Module 6 Section 6 - Ecosystems

Question 1

What is a habitat?

Answer 1

The place where an organism lives eg a rocky shore or a field

Question 2

What is a population?

Answer 2

All the organisms of one species in a habitat

Question 3

What is a producer?

Answer 3

An organism that produces organic molecules using sunlight energy eg plants

Question 4

What is a consumer?

Answer 4

An organism that eats other organisms eg animals and birds

Question 5

What is a decomposer?

Answer 5

An organism that breaks down dead or undigested organic material eg bacteria and fungi

Question 6

What is a trophic level?

Answer 6

A stage in the food chain occupied by a particular group of organisms, eg producers are the first trophic level in a food chain

Question 7

What is an ecosystem ?

Answer 7

An ecosystem is all the organisms living in a certain area and all the non-living conditions found there. It is a dynamic system- as it is constantly changing

Question 8

What type of factors are in ecosystems?

Answer 8

1) biotic factors - the living features of an ecosystem
For example the presence of predators and food

2) abiotic factors - the non-living feathers of an ecosystem.
For example, temperature, rainfall and soil nutrient availability

Question 9

How do biotic and abiotic factors affect Rock pools?

Answer 9

Biotic factors- seaweed can be a common source of food for consumers such as limpets that graze on this producer. Intense competition for food such as seaweed can limit the number of organisms that are present in a small rock pool ecosystem.

Abiotic factors - rock pools are heavily influenced by the tide. At high tide, they are completely submerged by the ocean so experience similar abiotic factors eg pH, salinity, temperature to the ocean ecosystem. However at low tide, they experience more extreme abiotic factors eg higher salinity and temperatures, only some organisms can tolerate these conditions.

Question 10

How do biotic and abiotic factors affect a playing field?

Answer 10

Biotic factors - producers eat grass and other plants such as daisies, clover and dandelions. The large amount of these plants might attract a large number of organisms that use them as a food source eg rabbits and caterpillars

Abiotic factors - rainfall and sunlight affect the growth of the producers. In a very wet year, the soil may become waterlogged, making it difficult for plants to grow. Poor plant growth may decrease the number of consumers the ecosystem is able to support.

Question 11

How do biotic and abiotic factors affect a large tree?

Answer 11

Biotic factors - insects such as caterpillars, can use the leaves of a tree as a source of food. However if they consume all the leaves in a tree, they can slow down tree growth and even lead to its death.

Abiotic factors - drought conditions can negatively impact the growth of a tree. In sever cases it can cause the whole tree dying.

Question 12

How does energy enter an ecosystem?

Answer 12

The main route is photosynthesis. During photosynthesis, plants covert sunlight energy into a form that can be used by other organisms. They store energy as biomass.

Some energy enters sea ecosystems when bacteria use chemicals from deep sea vents as an energy source.

Question 13

What is biomass?

Answer 13

It is the mass of living materials eg the mass of plant material

Question 14

How is energy transferred though an ecosystem?

Answer 14

Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms. Organisms that eat producers are primary consumers and primary consumers are eaten by secondary consumers and these by tertiary consumers. These are called biomass transfers.

Question 15

How can we show the transfer of energy in an ecosystem?

Answer 15

1) food chains- these show simple lines of energy transfer

2) food webs - show lots of food chains in an ecosystem and how they overlap.

Question 16

What happens to energy that cannot be consumed?

Answer 16

Energy locked up in the things that can be eaten eg bones and faeces gets recycled back into the ecosystem by decomposers.

Question 17

What are decomposers?

Answer 17

Organisms that break down dead or undigested material eg bacteria and fungi.

Question 18

What percentage of energy is transferred between trophic levels?

Answer 18

10%

Question 19

Why is some of the energy never taken in by organisms ?

Answer 19

60% of available energy is never taken in

1) plants can’t use all the light energy that reaches their leaves eg some is the wrong wavelength and some is reflected, and some passes straight through the leaves.

2) some sunlight can’t be used because it hits parts of the plant that do not photosynthesise eg the bark of a tree.

3) some parts of food eg roots or bones aren’t eaten by organisms so energy isn’t taken in, it is passed to decomposers.

4) some parts of food are indigestible so pass through organisms and come out as waste eg faeces. This also passes to decomposers.

Question 20

What is gross productivity?

Answer 20

The energy that is taken in and absorbed . This is around 40%

Question 21

How is energy lost after it has been absorbed?

Answer 21

1) 30% of the total energy available is lost to the environment when organisms use energy produced from respiration for movement or body heat. This is called respiratory loss.

2) 10% of the total energy available becomes biomass. This is net productivity.

Question 22

What is net productivity + formula?

Answer 22

Net productivity is the amount of energy that available to the next trophic level.

Net productivity = gross productivity - respiratory loss

Question 23

What is the formula for efficiency of energy transfer?

Answer 23

Energy transferred / energy intake. X 100

Question 24

How can you measure energy transfer between trophic levels?

Answer 24

1) you can calculate the amount of energy in a trophic level by measuring the dry mass of the organisms (their biomass)

2) first you calculate the amount of biomass in a sample of the organisms eg 1m2 of wheat.

3) then you multiply this by the size of the total population eg a 10000 m2 field of wheat to give the total amount of energy in the organisms of that trophic level

4) repeat for the other trophic level.

5) the difference in energy transfer between the trophic levels is the amount of energy transferred.

Question 25

How can you measure dry mass?

Answer 25

You need to dry out an organism. This can be done by hearing it up to 80 degrees Celsius until all the water has evaporated (weight is constant). Then you weigh the organism.

Question 26

What is a problem with measuring energy transfer between trophic levels?

Answer 26

the consumers may have taken in energy from sources other than the producer measure. This means the difference between the two figures calculated wouldn’t be accurate estimate of energy transferred between only those two organisms. For accuracy, you have to include all the organisms at a trophic level.

Question 27

Why is energy transfer between consumers more efficient than producers?

Answer 27

Plants contain a greater proportion of indigestible material eg cellulose within a plant cell wall, than animals which contain a relatively high proportion of digestible meat.

Question 28

What human activities are used to increase the transfer of energy?

Answer 28

1) herbicides
2) fungicides
3) insecticides
4) natural predators
5) fertilisers
6) rearing livestock intensively

Question 29

How do herbicides increase energy transfer?

Answer 29

Herbicides kill weeds that compete with agricultural crops for energy. Reducing competition means crops receive more energy so they grow faster.

Question 30

How do fungicides increase energy transfer?

Answer 30

Fungicides kill fungal infections that damage agricultural crops. The crops use more energy for growth and less for fighting infection so they grow faster and become larger, increasing productivity.

Question 31

How do insecticides increase energy transfer?

Answer 31

Insecticides kill insect pests that eat and damage crops. Killing insect pests means less biomass is lost from crops, so they grow to be larger, which means productivity is greater.

Question 32

How do natural predators increase productivity?

Answer 32

Natural predators are introduced to the ecosystem to eat pest species eg ladybirds eat greenfly. This means crops lose less energy and biomass, increasing productivity

Question 33

How do fertilisers increase energy transfer?

Answer 33

Fertilisers provides crops with minerals needed for growth eg nitrates. Crops use up minerals in the soil as they grow, so their growth is limited where there aren’t enough minerals. Adding fertiliser replaces the lost minerals so more energy from the ecosystem can be used to grow, increasing the effiecncy of energy conversion.

Question 34

How can rearing stock intensively increase energy transfer?

Answer 34

Rearing stock intensively involves controlling the conditions they live in so more of the energy is used for growth and less for other acitivities. This increases energy conversion efficiency so more biomass is produced.

1) animals may be kept on warm, indoor pens where their movement is restricted. Less energy is wasted keeping warm and moving around.

2) animals may be given feed that’s higher in energy than in their natural food. This increases energy input, so more energy available for growth.

Question 35

Advantage and disadvantage of rearing stock intensively

Answer 35

Advantages- more food can be produced ina shorter space of time, often at a lower cost

Disadvantages- there are ethical issues. the conditions cause the animals pain, distress or restricts their natural behaviour so shouldn’t be done.

Question 36

What are the main stages in the carbon cycle

Answer 36

1) photosynthesis
2) decomposition
3) respiration
4) combustion
5) release from volcanoes
6) weathering
7) release and absorption into the ocean

Question 37

How is photosynthesis involved in the carbon cycle?

Answer 37

Carbon is absorbed by plants when they carry out photosynthesis . It becomes carbon compunds in plant tissue ans is passsd on to primary consumers when they eat the plants. It’s passed onto secondary and tertiary consumers by the same process.

Question 38

How are decomposers involved in the carbon cycle?

Answer 38

All living organisms due and are broken down by decomposers eg bacteria and fungi. Decomposers secrete enzymes which break down the carbon compounds eg starch in dead organic material. Decomposers then absorb the products of digestion for use in respiration. Feeding on dead organic matter is called saprobiontic nutrition.

Question 39

How is respiration involved in the carbon cycle?

Answer 39

Carbon is returned to the air as all living organisms including decomposers carry out respiration which releases CO2.

Question 40

How is combustion involved in the carbon cycle?

Answer 40

If dead organic matter ends up in areas with no decomposers eg deep oceans and bogs, it’s carbon compunds turn into fossil fuels over millions of years by heat and pressure. The carbon in fossil fuels is released when they’re burnt.

Question 41

How is release from volcanoes part of the carbon cycle?

Answer 41

As well as coal, other rocks such as limestone and chalk can be formed from dead organic matter and deposited on the sea floor. These rocks are mainly composed of calcium carbonate and comes from marine organisms like mussels, crabs and coral that utilise this compound to form shells.

These rocks can be drawn down deep into earth’s crust by movement of tectonic plates. They undergo chemical changes that release carbon dioxide which is eventually returned to the atmosphere by volcanoes.

Question 42

How is weathering involved in the carbon cycle?

Answer 42

Rocks can also eventually become land which is then weathered. This can happen chemically by rainwater and psychically eg plant roots. Chemical weathering causes mineral ions and bicarbonate ions ti be released from the rock into solution and enter ground water, from where they are transported into rivers and oceans. There they combine to form carbon containing compounds eg calcium carbonate.

Question 43

How is the ocean involved in the carbon cycle?

Answer 43

CO2 can dissolve directly into the oceans from the atmosphere and be transported in the ocean by deep water currents.

CO2 can remain in these slow moving currents for hundreds of years before returning to the surface and being released back into the atmosphere.

Question 44

Why do plants need nitrogen ?

Answer 44

To make proteins and nucleic acids (dna and rna). The atmosphere is made up of around 78% nitrogen but plants can’t use it in this form.

Question 45

What are the four processes in the nitrogen cycle

Answer 45

1) nitrogen fixation
2)ammonification
3) nitrification
4) denitrification

Question 46

What occurs during nitrogen fixation?

Answer 46

1) nitrogen fixation is when nitrogen gas in the atmosphere is turned into ammonia by bacteria such as Rhizobium and Aztobacter. The ammonia can then be used by plants. This is usually under anaerobic conditions

2) Rhizobium are found inside root nodules of leguminous plants eg peas and beans

3) they form a mutualistic relationship with plants. They provide the plant with nitrogen compounds and the plant provides them with carbohydrates.

4) Aztobacter are found living in the soil. They don’t form mutualistic relationships with plants.

Question 47

What occurs during ammonification?

Answer 47

1) ammonification is when nitrogen compounds from dead organisms are tuned into ammonia by decomposers,which goes into form ammonium ions.

2) animal waste also contains nitrogen compunds. These are also turned into ammonia by decomposers and form ammonium ions.

Question 48

What happens during nitrification?

Answer 48

1) nitrification is when ammonium ions in the soil are changed into nitrogen compounds that can then be used by plants (nitrates)

2) first nitrifying bacteria called nitrosomonas change ammonium ions into nitrites

3) then other nitrifying bacteria called nitrobacter change nitrites into nitrates.

Question 49

What happens during denitrification?

Answer 49

1) 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.

2) this happens under anaerobic conditions eg in waterlogged soils.

Question 50

What other ways can nitrogen get into an ecosystem?

Answer 50

1) lightning which fixes atmospheric nitrogen
2) artificial fertilisers produced from atmospheric nitrogen on an industrial scale in the Haber process

Question 51

What is succession?

Answer 51

Succession is the process of by which an ecosystem changes over time. The biotic conditions change as the abiotic conditions change.

Question 52

What is primary succession?

Answer 52

This happens on land that’s been newly formed or exposed eg where a volcano has erupted to Form a new rock surface. There is no soil or organic material to start with.

Question 53

What is the first stage of primary succession?

Answer 53

1) 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 the pioneer species.

2) the abiotic conditions are hostile eg no soil to retain water. Only pioneer species can grow because they’re specialised to cope with these conditions

3) the pioneer species change the abiotic conditions. they die and microorganisms decompose the dead organic material. This forms a basic soil

4) this makes conditions less hostile eg basic soil helps retain water so new organism can move in and grow making the soil richer in minerals. First grasses grow and then die. This means larger plants eg shrubs can start to grow and retain even more water. As more plants move in they create more habitats so more animals move in.

Question 54

What is the second stage of primary succession?

Answer 54

1) at each stage, different plants and animals that are better adapted to the conditions out compete the plants and animals already there and become the dominant species in the ecosystem

2) as succession goes on, the ecosystem becomes more complex. New species move in alongside existing species, which means the species diversity increases.

3) the amount of biomass increases because plants at later stages are larger and more dense eg woody trees.

4) the final stage is the climax community. The ecosystem is supporting the most complex community of animals and plants that it can. It won’t change much more and is steady.

Question 55

What is an example of primary succession?

Answer 55

1) pioneer species colonise rocks. Eg lichen grow on and break down rocks, releasing minerals

2) the lichens die and are decomposed helping to form a thin soil, which thickens as more organic material is formed so other species eg mosses can grow.

3) larger plants that need more water can move in as soil depends eg grasses and small flowering plants. The soil continues to deepen as the larger plants die and are decomposed.

4) shrubs, ferns and small trees begin to grow, out-competing the grasses and smaller plants to become the dominant species. Diversity increases.

5) finally, the soil is deep and rich enough in nutrients to support large trees. These become the dominant species, and the climax community is formed.

Question 56

What is secondary succession?

Answer 56

This happens on land that’s been cleared of all plants but where soil remains eg after a forest fire. It happens in the same way as primary succession but as there is already a soil layers succession starts at a later stage. The pioneer species are larger plants eg shrubs.

Question 57

What is a climatic climax?

Answer 57

The climax community for a particular climate is called it’s climatic climax.

Question 58

Example of climatic climax community?

Answer 58

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 seasons. Large trees won’t ever be able to grow in these conditions so the climatic climax contains only herbs or shrubs.

Question 59

What is plagioclimax?

Answer 59

Human activities can prevent succession, stopping normal climax community from developing. When succession is stopped artificially like this, the climax community is called the plagioclimax.

Question 60

What is defected succession?

Answer 60

This is when succession is prevented by human activities but the plagioclimax that develops is one that different to any of the natural stages of the ecosystem.

Question 61

How can succession be deflected?

Answer 61

1) a regularly mown grassy field won’t develop woody plants, even if the climate of the ecosystem could support them

2) the growing points of the woody plants are cut off by the lawnmower, so larger plants can’t establish themselves. Only the grasses can survive being mowed so the climax community is a grassy field

3) a grassy field isn’t a natural stage, there should also be things like small flowering plants, so succession has been deflected.

Question 62

What two things do you measure when looking at population of organisms?

Answer 62

1) abundance -the number of individuals of one species in a particular area. The abundance of mobile species can be estimated by counting the number of individuals in samples. You could also use percentage cover.

2) distribution - where a particular species is within the area you’re investigating.

Question 63

How to take random sample from the area you’re investigating?

Answer 63

1) choose an area to sample, a small area within the area being investigated.

2) samples should be random to avoid bias eg picking random sample sites.

3) use an appropriate technique to take a sample eg Quadrat

4) repeat the process taking as many samples as possible. This gives a more precise estimate for the whole area

5) the number of Individuals can be estimated by taking an average of the data collected and multiplying it by the size of the area.

Question 64

How can frame Quadrats be used to investigate plant populations?

Answer 64

1) a frame Quadrat is a square frame divided into a grid of 100 smaller squares by strings

2) they’re placed on the ground at random points. This can be done by selecting random coordinates with an online number generator.

3) the number of individuals of each species is recorded in each Quadrat.

4) the percentage cover of a species can also be measured by counting how much of the Quadrat is covered by a species. You count a square if it’s more than half covered.

5) this is good for investigating areas with species small enough to fit in a Quadrat.

Question 65

How can point Quadrats be used to investigate plant populations?

Answer 65

1)a point Quadrat is a horizontal bar on two legs with a series of holes at set intervals along its length

2) point Quadrats are placed on the ground at random points within the area being investigated.

3) pins are dropped through the holes in the frame and every plant that each pin touches is recorded. If a pin touches several overlapping plants, all of them are recorded.

4) the number of individuals of each species are recorded in each Quadrat. You could also use percentage cover.

5) point Quadrats are useful in areas of dense vegetation close to the ground.

Question 66

What are the different types of transects

Answer 66

1) line transect- a tape measure is placed along the transect and the species that touch the tape measure are recorded

2) belt transects - data is collected along the transect using frame Quadrats placed next to each other.

3) interrupted transects- you take measurements along the tape measure at regular intervals eg by placing point Quadrats at right angles to the direction of the transect at set intervals eg every two metres