Photosynthesis long q

Question 1

Explain how the light-independent reactions of photosynthesis rely on the light-dependent reactions

Answer 1

Light dependent reaction produced ATP and reduced NADP. ATP is produced by chemiosmosis by photophosphorylation. Reduced NADP is produced by the electrons from photosystem I

RuBP + CO2 to produce a 6C catalysed by Rubisco, which is unstable and produces glycerate 3-phosphate, glycerate 3-phosphate is reduced to triose phosphate.

ATP and reduced NADP are used in light-independent reaction. ATP provides energy for the reduction of glycerate 3-phosphate and regeneration of RuBP, reduced NADP provides electrons to reduce glycerate 3-phosphate.

ATP and reduced NADP run out in darkness and Calvin cycle is only possible with light.

Question 2

Explain the role of hydrogen ions used in photosynthesis

Answer 2

hydrogen ions are obtained from photolysis of water.

Excited electrons from photosystem II contribute to generating a hydrogen ion gradient

ATP generates ATP by chemiosmosis, using the proton gradient.

excited electrons from photosystem II are passed through an electron transport chain.

Photosystem I electron is excited and allows NADP accepts H+ to produce reduced NADP.

ATP and reduced NADP are used by light-independent reactions, the Calvin cycle in the stroma.

In Calvin cycle, there is carbon fixation, CO2 fixes to Ribulose biphosphate and turns into a 6C molecule, which is then turned into turned into 2 G3P (glycerate 3-phosphate).

ATP and reduced NADP are used to transform G3P into triose phosphate

Question 3

Describe how the structure of the chloroplast is adapted to its function in photosynthesis

Answer 3

Thylakoids have a small internal volume to quickly increase the hydrogen concentration gradient

There are many thylakoids to give large surface area

thylakoids have photosynthetic pigments, chloroplast a, b and carotenoids.

Pigments are arranged into photosystems to allow maximum absorption of light energy

Stroma has enzymes and suitable pH for Calvin cycle (light independent reaction)

lamellae connects grana to maximize photosynthetic efficency

Question 4

Explain light dependent reaction

Answer 4

Photosynthetic pigment in photosystem II absorbs light. The light excites the electron and it passes through the electron transport chain through electron carriers.

The energy from the electrons are used to pump protons across thylakoid membrane into the thylakoid space. ATP is then produced when protons diffuse out through ATP synthase, known as chemiosmosis.

The electron from photosystem II is passed to photosystem I. Light excites the electron in photosystem I, which is used to produce NADPH.

Electrons from photolysis for photosystem II. Oxygen from photolysis is a waste product and is excreted.

In cyclic photophosphorylation, electrons from photosystem I returns to photosystem I.

Question 5

Explain light independent reaction

Answer 5

it takes place in the stroma of the chloroplast, produces carbohydrates.

Carbon fixation occurs as carbon dioxide fixes onto Ribulose biphosphate (5C) using Rubisco. The product is an unstable 6C molecule which turns into 2 Glycerate 3-phosphate (G3P).

G3P is then reduced to Triose phosphate (TP) using ATP and reduced NADPH, which were produced in the light dependent reaction.

Some triose phosphate are used to produce hexose sugars, while some are used to regenerate Ribulose biphosphate to restart the Calvin cycle.