Module 6: Section 6 - Ecosystems

Question 1

That’s right…

Answer 1

…it never ends

Question 2

define habitat

Answer 2

habitat - the place where an organism lives

if you didn’t get that right by now then you might as well fuck off out of here

Question 3

define population

Answer 3

population - all the organisms of one species in a habitat

Question 4

define producer

Answer 4

producer - an organism that produces organic molecules using sunlight

Question 5

define consumer

Answer 5

consumer - an organism that eats other organisms

Question 6

define decomposer

Answer 6

decomposer - an organism that breaks down dead or undigested organic material e.g. bacteria and fungi

Question 7

define trophic level

Answer 7

trophic level - a stage in a food chain occupied by a particular group of organisms, e.g. producers are the first trophic level in a food chain

Question 8

What are biotic factors?

Answer 8

biotic factors - the living features of an ecosystem. e.g. the presence of predators or food

Question 9

What are abiotic factors?

Answer 9

abiotic factors - the non-living features of an ecosystem. e.g. the temperature, rainfall…

Question 10

How do you calculate net productivity?

Answer 10

net productivity = gross productivity - respiratory loss

Question 11

Explain how you calculate energy transfer between trophic levels

Answer 11

1) to measure the energy transfer between two trophic levels you need to calculate the difference between the amount of energy in each level (the net productivity of each level)
2) you can calculate the amount of energy in a trophic level by measuring the dry mass of the organisms
3) first, calculate the amount of biomass in a sample of the organisms, e.g. a 1 m sq area of wheat or a single mouse that feeds on the wheat
4) then you multiply the results from the sample by the size of the total population to give the total amount of energy in the organisms at that trophic level
5) the difference in energy between the trophic levels is the amount of energy transferred

Question 12

Name some problems with the traditional method of calculating energy transfer between trophic levels

Answer 12

-the consumers might have taken in energy from sources other than the producer measured. this means the difference between the two figures calculated wouldn’t be an accurate estimate of the energy transferred between only those two organisms. for an accurate estimate you’d need to include all the individual organisms at each trophic level

Question 13

Give me six farming methods that increase productivity by increasing the transfer of energy through an ecosystem

Answer 13

1) herbicides - kill weeds that compete with agricultural crops
2) fungicides - kill fungal infections that damage agricultural crops
3) insecticides - kill insect pests
4) natural predators - introduced to an ecosystem eat the pest species
5) fertilisers - provide nutrients that aid growth, e.g. nitrates
6) rearing livestock intensively involves controlling the conditions they live in, so more of their energy is used for growth and less for other activities

Question 14

What are some pros and cons of rearing livestock intensively

Answer 14

the benefits are that more food can be produced in a shorter space of time, often at lower cost. However, enhancing productivity by intensive rearing raises ethical issues

Question 15

Please explain the first stage of the nitrogen cycle: nitrogen fixation

Answer 15

• nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by bacteria such as rhizobium and azotobacter. The ammonia can then be used by plants
• rhizobium are found inside root nodules of leguminous plants
• they form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the plant provides them with carbohydrates
• azotobacter are found living in the soil. They don’t form mutualistic relationships with the plants

Question 16

Please explain the second stage of the nitrogen cycle: ammonification

Answer 16

• ammonification is when nitrogen compounds from dead organisms are turned into ammonia by decomposers, which goes onto form ammonium ions
• animal waste also contains nitrogen compounds. These are also turned into ammonia by decomposers and go on to form ammonium ions

Question 17

Please explain the third stage of the nitrogen cycle: nitrification

Answer 17

• nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates)
• first nitrifying bacteria called nitrosomonas change ammonium ions into nitrates
• then other nitrifying bacteria called nitrobacter change nitrites into nitrates

Question 18

Please explain the fourth and final stage of the nitrogen cycle: denitrification

Answer 18

• denitrification is when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce nitrogen gas
• this happens under anaerobic conditions, e.g. in waterlogged soils

Question 19

Succession is the process by which an ecosystem changes over time. The biotic conditions (e.g. plant and animal communities) change as the abiotic conditions change (e.g. water availability). Please explain primary and secondary succession

Answer 19

1) primary succession - this happens on land that’s been newly formed or exposed, e.g. where a volcano has erupted to form a new rock surface, or where sea level has dropped exposing a new area of land. There’s no soil or organic material to start with, e.g. just bare rock
2) secondary succession - this happens on land that’s been cleared of all the plants, but where the soil remains, e.g. after a forest fire or where a forest has been cut down by humans

Question 20

Primary succession starts when species colonise a new land surface. Seeds and spores are blown in by the wind and begin to grow. The first species to colonise the area are called pioneer species - what are the conditions and what happens during the first stage of primary succession?

Answer 20

• the abiotic conditions are hostile. only pioneer species grow because they’re specialised to cope with the harsh conditions, e.g. marram grass can grow on sand dunes near the sea because it has deep roots to get water and can tolerate the salty environment
• the pioneer species chance the abiotic conditions - they die and microorganisms decompose the dead organic material (humus). This forms a basic soil
• this makes conditions less hostile which means new organisms can move in and grow. these then die and are decomposed, adding more organic material, making the soil deeper and richer in minerals. This means larger plants like shrubs can start to grow in the deeper soil, which retains even more water. As more plants move in they create more habitats, so more animals move in

Question 21

The final stage of succession is called climax community - please explain this

Answer 21

-the final stage is called the climax community - the ecosystem is supporting the largest and most complex community of plants and animals it can. It won’t change much more, it’s in a steady state

Question 22

Which species make up the climax community depends on what the climate’s like in an ecosystem. The climax community for a particular climate is called its climate climax. Please explain this using the example of a temperate climate

Answer 22

in a temperate climate there’s plenty of available water, mild temperatures and not much change between the seasons. The climatic climax will contain large trees because they can grow in these conditions once deep soils have developed. In a polar climate there’s not much available water, temperatures are low and there are massive changes between the seasons. Large trees won’t ever be able to grow in these conditions, so the climatic climax contains only herbs or shrubs, but it’s still the climax community

Question 23

What does plagioclimax mean?

Answer 23

when succession is prevented artificially by humans, the climax community is called a plagioclimax

Question 24

When does deflected succession occur?

Answer 24

deflected succession is when succession is prevented by human activity, but the plagioclimax that develops is one that’s different to any of the natural stages of the ecosystem - the path of succession has been deflected from its natural course

Question 25

You need to be able to investigate populations of organisms, to do this you need to be able to define the terms abundance and distribution

Answer 25

1) abundance - the number of individuals of one species in a particular area. The abundance of mobile organisms and plants can be estimated by simply counting the number of individuals in samples taken. Percentage cover can also be used to measure the abundance of plants - this is how much of the area you’re investigating is covered by a species
2) distribution - this is where a particular species is within the area you’re investigating