Photosynthesis
- 2. Energy for life processes Energy is the ability to do work Work for a cell includes growth & repair, active transport across cell membranes, reproduction, synthesis of cellular products Autotrophs or producers convert sunlight, CO2, and H2O into glucose (their food) Plants, algae, and blue-green bacteria, some prokaryot es, are producers or autotrophs Only 10% of the Earth’s 40 million species are autotrophs Other autotrophs use inorganic compounds instead of sunlight to make food; process known as chemosynthesis Producers make food for themselves and heterotrophs (consumers that cannot make food for themselves) Heterotrophs include animals, fungi, & some bacteria, & protist s
- 3. Light Absorption Chloroplasts absorb light from the sun during the light dependent reactions Photosynthetic cells may have thousands of chloroplasts Chloroplasts are double membrane organelles with the an inner membrane folded into disc-shaped sacs called thylakoids Thylakoids, containing chlorophyll and other accessory pigments , are in stacks called granum (grana, plural) Grana are connected to each other & surrounded by a gel-like material called stroma Light-capturing pigments in the grana are organized into photosystems
- 4. Leaf Structure Most photosynthesis occurs in the palisade layer. Gas exchange of CO 2 and O 2 occurs at openings called stomata surrounded by guard cells on the lower leaf surface. Palisade Spongy
- 5. Chloroplast Structure Inner membrane called the thylakoid membrane. Thickened regions called thylakoids . A stack of thylakoids is called a granum . (Plural – grana) Stroma is a liquid surrounding the thylakoids.
- 6. Pigments Chlorophyll A is the most important photosynthetic pigment. Other pigments called antenna or accessory pigments are also present in the leaf. Chlorophyll B Carotenoids (orange / red) Xanthophylls (yellow / brown) These pigments are embedded in the membranes of the chloroplast in groups called photosystems .
- 7. Photosynthesis : The Chemical Process Occurs in two main phases. Light reactions Dark reactions (aka – the Calvin Cycle) Light reactions are the “photo” part of photosynthesis. Light is absorbed by pigments. Dark reactions are the “synthesis” part of photosynthesis. Trapped energy from the sun is converted to the chemical energy of sugars.
- 8. Calvin Cycle Carbon atoms from CO2 are bonded or "fixed" into organic compounds during a process called carbon fixation The energy stored in ATP and NADPH during the Light Reactions is used in the Calvin cycle The Calvin cycle has 3 main steps occurring within the stroma of the Chloroplast 1. Carboxylation - CO2 is covalently linked to a carbon skeleton (RuBP) 2. Reduction - carbohydrate is formed at the expense of ATP and NADPH 3. Regeneration - the CO2 acceptor RuBP reforms at the expense of ATP
- 9. Light Reactions Light-dependent reactions occur on the thylakoid membranes. Light and water are required for this process. Energy storage molecules are formed. (ATP and NADPH) Oxygen gas is made as a waste product.
- 10. Dark Reactions Dark reactions (light-independent) occur in the stroma. Carbon dioxide is “fixed” into the sugar glucose. ATP and NADPH molecules created during the light reactions power the production of this glucose.
- 11. Factors Determining the Rate of Photosynthesis Light intensity - As light intensity increases, the rate of photosynthesis initially increases and then levels off to a plateau Temperature - Only the dark, not the light reactions are temperature dependent because of the enzymes they use (25 oC to 37oC) Length of day Increasing the amount of carbon dioxide available improves the photosynthesis rate Level of air pollution
- 12. Photosynthesis in Overview Process by which plants and other autotrophs store the energy of sunlight into sugars. Requires sunlight, water, and carbon dioxide. Overall equation: 6 CO 2 + 6 H 2 0 C 6 H 12 O 6 + 6 O 2 Occurs in the leaves of plants in organelles called chloroplasts.