Abiotic Environment (Section E 1.2 of biology Syllabus 2004)

Importance of Physical environment to living organisms

The type and number of individuals in a particular environment are determined to a large extent by the physical factors within the environment.

1. Light

-Provides energy for photosynthetic organisms

-Light intensity affects the rate of photosynthesis

-Some plants prefer shade (e.g. ferns, bromeliads, and orchids) while other prefer bright light

-light intensity would affect living organisms, e.g. woodlice would move away from bright light. Also, of light cannot penetrate surface of water, there will be almost no plant at the bottom of the water

-wavelength of light affects photosynthesis. E.g. some algae use red light and some use green light

-Length of daylight affects flowering and fruiting of some plants esp. those in seasonal regions

2. Water

-It is essential for the process of photosynthesis. It also plays a vital role in most metabolic activities

-Terrestrial (land) plants and animals must always find a source of water. Therefore there is rich biodiversity in areas where there are plenty of rainfalls e.g. rainforest, and low biodiversity in desert regions

- Several factors affect plant growth in aquatic environment or submerged mangrove seashore areas. These include: water pH, salt concentration, oxygen concentration, flow of water (current), water depth and light penetration

-Still water has less oxygen while fast moving water has more oxygen dissolved in it

Importance of soil

1. Anchorage: soil provides anchorage for terrestrial plant roots.

2. Nutrient minerals: soil provides nutrients for plants. E.g. nitrates, phosphates, potassium salts etc.

3. Water: plants obtain water by their roots from the soil

4. Air: plant roots and soil organisms use air found in soil. A good soil type would have plenty air spaces

Soil Formation

Soil is formed from the weathering of rocks. There are three main types of weathering

a. Physical: action of water waves

b. Chemical: acid rain or carbonic acid in rain

c. Biological e.g. roots growing in rocks

Some important Soil Organisms

1. Earthworm:  -they mix the soil as they borrow, and help with drainage and irrigation of soil

                        - make soil finer: eat and grind soil to take out smaller organisms.

                        -fertilize soil, by helping to decompose organic matter e.g. leaves

2. Nematodes:  -Are decomposers living in soil spaces

                        - are parasites living in roots of plants causing stunted growth e.g. in tomatoes

                       

3. Millipede:    - feed on leaf litter or decaying plants releasing nutrients, thus helping to fertilize the                                soil

4. Snail or slugs:  - found on leaf litters or under stones (or moist areas). They feed on dead                                               supply nutrients) or living plants (pests)

5. Termites:      - mix soil when they borrow

                        -feed on decaying wood, therefore help to fertilize soil when nutrients are released

                        -cause damage to plants when they feed on them