EXCRETION
Excretion is the removal of waste metabolites from the body of a living organism. Examples of excretory products are sweat, urea, urine, carbon dioxide, oxygen (in plants), water (in plants), and uric acid.
TYPES OF EXCRETORY SYSTEM
GROWTH
Growth is an irreversible increase in size and or dry mass. Cell division by mitosis, cell enlargement and differentiation form the basis for growth.
Aspects of Growth
Increase in number of cells
Increase in number and size (height, length, breath, girth)
Increase in dry mass
Differentiation of cells into tissues and organs
Synthesis of new body material.
Process of Growth
Assimilation
Expansion of the cell
Cell division
Differences between Plants and Animals Growth
Similarities between growth in plants and animals
Both multicellular plants and animals grow by mitotic cell division of pre-existing cells to form new cells
Both achieve a certain amount of vegetative or body growth before reproductive growth sets in
Both show sigmoid growth curve in which the rate of growth is slow at first, becomes faster later until the maximum is reached, then growth rate starts to decline
Both plants and animals require food for growth
Both secrete growth hormones for growth
Growth is irreversible in both plants and animals.
Types of Cell Division
Mitosis: This is a process of cell or nuclear division during which each chromosome in the nucleus duplicates itself and two new cells are formed with equal number of chromosomes i.e. the division of a somatic cell into two daughter cells. It takes place in the somatic cells i.e. body cells that are not involved in the production of gametes.
Mitosis consists of a division of the nucleus followed by a division of the cytoplasm.
Stages of Mitosis
Interphase: during this stage, cell is not dividing; no chromosomes is visible
Prophase: there are two prophase stages: (a) early prophase and (b) late prophase.
Early prophase: during this stage, centriole pairs separate and move to opposite poles; aster rays form around centriole pairs; spindle fibres develop between the centriole pairs to form a spindle; chromosomes become visible in nucleus, then shorten and thicken. Each chromosome can be seen to be made up of two chromatids joined at the centromere.
Late prophase: during this stage, nuclear membrane disappears, and the chromosomes lie free in the cytoplasm.
Metaphase: during this stage, chromosomes come to lie around the equator of the cell.
Anaphase: during this stage, the two chromatids in each chromosome separate at the centromere, and are moved towards opposite poles, along the spindle fibres.
Telophase: this is the last stage of mitosis, during which chromatids arrive at the poles, spindle gradually disappears. A nuclear membrane forms around each set of chromatids. Chromatids gradually become invisible.
This is the end of nuclear division proper. It is followed by the division of the cytoplasm.
Importance or Role of Mitosis
It promotes cell growth
It helps in the replacement or repair of damaged tissues
It serves as basis of asexual or vegetative reproduction
It produces genetically or identical offspring which are identical to the parents
It maintains the diploid number of the chromosome of the cell
Life examples of mitotic process in animals
Formation of new cells in the malpighian layer of the skin
Production of red blood and white blood cells in the bone marrow
Cell division in the liver
Binary fission e.g. in Amoeba
Repair or healing of wound
Life examples of mitotic process in plants
Mitosis occurs in root tip or apex
It occurs in stem tip or apex
It occurs in cambium
It is found in meristems
(b) Meiosis: A kind of cell division during spermatogenesis (sperm formation) and oogenesis (egg formation) in which there is a reduction of chromosomes to half of the original number of chromosomes.
Note: during gametogenesis (sperm and egg formation), in humans, the 46 chromosomes are reduced to 23. Therefore, each sperm or egg now has 23 chromosomes. The fusion of the sperm and egg gives 46 chromosomes which every human being has.
Importance or Roles of Meiosis
It results in the formation of sperms in animals
It results in the formation of eggs in animals
It results in the formation of pollen grains in anthers of flowering plants
It results in the formation of ovules in ovary of flowering plants.
Life examples or areas where meiosis occurs in plants
Ovaries
Anthers
Life examples or areas where meiosis occurs in animals
Ovaries
Testes
Differences between Mitosis and Meiosis
Similarities between mitosis and meiosis
Both result in the formation of new daughter cells
Both involves division of nucleus preceding division of cytoplasm
Both require hormones
Both take place in plants and animals cells
Both pass through prophase, metaphase, anaphase, and telophase.
Regions of Fastest Growth in Plants
The regions of fastest growth in plants are the roots and stem apices i.e. apical meristems. The apical meristems consist of meristematic cells i.e. cells capable of active division.
Note: the stem apices include the terminal buds and the lateral axillary buds.
Roles of apical meristems
Bring about growth in length (height) of the plant
Give rise to branches, leaves and flower in the shoot
They bring about primary growth (i.e. the first growth) of a plant.
Factors Affecting Growth in Plants
External factors:
Warm temperature
Adequate sunlight
Adequate water/humidity
Mineral salts/nutrients availability
Sufficient oxygen/air
Adequate carbon dioxide
pH level
accumulation of metabolic products
Internal factors:
Hormones i.e. the growth hormones e.g. auxins, gibberellings and cytokinins
Genetic constitution
Factors Affecting Growth in Animals
Balanced diet
Oxygen/air
Warmth/suitable temperature
Heredity/genetic constitutions
Hormones
Growth curves
There is a pattern to which, by and large, is shared by both plants and animals.
Growth pattern in plants: in annual plants, a typical sigmoid growth curve is exhibited with limited growth, while in perennial plants; a series of sigmoid curve is exhibited with unlimited growth.
Growth pattern in animals: in most invertebrates, such as fishes, they show S-shaped or sigmoid curve with unlimited growth. In arthropods, such as insects, they moult time to time, hence this growth is called intermittent growth and the growth curve is sigmoid. In birds and mammals e.g. human they show limited growth with sigmoid curve.
Excretion is the removal of waste metabolites from the body of a living organism. Examples of excretory products are sweat, urea, urine, carbon dioxide, oxygen (in plants), water (in plants), and uric acid.
TYPES OF EXCRETORY SYSTEM
GROWTH
Growth is an irreversible increase in size and or dry mass. Cell division by mitosis, cell enlargement and differentiation form the basis for growth.
Aspects of Growth
Increase in number of cells
Increase in number and size (height, length, breath, girth)
Increase in dry mass
Differentiation of cells into tissues and organs
Synthesis of new body material.
Process of Growth
Assimilation
Expansion of the cell
Cell division
Differences between Plants and Animals Growth
Similarities between growth in plants and animals
Both multicellular plants and animals grow by mitotic cell division of pre-existing cells to form new cells
Both achieve a certain amount of vegetative or body growth before reproductive growth sets in
Both show sigmoid growth curve in which the rate of growth is slow at first, becomes faster later until the maximum is reached, then growth rate starts to decline
Both plants and animals require food for growth
Both secrete growth hormones for growth
Growth is irreversible in both plants and animals.
Types of Cell Division
Mitosis: This is a process of cell or nuclear division during which each chromosome in the nucleus duplicates itself and two new cells are formed with equal number of chromosomes i.e. the division of a somatic cell into two daughter cells. It takes place in the somatic cells i.e. body cells that are not involved in the production of gametes.
Mitosis consists of a division of the nucleus followed by a division of the cytoplasm.
Stages of Mitosis
Interphase: during this stage, cell is not dividing; no chromosomes is visible
Prophase: there are two prophase stages: (a) early prophase and (b) late prophase.
Early prophase: during this stage, centriole pairs separate and move to opposite poles; aster rays form around centriole pairs; spindle fibres develop between the centriole pairs to form a spindle; chromosomes become visible in nucleus, then shorten and thicken. Each chromosome can be seen to be made up of two chromatids joined at the centromere.
Late prophase: during this stage, nuclear membrane disappears, and the chromosomes lie free in the cytoplasm.
Metaphase: during this stage, chromosomes come to lie around the equator of the cell.
Anaphase: during this stage, the two chromatids in each chromosome separate at the centromere, and are moved towards opposite poles, along the spindle fibres.
Telophase: this is the last stage of mitosis, during which chromatids arrive at the poles, spindle gradually disappears. A nuclear membrane forms around each set of chromatids. Chromatids gradually become invisible.
This is the end of nuclear division proper. It is followed by the division of the cytoplasm.
Importance or Role of Mitosis
It promotes cell growth
It helps in the replacement or repair of damaged tissues
It serves as basis of asexual or vegetative reproduction
It produces genetically or identical offspring which are identical to the parents
It maintains the diploid number of the chromosome of the cell
Life examples of mitotic process in animals
Formation of new cells in the malpighian layer of the skin
Production of red blood and white blood cells in the bone marrow
Cell division in the liver
Binary fission e.g. in Amoeba
Repair or healing of wound
Life examples of mitotic process in plants
Mitosis occurs in root tip or apex
It occurs in stem tip or apex
It occurs in cambium
It is found in meristems
(b) Meiosis: A kind of cell division during spermatogenesis (sperm formation) and oogenesis (egg formation) in which there is a reduction of chromosomes to half of the original number of chromosomes.
Note: during gametogenesis (sperm and egg formation), in humans, the 46 chromosomes are reduced to 23. Therefore, each sperm or egg now has 23 chromosomes. The fusion of the sperm and egg gives 46 chromosomes which every human being has.
Importance or Roles of Meiosis
It results in the formation of sperms in animals
It results in the formation of eggs in animals
It results in the formation of pollen grains in anthers of flowering plants
It results in the formation of ovules in ovary of flowering plants.
Life examples or areas where meiosis occurs in plants
Ovaries
Anthers
Life examples or areas where meiosis occurs in animals
Ovaries
Testes
Differences between Mitosis and Meiosis
Similarities between mitosis and meiosis
Both result in the formation of new daughter cells
Both involves division of nucleus preceding division of cytoplasm
Both require hormones
Both take place in plants and animals cells
Both pass through prophase, metaphase, anaphase, and telophase.
Regions of Fastest Growth in Plants
The regions of fastest growth in plants are the roots and stem apices i.e. apical meristems. The apical meristems consist of meristematic cells i.e. cells capable of active division.
Note: the stem apices include the terminal buds and the lateral axillary buds.
Roles of apical meristems
Bring about growth in length (height) of the plant
Give rise to branches, leaves and flower in the shoot
They bring about primary growth (i.e. the first growth) of a plant.
Factors Affecting Growth in Plants
External factors:
Warm temperature
Adequate sunlight
Adequate water/humidity
Mineral salts/nutrients availability
Sufficient oxygen/air
Adequate carbon dioxide
pH level
accumulation of metabolic products
Internal factors:
Hormones i.e. the growth hormones e.g. auxins, gibberellings and cytokinins
Genetic constitution
Factors Affecting Growth in Animals
Balanced diet
Oxygen/air
Warmth/suitable temperature
Heredity/genetic constitutions
Hormones
Growth curves
There is a pattern to which, by and large, is shared by both plants and animals.
Growth pattern in plants: in annual plants, a typical sigmoid growth curve is exhibited with limited growth, while in perennial plants; a series of sigmoid curve is exhibited with unlimited growth.
Growth pattern in animals: in most invertebrates, such as fishes, they show S-shaped or sigmoid curve with unlimited growth. In arthropods, such as insects, they moult time to time, hence this growth is called intermittent growth and the growth curve is sigmoid. In birds and mammals e.g. human they show limited growth with sigmoid curve.
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