What is a biotic factor?
An interaction between living organisms in an ecosystem.
What is an abiotic factor?
An interaction between a non living event and an ecosystem.
Give some examples of abiotic factors.
Temperature, amount of water, light intensity, levels of pollutants
Give some examples of biotic factors.
What is parasitism? Give an example
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
What is the process of eutrophication?
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
What are invasive species?
Species introduced to an environment that are harmful to the local habitat and native species by reducing biodiversity and spreading disease.
What is the carbon cycle?
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.
What is an autotroph?
An organism that produces its own food.
What is a heterotroph?
An organism that does not produce its own food.
What is the water cycle?
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
What do denitrifying bacteria do?
Convert nitrates to nitrogen
What do nitrifying bacteria do?
Convert ammonia to nitrites, then into nitrates. Different species are responsible for producing nitrites and nitrates.
What do nitrogen fixing bacteria do?
Convert atmospheric nitrogen to ammonia
What do decomposers do?
Convert faeces, urea and proteins to ammonia
What are indicator species?
Species that can show the amount of pollution in an ecosystem by their presence or absence.
What are the indicator species for air?
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
What are the indicator species for water?
Clean water: stonefly larvae and freshwater shrimps
Polluted water: blood worms and sludgeworms
What are the three conditions needed for decay?
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
What is an individual?
A single organism
What is a population?
All the organisms of one species in a habitat
What is a community?
All the organisms of different species living in a habitat
What is an ecosystem?
A community of organisms along with all the non-living (abiotic) conditions
What is mutualism? Give an example
A relationship between two organisms, from which both organisms benefit
Bees pollinate plants and gain nectar from them.
What is a quadrat?
A square frame enclosing a certain area. It is used to count organisms in an area.
How can you estimate population size?
Work out the mean number of organisms per m^2 (based on quadrat counts). Multiply the mean by the total area of the habitat.
How do belt transects work?
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.
How is energy wasted along the food chain?
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.
How do you calculate efficiency between levels in a food chain?
Efficiency = (energy transferred to next level / energy available at previous level) x 100
How can fish farming reduce biodiversity?
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.
How can reforestation increase biodiversity?
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.
How do conservation schemes protect at-risk species?
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
What are the benefits of maintaining biodiversity?
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.
What is food security?
Everyone having access to enough food that is safe to eat and has the right balance of nutrition
What factors are affecting food security?
Increasing human population
Increasing consumption of meat and fish and increasing animal farming
Environmental changes caused by human activity
New pests and pathogens
How does the increasing consumption of meat and fish and increasing animal farming affect food security?
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.
How do environmental changes caused by human activity affect food security?
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.
How can sustainability affect food security?
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.
How can the introduction of non-indigenous species reduce biodiversity?
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
How do pyramids of biomass work?
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.
How do new pests and pathogens affect food security?
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.
What is a drought?
A prolonged period of water scarcity caused by a lack of precipitation
What is desalination?
Removing salts (mineral ions) from salt water
What is thermal desalination?
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.
What is reverse osmosis?
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.
What ways can atmospheric nitrogen turn into nitrogen containing ions in the soil (nitrogen fixing)?
Nitrogen-fixing bacteria in roots and soil
What is the nitrogen cycle?
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.
What is the mutualistic relationship between nitrogen-fixing bacteria and plants?
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.
How can farmers increase the amount of nitrates in the soil?
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.
What are some other (non-living) indicators of pollution?
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.
How can we slow decomposition in food?
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
How do compost bins have ideal conditions for decomposition?
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