BIOLOGY · Stage 7 · Chapter 4: The Physical Environment and Water Cycle
Biology 4.1 The physical environment — Abiotic Factors and Ecosystems — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Lesson summary
4.1 The physical environment — Abiotic Factors and Ecosystems — Alhussan International Academy — Biology (Stages 7–9) notes: Define an ecosystem, describe how abiotic and biotic factors affect where organisms live and explain why water is important.Ecosystem = a community of livi…
- Population
- Rocks, soil and sand
- Temperature
- Oxygen in water
- Adaptation
- Earth's water
Section 1 of 7Ecosystems and habitats
- Ecosystem = a community of living organisms together with the non-living environment in which they live and interact.
- Ecosystems can be as small as a puddle or as large as a rainforest.
- Habitat = the place where a particular organism lives, such as a pond or a rotting log.
- Population = all the members of one species in a habitat.
- Community = all the populations living together in a habitat.
- Physical environment
- sand, rocks, pebbles and the water in lakes, rivers and oceans are not living, but they are where organisms live.
Section 2 of 7Abiotic and biotic factors
- Abiotic factors
- the non-living parts of the environment.
- Biotic factors
- the living parts, including other organisms.
| Abiotic | Biotic |
|---|---|
| Temperature | Predators |
| Light intensity | Competition for food and space |
| Water availability and rainfall | Disease-causing pathogens |
| Soil type and pH | Food supply |
| Oxygen in water | Pollinators |
| Wind speed, salinity | Decomposers |
Section 3 of 7How abiotic factors affect organisms
- Rocks, soil and sand
- they decide which plants and animals survive in a landscape.
- Organisms on a rocky mountainside differ from those in the rich soil of a river valley.
- Soil pH, minerals and drainage decide which plants grow.
- Temperature
- it affects enzyme activity and the speed of life processes, with a big impact on what can grow and survive.
- Organisms in a hot environment differ from those where the temperature is often below freezing.
- Cold regions support fewer species than warm ones.
- Light
- plants need light for photosynthesis.
- In a woodland, ground plants flower in early spring before tree leaves block the light.
- Water
- all organisms need water, so the amount available affects all life.
- Deserts, hot or cold, are limited by the lack of water.
- Cacti store water in thick stems and have spines instead of leaves to reduce water loss.
- Oxygen in water
- warm water holds less oxygen, so fish may die in hot weather or after pollution.
- Adaptation
- organisms are adapted to the abiotic conditions of their habitat and cannot survive outside their range.
Section 4 of 7Why water is important
1Earth's water2 points
- about 71% of the surface of the Earth is covered in water.
- 96.5% of it is in the oceans, so fresh water is rare and precious.
2In organisms3 points
- water fills cells, and up to 60% of an adult human is water.
- Jellyfish are up to 90% water.
- Plants need water to transport food and minerals and for support, and to make food in photosynthesis.
| Organ | Water % |
|---|---|
| Lungs | 83 |
| Muscles | 79 |
| Kidneys | 79 |
| Heart | 73 |
| Brain | 73 |
| Skin | 64 |
| Bones | 31 |
Section 5 of 7Properties of water
1Good solvent3 points
- many substances dissolve in it, and all the chemical reactions of life take place in solution in water.
- Sea water contains 3.5% dissolved sodium chloride and many other minerals.
- Blood is water containing dissolved food molecules, mineral salts, chemical messengers and blood cells.
2High heat capacity2 points
- it takes a lot of energy to heat water and it cools very slowly.
- The temperature of oceans and big lakes is very stable, so water organisms do not face big temperature changes.
3Ice floats2 points
- solid ice floats on liquid water and forms an insulating layer.
- The water under the ice does not freeze, so animals and plants survive until warmer weather returns.
Section 6 of 7Measuring abiotic factors
- Instruments
- a thermometer for temperature, a light meter for light intensity, a rain gauge for rainfall, a pH meter or indicator for soil acidity and an oxygen probe for water.
- Reliability
- repeat measurements at different places and times and calculate a mean.
Section 7 of 7Investigating distribution along a transect
- Choose a habitat where the factor varies, for example from the open edge of a field to the shade under a hedge.
- Lay a tape measure to make a line transect.
- Place a quadrat every two metres and count a chosen plant species.
- At each point measure light intensity with a light meter and soil moisture with a probe.
- Plot both sets of data on graphs.
- Interpretation
- if the plant is common in bright light and rare in the shade, light affects its distribution.
- Repeat on another day to check reliability.
- Other factors such as soil may also be involved.
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