Photosynthesis

Question 1

What are three examples of metabolic processes?

Answer 1

• active transport
• catabolic reactions
• movement

Question 2

What is photosynthesis?

Answer 2

light gets trapped by chlorophyll molecules, the energy is used to drive the synthesis of glucose from C02 and water

Question 3

What is respiration?

Answer 3

where organic molecules e.g. glucose are broken down into inorganic molecules such as water and C02

Question 4

What is the reversible equation for ATP?

Answer 4

ADP + Pi = ATP
(ATP Synthase)
ATP = ADP + Pi
(ATPase)

Question 5

What is chemiosmosis?

Answer 5

movement of protons form a region of high concentration to a region of low concentration, through a partially permeable membrane

Question 6

What are autotrophs?

Answer 6

can synthesis complex organic molecules e.g. carbohydrates and lipids from inorganic molecules

Question 7

What are heterotrophs?

Answer 7

cannot make their own food, digest complex organic molecules releasing the chemical potential energy stored in them e.g. animals

Question 8

What do both heterotrophs and autotrophs do?

Answer 8

respire and hydrolyse complex organic molecules

Question 9

What happens in the light dependent stage of photosynthesis?

Answer 9

• energy capture via photosystems (PS) 1 and 2 + photolysis

Question 10

Where does the light dependent stage occur?

Answer 10

Chloroplasts
Grana (thylakoids)

Question 11

What happens in the light independent stage of photosynthesis?

Answer 11

• carbon fixation via the Calvin cycle

Question 12

Where does the light independent stage occur?

Answer 12

Chloroplasts
Stroma

Question 13

What is a thylakoid membrane?

Answer 13

Flattened sacs, site of photosystems, electron carriers and ATP synthase

Question 14

What is a granum?

Answer 14

(single)
membranes are arranged into stacks to increase the surface area for the photosystems

Question 15

What are Lamella?

Answer 15

membranes which join the grana to one another

Question 16

What are stroma?

Answer 16

(equivalent to cytoplasm)
contains photosynthetic enzymes, where the Calvin cycle takes place

Question 17

Where are the ribosomes located in a chloroplast?

Answer 17

suspended in the Stroma

Question 18

What are photosynthetic pigments?

Answer 18

molecules that absorb light energy

Question 19

What are primary pigments?

Answer 19

Chlorophyll A

Question 20

Where are chlorophyll A found?

Answer 20

In the reaction centre = where reactions involved in photosynthesis take place

Question 21

What is a photosystem?

Answer 21

(the light harvesting system + reaction centre as a collective)

a funnel shaped light harvesting cluster of photosynthetic pigments, held in place in the thylakoid membrane

Question 22

What are accessory pigments?

Answer 22

absorb different wavelengths

e.g. Carotene and xanthophyll absorb red light

Question 23

What is PS1?

Answer 23

has Chlorophyll A (p700) as its reaction centre (peak of red light absorbance at 700nm) found in the lamellae

Question 24

What is PS2?

Answer 24

has Chlorophyll A (p680) as its reaction centre (peak of red light absorbance at 680nm) found in the grana

Question 25

Apart from red light, what other colour light does Chlorophyll A absorb?

Answer 25

blue at wavelength 450nm

Question 26

What colour light does Chlorophyll B absorb?

Answer 26

yellow/orange at wavelength 640nm

Question 27

Draw the structure where the light dependent stage takes place?

Answer 27

Picture on phone taken 10.04.2025

Question 28

What happens during ATP synthesis of the light dependent stage?

Answer 28

1. light reaches PS2 2. electrons are excited and leaves the chlorophyll, becomes oxidised 3. the electrons move from a high energy level to a low energy level cytochromes, pumping hydrogen ions into the thylakoid space 4. this establishes a proton gradient across the membrane (chemiosmosis) 5. protons flow down the conc. gradient through channels associated with ATP synthase 6. Photophosphorylation occurs and the ATP synthase triggers the production of ATP

Question 29

What is meant by photophosphorylation?

Answer 29

with light, adding a phosphate (to ADP)

Question 30

What happens during the formation of NADPH in the light dependent stage?

Answer 30

1. Light hits PS2 2. Electrons excited and become oxidised 3. Photolysis occurs (splitting of water) into H+ ions and E- 4. the electrons move from high energy level to low energy level cytochromes 5. There is the same proton gradient, as H+ is pumped into thylakoid space 6. Chemiosmosis - H+ moves into stroma, photophosphorylation 7. Light hits PS1 which excited the electrons so that : NADP + e- + H+ = NADPH (made in stroma) 8. Ferredoxin acts as the final electron acceptor

Question 31

What is cyclic photophosphorylation?

Answer 31

electrons leaving the electron transfer chain after PS1 can be returned to PS2, instead of being used to produce reduced NADPH = not photolysis, small amounts of ATP made

Question 32

What is non-cyclic photophosphorylation?

Answer 32

involves PS2, followed by PS1 and NADPH is formed

Question 33

What are the main products of the Light independent stage?

Answer 33

- Ribulose Biphosphate RuBP (5 carbon) - Glycerate 3 - Phosphate GP (3 carbon) - Triose Phosphate TP (3 carbon)

Question 34

Draw out the carbon cycle?

Answer 34

Picture taken on phone on 10.04.2025

Question 35

What is meant by fixation (carbon cycle)?

Answer 35

CO2 is fixed, incorporated into organic molecule

Question 36

What is meant by reduction (carbon cycle)?

Answer 36

GP is reduced to TP by the + of H+ from reduced NADP using energy supplied from the recycled TP

Question 37

What is meant by regeneration (carbon cycle)?

Answer 37

RuBP is regenerated from recycled TP

Question 38

What are the three factors that can influence the rate of photosynthesis?

Answer 38

1. CO2 conc. 2. Light Intensity 3. Temperature

Question 39

How does the CO2 concentration affect the rate of photosynthesis?

Answer 39

- if there is a high co2 conc... -leads to an increase in carbon fixation in the calvin cycle - leads to more molecules of TP, converted to hexose sugar, thus more generation of RuBP

Question 40

What happens to the rate of photosynthesis if the light intensity is increased?

Answer 40

rate of photosynthesis increases -it causes the stomata to open so more CO2 can enter - it is trapped by chlorophyll, where it excites electrons - it splits water molecules (photolysis) to produce protons

Question 41

What happens to the rate of photosynthesis when there is a decrease in light intensity?

Answer 41

reduces the rate of photosynthesis - reduces the levels of ATP and NADPH (reduced) - GP will accumulate and can't be reduced to TP - levels of RuBP will fall, as it can't be generated

Question 42

If the temperature increases, what happens to the rate of photosynthesis?

Answer 42

- rate of photosynthesis increases - the enzyme catalysed reactions of the Calvin Cycle, affected by temp - enzymes used in photolysis also impacted

Question 43

What is meant by Q10?

Answer 43

where Q10 = 2, a doubling of rate over 10 degrees temp increase is indicated

Question 44

What is the equation for Q10?

Answer 44

rate of O2 production at (t + 10degrees) ---------------------------------------------------------- rate of O2 production at t degrees = 2

Question 45

How does light energy lead to an excited electron?

Answer 45

- light energy is captured by accessory pigment - passed from one to the next accessory pigment - until it reaches the primary pigment (chlorophyll a) - when the accessory pigments absorb light energy, the electron is excited - when the primary pigment absorbs light energy, an electron is excited to a higher energy level, and is accepted by a primary electron acceptor