SUBJECT: BIOLOGY
CLASS: SS2
DATE:
TERM: 3RD TERM
REFERENCES
- Modern Biology for Senior Secondary Schools by S.T. Ramalingam
- Essential Biology by M.C Michael
- New School Biology by H. Stone and Cozen
- SSCE Past Questions and Answers
- New System Biology by Lam and Kwan
- College Biology by IdodoUmeh
- UTME and Cambridge Past Questions and Answers
- Biology Practical Textbook
WEEK TEN
BALANCE IN NATURE AND FAMILY PANNING (Cont.)
CONTENT
- Dynamic Equilibrium in Nature
- Factors Affecting Population
- Abiotic Factors Affecting Population
- Biotic factors affecting Population
- Family planning and birth control
DYNAMIC EQUILBRIUM IN NATURE
When population-influenced factors (abiotic and biotic) are favourable, growth is promoted but when they are unfavourable growth is retarded. A factor which limits the population growth is called a LIMITING FACTOR. The sum of all the limiting factors is known as ENVIRONMENTAL RESISTANCE
The net effect of the abiotic and biotic factors is at a point, the population size of living organisms tends towards a dynamic equilibrium known as BALANCE IN NATURE. When the population increases, the environmental resistance increases too. For instance, food decreases in a population and this results into competition which later leads to the death of the weaker organisms, thereby keeping the population relatively constant
FACTORS AFFECTING POPULATION OF ORGANISMS
Population is the total number of organisms of the same species living together in a given area at a particular time. In an ecosystem, the community is made up of many populations of different species of organisms. When various population or biotic community of an established ecosystem is generally stable, such a community is said to be balanced.
The various factors controlling the population of organisms in a particular habitat are generally referred to as ENVIRONMENTAL RESISTANCE. These factors can be grouped into two;
ABIOTIC FACTORS AFFECTING A POPULATION OF ORGANISMS
These include heat, water, space, light and nutrients.
- HEAT: Organisms do run away from hot environment because heat can cause stress or death.
- WATER: The availability of water determines the survival rate of organisms in any population. Therefore water availability increases the population while lack of it causes a decrease in population.
- SPACE: This is important for normal growth and development. Lack of space results in overcrowding and competition among the organisms.
- LIGHT: This is of utmost importance in plant community. Without light producers may not be able to manufacture food needed by all organisms in the habitat. Low light intensity also results in weak plants which adversely reduce the quantity of food.
- NUTRIENTS: To manufacture their food, plants require nutrients in the soil. Lack of these nutrients leads to deficiency symptoms noticed in plants e.g. stunted growth. This eventually results in poor yield of crops.
EVALUATION
- What is limiting factor?
- How is balance reached in nature?
BIOTIC FACTORS AFFECTING A POPULATION OF ORGANISMS
These are activities of organisms affecting other organisms and they include food, competition, natality, mortality, dispersal, parasite, predators and pathogen.
- FOOD: This is the basic material required for survival of the organisms, for their growth and development and reproduction.
- COMPETITION: This arises among organisms due to lack of space, food and other resources in the environment. Competition aggravate into fighting and cannibalism among animals.
- NATALITY: This is the rate of birth. High birth rate increases population and results in overcrowding.
- MORTALITY: This is the rate of death. Low death rate increases population, but high death rate reduces it. With low death rate there will be food shortage and overcrowding.
- DISPERSAL: Among plants, seeds and fruits dispersal through water, wind, animals and insects reduces the chances of overcrowding. This in turn prevents overpopulation.
- PARASITE: These are organisms that feed on or in another organism (the host). Their action can cause damage or death of the host, thus reducing the population.
- PREDATORS: These are organisms which feed on weaker ones (the prey). If predation is high, it reduces the population of the prey.
- PATHOGEN: These are disease causing organisms e.g. bacteria, viruses, fungi, protozoa. Their actions affect the health of other organisms. The population of the host organisms is thus reduced when the pathogenic attack is high.
EVALUATION
- List the abiotic factors affecting the population of organisms.
- What is the difference between limiting factors and environmental resistance.
FAMILY PLANNING AND BIRTH CONTROL
In nature, biological equilibrium is attained by predator-prey relationship. However, this is achieved in human beings by family planning and birth control. Family planning is a device by which couples determine the number of children they want and when they want them.
Birth control refers to the method used to prevent a woman from becoming pregnant for as long as she wishes.
Without family planning, the population of a nation can rise indiscriminately and may not be able to match the available food and other resources. Famine and death can eventually result.
Family planning is all about prevention of pregnancy and not termination of life. Carefully planned family planning prevents unwanted pregnancies. The birth control or family planning devices include the following;
- Use of condom
- Sterilization
- Spermicides
- Intra-uterine device (IVD)
- Contraceptive pills or injection
- Rhythm method
- Withdrawal method
GENERAL EVALUATION
- What do you understand by environmental resistance
- List the abiotic factors affecting the population of organisms.
- State five of the biotic factors affecting the population of organisms.
- Differentiate between family planning and birth control.
- State five devices that can be used in family planning
READNG ASSIGNMENT
College Biology, chapter 23, pages 542-544
WEEKEND ASSIGNMENT
SECTION A
- Population means …………. A. number of organisms in an habitat B. total number of organisms of the same species C. total number of organisms of different species D. total number of organisms
- The biotic factors affecting population include the following except A. parasite B. predator C. water D. mortality
- These are abiotic factors affecting population except A. space B. natality C. light D. nutrient
- The least effective method of birth control is the use of A. pills B. condom C. spermicide D. withdrawal method
- The activities of an organism which affect the survival of another organism in an habitat is referred to as ………… factor A. biotic B. abiotic C. edaphic D. climatic
SECTION B
- a) What is population? b) State six biotic factors affecting population of organisms
- What is dynamic equilibrium?
