Biodiversity

Question 1

Describe the process of succession. (4)

Answer 1

The process by which an ecosystem changes over time
Happens in a series of stages
At each stage, the species in an area slowly change the environmental conditions
This makes the conditions more suitable for other species

Question 2

Explain the pioneer stage of succession. (7)

Answer 2

Starts when species colonise a new land surface (pioneer species)
The abiotic conditions are hostile but pioneer species are well adapted to grow
The pioneer species change the abiotic conditions – they die and microorganisms decompose the dead organic material (humus) forming a basic soil
This makes the conditions less hostile so new organisms can move in and grow
The death and decomposition process continues to add more organic material
Nitrogen-fixing bacteria add ammonia which can be used by plants
This means larger plants like shrubs can grow in the deeper soil which retains even more water and contains more nutrients

Question 3

Give three examples of pioneer species and describe how they are well adapted to survive in harsh conditions. (6)

Answer 3

Marram Grass - can grow on sand dunes near the sea because it has deep roots to get water and can tolerate the salty environment
Lichens - usually made up of a fungus and an alga. They’re able to survive in rocky conditions because the fungus secretes acids which erode the rock, releasing minerals
Shrubs of the Calligonum Genus - can grow in areas that experience periodic drought

Question 4

Explain the later stages of succession. (5)

Answer 4

As succession goes on, the ecosystem becomes more complex
New species move in alongside existing species, which means the species diversity increases Plants create more habitats for animals, the abiotic conditions become less hostile and the amount of biomass increases
Eventually these changes result in a 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 5

Describe an example of primary succession resulting in a climax community. (9)

Answer 5

Lichens are able to survive on bare rock
They grown in cracks to avoid the wind, break down rocks to release minerals and can survive period of drought
The lichens die and are decomposed to form a thin soil
The soil thickens as more organic material is formed – allowing more species to grow e.g. mosses
Larger plants that need more water can move in as the soil deepens e.g. grasses
The soil continues to deepen as the larger plants die and decompose
Shrubs, ferns and small trees grow and out-compete the smaller plants to become the dominant species
Finally, the soil is deep and rich enough to support large trees which become the dominant species
The climax community is formed

Question 6

Describe the process of secondary succession. (4)

Answer 6

Secondary succession 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
The established community of species is usually destroyed, but without too much disturbance to the soil
As there’s already a soil layer, secondary succession starts at a later stage - the pioneer species are larger plants, e.g. shrubs

Question 7

State the definition of climatic climax. (1)

Answer 7

The climax community for a particular climate

Question 8

State the definition of a plagioclimax. (1)

Answer 8

When human activities prevent succession, stopping the normal climax community from developing

Question 9

State the definition of deflected succession. (1)

Answer 9

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

Question 10

State the definition of abundance. (1)

Answer 10

The number of individuals of one species in a particular area

Question 11

Describe the process of random sampling. (6)

Answer 11

Choose an area to sample - a small area within the area being investigated.
Samples should be random to avoid bias, e.g., by using a random number generator to generate co-ordinates
Use an appropriate technique to take a sample of the population e.g. using a frame quadrat
Use a key to identify the species and count each species or estimate percentage cover
Repeat the process, taking as many samples as possible in the time you have available. This gives a more precise estimate for the whole area
The number of individuals for the whole area can then be estimated by taking an average of the data collected in each sample and multiplying it by the size of the whole area

Question 12

Describe how to use a point quadrat to sample organisms. (4)

Answer 12

Point quadrats are placed on the ground at random points within the area you’re investigating
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
The number of individuals of each species is recorded in each quadrat

Question 13

Describe the three ways that transects can be used in sampling. (6)

Answer 13

Line Transects - A tape measure is placed along the transect and the species that touch the tape measure are recorded.
Belt Transects - Data is collected along the transect using frame quadrats placed next to each other.
Interrupted Transects - Instead of investigating the whole length of either a line or belt, measurements are taken at intervals.

Question 14

Describe three ways that mobile organisms can be sampled. (6)

Answer 14

Nets – can be used for aquatic animals or flying animals
Pitfall trap – can be used for ground insects
Sweep net – for flying insects

Question 15

Describe three ways that mobile organisms can be sampled. (6)

Answer 15

Nets – can be used for aquatic animals or flying animals
Pitfall trap – can be used for ground insects
Sweep net – for flying insects

Question 16

State the definition of producer. (1)

Answer 16

An organism that produces organic molecules using sunlight energy

Question 17

State the definition of consumer. (1)

Answer 17

An organism that eats another organism

Question 18

State the definition of a decomposer. (2)

Answer 18

Organisms that break down dead or undigested organic material
e.g. bacteria and fungi

Question 19

State the definition of a tropic level. (1)

Answer 19

A stage in a food chain that’s occupied by a particular group of organisms

Question 20

State the definition of a biotic factor and give two examples. (3)

Answer 20

The living features of an ecosystem
e.g. predators and food

Question 21

State the definition of an abiotic factor and give two examples. (3)

Answer 21

The non-living features of an ecosystem
e.g. temperature and rainfall

Question 22

State the definition of an ecosystem. (2)

Answer 22

All of the organisms living in a certain area and all of the non-living factors found there
It is a dynamic system – it is changing all the time

Question 23

Describe how energy is transferred through ecosystems. (3)

Answer 23

Plants store energy as biomass
Energy is transferred through the living organisms of an ecosystem when organisms eat other organisms
Food chains and food webs show how energy is transferred through an ecosystem

Question 24

State the definition of an ecosystem. (2)

Answer 24

All of the organisms living in a certain area and all of the non-living factors found there
It is a dynamic system – it is changing all the time

Question 25

Give four reasons why some of the available energy is never taken in by organisms. (4)

Answer 25

Plants can’t use all the light energy that reaches their leaves, 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 parts of the plant that can’t photosynthesize, e.g. the bark of a tree. Some parts of food, e.g. roots or bones, aren’t eaten by organisms so the energy isn’t taken in — they pass to decomposers. Some parts of food are indigestible so pass through organisms and come out as waste, e.g. fibres — this also passes to decomposers.

Question 26

State the definition of respiratory loss. (1)

Answer 26

The energy lost to the environment when organisms use energy released from respiration for movement or heat

Question 27

Give four reasons why some of the available energy is never taken in by organisms. (4)

Answer 27

Plants can’t use all the light energy that reaches their leaves, 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 parts of the plant that can’t photosynthesize, e.g. the bark of a tree. Some parts of food, e.g. roots or bones, aren’t eaten by organisms so the energy isn’t taken in — they pass to decomposers. Some parts of food are indigestible so pass through organisms and come out as waste, e.g. fibres — this also passes to decomposers.

Question 28

State the definition of gross productivity and how to calculate it. (2)

Answer 28

The energy taken in from the energy available Gross productivity = energy available – energy not taken in

Question 29

State the definition of net productivity and how to calculate it. (3)

Answer 29

The total energy available that becomes biomass This energy is available to the next trophic level Net productivity = gross productivity – respiratory loss

Question 30

Describe how to calculate efficiency of energy transfer. (1)

Question 31

Describe how the efficiency of energy transfers changes between trophic levels. (4)

Answer 31

As you move up the food chain, energy transfer becomes more efficient From sun to producer, the efficiency of energy transfer is approximately 2-3% From producer to consumer, the efficiency of energy transfer is approximately 5-10% From consumer to consumer, the efficiency of energy transfer is approximately 15-20%

Question 32

Explain six ways that human activities can manipulate the flow of energy through ecosystems. (12)

Answer 32

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 infection, so they grow faster and become larger, increasing productivity. 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. Natural predators - introduced to the ecosystem eat the pest species, e.g., ladybirds eat greenfly. This means the crops lose less energy and biomass, increasing productivity. Fertilisers - chemicals that provide crops with minerals needed for growth, e.g., nitrates. Adding fertiliser replaces the lost minerals, so more energy from the ecosystem can be used to grow, increasing the efficiency of energy conversion. Rearing livestock intensively - involves controlling the conditions they live in and when they’re slaughtered, so more of their energy is used for growth and less is used for other activities - the efficiency of energy conversion is increased so more biomass is produced and productivity is increased.

Question 33

Explain the processes and organisms involved in the carbon cycle. (14)

Answer 33

Photosynthesis - Carbon (in the form of CO2 from air and water) is absorbed by plants when they carry out photosynthesis — it becomes carbon compounds in plants. Carbon is passed on to consumers when they are eaten Decomposition - All living organisms die and are broken down by microorganisms called decomposers, e.g., bacteria and fungi. Decomposers secrete enzymes which break down the carbon compounds in dead organic material to be absorbed Respiration - Carbon is returned to the air living organisms carry out respiration, which produces CO2. Combustion - If dead organic matter ends up in places where there aren’t any decomposers, its carbon compounds are turned in to fossil fuels which release carbon when burnt Release from Volcanoes - As well as coal, other types of rock can be formed from dead organic matter deposited on the sea floor. For example, rocks such as limestone and chalk are mainly composed of calcium carbonate (CaCO3), from shells of marine organisms. This carbon can be retuned to the atmosphere when the rocks are drawn into the earth’s crust by tectonic activity and undergo chemical changes to produce carbon dioxide to be released from volcanoes Weathering – chemically, by slightly acidic rainwater (releases HCO3 which combines with water to form CaCO3) or physically, by plant roots and animals. Release from and Absorption into the Ocean - CO2 can also dissolve directly into the oceans from the atmosphere and can remain hundreds of years before returning to the surface and being released back into the atmosphere.

Question 34

Explain the processes and organisms involved in the nitrogen cycle. (10)

Answer 34

Nitrogen Fixation -nitrogen gas in the atmosphere is converted to 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. Ammonification - nitrogen compounds from dead organisms are turned into ammonia in the soil, which goes on to form ammonium ions. These also turned into ammonia which can be taken up by plants. Nitrification - when ammonium ions in the soil are changed into nitrogen compounds that can be absorbed by plants (nitrates). First nitrifying bacteria called Nitrosomonas change ammonium ions into nitrites. Then another nitrifying bacteria called Nitrobacter convert nitrites into nitrates. Denitrification - when nitrates in the soil are converted into nitrogen gas by denitrifying bacteria — they use nitrate instead of oxygen for respiration and give off nitrogen gas under anaerobic conditions Other ways for nitrogen to enter an ecosystem – lightning (fixes atmospheric nitrogen) or by artificial fertilisers (produced in the Haber process)

Question 35

Explain the processes and organisms involved in the carbon cycle. (14)

Answer 35

Photosynthesis - Carbon (in the form of CO2 from air and water) is absorbed by plants when they carry out photosynthesis — it becomes carbon compounds in plants. Carbon is passed on to consumers when they are eaten Decomposition - All living organisms die and are broken down by microorganisms called decomposers, e.g., bacteria and fungi. Decomposers secrete enzymes which break down the carbon compounds in dead organic material to be absorbed Respiration - Carbon is returned to the air living organisms carry out respiration, which produces CO2. Combustion - If dead organic matter ends up in places where there aren’t any decomposers, its carbon compounds are turned in to fossil fuels which release carbon when burnt Release from Volcanoes - As well as coal, other types of rock can be formed from dead organic matter deposited on the sea floor. For example, rocks such as limestone and chalk are mainly composed of calcium carbonate (CaCO3), from shells of marine organisms. This carbon can be retuned to the atmosphere when the rocks are drawn into the earth’s crust by tectonic activity and undergo chemical changes to produce carbon dioxide to be released from volcanoes Weathering – chemically, by slightly acidic rainwater (releases HCO3 which combines with water to form CaCO3) or physically, by plant roots and animals. Release from and Absorption into the Ocean - CO2 can also dissolve directly into the oceans from the atmosphere and can remain hundreds of years before returning to the surface and being released back into the atmosphere.