3.5 Energy Transfers

Question 1

What is the role of producers and how is it limited?

Answer 1

Plants photosynthesise and form biological molecules to form biomass

Limited:
•not enough light hitting the chlorophyll
•light can be reflected off
•different wavelengths of light

Question 2

How can biomass be measured?

Answer 2

•mass of carbon
•dry mass of tissue per given area, where its chemical energy is measured using calorimetry

Question 3

How is energy lost between trophic levels?

Answer 3

•lost by respiration
•excretion where energy contained in faeces and urine is transferred to decomposers
•not all parts are digested = egestion

(Cannot sustain many trophic levels)

Question 4

What is Gross and Net primary production? (+equation)

Answer 4

GPP= The chemical energy store in plant biomass, in a given area or volume, resulting from photosynthesis

NPP= The chemical energy store in the plant biomass, taking into account the energy lost due to respiration. (Represents dry mass of C)

NPP=GPP-R

Question 5

What is the equation for net production of consumers?

Answer 5

N= I - (F + R)
I:chemical energy store in ingested food
F:chemical energy lost to environment in faeces/urine
R:respiratory losses

Question 6

Why is rate of production measured in KJ ha-1 year-1?

Answer 6

•per unit area to standardise, allowing environments to be compared as it takes into account different environments will vary in size
•per year to take into account the impact of seasons on weather, providing an annual average to allow fair comparison between environments

Question 7

What methods are used in intensive farming?

Answer 7

•temperature controlled so less respiration to maintain body temp.
•limited space so restricted movement so less respiration
•controlled nutrients/high protein

(Less biomass is wasted in respiration)

Question 8

What are the disadvantages of intensive farming?

Answer 8

•infectious diseases can spread quickly so lots of antibiotics used which increases risk of antibiotic resistant bacteria
•unethical as animals get stressed

Question 9

Why is the biomass of the primary consumer higher than the producer (sometimes in a pyramid)?

Answer 9

Producers are reproducing slower than they are being consumed

Question 10

Why is intensive farming produce cheaper?

Answer 10

•faster rate of growth
•high survival rate so more plentiful food supply

Question 11

Why does higher biodiversity compared to monoculture cause higher food yields?

Answer 11

•pests tend to be specific so will not destroy all crops
•different species have different root length so less competition for e.g water/mineral nutrients

Question 12

Why does crop rotation lead to high crop yields?

Answer 12

•soils can regain mineral nutrients by e.g planting legumes (N-fixing bacteria)
•less spread of disease as different crops have different diseases
•different plants use different minerals so continued growth

Question 13

What is nitrogen fixing?

Answer 13

Nitrogen fixing bacteria e.g in legumes root nodules will convert N2 gas into ammonium or nitrates

Question 14

What is nitrification?

Answer 14

Nitrifying bacteria will turn ammonium into nitrites and then nitrates (aerobic conditions)

Question 15

What is the role of saprobiotic bacteria in the nitrogen cycle?

Answer 15

They will do extracellular digestion to hydrolyse proteins (faeces/urea), forming ammonium (ammonification)

Question 16

What is denitrification and what conditions does it need?

Answer 16

•Denitrifying bacteria converts nitrates into N2 gas
•waterlogged/poorly aerated (e.g no ploughing) so less O2 = anaerobic conditions

Question 17

What is mycorrhizae?

Answer 17

•Mutualistic relationship= fungal association between plant roots and beneficial fungi

1.fungi increases SA for water/mineral absorption
2.mycorrhizae holds water/minerals around roots
3.plants is more drought resistant and able to take up more inorganic ions

Question 18

What is the phosphorus cycle?

Answer 18

•sedimentary rocks are weathered/eroded to release PO4 3- into soils/water
•taken up by producers/consumers
•saprobionts will decompose dead matter/excretions to release into soil/oceans or to form sediment

Question 19

Why are fertilisers used?

Answer 19

To replace nitrates and phosphate ions in soil, lost when plants are harvested + removed from nutrients cycles as crop

Question 20

What are the advantages/disadvantages of natural fertilisers?

Answer 20

Ad:•cheaper/free as manure
•less soluble so less risk of leaching

Dis:•exact mineral proportion cannot be controlled
•smells
•unwanted material e.g fungal spores

Question 21

What are the advantages/disadvantages of artificial fertilisers?

Answer 21

Ad:•control exact proportion of mineral nutrients

Dis: •more water soluble so higher risk of leaching
•expensive

Question 22

What is eutrophication?

Answer 22

1.nitrogen fertiliser leaches into water
2.nitrates increase growth of algae and make a blanket on surface of water that blocks light
•plants below cannot photosynthesise and will die
•bacteria does microbial respiration as it decomposes dead matter
•decreases O2 content in water so organisms cannot respire and will die

Question 23

Why do natural fertilisers cause less leaching?

Answer 23

1.made of organic matter
2.which needs to be broken down by microorganisms in soil before
3.it means the release of mineral nutrients is more controlled and it is less likely to be leached into ponds/rivers

Question 24

What is the light dependent reaction and where does it occur?

Answer 24

In the thylakoid membrane
1.photoionisation=chlorophyll absorbs light energy and an e- is excited, lost and passed onto an e-acceptor
2.the e- will be transferred across an e-transport chain and will release energy in a series of redox reactions in the thylakoid membrane
3.energy is used to actively transport H+ from the stroma to the membrane which produces an electrochemical gradient
4.H+ will move back to the stroma via ATP synthase that will catalyse ADP + Pi = ATP
5.NADPH forms when NADP picks up H+ and an e-

Question 25

What is photolysis?

Answer 25

Light energy is absorbed by chlorophyll to split water into H+ , e- and O2
•chlorophyll will become oxidised as it loses e-

Question 26

What is the light independent reaction?

Answer 26

1.CO2 reacts with RuBP to from 2x GP. Catalysed by rubisco
2.ATP = ADP + Pi to release energy and NADPH release H+ and e- which are needed to reduce GP to triose phosphate
3.some triose phosphate is used to regenerate RuBP and some is converted to useful organic substances
4.This occurs in the stroma

Question 27

Why does the Calvin cycle slow down when there is low light energy?

Answer 27

•less NADPH and ATP will form in the light dependent reaction
•so less GP converts into Triose phosphate
•less RUPB is regenerated to join with co2

Question 28

Where and what occurs in glycolysis?

Answer 28

•cytoplasm
•phosphorylation of glucose to glucose phosphate, using x2 ATP= ADP
•2 triose phosphate are made
• x2 TP is oxidised to pyruvate (2x ADP +Pi = ATP and NAD to NADH)

Question 29

What is the net gain in glycolysis?

Answer 29

2 ATP
2 NADH
2 pyruvate

Question 30

Where and what happens in the link reaction?

Answer 30

•mitochondrial matrix
•pyruvate (3C) is oxidised to acetate
(2C)(NAD to NADH) by releasing CO2
•acetate will combine with coenzyme A to form acetyl coenzymeA (2C)

Question 31

What is the net gain in the link reaction?

Answer 31

2 NADH
2CO2
2 acetyl coenzyme A

Question 32

Where and what happens in the kreb’s cycle?

Answer 32

•mitochondrial matrix
•acetyl coenzyme A (2C) reacts with 4C to form 6C compound.
•The 6C is decarboxylated and dehydrogenated
•6C into 5C by loss of CO2 and NAD being reduced to NADH
•5C to 4C by loss of CO2, 2NAD into 2NADH, FAD into FADH and forming of ATP

Question 33

What is the net gain in the Kreb’s cycle?

Answer 33

•2 ATP
•6 NADH
•2 FADH
•4 CO2

Question 34

What occurs in oxidative phosphorylation?

Answer 34

•NADH/FADH is oxidised and releases an e- which is transferred to e- carriers in the inner membrane
•the e- are passed down a chain of e- carriers in a series of redox reactions, releasing energy
•this energy is used to actively transport H+ from the matrix to the intermembrane space (electrochemical gradient)
•H+ move back to matrix via ATP synthase, which catalyses ATP from ADP + Pi
•O2 is the last e- acceptor and will combine with H+ and e- to form H2O (recycles NADH and FADH)

Question 35

What happens in anaerobic respiration and where?

Answer 35

Cytoplasm:
•Pyruvate formed in glycolysis is reduced to from ethanol/CO2 (plants) or lactate (animals) by gaining H from NADH
•NAD can be reused in glycolysis so ATP production continues

Question 36

Why is anaerobic respiration useful and why can it not continue for long?

Answer 36

When no O2 is present, ATP is still released but lots of lactic acid/ethanol can denature enzymes in glycolysis

Question 37

How can lipids and proteins be used as substrates in respiration?

Answer 37

Lipids:
•3C glycerol enters glycolysis to be converted to pyruvate
•fatty acids = 2C to from acetyl coA

Proteins:
•amino group in aa is removed (deamination), so C part of aa can be converted to pyruvate or enter kreb’s cycle

Question 38

Why are lipids and carbs preferably used in respiration over proteins?

Answer 38

Many proteins have essential structural functions in body, so breakdown can cause health problems and even death

Question 39

What happens to lactate after production?

Answer 39

•oxidised back to pyruvate to enter link
•converted to glycogen for storage in liver

Question 40

Why is the apparatus left for 10 mins to calibrate in a respirometer?

Answer 40

1.reach equilibrium
2.allow for pressure change in apparatus
3.allow for respiration rate to stabilise