3.5.1 photosynthesis

Question 1

where does photosynthesis occur

Answer 1

in the chloroplast

Question 2

describe the chloroplast membrane

Answer 2

double membrane envelope

Question 3

what are the grana and the stroma?

Answer 3

Grana are stacks of disc structures called thylakoids, LDR occurs here, lamella join adjacent grana
Stroma is a fluid filled matrix where LIR occurs these may contain starch grains

Question 4

what are photosynthetic pigments

Answer 4

coloured substances that absorb light energy

Question 5

what does the thylakoid membrane contain

Answer 5

pigments, enzymes and electron carriers for LDR

Question 6

why do thylakoids have a large surface area?

Answer 6

to allow maximum light energy absorption

Question 7

what is the function of a starch grain?

Answer 7

to store products of photosynthesis (sugar)

Question 8

describe a photosystem

Answer 8

funnel-like structure found in the thylakoid membrane, made from accessory pigments that absorb light energy and transfer it to the primary pigment reaction centre.

Question 9

what is the first step in the light dependent reaction

Answer 9

photolysis of water. light energy is absorbed by chlorophyll and splits H20 into O2, H+ and ELECTRONS in the thylakoid lumen. this forms a proton gradient in the thylakoid lumen

Question 10

what does photolysis of water produce?

Answer 10

protons, electrons and oxygen

Question 11

what is the equation for photolysis of water

Answer 11

H20 -> 1/2 O2 + 2e- + 2H+

Question 12

what is the second stage of LDR?

Answer 12

photoionization of chlorophyll. light energy is absorbed by the chlorophyll which results in electrons becoming excited to a higher energy level and leave the chlorophyll molecule. energy from released e- is used to make ATP and reduced NADP in chemiosmosis.

Question 13

what does ‘become excited’ mean

Answer 13

gains energy

Question 14

what is PSII and PSI

Answer 14

photosystem II and photosystem I located in the electron transport chain

Question 15

describe the first 3 steps of chemiosmosis

Answer 15

1. the excited electrons that left the chlorophyll are passed along the ETC.
2. as they move along each protein carrier, they release energy. this energy is used to actively transport the H+ protons from the stroma to the thylakoid lumen.
3. this results in a proton gradient. high conc of H+ in the thylakoid lumen and low conc in the stroma. there is also H+ present in the stroma due to photolysis

Question 16

why is the movement of electrons described as a redox reaction

Answer 16

The electron carriers are reduced (as they gain an electron) and then oxidised (lose the electron by passing it to next carrier)

Question 17

describe the last four steps of chemiosmosis

Answer 17

4. protons move down their conc gradient via ATP synthase.
5. the energy from this movement combines ADP and an inorganic phosphate to form ATP. this is phosphorylation.
6. light energy is absorbed by PS1 which excites e- to an even higher energy level.
7. electrons and H+ are transferred to co enzyme NADP to form reduced NADP.

Question 18

describe the way in which ATP and reduced NADP are produced in the light dependent reaction of photosynthesis (5)

Answer 18

ATP: light energy excites electrons to a higher energy level. energy is released as they move along carriers. this energy combines ADP+Pi.
NADP: excited electrons and H+ from photolysis

Question 19

describe how the structure of a chloroplast is adapted to its function in photosynthesis (3)

Answer 19

membrane disc shape provides a large SA for efficient light absorption. membrane layers allows many pigment molecules. stroma contains enzymes for LIR

Question 20

describe the role of water in the LDR (2)

Answer 20

splits water into electrons, H+ and oxygen. electrons are used to provide energy to form ATP and reduced NADP. H+ is used to form reduced NADP

Question 21

describe how plants absorb light energy from the sun and use this energy to produce useful substances in the LDR (5)

Answer 21

light energy is absorbed by PS2 in chlorophyll. this energy excites electrons to higher energy level and leave the chlorophyll molecule. electrons are passed along ETC/carriers releasing energy each time. this energy is used to make ATP from ADP + Pi and to form reduced NADP using H+ from photolysis

Question 22

DNP is a substance which allows electron transport to take place without production of ATP. when DNP is given to rats, their body temp rises. explain why (2)

Answer 22

energy is released as heat as it is not being used to produce ATP

Question 23

whats the function of ATP

Answer 23

to supply energy