6.5 - C - Ecosystems

Question 1

What is an ecosystem?

Answer 1

Any group of living organisms and non‐living things occurring
together and the interrelationships between them.

Question 2

What is a habitat?

Answer 2

The place where an organism lives.

Question 3

What is a population?

Answer 3

All of the organisms of one species who live in the same place, at the same time and breed together.

Question 4

What is a community?

Answer 4

All the populations of different species who live in the same place at the same time and can interact with each other.

Question 5

What is a niche?

Answer 5

The role of an organism in the ecosystem.

Question 6

What is a biotic factor?

Answer 6

Living organisms in an ecosystem that can affect each other.

Question 7

What is an abiotic factor?

Answer 7

Non‐living things in an ecosystem that can affect the living organisms.

Question 8

Ecosystems are dynamic.
What does this mean?
How are ecosystems dynamic?

Answer 8

This means they are constantly changing.
As abiotic/biotic factors change they can have an affect on other factors:
Cyclic changes and repeat in a regular pattern.
Directional changes do not repeat, tend to be long lasting and go in one direction e.g. erosion.
Erratic changes cannot be predicted and are neither cyclic or
directional e.g. effects of lightning.

Question 9

What is a producer?

Answer 9

Start of food chains (plants and some photosynthetic bacteria), that convert energy from sunlight into chemical energy (glucose) in photosynthesis. They supply the chemical energy to the rest of the food chain.

Question 10

What are the different consumers?

Define them.

Answer 10

Primary consumers are herbivores, which feed on plants, and which are eaten by:
Secondary consumers. These in turn are eaten by carnivorous:
Tertiary consumers.

Question 11

What are decomposers?

Give examples.

Answer 11

They feed on waste material or dead organisms.
They include bacteria, fungi and some animals.
Bacteria, fungi and some animals.

Question 12

State the 3 types of change in ecosystems that affect population size

Answer 12

Cyclic changes.
Directional changes.
Unpredictable/erratic changes.

Question 13

Explain cyclic changes.

Give examples.

Answer 13

These are changes that repeat themselves in a rhythm.

Eg: tide movements, changes in day length, the way in which predator and prey species fluctuate.

Question 14

Explain directional changes

Answer 14

These changes are not cyclic. They go in one direction, and tend to last longer than the lifetime of organisms within the ecosystem. Within such change, particular variables continue to increase or decrease.
Eg: deposition of silt in an estuary, or the erosion of the coastline.

Question 15

Explain unpredictable/erratic changes.

Give examples.

Answer 15

These have no rhythm and no constant direction.

Eg: the effects of lighting or hurricanes.

Question 16

What is a trophic level?

Answer 16

The level at which an organism feeds

Question 17

Define biomass.
Define biomass transfer.
Explain biomass.

Answer 17

The dry mass of the organic material in an organism.
Transfer of biomass from one trophic level to another.
Biomass flows through food chains and food webs ‐ it can give an
indication of the energy flow through the food chains too.

Question 18

Why are food webs useful?

Answer 18

Food webs more accurately describe the relationships in an ecosystem.

Question 19

There is a loss of biomass (and energy) from food chains at each trophic level.
Why?

Answer 19

Some food not eaten e.g. bones.
Respiration releases energy from organic molecules e.g. glucose and materials e.g. CO2 are lost & energy is also released as heat.
Waste products and dead organisms contains biomass which will only be available to decomposers.

Question 20

Explain pyramids of numbers

Answer 20

They reflect numbers in a food chain.

The area of the bar is proportional to numbers of individuals.

Question 21

Compare pyramids of numbers vs pyramids of biomass

Answer 21

Pyramids of biomass are more useful to scientists because they take into account the size of organisms and the mass of material at each level. They give an indication of the energy contained at each trophic level.

Question 22

What might the problems be with constructing pyramids of biomass?

Answer 22

To measure biomass:
Organisms have to be heated in an oven to evaporate all water.
Weighed periodically until all water evaporated and mass doesn’t
reduce any more.
This is very destructive (organism dies) ‐ instead, wet mass is
measured and dry mass is estimated using old published data.

Question 23

Define productivity.

Why is this important?

Answer 23

The rate of production of new biomass/the rate of energy flow
through each trophic level.
Reflects how much biomass/energy is available to organisms of a trophic
level, per m^2 (usually) per year (usually).
e.g. Units: kg/MJ m^-2 yr^-1.

Question 24

Define primary productivity.

Define gross primary productivity.

Answer 24

Total amount of energy fixed by photosynthesis.

The rate at which plants convert light energy into chemical energy through photosynthesis.

Question 25

Define NPP. What does it stand for? Give the equation for it.

Answer 25

The rate of production of new biomass available for heterotrophic consumption and therefore the amount of energy available to them. Net primary productivity. NPP = gross primary productivity ‐ respiration (R)

Question 26

Why is about 90% of the sunlight not converted into biomass (net primary productivity)?

Answer 26

Reflected off plant/only certain wavelengths of light can be absorbed. Absorbed by non‐photosynthetic parts e.g. bark. Misses chlorophyll/chloroplasts. Some energy is 'lost' as heat that is used in respiration.

Question 27

What must be done to improve NPP? | Why would farmers want to do this?

Answer 27

Make energy conversion more efficient, reduce energy losses. | Increases crop yield.

Question 28

Explain how you would ensure max rate of photosynthesis by ensuring limiting factors are controlled in order to improve NPP

Answer 28

Light levels ‐ grow with light banks/plant early to give longer growing season. Temperature ‐ greenhouses. CO2 conc. ‐ levels increased in greenhouses. water ‐ irrigation techniques and drought resistant plants. Nutrients ‐ fertilisers, crop rotation with legumes (nitrogen fixing). Reduced yield from pests ‐ use of pesticides, pest‐resistant plants containing Bt gene. Competition from weeds ‐ herbicides.

Question 29

Define improving secondary productivity. Why is this necessary for farmers? How might they go about doing this?

Answer 29

Improving the rate of generation of biomass in heterotrophs. i.e. making sure animals grow as large as possible to increase mass of meat production. Necessary because energy transfer from producers to consumers is very inefficient. A lot of energy is lost from food chains as the producers can't digest everything they eat (cellulose), they don't eat all of the plant, heat loss in respiration, egestion losses. Growth steroid treatment ‐ illegal. Selective breeding. Antibiotics ‐ less energy lost fighting pathogens. Battery farming ‐ reduce movement so less energy used in respiration for energy; warm stable temperatures so less energy used in maintaining body temp.

Question 30

State the equation for ecological efficiency

Answer 30

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

Question 31

Define succession. | When does this happen?

Answer 31

A natural directional change in species composition in an area over a period of time, from the original colonisers to the climax community. Succession happens in a series of recognisable stages (sere). Where one community changes the conditions for the next. e.g. depth of soil.

Question 32

Define primary succession

Answer 32

When succession begins in an area where previous life has not previously existed. Eg: bare rock, bare sand dunes.

Question 33

Define secondary succession

Answer 33

When is succession begins in an area where previous life had existed but was destroyed. Eg: by a fire, deforestation.

Question 34

What is a pioneer species?

Answer 34

Organisms with suitably adapted characteristics that enable them to colonise an area with no organisms they are usually hardy species adapted to hostile environments.

Question 35

What is a climatic climax community?

Answer 35

A stable, self-sustaining community, in equilibrium with its environment. This is dependent on the climate of an area.

Question 36

What are seres?

Answer 36

Seral stages. The various stages through which succession takes place.

Question 37

What is a plagioclimax?

Answer 37

When succession is held at an earlier stage, usually by human interference. Eg: grazing, trampling, cutting.

Question 38

State the six seral stages

Answer 38

Migration, colonisation, establishment, competition, stabilisation, climax.

Question 39

How does a pioneer species stabilise the environment?

Answer 39

Developing the soil e.g. make it deeper (from rotting organisms). Cause and increase in availability of water. Cause more minerals to be availble (some carry out nitrogen fixation). Create habitats and provide shelter. Change soil pH.

Question 40

Explain what happens as succession continues

Answer 40

``` Development of deeper soil. Soil becomes accumulates more minerals and is more fertile. Dominant species change. Plant species get larger. ```

Question 41

What is a climax community?

Answer 41

The final stage of succession. | The community was in equilibrium with the environment.

Question 42

Explain deflected succession

Answer 42

When something e.g. grazing/burning/trampling of plants prevents succession and therefore the establishment of the next community. The sub‐climax community is called the plagioclimax.

Question 43

Why does succession occur?

Answer 43

Each community changes the conditionse.g. depth of soil which allow for a new community to establish.

Question 44

How does succession lead to the development of an ecosystem?

Answer 44

Every time the plant community changes in succession, the habitat changes, changing the ecosystem. Generally the later the stage of succession, the large the plant species ‐ therefore more habitats are created, developing the ecosystem further.

Question 45

Why do we study habitats and/or ecosystems?

Answer 45

To measure the biodiversity of a habitat (to monitor population sizes/habitat destruction). To find out if abundance of one species depends on another/an abiotic factor.

Question 46

We study habitats and ecosystems by sampling. Why? How do we use sampling to find out about the whole habitat?

Answer 46

It's impossible to count all of every organism in a habitat, so we study a small area closely and then extrapolate the data to. e.g. estimate numbers in the habitat.

Question 47

What is important that sampling should be?

Answer 47

Sampling should be representative of the habitat and so needs to sample the range of species in the habitat.

Question 48

What are the 2 variations of sampling?

Answer 48

Random and non-random

Question 49

How could you do random sampling? | Give an example.

Answer 49

Use random numbers generated by a computer to create coordinates (on a map or within a grid you set).

Question 50

What are the 3 types of non-random sampling?

Answer 50

Opportunistic, stratified, systematic.

Question 51

Explain and evaluate opportunistic sampling

Answer 51

Prior knowledge of a site determines the sample site. You may deliberately sample an area where you know an organism is present. + quicker than random sampling. - this may introduce bias to the data ‐ if you sample an area where you know an organism is present this could lead to an overestimation of its abundance or biodiversity generally.

Question 52

Explain and evaluate stratified sampling

Answer 52

Sampling areas in a habitat which seem very different, separately. + ensures all different areas in the habitat are sampled ‐ ensures no under representation (random sampling may miss areas). - if too many samples are taken in proportionally smaller areas, it could lead to over representation of some areas.

Question 53

Explain and evaluate systematic sampling

Answer 53

Samples are taken at regular, predetermined intervals across a habitat e.g. belt or line transects. + if there is a clear gradual change in an environmental factor across an environment, a transect can show how species abundance changes with it and therefore the effect of the factor on the different plant species. Or studying the signs of succession ‐ gradual change in species composition. - species which do not fall on the line or in the belt may be missed and therefore the sample would not be representative and there would be an underestimation in the biodiversity.

Question 54

State and define the 3 types of transects

Answer 54

Line transect ‐ record plants touching the line at regular intervals. Belt transect ‐ move a quadrat along the line with no intervals. Interrupted belt transect ‐ place a quadrat at set intervals along the line.

Question 55

Explain kite diagrams

Answer 55

Used to show change in abundance of a species across a line transect. Good for showing how one species goes from dominance to absence and a new species becomes dominant - indication of succession. Good for comparing abundance of difference species with abiotic factors as each changes across a habitat.

Question 56

How many sites should you sample? | How would you do this?

Answer 56

It depends on the size of the habitat ‐ the number of samples should be representative of the number and relative abundance of all species in the habitat. 1) Take random samples. 2) Make a cumulative freq. table against showing the number of new sp. found in each quadrat. 3) Plot quadrat number against cumulative frequency ‐ the point when the curve levels off tells you how many quadrats to use.

Question 57

What is a quadrat? What do you use them to sample? Explain how you use them to sample this.

Answer 57

A square frame to define edges of sample site ‐ usally 1m x 1m. Plants. 1) Place at your sample sites (random coordinates/points on transect). 2) Identify plants within the quadrat using a key. 3) Measure the abundance of each species (and bare ground) by using one of the following: Abundance scale e.g. ACFOR scale (assign each sp. an abundance score). Estimate percentage cover. Measure percentage cover using a point frame (frame with 10 needles, put down 10 times in quadrat ‐ each plant touching the pin has 1% cover).

Question 58

What does ACFOR stand for? | What is good/bad about it?

Answer 58

``` ACFOR is not very quantitative and is subjective. A ‐ abundant C ‐ common F ‐ frequent O ‐ obvious R ‐ rare ```

Question 59

Explain how and why we sample animals

Answer 59

Since animals move, they must be trapped to be sampled. We only sample small animals like this, larger animals must be done visually without trapping. Once caught, animals/insects must be identified and counted using keys.

Question 60

State the 6 animals traps

Answer 60

``` Pooter, Tullgren funnel, Sweep net, Longworth trap, Pitfall trap, Light trap. ```

Question 61

What is the equation for the population size of a species?

Answer 61

Mean number of individuals of the species in each quadrat / fraction of the total habitat area covered by a single quadrat

Question 62

Define nitrogen fixation

Answer 62

Converting nitrogen into compounds useable for plants (nitrates/ammonium ions)

Question 63

State the 2 types of nitrogen fixing bacteria

Answer 63

Azotobacter bacteria | Rhizobium bacteria

Question 65

Explain azotobacter bacteria

Answer 65

Nitrogen fixing bacteria (fix ammonium ions) live free in the soil ‐ provide ammonium ions for nitrifying bacteria.

Question 66

Explain rhizobium bacteria

Answer 66

Nitrogen fixing bacteria (fix ammonium ions). They use the nitrogen to make their amino acids and are found in root nodules of legumes (clover/peas). They have a mutualistic relationship ‐ fixed nitrogen for plant for their amino acid production, glucose for Rhizobium.

Question 67

Where is leghaemoglobin found? What does it do? What conditions does it do this in?

Answer 67

Nodules. Absorbs O2. Aerobic conditions.

Question 68

What can rhizobium do in aerobic conditions?

Answer 68

Use nitrogen reductase to reduce N2 to NH4

Question 69

Explain nitrifying bacteria

Answer 69

Nitrifying bacteria are chemoautotropic ‐ release energy by oxidising: Nitrosomonas bacteria ‐ ammonium ions to nitrites (NO2‐) Nitrobacter bacteria ‐ nitrites (NO2‐) to nitrates (NO3‐). Requires O2 only happens in well aerated soils i.e. not bogs etc. Nitrates are directly absorbed from soil by active transport by plants for amino acid production.

Question 70

Explain denitrification

Answer 70

Done by denitrifying bacteria. Remove nitrates from the soil byconverting nitrates to nitrogen gas. Done in anaerobic conditions i.e. bogs/waterlogged soil. Use nitrates as oxygen source for respiration.

Question 71

Explain the importance of the nitrogen and carbon cycles

Answer 71

There are finite amounts of nitrogen and carbon in the world. Living organisms need carbon to make carbon containing compounds such as carbohydrates and nitrogen to make nitrogen containing compounds such as proteins ‐ without these they couldn't exist. When these organisms die if decomposers didn't break down the N and C containing compounds then they would remained 'locked in' and run out.

Question 72

Explain eutrophication

Answer 72

Occurs when nitrates leech into rives etc. Cause algal bloom (nitrates allow rapid protein production/growth). Blocks light for photosynthetic plants below algae. Plants die and are decomposed. Decomposers use up O2 in water. Aquatic life dies as no O2 for respiration.

Question 73

Explain crop rotation

Answer 73

Different crops grown in the field each year ‐ some years nothing planted. Different crops have different nitrate requirements. Each year nitrates not being removed at the same rate. In year of no crops no nutrients removed and so build back up. Use legumes in rotation to put ammonium ions.

Question 74

Explain what decomposers are and do

Answer 74

Microorganisms which break down dead and waste organic material e.g. bacteria, fungi. Recycle what would otherwise be 'trapped' nutrients. Saprotrophic feeders (extra cellular digestion). Respiration of decomposers ‐ releases CO2 ‐ used in photosynthesis. Decomposers carry out ammonification ‐ convert nitrogen‐ containing compounds e.g. in urea/protein into ammonium ions. Help to create humus in soil (by decomposing dead/waste material) ‐this increases water retention.

Question 75

Define nitrification

Answer 75

Absorbing ammonium ions ‐ done by nitrifying bacteria