Photosynthesis

Question 1

What is the photosynthesis

Answer 1

Photosynthesis is the process where organisms convert light energy from the sun into organic molecules. It takes place in the chloroplasts
Carbon dioxide + water + sunlight - oxygen + glucose

Question 2

How are photosynthesis and respiration related?

Answer 2

CO2 and H2O are the raw materials for photosynthesis and the products of respiration
O2 and glucose are the raw materials for photosynthesis and the products of respiration

Question 3

What is the structure of a chloroplast

Answer 3

Large SA - maximises absorption of light
Lots of thylakoids which are stacked to form grana
Lots of mitochondria
Stroma - fluid filled matrix with high enzyme substrate concentration and own loop of DNA

Question 4

What are the two main stages of photosynthesis

Answer 4

Light dependent stage - energy from sunlight is absorbed and used to form ATP. Hydrogen from water is used to reduce coenzyme NADP to reduced NADP
Light independent stage - hydrogen from reduced NADP and CO2 is used to build organic molecules like glucose

Question 5

What are the photosynthetic pigments and why are they important

Answer 5

Primary pigments - chlorophyll ( a and b) found in photostems
Accessory pigments - carotenoids (carotene and xanthophylls) found in light harvesting systems

Question 6

What is the light dependent stage of photosynthesis

Answer 6

1. Photoionisation - chlorophyll molecules absorb energy from photons of light, this excites 2 electrons causing them to be released
2. Electron transfer chain - electrons released move down a series of carrier proteins embedded in thylakoid membrane and undergo redox reactions which release energy
3. Chemiosmosis - some energy released from ETC is used to help active transport of H+ ions from stroma into thylakoid space. These move down a concentration gradient from thylakoid space into stroma via transmembrane channel protein ATP synthase, this catalyses ADP + Pi - ATP

Question 7

Describe non cyclic photophosphorylation

Answer 7

It uses photsystems I and II, excited electrons enter ETC to produce ATP. NADP acts as final electron acceptor and is reduced.
Water is photolyses to release electrons to replace those lost from PSII
It produced ATP and reduced NADP for the Calvin cycle to produce biological compounds

Question 8

Describe cyclic photophosphorlyation

Answer 8

Uses photosystem I, excited electrons enter ETC to produce ATP then return directly to photosystem so no reduction of NADP and no water is needed to replace lost electrons
It produced additional ATP to meet surplus energy demands of cell

Question 9

What are the stages of the light independent reaction

Answer 9

1. Carbon fixation - reaction between CO2 and RuBP catalysed by RuBisCo. Forms unstable 6C intermediate which breaks down into 2 x GP
2. Reduction - 2 x GP reduced to 2 x TP, it requires 2 x reduced NADP and 2 x ATP. It forms 2 x NADP and 2 x ADP
3. TP - raw material: 1C leaves the cycle to produce monosaccharides, AA and other molecules. It is involved in the regeneration of RuBP after 1C leaves cycle the 5C compound RuP forms. RuP is converted into RuBP using ATP. Forms ADP

Question 10

What affects the rate of photosynthesis

Answer 10

Light intensity - higher = faster reaction more ATP and NADPH produced to convert GP to TP.
CO2 levels -
Temperature -

Question 11

What are the uses of triose phosphate (TP)

Answer 11

Used to make a range of biological molecules including carbohydrates, nucleic acids, lipids to regenerate ribulose bisphosphate

Question 12

How can TLC be used to separate photosynthetic pigments

Answer 12

1. Use a capillary tube to spot pigment onto pencil start line
2. Place chromotography paper in solvent
3. Allow solvent to run until it almost touches the end of the paper
   Different pigments move different distances