• Created by: Evie1505
  • Created on: 01-11-19 13:18


An individual is part of a species that lives in its habitat within a population. Many different populations interact in the same habitat, creating a community. The populations are often dependent on each other. An ecosystem is the interaction of a community with abiotic (non-living) parts of the environment. Organisms are adapted to live in the conditions of their environment. 

Organisms which need the same resources compete for it. There may be competition within a species (intraspecific competition) or with other species (interspecific competition). 

  • Plants may compete for light, space, water and mineral ions
  • Animals may compete for space, food, water and mating partners.

Interdependence is the dependency on other species for food, shelter, pollination etc. The removal or addition of species to the community can affect the populations of others by changing prey or predator numbers. 

A stable community is one where all the biotic (living) and abiotic (non-living) factors are in balance so that the population size remains roughly constant. Examples include tropical rainforests, oak woodlands and coral reefs. 

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Abiotic Factors

An abiotic factor is a non-living factor. These can affect a community:

  • Light intensity - light required for photosynthesis affecting the rate of growth for a plant which can be food sources or shelter for other organisms
  • Temperature - affects the rate of photosynthesis
  • Moisture Levels - both plants and animals need water to survive
  • Soil pH and mineral content - soil pH affects the rate of decay and therefore how fast mineral ions return to soil which is taken up by other plants; different plant species need different nutrient concentration levels
  • Wind intensity and direction - wind affects the rate of transpiration (movement of water from root to leaves) in plants which affects the temperature of the plant and the rate of photosynthesis because it transports water and mineral ions to the leaves
  • Carbon dioxide levels - carbon dioxide affects the rate of photosynthesis in plants and also affects the distribution of organisms as some thrive in high carbon dioxide environments
  • Oxygen levels for aquatic animals - levels in water varies greatly and most fish need a high concentration of oxygen to survive
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Biotic Factors

A biotic factor is a living factor. These can affect a community:

  • Food availability - more food means organisms can breed more successfully and so the population can increase in numbers
  • New predators - can decrease the population of preys (predator-prey relationships)
  • New pathogens - when a new pathogen arises, the population has no resistance to it so they can be wiped out quickly
  • Competition - if one species is better adapted to the environment than another, then it will outcompete it until the numbers of the lesser adapted species are insufficient to breed

Red and grey squirrels live in the same habitat and eat the same food. Grey squirrels outcompete the red squirrels so the population of red squirrels are decreasing.

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Organisms have adaptations allowing them to survive in conditions where they live including:

  • Structural (features of an organism's body structure ie. shape or colour)
  • Behavioural (the way an organism behaves)
  • Functional (involved in processes such as reproduction and metabolism )

Extremophiles live in environments which have extreme conditions including high temperatures, pressures or salt concentrations. For example, a species of bacteria live in deep sea vents where the pressure is very high.

In cold environments, animals may have a smaller surface area to volume ratio to reduce heat loss of have lots of insulation (blubber, fur coat).

In dry climates, animals may have adaptations in their kidneys so they can retain lots of water producing very concentrated rine, be active in the early morning and evenings when it is cooler, rest in shady areas or have a large surface area to volume ration to increase heat loss.

Plants may have curled leaves to reduce water loss, extensive root systems to take in as much water as possible, waxy cuticle to stop water evaporating or a water storing tissue in the stem. 

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Levels of Organisation

Feeding relationships are shown by food chains, beginning with a producer who is always a photosynthetic organism (usually a green plant/algae). They make glucose by photosynthesising which is used to make other biological molecules in the plant, making up the biomass. Producers are eaten by primary consumers and energy is transferred through organisms in an ecosystem when one is eaten by another. Primary consumers are eaten by secondary consumers who are eaten by tertiary consumers. Predators kill and consume preys

To work out the distribution and abundance of species in an ecosystem, transects and quadrats are used. You can then process this information by calculation the mean and drawing a graph. 

A stable community will show population cycles between the predators and prey.

  • If the population of prey increases, the population of predators will also increase
  • Eventually, the number of prey decreases as more would be consumed by the increased number of predators
  • When there isn't enough prey to feed all the predators, the population of predators will decrease, which allows the population of prey to increase again
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The Carbon Cycle and The Water Cycle

The Carbon Cycle

  • Carbon dioxide is removed from the air in photosynthesis by green plants and algae - they use carbon to make carbohydrates, proteins and fats. They are eaten and the carbon moves up the food chain. 
  • Carbon dioxide is returned when plants, algae and animals respire. Decomposers also respire to break down dead organisms and any waste, so they return mineral ions to the soil.
  • Carbon dioxide is returned to the air when wood and fossil fuels are burnt (combustion) as they contain carbon from photosynthesis. 

The Water Cycle

  • The Sun's energy causes water to evaporate from the sea and lakes, forming water vapour. Water vapour is also formed as a result of transpiration in plants. 
  • Water vapour rises and then condenses to form clouds. 
  • Water is returned to the land by precipitation (rain, snow or hail), and this runs into lakes to provide water for plants and animals. 
  • This then runs into seas and the cycle begins again
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Factors affecting the rate of decomposition:

  • Temperature - chemical reactions generally work faster in warmer conditions but if it is too hot, enzymes can denature and stop decomposition
  • Water - microorganisms grow faster in conditions with water as it is needed for respiration; it also makes food easier to digest
  • Availability of oxygen - most decomposers respire aerobically 

When biological material decays, it produces compost. It is used by farmers and gardeners as a natural fertiliser but they need to provide optimum conditions for decay. If more oxygen is available they respire aerobically producing heat. Increased temperature increases the rate of decay so compost is made quicker.

Microorganisms decompose waste anaerobically to produce biogas (made of methane), which can be burned as a fuel. Biogas generators are used to produce methane. It requires a constant temperature  (30°C) so the microorganisms keep respiring. It cannot be stored as a liquid (as it needs a very high pressure) so needs to be used immediately - for heating, cooking etc.

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Investigating Decay

You can investigate the effects of temperature on decay by measuring the pH of fresh milk in the presence of the enzyme lipase. 

  • Make a solution of milk and phenolphthalein indicator in a test tube and label 
  • In another test tube add lipase solution and label 
  • Add sodium carbonate to the solution of milk and phenolphthalein indicator which will cause the solution to become alkaline and therefore appear pink
  • Place both test tubes in a water bath at a specific temperature 
  • Add the lipase enzyme and begin the stopwatch 
  • Time how long it takes for the pink colour to disappear (ie. when the pH has decreased) 
  • Repeat this at different temperatures to see at which temperature the pink colour disappears the quickest, indicating the quickest decomposition 

You can calculate the rate of decay using:

Rate = 1000 ÷ time

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Impact of Environmental Change

Environmental changes affect the distribution of species in an ecosystem:

  • Temperature - climate change may lead to insects migrating to places in the world which are becoming hotter
  • Water Availability - populations will migrate to find water 
  • Atmospheric gas composition - certain pollutants can affect the distribution of organisms (ie.lichen cannot grow in places where sulfur dioxide is present)

These changes may be seasonal, geographic or caused by human interaction.

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Biodiversity and Waste

Biodiversity is the variety of different species of organisms on Earth or within an ecosystem 

High biodiversity means the ecosystem will be stable because biodiversity allows species to be less dependent on each other for things such as food and shelter.

Many human activities are having a negative effect on biodiversity. The future of humans on Earth depends on maintaining biodiversity (for example for food and new medicines).

The impact of our activities is getting bigger as the population is increasing because more resources are being used and more waste is being produced:

  • More land is being used for houses, farming, shops, roads and factories destroying habitats
  • Pollution kills plants and animals (smoke and acidic gases pollute the air // landfill and toxic chemicals pollute the land // sewage, fertilisers and toxic chemicals pollute the water)
  • We are using raw materials quicker than they are being produced

Humans have only tried to reduce their impact recently.

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Deforestation is the cutting down of a large number of trees in the same area in order to use the land for something else.

It happens in tropical areas to:

  • Provide land for cattle and rice fields
  • To grow crops (ie. sugarcane, maize) for biofuels which are used to produce energy 

Deforestation has negative consequences

  • Trees contain carbon, so burning them results in more carbon dioxide being released into the environments, contributing to global warming
  • After deforestation, microorganisms decompose the dead vegetation, producing carbon dioxide as they respire
  • Trees take in carbon dioxide when they photosynthesise so fewer trees mean less carbon dioxide is taken in
  • The number of habitats is reduced, decreasing biodiversity
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Global Warming

Global warming refers to the fact that the temperature around the world is increasing because we are producing more greenhouse gases (carbon dioxide and methane), resulting in more heat being absorbed and reflected back to the Earth, heating it up.

The consequences of this temperature increase are:

  • Melting of ice caps, reducing habitats
  • Rising sea levels, reducing habitats as low lying areas will be flooded with salty water
  • Temperature and rainfall levels will affect migration and therefore the distribution of different species, as they may no longer be able to survive where they live
  • Organisms will become extinct as their habitats are lost, reducing biodiversity
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Human Interactions with Ecosystems

Positive Human Interactions with Ecosystems 

  • Maintaining rainforests, ensuring habitats are not destroyed
  • Reducing water pollution and monitoring the changes over time 
  • Preserving areas of scientific interest by stopping humans from going there
  • Replanting hedgerows and woodlands to provide habitats which were previously destroyed

Negative Human Interactions with Ecosystems 

  • Production of greenhouse gases leading to global warming
  • Production of sulfur dioxide in factories leading to acid rain which affects habitats
  • Chemicals used in farming leaks into the environment 
  • Clearing land in order to build on, reducing the number of habitats

Problems with Maintaining Biodiversity

  • Costs money when it can be prioritised for other things
  • Costs the livelihoods of the local people (ie. causes unemployment)
  • Conflicts between protecting biodiversity and protecting our food security 
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Maintaing Biodiversity

To reduce our negative impact on ecosystems, programs have been put in place to maintain biodiversity:

  • Breeding programs stop endangered species from becoming extinct by breeding them in captivity to make sure the species survives if it dies out in the wild
  • Protection of rare habitats stop species from becoming extinct so if they are damaged they may even be regenerated to encourage populations to live here
  • Reintroduction of hedgerows and field margins around the land where only one type of crop is grown maintains biodiversity as the hedgerows provide habitat for lots of organisms (because a field of one crop would not support many organisms) and field margins provide areas where wildflowers and grasses can grow)
  • Reduction of deforestation and carbon dioxide production reduces the rate of global warming, slowing down the rate that habitats are destroyed
  • Recycling rather than dumping waste in landfill reduces the amount of land taken up for landfills and slows the rate we are using up natural resources
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Trophic Levels

Trophic levels are different stages in the food chain, represented by numbers

  • Level 1 - organisms that make their own food by photosynthesis are called producers (ie. plants and algae)
  • Level 2 - primary consumers are herbivores as they only eat plants
  • Level 3 - secondary consumers are carnivores as they eat herbivores
  • Level 4 - tertiary consumers are also carnivores as they eat other carnivores; since they have no other predators because they are at the top of the food chain they are apex predators

Decomposers break down dead plant and animal matter by secreting enzymes. The matter is broken down into small soluble food molecules and they move into the microorganism by diffusion.

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Pyramids of Biomass

Pyramids of biomass show the relative biomass at each trophic level. It shows the relative weights of material at each level and the biomass decreases as you move up the trophic levels. Not all the food consumed by an animal is converted into biomass meaning the biomass of the organism in the level above another will always be higher as not all the organism is consumed and converted into biomass. 

Producers transfer about 1% of the incident energy from light for photosynthesis as not all the light lands on the green (photosynthesising) parts of the plant.

Only ~10% of the biomass of each trophic level is transferred to the next. Not all the biomass can be eaten. Carnivores cannot generally eat bone, hooves, claws and teeth. Not all the biomass eaten is converted into the biomass of the animal eating it. Lots of glucose is used in respiration, which produces carbon dioxide as a waste product. Urea is a waste substance released in urine. Biomass can be lost as faeces - as herbivores don't have all the enzymes to digest all the material they eat, so it is egested instead. 

Efficiency = (biomass transferred to next level/biomass at previous level) * 100

Because less biomass is transferred each time, fewer animals are found in the higher trophic levels.

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Factors Affecting Food Security

Food security is having sufficient food to feed the population. Factors which affect it:

  • Increasing birth rate means more food is required
  • Changing diets in developed countries means food resources which are already in low amounts become even more scarce as the demand for them increase
  • New pests and pathogens can destroy crops
  • Climate change affects food production (ie. no rain resulting in crops failing)
  • Conflicts in some countries can affect the availability of water and food 

To feed everyone on Earth, sustainable methods are needed to ensure food supplies can be preserved for future generations too. 

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Farming Techniques

Farmers aim to increase the amount of energy (from food) that is converted to biomass in livestock because this is more efficient. This is done by reducing the energy transfer from the animals to the environment:

  • Raising them in small cages so there is less movement and therefore less energy wasted on this
  • Areas, where they are kept, have high temperatures and they stand close to each other so less energy is wasted on controlling body temperature

To increase growth they are also given high protein foods. They are pumped with antibiotics so that energy is not wasted on fighting off the disease or so that it does not spread and passed up the food chain

This type of farming has many ethical objections because lots of animals are kept in a small place, causing distress. It also increases the risk of spread of infection. It is carried out to increase profits and efficiency, but the standard of living is very low for the animals.

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Sustainable Fisheries

Overfishing is declining fish stocks because humans are fishing at a faster rate than the populations can regenerate. To avoid species disappearing in some areas, the populations need to stay above a certain level so breeding can continue. Some restrictions have been put in place:

  • There are limits of net sizes (making them bigger) so smaller fish are not caught and can reach breeding age to replenish the population
  • Fishing quotas mean only a certain number of a species can be caught (in an area and over a period of time) to prevent overfishing
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Role of Biotechnology

Biotechnology can be used to help feed the population and potentially provide treatments for a number of diseases. 

The fungus Fusarium can produce mycoprotein which is a protein-rich food source suitable for vegetarians. It is grown on glucose syrup in aerobic conditions. The fungus is then harvested and purifies so it can be consumed. Protein without animals:

  • Reduces land use as a lot of land is required to rear animals and also areas to grow crops to feed them 
  • Reduces our methane contribution to global warming (cows produce methane)

Genetically modified bacteria produces insulin which is then purified to treat people with diabetes. 

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Pros and Cons of GM Crops

Genetically modifying crops has advantages:

  • Modifying them to be resistant to pests / extreme weather conditions can increase yields
  • Modifying them to increase their nutritional value is beneficial where they lack access to vitamins (ie. 'golden rice')

But not everyone agrees:

  • Most people argue that people go hungry because they can't afford it so they argue you need to tackle poverty first
  • There are fears that countries may become dependent on companies who sell GM seeds
  • Sometimes poor soil is the main reason why crops fail and even GM crops won't survive
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