PHOTOSYNTHESIS Photosynthesis anabolisme endergonik carbon dioxida CO 2

PHOTOSYNTHESIS

Photosynthesis • anabolisme, endergonik, carbon dioxida (CO 2) proses yang menggunakan energi cahaya (photon) dan air (H 2 O) untuk menghasilkan molekul organik (glucose). SUN photon 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 klorofil Enzym glucose

Struktur Daun • Umumnya FS terjadi pada lapisan palisade. • Pertukaran gas antara CO 2 dan O 2 terjadi melalui stomata

Stomata (stoma) • Pori-pori pada permukaan daun, tempat terjadinya pertukaran air dan gas antara tumbuhan dan atm. Oxygen (O 2) Carbon Dioxide (CO 2) Guard Cell

Struktur Kloroplas • Membran bagian dalam thylakoid. • Bagian yang menebal disebut thylakoids. Satu grup thylakoid disebut granum. (jamak – grana) • Stroma cairan disekitar (yang meyelimuti) thylakoids.

Chloroplast • Organel dimana photosynthesis berlangsung Stroma Membran luar Membran dalam Thylakoid Granum

Thylakoid Membrane Granum Thylakoid Space

Molekul Klorofil • Terdapat pada membran thylakoid • Terdapat Mg++ pada pusat. • Pigmen klorofil menangkap energi cahaya (photon) dengan menyerap panjang gelombang tertentu (biru-420 nm dan merah -660 nm yang paling penting). • Tumbuhan tampak hijau ?

Pigmen • Klorofil A merupakan pigmen FS yang paling penting. • Pigmen lain disebut antena atau pigmen tambahan juga terdapat di dalam daun. – Klorofil B – Carotenoids (oranye/ merah) – Xanthophylls (kuning / coklat) • Pigmen ini terbenam di dalam membran kloroplas yang disebut photosystems.

Panjang gelombang Cahaya (nm) 400 500 600 700 Short wave Long wave (more energy) (less energy)

Absorpsi Cahaya oleh Klorofil Absorpsi violet blue green yellow orange Panjang gelombang red

Reaksi Redox • Transfer satu atau lebih elektron dari satu reaktan ke yang lain • Dua jenis: 1. Oxidasi 2. Reduksi

Reaksi Oksidasi • Hilangnya elektron dari satu senyawa • Atau bertambahnya oksigen pada suatu senyawa. Oxidation 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 glucose

Reaksi Reduksi • Bertambahnya elektron pada suatu senyawa • Atau hilangnya Oxygen dari suatu senyawa. Reduction 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 glucose

Tahapan Photosynthesis • Dua tahapan utama (reaksi). 1. Reaksi Cahaya atau Reaksi yang tergantung cahaya Menghasilkan energi dari energi cahaya (photon) dalam bentuk ATP dan NADPH 2. Siklus Calvin atau Fikasasi Carbon atau Fixation C 3 : Tidak tergantung cahaya Menggunakan energy (ATP and NADPH) dari reaksi cahaya untuk membuat gula (glucose).

1. Reaksi Cahaya (Aliran Elektron) • Berlangsung di membran Thyllakoid • Selama Reaksi Cahaya, ada dua jalur aliran elektron. A. Aliran elektron siklik B. Aliran elektron nonsiklik

A. Aliran Elektron Siklik • • Terjadi di membran thylakoid. Menggunakan hanya Photosystem I P 700 - klorofil a Menggunakan Rantai Transport Elektron (RTE). • Hanya menghasilkan ATP ADP + P ATP

A. Aliran Elektron Siklik Primary Electron Acceptor SUN ee- e. Photons P 700 Accessory Pigments Photosystem I e- ATP Dihasilkan RTE

B. Aliran Elektron Nonsiklik • Berlangsung di Thyllakoid membran • Menggunakan PS II dan PS I • P 680 pusat reaksi (PSII) – klorofil a • P 700 pusat reaksi (PS I) – klorofil a • Menggunakan rantai Transport Elektron • Menghasilkan O 2, ATP dan NADPH

B. Aliran Elektron Nonsiklik Elektron Acceptor primer SUN 2 e- Photon H 2 O 1/2 O 2 + 2 H+ Reaksi Enzym 2 e- ETC 2 e- P 700 NADPH ATP P 680 Photosystem II Photon Photosystem I

B. Aliran Elektron Nonsiklik • ADP + P ATP (Reduced) • NADP+ + H NADPH (Reduced) • Oxygen berasal dari peruraian H 2 O, bukan CO 2 H 2 O (Oxidized) 1/2 O 2 + 2 H+

Chemiosmosis • Mendorong synthesis ATP • Berlangsung di membran thylakoid • Menggunakan RTE dan ATP synthase (enzyme) untuk membuat ATP. • Photophosphorylasi: Penambahan phosphate ke ADP untuk membuat ATP

Chemiosmosis SUN H+ H + Thylakoid E PS II (Pompa Proton ) T PS I C H+ H+ H + H+ ADP + P H+ H+ Konsentrasi H+ Tinggi ATP Synthase ATP Rongga Thylakoid Konsentrasi H+ rendah

Siklus Calvin • Fikasai Carbon (tidak tergantung cahaya ). • Tumbuhan C 3 (80% tumbuhan di bumi). • Berlangsung di stroma. • Menggunakan ATP dan NADPH dari reaksi cahaya. • Menggunakan CO 2. • Untuk menghasilkan glukosa: Perlu 6 putaran dan menggunakan 18 ATP dan 12

Siklus Calvin ( Fiksasi C 3) (36 C) 6 C-C-C-C (6 C) 6 CO 2 (unstable) (30 C) 6 C-C-C Ru. BP (30 C) glucose 6 C-C-C 12 PGA (36 C) 6 ATP 6 NADPH 6 C-C-C 6 ATP C 3 6 C-C-C (36 C) 6 C-C-C 12 G 3 P (6 C) C-C-C-C Glucose

Photorespirasi • Terjadi pada saat panas, kering, dan hari cerah • Stomata tertutup. • Fixasi O 2 bukan CO 2 (instead of CO 2) • Menghasilkan Molekul 2 -C bukan (instead ( gula berkarbon 3 -C ). • Tidak menghasilkan gula dan ATP.

Photorespirasi • Tanaman beradaptasi untuk mengurangi dampak fotorespirasi. 1. Tumbuhan C 4 2. Tumbuhan CAM

Tumbuhan C 4 • Panas dan lingkungan lembab (kelembaban tinggi). • 15% tumbuhan (rumput-rumputan, jagung, tebu). • Fotosintesis berlangsung di dua tempat. • Reaksi terang – pada sel-sel mesofil • Siklus Calvin - pada sel-sel selubung (bundle sheath cells).

ANATOMI DAUN JAGUNG (Zea mays sp. )

Tumbuhan C 4 Malat C-C-C-C Di transport CO 2 C 3 glukosa C-C-C PEP ATP Sel Mesofil C-C-C Asam piruvat Sel Bundle (Selubung) Vascular Tissue

Tumbuhan CAM • Panas, lingkungan kering. • 5% dari tumbuhan (cactus) • Stomata menutup pada siang hari. • Stomata membuka pada malam hari • Reaksi terang - berlangsung pada siang hari • Siklus Calvin – berlangsung bila CO 2 tersedia.

Tumbuhan CAM Malam hari (Stomata terbuka Siang hari (Stomata menutup) Vacuole CO 2 C-C-C-C Malate CO 2 C-C-C PEP ATP C-C-C Pyruvic acid C 3 glucose

Diskusi • Mengapa tumbuhan CAM menutup stomatanya pada siang hari ?

Faktor –Faktor yang Mempengaruhi Laju Fotosintesis & Jalur alternatif

• Tujuan: - Membahas faktor-faktor yang mempengaruhi laju fotosintesis. - Membahas jalur alternatif yang digunakan tumbuhan untuk membuat glukosa

Faktor yang mempengaruhi fotosintesis • Tiga faktor lingkungan penting yang dapat mempengaruhi laju fotosintesis: – Intensitas cahaya – Kadar CO 2 – Temperatur

Intensitas Cahaya • Semakin tinggi intensitas cahaya laju FS meningkat kemudian konstan. – Laju FS yang konstan menunjukkan laju FS maximum

Kadar CO 2 The Effect of the Level of Carbon Dioxide on the Rate of Photosynthesis • Semakin tinggi kadar CO 2 , laju FS meningkat, kemudian konstan. – Laju FS yang konstan menunjukkan laju FS maximum

Temperatur/Suhu • Awalnya, semakin meningkat temperatur laju FS meningkat. • Laju FS maximum kemudian menurun sebab: – Enzym yg mengkatalisa reaksi menjadi tidak aktif. – Stomata mulai menutup, CO 2 yang masuk melalui stomata terhambat. The Effect Temperature on the Rate of Photosynthesis

Tumbuhan C 3 • REVIEW: Siklus Calvin, CO 2 digunakan untuk mensintesis gula • Tumbuhan C 3 (kedelai, wheat, padi) hanya menggunakan Siklus Calvin un tuk memfixaxi CO 2 – Disebut Tumbuhan C 3, karena CO 2 pertama-tama berikatan dengan senywa berkarbon 3. • Tumbuhan ini beroperasi pada siang hari

Jalur Alternatif • Beberapa tumbuhan di daerah panas, kering beradaptasi untuk meminimalkan kehilangan air sementara FS tetap berlangsung. – Tumbuhan C 4 – Tumbuhan CAM • CO 2 tidak segera/langsung masuk Siklus Calvin seperti halnya tumbuhan C 3

Tumbuhan C 4 • Stomata sebagian menutup (celah lebih kecil) pada siang hari • Memiliki jalur khusus untuk memfixaxi kadar CO 2 yang rendah dan terbentuk senyawa berkarbon 4 yang masuk Siklus Calvin. • Contoh: Tebu, jagung

Tumbuhan CAM • Tumbuhan CAM membuka stomata pada malam hari dan menutup pada siang hari • Memiliki jalur khusus untuk menyerap CO 2 pada malam hari untuk mensintesis berbagai senyawa asam organik – Kemudian pada siang hari, enzym-enzym menguraikan asam organik tersebut, dengan melepas CO 2 yang kemudian masuk ke siklus Calvin.

Online Simulation • Examined the effect of varying colors of light, light intensity, and amount of carbon dioxide on the rate of photosynthesis • Measured the number of bubbles (oxygen) after 30 seconds

Translokasi Fotosintat: Sources and sinks • Source: – Any exporting region that produces photosynthate above and beyond that of its own needs • Sink: – any non-photosynthetic organ organ that does not produce enough photosynthate to meets its own needs

Bagaimana fotosintat di translokasikan keseluruh bagian tumbuhan Photosynthesis Translocatio n New growth A system of vascular tissue runs through all higher plants. It evolved as a response to the increase in the size of plants, which caused an progressing separation of roots and leaves in space. The phloem is the tissue that translocates assimilates from mature leaves to growing or storage organs and roots.

Sources and sinks Photosynthesis provides a sugar source Translocat ion New growth is a sugar sink Direction of transport through phloem is determined by relative locations of areas of supply, sources and areas where utilization of photosynthate takes place, sinks. Source: any transporting organ capable of mobilizing organic compounds or producing photosynthate in excess of its own needs, e. g. , mature leaf, storage organ during exporting phase of development.

Source Multiple sources and sinks Developi ng Sink apex Source Translocat ion Sink Sink The flow of water in plants is almost always from roots to leaves. Translocation of sucrose can be in any direction – depending on source and sink location and strength. Examples: Beta maritima (wild beet) root is a sink during the first growing season. In the second season the root becomes a source, sugars are mobilized and used to produce a new shoot. In contrast, in cultivated sugar beets roots are sinks during all phases of development.

Translokasi Fotosintat Penyaluran fotosintat/gula terjadi dari sugar source (sel penghasil) ke sugar sink (sel gudang). Teori : aliran tekanan/massa gula dialirkan dari lokasi dengan konsentrasi gula tinggi ke rendah. Mekanisme : o Gula dimuat ke dalam floem secara transpor aktif. o Air masuk ke dalam floem secara osmosis. o Gula dialirkan dari sugar source ke sugar sink. Air melalui proses osmosis kembali ke xilem. BIO 100/101 Tumbuhan 2 2 24

The mechanism of phloem transport The Pressure-Flow Model

The Pressure-Flow Model Translocation is thought to move at 1 meter per hour – Diffusion too slow for this speed • The flow is driven by an osmotically generated pressure gradient between the source and the sink. • Source – Sugars (red dots) is actively loaded into the sieve elementcompanion cell complex • Called phloem loading • Sink – Sugars are unloaded • Called phloem unloading

• yw = ys + yp + yg • In source tissue, energy driven phloem loading leads to a buildup of sugars – Makes low (-ve) solute potential – Causes a steep drop in water potential – In response to this new water potential gradient, water enters sieve elements from xylem • Thus phlem turgor pressure increases • In sink tissue, phloem unloading leads to lower sugar conc. – Makes a higher (+ve) solute potential – Water potential increases – Water leaves phloem and enters sink sieve elements and xylem • Thus phloem turgor pressure decreases The Pressure -Flow Model

• yw = ys + yp + yg • In source tissue, energy driven phloem loading leads to a buildup of sugars – Makes low (-ve) solute potential – Causes a steep drop in water potential – In response to this new water potential gradient, water enters sieve elements from xylem • Thus phlem turgor pressure increases • In sink tissue, phloem unloading leads to lower sugar conc. – Makes a higher (+ve) solute potential – Water potential increases – Water leaves phloem and enters sink sieve elements and xylem • Thus phloem turgor pressure decreases The Pressure -Flow Model

The Pressure-Flow Model • So, the translocation pathway has cross walls – Allow water to move from xylem to phloem and back again – If absent- pressure difference from source to sink would quickly equilibrate • Water is moving in the phloem by Bulk Flow – No membranes are crossed from one sieve tube to another – Solutes are moving at the same rate as the water • Water movement is driven by pressure gradient and NOT water potential gradient

Phloem Loading: Where do the solutes come from? • Triose phosphate – formed from photosynthesis during the day is moved from chloroplast to cytosol • At night, this compound, together with glucose from stored starch, is converted to sucrose – Both these steps occur in a mesophyll cell • Sucrose then moves from the mesophyll cell via the smallest veins in the leaf to near the sieve elements – Known as short distance pathway – only moves two or three cells

What is transported in phloem?

Phloem Loading: Where do the solutes come from? • Triose phosphate – formed from photosynthesis during the day is moved from chloroplast to cytosol • At night, this compound, together with glucose from stored starch, is converted to sucrose – Both these steps occur in a mesophyll cell • Sucrose then moves from the mesophyll cell via the smallest veins in the leaf to near the sieve elements – Known as short distance pathway – only moves two or three cells

Summary • Pathway of translocation: – Sugars and other organic materials are conducted throughout the plant in the phloem by means of sieve elements • Sieve elements display a variety of structural adaptations that make the well suited for transport • Patterns of translocation: – Materials are translocated in the phloem from sources (usually mature leaves) to sinks (roots, immature leaves)

Summary • Materials translocated in phloem: – Translocated solutes are mainly carbohydrates – Sucrose is the most common translocated sugar – Phloem also contains: • Amino acids, proteins, inorganic ions, and plant hormones • Rate of translocation: – Movement in the phloem is rapid, well in excess of rates of diffusion • Average velocity is 1 meter per hour

General diagram of translocation Physiological process of loading sucrose into the phloem Pressure-flow Phloem and xylem are coupled in an osmotic system that transports sucrose and circulates water. Physiological process of unloading sucrose from the phloem into the sink

The pressure-flow process Pressure flow schematic Build-up of pressure at the source and release of pressure at the sink causes source-to-sink flow. At the source phloem loading causes high solute concentrations. y decreases, so water flows into the cells increasing hydrostatic pressure. y At the sink is lower outside the cell due to unloading of sucrose. Osmotic loss of water releases hydrostatic pressure. Xylem vessels recycle water from the sink to the source.