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 the light dependent reaction and where does it occur?

Answer 25

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 26

What is photolysis?

Answer 26

Light energy is absorbed to split water into H+ , e- and O2

Question 27

What is the light independent reaction?

Answer 27

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