CE Biology

CE Biology-A Summary

Part 6-Inter-relationship of Organism with each other & with their environment

歡迎教師及學生使用本網站資料作學術用途，共同推廣教育，但請註明出處資料來自網站「HKCEE Support Centre」http://www.oocities.org/hk/littleuniverse1/hkce.htm OR http://hkce.iscool.net），謝謝！

若是用作出版或放在網頁上，須先知會我們。

Note: This set of WebPages is meant to help you in your revision. You have to refer to your textbook (say English Usage when doing your revision.)

Section 6 Inter-relationship of organisms with each other and with their environment

Ecosystem	The biotic community together with the physical environment
*Community*	All of the populations i.e. all of the living organisms within a given physical area
*Population*	All of the members of the same species within a given physical area

An ecosystem is a self-sustaining environment of living organisms that does not require input of material. However there must be a continuous supply of energy that cannot be recycled as material.

Food chain and food web

1. A food chain is a sequence of feeding relations through energy is transferred.

2. Each organism in a food chain is assigned to a different trophic level.

3. A food web is a number of food chains interconnected.

Energy flow

1. Solar energy is the ultimate source of energy of ecosystems.

2. The input of energy into an ecosystem is mainly through the process of photosynthesis by producers.

3. Energy is lost as heat and excreta when it is passed from a trophic level to another.

Pyramids of numbers and biomass

1. The total number of individuals decreases along a food chain from producer to consumer.

2. The total biomass of individuals decreases along a food chain from producer to consumer.

Reasons:

1. There is energy lost at each trophic level.

2. The size of organisms usually increases.

Cycling of materials

Carbon cycle

Nitrogen cycle

Association between individual of different species of organisms

1. Commensalism – two organisms live together. One of them gains benefit but the other is neither harmed nor gained. E.g. Barnacles live on shell of crab.

2. Mutualism – two organisms live together and both gain benefits from each other. E.g. Lichen – an association of an alga and a fungus

3. Parasitism – organisms, which live in or on other organisms for food. E.g. Tapeworm.

4. Competition

5. Predator-prey relationship

Useful microorganisms

1. Yeast – alcoholic fermentation by yeast is widely employed in wine making and bread-making.

2. Decomposers – bacteria and fungi break down dead bodies and excreta to form inorganic substances, which can be absorbed by plants. Thus they help to maintain recycling of materials.

3. Symbiotic bacteria in leguminous plants – these bacteria fix atmospheric nitrogen to form nitrates and useful nitrogenous compounds for legumes.

Harmful effects of microorganisms

1. Some microorganism are pathogens and cause diseases in animals and plants.

2. Microorganisms cause food spoilage.

3. Saprophytes destroy man’s property, which are organic in nature.

Importance of antibiotics

Antibiotics are chemicals produced by microorganisms to kill bacteria. They can be extracted and used as drugs to cure human diseases.

Food preservation

Killing the microorganism or slowing down their activities in the food substances can prevent food spoilage. Food preservation methods include:

1. High temperature – boiling, pasteurization, UHT

2. Low temperature – refrigeration, freezing

3. Dehydration – drying under sunlight

4. Osmotic preservation – food is kept in concentrated salt or sugar solution or vinegar.

5. Smoking

6. Radiation

The possible effects of deforestation and monoculture

1. Increase in atmospheric carbon dioxide

2. Erosion of soil

3. Destruction of natural habitats

4. Loss of species

5. Increase in pest population

Pollution is the contamination of the environment by substances produced as the result of the activities of man.

1. Air pollution – in Hong Kong mainly come from exhaust fumes of automobile and factories. These include sulphur dioxide, nitrogen oxides, carbon monoxide, lead and smoke. Smoke may combine with fog to form smog.

2. Water pollution – in Hong Kong ,the water pollutants mainly come from domestic sewage, industrial waste water and agricultural wastes, especially those from animals farms. They decrease dissolved oxygen and kill aquatic organisms. Increase in inorganic nutrients and phosphates may cause red tides.

3. Sound pollution – noise increases the psychological stress on man. Constant exposure to noise over 60 dB can cause impairment to hearing and finally deafness.

Conservation can be described as the wise management of our environment so that the delicate balance of biosphere is maintained. It is more than preservation or protection.

The need for conservation – rapid growth of population has led to an increase in demand of land and results in the destruction of natural habitats. The waste produced by man are much greater than the environment can cope with. This leads to pollution. Also a large population has a greater demand for natural resources. The balance of nature is thus disturbed. Therefore there is a need for conservation.

Conservation can be achieved by

1. Reduction of wastage of natural resources

2. Recycling of used materials

3. Controlling pollution

4. Population control

Significance of legislation and education in conservation

1. Legislation – law must be established to protect wildlife, prohibit contamination of environment and control waste treatment .

2. Education – in long term, all citizens must be educated to know the importance of conservation and behave accordingly.

End