CELL REACTIONS TO ITS ENVIRONMENT
Responses
There are three types of responses. These are tactic, nastic, and tropic movements.
The ability of a living organism to respond to stimulus is called irritability. A stimulus is an environmental change which induces or brings about a response in a cell or organism.
Taxis or Tactic Movements
Taxis is the directional movement of a whole organism or a free moving part of it, towards or away from a stimulus. This type of response is positive if the organism moves towards the stimulus, and negative if it moves away from it.
Examples of tactic responses:
Nastism or Nastic Movements
Nastism is a non-directional movement(response) of part of a plant to a non-directional stimuli.
Examples of nastic movements are:
closing of the morning glory flower when the light intensity is low;
the petals of sunflower which open in the light and close in the dark;
the folding of the leaflets of the Mimiosa plant when it is touched;
the closing of the leaflets of the flamboyant tree i.e. sleeping movements due to low light intensity.
Tropism or Tropic Movements
This is a directional movement of part of a plant to a directional stimuli; either towards or away the stimuli. It is a very slow growth movements. It is a bending growth movement, by a plant organ, in response to a stimulus from one direction, by which the plant organ assumes from one direction, by which the plant organ assumes a particular posture or orientation, which bears a relationship to the direction from which the stimulus is received. This type of response is positive if the plant organ moves towards the stimulus, and negative if it moves away from it.
Examples of tropic response:
Class work
In a tabular form, give five differences between;
tropic movement and nastic movement;
tactic movement and tropic movement;
tactic movement and nastic movement.
2. Mention five organs of higher plants that respond to stimuli.
Experiment 1
Aim: To show that shoots are positively phototropic.
Materials required: two boxes, seedlings growing in pot, knife, aluminium foil.
Procedure: The two boxes are arranged as seen in the diagrams below. Some germinating bean seeds/or maize seeds are placed in two boxes with a hole cut at one end. Box A contains normal seedlings while box B contains seedlings with caps of aluminium foil over the tips of the shoots. The inside of each box is painted black to prevent light reflection. The entire experiment is put on the window and observed for a few days.
Observation: The shoot of the seedlings in box A will be observed to bend towards the source of light while those in box B grow straight.
Conclusion: Since the shoot of seedlings bend towards light, it shows that the shoot is positively phototropic.
Experiment 2
Aim: To show that the roots of plants are positively hydrotropic.
Materials required: Two large beakers, water, maize/beans seedlings.
Procedure: Two large beakers in which some bean seedlings are growing by the sides are used. Small holes are made at the center of the two beakers as shown below. A little water is poured at the center in one of the beakers (i.e. control experiment) while there is no water in the second beaker. The entire set-up is allowed to remain for few days.
A B
Observation: At the end of the experiment, the seedlings from both beakers are removed. The seedlings in which the beaker contains water bend their roots towards the source of water while the roots of the other beaker with no water remain straight.
Conclusion: The bending of the roots towards the source of water shows that the roots are positively hydrotropic.
Movement
Movement is the ability of living organisms to change position in response to stimulus (internal or external). It brings about a change of shape, form or position; effects of movement.
Protoplasmic streaming or cyclosis.
Cyclosis is the circulation of protoplasm in cells.
Importance of cyclosis: brings about circulation of materials within the cell. This results in bringing cell to life.
Causes of cyclosis.
Cyclosis is brought about by two actions. They are:
Ability of cytoplasm to change from plasma gel to plasma soil, progressively, from the anterior end to the posterior end of the stream;
Exertion of pressure at the posterior end of plasmasol by the cytoplasm causing the cell to move forward.
Examples of cyclosis.
Amoeboid movement by Amoeba and white blood cell.
Reproduction
Reproduction is the ability of living organisms to give rise to new individuals of the same species.
Forms or types of reproduction.
There are two main types of reproduction. These are asexual and sexual reproduction.
Asexual reproduction does not involve fusion of gametes, while sexual reproduction involves the fusion of sex cells or gametes.
Differences between Asexual and Sexual Reproduction
Asexual Reproduction.
It is common among simple organisms, as well as, flowering plants. It can be divided into two, namely:
Natural asexual reproduction;
Vegetative reproduction.
Note: In organisms which can reproduce both sexually and asexually, asexual reproduction occurs when food is plentiful and environmental conditions are favorable for growth.
Types of natural asexual reproduction in plants and animals:
Binary fission in Amoeba Budding in yeast
Spore formation in Rhizopus
Types of Vegetative Reproduction
There are two types of vegetative reproduction. These are:
Natural vegetative reproduction; and
Artificial vegetative reproduction.
Natural vegetative reproduction: This method involves the production of new individuals from the vegetative parts of the plants. Such vegetative parts include stems, roots and leaves.
Forms of natural vegetative reproduction are:
I.Use of modified underground stem:
II. Use of fleshy leaves to produce buds:
Bryophyllum leaf. Corm of Cocoyam. An onion bulb.
2. Artificial vegetative reproduction: This involves the use of intelligence by man to grow new plants from cut portion of the vegetative body of an older parent plants.
Cassava stem cutting Layering in cocoa Budding using Lemon (as a stock) and orange (as a scion)
Grafting using lemon (as a stock) and orange (as a scion)
Marcotting (stages a, b, c and d)in Mango
Importance of budding and grafting
They are used to propagate many fruit trees, especially citrus trees
Such trees propagated by budding and grafting bear fruits quickly
The trees possess resistance to diseases and other environmental resistance.
Advantages of vegetative propagation
Growth in young plant is rapid since there is no resting period.
Plants that do not produce seeds can only be propagated vegetatively.
Offspring are identical to the parent.
Young plant uses food reserves of the parent as it becomes easily established.
Only one parent is needed.
Desirable characters are retained.
Offspring mature more rapidly.
Plants are less susceptible to adverse weather condition.
It is independent of agents of pollination.
While becoming established, plants grown vegetatively require less care than seedlings.
Disadvantages of vegetative propagation
It may lead to overcrowding of plants.
No new variety of species are produced.
Disease of parents can easily be transmitted to offspring.
There is no mixing of characters.
It reduces resistance to disease.
Undesirable characters are easily transmitted to offspring.
It brings about competition among offspring and parents.
It reduces resistance to changes in climate.
Colonization of new localities is unlikely since offspring are always produced close to parent plant.
Sexual Reproduction.
In sexual reproduction, offsprings are produced by fusion of two different sex cells (gametes) which usually come from two different parents. When the two gametes come together, their nuclei fuse, and this is called fertilization. This fusion results in the formation of zygote, which later develops into an embryo.
Types of sexual reproduction
There are two major types of sexual reproduction. These are:
conjugation,
fusion of gametes.
Conjugation: This is the process by which nuclear material is passed from one cell to another. That is, the whole cell act as a gamete, and pair with another similar whole cell and exchange nuclei. It is common among lower organisms. Examples include Mucor, Rhizopus, Paramecium and Spirogyra.
Fusion of gametes: This is the union of the haploid male and female gametes to produce diploid organisms called zygote. The male gamete is the sperm in animal and the pollen grains in flowering plants, while the female gamete is the egg or ovum in animal and the ovule or egg in flowering plants. Examples of organisms using this methods include Moss, Ferns, all flowering plants, Hydra, Earthworm, Insects, and all vertebrates.
Advantages of sexual reproduction.
It enhances speciation or formation of new species or formation of new species and allows for the continuity of the species.
It provides the means for the maintenance of chromosome number from generation to generation.
It permits variability of individuals, i.e. new varieties are produced.
It enhances survival in new or changing environment.
It allows for the production of hybrids for some desirable traits.
Responses
There are three types of responses. These are tactic, nastic, and tropic movements.
The ability of a living organism to respond to stimulus is called irritability. A stimulus is an environmental change which induces or brings about a response in a cell or organism.
Taxis or Tactic Movements
Taxis is the directional movement of a whole organism or a free moving part of it, towards or away from a stimulus. This type of response is positive if the organism moves towards the stimulus, and negative if it moves away from it.
Examples of tactic responses:
Nastism or Nastic Movements
Nastism is a non-directional movement(response) of part of a plant to a non-directional stimuli.
Examples of nastic movements are:
closing of the morning glory flower when the light intensity is low;
the petals of sunflower which open in the light and close in the dark;
the folding of the leaflets of the Mimiosa plant when it is touched;
the closing of the leaflets of the flamboyant tree i.e. sleeping movements due to low light intensity.
Tropism or Tropic Movements
This is a directional movement of part of a plant to a directional stimuli; either towards or away the stimuli. It is a very slow growth movements. It is a bending growth movement, by a plant organ, in response to a stimulus from one direction, by which the plant organ assumes from one direction, by which the plant organ assumes a particular posture or orientation, which bears a relationship to the direction from which the stimulus is received. This type of response is positive if the plant organ moves towards the stimulus, and negative if it moves away from it.
Examples of tropic response:
Class work
In a tabular form, give five differences between;
tropic movement and nastic movement;
tactic movement and tropic movement;
tactic movement and nastic movement.
2. Mention five organs of higher plants that respond to stimuli.
Experiment 1
Aim: To show that shoots are positively phototropic.
Materials required: two boxes, seedlings growing in pot, knife, aluminium foil.
Procedure: The two boxes are arranged as seen in the diagrams below. Some germinating bean seeds/or maize seeds are placed in two boxes with a hole cut at one end. Box A contains normal seedlings while box B contains seedlings with caps of aluminium foil over the tips of the shoots. The inside of each box is painted black to prevent light reflection. The entire experiment is put on the window and observed for a few days.
Observation: The shoot of the seedlings in box A will be observed to bend towards the source of light while those in box B grow straight.
Conclusion: Since the shoot of seedlings bend towards light, it shows that the shoot is positively phototropic.
Experiment 2
Aim: To show that the roots of plants are positively hydrotropic.
Materials required: Two large beakers, water, maize/beans seedlings.
Procedure: Two large beakers in which some bean seedlings are growing by the sides are used. Small holes are made at the center of the two beakers as shown below. A little water is poured at the center in one of the beakers (i.e. control experiment) while there is no water in the second beaker. The entire set-up is allowed to remain for few days.
A B
Observation: At the end of the experiment, the seedlings from both beakers are removed. The seedlings in which the beaker contains water bend their roots towards the source of water while the roots of the other beaker with no water remain straight.
Conclusion: The bending of the roots towards the source of water shows that the roots are positively hydrotropic.
Movement
Movement is the ability of living organisms to change position in response to stimulus (internal or external). It brings about a change of shape, form or position; effects of movement.
Protoplasmic streaming or cyclosis.
Cyclosis is the circulation of protoplasm in cells.
Importance of cyclosis: brings about circulation of materials within the cell. This results in bringing cell to life.
Causes of cyclosis.
Cyclosis is brought about by two actions. They are:
Ability of cytoplasm to change from plasma gel to plasma soil, progressively, from the anterior end to the posterior end of the stream;
Exertion of pressure at the posterior end of plasmasol by the cytoplasm causing the cell to move forward.
Examples of cyclosis.
Amoeboid movement by Amoeba and white blood cell.
Reproduction
Reproduction is the ability of living organisms to give rise to new individuals of the same species.
Forms or types of reproduction.
There are two main types of reproduction. These are asexual and sexual reproduction.
Asexual reproduction does not involve fusion of gametes, while sexual reproduction involves the fusion of sex cells or gametes.
Differences between Asexual and Sexual Reproduction
Asexual Reproduction.
It is common among simple organisms, as well as, flowering plants. It can be divided into two, namely:
Natural asexual reproduction;
Vegetative reproduction.
Note: In organisms which can reproduce both sexually and asexually, asexual reproduction occurs when food is plentiful and environmental conditions are favorable for growth.
Types of natural asexual reproduction in plants and animals:
Binary fission in Amoeba Budding in yeast
Spore formation in Rhizopus
Types of Vegetative Reproduction
There are two types of vegetative reproduction. These are:
Natural vegetative reproduction; and
Artificial vegetative reproduction.
Natural vegetative reproduction: This method involves the production of new individuals from the vegetative parts of the plants. Such vegetative parts include stems, roots and leaves.
Forms of natural vegetative reproduction are:
I.Use of modified underground stem:
II. Use of fleshy leaves to produce buds:
Bryophyllum leaf. Corm of Cocoyam. An onion bulb.
2. Artificial vegetative reproduction: This involves the use of intelligence by man to grow new plants from cut portion of the vegetative body of an older parent plants.
Cassava stem cutting Layering in cocoa Budding using Lemon (as a stock) and orange (as a scion)
Grafting using lemon (as a stock) and orange (as a scion)
Marcotting (stages a, b, c and d)in Mango
Importance of budding and grafting
They are used to propagate many fruit trees, especially citrus trees
Such trees propagated by budding and grafting bear fruits quickly
The trees possess resistance to diseases and other environmental resistance.
Advantages of vegetative propagation
Growth in young plant is rapid since there is no resting period.
Plants that do not produce seeds can only be propagated vegetatively.
Offspring are identical to the parent.
Young plant uses food reserves of the parent as it becomes easily established.
Only one parent is needed.
Desirable characters are retained.
Offspring mature more rapidly.
Plants are less susceptible to adverse weather condition.
It is independent of agents of pollination.
While becoming established, plants grown vegetatively require less care than seedlings.
Disadvantages of vegetative propagation
It may lead to overcrowding of plants.
No new variety of species are produced.
Disease of parents can easily be transmitted to offspring.
There is no mixing of characters.
It reduces resistance to disease.
Undesirable characters are easily transmitted to offspring.
It brings about competition among offspring and parents.
It reduces resistance to changes in climate.
Colonization of new localities is unlikely since offspring are always produced close to parent plant.
Sexual Reproduction.
In sexual reproduction, offsprings are produced by fusion of two different sex cells (gametes) which usually come from two different parents. When the two gametes come together, their nuclei fuse, and this is called fertilization. This fusion results in the formation of zygote, which later develops into an embryo.
Types of sexual reproduction
There are two major types of sexual reproduction. These are:
conjugation,
fusion of gametes.
Conjugation: This is the process by which nuclear material is passed from one cell to another. That is, the whole cell act as a gamete, and pair with another similar whole cell and exchange nuclei. It is common among lower organisms. Examples include Mucor, Rhizopus, Paramecium and Spirogyra.
Fusion of gametes: This is the union of the haploid male and female gametes to produce diploid organisms called zygote. The male gamete is the sperm in animal and the pollen grains in flowering plants, while the female gamete is the egg or ovum in animal and the ovule or egg in flowering plants. Examples of organisms using this methods include Moss, Ferns, all flowering plants, Hydra, Earthworm, Insects, and all vertebrates.
Advantages of sexual reproduction.
It enhances speciation or formation of new species or formation of new species and allows for the continuity of the species.
It provides the means for the maintenance of chromosome number from generation to generation.
It permits variability of individuals, i.e. new varieties are produced.
It enhances survival in new or changing environment.
It allows for the production of hybrids for some desirable traits.
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