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AQA A Level Biology > 3.3.4 Energy Transfer Through Ecosystems > Flashcards

3.3.4 Energy Transfer Through Ecosystems Flashcards

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1
Q

What is biomass?

A

Mass of living material

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2
Q

What can biomass be thought as?

A

Chemical energy stored in organisms

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3
Q

How is biomass measured in terms of? (2x)

A
  • Mass of carbon that organism contains
  • Dry mass of organism’s tissue per unit area
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4
Q

What is dry mass?

A

Mass of organism with water removed

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5
Q

Describe how you would measure dry mass

A
  1. Sample of organism is dried in oven set at low temp (heat to evaporate water)
  2. Sample weighed at regular intervals (every day)
  3. Once mass becomes constant = all water is removed
  4. Weigh the dry mass
  5. (Result from sample can be scaled to give dry mass (biomass) of total population or area being investigated)
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6
Q

Mass of carbon present is generally __% of dry mass

A

50

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7
Q

How you can estimate the amount of chemical energy stored in biomass?

A

By burning biomass in calorimeter

Heat given off = how much energy is in it

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8
Q

Describe how you can estimate the amount of chemical energy stored in biomass using calorimetery

A
  1. Sample of dry biomass is burnt and energy released is used to heat known volume of water
  2. Change in temperature of water is used to calculate the chemical energy of dry biomass
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9
Q

What’s the unit for biomass?

A

kg m-2

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10
Q

Name reasons why most of the sun’s energy isn’t converted to
organic matter by photosynthesis

A
  1. Most of Sun’s energy is reflected by into space
  2. Not all wavelengths of light can absorbed & used for photosynthesis
  3. Light may not fall on chlorophyll molecule
  4. Factor e.g. CO2 levels may limit rate of photosynthesis
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11
Q

State the equation to work out the efficiency of energy transfers

A

Energy transfer = energy available after transfer ÷ energy available before the transfer x 100

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12
Q

Name 2 cons of pyramids of numbers

A
  • No account of size is taken e.g. one giant tree = one tiny aphid
    • ∴ sometime pyramid is not a pyramid
  • Number of individuals can be so large that it’s impossible represent them accurately on same scale as other species in food chain
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13
Q

Name a pro of pyramids of biomass

A
  • More reliable, quantitative descriptions of food chain
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14
Q

Name 2 cons of pyramids of biomass

A
  • Only represents the organisms present at the time
    • Doesn’t account for seasonal differences
  • Organisms must be killed ∴ small sample = may not be representative
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15
Q

Name 2 pros of pyramids of energy

A
  • Most accurate representation of energy flow through food chain
  • Results are more reliable than biomass
    • Two animals could have same dry mass but store different amounts of energy
      • e.g. organism with more stored fat = more energy than other organism will less fat
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16
Q

Name a con of pyramids of energy

A
  • Collecting data is difficult + complicated
    • Data has to be collected in given area for set period of time
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17
Q

Define gross primary production (GPP)

A

Total amount of chemical energy converted from light energy by plants, in given area

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18
Q

50% of gross primary production is lost to environment as heat as _____ _____. What is this known as?

A

50% of gross primary production is lost to environment as heat plants respire

Respiratory loss (R)

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19
Q

What is net primary production (NPP)?

A
  • Remaining chemical energy (after respiratory loss)
    • Energy available to plant for growth and reproduction (i.e. energy stored in its biomass)
    • Also energy available to organisms at next stage in food chain i.e. herbivores and decomposers
20
Q

State the equation to work out net primary production (NPP)

A

NPP = GPP - R

21
Q

What is primary productivity?

A

Rate at which plants convert light energy into chemical energy

kJ ha-1 year-1

22
Q

Name 3 reasons why not all chemical energy stored in consumers’ food is transferred to next trophic level

A
  • Not all parts of food is eaten
  • Parts that are ingested:
    • Some are indigestible ∴ egested as faeces
      • Chemical energy stored in these parts ∴ lost to environment
    • Some energy is lost environment though respiration or execration of urine
23
Q

What is consumers’ net production AKA secondary production?

A

Energy that’s left i.e. stored in consumers’ biomass & is available to next trophic level

24
Q

State how net production of consumers can be calculated

A
25
Q
A
26
Q
A
27
Q

Calculate net primary productivity

A
28
Q

What do food chains + webs show?

A

How energy is transferred through ecosystem

29
Q

What is each stage in a food chain called?

A

Trophic level

30
Q

Name the 2 main ways farming practice increases the amount of energy available for human consumption

A
  1. Energy lost to other organisms (e.g. pests) can be reduced
  2. Energy lost through respiration can be reduced
31
Q

Explain how simplifying food webs reduces energy loss to other organisms

A
  1. Pests (weed, mouse and aphid) reduce amount of energy available for crop growth & ∴ NPP
    • = reduces amount of energy available for humans
  2. By simplifying the food web (get rid of food chains that don’t involve humans) = energy losses will be reduced & NPP of crop increase
32
Q

Name 2 ways to simplify food webs to reduce energy loss to other organisms

A
  1. Reduce pest numbers by using chemical pesticides
  2. Biological agents also reduce number of pests
33
Q

Describe 2 examples of chemical pesticides that be used to reduce pest numbers

A
  • Insecticides
    • Killing insect pests = less biomass is lost from crops = grow larger = NPP is greater
  • Herbicides
    • Killing pests = further reduce their numbers & simplify food web
34
Q

Give 2 examples of biological agents that can reduce the number of pests

A
  • Parasites live in or lay their eggs on pest insect
    • Kill insect or reduce its ability to function
  • Pathogenic bacteria and viruses kill pests
35
Q

Why do farmers use integrated systems that combine both chemical and biological methods?

A

Combined effect = reduce pest numbers even more = NPP increased even more

36
Q

Explain how controlling the conditions livestock are in can lead to an increase in net production

A
  • So more of their energy used for growth & less lost through respiration
  • Means more biomass is produced & more chemical energy can be stored
  • = increases net production & efficiency of energy transfer to humans
37
Q

Name 2 conditions livestock are kept and explain why

A
  • Movement increases rate of respiration ∴ animals kept in pens where movement is restricted
  • Pens are indoors and kept warm = less energy is wasted generating body heat
38
Q

Name some benefits of restrictive farming

A

More food in shorter amount of time + at lower cost

39
Q

Name some drawbacks of restrictive farming

A

Ethical issues: conditions = pain, distress or restricts natural behaviour

40
Q

Potatoes are food storage organs, called tubers.

When this variety was grown in a hot climate, with a mean daytime temperature of 23.5˚C, it failed to produce tubers. Explain why no tubers were produced. (3)

A
  • Photosynthesis rate only just above respiration rate
  • Little gain in biomass OR net loss in biomass due to (night-time) respiration
  • No excess production for storage in tubers
41
Q

Explain the change in the pest population over the period when they were treated with insecticide alone (4)

A
  • Most pests killed
  • (Some survive because) some resistant/insecticide does not reach all individuals
  • Survivors reproduce
  • Because of reduced competition/greater availability of food
42
Q

In plants: Explain why CO2 uptake is a measure of net productivity (1)

A

Shows (gross) photosynthesis

i.e. net productivity = (gross) photosynthesis – (minus) respiration

43
Q

The ratio of the dry biomass of animals to the dry biomass of seaweeds is always a lot less than the one. Explain why. (2)

A
  • Seaweeds/plants are producers / animals are consumers
  • Loss of energy between trophic levels as a result of respiration / as heat
44
Q

Conservation officers were working on the beaches used in this investigation. They noticed that there were fewer larger seaweeds on beaches used by a large number of people than on beaches visited by only a few people. Explain how the data in Figure 3 support this. (2)

A
  • Site U with most people has the largest ratio / 3.24
  • (Large value of ratio due to) large biomass ÷ small number
45
Q

What is the advantage of using dry mass and not fresh mass to compare the yield of plants? (2)

A
  • Amount of water present will vary
  • This will affect fresh mass / will not affect dry mass

AQA A Level Biology (41 decks)

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