Ecosystems and Nutrient Cycles

Question 1

What is a biotic factor?

Answer 1

An interaction between living organisms in an ecosystem.

Question 2

What is an abiotic factor?

Answer 2

An interaction between a non living event and an ecosystem.

Question 3

Give some examples of abiotic factors.

Answer 3

Temperature, amount of water, light intensity, levels of pollutants

Question 4

Give some examples of biotic factors.

Answer 4

Competition, predation

Question 5

What is parasitism? Give an example

Answer 5

Where a parasite lives in or on a host organism, so that the parasite benefits but the host does not.
Fleas feed on their host’s blood (mammals) but do not offer,anything back

Question 6

What is the process of eutrophication?

Answer 6

Fertiliser is spread on land in farming
Excess fertiliser is washed down by rain and absorbed by the soil, then is transported to a lake by underground water, or directly runs into lakes
The presence of nitrates in the fertiliser in the lake causes overgrowth of algae and aquatic plants
No sunlight can reach the lower part of the lake, causing plants to die
Bacteria decompose the plants, using up oxygen in the lake, making it anoxic
All living organisms in the lake die

Question 7

What are invasive species?

Answer 7

Species introduced to an environment that are harmful to the local habitat and native species by reducing biodiversity and spreading disease.

Question 8

What is the carbon cycle?

Answer 8

Photosynthesis - green plants absorb carbon dioxide from the atmosphere to photosynthesise. This process creates carbohydrates, fats, and proteins from carbon.
Eating - primary consumers eat plants, then higher level consumers eat primary consumers, passing carbon along the food chain.
Decomposition - animals and plants die and are decomposed by microorganisms e.g. bacteria and fungi. Waste from consumers can also be broken down by microorganisms, which recycles carbon into the soil.
Respiration - bacteria, plants and large animals and primary consumers perform respiration, which takes in oxygen and releases carbon dioxide into the atmosphere.
Burning - wood and fossil fuels are burnt. Carbon dioxide is released into the atmosphere.

Question 9

What is an autotroph?

Answer 9

An organism that produces its own food.

Question 10

What is a heterotroph?

Answer 10

An organism that does not produce its own food.

Question 11

What is the water cycle?

Answer 11

Energy from the Sun makes water evaporate from land, sea, and plants (transpiration) into water vapour
The warm water vapour rises, cools and condenses to form clouds
Water falls as precipitation onto land
This water drains into the sea and the process repeats

Question 12

What do denitrifying bacteria do?

Answer 12

Convert nitrates to nitrogen

Question 13

What do nitrifying bacteria do?

Answer 13

Convert ammonia to nitrites, then into nitrates. Different species are responsible for producing nitrites and nitrates.

Question 14

What do nitrogen fixing bacteria do?

Answer 14

Convert atmospheric nitrogen to ammonia

Question 15

What do decomposers do?

Answer 15

Convert faeces, urea and proteins to ammonia

Question 16

What are indicator species?

Answer 16

Species that can show the amount of pollution in an ecosystem by their presence or absence.

Question 17

What are the indicator species for air?

Answer 17

Lichens are plants that grow in exposed places. Air pollutants, especially sulphur dioxide, can damage lichens. Green bushy lichens grow in clean air, leafy lichens can survive a little air pollution, crusty lichens can survive polluted air. The less lichen there are, the less pollution
Blackspot fungus on rose leaves are sensitive to sulphur dioxide, so their presence shows clean air

Question 18

What are the indicator species for water?

Answer 18

Clean water: stonefly larvae and freshwater shrimps

Polluted water: blood worms and sludgeworms

Question 19

What are the three conditions needed for decay?

Answer 19

Temperature - warm temperatures speed up enzyme controlled reactions in microbes, but enzymes denature at too high temperatures
Water content - decay is faster in moist environments because organisms involved in decay need water to survive
Oxygen availability - many microbes, especially the ones that can decompose more quickly, need oxygen for aerobic respiration, so more oxygen means decomposition rate is faster

Question 20

What is an individual?

Answer 20

A single organism

Question 21

What is a population?

Answer 21

All the organisms of one species in a habitat

Question 22

What is a community?

Answer 22

All the organisms of different species living in a habitat

Question 23

What is an ecosystem?

Answer 23

A community of organisms along with all the non-living (abiotic) conditions

Question 24

What is mutualism? Give an example

Answer 24

A relationship between two organisms, from which both organisms benefit
Bees pollinate plants and gain nectar from them.

Question 25

What is a quadrat?

Answer 25

A square frame enclosing a certain area. It is used to count organisms in an area.

Question 26

How can you estimate population size?

Answer 26

Work out the mean number of organisms per m^2 (based on quadrat counts). Multiply the mean by the total area of the habitat.

Question 27

How do belt transects work?

Answer 27

Sometimes abiotic factors change across a habitat, called a gradient. You can count population changes by lining up quadrats, forming a belt transect. You can then count populations to see how they change.

Question 28

How is energy wasted along the food chain?

Answer 28

Energy is used at all stages for organisms to stay alive e.g. in respiration, which provides energy for movement and all other processes. Energy is also lost to the surroundings as heat.
Not all of an organism gets eaten and not all eaten parts can be digested.

Question 29

How do you calculate efficiency between levels in a food chain?

Answer 29

Efficiency = (energy transferred to next level / energy available at previous level) x 100

Question 30

How can fish farming reduce biodiversity?

Answer 30

Food is added to nets to feed fish, which produces waste.
The food and waste can leak into open water, causing eutrophication.
Parasites can breed in fish farms.
Predators can get trapped in nets and die.
Farmed fish can escape, competing with indigenous species.

Question 31

How can reforestation increase biodiversity?

Answer 31

It is replanting trees in an area previously covered with forest to form a new forest. They generally have high biodiversity from different tree and animal species. They have to be carefully planned; for example, it is better to replant lots of tree species than only a single type.

Question 32

How do conservation schemes protect at-risk species?

Answer 32

Protect a species’ natural habitat
Protect species in safe areas outside their natural habitat (e.g. zoos) and introducing captive breeding programmes to increase numbers
Using seed banks to store and distribute seeds of rare and endangered plants

Question 33

What are the benefits of maintaining biodiversity?

Answer 33

Protecting the human food supply - overfishing reduces fish stocks in oceans
Ensuring minimal damage to food chains - if one species becomes extinct it affects the whole food chain
Providing future medicines - many medicines come from plants, so new ones may be discovered
Cultural aspects - some species may be important to a culture e.g. the bald eagle in America
Ecotourism - people visiting unspoilt landscapes
Providing new jobs - through ecotourism, conservation schemes etc.

Question 34

What is food security?

Answer 34

Everyone having access to enough food that is safe to eat and has the right balance of nutrition

Question 35

What factors are affecting food security?

Answer 35

Increasing human population
Increasing consumption of meat and fish and increasing animal farming
Environmental changes caused by human activity
Sustainability
New pests and pathogens

Question 36

How does the increasing consumption of meat and fish and increasing animal farming affect food security?

Answer 36

There is less biomass at higher levels in the food chain, so less food can be produced by grazing animals than by growing plants in the same area. Animals have to eat crops that humans can eat. Over fishing can reduce supplies.

Question 37

How do environmental changes caused by human activity affect food security?

Answer 37

Burning fossil fuels causes global warming. Other types of climate change such as changing rainfall patterns coupled with global warming may affect the growth of crops, which could reduce yields. Other changes such as soil pollution can also reduce the ability to grow crops.

Question 38

How can sustainability affect food security?

Answer 38

Diesel and petrol from crude oil are running out. This means more crops are being grown to make biofuels, such as bioethanol. These take up land that could be used for farming.
The high input costs of farming may make it too expensive to farm and maintain food production in some areas.

Question 39

How can the introduction of non-indigenous species reduce biodiversity?

Answer 39

Competition for resources such as food and shelter. They can be better than native species and out-compete them, causing them to die out
Bringing new diseases, which infect and kill native species, reducing biodiversity

Question 40

How do pyramids of biomass work?

Answer 40

They show the total mass of each population in a food chain. The producer is at the bottom with the highest consumer at the top. The mass decreases at each level and is drawn to scale.

Question 41

How do new pests and pathogens affect food security?

Answer 41

Pests and pathogens can damage crops and livestock. This can negatively impact yields. New pests and pathogens can be even worse as crops and livestock may not have any defences.

Question 41

What is a drought?

Answer 41

A prolonged period of water scarcity caused by a lack of precipitation

Question 41

What is desalination?

Answer 41

Removing salts (mineral ions) from salt water

Question 41

What is thermal desalination?

Answer 41

A method of desalination where salt water is boiled, so water evaporates. The steam rises to the top and travels down a pipe, then condenses back into pure water.

Question 41

What is reverse osmosis?

Answer 41

A modern method of desalination: salt water is treated to remove solids, then fed at very high pressure into a vessel containing a partially permeable membrane. This pressure causes the water to move in the opposite direction to osmosis: from high salt concentration to low salt concentration. The salts are left behind, removing them from the water.

Question 41

What ways can atmospheric nitrogen turn into nitrogen containing ions in the soil (nitrogen fixing)?

Answer 41

Lightning

Nitrogen-fixing bacteria in roots and soil

Question 41

What is the nitrogen cycle?

Answer 41

Nitrogen in the atmosphere is converted into nitrates in the soil by lightning or ammonia in the soil by nitrogen-fixing bacteria.
Decomposers decompose proteins and urea into ammonia in the soil.
Ammonia forms ammonium ions in solution that plants can use.
Nitrifying bacteria turn ammonia into nitrates then nitrates, which plants can also use.
Denitrifying bacteria turn nitrates into nitrogen gas. This is of no benefit to living organisms; they are often found in waterlogged soils.

Question 42

What is the mutualistic relationship between nitrogen-fixing bacteria and plants?

Answer 42

Some nitrogen-fixing bacteria live in nodules on the roots of legume plants. The bacteria get food (sugars) from the plant and the plant gets nitrogen ions from the bacteria to make into proteins.

Question 43

How can farmers increase the amount of nitrates in the soil?

Answer 43

Crop rotation - planting different crops each year in a cycle, including a nitrogen-fixing crop (e.g. peas or beans) once a cycle to put nitrates back into the soil
Fertilisers - spreading animal manure or compost on fields, which decomposers can convert into ammonia. Using artificial fertilisers containing nitrates and other mineral ions.

Question 44

What are some other (non-living) indicators of pollution?

Answer 44

Dissolved oxygen metres and chemical tests to accurately measure the concentration of dissolved oxygen in water, to show the change in level of water pollution.
Electronic metres and laboratory tests to accurately measure the concentration of sulphur dioxide in air.

Question 45

How can we slow decomposition in food?

Answer 45

Storing foods in a fridge or freezer - lowers temperature, which slows down decomposers’ rate of reproduction (or stops it in freezing)
Storing food in airtight cans - stops microbes getting in. Cans are then sealed and sterilised at a high pressure and temperature to kill any microbes
Drying food - removes water that microbes need to survive and reproduce.
Adding salt or sugar - causes microbes to lose water by osmosis

Question 46

How do compost bins have ideal conditions for decomposition?

Answer 46

Some have mesh sides to increase oxygen availability
The material is kept moist
Heat is generated by the decomposers themselves
Some compost bins are insulated to increase temperature further