3.2 Photosynthesis

Question 1

What is a chloroplast?

Answer 1

An organelle found in plants and algae that is the site of photosynthesis

Question 2

Describe the structure of a chloroplast

Answer 2

• double membrane
• Grana - stacks of thylakoids that contain photosystems, ETC, ATP synthase
• Grana are connected by lamellae
• Stroma - fluid filled matrix containing enzymes

Question 3

Where are chloroplasts located in an angiosperm leaf?

Answer 3

Mainly found in the mesophyll layers

Question 4

How are chloroplasts adapted for photosynthesis ?

Answer 4

• thylakoids give large surface area for light-independent reactions
• photosynthetic pigments to maximise light absorption
• inner membrane less permeable to control movement of substances

Question 5

What is a transducer?

Answer 5

Something that converts one type of energy to another, chloroplasts transducer light energy into chemical

Question 6

What is a photosynthetic pigment?

Answer 6

Absorbs certain wavelengths of light

Question 7

Give some examples of photosynthetic pigment

Answer 7

• Chlorophylls a and b
• beta carotene
• xanthophylls

Question 8

What is the purpose of chromatography

Answer 8

To separate different products from a mixture

Question 9

State the equation used to calculate retention value (Rf)

Answer 9

Distance travelled by component ÷ distance travelled by solvent

Question 10

What is photosynthesis

Answer 10

A complex metabolic pathway that synthesised organic molecules in the presence of light

Question 11

What is the equation for photosynthesis

Answer 11

Carbon dioxide + water -> glucose + oxygen

Question 12

Name the two stages of photosynthesis

Answer 12

Light dependant stage and light independent stage

Question 13

What is a photo system?

Answer 13

• protein complex
• consists of antenna complex and reaction centre
• absorbs light and transfers electrons
• photo system I and II

Question 14

How do photosystems I and II differ?

Answer 14

They absorb different wavelengths of light

Question 15

Describe the process of light harvesting

Answer 15

• The antenna complex absorbs light energy and transfers it to the reaction centre
• energy is absorbed by two chlorophyll a molecules which emits excited electrons

Question 16

What is an absorption spectra?

Answer 16

A graph showing the wavelengths of light absorbed by a pigment

Question 17

What is an action spectra?

Answer 17

A graph of the rate of photosynthesis against each wavelength of light absorbed by a pigment

Question 18

Describe the light dependant- stage of photosynthesis

Answer 18

• first stage of photosynthesis
• takes place in the thylakoids of the chloroplast
• uses light energy to produce ATP, reduced NADP and oxygen

Question 19

State the sources of electrons for the electron transport chain

Answer 19

Cyclic and non cyclic photo phosphorylation

Question 20

Define cyclic photophosphorylation

Answer 20

The formation of ATP involving photosystem I only.

Question 21

Outline cyclic photo phosphorylation

Answer 21

• Photosystem I only

- excited electrons enter the ETC to produce ATP and then return to photosystem I

Question 22

What is the purpose of cyclic photo phosphorylation

Answer 22

Produces additional ATP to meet surplus energy demands of the cell

Question 23

Define non-cyclic photophosphorylation

Answer 23

The formation of ATP and reduced NADP involving both Photosystems

Question 24

Outline non-cyclic photophosphorylation

Answer 24

• both photosystems
• excited electrons enter the ETC to produce ATP
• NADP acts as final electron acceptor
• water is photolysed to replace electrons

Question 25

What is the purpose of non-cyclic photophosphorylation

Answer 25

Produces ATP and reduced NADP for Calvin cycle

Question 26

How does chemiosmosis produce ATP in the light-dependant stage

Answer 26

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

Question 27

Describe photolysis

Answer 27

Splitting of water molecule in the presence of light during light-dependant stage. Produces protons, electrons and oxygen.

Question 28

What happens to the products of photolysis

Answer 28

- H+ used in proton pumping and to reduce NADP - electrons replace those lost in photosystem II - oxygen diffuses out of leaf as waste

Question 29

Describe the light-independent stage of photosynthesis

Answer 29

- Second stage of photosynthesis - does not require light energy and takes place in the stroma - uses carbon dioxide and the products of the light-dependant stage to build organic molecules

Question 30

Name the three main stages of the light-independent stage

Answer 30

1. Carbon fixation 2. Reduction 3. Regeneration

Question 31

What is carbon fixation

Answer 31

It is a reaction between CO2 and RuBP catalysed by RuBP carboxylase. It forms an unstable 6C compound that breaks down into to molecules of glycerate 3-phosphate

Question 32

What happens during reduction of the Calvin cycle

Answer 32

* 2x GP are reduced to 2x triode phosphate (TP) * Requires 2x reduced NADP and 2x ATP formed during the light-dependant reaction * Forms 2x NADP and 2x ADP that enter the light-dependant reaction

Question 33

What happens during regeneration of the Calvin cycle

Answer 33

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

Question 34

How are nutrients produced as a result of photosynthesis?

Answer 34

* formation of amino acids from GP (requires nitrates and sulfates) * TP molecules used to produce sugars e.g glucose, fructose, sucrose

Question 35

What is a limiting factor?

Answer 35

A variable that limits the rate of a particular reaction

Question 36

Name the factors that limit the rate of photosynthesis. What stage do they limit?

Answer 36

* light intensity - light dependant state * CO2 levels - light-independent stage * temperature/ pH - enzyme-controlled reactions

Question 37

Describe the role of nitrogen in plant metabolism

Answer 37

Synthesis of amino acids, nucleotides and chlorophyll

Question 38

What does nitrogen deficiency in plants cause?

Answer 38

* stunted growth | * chlorosis ( yellowing of leaves )

Question 39

Describe the role of magnesium in plant metabolism

Answer 39

Synthesis of chlorophyll

Question 40

What does magnesium deficiency in plants cause?

Answer 40

Chlorosis (yellowing of leaves)