S3 Level 4 Biology Course
Unit 3 Summary Notes
Section 1: Ecosystems:
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An ecosystem is a natural biological system made up of living and non-living parts
An ecosystem can also be described as the habitat plus the community
The habitat is the place where an organism lives
This is the non-living part of an ecosystem
The community is all the living organisms in an area
This is the living part of the ecosystem
There are many different ecosystems on Earth e.g. Scottish woodland, tropical rain forest etc
These different ecosystems will have different communities of living organisms
Another word for non-living factors is Abiotic (e.g. rainfall, temperature and light)
Another word for living factors is Biotic (e.g. Food supply, predators and disease)
Abiotic factors can be sampled using special equipment (e.g. a light meter to sample the
light levels and a moisture meter to sample the soil moisture levels, quadrat to sample plant
abundance)
Plants need light for photosynthesis and water to keep the cells the correct shape
Producers are green plants that get their energy from the sunlight
Consumers are organisms that eat green plants or other consumers
Decomposers are organisms that gets their energy from breaking down waste material (e.g.
bacteria, fungi, worms, beetles etc.)
A herbivore is an animal that eats plants
A carnivore is an animal that eats other animals
An omnivore is an animal that eats both plants and animals
A food chain is a feeding relationship between organisms in an ecosystem
A food web is many food chains linked together
The arrows in a food chain or food web indicate the direction of energy flow
The removal of one organism from a food web can have a significant effect on many other
organisms
Section 2: Adaptation and Natural Selection
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Adaptation is the process by which organisms change to increase their chances of survival
Good examples of adaptations are thick white hair in the polar bear and a waxy skin in the
cactus
These and other adaptations give the organism a better chance of survival in their habitat
Humans are very well adapted (e.g. their opposable thumb and high intelligence)
Natural selection is a process in which those organisms best suited to their environment
survive and pass on their characteristics to their offspring
This theory was first proposed by Charles Darwin who called it ‘survival of the fittest’
Two organisms are said to be of the same species if they are able to breed and produce
fertile offspring
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Species such as the peppered moth show high speed evolution
Section 3: Growing Plants
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Plants use photosynthesis to convert light energy to chemical energy
A plant needs water and soil nutrients to grow healthily
A plant takes these materials in through their roots
Soil nutrients are used to build carbohydrates, proteins and fats
Plants reproduce sexually using seeds and asexually using tubers, bulbs and plantlets
Plants get their initial energy for grow from inside the seed, tuber or bulb
The energy source for initial growth could be starch or sugar
Plant material can be tested for starch using iodine solution (positive result = orange to
black)
Plant material can be tested for sugar using Benedict’s solution (positive result = blue to
orange when heated)
Starch in a plant must be converted to sugar before it can be used for energy
Crops grown outside in Scotland include potatoes, wheat, barley, oats and carrots
Crops grown inside in Scotland include tomatoes, peppers, cucumbers and strawberries
Some crops need to be grown inside to protect them from the frost and cold temperatures
Section 4: Nutrient Cycles, fertilisers and pollution
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A nutrient is a chemical substance required by an organism for healthy growth
The main nutrients required by plants and animals are carbon, nitrogen, phosphate
potassium, magnesium and iron
Plants need carbon to make carbohydrates, proteins and fats
Plants get their carbon by absorbing CO2 through their leaves
Plants need nitrogen (N) for making protein and for leaf growth, phosphorous (P) for flower
growth and potassium (K) for fruit growth
Plants get all these nutrients through their roots from the soil
Animals get all the nutrients they need in their diet.
Animals need carbon for carbohydrates, proteins and fat
Animals need N for proteins, P for ATP (energy) and iron for red blood cells (haemoglobin)
Nutrients are cycled in the environment. They are released from the waste and dead bodies
of organisms to be reused by other organisms
Two important cycles are the carbon and the nitrogen cycles
Bacteria and fungi are involved in releasing nutrients from organic matter
Bacteria help to capture nitrogen from the atmosphere to make it available to plants
The CO2 needed for photosynthesis is released into the atmosphere during respiration
The oxygen needed for respiration is released into the atmosphere during photosynthesis
Over-use of fertilisers can lead to environmental pollution
Burning of fossil fuels can lead to acid rain and global warming
The use of CFCs can affect the ozone layer
Other pollutants include agricultural, industrial and domestic wastes