Asexual and Sexual Reproduction
Asexual Reproduction
Mitosis
Bacteria
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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
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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)
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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
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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
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Simple and fast
Only one parent needed
Rapid spreading
Plants – no need for agents of pollination or seed dispersal
Disadvantages of asexual reproduction
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Genetically identical – no variation
Diseases can spread rapidly
Overcrowding
Sexual Reproduction
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The fusion of haploid male and female gametes
o Animals
 Male – Sperm
 Female – Ovum
o 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
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Increased variation – Better chance of survival in changing conditions
Offspring are more vigorous (stronger)
Disadvantage of sexual reproduction
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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
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Only occurs in the reproductive tissues of organisms
o Animals
 Male: Testis
 Female: Ovaries
o Plants
 Male: Stamens
 Female: Ovaries
Cells involved:
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Parent cells
o Diploid
o Full number of chromosomes
Daughter cells
o Diploid
o Full number of chromosomes
Gametes
o Haploid
o Half the number of chromosomes
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:
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Benign
o Shows no tendency to invade surrounding tissue
o Often easy to surgically remove and can be cured
o Are still dangerous due to growth
 Can crush or displace healthy tissue
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Malignant
o Invade surrounding tissue
o Can invade bloodstream sending cancerous cells all over the body
o Secondary tumours then occur
o Difficult to treat
Carcinogens
Factors which increase the risk of cancer.
Examples:
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X-Rays, Gamma rays, alpha particles and beta particles from nuclear radiation
Ultraviolet light
Asbestos dust
Fungal poisons
Hydrocarbons
Alcohols
Smoking and cancer
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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.
o This gives them a high risk of getting cancer.
o Non-smokers are also susceptible due to inhaling second-hand smoke.
Industrial causes
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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
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A stem is cut off a living plant
It may be planted straight into the soil, or first kept in water
o Rooting compounds can be used to stimulate root growth
Micropropagation
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Many more new plants can be propagated from a single parent plant.
This is achieved by using totiponent plant cells
o Totipotency is the property of a plant cell that allows it to generate an entirely new plant from that
one cell.
o These cells are usually taken from the tip of a growing shoot.
Process
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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
o Small roots develop
o 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
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Produce genetically identical plants
o Growth rate, harvest time, quality, size and the amount of produce are all the same.
Disadvantages of asexual propagation
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All are susceptible to the same diseases, bacteria, fungi and other plant pests
o 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
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Genetically different
o Natural selection will result in a high proportion of plants with characteristics of high yield and
disease resistance.
Disadvantages of sexual propagation
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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)