Environmental Interactions - cycles

Question 1

how is a community formed in ecology?

Answer 1

• formed of the populations of all the species present in an ecosystem at a particular time

Question 2

What are the ways in which the species in a community continuously interact with each other and the physical environment?

Answer 2

• feeding on each other- this allows nutrients to be recycled
• competition for resources (e.g. food, mates, nesting sites, light, mineral ions)
• using abiotic resources - e.g. absorbing mineral ions from the soil and using water

Question 3

How can we simply show feeding relationships in an ecosystem?

Answer 3

• using food chains - simple, but helps us to make measurements (like counting the number of organisms)

Question 4

What do the arrows in a food chain represent?

Answer 4

• means “is eaten by” / flow of energy
  -show direction that energy and biomass moves, from the species that is eaten to the animal that eats it.

Question 5

What are the stages in a food chain/ web called?

Answer 5

Trophic levels

Question 6

How can we label the organisms in food chains/webs?

Answer 6

• producers and consumers
• first animal is primary consumer, second, secondary consumer and then the tertiary consumer

Question 7

What are de composers vital for?

Answer 7

• recycling nutrients- however they are rarely drawn in food chains and webs

Question 8

What does a food web represent?

Answer 8

• more complex
• shows links between many species
• particularly useful for understanding the links between the species in a community
• e.g. if the leap off seals were all removed from the environment, we can use a food web to predict what will happen.

Question 9

What can we use to represent the relative amounts of organisms at each trophic level?

Answer 9

• ecological pyramids

Question 10

What are pyramids of number?

Answer 10

• drawn to show the number of each organism counted in the ecosystem
• they can be off shapes due to the different masses of organisms

Question 11

What are pyramids of biomass?

Answer 11

• drawn to show the total mass of the organisms in each trophic level (i.e. the mass of an individual x the number of individuals)
• these are a more accurate way of looking at the relative amounts of organisms

Question 12

What are pyramids of energy?

Answer 12

• drawn to show the total energy available in each trophic level per square metre per year
• there should be a decrease in energy between each trophic level

Question 13

What is the least efficient energy transfer?

Answer 13

• light energy to the producer

Question 14

Why is the least efficient energy transfer from light energy to the producer?

Answer 14

• this is because, some light will miss the plant or miss the plant’s chloroplasts
• some light will be reflected by the cuticle
• some light has the wrong wavelength to be absorbed by chlorophyll

Question 15

Approximately what percentage of energy is passed from one trophic level to the next?

Answer 15

10%

Question 16

Why is only 10% of energy passed from one trophic level to the next?

Answer 16

• some parts of the organisms aren’t eaten (so the biological molecules aren’t available for respiration)
• some parts are not digested and absorbed - they are egested as faeces (so the biological molecules aren’t available for respiration)
• some materials are respired to release energy- the energy is used for:
  - muscle contraction- e.g. movement and breathing
  - maintaining a constant body temperature (in mammals and birds)
  - synthesising biological molecules (including excretory products)
  - movement of molecules (active transport)
  - cell division

Question 17

What is the carbon cycle?

Answer 17

• when plants photosynthesise, carbon atoms from carbon dioxide become part of glucose molecules (which is stored as starch) in the plant.
  
  • some of this carbon is broken down by the plant in respiration, the carbon in the glucose becomes part of the carbon dioxide molecule again, and is released back into the air
  • some of the carbon compounds in the plant will be eaten by animals, the animals respire, releasing some of it back into the air as carbon dioxide
  • when the plant/animal dies, decomposers (bacteria and fungi) will feed on them. The Carbon becomes part of the decomposers’ bodies. When they respire, they release carbon dioxide into the air again
  • fossilisation - occurs when living things do not decay fully when they die because of the conditions in the soil, fossil fuels are then formed over millions of years by a process called locking in, which include coal, oil, natural gas and peat
  • when fossil fuels are burnt (combustion), carbon dioxide is released into the atmosphere.

Question 18

Label this picture of the carbon cycle.

Answer 18

*on notes *

Question 19

What is the nitrogen cycle?

Answer 19

1. Nitrogen fixing bacteria in the soul and roots of legume plants absorb nitrogen and reduce it to make ammonia. This process is called nitrogen fixation.
2. The ammonia is converted to nitrites and nitrates by nitrifying bacteria- this process is called nitrification.
3. Plant roots can only absorb the nitrates. They are combined with carbohydrates (from photosynthesis) to form amino acids which are then made into proteins, and nucleotides which are joined to make DNA and RNA.
4. Animals eat plants. They digest the proteins and the DNA, absorbing the small soluble molecules (amino acids and nucleotides). These are used by the animal to synthesise (make) new proteins and DNA (assimilation).
5. When a plant or animal dies it’s tissues are decomposed by bacteria and fungi (saprotrophic feeding)
6. Molecules containing nitrogen such as proteins are broken down by the bacteria and fungi and ammonia is released into the soil.
7. Some nitrates are converted into N2 by Denitrifying bacteria. This process is called denitrification.

Question 20

Why are bacteria and fungi called decomposers?

Answer 20

• because they break down the dead remains and release the chemicals for the plants to use again
• feeding and assimilation pass nitrogen- for example in protein molecules- along food chains

Question 21

Name the 4 processes in the nitrogen cycle.

Answer 21

• decomposition
• nitrification
• denitrification
• nitrogen fixation

Question 22

Decomposition:
- description
- bacteria involved

Answer 22

• Protein in dead plants and animals is broken down, ammonia is released into the soil
• Decomposing bacteria

Question 23

Nitrification:
- description
- bacteria involved

Answer 23

• Ammonia is converted into nitrates, and nitrites are converted into nitrates.
• Nitrifying bacteria

Question 24

Denitrification:
- description
- bacteria involved

Answer 24

• Nitrates are converted to nitrogen gas (denitrification reduces the amount of nitrate in the soil and therefore makes the soil less fertile)
• Denitrifying bacteria

Question 25

Nitrogen fixation:
- description
- bacteria involved

Answer 25

• Nitrogen gas is converted to ammonia in bacteria which is used to make proteins, when the bacteria die their proteins decompose, releasing ammonia back into the soil
• nitrogen-fixing bacteria found in soil and in root nodules of plants

Question 26

Where do some nitrogen fixing bacteria live?

Answer 26

• in small structures- nodules- on the roots of legume plants
• This is a mutualistic relationship- the bacteria receive glucose from the plant, while the plant absorbs ammonia from the bacteria in the nodule.

Question 27

What happens when nitrogen fixing bacteria decomposes?

Answer 27

• make soil much more fertile by releasing ammonia which can be converted into nitrates
• this is why farmers may rotate the crops they grow in each field
• they could grow clover but instead they grow leguminous plants which they can then sell such as peas