Topic: Some Properties And Functions Of The Cell
- Meaning Of Nutrition
- Usefulness Of Food
- Types Of Nutrition
- Meaning Of Cellular Respiration
- Types Of Cellular Respiration
- Meaning Of Excretion
- Meaning Of Growth
- Basis Of Growth
- Cell Reaction To Its Environment
- Meaning Of Movement
- Meaning Of Reproduction
- Types Of Reproduction
Some Properties And Functions Of The Cells
1. Nutrition (Feeding)
Definition: Nutrition is the process by which food is taken in by living organisms in order to supply the nutrients required for the continuos metabolic reactions going on in the body. Food is the source of nutrients.
Usefulness of Food
Living cells or organisms require food for various reasons. These reasons are:
1. To provide energy needed for various physical and metabolic activities.
2. To make essential substances such as hormones and enzymes.
3. To make new cells for growth and replacement of worn-out tissues.
4. To supply various substances required for healthy growth and development.
Types of Nutrition
There are two major types of nutrition. These are autotrophic and heterotrophic nutrition.
i. Autotrophic Nutrition: Autotrophic nutrition is the type of nutrition in which organisms are able to manufacture their own food. Organisms which can manufacture or synthesize their own food are called autotrophs. Two types of autotrophic nutrition are photosynthetic (holophytic) and chemosynthetic nutrition.
ii. Heterotrophic Nutrition: Heterotrophic nutrition is the type of nutrition in which organisms cannot manufacture their own food but depends directly or indirectly on plants (autotrophs) for their own food. Organisms which cannot manufacture their own food are called heterotrophs. Most animals, fungi, protozoa and some bacteria belong to this group.
Forms or types of heterotrophic nutrition include holozoic, parasitic, saprophytic and symbiotic nutrition.
2. Cellular Respiration
Definition: Cellular respiration involves the chemical activities of the cells in which glucose is broken down by a series of reactions controlled by enzymes to release energy. The energy so released is stored in adenosine trisphosphate (ATP). ATP is the form in which energy is carried, stored and used by all living cells for the various metabolic processes. The entire purpose of cellular respiration is to generate energy for various metabolic processed in all organisms.
Types Of Cellular Respiration
There are two main types of cellular respiration. These are aerobic and anaerobic respiration.
i. Meaning Of Aerobic Respiration: Aerobic respiration is the type of respiration which requires oxygen to break down glucose (substrates) into water, carbon dioxide and energy (ATP).
ii. Meaning Of Anaerobic Respiration: Anaerobic respiration is the type of respiration which does not require the presence of oxygen to provide energy. During anaerobic respiration, glucose is broken down to yield carbon dioxide, alcohol (ethanol) and energy.
Definition: Excretion is defined as the process by which organisms get rid of waste products during its metabolism. The reason for excretion by all living things is to get rid of metabolic wastes which are poisonous or toxic to the body system when they are not removed. Different organisms use different means of removing waste products from their body systems.
Forms in which Waste Products are Excreted
Waste products of various kind are excreted in three forms. These are:
i. Liquid form: Waste products which are of liquid form include water, uric acid, sweat, urine, urea, dissolved nitrogenous wastes, dissolved mineral salts, latex, gums etc.
ii. Gaseous form: Waste products which are excreted in gaseous form include carbon dioxide, oxygen, ammonia gas etc.
iii. Solid form: Waste products which are excreted in solid form include uric acid in some animals and tannins, alkaloids, mucillages in plants.
Definition: Growth is defined as an irreversible increase in size and complexity of an organism brought about by the synthesis of new protoplasm. For growth to occur, the rate of synthesis or building up of materials (anabolism) must exceed the rate of breaking down (catabolism).
Growth in plants is indefinite and apical while growth in animals is definite and uniform in all parts of the body.
Basis of Growth
For any organism to grow, it must pass through three phases usually referred to as the basis of growth. These are:
i. Cell division: Cell division involves cell multiplication. In order to multiply, the cells undergo certain divisions. One cell divides into two, two into four, four into eight and so on. Two types of cell division exist, according to the behaviour of chromosomes. These are mitosis and meiosis.
ii Cell enlargement: This is the process which follows cell division in which the daughter cells increase in mass and in size. That is, it enlarges in size.
iii. Cell differentiation: This takes place after cell enlargement in which each cell develops into a special type of cell by changing its shape and structure in order to carry out a specialised or a particular function. The kind of cell it becomes depends on its position in the body of the organism. For example, in human body, a cell may develop into a nerve cell if it is in the brain. Cell differentiation is important in the growth and development of a mature multicellular organisms.
5. Cell Reaction To Its Environment (Responses)
All living things are capable of responding to internal and external stimuli. The ability to do this is called irritability or sensitivity. By this means, plants and animals are able to detect and respond to changes in their environment.
Types of Responses
Generally, animals respond very quickly to external stimuli while plants respond slowly. Again, only certain organs respond to external stimuli in plants but in animals, often, the whole organism respond to the stimulus. There are three major types of responses. These are tactic, nastic and tropic movements.
i. Taxis or Tactic Movements: Taxis or Tactic response is a directional type of response or movement in which a whole organism moves from one place to another in response to external stimuli such as light, temperature, water or certain chemicals.
ii. Nastism or Nastic Movements: Nastism is a type of response in which a part of a plant moves in response to non-directional stimuli such as changes in light intensity, temperature or humidity. The response movements are also non-directional.
iii. Tropism or Tropic Movements: Tropism is a type of response to a directional stimulus. The direction of the response is related to that of the stimulus and is positive if the plant part grows towards the stimulus, and negative if the part grows away from it. Tropism are very slow growth movements. They are named according to the stimuli, elg. Phototropism is a response to light while hydrotropism is a response to water.
Meaning: Movement is the ability of living organisms to move from one place to another. Reasons for movement include searching for food, escape from danger, response to stimuli (either positively or negatively) and for the sake of reproduction. All organisms that can move are equipped with various organelles or organs and mechanisms for movement.
Meaning: Reproduction is the ability of living organisms to give rise to new individuals of the same species. The purpose of reproduction is to ensure the continuity of life.
Types of Reproduction
There are two main types of reproduction. These are asexual and sexual reproduction.
i. Asexual reproduction: Asexual is the type of reproduction in which new organisms are produced from a single parent without the production of gametes. The offspring called the clones are the same in all respects to each other and to the parent organisms that produced them.
ii. Sexual reproduction: Sexual reproduction involves the fusion of the male gametes, e.g. Sperm cells and the female gametes, e.g. Ova or egg cell to form a zygote which later develops to a young offspring.