Chapter Ten: Photosynthesis

Q1: why is photosynthese important?

A1: Photosynthses produces oxygen and food by plants as producers, so cunsumers can use these to live.

Q2: where does photosynthesis take place?

A2: In chloroplast

Q3: what is major process of photosynthsis?

A3: 1. the light reaction in which solar energy is captured and transformed into chemical energy 2. calvin cycle in which chemical energy s used to make organic molecules of food.

Five Facts:

1. photosynthesis converts light energy to the chemical energy of food

2. the light reactions convert solar energy to the chemical energy of ATP and NADPH

3. the calvin cycle uses ATP and NADPH to convert CO2 to sugar

4. alternative mechanisms of carbon fixation have evolved in hot, arid climates

5. 6CO2+12H2O+light energy=C6H12O6+6O2+6H2O

Figure:

In certain climates sunlight is very abundant, and seldom if ever becomes limiting to photosynthesis. However, such climates as found in dry, hot regions can produce another limiting factor "CO2".One can think of it in terms of availability of H2O and the loss of H2O.
When the plant is photosynthesising in bright sun, the CO2 must enter the leaves through the stomata. But when these holes are "open" H2O can also escape therefore, the plant dehydrates. If you close the stomata CO2 becomes limiting. In these C4 plants, CO2 is bound into phosphenol pyruvate (pep), (recall glycolysis) in cells in the leaf known as "mesophyll cells". As CO2-pep and The CO2 is released into the bundle sheath cells, which surround the vascular bundle. In these bundle sheath cells the CO2 enters the Calvin cycle as usual. In effect the mesophyll cells of a C4 plant pump CO2 into the bundle sheath cells, keeping the CO2 concentration in the bundle sheath cells high enough for RUBISCO to fix CO2 rather than Oxygen. In this way C4 plants can minimise photorespiration and maximise sugar production.

Summary:

Plants are autptrphs which can produce organic molecules from CO2 and inorganic. consumers are heterotrophs unable to make own food. Photosynthsis takes place in chloroplasts which contain chlorophyll, green pigment can absorb light energy. Chloroplast has bilayer. stoma is the liquid inside the membrane. thylakoids are sacs stack to grana. NADPH is energy carrier like NADH in CR. light is a form of energy known as electromagnetic energy travels in rhythmic waves. the distance between crests of electomagnetic waves is called wavelength. the entire range is electromagnetic spectrum. the radiation between 380nm to 750nm is visible light. photons are particles of light. substances that absorb visible light are known as pigments. different types of pigments make more efficient. chlorophyll molecule put electron from groud state to excited state more energy. a photosystem is composed of a protein complex called a reaction-center complex surrounded by several light-harvesting complexes. the reaction-center complex contains a molecule capable of accepting electrons and becoming reduced called primary electron acceptor.

Light reaction occurs in thylakoids of photosystemII and photosystemI. it requires light, water,ADP, NADP+;it produces oxygen, ATP,NADHP. photon first goes into photosystemII. water split into oxygen, hydrogen ions, and electons. Photon put electrons to primary acceptor have higher energy. then electron goes down to electron trasport chain and form ATP. then it goes into photosystemI. photon from light again push it to primary acceptor. it then goes down electron trasport chain and stored in NADPH. since light reaction needs light, also called light dependent reaction. Calvon cycle, also called dark reaction happens in stroma. it requires carbon dioxide, ATP,NADPH; it produces glucose. 6O2 first catalyzed byrubisco, rearranged. one G3P comes out from 6G3P as a sugar. However, the climate gonne be super hot. if stoma open, dehydration. if it closes, CO2 limited. C4 plants and CAM plants can still survive in that stuiation. CAM plants open their stomata at night, incorporation CO2 into organic acids, which are atored in mesophyll cells. during daytime, the stomata close, and the CO2 is released from th eorganic acids for use in the calvincycle.

Key Term:

1. absorption spectrum-The range of a pigment’s ability to absorb various wavelengths of light; also a graph of such a range.
2. action spectrum-A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.
3. bundle-sheath cell-in C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of A leaf.
4. C3 plant-A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.
5. carbon fixation-The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote).
6. carotenoid-An accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.
7. chlorophyll a-A photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy.
8. cyclic electron flow-A route of electron flow during the light reactions of photosynthesis that involves only photosystem I and that produces ATP but not NADPH or O2.
9. mesophyll cell-In C4 plants, a type of loosely arranged photosynthetic cell located between the bundle sheath and the leaf surface.
10. linear electron flow-A route of electron flow during the light reactions of photosynthesis that involves both photosystems (I and II) and produces ATP, NADPH, and O2. The net electron flow is from H2O to NADP+.

Video:

http://www.youtube.com/watch?v=C1_uez5WX1o