5.6 Photosynthesis

Question 1

What is an autotroph?

Answer 1

organisms that use light energy + inorganic molecules to make complex organic molecules

Question 2

What is a heterotroph?

Answer 2

digests complex organic molecules and releases energy

Question 3

What do many thylakoids make inside a choloroplast?

Answer 3

A granum

Question 4

Describe non-cyclic phosphorylation

Answer 4

Light strikes ps11, electrons of photosynthetic pigments vibrate and energy is channelled to primary pigment reaction centre (chlorophyll a)
Light energy excites a pair of electrons inside the chlorophyll a molecule which leave
Go through electron carrier, and are replaced by electrons from photolysis (electrons go thro ps1)
Going through carrier generates energy that’s used to pump H+ ions across the membrane
Causes gradient so H+ go back across membrane through ATP synthase forming ATP
The 2 electrons are taken by ferrodoxin which pass them to NADP in the stroma
NADP + 2e- + 2H+ –> NAPDH2 (reduced NADP)

Question 5

Describe cyclic phosphorylation

Answer 5

Light strikes ps1, electrons of photosynthetic pigments vibrate and energy is channelled to primary pigment reaction centre (chlorophyll a)
Light energy excites a pair of electrons inside the chlorophyll a molecule which leave
Go through electron carrier, H+ enters, goes back through ATP synthase forming ATP
The 2 electrons go back to PS1 again

Question 6

What is photophosphorylation?

Answer 6

The production of APT in presence of light

Question 7

Give an example of a photosynthetic pigment

Answer 7

Chlorophyll a b
Carotene
Xanthophyll

Question 8

What is the role of water in the light dependent stage of photosynthesis (4)

Answer 8

Source of protons (H+) used in photophosphroylation
Donates electrons to chlorophyll to replace those lost she light strikes chlorophyll
It’s a source of the by product, oxygen
Keeps plant cells turgid so they can function

Question 9

What are the 2 types of phosphorylation that make up the light dependant stage of photosynthesis?

Answer 9

Cyclic

Non cyclic

Question 10

What are the products of cyclic phosphorylation?

Answer 10

Small amount of ATP

Question 11

What are the products of non cyclic phosphorylation?

Answer 11

Reduced NADP
Half 02
ATP

Question 12

Describe the Calvin cycle (the light independant stage of photosynthesis)

Answer 12

RuBisCo enzyme converts RuBP and CO2 
to 2GP
(2ATP-2ADP+Pi) (reduced NADP-NADP)
2TP
(ATP-ADP)
RuBP

Question 13

3 photosynthesis limiting factors

Answer 13

Light intensity
Temp
Co2 conc

Question 14

Define photosynthetic pigments (3)

Answer 14

light absorbing/AW;
ref to excited electrons/AW;
used in light dependent stage;
ref. to location; e.g. chloroplasts, thylakoids,
photosystems, grana, lamellae
AVP; e.g. (long) hydrocarbon chains,
different pigments absorb different wavelengths.

Question 15

Explain difference between primary and accessory pigments (2)

Answer 15

(primary) act as reaction centres/where electrons are excited;
(accessory) other part of photosystem/antenna unit/surround reaction centre;
(accessory) absorb different wavelengths of light (not absorbed by primary);
(accessory pigments) transfer energy to primary pigments;