6.3.1 Ecosystems

Question 1

Define habitat

Answer 1

• the place where an organism lives

Question 2

Define population

Answer 2

• all the organisms of one species in a habitat

Question 3

Define producer

Answer 3

• an organism that produces organic molecules using sunlight energy e.g. plants

Question 4

Define consumer

Answer 4

• an organism that eats other organisms

Question 5

Define decomposer

Answer 5

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

Question 6

Define trophic level

Answer 6

• a stage in a food chain occupied by a particular group of organisms

Question 7

Define ecosystem

Answer 7

An ecosystem is a distinct, self-supporting system of organisms, interacting with each other and with a physical environment

• it is a dynamic system
• includes both biotic and abiotic factors

Question 8

What are biotic factors?

Answer 8

• the living features of an ecosystem

Question 9

What are abiotic factors?

Answer 9

• the non-living features of an ecosystem

e. g. pH, relative humidity, temperature

Question 10

What is a niche?

Answer 10

• the role of a species in an ecosystem

Question 11

What is the main route by which energy enter the ecosystem?

Answer 11

• in photosynthesis

Question 12

What is biomass?

Answer 12

• the mass of living materials

Question 13

How much of the total available energy is lost?

Answer 13

• around 90%

Question 14

Why is around 60% of the available energy not taken in by organism in the first place?

Answer 14

• plants can’t use all the light energy that reaches their e.g. some is the wrong wavelength some is reflected and some passes straight through the leaves
• some sunlight can’t be used because it hits part of the plant that can’t photosynthesise
• some parts of food e.g. roots or bones, aren’t eaten by organisms. this is passed to decomposers
• some parts of the food is indigestable, so pass through organisms and come out as waste and passes to decomposers

Question 15

What is gross productivity?

Answer 15

• the available energy (around 40%) that is absorbed

Question 16

How much of the gross productivity is taken to the next trophic level and why?

Answer 16

• 30% of total energy available (75% of gross productivity) is lost to the environment when organisms use energy produced from respiration for movement or body heat. this is called respiratory loss
• 10% of total energy available (25% of gross productivity) becomes biomass (e.g. stored or used for growth). this is called net productivity

Question 17

What is net productivity?

Answer 17

• net productivity or biomass is the amount of energy that’s available to the next trophic level
• the flow of energy transfer continues at the next trophic level
• net productivity = gross productivity - respiratory loss

Question 18

How do you measure the energy transfer between trophic levels?

Answer 18

• you need to calculate the difference between the amount of energy in each level (net productivity)
• measure the dry mass of the organisms as energy is stored as biomass
• calculate the amount of biomass in a sample of organisms
• 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
• different energy between the trophic levels is amount of energy transferred

Question 19

How do you calculate the efficiency of biomass transfer?

Answer 19

• (biomass at the higher trophic level / biomass at the lower trophic level) x 100

Question 20

What are some farming methods that increase productivity by increasing the transfer of energy through an ecosystem?

Answer 20

• herbicides kill weeds that compete with agricultural crops for energy. reducing competition means crops receive more energy, so they grow faster and become larger, increasing productivity
• fungicides kill fungal infections that damage agricultural crops. the crops use more energy for growth and less for fighting infections, so they grow faster and become larger, increasing productivity
• insecticides kill insect pests that eat and damage crops. less biomass is lost from crops, so they grow larger, meaning greater productivity
• natural predators introduced to the ecosystem eat the pest species e.g. ladybirds eat greenfly. means crops lose less energy and biomass, increasing productivity
• fertilisers provide minerals needed for growth e.g. nitrates. add fertilisers replaces lost minerals, meaning minerals won’t be the limiting factor. more energy from the ecosystem can be used to grow, increasing efficiency
• rearing livestock intensively includes controlling the conditions they live in, so more energy is used for growth and less for other activities. efficiency of energy conversion is increased so more biomass is produced and productivity is increased

Question 21

Give examples where livestock are controlled

Answer 21

• animals may be kept in warm, indoor pens where movements restricted
• less energy is wasted in keeping warm and moving \
• animals may be given feed that’s higher in energy than natural food. increases energy input, so more energy available for growth

Question 22

What is the carbon cycle?

Answer 22

• shows how carbon moves through living organisms and the non-living environment

Question 23

Describe the carbon cycle

Answer 23

• carbon in the form CO2 is absorbed by plants then they carry out photosynthesis. it becomes carbon compounds in plant tissues
• carbon is passed onto primary consumers when they eat the plants. then passed onto secondary and tertiary consumers when they eat other consumers
• all living organisms die and the carbon compounds in the dead organisms are digested by microorganisms called decomposer. feeding on dead organic matter is called saprotrophic nutrition
• carbon is returned to air and water as all living organisms carry put respiration, producing CO2
• if dead organic matter ends up in places without decomposers, their carbon compounds may turn into fossil fuel over millions of years
• the carbon fossil fuels are released when they’re burnt through combustion
• rocks such as limestone and chalk are composed of calcium carbonate which comes from dead organic matter such as crabs, mussels, sea urchins and coral. one way carbon can be returned to the atmosphere is through god movement of tectonic plates. undergo chemical changes and release CO2 by volcanic activity

Question 24

Draw the carbon cycle diagram

Answer 24

-GO!

Question 25

Why do plants and animals need nitrogen and what form of nitrogen does it use?

Answer 25

• to make proteins and nucleic acids (DNA and RNA)

- bacteria need to convert it into nitrogen compounds first

Question 26

Describe the four different process in the nitrogen cycle

Answer 26

1. Nitrogen fixation:
   - nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by bacteria such as Rhizobium or Azotobacter. ammonia can then be used by plants
   - Rhizobium are found inside root nodules of leguminous plants
   - they form a mutualistic relationship with plants as they provide nitrogen compounds and the plant provides them with carbohydrates
   - Azotobacter are found living in the soil and don’t form a mutualistic relationship with plants
2. Ammonification
   - ammonification is when nitrogen compounds from dead organisms are turned into ammonia by decomposer, which goes onto form ammonium ions
   - animal waste also contains nitrogen compounds. these are turned into ammonia by decomposers and go on to form ammonium compounds
3. Nitrification
   - this is when ammonium ions in the soil are changed into nitrogen compounds that can be used by plants (nitrates)
   - first nitrifying bacteria called Nitrosomonas change ammonium ions into nitrites (NO2-)
   - then Nitrobacter change nitrites to nitrates
4. Denitrifcation
   - when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria which use nitrates in the soil to carry out respiration and produce nitrogen gas
   - this happens under anaerobic conditions e.g. waterlogged soils

-nitrogen also gets into ecosystem as lighting also fixes atmospheric nitrogen and artificial fertilisers

Question 27

What is succession?

Answer 27

• succession is the process by which an ecosystem changes over time
• the biotic conditions change as the abiotic conditions change

Question 28

What are the two types of succession

Answer 28

• primary succession: this happens on land that has been newly formed or exposed. no soil or organic material to start with
• secondary succession: this happens on land that’s been cleared of all plants, but where soil remains

Question 29

Describe the stages of primary succession and in secondary succession

Answer 29

• primary succession starts when species colonise a new land surface. seeds and spores are blown in by the wind and begin to grow
• the pioneer species is the first species to colonise the area
• abiotic conditions are hostile, only pioneer species grown because they’re adapted to cope
• pioneer species change the abiotic conditions: they die and microorganisms decompose dead organic material (humus) and forms a basic soil
• this makes conditions less hostile e.g. basic soil helps retain water
• as organisms die and decomposed, soil becomes deeper and richer in minerals. larger plants e.g. shrubs, can grow
• as more plants move in, more habitats are created, so more animals move in
• at each stage, different plants and animals that are better adapted for the improved conditions move in and out compete the plants and animals already there, becoming the dominant species
• as succession goes on, ecosystem become more complex
• new species move in alongside existing increasing species diversity
• biomass increases
• final stage is climax community, the ecosystem supporting the largest and most complex community of plants and animals it can
• it won’t change much as it is in a steady state
• secondary succession happens in the same way but as there is already a soil layer, the pioneer species are larger plants

Question 30

Using an example, explain the stages of succession

Answer 30

sand dune succession:

• Embryo dunes: pioneer species like sea rocket and prickly sandwort (Salsa kali) colonise sand just above the high water mark. these can tolerate being sprayed with salty water, lack of fresh water and unstable sand
• Yellow mobile dunes: wind blown sand builds up around the base of these plants, forming mini mobile dunes. as plants die and decay, nutrients accumulate. as dune gets bigger, sea sandwort and sea couch grass colonise. the underground stems helps stabilise the sand
• fixed grey dunes: with more stability and accumulation of nutrients, sea splurge and marram grass grown. its shoots trap wind-blown sand and so shoots grow even taller
• wet slack: wet, moist and sheltered. has some denitrification. bigger shrubs and marshier plants in water
• climax community: sheltered, shady, mineral rich and stable. biodiverse with oak trees.

Question 31

What is a plagioclimax?

Answer 31

• when succession is stopped artificially

- e.g. human activities stopping normal climax community from developing

Question 32

What is the difference between deflected succession and plagioclimax?

Answer 32

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
- paths deflected from its natural course

Question 33

Give examples of plagioclimaxes

Answer 33

• a regular grown grassy field won’t develop woody plants, even if climate could support
• growing points of woody plants are cut off by lawnmower, so larger plants can’t establish themselves, only grosses than can survive been mowed
• climax community is a grassy field
• a grassy stage isn’t a natural stage and should have small flowering plants, so succession is deflected