HOW DO ORGANISMS REPRODUCE? – REVISION NOTES
1. Why Do Organisms Reproduce?
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Reproduction is not essential for survival of an individual.
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It is essential for:
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Continuity of species
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Maintenance of population
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Organisms reproduce to produce new individuals similar to themselves.
2. Do Organisms Create Exact Copies?
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Body design depends on DNA present in chromosomes.
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DNA provides information for protein synthesis.
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During reproduction:
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DNA is copied
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Copying is not perfectly accurate
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Results in variation
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Importance of DNA Copying
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Maintains body design
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Transfers characters
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Creates variation → basis of evolution
3. Importance of Variation
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Variations help organisms adapt to changing environment.
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Beneficial for species survival, not always for individuals.
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Example: heat-resistant bacteria survive temperature rise.
4. Modes of Reproduction
Reproduction occurs in two main ways:
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Asexual reproduction
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Sexual reproduction
5. Asexual Reproduction
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Involves single parent
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No formation of gametes
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Offspring are genetically similar
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Faster method
5.1 Binary Fission
One organism divides into two equal individuals
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Amoeba – division in any plane
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Leishmania – division in definite plane
5.2 Multiple Fission
One cell divides into many daughter cells
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Example: Plasmodium
5.3 Budding
Small outgrowth (bud) develops on parent body
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Bud detaches and becomes new individual
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Examples: Yeast, Hydra
5.4 Fragmentation
Body breaks into fragments
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Each fragment grows into new organism
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Example: Spirogyra
5.5 Regeneration
Ability to regrow lost body parts
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Examples: Planaria, Hydra
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Uses specialised cells
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Not true reproduction normally
5.6 Vegetative Propagation (Plants)
New plants from root, stem or leaf
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Examples:
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Potato (eyes)
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Bryophyllum (leaf buds)
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Sugarcane, Rose
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Advantages
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Early flowering and fruiting
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Genetically identical plants
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Useful for plants without seeds
Tissue Culture
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New plants grown from plant tissue in artificial medium
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Produces disease-free plants
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Used in ornamental plants
5.7 Spore Formation
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Spores formed inside sporangium
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Spores have thick walls
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Survive unfavourable conditions
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Example: Rhizopus
6. Sexual Reproduction
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Involves two parents
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Formation and fusion of gametes
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Produces more variation
Importance
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Combines DNA from two individuals
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Speeds up evolution
7. Sexual Reproduction in Flowering Plants
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Sepals – protection
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Petals – attraction
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Stamen – male part
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Pistil – female part (stigma, style, ovary)
Pollination
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Transfer of pollen from anther to stigma
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Self-pollination
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Cross-pollination (wind, water, animals)
Fertilisation
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Fusion of male and female gametes
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Forms zygote
After Fertilisation
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Zygote → embryo
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Ovule → seed
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Ovary → fruit
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Seed germinates into new plant
8. Reproduction in Human Beings
Humans reproduce sexually
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Reproductive organs mature during puberty
Changes at Puberty
Common Changes
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Hair growth in armpits & genital region
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Oily skin, pimples
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Emotional changes
Boys
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Facial hair
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Voice deepens
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Enlargement of reproductive organs
Girls
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Breast development
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Menstruation begins
Male Reproductive System
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Testes → produce sperms & testosterone
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Sperm formation requires lower temperature
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Sperms travel through vas deferens
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Seminal fluid provides nutrition
Female Reproductive System
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Ovaries produce eggs
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One egg released every month
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Fertilisation occurs in oviduct
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Embryo develops in uterus
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Placenta provides nutrition to embryo
9. Key Differences (Very Important)
Asexual vs Sexual Reproduction
| Asexual | Sexual |
|---|---|
| One parent | Two parents |
| No gametes | Gametes formed |
| Less variation | More variation |
| Fast | Slow |