Photosynthesis

Question 1

What is the chloroplast?

Answer 1

An organelle found in plants and algae that is the site of photosynthesis
They are transducers and convert light energy into chemical energy

Question 2

Where is the chloroplast found in plants?

Answer 2

Palisade mesophyll

Question 3

How are chloroplasts adapted for photosynthesis?

Answer 3

Thylakoids give A large surface area for light-independent reactions
Storma directly surrounds grana- products of photosynthesis diffuse directly into storms
Contain their own DNA and ribosomes

Question 4

What is a photosynthetic pigment? And give some examples

Answer 4

A molecule present in chloroplasts that absorbs certain wavelengths of light
Chlorophylls a and b
Beta carotene

Question 5

What is chromatography used for?

Answer 5

Used to observe and identity the pigments involved in photosynthesis

Question 6

How is the Rf value calculated?

Answer 6

Distance travelled by pigment / distance travelled by solvent front

Question 7

Explain the process of chromatography.

Answer 7

1) mixture of pigments is extracted from the leaves and applied the to origin.
2) chromatogram is placed in solvent and left to run
3) pigments travel different distances according to solubility
4) Rf value is calculated and compared to known data to identify pigments.

Question 8

What is a photosystem?

Answer 8

Light capturing complexes located in the thylakoid membrane that contains different pigments that absorb different wavelengths.

Question 9

Describe the structure of a photosystem

Answer 9

• the antennae complex contains chlorophyll a, chlorophyll b and the carotenoids xanthophyll and beta carotene. Light energy is absorbed and passed to the reaction centre
• reaction centre contains 2 molecules of chlorophyll a. Electrons in these molecules are excited and rise to a higher level.

Question 10

Describe the non-cyclic photophosphorylation light dependent reaction

Answer 10

1) photon of light absorbed by pigment in the antennae complex of PSll. Energy passed to reaction centre, an electron from each of the chlorophyll a molecules is excited. This leaves the oxidised chlorophyll a
2) electrons pass through the ETC. Flow of protons allow ATP synthesis
3) A photon of light hits PSl and the same reaction occurs as stage 1. But electron acceptors pass it to NADP forming reduced NADP
4) photolysis of water. Water splits into hydrogen oxygen and electrons. Electrons replace those lost by chlorophyll a. O2 is a by product of

Question 11

Describe cyclic photophosphorylation

Answer 11

Electron acceptor that received electrons from PSl passes them back down the PSl.

Question 12

How does chemiosmosis produce ATP in the light- dependent stage?

Answer 12

• protons flow down their concentration gradient from the thylakoid space into the stroma via ATP synthase
• ATP synthase phosphorylates ADP to fuel ATP as protons flow through it

Question 13

Describe photolysis

Answer 13

The splitting of A molecule of water in the presence of light that occurs during the light-dependent stage. Producing protons, electrons and oxygen
H2O > 2H+ + 2e + 1/2O2

Question 14

What happens to the products of photolysis?

Answer 14

H+ = used in proton pump and to reduce NADP
e- = replaces electrons lost from chlorophyll a in PSll
O2 = by-product, used for respiration or diffuses out of the leaf as waste gas

Question 15

What is the light independent stage also known as?

Answer 15

The Calvin Cycle

Question 16

Name the 3 main stages of the Calvin cycle

Answer 16

1) Carbon fixation
2) Reduction
3) Regeneration

Question 17

What happens during carbon fixation of the Calvin cycle?

Answer 17

• reaction betweenCO2 and ribulose bisphosphate (RuBP) catalysed by enzymes RuBisCo
  -Firming unstable 6C intermediate that breaks down into two molecules of glycerate 3- phosphate

Question 18

What happens during reduction of the Calvin Cycle?

Answer 18

2x GP are reduced to 2x triose phosphate
This requires 2x reduced NADP and 2x ATP formed during the light dependent reaction
Forms 2x NADP and 2x ADP that enter the light dependent reaction

Question 19

What happens during regeneration of the Calvin cycle

Answer 19

After 1C leaves the cycle, the 5C compound RuP forms
RuBP is regenerated from RuP using ATP
Forming 1 ADP

Question 20

What are the essential minerals in A plant and what is their function?

Answer 20

Magnesium - Chlorophyll production
Nitrogen ( as nitrates or ammonium) - Synthesis of nuclei acids, proteins and chlorophyll

Question 21

What happens if there is a lack of essential minerals?

Answer 21

Nitrogen- reduce growth of all organs and yellowing of leaves
Magnesium - Yellowing of the leaves

Question 22

What is a limiting factor ?

Answer 22

A variable that limits the rate of a particular reaction.