photosynthesis (energy transfers in and between organisms)

Question 1

where in the chloroplasts do each of the stages of photosynthesis take place

Answer 1

light dependent reaction - thylakoids
light independent reaction - stroma

Question 2

explain the role of light in photoionisation

Answer 2

chlorophyll molecules absorb light energy which excites 2 electrons (raises them to a higher energy level), causing them to be released from chlorophyll

Question 3

name the 2 main stages of the light dependent reaction

Answer 3

electron transfer chain
chemiosmosis

Question 4

what happens in the electron transfer chain?

Answer 4

electrons removed from chlorophyll move down a series of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions which releases energy

Question 5

how is a proton concentration gradient established during chemiosmosis?

Answer 5

some energy released from the etc is coupled to the active transport of H+ ions from the stroma into the thylakoid space

Question 6

how does chemisosmosis produce atp in the light dependent stage

Answer 6

H+ ions move down their concentration gradient from the thylakoid space into the stroma via the channel protein, ATP
synthase

Question 7

Explain the role of light in photolysis

Answer 7

Light energy splits molecules of water
2H2O > 4H+ + 4e- + O2

Question 8

What happens to the products of the photolysis of water

Answer 8

H+ ions: move out of the thylakoid space via ATP synthase and are used to reduce the coenzyme NADP
e-: replace electrons lost from chlorophyll
O2: used for respiration or diffuses out of leaf as waste gas

Question 9

How and where is reduced NADP produced in the light-dependent reaction?

Answer 9

NADP + 2H+ + 2e- > reduced NADP.
Catalysed by dehydrogenase enzymes
Stroma of chloroplasts

Question 10

Where do the H+ ions and electrons used to reduce NADP come from?

Answer 10

H+ ions: photolysis of water
electrons: NADP acts as the final electron acceptor of the electron transfer chain

Question 11

Name the 3 main stages in the Calvin Cycle

Answer 11

Carbon fixation
Reduction
Regeneration

Question 12

What happens during carbon fixation?

Answer 12

Reaction between CO2 and ribulose bisphosphate (RuBP) catalysed by the enzyme rubisco
forms unstable 6C intermediate that breaks down into 2x glycerate 3-phosphate (GP)

Question 13

What happens during reduction in the calvin cycle

Answer 13

2x GP are reduced to 2x triose phosphate (TP)
requires 2x reduced NADP and 2xATP
forms 2xNADP and 2x ATP

Question 14

How does the light independent reaction result in the production of useful organic substances

Answer 14

1C leaves the cycle (Some of the TP is converted into useful organic molecules)

Question 15

What happens during regeneration in the calvin cycle

Answer 15

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

Question 16

state the roles of ATP and (reduced) NADP in the light independent reaction

Answer 16

ATP: reduction of GP to TP and provides phosphate group to convert RuP into RuBP
(reduced) NADP: coenzyme transports electrons needed for reduction of GP to TP

Question 17

State the number of carbon atoms in RuBP, GP and TP

Answer 17

RuBP : 5
GP: 3
TP: 3

Question 18

Describe the structure of a chloroplast

Answer 18

usually disc shaped
double membrane (envelope)
thylakoids: flattened dics to form grana
intergranal lamellae: tubular extensions attach thylakoids in adjacent grana
stroma: fluid-filled matrix

Question 19

How does the structure of the chloroplast maximise the rate of the light-dependent reaction?

Answer 19

ATP synthase channels within granal membrane
large surface area pf thylakoid membrane for ETC
photosystems position chlorophyll to enable maximum absorption of light

Question 20

How does the structure of the chloroplast maximise the rate of the light-independent reaction

Answer 20

own DNA and ribosomes for synthesis of enzymes
concentration of enzymes and substrates in stroma is high

Question 21

define limiting factor

Answer 21

factor that determines maximum rate of a reaction, even if other factors change to become more favourable

Question 22

name 4 environmental factors that can limit the rate of photosynthesis

Answer 22

light intensity (LDR)
CO2 levels (light-independent reaction)
temperature ( enzyme-controlled steps)
mineral/magnesium levels (maintain normal functioning of chlorophyll

Question 23

outline some common agricultural practices used to overcome the effect of limiting factors in photosynthesis

Answer 23

artificial light
artificial heating
addition of CO2 to greenhouse atmosphere

Question 24

Why do farmers try to overcome the effect of limiting factors

Answer 24

to increase yield

Question 25

Suggest how a student could investigate the effect of a named variable on the rate of photosynthesis

Answer 25

dependent variable: rate of O2 production / CO2 consumption
1. use a potometer
2. place balls of calcium alginate containing green algae in hydrogencarbonate indicator (colour change orange to magenta as CO2 is consumed and pH increases)

Question 26

state the purpose and principle of paper chromatography

Answer 26

molecules in a mixture are separated based on their relative attraction to the mobile phase (running solvent) vs the stationary phase (chromatography paper)

Question 27

Outline a method for extracting photosynthetic pigments

Answer 27

use a pestle and mortar to grind a leaf with an extraction solvent (propanone)

Question 28

outline how paper chromatography can be used to seperate photosynthetic pigments

Answer 28

1. use a capillary tube to spot pigment extract onto pencil ‘start line’ 1cm above the bottom of the paper
2. place chromatography paper in the solvent (origin should be above the solvent level)
3. allow solvent to run until it almost touches the other end of the paper. pigments move different distances

Question 29

What are Rf values and how can they be calculated

Answer 29

Ratios that allow comparison of how far molecules have moved in chromatograms.
Rf value = distance between origin and centre of pigment spot / distance between origin and solvent front