5. energy transfers in and between organisms P2

Question 1

PHOTOSYNTHESIS

Describe how crop plants use light energy during the light-dependent reaction [5]

Answer 1

• the photolysis of water produces protons, electrons and oxygen.
• light excites electrons
• electrons move along electron transfer chain releasing energy.
• the energy is used to (pump protons from thylakoid to stroma creating an electrochemical gradient and then through ATP synthase via chemiosmosis) forming ATP from ADP and Pi.
• NADP reduces by electrons and protons.

Question 2

PHOTOSYNTHESIS

explain the role of light in photolysis

Answer 2

light energy splits water molecules into protons, electrons and oxygen

Question 3

PHOTOSYNTHESIS
what is the role of light in photoionisation in the light dependent stage of photosynthesis [2]

Answer 3

• chlorohyll absorbs light
• light excites electrons in chrolophyll
• electrons are lost

Question 4

PHOTOSYNTHESIS

what happens in the electron transfer chain?

Answer 4

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

Question 5

PHOTOSYNTHESIS

how is proton concentration gradient established during chemiosmosis?

Answer 5

some energy released from ETC is coupled to active transport of protons from stroma into thylakoid space

Question 6

PHOTOSYNTHESIS

how does chemiosmosis produce ATP in light-dependent reaction?

Answer 6

protons move down concentration gradient from thylakoid space into stroma through ATP synthase.

ATP synthase catalyses ADP+Pi—>ATP

Question 7

PHOTOSYNTHESIS

what happens to the products of photolysis of water?

Answer 7

protons move out of thylakoid space via ATP synthase and are used to reduce the coenzyme NAPD along with the electrons.

oxygen is used for respiration and diffuses out of leaf as waste gas

Question 8

PHOTOSYNTHESIS

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

Answer 8

NADP + proton + electron —> reduced NADP

Question 9

PHOTOSYNTHESIS

name the three main stages in the calvin cycle

Answer 9

carbon fixation
reduction
regeneration

Question 10

PHOTOSYNTHESIS

what happens during carbon fixation?

Answer 10

reaction between carbon dioxide and RuBP (ribulose biphosphate)

forms unstable 6 carbon molecule (2x GP)

Question 11

PHOTOSYNTHESIS

what happens during reduction in the calvin cycle?

Answer 11

2 x GP is reduced to 2 x TP (triose phosphate) which requires reduced NADP and ATP for energy.

forms NADP and ATP

Question 12

PHOTOSYNTHESIS

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

Answer 12

one carbon leaves the cycle

6 cycles to make glucose

Question 13

PHOTOSYNTHESIS

what happens during regeneration in the calvin cycle?

Answer 13

after 1C leaves the cycle, 5C is used to regenerate RuBP using ATP

(ATP—>ADP +Pi)

Question 14

PHOTOSYNTHESIS

state the roles of ATP and NADPH in the light independent reaction

Answer 14

ATP: reduction of GP to TP and provides energy to regenerate RuBP

NADPH: coenzyme transports electrons needed for the reduction of GP to TP

Question 15

PHOTOSYNTHESIS

a decrease in the activity in the enzyme rubisco would limit the rate of photosynthesis. explain why.

Answer 15

Less Co2 reacts with RuBP, so less GP

Question 16

PHOTOSYNTHESIS
where precisely is rubisco found in a cell?

Answer 16

stroma

Question 17

PHOTOSYNTHESIS

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves.

Answer 17

absorb different wavelengths of light for photosynthesis

Question 18

PHOTOSYNTHESIS

describe the structure of a chloroplast

Answer 18

usually disc shaped, double membrane

thylakoids - flattened discs stack to form grana

lamellae- tubular extensions attach thylakoids in adjacent grana

stroma - fluid-filled matrix

Question 19

PHOTOSYNTHESIS
in natural ecosystems, most of the light falling on producers is not used in photosynthesis. Give 2 reasons why

Answer 19

• light is reflected
• light is wrong wavelength

Question 20

PHOTOSYNTHESIS

how does the structure of the chloroplast maximise the rate of the light dependent reaction?

Answer 20

ATP synthase channels within granal membrane

large surface area of thylakoid membrane for electron transport chain.

photosystems position chlorophyll to enable maximum absorption of light

Question 21

PHOTOSYNTHESIS

how does the structure of the chloroplast maximise the rate of the light independent reaction?

Answer 21

own DNA and ribosomes for synthesis of enzymes (rubisco)

concentration of enzymes and substrates in stroma is high.

Question 22

PHOTOSYNTHESIS
explain why a decrease in the light-dependent reaction leads to a decrease in the light-independent reaction.

Answer 22

less ATP
less reduced NADP

Question 23

PHOTOSYNTHESIS

name 4 environmental factors that could limit the rate of photosynthesis

Answer 23

light intensity (light dependent stage)

CO2 levels (light independent stage)

temperature (enzyme controlled steps)

mineral/ magnesium levels (maintain normal functioning of chlorophyll)

Question 24

PHOTOSYNTHESIS

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

Answer 24

artificial light, especially at night

artificial heating

addition of CO2 to greenhouse atmosphere

Question 25

**PHOTOSYNTHESIS** why do farmers try to overcome the effect of limiting factors?

Answer 25

to increase yield additional cost must be balanced with yield to ensure maximum profit

Question 26

**PHOTOSYNTHESIS** as light is increased, it then plateaus. explain why

Answer 26

all NADP has become reduced from the non-cyclic photophosphorylation (light-dependent)

Question 27

**PHOTOSYNTHESIS** as CO2 concentration increases, so does photosynthesis up to a point. why does it stop increasing?

Answer 27

no more RuBP available as all combines with CO2 or no more rubisco (all have formed ES complexes)

Question 28

**PHOTOSYNTHESIS** as temperature increases, so does photosynthesis, up to a point. explain why it stops increasing

Answer 28

changed to tertiary structure of ATP synthase/ rubisco

Question 29

**PHOTOSYNTHESIS** how do plants use the sugars from photosynthesis?

Answer 29

- primarily as respiratory substrates - to synthesise other biological molecules e.g. cellulose

Question 30

**RESPIRATION** name the four main stages in aerobic respiration and where they occur

Answer 30

**glycolysis** - cytoplasm **link reaction** - mitochondrial matrix **Krebs cycle** - mitochondrial matrix **oxidative phosphorylation** - cristae

Question 31

**RESPIRATION** describe the process of glycolysis

Answer 31

- glucose is phosphorylated using ATP to form hexose biphosphate - this splits to form 2x triose phosphate - 2x TP is oxidised to form pyruvate - net gain of 2x reduced NAD and 2x ATP per glucose

Question 32

**RESPIRATION** outline the stages of the link reaction

Answer 32

- pyruvate is oxidised/ decarboxylated to acetate (NAD reduced) - acetate combines with coenzyme A to form acetyl-coenzyme A produces 2Co2, 2NADH and 2Acetyl coeunzyme A

Question 33

**RESPIRATION** give a summary equation for the link reaction

Answer 33

pyruvate + NAD + CoA —> acetyl CoA + NADH + CO2

Question 34

**RESPIRATION** outline the stages of the Krebs cycle

Answer 34

- acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6c) - CoA is released back to the link reaction to combine with acetate again - citrate is decarboxilated, NAD is reduced and ATP is used for energy (ADP+pi) - decarboxilated again to reform oxaloacetate. NAD is reduced and so is FAD

Question 35

**RESPIRATION** what is the electron transfer chain? (oxidative phosphorylation)

Answer 35

series of carrier proteins embedded in membrane of the cristae of mitochondria produces ATP through oxidative phosphorylation via chemiosmosis during aerobic respiration

Question 36

**RESPIRATION** what happens in the electron transfer chain (oxidative phosphorylation)

Answer 36

electrons released from NAD and FAD undergo redox reactions. the energy released maintains a proton gradient (protons move from matrix to cristae) oxygen acts as a final electron acceptor

Question 37

**RESPIRATION** how is a proton gradient established during chemiosmosis in aerobic respiration?

Answer 37

some energy released from the ETC is coupled to the active transport of H+ ions from the mitochondrial matrix to the cristae

Question 38

**RESPIRATION** how does chemiosmosis produce ATP during aerobic respiration?

Answer 38

H+ ions move down the electrochemical gradient from the cristae to the matrix via ATP synthase ATP synthase catalyses ADP+Pi —> ATP

Question 39

**RESPIRATION** state the role of oxygen in aerobic respiration

Answer 39

final electron acceptor in ETC (produces water)

Question 40

**RESPIRATION** what is the benefit of an electron transport chain rather than a single reaction?

Answer 40

energy is released gradually less energy is released as heat

Question 41

**RESPIRATION** name 2 types of molecule that can be used as alternative respiratory substrates

Answer 41

proteins lipids

Question 42

**RESPIRATION** what happens during anaerobic respiration in animals?

Answer 42

pyruvate +NADH —> lactate +NAD

Question 43

**RESPIRATION** what happens in anaerobic respiration in plants and yeast cells?

Answer 43

pyruvate is decarboxilated to form ethanal. ethanal is reduced to ethanol using NADH to produce oxidised NAD for further glycolysis

Question 44

**RESPIRATION** Explain why converting pyruvate to lactate allows the continued production of ATP by anaerobic respiration?

Answer 44

regenerates/ produces NAD so glycolysis can continue

Question 45

**RESPIRATION** compare aerobic and anaerobic respiration

Answer 45

both involve glycolysis both require NAD both produce ATP

Question 46

**RESPIRATION** describe the advantage of the bohr effect during intense exercise

Answer 46

increases dissociation of oxygen for aerobic respiration at the tissues/muscles/cells

Question 47

**ENERGY** what is biomass?

Answer 47

total dry mass of tissue or mass of carbon per given area and time

Question 48

**ENERGY** how can the chemical energy store in dry biomass be estimated?

Answer 48

using Calorimetry

Question 49

**ENERGY** how could a student ensure that all water had been removed from a sample before weighing?

Answer 49

heat the sample and reweigh it until the mass reading is constant

Question 50

**ENERGY** give the formula showing the relationship between GPP and NPP

Answer 50

NPP = GPP - R R = respiratory losses.

Question 51

**ENERGY** define gross primary production (GPP)

Answer 51

Total chemical energy in plant biomass within a given volume or area

Question 52

**ENERGY** define net primary productivity(NPP)

Answer 52

chemical energy store in plant biomass after respiratory losses to the environment have been taken into account

Question 53

**ENERGY** why is most of the suns every not converted to organic matter?

Answer 53

most solar energy absorbed by atmosphere or reflected in clouds. photosynthetic pigments cannot absorb some wavelengths of light. energy is lost as heat during respiration/photosynthesis.

Question 54

**ENERGY** how can the net production of consumers (N) be calculated?

Answer 54

N = I - (F+R) I = chemical energy lost by ingested food F= chemical energy lost by faeces. R= respiratory losses to environment.

Question 55

**ENERGY** why does biomass decrease along a food chain?

Answer 55

- energy lost in urine and faeces. - some of the organism isn’t consumed - energy lost to surroundings as heat.

Question 56

**ENERGY** define primary and secondary productivity

Answer 56

- rate of primary/ secondary production. - measured by biomass in a specific area over a given time period.

Question 57

**ENERGY** outline some common farming practices used to increase the efficiency of energy transfer

Answer 57

- simplifying food webs (exclusion of predators) to reduce energy lost to non-human food chains - artificial heating: reduce energy lost to maintain constant body temperature.

Question 58

**ENERGY** give the equation for % efficiency

Answer 58

energy converted to a useful form/ total energy supplied x100

Question 59

**ENERGY** explain why the length of food chains is limited

Answer 59

energy is lost at each trophic level so there is insufficient energy to support a higher trophic level.

Question 60

**NUTRIENT CYCLES** name the 4 main stages of the nitrogen cycle

Answer 60

nitrogen fixation ammonification nitrification denitrification

Question 61

**NUTRIENT CYCLES** outline the role of bacteria in nitrogen fixation

Answer 61

nitrogen fixing bacteria consume nodules of legumes for energy.

Question 62

**NUTRIENT CYCLES** outline the role of bacteria in ammonification

Answer 62

saprobionts

Question 63

**NUTRIENT CYCLES** describe the role of saprobionts in the nitrogen cycle

Answer 63

bacteria that decompose proteins which produces ammonium

Question 64

**NUTRIENT CYCLES** eutrophication can cause water to become cloudy. describe how you would obtain a quantitative measurement of their cloudiness.

Answer 64

- use of colorimeter - measure absorbance of light - standardised method, e.g. same volume of water, same wavelength of light etc.

Question 65

**NUTRIENT CYCLES** what is mycorrhizae?

Answer 65

symbiotic relationship between fungi and roots. Increases the surface area of roots

Question 66

**NUTRIENT CYCLES** what is nitrogen fixation?

Answer 66

nitrogen gas is converted into ammonium ions using nitrogen fixing bacteria

Question 67

**NUTRIENT CYCLES** what is ammonification?

Answer 67

dead organisms broke down (e.g. into amino acids). ammonia is released into the soul.

Question 68

**NUTRIENT CYCLES** what are the two stages of nitrification?

Answer 68

conversion of ammonium ions into nitrites conversion nitrites into nitrates using nitrifying bacteria

Question 69

**NUTRIENT CYCLES** what is denitrification?

Answer 69

nitrates being converted into nitrogen gas using denitrifying bacteria, in anaerobic conditions such as waterlogged soil or reduced O2

Question 70

**NUTRIENT CYCLES** other than biological nitrogen fixation, what are two other ways nitrogen can get into an ecosystem?

Answer 70

lighting artificial fertilisers

Question 71

**NUTRIENT CYCLES** why do plants and animals need phosphorus?

Answer 71

to make ATP, DNA, RNA, phospholipids

Question 72

**NUTRIENT CYCLES** Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions. Suggest why these soils contain relatively high conc of ammonium and low conc of nitrite/nitrate ions.

Answer 72

Less nitrification, less conversion of ammonium ions to nitrite and nitrate ions. More denitrification

Question 73

use your knowledge of NPP to explain why freshwater marshes have a high carbon use efficiency and the advantage of this

Answer 73

low respiration more biomass

Question 74

suggest one way in which an increase in the uptake of phosphate could increase plant growth.

Answer 74

used to produce ATP in cells

Question 75

give two examples of bio molecules containing nitrogen that would be removed when a crop is harvested

Answer 75

proteins DNA/ RNA