3.2 Photosynthesis 5

Question 1

What is a cholorplast?

Answer 1

An organelle found in plants and algae, site of photosynthesis

Question 2

Describe structure of chloroplast

Answer 2

Double membrane
Grana - stacks of thylakoids that contain photosystems, electron transport chains, ATP Synthase
Grana connected by Intergranal lamellae
Stroma - fluid filled matrix containing enzymes

Question 3

Where are chloroplasts located in an angiosperm leaf?

Answer 3

Mainly found in mesophyll layers

Question 4

How are chloroplasts adapted for photosynthesis?

Answer 4

• Thylakoids have large surface area for light dependent reactions
• Photosynthetic pigments arranged into photosystems to maximise light absorption
• Stroma directly surrounds grana - products of photosynthesis diffuse directly into stroma
• Contain their own DNA and ribosomes
• Inner chloroplast membrane less permeable than outer allows control over the movement of substances

Question 5

How are angiosperm leaves adapted for photosynthesis?

Answer 5

• Large surface area to maximise light absorption
• Upper epidermis transparent to allow light to strike mesophyll layers
• Palisade layers densely packed to contain many chloroplasts
• Vein network - transports water and minerals to leaf and takes away sugars
• Air spaces reduce diffusion distance for CO2
• Thin to reduce diffusion distance for CO2
• Stomata - allows CO2 to diffuse into the leaf

Question 6

What is a transducer? Why are chloroplasts described as transducers?

Answer 6

Something that converts one form of energy into another
Chloroplasts convert light energy into the chemical energy of ATP

Question 7

What is a photosynthetic pigment?

Answer 7

A molecule present in chloroplast that absorb certain wavelengths of light

Question 8

Examples of photosynthetic pigments

Answer 8

Chlorophyll a
Chlorophyll b
Xanthophyll
Beta Carotene

Question 9

Purpose of chromatography?

Answer 9

To separate different products from a mixture

Question 10

Equation used to calc the retention value (Rf)

Answer 10

Retention value (Rf)= distance travelled by component/ distance travelled by solvent

Question 11

What is photosynthesis?

Answer 11

Complex metabolic pathway that synthesises organic molecules in the presence of light: 6CO2+6H2O -> C6H12O6 + 6O2

Question 12

Two stages of Photosynthesis:

Answer 12

Light dependent stage
Light independent stage

Question 13

What is a Photosystem?

Answer 13

• Two types: Photosystem I and Photosystem II
• Protein complex consisting of an antenna complex and a reaction centre
• Involved in the absorption of light and transfer of electrons in photosynthesis

Question 14

Difference between Photosystems I & II

Answer 14

They absorb different wavelengths of light

Question 15

Describe the process of light harvesting:

Answer 15

Antenna complex absorbs light energy of varying wavelengths and transfers to the reaction centre
Energy absorbed by two chlorophyll a molecules which emit excited electrons.

Question 16

Absorption Spectra?

Answer 16

Graph showing wavelengths of light absorbed by a pigment

Question 17

Action Spectra?

Answer 17

Graph of the rate of photosyntesis against each wavelength of light absorbed by a pigment

Question 18

The sources of electrons for the electron transport chain

Answer 18

cyclic and non-cyclic photophosphorylation

Question 19

Define cyclic photophosphorylation

Answer 19

The formation of ATP invovling Photosystem I only

Question 20

Outline cyclic photophosphorylation

Answer 20

Involves only Photosystem I
Excited electrons enter the electron transport chain to produce ATP and return to Photosystem I
No reduction of NADP and no water required to replace lost electrons

Question 21

What is the purpose of cyclic photophosphorylation

Answer 21

Produces additional ATP to provide surplus energy demands of the cell

Question 22

Define non-cyclic photophosphorylation

Answer 22

The formation of ATP and reduced NADP involving both Photosystems I and II

Question 23

Outline non-cyclic photophosphorylation

Answer 23

Involves Photosystems I and II
Excited electrons enter the electron transport chain to produce ATP
NADP acts as a final electron acceptor and is reduced
Water is photolysed to compensate for electrons lost from Photosystem II

Question 24

What is the purpose of non-cyclic photophosphorylation?

Answer 24

Produces ATP and reduced NADP for the Calvin cycle

Question 25

How does chemiosmosis produce ATP in the light dependent stage?

Answer 25

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 26

Describe photolysis

Answer 26

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

Question 27

What happens to the products of photolysis?

Answer 27

H+ - used in proton pumping and to reduce NADP e- - replaces electrons lost from chlorophyll a in PSII O2 - by-product used in respiration or diffuses out of leaf as waste gas.

Question 28

Explain how the electron transport chain results in the production of reduced NADP.

Answer 28

NADP acts as a final electron acceptor, is subsequently reduced

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-dependent stage to build organic molecules

Question 30

What is the light-independent stage also known as?

Answer 30

The Calvin Cycle

Question 31

The three main stages of the Calvin Cycle:

Answer 31

1. Carbon fixation 2. Reduction 3. Regeneration

Question 32

What happens during the carbon fixation of the Calvin Cycle?

Answer 32

- Reaction between CO2 and ribulose biphosphate (RuBP) catalysed by the enzyme RuBisCo - Forms unstable 6C intermediate that breaks down into two molecules of glycerate 3-phosphate (GP)

Question 33

What happens during the reduction of the Calvin Cycle?

Answer 33

2x GP are reduced to 2x triose phosphate (TP) 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 34

What happens during the regeneration of the Calvin Cycle?

Answer 34

After 1C leaves the cycle the 5C compound RuP forms RuBP is regenerated fron RuP using 1x ATP Forms 1x ADP

Question 35

How are nutrients produced as a result of photosynthesis?

Answer 35

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

Question 36

What is a limiting factor?

Answer 36

A variable that limits the rate of a particular reaction

Question 37

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

Answer 37

Light intensity - light-dependent stage Light wavelength - absorption of chlorophyll CO2 levels - light-independent stage Temperature - enzyme-controlled reactions pH - enxyme-controlled reactions

Question 38

Describe the role of nitrogen in plant metabolism.

Answer 38

Synthesis of amino acids, nucleotides and chlorophyll.

Question 39

What does nitrogen deficiency in plants cause?

Answer 39

Stunted growth Chlorosis (yellowing of the leaves)

Question 40

Describe the role of magnesium in plant metabolism.

Answer 40

Synthesis of chlrophyll

Question 41

What does magnesiumdeficiency in plants cause?

Answer 41

Chlorosis (yellowing of the leaves)