11.Photosynthesis

Question 1

What’s the sites of photosynthesis

Answer 1

In the leaf in chloroplasts

Question 2

What are the adaptations of leaf (to bring together water, carbon dioxide and light)

Answer 2

Large SA for Sun,hit absorption
leaf arrangement
Thin-short diffusion pathway for gases/light
Transparent cuticle and epidermis let light to mesophyll cells
Long narrow mesophyll cells packed together collect light
Numerous stomata for gaseous exchange
Stomata open and close in response to light intensity
Air spaces in lower mesophyll layer rapid diffusion of gase
Xylem network brings water to leaf cells

Question 3

What’s the equation for photosynthesis

Answer 3

6co2 + 6h2o —-> c6h12o6 + 6o2

Question 4

What’s the three main stages of photosynthesis

Answer 4

1-capturing of light energy by chloroplast pigments eg chlorophyll
2-light dependent reaction light energy absorbed into chemical bonds , electron flow created causes water to split into protons electrons oxygen, procure nadp atp oxygen
3-independent reaction in which protons and hydrogen ions used to produce sugars and organic molecules

Question 5

What’s structure and role of chloroplasts in photosynthesis

Answer 5

Grana-stacks of disc structures called thylakoids(light dependent reaction takes place) within thylakoid is chlorophyll pigment, intergranal lamellae join thylakoids to other adjacent grana

Stroma-fluid filled matrix where light independent reaction takes place, within stroma is starch grains

Question 6

What is oxidation

What is reduction

Answer 6

Oxidation-gain of oxygen or loss of hydrogen or loss of electrons

Reduction-loss of oxygen or gain of hydrogen or gain of electrons

O.i.l.r.i.g

Question 7

What happens in the light dependent reaction

Answer 7

• Light strikes PSII, embedded in the thylakoid membrane. energy funneled down and absorbed by chlorophyll a in reaction centre.
• raises energy level of two electrons in chlorophyll a molecule.
• ‘excited electrons’ become energised, they leave the chlorophyll molecule -photoionisation of chlorophyll
• chlorophyll molecule is oxidised which initiates photolysis (the splitting of water) into 1O, 2H+ and 2e-. -2e- replace the 2 lost from the chlorophyll molecule.
• two high energy electrons that left pass along electron carriers in the membrane (cytochromes), called the electron transfer chain, through a series of redox reactions.
• As electrons pass along they release energy. electron carriers double up as proton pumps and energy from electrons powers them
• electrochemical grad set up by pumping protons into thyklakoid against chem grad
• protons diffuse down their electrochemical gradient through the ATP synthase channel-chemiosmosis
• triggers shape change in ATP synthase, resulting in the phosphorylation of ADP to form ATP.
• two electrons that have passed through the electron transfer chain are then transferred to PSI, where they are re-energised when light strikes PSI.
• The two high energy electrons reduce NADP+ into reduced NADP / NADPH (catalysed by NADP reductase).

Question 8

What’s photolysis of water

Answer 8

-loss of electrons when light strikes chlorophyll molecules leaves it short of electrons. If chlorophyll is absorbing light energy then electrons must be replaced, replacement electrons are providing when water molecules split using light energy

2h2o ——> 4H+ + 4e- + o2

Question 9

Why is reduced NADP important

Answer 9

It is potential source of chemical energy for plant, oxygen is by-product of photolysis and is either used in respiration. Or diffuses pout fo leaf as waste product

Question 10

How are chloroplasts structurally adapted for their function of capturing light and carry out LDR

Answer 10

• thylakoid membrane = large SA Fro attachment of chlorophyll, eclrron carriers, and enzymes that carry out LDR
• networks of proteins in gran hold chlorophyll in precise manner
• granal membranes have atp synthase channels, selectively permeable allow establishment of proton grad, and synthesise atp
• chloroplast contain both dna and ribosomes to produce proteins involved quickly

Question 11

What happens in Calvin cycle

Answer 11

• carbon dioxide diffuses into leaf through stomata and dissolves in water around walls of mesophyll cells, diffuses through c.s membrane into stroma of chloroplast
• carbon dioxide reacts with 5 carbon compound ribulose bisphosphate (RuBP) a reaction catalysed by rubisco
• reaction produces 2 molecules of glycerate 3-phosphate
• redNADP used to reduce GP to triose phosphate using ATP
• NADP reformed and goes back to LDR
• some TP converted to organic substances eg glucose
• most TP used to regenerate ribulose bisphosphate (RuBP) using ATP