermanfaat.
Download : DRIVER LASERJET 1005
Klik downloadnya, tunggu 5 detik, di pojok kanan atas, klik SKIP AD, maka akan terbuka halaman downloadnya.
Download : DRIVER LASERJET 1005
Klik downloadnya, tunggu 5 detik, di pojok kanan atas, klik SKIP AD, maka akan terbuka halaman downloadnya.
Senin, 24 Desember 2012
Trik dan Tips Fotografi
1. ISO/ASA/DIN
2. Aperture/Bukaan Diafragma
3. Speed
Dicoba set ISOnya berapa, aperturenya berapa, sama speednya berapa. coba kombinasi sendiri dan lihat hasilnya seperti apa, dibedakan dengan setting AUTO. 1. ISO/ASA/DIN (ISO=istilah internasional, ASA=istilah jepang, DIN=istilah eropa, kesemuanya sama aja)
ini adalah standar internasional untuk “kepekaan film negatif/CCD menyerap cahaya”. tambah tinggi angkanya, tambah peka media tersebut menyerap cahaya. kalo jaman dulu lo suka beli film negatif ke fuji, dengan ASA 200, ASA 400, dsb. ya itulah dia. karakternya kayak begini:
a. Bila memakai ISO tinggi (misal: ISO 800, ISO 1200, ISO 1600)
penyerapan cahaya makin peka. bagus buat night shot. kemungkinan gambar shaking akan lebih kecil, karena karakternya yg kuat menyerap cahaya, jadi bisa motret dengan speed tinggi yang mengurangi efek shaking dari tangan lo yang bergetar saat memotret. Kekurangannya, semakin tinggi ISO, noise warna makin banyak karena sifatnya yang sangat peka itu. jadi, kalau memotret pake ISO tinggi, hasil cetakan foto akan lebih jelek kalau diperbesar. efek noise atau grainy-nya sangat mengganggu.
b. kalo ISO rendah (misal: ISO 200, ISO 100, ISO 75, ISO 25)
Penyerapan cahaya makin kurang peka. bagus buat daylight shot, atau ketika cahaya cukup memadai. tapi begitu memotret di tempat yg agak gelap, akan sangat sulit memotret dengan speed tinggi. kemungkinan shaking lebih besar, dan pemakaian tripod jadi sebuah keharusan. tapi kelebihannya, semakin rendah ISO, noise warna makin sedikit karena sifatnya yang tidak peka itu. jadi, kalo ISO rendah, hasil cetakan foto jika diperbesar, akan tetep bagus dan bening. efek noise atau grainy-nya bisa dibilang tidak terlihat.
kelebihan kamera digital sekarang, kamu bisa nge-set ISOnya kapanpun mau. begitu cahaya agak gelap, naikan ISOnya. begitu terang, ya gak usah pake ISO tinggi-tinggi, tinggal di set aja di menunya. beda sama jaman film dulu, kalo beli film yg ISO 200, ya musti ganti film dulu buat ganti ISO.
2. aperture/bukaan diafragma (simbolnya: f/…)
diafragma, fungsinya sama persis dengan pupil mata kita. yaitu, mengatur seberapa banyak intensitas cahaya yang akan masuk jatuh ke retina-mata/film negatif/CCD untuk selanjutnya diolah di otak/memory-card sebagai sebuah visual/gambar. di dunia fotografi, ditetapkan angka2 tertentu untuk menentukan seberapa lebar bukaan diafragma. contohnya, ada bukaan f/2.8, bukaan f/4, f/5.6, f/8, f/11, f/16, f/22. setiap angka bukaan itu, punya karakternya masing-masing. yang perlu menjadi catatan penting di sini adalah, semakin kecil angka diafragma maka semakin lebar bukaan diafragmanya, dan semakin besar angka diafragma maka semakin kecil bukaan diafragmanya.
misal: angka 2.8 memiliki bukaan lebar, sedangkan angka 22 memiliki bukaan sempit.
bukaan lebar (misal: f/2.8 ), memiliki karakter yang akan membuat intensitas cahaya banyak masuk ke film-negatif. efek pada gambar adalah, objek fokus akan sangat detail sedangkan background/foregroundnya akan kabur/blur/bokeh. bukaan ini sering dipakai untuk foto potret dimanaa lo pengen gambar yang hanya tajam di objek dan kabur di backgroundnya.
bukaan sempit (misal: f/22), memiliki karakter yang akan membuat intensitas cahaya sedikit masuk ke film-negatif. efek pada gambar adalah, tidak hanya objek fokus yang akan sangat detail, background/foregroundnya akan juga ikutan detail. bukaan ini sering dipakai untuk foto landscape dimana lo pengen gambar yang tajam dari ujung dekat ke ujung jauh.
ngerti cara kerja diafragma, berarti lo harus paham apa itu Depth of Field (DOF). atau bahasa indonesianya, ruang tajam gambar. bukaan lebar, DOF akan semakin sempit. bukaan sempit, DOF akan semakin lebar.
nah, diafragma sama speed, hubungannya sangat kuat. semakin lebar bukaannya, maka semakin gampang lo ambil gambar high-speed karena intensitas cahaya yang banyak. sebaliknya, semakin sempit bukaannya, akan terasa sulit mendapatkan high-speed karena intensitas cahayanya yang berkurang, yg mana pemakaian tripod untuk menghindari hand-shaking menjadi sangat mutlak.
3. speed
nah kalo yang ini, dah pada tau lah artinya apa. adalah kecepatan interval mirror di kamera membuka dan menutup saat menangkap gambar. semakin cepat speednya, kamu bisa dapet gambar yang freeze/beku.
kalo lo motret air mancur dengan speed tinggi, gambar airnya bakalan dapet bulet2 gitu.
(Coba pake speed 1/8000 sec, f/3.8, ISO200.)
kalo lo pake low-speed, kamu bakalan dapet gambar dengan efek gerakan, contoh speed 1/15 sec, f/4.5, ISO 200.
nah, yang terakhir untuk kesimpulan dari segitiga fotografi:
4. metering
usahain saat motret, metering ada di posisi nol. nggak mutlak sih, tapi untuk dapet cahaya yg pas, mending diusahain di posisi nol. metering, cuma ada di kamera SLR. kamera pocket, saya blm pernah liat. icon metering, ada di viewfinder saat lo motret. kurang lebih bentuknya kayak gini: (+_____|_____-) nah usahain, pointernya ada di tengah. kalo pointernya agak menjorok ke arah plus, berarti hasil gambar lo akan Over Exposure (terlalu terang). kalo pointernya agak menjorok ke arah minus, berarti hasil gambar lo akan Under Exposure (terlalu gelap). pengaturan metering adalah dengan cara maen2in bukaan diafragma, speed, dan ISO-nya, diturunin atao dinaekin, terserah elo pengen jadi gambar gimana.
sebenernya, di jaman digital gini dimana kamera semakin canggih, masih ada satu bahasan lagi tentang dasar-dasar fotografi, selain segitiga fotografi yang saya terangkan di atas, yaitu:
5. white balance (WB)
white balance adalah seberapa besar kamera menyesuaikan sensitifitasnya terhadap cahaya yang ada (available light) untuk menyamakan warna putih yang “sebenarnya” pada kondisi cahaya tertentu, agar bisa mendapatkan warna-warna yang true color. sayangnya, kamera2 jaman dulu belom ada fitur setting WB ini. tapi, untuk kamera2 digital jaman sekarang, udah ada.
ngomongin white balance, musti tau dulu definisi apa itu “warna putih sempurna”. ketika sebuah besi baja dibakar, maka baja tersebut akan berubah warna sampai memerah, jika terus dibakar maka baja tersebut semakin panas hingga berwarna putih, dan jika masih terus dibakar maka akan berubah berwarna biru.
nah warna putih sempurna, akan didapatkan ketika baja tersebut dibakar berubah menjadi warna putih suci. kalo saya nggak lupa (CMIIW), suhu baja tersebut saat berwarna putih adalah berkisar antara 5200-5400K (derajat kelvin). nah, itu yang dinamakan putih sempurna. kalo warna putihnya kemerahan, berarti suhunya di bawah 5200K. kalo warna putihnya kebiruan, berarti suhunya di atas 5400K.
saat memotret, kita akan mendapatkan kondisi sumber cahaya yang berbeda-beda, yang mana akan berpengaruh pada objek yang warna putih. kalo setting WB kita asal2an, atau kita set auto, kadang kita nggak puas sama warna yang kita mau, alias warnanya nggak keluar. kalo kita nggak nge-set WB secara manual, kadang warna putih yang kita dapatkan akan kebiruan, atau kemerahan. di saat seperti itu, kita perlu setting WB secara benar. di setiap kamera, cara setting WB berbeda-beda, bisa dibaca di manualnya masing2.
kalo lo udah kuasain konsep segitiga fotografi ini, dijamin gambar lo bagus2. tapi itu baru dasarnya banget. baru sekedar cara untuk memotret. selebihnya, banyak2 ngejepret + tambahin belajar konsep, angle, komposisi, lighting, dan tentu saja…moment!!! karena, cabang2 fotografi masih banyak lagi dah lebih dalam lagi kalo mau diexplore.
Jumat, 16 November 2012
Shalat Subuh menyimpan Berjuta Rahasia
Dari sisi rohani, Shalat Subuh mempunyai banyak keutamaan, di antaranya menyelamatkan dari azab, mendapat pahala setara pahala haji dan umrah, terbebas dari api neraka, terhindar dari kemunafikan, serta mendapat perlindungan dari Allah subhanahu wa ta’ala.
Rasulullah Shallallahu’alaihi Wasallam bersabda “Berpagi-pagilah kalian dalam menunaikan Shalat Subuh karena itulah pahala yang paling mulia.” (Hadist Riwayat Turmudzi).
Dari sisi kesehatan, bangun pagi untuk melaksanakan Shalat Subuh pun mampu menormalkan kinerja syaraf dan otak. Apalagi saat pagi hari kadar ozon (O3) cukup tinggi yang mampu membantu aktivitas syaraf dan otak. Termasuk mengurangi risiko penyumbatan pembuluh darah dan serangan jantung.
Bahkan, Shalat Subuh bermanfaat bagi kesuksesan dalam kehidupan. Sebab, saat pagi hari sampai fajar pintu-pintu rezeki di buka oleh Allah subhanahu wa ta’ala. Karena itu, setelah melaksanakan Shalat Subuh dilarang tidur kembali, sebaliknya sangat dianjurkan mulai beraktivitas, berzikir, dan berdoa.
Menyingkap 1001 Hikmah Shalat Subuh
“Sesungguhnya amal manusia yang pertama kali dihisab pada hari kiamat adalah shalatnya” Jika shalatnya baik, maka baik pula seluruh amalnya; dan kalau jelek, maka jeleklah seluruh amalnya. Bagaimana mungkin seorang mukmin mengharapkan kebaikan di akhirat, sedang pada hari kiamat bukunya kosong dari shalat Subuh tepat waktu?
“Sesungguhnya shalat yang paling berat bagi orang munafik adalah shalat Isya’ dan shalat Subuh. Sekiranya mereka mengetahui apa yang terkandung di dalamnya, niscaya mereka akan mendatangi keduanya (berjamaah di masjid) sekalipun dengan merangkak” [HR Al-Bukhari dan Muslim]
Shalat Subuh memang shalat wajib yang paling sedikit jumlah rekaatnya; hanya dua rekaat saja. Namun, ia menjadi standar keimanan seseorang dan ujian terhadap kejujuran, karena waktunya sangat sempit (sampai matahari terbit)
Ada hukuman khusus bagi yang meninggalkan shalat Subuh. Rasulullah saw telah menyebutkan hukuman berat bagi yang tidur dan meninggalkan shalat wajib, rata-rata penyebab utama seorang muslim meninggalkan shalat Subuh adalah tidur.
“Setan melilit leher seorang di antara kalian dengan tiga lilitan ketika ia tidur. Dengan setiap lilitan setan membisikkan, ‘Nikmatilah malam yang panjang ini’. Apabilaia bangun lalu mengingat Allah, maka terlepaslah lilitan itu. Apabila ia berwudhu, lepaslah lilitan yang kedua. Kemudian apabila ia shalat, lepaslah lilitan yang ketiga, sehingga ia menjadi bersemangat. Tetapi kalau tidak, ia akan terbawa lamban dan malas”
“Berikanlah kabar gembira kepada orang-orang yang banyak berjalan dalam kegelapan (waktu Isya’ dan Subuh) menuju masjid dengan cahaya yang sangat terang pada hari kiamat” [HR. Abu Dawud, At-Tarmidzi dan Ibnu Majah]
Allah akan memberi cahaya yang sangat terang pada hari kiamat nantinya kepada mereka yang menjaga Shalat Subuh berjamaah (bagi kaum lelaki di masjid), cahaya itu ada dimana saja, dan tidak mengambilnya ketika melewati Sirath Al-Mustaqim, dan akan tetap bersama mereka sampai mereka masuk surga, Insya Allah.
“Shalat berjamaah (bagi kaum lelaki) lebih utama dari shalat salah seorang kamu yang sendirian, berbanding dua puluh tujuh kali lipat. Malaikat penjaga malam dan siang berkumpul pada waktu shalat Subuh”. “Kemudian naiklah para Malaikat yang menyertai kamu pada malam harinya, lalu Rabb mereka bertanya kepada mereka – padahal Dia lebih mengetahui keadaan mereka – ‘Bagaimana hamba-2Ku ketika kalian tinggalkan ?’ Mereka menjawab, ‘Kami tinggalkan mereka dalam keadaan shalat dan kami jumpai mereka dalam keadaan shalat juga’. ” [HR Al-Bukhari]
Sedangkan bagi wanita – walau shalat di masjid diperbolehkan shalat di rumah adalah lebih baik dan lebih banyak pahalanya, yaitu yang mengerjakan shalat Subuh pada saat para pria sedang shalat di masjid. Ujian yang membedakan antara wanita munafik dan wanita mukminah adalah shalat pada permulaan waktu.
“Barang siapa yang menunaikan shalat Subuh maka ia berada dalam jaminan Allah. Shalat Subuh menjadikan seluruh umat berada dalam jaminan, penjagaan, dan perlindungan Allah sepanjang hari. Barang siapa membunuh orang yang menunaikan shalat Subuh, Allah akan menuntutnya, sehingga Ia akan membenamkan mukanya ke dalam neraka” [HR Muslim, At-Tarmidzi dan Ibnu Majah]
Banyak permasalahan, yang bila diurut, bersumber dari pelaksanaan shalat Subuh yang disepelekan. Banyak peristiwa petaka yang terjadi pada kaum pendurhaka terjadi di waktu Subuh, yang menandai berakhirnya dominasi jahiliyah dan munculnya cahaya tauhid. “Sesungguhnya saat jatuhnya adzab kepada mereka ialah di waktu Subuh; bukankah Subuh itu sudah dekat?” (QS Huud:81)
Rutinitas harian dimulainya tergantung pada pelaksanaan shalat Subuh. Seluruh urusan dunia seiring dengan waktu shalat, bukan waktu shalat yang harus mengikuti urusan dunia.
“Jika kamu menolong (agama) Allah, maka ia pasti akan menolongmu dan meneguhkan kedudukanmu” (QS
Muhammad : 7)
“Sungguh Allah akan menolong orang yang menolong agamanya, sesungguhnya Allah Maha Kuat dan Maha Perkasa” (QS Al-Hajj:40)
TIPS MENJAGA SHALAT SUBUH :
- Ikhlaskan niat karena Allah, dan berikanlah hak-hak-Nya
- Bertekad dan introspeksilah diri Anda setiap hari
- Bertaubat dari dosa-dosa dan berniatlah untuk tidak mengulangi kembali
- Perbanyaklah membaca doa agar Allah memberi kesempatan untuk shalat Subuh
- Carilah kawan yang baik (shalih)
- Latihlah untuk tidur dengan cara yang diajarkan Rasulullah Shallallahu’alaihi Wasallam (tidur awal; berwudhu sebelum tidur; miring ke kanan; berdoa)
- Mengurangi makan sebelum tidur serta jauhilah teh dan kopi pada malam hari
- Ingat keutamaan dan hikmah Subuh; tulis dan gantunglah di atas dinding
- Bantulah dengan 3 buah bel pengingat(jam weker; telpon; bel pintu)
- Ajaklah orang lain untuk shalat Subuh dan mulailah dari keluarga
Fadhilah Shalat Subuh
Di antara shalat-shalat yang ada, shalat subuh adalah yang mengawali hari. Ia adalah shalat yang paling penting yang harus dijaga betul pelaksanaannya, sebab tidak semua orang bisa konsisten, bahkan shalat ini terasa berat bagi orang-orang munafik.“Shalat yang paling berat bagi orang-orang munafik adalah shalat isya’ dan shalat subuh” (HR.Ahmad)
Shalat subuh berjamaah adalah tolok ukur sejauh mana kejujuran dan keimanan seorang muslim. Di dalam sebuah riwayat shahih bahwa Ibnu Umar ra pernah berkata:
“Ketika kami tidak melihat seseorang dalam shalat subuh atau isya’, kami langsung berprasangka buruk kepadanya.”
Ini wajar, mengingat shalat-shalat lain selain subuh dan isya bisa dilakukan oleh seseorang dengan mudah karena memang waktunya bertepatan dengan saat bekerja dan terjaga. Oleh karena itu tidak ada yang mampu konsisten menjaga shalat isya’ dan subuh secara berjamaah selain orang beriman yang diharapkan ada kebaikan muncul darinya.
Karena hal tersebut di atas, maka banyak keutamaan yang didapatkan dari shalat subuh berjamaah, di antaranya:
1. Shalat subuh adalah faktor dilapangkannya rizki
Seorang hamba walau sezuhud apapun dan sangat tidak peduli dengan urusan dunia, ia tetap senang kalau lapang rizkinya minimal mencukupi kebutuhan diri sendiri untuk menyelamatkan muka dari hinanya meminta-minta. Dan demi Allah untuk mencapai ini jalannya adalah dengan menaati Allah.
Pernah suatu ketika Nabi Muhammad Shallallahu’alaihi Wasallam shalat subuh. Begitu selesai, beliau pun kembali ke rumah dan mendapati puterinya Fathimah ra sedang tidur. Maka beliau pun membalikkan tubuh Fatimah dengan kaki beliau, kemudian mengatakan kepadanya : “Hai Fathimah, bangun dan saksikanlah rizki Rabb-mu karena Allah membagi-bagikan rizki para hamba antara shalat subuh dan terbitnya matahari.”
Ini bukan berarti orang yang melaksanakan shalat subuh pasti pulang dengan kantong penuh uang, tetapi yang dimaksud adalah bahwa ketaatan kepada Allah dengan cara menjaga untuk terus istiqomah dalam shalat subuh berjamaah akan mendatangkan taufik dari Allah sehingga nantinya seorang hamba memperoleh keridhoan dan kelurusan dari Rabb-nya yang pada gilirannya ia akan menghabiskan sisa harinya dalam pertolongan dan kemudahan dari Allah dalam urusan-urusannya.
“Barang siapa yang bertakwa kepada Allah, niscaya Dia akan mengadakan baginya jalan keluar. Dan memberinya rizki dari arah yang tidak disangka-sangkanya”
(QS.Ath Thalaq : 2-3)
2. Shalat subuh menjaga diri seorang muslim
“Barang siapa yang melaksanakan shalat subuh maka dia berada dalam jaminan Allah, maka jangan sampai Allah menarik kembali jaminan-Nya dari kalian dengan sebab apa pun. Karena siapapun yang Allah cabut jaminan-Nya darinya dengan sebab apa pun, pasti akan tercabut. Kemudian Allah akan telungkupkan wajahnya dalam neraka jahannam.” (HR.Muslim)
Makna berada dalam jaminan Allah adalah dalam lindungan, penjagaan, dan pemeliharaan dari-Nya. Sungguh itu semua adalah rahmat, yang kalau menaungi kita, maka semua kepedihan berubah menjadi harapan. Sungguh itu semua adalah kelembutan Allah, yang jika turun kepada kita akan sanggup menjadikan api menjadi dingin dan damai. Itulah hikmah, kemuliaan, dan kehendak yang tak terkalahkan. Jika ia datang, mampu merubah musuh menjadi teman setia, dan mampu merubah singa yang buas menjadi kucing yang penurut.
3. Shalat subuh sama dengan shalat malam semalam suntuk
Alangkah besar keutamaan yang Allah berikan kepada umat ini. Pertama kali, Allah wajibkan shalat malam dalam firman Allah yang artinya:
”Wahai orang yang berselimut bangunlah untuk shalat di malam hari kecuali sedikit” (QS.Al Muzzammil : 1-2)
Setelah itu Allah menghapus perintah tersebut sebagai bentuk peringanan dalam firman-Nya dalam QS.Al Muzzammil : 20.
Setelah menghapuskan kewajiban shalat malam, Allah tetap menetapkan bagi kita keutamaannya sebagaimana hadits berikut:
”Barang siapa yang melaksanakan shalat isya’ secara berjamaah maka ia seperti shalat malam separuh malam. Dan barang siapa melaksanakan shalat subuh secara berjamaah maka ia seperti shalat malam satu malam penuh.” (HR.Muslim)
Maka usahakanlah untuk tidak menyia-nyiakan kesempatan emas ini. Oleh karena itu para ulama ada yang memakruhkan begadang hingga terlalu larut malam walaupun untuk membaca Al Qur’an atau shalat malam jika akan berakibat tidak terlaksananya shalat subuh dengan baik. Tetapi jangan salah paham dulu, para salafus shalih selalu melaksanakan shalat isya’ dan subuh secara berjamaah tetapi mereka tetap bersemangat tanpa henti dalam melaksanakan shalat malam.
4. Shalat subuh tolok ukur keimanan
Orang yang mengaku beriman tidak perlu sulit-sulit mengetahui kadar keimanannya, ia cukup mengukurnya dengan shalat subuh untuk mengetahui apakah dirinya termasuk jujur dalam beriman ataukah berdusta, apakah ia beriman di atas keikhlashan ataukah riya.
Rasulullah Shallallahu’alaihi Wasallam bersabda: “Shalat terberat bagi orang-orang munafik adalah shalat isya’ dan subuh. Padahal seandainya mereka mengetahui pahala pada kedua shalat tersebut, tentu mereka akan mendatanginya walaupun harus merangkak .” (HR.Ahmad)
5. Shalat subuh adalah penyelamat dari neraka
Nabi Muhammad Shallallahu’alaihi Wasallam bersabda, “Tidak akan masuk neraka, orang yang melaksanakan shalat sebelum matahari terbit dan sebelum tenggelamnya.” (HR.Muslim)
Ini adalah ketetapan Nabi yang mulia, bahwa siapa yang memelihara pelaksanaan shalat subuh dan ashar maka dia tidak akan masuk neraka dengan izin Allah subhanahu wa ta’ala.
6. Shalat subuh adalah penyebab orang masuk surga
Nabi Muhammad Shallallahu’alaihi Wasallam bersabda, “Siapa yang melaksanakan dua shalat bardain dia masuk syurga” (HR.Bukhari).
Shalat bardain adalah shalat subuh dan ashar. Disebut Al Bardain (dua waktu dingin) karena keduanya dilaksanakan pada waktu dinginnya siang, tepatnya pada kedua ujung siang ketika suasana teduh dan tidak ada terik panas.
7. Shalat subuh akan mendatangkan nikmat berupa bisa melihat wajah Allah yang mulia
“Apabila penghuni syurga telah memasuki syurga. Allah berfirman,’Apakah kalian ingin akuberi tambahan ?’ Mereka menjawab,’Bukankan Engkau telah memutihkan wajah-wajah kami? Bukankan Engkau telah memasukkan kami ke dalam syurga? Dan Engkau selamatkan kami dari neraka?’ Rasulullah melanjutkan,”Kemudian dibukalah tabir, maka tidak ada lagi nikmat yang lebih besar daripada nikmat bisa melihat Rabb mereka. Inilah nikmat tambahan itu.” Lalu beliau membaca surat Yunus : 26 yang artinya: “Bagi orang-orang yang berbuat baik ada pahala yang terbaik jannah dan tambahannya.” (HR.Muslim)
8. Shalat subuh adalah suatu syahadah khususnya bagi yang konsisten memeliharanya
“Malaikat-malaikat siang bergantian mendampingi kalian dengan malaikat-malaikat malam, dan
mereka berkumpul pada waktu shalat subuh dan ashar setelah itu malaikat yang semalaman menjaga kalian naik ke langit. Lalu Allah bertanya kepada mereka – dan dia lebih tahu tentang mereka – ,’Bagaimana kalian tinggalkan hamba-hambaku?’ Mereka menjawab,’Kami menginggalkan mereka dalam keadaan shalat dan kami datang kepada mereka ketika mereka shalat’” (HR.Bukhari)
9. Shalat subuh adalah kunci kemenangan
“Bahwa Rasulullah apabila hendak menyerbu suatu kaum, beliau menundanya hingga tiba waktu subuh.” (HR Bukhari)
Dikisahkan pasca meletusnya perang Mesir-Israel tahun 1973 ada seorang tentara Mesir yang mengajak berbicara tentara Yahudi yang paham bahasa Arab.
Tentara Mesir itu berkata, “Demi Allah, kami akan memerangi dan mengalahkan kalian sampai ada di antara kalian yang bersembunyi di balik pohon dan batu, kemudian pohon dan batu itu mengatakan,’hai hamba Allah, hai Muslim, ini ada Yahudi di belakangku, ke mari dan bunuhlah dia’”
Tentara Yahudi menjawab,”Semua itu tidak akan terjadi sebelum shalat subuh kalian sama dengan shalat Jumat.”
10. Shalat subuh lebih baik daripada dunia seisinya “Dua rakaat shalat subuh, lebih baik daripada dunia dan
seisinya.” (HR.Muslim dan Ahmad)
Mengenai shalat dua rakaat sunah sebelum subuh Rasulullah bersabda, “Dua rakaat itu lebih aku sukai daripada dunia seluruhnya.” (HR.Muslim)
Rabu, 25 Mei 2011
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Sabtu, 16 Januari 2010
Hanjeli, dapatkah menggantikan beras
Sebagian petani di desa Sukarasa kecamatan Darma Kab. Kuningan enggan menanam padi, lebih manyukai menanam hanjeli. Tindakan itu disebabkan harga gabah pada saat ini sedang anjlok di pasaran. Justru harga hanjeli relatif lebih stabil dibanding harga gabah.
Sumber : id.wordpress.com (2010).
Harga gabah kering dari tangan petani sekira Rp. 1.200 sampai Rp. 1.500/Kg, sedangkan hanjeli mentah harganya Rp.1.500/kg, setelah diproses menjadi bubur hanjeli seharga Rp.3.000/Kg. Harga hanjeli yang menggiurkan itu membuat para petani desa Sukarasa meninggalkan padi.
Menurut keterangan Hj. Inoh (54) seorang petani sekaligus penampung hanjeli di desa Sukarasa saat ditemui. Hanjeli merupakan makanan pokok alternatif setelah beras, jagung dan gandum. Hanjeli dapat menggantikan fungsi beras, sebab jika diolah akan menghasilkan beras dan tepung hanjeli.
“Beras dan tepung hanjeli, sekarang ini telah menjadi bahan pokok alternatif khususnya di kota-kota besar. Selain harganya lebih murah juga rasanya tidak jauh berbeda dengan nasi jika sudah ditanak,” tandas Hj. Inoh.
Selama ini yang mengkonsumsi beras dan tepung hanjeli, tutur Hj. Inoh, masih kebanyakan orang WNI keturunan. Sedangkan warga masyarakat Indonesia belum sepenuhnya mengenal. Padahal bagi masyarakat yang suka jajan di rumah makan milik orang Tionghoa, bubur yang digunakannya yakni bubur hanjeli. Hanjeli memang relatif tidak dikenal, mungkin di Kab. Kuningan hanya di desa Sukarasa saja yang menanamnya.
Padahal pembudidayaannya sudah berlangsung sepuluh tahun yang lalu, atas prakarsa Hj. Inoh sepulang dari tanah Mekah. Tiba-tiba ada salah seorang warga Tionghoa yang mengenalkan jenis tanaman mirip gandum. Semula dirinya tidak tertarik untuk menanam, tapi setelah diyakinkan oleh warga Tionghoa, dan siap untuk membantu pemasarannya maka Hj. Inoh menanamnya. Lama-kelamaan dirinya tertarik dan lebih serius membudidayakannya. Musim panen sekarang ia menanam hanjeli seluas 3 hektar, dan siap dipanen dua bulan di muka.
“Hanjeli merupakan tumbuhan tanpa kambium, seperti pohon jagung atau gandum. Buahnya bulat kecil-kecil, jika belum matang warna hijau sedangkan yang matang warnanya merah hati. Jika dibelah oleh kuku, dagingnya berwarna putih lunak,” tutur Hj.Inoh.
Warga masyarakat disini pun, sekarang ini sudah jarang menanam padi. Jika dijumlahkan lahan yang ditanami hanjeli seluruhnya sekira 10 ha. Perubahan orientasi petani dikarenakan perhitungan untung rugi, jika jenis tanaman hanjeli lebih menguntungkan kenapa tidak? Kalau padi dapat memberikan keuntungan bagi petani, mungkin mereka juga akan menanam padi.
Selain itu, kata Hj. Inoh, pasar sudah membuka diri terhadap hanjeli sehingga pihak petani tidak merasa dipusingkan oleh fluktuatifnya harga. Pasar potensial bagi pemasaran hanjeli adalah Cirebon, Jakarta dan Surabaya. Cirebon prosentasenya paling tinggi sekira 70 persen, dibanding daerah-daerah lain, kedua Jakarta dan ketiga Surabaya. Kami tidak tahu apakah di Cirebonnya hanya untuk dikonsumsi oleh lingkungannya sendiri atau menjual kembali ke pedagang besar lainnya.Sumber : id.wordpress.com (2010).
Sabtu, 05 Desember 2009
PHOTOSYNTHESIS
PHOTOSYNTHESIS
The free chemical energy required for life processes is derived from organic food materials by a process called biological oxidation. If organisms are allowed to utilize the existing food materials on this planet, it will be exhausted in no time. However, nature has devised a unique mechanism by means of which it replenishes the organic food materials in excess and this is achieved by harnessing the solar energy by plants.
Definition: Photosynthesis can be defined as a “series of processes in which solar electro magnetic radiation energy (SEMR) is captured, converted and conserved in the form of chemical energy by green plants”. Biochemically this process can also be defined “as light sensitized Red-Ox process” for it involves light induced Oxidation-Reduction processes.
Solar Energy
Sun emits light in the form of solar electro magnetic radiation (SEMR) of which only 40% reaches the surface of earth and rest is absorbed by O2, O3, CO2, dust and H2O present in outer atmosphere of the earth. Out of this only 1% is used by land plants which form about 15% of total plant population, and oceanic plants (about 85%) in fixing a total of 35-146 billion tones of carbon every year which is equivalent to 1.8-13 x 1012 K.Cals, of chemical energy.
SEMR Spectrum: The SEMR spectrum is quite large, consisting of cosmic rays at one extremity and radio waves at the other, of which, plants use only blue and red parts of the visible for photosynthesis. Light travels in waves, in the form of discrete energy packets called photons. The energy content of each photo varies and depends upon the frequency and speed of the light. For example, light with shorter wavelength has more energy than the light with longer wave length (Blue light has more energy than the red light). Einstein of Red light (700 nm) has 80 K. cal. per mole-1.
Historical Account
Though Aristotle observed the effect of light on greening of the plants, it was Joseph Priestley who discovered that the plants are capable of purifying the air and called this process as dephlogistication. But Jan Ingen Houze demonstrated that plants can dephlogistication the air (by liberating O2) only in the presence of light. In dark, plants and animals behave similarly by releasing CO2 and phlogisticating the air (impurifying the air). However, it was Jean Senebier, who postulated that plants fix the atmospheric CO2 (fixed air) into organic compound and the oxygen that is liberated comes from CO2.
Plants – O2 (Priestley)
Light
Plants --- O2 (Jan Ingen Houze)
Light
Plants + CO2 --- Organic carbon + O2 (Jean Senebier)
At this juncture, Nicholas Theodore de Saussure postulated that H2O is used up in fixing the CO2 into organic compounds. This was an important step in understanding photosynthesis.
Light light
H2O + CO2 ------------- C + O2 C + H2O ---- (CH2O) n
plant plants
Robert Mayer, who was responsible for the theory, “that energy can neither be created nor destroyed”, clearly elucidated that the plants capture solar energy and store it in the form of chemical energy.
Meanwhile the importance of chloroplast and chlorophyll in fixing CO2 in the presence of light was made clear. But people still believed that the oxygen that is liberated during photosynthesis comes from the splitting of CO2 into C and O2. However it was Robert Hill and Van Neil using radio active isotopes demonstrated that the oxygen that is liberated comes from the H2O and not from CO2 as it was believed earlier.
4H2O ----------- 2H2 + 2O2
Since then numerous workers have contributed their part in understanding various aspects of photosynthesis. Blackman, Calvin, Arnon, Emerson, Park, Sanpeitro, Govindjee, Ellis, Parker, are the notables among the stalwarts who have made significant contributions in understanding the structure and functional aspects of Photosynthesis.
Photosynthetic Organelles: Chloroplasts
Plastids are the unique organelles found exclusively in plants (with the exception of fungi).
A fully developed chloroplast is bounded by a double membrane system within which, a fluid or a matrix called stroma is found. In this liquid 30-40 highly organized circular membranous structures are found. These are called Grana. Each Granum is made up 10-100 circular flat membranous discs called thylakoids. In these thylakoids the photosynthetic pigments and their associated pigments are organized into photosynthetic units. Refer page No.190 for the details of chloroplast structure.
If thylakoids are cut open by freeze fracture method and observed under an electron microscope, four surfaces can be made out as shown in the (fig). These surfaces are studded with numerous granular structures. Those structures found in the inner core of the membranes are called Quantasomes which act as photosynthetic units.
Photosynthetic units: Park and Branton discovered the presence of array crystalline particles, associated with the protein curried in thylakoid membranes. Such particles are called Quantasomes, which are nothing but photosynthetic units which are capable of absorbing solar energy as well as performing photo-chemical reactions. The larger particle is P.S-II and the smaller is P.S-I. Park and Sane have succeeded in isolating P-S-I and P.S-II by sonication and differential ultra centrifugation methods. This has led to the study of chemical analysis and function of each of these units.
Photosynthetic Unit I: It is smaller of the two photo-systems. The inter-granal lamellae or stromal lamellae have just P.S-I particles. But the granal thylakoid membranes are associated with P.S-II system. P.S-I is made up of 230-250 chlorophyll-a molecules. Along with the chlorophyll-b, Carotenoids, 25 K.D light harvesting proteins and unique molecule called chlorophyll-a 700, which exists in the form of a dimmer, are also present. This system is also associated with Fe-S containing Ferrodoxin (a reducing substance), a non heme-iron protein called Ferrodoxin (FRS), Cytochrome-b 6, and Plastocyanin and ATP dependent NADP reductase. In inter-granal lamellae cyclic photo-phosphorylation occurs, but in granal membranes the reduction of NADP to NADPH2 occurs. Recently Arnon came out with a view that P.S-I is totally absent in granal membranes but it is found only in stromal lamellae.
Photosynthetic Unit II: It is the larger photosynthetic unit, exclusively found or restricted to granal membranes. It is made up of a number of chlorophyll-a (more), chlorophyll-b, Carotenoids, 25 K.D. light harvesting proteins, specific Mn2* associated Z-protein complex (32 KD), Pheophytin, Plasto Quinone and Cytochrome-b 559. It also has a unique, Chlorophyll-a 680 molecule which exists in the form of a dimmer. Its major function is to liberate O2 and donate electrons to P.S-I system. However Arnon feels that the originally believed P.S-I involved in the reduction of NADP is not P.S-I but it is another form of P.S-II system. Only time will tell the reality of its structure and function.
Transfer of energy: These two photo systems with their respective pigments and light harvesting proteins are oriented in the membrane in such a way; they can capture the fleeting photons randomly. All the molecules in each of these photo-synthetic units are spaced and oriented in such a way, captured photons are transferred from molecule to molecule by a phenomenon called inductive resonance. Here the unit of energy that is transferred to as exciton. The transfer of captured light energy is ultimately drawn to active centers.
Chlorophyll-a --- Chlorophyll-a 680
Carotenoids ---
Chlorophyll-b --- Chlorophyll-a 700
Photosynthetic pigments
Pigment analysis of photosynthetic organelles, shows that chloroplasts contain green pigments (chlorophylls) and yellow pigments (carotinoids). Among chlorophylls, chlorophyll-a acts as the primary pigment and it is present in all photosynthetic organisms, with the exception of photosynthetic bacteria where the primary pigment is Bacteriochlorophyll. All other pigments act as secondary pigments.
Absorption Spectrum: The absorption spectrum of these pigments indicates that, chlorophyll-a shows maximum absorption and at 430 nm (blue light) and 662 nm (red light). Similarly chlorophyll-b has absorption spectrum at 453 nm to 642 nm and carotinoids have an absorption band between 430 nm – 490 nm.
Action spectrum and Enhancement effects
Though individual pigments absorb light at different wave lengths, not all the wave lengths are efficient in photosynthetic process either in terms of oxygen liberation or carbon fixation. If red light or blue light is provided alone, oxygen liberation would be inefficient on the other hand if both the lights are given simultaneously the photosynthesis. Though carotinoids absorb light at green and orange regions, instead of direct action, they transfer the energy to other pigments like chlorophyll-b and chlorophyll-a for effective function.
Mechanism of Photosynthesis
The process of light capturing and carbon dioxide fixation are separated by time and space. Structurally Grana perform the photochemical act by capturing, converting and conserving the solar energy in the form of chemical bonds in ATP and NADPH + H*. This is also involved in the liberation of O2. In this primary process, though certain steps are temperature dependent, others are light dependent and temperature independent reactions.
Stromatic fluid is the site for the utilization of light dependent granal products in carbon fixation. As this process is controlled by a number of enzymes, it is considered as a temperature dependent process. However light induced photochemical reactions are extremely fast reactions are relatively slow and take place later as they depend upon the products of light reactions. The entire process can be simplified in the following equation and in the scheme.
Light Reactions
As the first phase of photosynthesis is light dependent, it is referred to as light reaction; however this is also called. Hill’s reaction for, it was first demonstrated by Robert Hill.
Basic principles involved in photosynthesis is capturing of solar electromagnetic radiations at a particular wave length by pigment/protein complexes. The pigments act as antennas for capturing light rays in the form of photons in terms of quantums.
The light captured, with photons containing specific quantum of energy, is translocated among the atoms of pigment, where at a particular site an electron accepting the light energy jumps to a higher orbit. The orbit to which it jumps depends upon the amount of energy a captured photon provides. In the orbit the excited (higher energy electron) electron stays for a very short period of time, say -10^ 14 sec and then drops to down to the next lower orbit where it stays only for a very short time, then it falls back to its original orbit (ground state).
During downward fall the energy rich electron can be transferred to another compound. Thus the light energy accepted by the electron is transferred to another substance. This is a simple explanation of light harvesting process. If the energy rich electron is not used, the captured energy is released either in the form of fluorescence or heat
Photoionization: To begin with, the absorption of photons of SEMR by pigment systems makes them excited.
Chlorophyll + Protein complex + light --- Chlorophyll -
(Ground state) - protein complex (CPC) (excited)
The excited chlorophyll-protein complex reacts with water and splits the water into hydrogen ion (OH-). This phenomenon is called photoionization.
Chlorophyll-protein complex (Excited) + H2O
------- Chlorophyll – Protein complex + H* _ OH – (Ground state)
The photocopied products like H* + OH – ions are simultaneously accepted by the photosystem I and photosytem II respectively, found in granal membranes.
Production of reducing power: It is now certain that the synthesis of NADPH + H* is the co-ordinate function of P.S-I and P.S-II, where P.S-I is directly involved in the reduction of NADP.
When the light strikes the photosystem I units, photons of the SEMR are trapped by a number of antenna like chlorophyll-protein complexes. This energy is transferred from molecule to molecule towards the special molecule called chlrophyll-a 700, which acts as the reaction centre or energy trap. When a Quantum of light energy is conveyed a chlorophyll-a 700, an electron at a particular site gets the energy and it is boosted to the next higher orbit or higher stage of energy.
In this process the energy that is responsible for boosting the electrons is now stored in NADPH + H*. This is a powerful reducing agent required for carbon fixation and it is released into the stromatic fluid as it is synthesized.
As the electrons from chlorophyll-a 700 are lost to NADP, the chlorophyll-700 molecules are rendered electrically positive. If electrons are not provided, these molecules become active and this condition is called photo-bleaching. However the electrons for chlorophyll a 700 come from P.S.II which is also moved in the act of electron transport.
Liberation of oxygen: Along with P.S.I, P.S.II units also capture photons and transfer the excitons to the active centre called chlorophyll-a 680 which exists in the form of a dimer. Similar to chlorophyll-a 700, chlorophyll-680 molecules also boost up the chlorophyll-a 700, chlorophyll-a 680 molecules also boost up the electrons to higher state of energy. As chlorophyll-a exists in dimmers, utilizing 2 Quanta of light, 2 accepted by photo system II, the larger photosynthetic unit of the two, has 32 K.D. Z protein complexed with manganese ions as active centre. With the loss of every electron from the terminal chlorophyll a 680 molecule, an electron is supplied by “Z” protein Mn2+ complex and thus this protein complex gets activated with every photon absorbed.
As a result, the positively charged Mn2*- Z protein complex readily reacts with negatively charged OH ions in water.
One more boosting of a pair of electrons are to be released from Z-Mn complex to receive two more OH – ions. When 4 such OH- ions are brought on to the two Mn-Z protein complexes, in such a way, the OH orbitals may overlap on each other. This may result in reorientation and reaction to produce 2H2O and a molecule of O2. This leaves Z – Mn2* complex free to receive another set of OH ions.
PS –II Z –Mn2* Complex + 4 OH –4 photons
PS II – Z Mn2* + 2H2O + O2
Non-Cyclic Photophosphorylation
The electrons that are boosted to higher state of energy from PS-II Chl a 680 – are immediately accepted by pheophytin.
Then the electrons are shuttled to a labile molecule called plastoquinones (PQ). The molecule simultaneously accepts 2H* ions and 2 electrons and gets reduced to PQH2, which in turn releases the H* protons into inner thylakoid space and simultaneously transfer the electrons to Cytochrome 559. This is accompanied with the loss of small amount of energy is released. This energy is utilized and stored in the terminal bond of ATP molecule. This phenomenon is referred to as non-cyclic photophosphorylation. From Cytochrome f, the electrons reach Chl a 700 through copper containing neutral and now they are ready for another cycle of electron boosting process. Meanwhile, as the electrons are lost from chlorophyll a 680 to chlorophyll a 700 the former molecule becomes positively charged. The electrons that neutralize Chl a 680 come from (OH) ions.
Cyclic photo phosphorylation: Photosynthetic unit-I that is found exclusively in inter granal lamellae is involved in a cyclic electron flow. During the down hill journey of electrons, energy is liberated and the same is utilized in the phosphorylation of ADP + Pi to ATP.
P.S-I absorb photons and energy is conveyed to the terminal Chl a 700 which exists in dimer form. The electrons are boosted to higher orbital, which is accepted by FRS. Then electrons are channeled through a series of electron accepters back to Chl a 700 molecule. When the electrons are transferred from FD to cytochrome b 6and form Cyt b 6 to Cytochrome 1, sufficient amount of energy is released. The energy that is released during this shuttle is due to the difference in the Red-O potential between the oxidant and reductant. This energy is captured and utilized in the formation of a high energy terminal bond of ATP molecule.
Light reaction and its products
During light reaction solar energy is absorbed by chlorophyll light harnessing complex and utilize water for photochemical reaction to produce 3 ATP, 1 NADPH + H*, 2H2O, 1 O2 per cycle of reactions.
Particularly ATP and NADPH + H* are released into stromatic fluid. Oxygen either escapes or it is utilized by respiratory process.
Dark reaction or Calvin Cycle
Stromatic fluid consists of all the enzymes required for carbon dioxide fixation. Calvin et al, have elucidated all the biochemical steps involved in this process. Calvin is probably the one and the only biochemist, who has been awarded the Nobel Prize for this kind of work.
This pathway is also called C 3 pathway, for the first stable intermediate product produced is a 3 Carbon organic acid; further it is these 3 carbon components that play an important role in the synthesis of Glucose. This process takes place in 3 steps: 1) Carbon oxidation 2) Reduction 3) Regeneration.
Carbon Fixation
Ribulose monophosphate (5C) an intermediate component of carbohydrate metabolism first gets phosphorylated by an enzyme Ribulose kinase and a molecule of Ribulose di phosphate is synthesized.
RUMP + ATP – RUDP + ADP. 1
The RUDP (5C) acts as an acceptor of CO2 found dissolved in the stromatic fluid. RUDP carboxylase is responsible for the addition of CO2 to RUDP, when a highly stable 6C compound, formed, break up into two 3 Carbon compounds called 3-Phosphoglyceric acid (PGA).
RUDP + CO2 – 2 PGA 2
(5C) (1C) (3C)
Reduction
Before the 3-PGA gets reduced, the 3-PGA is primed up by phosphorylation by phosphoglycerokinase to produce. Di phosphoglycerate (Di PGA). A molecule of ATP is consumed in the process.
3-PGA + ATP = 1, 3 – DiPGA + ADP
(3C) (3C)
The DiPGA gets reduced by NADPH + 1H*to
Phospho glyceraldehydes (2 PGALD). The enzyme involved is glyceraldehydes dehydrogenase.
DiPGA + NADPH + H = PGALD + NADP + Pi
(3C) (3C)
For the fixation of one molecule of CO2 into 2 molecules of PGALD, one molecule of RUMP, 3 molecules of ATP and 2 molecules of NADPH + H* are required. The sum of Carboxylation and reduction process to produce one molecule of Glucose has been given in the following equation.
6 CO2 + 6 RMP + 18 ATP + 12 NADPH + H* = 12 PGALD + NADP + 18 ADP + 12 Pi
Regeneration
In this process, 12 PGALD are subjected to a regeneration process in which 6 RUMPs initially consumed are regenerated. At the same time one molecule of glucose is produced.
Out of 12 PGALD, five are converted into Dihydroxy Acetone Phosphate (DiHAP) by an isomerase enzyme.
5 PGALD = 5 Di HAP 6
In the next step, 3 molecules of PGALD combine with 3 molecules of Di HAP to form 3 molecules of Fructose-1, 6-Di Phosphate. The enzyme is Aldolase.
3 PGALD + 3 Di HAP --- 3 Fructose-1, 6-Di P
(3c) (3c) (6c)
These Fructose-1, 6 di phosphates are subjected to phosphate action in which one phosphate is removed to produce Fructose-6 phosphates.
3 Fructose-1, 6-diphosphate --- 3 Fructose-6-phosphate.
Out of the 3 Fructose 6-phosphates, one is converted into Glucose 6-phosphate by phosphogluco isomerase.
1 Fructose 6-p ------ I Glucose 6-p
(6c) (6c)
The remaining 2 Fructose-6 phosphates combine with 2 molecules of phosphoglyceraldehyde, to undergo a rearrangement process in which 2 molecules of Xylulose phosphates are produced. The enzyme is transketolase.
2 Fructose6-p + 2 PGALD
(6c) (6c)
= 2 Erythorose-4-p + 2 Xylulose-5-p
Then 2 Erythrose 4-P combine with 2 Dihydroxy acetone-P by another Transketolase enzyme to form a carbon Sedoheptulose-1, 7-diphosphate, which immediately undergoes phosphotase action to produce sedopheptulose7-phosphate.
2 Erythrose-P + 2 Di HAP
(4c) (3c)
= 2 Sedoheptulose-1, 7-di P
2 Sedoheptulose-1, 7-di P- 2 Sedoheptulose-7-p
The two sedoheptulose 7-phosphates thus produced combine with the rest of 2 molecules of phosphoglyceraldehyde to produce 2 molecules of Ribose-5-phosphate and 2 molecules of xylulose 5-phosphate. The enzyme involved is Aldolase.
2) Sedoheptulose-7 – P + 2 PGALD
(7c) (3c)
= 2 Ribose-5 – P + 2 xylulose-5 – P
(5c) (5c)
The two ribose-5 – phosphates and four xylulose-5 – phosphates (reaction 9 &12) are converted to Ribulose monophosphate by the isomerase and epimerase respectively.
2 Ribose – 5 – P = 2 Ribulose 5 – P
(5c) (5c)
4 Xylulose 5 – P = 4 Ribulose 5 – P
(5c) (5c)
The RUMPs thus produced are again used up in another cycle of CO2 fixation. The results of the pathway can be summed up as.
7 PGALD + 5 Di HAP = 1 Glucose + 6 RUMP
Hetch & Slack pathway or C4 pathway
Though Calvin cycle or C3 pathway is prevalent in the majority of Dicot plants some tropical Graminae or Grasses operate carbon fixation by another pathway called Hatch and Slack pathway. (This is named after the discoverers). This is also called C4 pathway because the first intermediate compound synthesized, during carbon fixation is a four carbon organic acid. This method is considered as an efficient method of carbon fixation. The uniqueness of this process is that C4 pathway and C3 pathway operate in the same plant, but in different structures. In Graminae members like Sorghum and Sugarcane the vascular bundles found in the vines are surrounded by a single layer of bundles heath cells, which in turn are surrounded by mesophyll cells. Chloroplasts found in mesophyll cells and bundle cells show different structure as well as functions.
Factors that control photosynthesis
Photosynthesis being a photo biochemical process, it is controlled by various factors to achieve maximum yield. Under optimal conditions if any one of the factors is deficient the rate of photosynthesis suffers. If such a factor is increased the rate also increases. Thus the rate under controlled conditions shows minimal or optimal or maximal quantities. For example, when photosynthesis is operating under optimal condition, if carbon dioxide is deficient, the rate of reaction increases, but reaches saturation point at which condition, another factor, say light, may act as a limiting factor. If the intensity of light is increased, again the rate increases to maximum and reaches saturation point. This may be further increased on increasing the concentration of enzymes. Thus in living systems various factors and their concentration readily affect the efficiency of photosynthesis.
Pigments: Green chloroplasts contain green as well as yellow pigments. Among green pigments, Chl-a & Chl-b are invariable present; among yellow pigments carotenes and xanthophylls are present; chlorophyll-a, particularly Chl-a 700 and Chl-a 680 are directly involved in the primary process of photochemical reactions. All other pigments act as secondary pigments. Even though Chl-a 700 and Chl-a 680 act as active centers, other pigments absorb light at specific wave lengths and they are conveyed from molecule to molecule towards active centers. Here, the energy is transferred by inductive resonance in the form of excitons.
These pigments get organized in the thylakoid membranes in the form of photosynthetic units called P.S-I and P.S-II. Both P.S-I and P.S-II are found in thylakoid membranes, but P.S-I is exclusively found in the inter granal lamellae. In thylakoid membranes, P.S I and P.S-II are uniquely oriented towards each other, in such a way, their function is co-coordinated and they are responsible for oxygen liberation (P.S-II) and NADP reduction to NADPh2 (P.S-I). During the electron flow from P.S-I, the light energy is converted to chemical bond energy (ATP) by Non-Cyclic photo-phosphorylation.
Generally, at high intensity of light, chlorophyll molecules get bleached by photo-oxidation, but carotinoids that are present, protect the chlorophyll molecules from photo-oxidation. If there is any deficiency in any of the pigments and required factors for their organization, it affects the process drastically; sometimes the effect may be lethal too.
Light:
In photosynthesis light provides energy. At the same time it stimulates the entire process. Basically this process is controlled by the quality and the quantity of light that is received.
The solar electro-magnetic radiation consists of a wide spectrum of individual rays, which differ in their wave lengths. These radiations travel in the form of discrete energy packets called photons. The amount of energy in each photon is called Quantum, which mainly depends upon the wave length of the radiation. Shorter the wave length, greater is the energy of longer the wave length lesser is the energy of the photon. For example, the red light of the visible spectrum (white light) has longer wave length and lesser energy when compared to the shorter wave length of the blue light which has higher amount of energy.
This energy relationship between photon and wave length is shown in the figure 87.
Quantity of light
Chlorophyll a, Chl.B B-carotenes and Xanthophylls absorb different wave lengths of visible light (Cal a, chl. B, B-carotene & xanthophylls). This is called the absorption spectrum. Even though these pigments absorb light at shorter wave lengths, the photons are transferred to the active centers which have an absorption spectrum at longer wave lengths.
Chlorophyll molecules, because of heterogeneity in their structure absorb white light at Blue as well as Red wave lengths. If blue or red light is given singly photosynthesis will be never efficient; on the other hand, if both the lights are given simultaneously, the process becomes efficient in releasing O2. This effect is called Emerson’s enhancement effect. That means photosynthesis requires both red and blue lights for its efficient function.
Quantity and intensity of lights: The intensity of the light depends upon the distance of the source, and it is measured in terms of foot-candles. It has been found that at low intensity, photosynthesis is at its minimum but with the increase in intensity the rate increases and reaches saturation at about 2000 to 2500 foot candles. At higher intensities, however, pigments get bleached and the process suffers. The inhibition of photosynthesis by photo-oxidation at higher intensities is called ‘Solarization’.
Quantum requirement / efficiency
Light is measured either in terms of quanta or intensity of light. The efficiency of light is measured in terms of number quanta required for either the liberation of a molecule of O2 or for the fixation of a molecule CO2 into Glucose. Quantitative measurement of red light required for the liberation of one molecule of O2 is found to be about 4 quanta and another four are required for the production of two molecules of NADPH*. During this process 2 molecules of ATPs are also synthesized; totally 8 quanta are required.
In Cylic photophosphorylation 2 molecules of ATP are synthesized per 2 quanta of light. 2 ATP cyclic 2 quanta.
6 molecules of CO2, 18 molecules of ATP and 12 molecules of NADPH2 are required. This is approximately equivalent to 60 quanta.
6 CO2 + 6 RUMP + 18 ATP + 12 NADPH + H ---------- C6 H12 O6 + 12 NADP + 18 ADP + 18 Pi.
But the amount of total energy that is actually stored in a molecule of Glucose is about 696 or 700 K. cal. Thus the efficiency or photosynthesis in terms of energy required and stored, gives the value of 60%. Probably the other 70% of the energy that is not fixed may be released in the form of heat which may be utilized for enzymatic and other cellular activities.
Carbon dioxide (CO2)
It has been estimated that about 300 million years ago the percentage of CO2 in the atmosphere was about 20%. Today, with burning of all kinds of fuels (including biological oxidation) the concentration of CO2 in the atmosphere is just 0.03%. Naturally one will be tempted to ask “What has happened to the rest of the CO2?” Nature has fixed this CO2 in the form of organic fuels by photosynthetic process and the same is stored as the organic fuel in the inner depth of earth. Nevertheless, plants growing on land and in ocean fix about 146 billion tons of carbon annually which is approximately equivalent to the fixation of 13x 1012 K.cals. of solar energy.
Generally, in a vast landscape full of green plants, CO2 becomes deficient by about mid-day, and photosynthesis and its yield suffers. By increasing the concentrate of CO2, the rate of photosynthesis increases, so also its yield. Different plants have different optima for CO2. C4 plants are considered as highly efficient plants than C2 plants with respect to carbon fixation.
Water: Water being sole source for electrons and protons, its supply is very important in photosynthesis. But under water deficit conditions, the rate of photosynthesis falls drastically, if higher concentration of H2O does not show any enhancing effect.
Temperature: Photosynthesis, which is a photo-chemical reaction, requires enzymes for its various biochemical activities temperature has a significant effect on controlling the rate of photosynthesis. Different plants have different optimal temperature. Desert plants have higher optimal temperature of 35-400 C. On the other hand, other mesophytic and water plants function efficiently at 25-300C.
Internal and Genetic factors
Even under optimal environmental conditions, without the proper cellular machinery, no metabolic activity can function efficiently. The synthesis of various cellular factors ultimately depends upon the genetic potential and its expression. Plants with superior genetic potential can function very efficiently when compared to inferior ones. All enzymes, pigments, light harvesting proteins, co-enzymes, and their synthesis things is of utmost importance in the proper functioning of photosynthesis which ultimately controls the photo-synthetic yield.
Created by :
http://preuniversity.grkraj.org/html/7_PHOTOSYNTHESIS.htm
The free chemical energy required for life processes is derived from organic food materials by a process called biological oxidation. If organisms are allowed to utilize the existing food materials on this planet, it will be exhausted in no time. However, nature has devised a unique mechanism by means of which it replenishes the organic food materials in excess and this is achieved by harnessing the solar energy by plants.
Definition: Photosynthesis can be defined as a “series of processes in which solar electro magnetic radiation energy (SEMR) is captured, converted and conserved in the form of chemical energy by green plants”. Biochemically this process can also be defined “as light sensitized Red-Ox process” for it involves light induced Oxidation-Reduction processes.
Solar Energy
Sun emits light in the form of solar electro magnetic radiation (SEMR) of which only 40% reaches the surface of earth and rest is absorbed by O2, O3, CO2, dust and H2O present in outer atmosphere of the earth. Out of this only 1% is used by land plants which form about 15% of total plant population, and oceanic plants (about 85%) in fixing a total of 35-146 billion tones of carbon every year which is equivalent to 1.8-13 x 1012 K.Cals, of chemical energy.
SEMR Spectrum: The SEMR spectrum is quite large, consisting of cosmic rays at one extremity and radio waves at the other, of which, plants use only blue and red parts of the visible for photosynthesis. Light travels in waves, in the form of discrete energy packets called photons. The energy content of each photo varies and depends upon the frequency and speed of the light. For example, light with shorter wavelength has more energy than the light with longer wave length (Blue light has more energy than the red light). Einstein of Red light (700 nm) has 80 K. cal. per mole-1.
Historical Account
Though Aristotle observed the effect of light on greening of the plants, it was Joseph Priestley who discovered that the plants are capable of purifying the air and called this process as dephlogistication. But Jan Ingen Houze demonstrated that plants can dephlogistication the air (by liberating O2) only in the presence of light. In dark, plants and animals behave similarly by releasing CO2 and phlogisticating the air (impurifying the air). However, it was Jean Senebier, who postulated that plants fix the atmospheric CO2 (fixed air) into organic compound and the oxygen that is liberated comes from CO2.
Plants – O2 (Priestley)
Light
Plants --- O2 (Jan Ingen Houze)
Light
Plants + CO2 --- Organic carbon + O2 (Jean Senebier)
At this juncture, Nicholas Theodore de Saussure postulated that H2O is used up in fixing the CO2 into organic compounds. This was an important step in understanding photosynthesis.
Light light
H2O + CO2 ------------- C + O2 C + H2O ---- (CH2O) n
plant plants
Robert Mayer, who was responsible for the theory, “that energy can neither be created nor destroyed”, clearly elucidated that the plants capture solar energy and store it in the form of chemical energy.
Meanwhile the importance of chloroplast and chlorophyll in fixing CO2 in the presence of light was made clear. But people still believed that the oxygen that is liberated during photosynthesis comes from the splitting of CO2 into C and O2. However it was Robert Hill and Van Neil using radio active isotopes demonstrated that the oxygen that is liberated comes from the H2O and not from CO2 as it was believed earlier.
4H2O ----------- 2H2 + 2O2
Since then numerous workers have contributed their part in understanding various aspects of photosynthesis. Blackman, Calvin, Arnon, Emerson, Park, Sanpeitro, Govindjee, Ellis, Parker, are the notables among the stalwarts who have made significant contributions in understanding the structure and functional aspects of Photosynthesis.
Photosynthetic Organelles: Chloroplasts
Plastids are the unique organelles found exclusively in plants (with the exception of fungi).
A fully developed chloroplast is bounded by a double membrane system within which, a fluid or a matrix called stroma is found. In this liquid 30-40 highly organized circular membranous structures are found. These are called Grana. Each Granum is made up 10-100 circular flat membranous discs called thylakoids. In these thylakoids the photosynthetic pigments and their associated pigments are organized into photosynthetic units. Refer page No.190 for the details of chloroplast structure.
If thylakoids are cut open by freeze fracture method and observed under an electron microscope, four surfaces can be made out as shown in the (fig). These surfaces are studded with numerous granular structures. Those structures found in the inner core of the membranes are called Quantasomes which act as photosynthetic units.
Photosynthetic units: Park and Branton discovered the presence of array crystalline particles, associated with the protein curried in thylakoid membranes. Such particles are called Quantasomes, which are nothing but photosynthetic units which are capable of absorbing solar energy as well as performing photo-chemical reactions. The larger particle is P.S-II and the smaller is P.S-I. Park and Sane have succeeded in isolating P-S-I and P.S-II by sonication and differential ultra centrifugation methods. This has led to the study of chemical analysis and function of each of these units.
Photosynthetic Unit I: It is smaller of the two photo-systems. The inter-granal lamellae or stromal lamellae have just P.S-I particles. But the granal thylakoid membranes are associated with P.S-II system. P.S-I is made up of 230-250 chlorophyll-a molecules. Along with the chlorophyll-b, Carotenoids, 25 K.D light harvesting proteins and unique molecule called chlorophyll-a 700, which exists in the form of a dimmer, are also present. This system is also associated with Fe-S containing Ferrodoxin (a reducing substance), a non heme-iron protein called Ferrodoxin (FRS), Cytochrome-b 6, and Plastocyanin and ATP dependent NADP reductase. In inter-granal lamellae cyclic photo-phosphorylation occurs, but in granal membranes the reduction of NADP to NADPH2 occurs. Recently Arnon came out with a view that P.S-I is totally absent in granal membranes but it is found only in stromal lamellae.
Photosynthetic Unit II: It is the larger photosynthetic unit, exclusively found or restricted to granal membranes. It is made up of a number of chlorophyll-a (more), chlorophyll-b, Carotenoids, 25 K.D. light harvesting proteins, specific Mn2* associated Z-protein complex (32 KD), Pheophytin, Plasto Quinone and Cytochrome-b 559. It also has a unique, Chlorophyll-a 680 molecule which exists in the form of a dimmer. Its major function is to liberate O2 and donate electrons to P.S-I system. However Arnon feels that the originally believed P.S-I involved in the reduction of NADP is not P.S-I but it is another form of P.S-II system. Only time will tell the reality of its structure and function.
Transfer of energy: These two photo systems with their respective pigments and light harvesting proteins are oriented in the membrane in such a way; they can capture the fleeting photons randomly. All the molecules in each of these photo-synthetic units are spaced and oriented in such a way, captured photons are transferred from molecule to molecule by a phenomenon called inductive resonance. Here the unit of energy that is transferred to as exciton. The transfer of captured light energy is ultimately drawn to active centers.
Chlorophyll-a --- Chlorophyll-a 680
Carotenoids ---
Chlorophyll-b --- Chlorophyll-a 700
Photosynthetic pigments
Pigment analysis of photosynthetic organelles, shows that chloroplasts contain green pigments (chlorophylls) and yellow pigments (carotinoids). Among chlorophylls, chlorophyll-a acts as the primary pigment and it is present in all photosynthetic organisms, with the exception of photosynthetic bacteria where the primary pigment is Bacteriochlorophyll. All other pigments act as secondary pigments.
Absorption Spectrum: The absorption spectrum of these pigments indicates that, chlorophyll-a shows maximum absorption and at 430 nm (blue light) and 662 nm (red light). Similarly chlorophyll-b has absorption spectrum at 453 nm to 642 nm and carotinoids have an absorption band between 430 nm – 490 nm.
Action spectrum and Enhancement effects
Though individual pigments absorb light at different wave lengths, not all the wave lengths are efficient in photosynthetic process either in terms of oxygen liberation or carbon fixation. If red light or blue light is provided alone, oxygen liberation would be inefficient on the other hand if both the lights are given simultaneously the photosynthesis. Though carotinoids absorb light at green and orange regions, instead of direct action, they transfer the energy to other pigments like chlorophyll-b and chlorophyll-a for effective function.
Mechanism of Photosynthesis
The process of light capturing and carbon dioxide fixation are separated by time and space. Structurally Grana perform the photochemical act by capturing, converting and conserving the solar energy in the form of chemical bonds in ATP and NADPH + H*. This is also involved in the liberation of O2. In this primary process, though certain steps are temperature dependent, others are light dependent and temperature independent reactions.
Stromatic fluid is the site for the utilization of light dependent granal products in carbon fixation. As this process is controlled by a number of enzymes, it is considered as a temperature dependent process. However light induced photochemical reactions are extremely fast reactions are relatively slow and take place later as they depend upon the products of light reactions. The entire process can be simplified in the following equation and in the scheme.
Light Reactions
As the first phase of photosynthesis is light dependent, it is referred to as light reaction; however this is also called. Hill’s reaction for, it was first demonstrated by Robert Hill.
Basic principles involved in photosynthesis is capturing of solar electromagnetic radiations at a particular wave length by pigment/protein complexes. The pigments act as antennas for capturing light rays in the form of photons in terms of quantums.
The light captured, with photons containing specific quantum of energy, is translocated among the atoms of pigment, where at a particular site an electron accepting the light energy jumps to a higher orbit. The orbit to which it jumps depends upon the amount of energy a captured photon provides. In the orbit the excited (higher energy electron) electron stays for a very short period of time, say -10^ 14 sec and then drops to down to the next lower orbit where it stays only for a very short time, then it falls back to its original orbit (ground state).
During downward fall the energy rich electron can be transferred to another compound. Thus the light energy accepted by the electron is transferred to another substance. This is a simple explanation of light harvesting process. If the energy rich electron is not used, the captured energy is released either in the form of fluorescence or heat
Photoionization: To begin with, the absorption of photons of SEMR by pigment systems makes them excited.
Chlorophyll + Protein complex + light --- Chlorophyll -
(Ground state) - protein complex (CPC) (excited)
The excited chlorophyll-protein complex reacts with water and splits the water into hydrogen ion (OH-). This phenomenon is called photoionization.
Chlorophyll-protein complex (Excited) + H2O
------- Chlorophyll – Protein complex + H* _ OH – (Ground state)
The photocopied products like H* + OH – ions are simultaneously accepted by the photosystem I and photosytem II respectively, found in granal membranes.
Production of reducing power: It is now certain that the synthesis of NADPH + H* is the co-ordinate function of P.S-I and P.S-II, where P.S-I is directly involved in the reduction of NADP.
When the light strikes the photosystem I units, photons of the SEMR are trapped by a number of antenna like chlorophyll-protein complexes. This energy is transferred from molecule to molecule towards the special molecule called chlrophyll-a 700, which acts as the reaction centre or energy trap. When a Quantum of light energy is conveyed a chlorophyll-a 700, an electron at a particular site gets the energy and it is boosted to the next higher orbit or higher stage of energy.
In this process the energy that is responsible for boosting the electrons is now stored in NADPH + H*. This is a powerful reducing agent required for carbon fixation and it is released into the stromatic fluid as it is synthesized.
As the electrons from chlorophyll-a 700 are lost to NADP, the chlorophyll-700 molecules are rendered electrically positive. If electrons are not provided, these molecules become active and this condition is called photo-bleaching. However the electrons for chlorophyll a 700 come from P.S.II which is also moved in the act of electron transport.
Liberation of oxygen: Along with P.S.I, P.S.II units also capture photons and transfer the excitons to the active centre called chlorophyll-a 680 which exists in the form of a dimer. Similar to chlorophyll-a 700, chlorophyll-680 molecules also boost up the chlorophyll-a 700, chlorophyll-a 680 molecules also boost up the electrons to higher state of energy. As chlorophyll-a exists in dimmers, utilizing 2 Quanta of light, 2 accepted by photo system II, the larger photosynthetic unit of the two, has 32 K.D. Z protein complexed with manganese ions as active centre. With the loss of every electron from the terminal chlorophyll a 680 molecule, an electron is supplied by “Z” protein Mn2+ complex and thus this protein complex gets activated with every photon absorbed.
As a result, the positively charged Mn2*- Z protein complex readily reacts with negatively charged OH ions in water.
One more boosting of a pair of electrons are to be released from Z-Mn complex to receive two more OH – ions. When 4 such OH- ions are brought on to the two Mn-Z protein complexes, in such a way, the OH orbitals may overlap on each other. This may result in reorientation and reaction to produce 2H2O and a molecule of O2. This leaves Z – Mn2* complex free to receive another set of OH ions.
PS –II Z –Mn2* Complex + 4 OH –4 photons
PS II – Z Mn2* + 2H2O + O2
Non-Cyclic Photophosphorylation
The electrons that are boosted to higher state of energy from PS-II Chl a 680 – are immediately accepted by pheophytin.
Then the electrons are shuttled to a labile molecule called plastoquinones (PQ). The molecule simultaneously accepts 2H* ions and 2 electrons and gets reduced to PQH2, which in turn releases the H* protons into inner thylakoid space and simultaneously transfer the electrons to Cytochrome 559. This is accompanied with the loss of small amount of energy is released. This energy is utilized and stored in the terminal bond of ATP molecule. This phenomenon is referred to as non-cyclic photophosphorylation. From Cytochrome f, the electrons reach Chl a 700 through copper containing neutral and now they are ready for another cycle of electron boosting process. Meanwhile, as the electrons are lost from chlorophyll a 680 to chlorophyll a 700 the former molecule becomes positively charged. The electrons that neutralize Chl a 680 come from (OH) ions.
Cyclic photo phosphorylation: Photosynthetic unit-I that is found exclusively in inter granal lamellae is involved in a cyclic electron flow. During the down hill journey of electrons, energy is liberated and the same is utilized in the phosphorylation of ADP + Pi to ATP.
P.S-I absorb photons and energy is conveyed to the terminal Chl a 700 which exists in dimer form. The electrons are boosted to higher orbital, which is accepted by FRS. Then electrons are channeled through a series of electron accepters back to Chl a 700 molecule. When the electrons are transferred from FD to cytochrome b 6and form Cyt b 6 to Cytochrome 1, sufficient amount of energy is released. The energy that is released during this shuttle is due to the difference in the Red-O potential between the oxidant and reductant. This energy is captured and utilized in the formation of a high energy terminal bond of ATP molecule.
Light reaction and its products
During light reaction solar energy is absorbed by chlorophyll light harnessing complex and utilize water for photochemical reaction to produce 3 ATP, 1 NADPH + H*, 2H2O, 1 O2 per cycle of reactions.
Particularly ATP and NADPH + H* are released into stromatic fluid. Oxygen either escapes or it is utilized by respiratory process.
Dark reaction or Calvin Cycle
Stromatic fluid consists of all the enzymes required for carbon dioxide fixation. Calvin et al, have elucidated all the biochemical steps involved in this process. Calvin is probably the one and the only biochemist, who has been awarded the Nobel Prize for this kind of work.
This pathway is also called C 3 pathway, for the first stable intermediate product produced is a 3 Carbon organic acid; further it is these 3 carbon components that play an important role in the synthesis of Glucose. This process takes place in 3 steps: 1) Carbon oxidation 2) Reduction 3) Regeneration.
Carbon Fixation
Ribulose monophosphate (5C) an intermediate component of carbohydrate metabolism first gets phosphorylated by an enzyme Ribulose kinase and a molecule of Ribulose di phosphate is synthesized.
RUMP + ATP – RUDP + ADP. 1
The RUDP (5C) acts as an acceptor of CO2 found dissolved in the stromatic fluid. RUDP carboxylase is responsible for the addition of CO2 to RUDP, when a highly stable 6C compound, formed, break up into two 3 Carbon compounds called 3-Phosphoglyceric acid (PGA).
RUDP + CO2 – 2 PGA 2
(5C) (1C) (3C)
Reduction
Before the 3-PGA gets reduced, the 3-PGA is primed up by phosphorylation by phosphoglycerokinase to produce. Di phosphoglycerate (Di PGA). A molecule of ATP is consumed in the process.
3-PGA + ATP = 1, 3 – DiPGA + ADP
(3C) (3C)
The DiPGA gets reduced by NADPH + 1H*to
Phospho glyceraldehydes (2 PGALD). The enzyme involved is glyceraldehydes dehydrogenase.
DiPGA + NADPH + H = PGALD + NADP + Pi
(3C) (3C)
For the fixation of one molecule of CO2 into 2 molecules of PGALD, one molecule of RUMP, 3 molecules of ATP and 2 molecules of NADPH + H* are required. The sum of Carboxylation and reduction process to produce one molecule of Glucose has been given in the following equation.
6 CO2 + 6 RMP + 18 ATP + 12 NADPH + H* = 12 PGALD + NADP + 18 ADP + 12 Pi
Regeneration
In this process, 12 PGALD are subjected to a regeneration process in which 6 RUMPs initially consumed are regenerated. At the same time one molecule of glucose is produced.
Out of 12 PGALD, five are converted into Dihydroxy Acetone Phosphate (DiHAP) by an isomerase enzyme.
5 PGALD = 5 Di HAP 6
In the next step, 3 molecules of PGALD combine with 3 molecules of Di HAP to form 3 molecules of Fructose-1, 6-Di Phosphate. The enzyme is Aldolase.
3 PGALD + 3 Di HAP --- 3 Fructose-1, 6-Di P
(3c) (3c) (6c)
These Fructose-1, 6 di phosphates are subjected to phosphate action in which one phosphate is removed to produce Fructose-6 phosphates.
3 Fructose-1, 6-diphosphate --- 3 Fructose-6-phosphate.
Out of the 3 Fructose 6-phosphates, one is converted into Glucose 6-phosphate by phosphogluco isomerase.
1 Fructose 6-p ------ I Glucose 6-p
(6c) (6c)
The remaining 2 Fructose-6 phosphates combine with 2 molecules of phosphoglyceraldehyde, to undergo a rearrangement process in which 2 molecules of Xylulose phosphates are produced. The enzyme is transketolase.
2 Fructose6-p + 2 PGALD
(6c) (6c)
= 2 Erythorose-4-p + 2 Xylulose-5-p
Then 2 Erythrose 4-P combine with 2 Dihydroxy acetone-P by another Transketolase enzyme to form a carbon Sedoheptulose-1, 7-diphosphate, which immediately undergoes phosphotase action to produce sedopheptulose7-phosphate.
2 Erythrose-P + 2 Di HAP
(4c) (3c)
= 2 Sedoheptulose-1, 7-di P
2 Sedoheptulose-1, 7-di P- 2 Sedoheptulose-7-p
The two sedoheptulose 7-phosphates thus produced combine with the rest of 2 molecules of phosphoglyceraldehyde to produce 2 molecules of Ribose-5-phosphate and 2 molecules of xylulose 5-phosphate. The enzyme involved is Aldolase.
2) Sedoheptulose-7 – P + 2 PGALD
(7c) (3c)
= 2 Ribose-5 – P + 2 xylulose-5 – P
(5c) (5c)
The two ribose-5 – phosphates and four xylulose-5 – phosphates (reaction 9 &12) are converted to Ribulose monophosphate by the isomerase and epimerase respectively.
2 Ribose – 5 – P = 2 Ribulose 5 – P
(5c) (5c)
4 Xylulose 5 – P = 4 Ribulose 5 – P
(5c) (5c)
The RUMPs thus produced are again used up in another cycle of CO2 fixation. The results of the pathway can be summed up as.
7 PGALD + 5 Di HAP = 1 Glucose + 6 RUMP
Hetch & Slack pathway or C4 pathway
Though Calvin cycle or C3 pathway is prevalent in the majority of Dicot plants some tropical Graminae or Grasses operate carbon fixation by another pathway called Hatch and Slack pathway. (This is named after the discoverers). This is also called C4 pathway because the first intermediate compound synthesized, during carbon fixation is a four carbon organic acid. This method is considered as an efficient method of carbon fixation. The uniqueness of this process is that C4 pathway and C3 pathway operate in the same plant, but in different structures. In Graminae members like Sorghum and Sugarcane the vascular bundles found in the vines are surrounded by a single layer of bundles heath cells, which in turn are surrounded by mesophyll cells. Chloroplasts found in mesophyll cells and bundle cells show different structure as well as functions.
Factors that control photosynthesis
Photosynthesis being a photo biochemical process, it is controlled by various factors to achieve maximum yield. Under optimal conditions if any one of the factors is deficient the rate of photosynthesis suffers. If such a factor is increased the rate also increases. Thus the rate under controlled conditions shows minimal or optimal or maximal quantities. For example, when photosynthesis is operating under optimal condition, if carbon dioxide is deficient, the rate of reaction increases, but reaches saturation point at which condition, another factor, say light, may act as a limiting factor. If the intensity of light is increased, again the rate increases to maximum and reaches saturation point. This may be further increased on increasing the concentration of enzymes. Thus in living systems various factors and their concentration readily affect the efficiency of photosynthesis.
Pigments: Green chloroplasts contain green as well as yellow pigments. Among green pigments, Chl-a & Chl-b are invariable present; among yellow pigments carotenes and xanthophylls are present; chlorophyll-a, particularly Chl-a 700 and Chl-a 680 are directly involved in the primary process of photochemical reactions. All other pigments act as secondary pigments. Even though Chl-a 700 and Chl-a 680 act as active centers, other pigments absorb light at specific wave lengths and they are conveyed from molecule to molecule towards active centers. Here, the energy is transferred by inductive resonance in the form of excitons.
These pigments get organized in the thylakoid membranes in the form of photosynthetic units called P.S-I and P.S-II. Both P.S-I and P.S-II are found in thylakoid membranes, but P.S-I is exclusively found in the inter granal lamellae. In thylakoid membranes, P.S I and P.S-II are uniquely oriented towards each other, in such a way, their function is co-coordinated and they are responsible for oxygen liberation (P.S-II) and NADP reduction to NADPh2 (P.S-I). During the electron flow from P.S-I, the light energy is converted to chemical bond energy (ATP) by Non-Cyclic photo-phosphorylation.
Generally, at high intensity of light, chlorophyll molecules get bleached by photo-oxidation, but carotinoids that are present, protect the chlorophyll molecules from photo-oxidation. If there is any deficiency in any of the pigments and required factors for their organization, it affects the process drastically; sometimes the effect may be lethal too.
Light:
In photosynthesis light provides energy. At the same time it stimulates the entire process. Basically this process is controlled by the quality and the quantity of light that is received.
The solar electro-magnetic radiation consists of a wide spectrum of individual rays, which differ in their wave lengths. These radiations travel in the form of discrete energy packets called photons. The amount of energy in each photon is called Quantum, which mainly depends upon the wave length of the radiation. Shorter the wave length, greater is the energy of longer the wave length lesser is the energy of the photon. For example, the red light of the visible spectrum (white light) has longer wave length and lesser energy when compared to the shorter wave length of the blue light which has higher amount of energy.
This energy relationship between photon and wave length is shown in the figure 87.
Quantity of light
Chlorophyll a, Chl.B B-carotenes and Xanthophylls absorb different wave lengths of visible light (Cal a, chl. B, B-carotene & xanthophylls). This is called the absorption spectrum. Even though these pigments absorb light at shorter wave lengths, the photons are transferred to the active centers which have an absorption spectrum at longer wave lengths.
Chlorophyll molecules, because of heterogeneity in their structure absorb white light at Blue as well as Red wave lengths. If blue or red light is given singly photosynthesis will be never efficient; on the other hand, if both the lights are given simultaneously, the process becomes efficient in releasing O2. This effect is called Emerson’s enhancement effect. That means photosynthesis requires both red and blue lights for its efficient function.
Quantity and intensity of lights: The intensity of the light depends upon the distance of the source, and it is measured in terms of foot-candles. It has been found that at low intensity, photosynthesis is at its minimum but with the increase in intensity the rate increases and reaches saturation at about 2000 to 2500 foot candles. At higher intensities, however, pigments get bleached and the process suffers. The inhibition of photosynthesis by photo-oxidation at higher intensities is called ‘Solarization’.
Quantum requirement / efficiency
Light is measured either in terms of quanta or intensity of light. The efficiency of light is measured in terms of number quanta required for either the liberation of a molecule of O2 or for the fixation of a molecule CO2 into Glucose. Quantitative measurement of red light required for the liberation of one molecule of O2 is found to be about 4 quanta and another four are required for the production of two molecules of NADPH*. During this process 2 molecules of ATPs are also synthesized; totally 8 quanta are required.
In Cylic photophosphorylation 2 molecules of ATP are synthesized per 2 quanta of light. 2 ATP cyclic 2 quanta.
6 molecules of CO2, 18 molecules of ATP and 12 molecules of NADPH2 are required. This is approximately equivalent to 60 quanta.
6 CO2 + 6 RUMP + 18 ATP + 12 NADPH + H ---------- C6 H12 O6 + 12 NADP + 18 ADP + 18 Pi.
But the amount of total energy that is actually stored in a molecule of Glucose is about 696 or 700 K. cal. Thus the efficiency or photosynthesis in terms of energy required and stored, gives the value of 60%. Probably the other 70% of the energy that is not fixed may be released in the form of heat which may be utilized for enzymatic and other cellular activities.
Carbon dioxide (CO2)
It has been estimated that about 300 million years ago the percentage of CO2 in the atmosphere was about 20%. Today, with burning of all kinds of fuels (including biological oxidation) the concentration of CO2 in the atmosphere is just 0.03%. Naturally one will be tempted to ask “What has happened to the rest of the CO2?” Nature has fixed this CO2 in the form of organic fuels by photosynthetic process and the same is stored as the organic fuel in the inner depth of earth. Nevertheless, plants growing on land and in ocean fix about 146 billion tons of carbon annually which is approximately equivalent to the fixation of 13x 1012 K.cals. of solar energy.
Generally, in a vast landscape full of green plants, CO2 becomes deficient by about mid-day, and photosynthesis and its yield suffers. By increasing the concentrate of CO2, the rate of photosynthesis increases, so also its yield. Different plants have different optima for CO2. C4 plants are considered as highly efficient plants than C2 plants with respect to carbon fixation.
Water: Water being sole source for electrons and protons, its supply is very important in photosynthesis. But under water deficit conditions, the rate of photosynthesis falls drastically, if higher concentration of H2O does not show any enhancing effect.
Temperature: Photosynthesis, which is a photo-chemical reaction, requires enzymes for its various biochemical activities temperature has a significant effect on controlling the rate of photosynthesis. Different plants have different optimal temperature. Desert plants have higher optimal temperature of 35-400 C. On the other hand, other mesophytic and water plants function efficiently at 25-300C.
Internal and Genetic factors
Even under optimal environmental conditions, without the proper cellular machinery, no metabolic activity can function efficiently. The synthesis of various cellular factors ultimately depends upon the genetic potential and its expression. Plants with superior genetic potential can function very efficiently when compared to inferior ones. All enzymes, pigments, light harvesting proteins, co-enzymes, and their synthesis things is of utmost importance in the proper functioning of photosynthesis which ultimately controls the photo-synthetic yield.
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