Biology: Factors Affecting Growth

Topic: Factors Affecting Growth
Factors which affect the growth of organisms are grouped into two parts which are:
a. External factors which include availability of nutrients, humidity, light, temperature, pH and accumulation of metabolic product.
b. Internal factors which include the hormones.
External Factors Affecting Growth
1. Availability of nutrients: All living organisms require nutrients or food and water which are necessary for the normal growth and development of the body.
2. Humidity: All living things also require certain level of humidity to enable them grow. Too low or too high of it will affect growth.
3. Light: Most plants require the presence of sunlight to enable them carry out photosynthesis. It is from this source that they derive their energy and food. Most animals, bacteria and fungi can live in darkness and grow in their habitat.
4. Temperature: All metabolic processes are accelerated at a certain level of temperature. Too low or too high a temperature can adversely retard major processes in the body.
5. pH: The pH of the fluid in contact with a cell has a profound effect on all its activities. Growth can be hampered at certain level of acidity or alkalinity.
6. Accumulation of Metabolic Products: Most metabolic products which accumulate within the body can affect growth. Excessive accumulation is toxic or harmful to the body system and will eventually retard growth.
Internal Factors Affecting Growth
7. Hormones: Hormones are internal factors which are known to affect the growth of plants and animals. Plant hormones which affect the growth of plants are auxins and gibberellins. Auxins promote or inhibit cell elongation in stems and roots. They also stimulate cell division.
Gibberellins promote cell elongation and bring about growth in the stem. They also affect cell division and cell differentiation to a certain extent.
In animals, hormones are secreted by endocrine glands. The hormones mainly concerned with growth are secreted by interior pituitary gland, the thyroid gland and gonads. Abnormal growth in humans, like dwarfism or gigantism is due to errors in the secretion of one of these hormones.