Ecosystems

Question 1

What is meant by a population?

Answer 1

The number of organisms of the same species living within an area

Question 2

What is meant by a community?

Answer 2

All of the populations of species living in an area

Question 3

What is meant by a habitat?

Answer 3

An environment where an organism naturally lives

Question 4

What is meant by an ecosystem?

Answer 4

• An area with many biotic and abiotic factors interacting with eachother
• They can be large or small

Question 5

How would you investigate the population size of an organism in two different areas?

Answer 5

• Measure the total area of the habitats (e.g. fields)
• Use a random number generator to find two different locations, one in each habitat
• Place two 1m² quadrats in both of these locations
• Count the number of plants of the given species found inside each quadrat, and multiply it by the total number of m² of the habitat to find the approximate population size in that habitat
• Compare the results for the two habitats
• The biodiversity in two different areas can be measured by counting the number of species in each quadrat and working out the percentage cover of each organism by measuring what percentage of squares (out of the 100) in the quadrat are occupied by a certain organism

Question 6

What is meant by biodiversity?

Answer 6

• The range and variety of species in an ecosystem
• It takes into account the number of different species, but not the population size
• However it does take into account the distribution - the more evenly distributed the populations of each organism in an ecosystem are, the higher the biodiversity

Question 7

How do biotic factors affect the population size and distribution of organisms?

Answer 7

• Higher numbers of prey mean more food is available and organisms can survive and reproduce for longer
• Higher numbers of predators means organisms may die before having the chance to reproduce
• If there are multiple organisms competing for the same resources (e.g. prey), the better adapted organism will get the resource more and survive longer while the other one may die before reproducing

Question 8

How do abiotic factors affect the population size and distribution of organisms?

Answer 8

• Higher light intensity, carbon dioxide levels and wind speed (because it increases the rate of transpiration and therefore movement of water) will increase the rate of photosynthesis, increasing the population of plants
• Plants and animals require the correct temperature, levels of moisture, and levels of oxygen for survival
• Plants also rely on soil pH and mineral content

Question 9

What are the six different trophic levels and what do each of them do?

Answer 9

• Producers - They produce their own nutrients from the sun
• Primary consumers - They feed on producers
• Secondary consumers - They feed on primary consumers
• Tertiary consumers - They feed on secondary consumers
• Quaternary consumers - They feed on tertiary consumers
• Decomposers - They feed on dead organisms or undigested waste through extracellular enzymes

Question 10

What is a food chain?

Answer 10

They show the transfer of energy from one organism to the next through the consumption of eachother

Question 11

What is a food web?

Answer 11

• A network of interconnected food chains
• It is a more realistic representation than a food chain because organisms rarely rely on just one other

Question 12

What is a pyramid of numbers?

Answer 12

• A pyramid showing the number of each organism at each trophic level
• It is usually a pyramid shape though not always as 1 tree can feed 500 ladybugs (for example)

Question 13

What is a pyramid of biomass?

Answer 13

• A pyramid showing the total biomass of the organisms at each trophic level (excluding the water levels)
• They will always be pyramid shaped as it is impossible for a larger mass to feed on a smaller mass
• They are much better at representing the amount of each organism and therefore the interdependence

Question 14

What is a pyramid of energy transfer?

Answer 14

• They illustrate the amount of energy contained within the biomass of the organisms within a trophic level
• They will also always be pyramids as large amounts of energy are lost as you ascend the trophic levels

Question 15

How is energy transferred along a food chain?

Answer 15

• Light energy from the sun is converted into chemical energy by producers, some of which is used for the plant to grow
• Primary consumers eat the producers and secondary consumers and tertiary consumers then eat eachother, using some of the energy they derive from the biomass of their food to grow
• Eventually, once the tertiary/quaternary consumers die, most of the energy is transferred to the environment - therefore this process is non-cyclical

Question 16

On average, what percentage of energy is transferred to the next trophic level in a food chain?

Answer 16

Approximately, only 10%

Question 17

Why is most of the energy lost from trophic level to trophic level?

Answer 17

• Organisms rarely eat every part of the organism they are consuming
• Not all the ingested material is digested and absorbed, some is egested as faece
• Energy is used for movement
• Energy is used to generate heat
• Energy is used for metabolic processes

Question 18

What are the ways in which organisms lose energy while they are alive?

Answer 18

• Energy is used for movement
• Energy is used to generate heat
• Energy is used for metabolic processes
• Some absorbed material is lost as waste:
  
  • Carbon dioxide and water are waste products of respiration
  • Water and urea are the waste products in the urine

Question 19

What are the stages of the carbon cycle?

Answer 19

• Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
• It is passed on to animals (and microorganisms) by feeding
• It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
• If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels
  -When fossil fuels are burned, the carbon combines with oxygen and carbon dioxide is released into the atmosphere

Question 20

What are the stages of the Nitrogencycle?

Answer 20

• Neither plants nor animals can absorb it from the air as N2 gas is very stable and cannot be easily broken down
• Nitrogen fixing bacteria convert N2 gas into ammonium compounds, which can then be converted to usable nitrates
• Plants absorb nitrogen from the soil in the form of nitrates and use it to build proteins
• Animals eat the plants and get the nitrogen they need from the plant proteins
  -Waste (urine and faeces) from animals sends nitrogen back into the soil in the form of ammonium compounds
• The bodies of dead plants and animals decay and all the proteins inside them are broken down into ammonium compounds by decomposers
• The plants can’t absorb ammonium compounds, so nitrifying bacteria convert the ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants – and so the cycle goes on
  -Denitrifying bacteria take nitrates out of the soil and convert them back into N2 gas