SB9: Ecosystems and Material Cycles

Outline the levels of organisation in an ecosystem

Individual; population; community; ecosystem

Define individual

A single organism

Define population

All the organisms of the same species living together in a habitat

Define community

The populations of different species living together in a habitat

Define ecosystem

A biological community of interacting organisms and their physical environment.

What does interdependent mean

Organisms are dependent on each other; A change in the population of one species can affect other populations within a community.

What are some examples of interdependence?

Plants depend on pollinators e.g. bees; herbivores are dependent on plants; animals are dependent on mates.

What is mutualism?

The interactions between individuals of different species that benefit both partners

What is parisitism?

The interaction in which one organism, the parasite, benefits from the interaction, but harms the other organism, the host.

What are abiotic factors?

Non-living factors of the environment e.g. temperature, water availability, light intensity, pollutants.

Describe how communities are affected by environmental conditions

Environmental conditions (e.g. temperature) affect the abundance and distribution of organisms within the community. An example is light intensity affecting the rate of photosynthesis in producers which serve as a food source and shelter for other organisms.

What are biotic factors?

Living factors of the environment e.g. competition, predation

Describe how competition affects communities

The presence of competitors affects population distribution and size; If one species is better adapted to survive in a certain environment, it will outcompete other species, causing their populations to decline

Describe how predation affects communities

Predation affects prey populations within a community e.g. if the number of predators decreases, the number of prey will increase as fewer are killed; Populations of all other organisms within the food chain will also be affected

What is used to measure the abundance and distribution of organisms in an area?

Quadrat

What is used to study the distribution of organisms across a gradient?

Belt transect

What does a food chain show?

The flow of energy as it passes from one organism to the next

What is biomass?

The total mass of living material

What are trophic levels?

The stages in a food chain

Describe a simple food chain

Producer → Primary consumer → Secondary consumer → Tertiary consumer → ...

Why are producers the first trophic level?

Producers provide all biomass for the food chain (production of glucose via photosynthesis); The rest of the food chain involves the transfer of this biomass.

What does a pyramid of biomass represent?

It represents the dry mass of living material at each trophic level of a food chain.

Why is a pyramid of biomass almost always pyramid-shaped?

Producers are at the bottom as they have the most biomass; As you go up the food chain, biomass is lost so bars decrease.

Why is biomass lost between each trophic level in the food train?

Glucose is immediately used for respiration in plants to generate heat energy, energy for movement etc; some parts of organisms are indigestible; egestion, excretion

What is the equation to calculate efficiency of biomass transfers between each trophic level?

Efficiency \= (biomass available after transfer/biomass available before transfer) x 100

What is biodiversity?

The variety of living organisms within an ecosystem

How does fish farming impact biodiversity?

Food used to feed the fish and waste can leak into water sources, causing eutrophication. Parasites from fish farms may spread and contaminate surrounding ecosystems. Other organisms may become tangled in netting

How does the use of fertilisers affect biodiversity?

Excess fertiliser can wash into water sources causing death and the eutrophication of many species, reducing biodiversity.

Describe how fertilisers can cause eutrophication

Fertiliser run-off into rivers and lakes. Nutrients build-up in water. Algal bloom blocks sunlight. Aquatic plants cannot photosynthesise which leads to less oxygen produced. They die and decompose. Decomposers further deplete oxygen levels. Animals can no longer respire aerobically so die.

How does the introduction of non-indigenous species affect biodiversity?

NI species may out-compete native species, causing a reduction in population numbers. Native species may become the prey of NI species. They may bring diseases which can kill a large number of native species, reducing biodiversity.

How can humans more positively impact biodiversity?

Protection of endangered species e.g. make hunting illegal, breeding programs increase population sizes; Conservation schemes e.g. national parks, seed banks, zoos; Reforestation; Sustainable farming e.g. fewer pesticides; Minimising global greenhouse gas production

What is reforestation?

Replanting forests to help restore biodiversity

How do conservation schemes protect biodiversity?

They prevent species from becoming extinct and increase population numbers, maintaining biodiversity.

Outline the benefits of maintaining biodiversity

Ensures future food requirements can be met, reduces damage to food chains; Increases the likelihood of species adapting to future environmental change; Many plant species are yet to be discovered and may contain chemicals that could be used in future medicines; Safeguarding valuable future resources e.g. fuels, paper; Aesthetics - culture, ecotourism etc; Jobs provided by ecotourism, reforestation and conservation schemes

What is food security?

Ensuring the world's population is supplied with enough food to be healthy

What are the biological factors affecting food security

Rising human population; changing diets; new pests and pathogens; environmental change; sustainability

Describe how the rising human population affects food security

As human population increases, global food production must also increase in order to meet the growing demand for food.

Describe how changing diets affect food security

Greater consumption of meat and fish in wealthier populations. Less energy and biomass available from livestock than crops. Livestock use land for grazing and are fed crops that could otherwise be used for human consumption. Less food is available for humans ∴ reduction in food security

Describe how new pests and pathogens affect food security

Pests and pathogens can reduce or destroy crop yield, negatively impacting food security.

Describe how sustainability affects food security

Unsustainable farming methods disrupt food chains, compromising the ability to meet future food requirements; Due to the high input costs, many LEDCs cannot maintain modern farming methods; Using land for biofuel production reduces land available for crops

Describe how environmental changes due to human activity affects food security

Emissions of greenhouse gases have been linked with global warming which may affect crop growth; Salinisation reduces agricultural potential of soil.

What are the three nutrient cycles?

Water, Carbon, Nitrogen

Why are the nutrient cycles important?

Carbon, water and nitrogen are essential to life. There is a fixed amount of nutrients on Earth which must be constantly recycled

Describe the stages of the carbon cycle

Photosynthesising plants remove CO2 from the atmosphere. Eating passes carbon compounds along a food chain. Respiration in plants and animals returns CO2 to the atmosphere. Organisms die and decompose. Decomposers (bacteria and fungi) break down dead material and release CO2 via respiration. Combustion of materials (e.g. wood, fossil fuels) releases CO2

Describe the stages of the water cycle

Energy from the sun evaporates water from sources such as lakes and oceans. Transpiration also releases water vapour. Water vapour rises, cools and condenses forming clouds. Precipitation occurs. Water is absorbed by the soil and taken up by roots. Some is used in photosynthesis or becomes part of the plant, entering the food chain. Excretion returns water to the soil. Surface runoff returns to streams, rivers and eventually the sea

What is desalination?

The process of obtaining fresh water from salt water by removing the salt.

Name two methods of desalination

Thermal desalination; Reverse osmosis

What is potable water?

Drinkable water

Describe thermal desalination

Salt water is boiled. Water evaporates, rises and condenses down a pipe. This separates pure water from salts.

Describe reverse osmosis

Saline water pumped into a vessel containing a partially permeable membrane at high pressure. High pressure forces water molecules to move from an area of low water concentration (high salt concentration) to an area of high water concentration (low salt concentration). Pure water separated from salts

What do plants use to make proteins?

Nitrates (nitrogen compounds)

Why can nitrogen be used directly from plants to form proteins?

Nitrogen is unreactive

What are the four types of bacteria involved in the nitrogen cycle?

Decomposers, nitrogen-fixing bacteria, nitrifying bacteria, denitrifying bacteria

What is the role of decomposers in the nitrogen cycle?

Breaks down proteins and urea into ammonia; Ammonia dissolves in solution forming ammonium ions

What is the role of nitrogen-fixing bacteria in the nitrogen cycle?

Converts nitrogen gas into ammonia; Ammonia dissolves in solution forming ammonium ions

Where are nitrogen-fixing bacteria found?

In the soil or in the nodules of the roots of legumes such as soybeans, peas, alfalfa

What type of relationship is exhibited between nitrogen fixing bacteria and legumes?

Mutualistic relationship; Plants receives ammonium ions from bacteria; Bacteria gains sugars from plants

What is the role of nitrifying bacteria in the nitrogen cycle?

Convert ammonium ions into NITRITES; Converts NITRITES into NITRATES.

What is the role of denitrifying bacteria in the nitrogen cycle?

Converts nitrates into nitrogen gas

Where are denitrifying bacteria commonly found?

Waterlogged soils

Describe the stages of nitrogen cycle

Lighting and nitrogen-fixing bacteria convert nitrogen gas to ammonia which dissolves to form ammonium ions. Nitrifying bacteria convert ammonium ions to nitrate ions which are taken up by plants and used to build proteins. Feeding passes nitrogen through the food chain. Organisms die and decompose. Decomposers break down proteins and urea to form ammonia which dissolves to form ammonium ions. Denitrifying bacteria convert nitrates in the soil back to nitrogen gas.

How can the amount of nitrates in the soil be increased?

Using fertilisers e.g. animal manure, compost, artificial fertilisers. Crop rotation replenishes nitrates that may have been depleted by the previous crop e.g. planting nitrogen-fixing crop

What is meant by decomposition?

The breakdown of dead materials into simpler organic matter

How do decomposers break down dead matter?

Decomposers release enzymes which catalyse the breakdown of dead material into smaller molecules.

What factors affect the rate of decomposition?

Oxygen availability, temperature and water content

Why is oxygen required for decomposition?

Most decomposers require oxygen for aerobic respiration

How is the availability of oxygen affect the rate of decomposition?

As oxygen levels increase, the rate of decomposition increases and vice versa

Why can decomposition still occur in the absence of oxygen?

Some decomposers respire anaerobically.

How does temperature affect the rate of decomposition?

Decomposers release enzymes; Rate highest at 50°C; Higher temperature, enzymes denature and rate of decay is slower. Lower temperature, enzymes work too slowly, rate of decay is slower

How does soil water content affect the rate of decomposition?

In moist conditions the rate of decomposition is high; In waterlogged soils there is little oxygen for respiration so the rate of decomposition decreases.

What conditions are required to make compost?

Conditions that give a high rate of decomposition: plentiful supply of oxygen, warm, moist etc.

Describe the methods of food storage used to slow down the rate of decomposition

Stored in a fridge/freezer to slow down the activity of microbes. Stored in airtight cans to prevent the entry of microorganisms. High temperature sterilise cans, destroying any bacteria. Adding salt or sugar kills microbes (lose water by osmosis). Food kept dry to reduce the ability of microorganisms to survive.

What is an indicator species?

A species whose presence or absence in an environment provides indication of environmental conditions e.g. pollution levels

What indicator species can be used to identify polluted water?

Bloodworms and sludgeworms

What indicator species can be used to identify clean water?

Freshwater shrimps and stoneflies.

What indicator species can be used to identify clean air?

Blackspot fungus on rose leaves (sensitive to sulfur dioxide concentrations so can only survive in clean air)

What are lichens used for?

Used to monitor air pollution

How can lichens indicate air pollution?

Sensitive to the concentration of Sulfur dioxide. Different types of lichens grow in different levels of air pollution e.g. bushy lichens grow in cleaner air than crusty lichens. Abundance and distribution of lichens indicate levels of pollution.

Evaluate the use of using an indicator species as a measure of pollution

Cheaper and simpler; used to monitor pollution levels over a long period of time. However, it is less accurate than non-living indicators; Does not provide a definitive figure for pollution levels