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Asexual-Reproduction
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Uploaded: 7 years ago
Category: Biology
Type: Lecture Notes
Tags: asexual, sexual, plants, identical, growth, sporangium, occurs, produce, parent, quality, cancerous, surrounding, invade, called, pollination
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Filename: Asexual-Reproduction.docx
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Transcript
Asexual and Sexual Reproduction
Asexual Reproduction
50482586233000Mitosis
Bacteria
A copy of the DNA is made.
Splits into two separate parts of the cell (Cleavage forms)
Cell splits to form identical daughter cells
Fungi
A aerial hypha is grown
A sporangium grows
Spores are made in the sporangium by mitosis
The sporangium dries out and breaks, releasing the spores
Flowering plant (Potato)
An underground stem develops and becomes swollen to forma stem tuber
New shoots can develop from the dormant auxillary buds of the tuber
These new shoots form a new plant
Farmer’s use the fact that all the potatoes produced asexually are identical and therefore provide uniform quality in the field.
Advantages of asexual reproduction
Simple and fast
Only one parent needed
Rapid spreading
Plants – no need for agents of pollination or seed dispersal
Disadvantages of asexual reproduction
Genetically identical – no variation
Diseases can spread rapidly
Overcrowding
Sexual Reproduction
The fusion of haploid male and female gametes
Animals
Male – Sperm
Female – Ovum
Plants
Male – Pollen
Female – Ovule
Male gamete usually moves to fertilize female gamete
A zygote is formed
Mitosis occurs in the gamete to form the new organism
Advantages of sexual reproduction
Increased variation – Better chance of survival in changing conditions
Offspring are more vigorous (stronger)
Disadvantage of sexual reproduction
Two parents are required
Young may be vulnerable and take a long time to develop into adults
Plants: Agents of pollination and dispersal may be needed
Meiosis
Only occurs in the reproductive tissues of organisms
Animals
Male: Testis
Female: Ovaries
Plants
Male: Stamens
Female: Ovaries
Cells involved:
Parent cells
Diploid
Full number of chromosomes
Daughter cells
Diploid
Full number of chromosomes
Gametes
Haploid
Half the number of chromosomes
3124200-847217000
Cancer and carcinogens
Cancer
When a mutation in the DNA of a cell occurs, the cell may start to reproduce uncontrollably and fail to differentiate.
Tumours
A group of cancerous cells is called a tumour. There are two types:
Benign
Shows no tendency to invade surrounding tissue
Often easy to surgically remove and can be cured
Are still dangerous due to growth
Can crush or displace healthy tissue
Malignant
Invade surrounding tissue
Can invade bloodstream sending cancerous cells all over the body
Secondary tumours then occur
Difficult to treat
Carcinogens
Factors which increase the risk of cancer.
Examples:
X-Rays, Gamma rays, alpha particles and beta particles from nuclear radiation
Ultraviolet light
Asbestos dust
Fungal poisons
Hydrocarbons
Alcohols
Smoking and cancer
Tobacco smoke contains tar, a carcinogen. Smoking is the biggest single cause of lung cancer.
Smokers expose themselves to high concentrations of this smoke for prolonged periods.
This gives them a high risk of getting cancer.
Non-smokers are also susceptible due to inhaling second-hand smoke.
Industrial causes
Industrial area’s have higher levels of carcinogens in the atmosphere.
There are risks of the radioactive gas, Radon, building up in houses near granite rock.
Artificial Propagation of Plants
A breeder can use asexual methods to produce perfect copies or clones of a parent plant.
Cuttings
A stem is cut off a living plant
It may be planted straight into the soil, or first kept in water
Rooting compounds can be used to stimulate root growth
Micropropagation
Many more new plants can be propagated from a single parent plant.
This is achieved by using totiponent plant cells
Totipotency is the property of a plant cell that allows it to generate an entirely new plant from that one cell.
These cells are usually taken from the tip of a growing shoot.
Process
The cells are seperated and put into a culture medium that contains plant growth substances
The growth substances stimulate the mitotic division of the totipotent cells
Small roots develop
It is now called a plantlet
The plantlet is placed in a new culture medium that stimulates the growth of the shoot.
Once large enough, these plantlets can be planted in soil and be allowed to grow like a normal plant.
ASEXUAL PROPAGATION OF CROP PLANTS
Advantages of asexual propagation
Produce genetically identical plants
Growth rate, harvest time, quality, size and the amount of produce are all the same.
Disadvantages of asexual propagation
All are susceptible to the same diseases, bacteria, fungi and other plant pests
A farmer can lose his entire crop very quickly
Farmers are unable to improve the characteristics of their plants
SEXUAL PROPAGATION OF CROP PLANTS
Advantages of sexual propagation
Genetically different
Natural selection will result in a high proportion of plants with characteristics of high yield and disease resistance.
Disadvantages of sexual propagation
Slow process
Many generations of plants are needed to produce the plants with the best characteristics
Pollination is very laborious (as it may need to be done by hand)
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