INTRODUCTION – WHY DO ORGANISMS REPRODUCE?
Reproduction is one of the important characteristics of
living organisms. Unlike nutrition, respiration, or excretion, reproduction is not
essential for the survival of an individual organism, but it is necessary
for the continuation of a species.
Without reproduction:
- Species
would disappear from Earth.
- Population
of organisms would decrease.
- Life
would not continue from one generation to another.
Organisms reproduce and produce new individuals that
resemble themselves.
Example:
- Human
beings give birth to humans.
- Mango
plants produce mango plants.
7.1 DO ORGANISMS CREATE EXACT COPIES OF THEMSELVES?
Organisms look similar because their body designs
(blueprints) are similar.
The blueprint for body design is stored in:
DNA (Deoxyribonucleic Acid)
DNA contains hereditary information and controls body
features.
DNA COPYING IN REPRODUCTION
During reproduction:
- DNA
creates copies of itself.
- Cellular
apparatus also duplicates.
- Cell
divides into two daughter cells.
DNA copying is important because it transfers
characteristics from parents to offspring.
ARE COPIES ALWAYS IDENTICAL?
No.
Biochemical reactions are never completely accurate.
Hence, small differences appear in DNA copies.
These differences are called:
Variations
Some variations are useful while some may not be useful.
Example:
- Children
resemble parents but are never completely identical.
IMPORTANCE OF VARIATION
Variation increases chances of survival when environmental
conditions change.
Example given in textbook:
If global warming increases water temperature:
- Most
bacteria living in temperate water may die.
- Heat-resistant
bacteria survive and reproduce.
Thus:
Variation helps species survive over long periods.
MODES OF REPRODUCTION USED BY SINGLE ORGANISMS
Reproductive methods depend on body design of organisms.
ASEXUAL REPRODUCTION
Reproduction involving only one parent without fusion
of gametes is called:
Asexual Reproduction
Characteristics:
- One
parent involved
- No
gamete formation
- Offspring
genetically similar
- Fast
process
TYPES OF ASEXUAL REPRODUCTION
1. FISSION
In unicellular organisms, one cell divides and forms new
organisms.
Binary Fission
One parent divides into two daughter cells.
Examples from textbook:
- Amoeba
- Leishmania
- Bacteria
Amoeba
Binary fission occurs in any plane.
Process:
Amoeba → nucleus divides → cytoplasm divides → two Amoeba
formed
Leishmania
Leishmania has a whip-like structure (flagellum).
Binary fission occurs in a definite orientation.
Example:
Leishmania causes:
Kala-azar
Multiple Fission
One organism divides into many daughter cells
simultaneously.
Example:
Plasmodium (malaria parasite)
Activity 7.1 — Yeast Observation
Procedure:
- Dissolve
sugar in water.
- Add
yeast granules.
- Keep
in warm place.
- Observe
under microscope.
Observation:
Yeast forms small buds.
2. BUDDING
A small outgrowth called bud develops on the parent
body and grows into a new organism.
Examples:
- Hydra
- Yeast
Process in Hydra:
- Cells
divide repeatedly.
- Bud
develops.
- Bud
grows.
- Bud
detaches and becomes independent.
3. FRAGMENTATION
The body breaks into smaller pieces and each piece develops
into a new individual.
Example:
Spirogyra
Process:
Mature Spirogyra filament → breaks into fragments → each
fragment grows into new organism
Activity 7.4 — Spirogyra Observation
Observation:
Spirogyra contains filament-like structures.
4. REGENERATION
The ability to form complete organisms from body fragments.
Examples:
- Hydra
- Planaria
Special cells divide repeatedly and develop into tissues and
organs.
Important:
Regeneration is not exactly reproduction because
organisms normally do not reproduce by being cut into pieces.
5. VEGETATIVE PROPAGATION
Formation of new plants from roots, stems, or leaves.
Examples from textbook:
- Sugarcane
- Rose
- Grapes
- Banana
- Orange
- Jasmine
- Bryophyllum
Methods:
- Layering
- Grafting
Advantages:
✔ Plants grow faster
✔ Earlier flowers and fruits
✔ Plants remain genetically similar
✔ Useful for seedless plants
Example: Bryophyllum
Buds present in leaf margins fall on soil and develop into
new plants.
Activity 7.5 – Potato Experiment
Observation:
Potato pieces containing buds develop roots and shoots.
Activity 7.6 – Money Plant
Observation:
Only portions containing nodes and leaves develop into new
plants.
TISSUE CULTURE
A technique in which new plants are produced from tissues
grown on artificial medium.
Uses:
- Disease-free
plants
- Large-scale
production
- Ornamental
plants
6. SPORE FORMATION
Spores are special reproductive structures protected by
thick walls.
Example:
Rhizopus (Bread mould)
Structures:
- Hyphae
→ thread-like structures
- Sporangia
→ contain spores
Advantages:
✔ Survive unfavorable conditions
✔ Easy dispersal
✔ Large numbers produced
SEXUAL REPRODUCTION
Reproduction involving two parents and fusion of male
and female gametes.
Characteristics:
- Two
parents involved
- Gamete
formation occurs
- Greater
variations produced
WHY SEXUAL REPRODUCTION?
Advantages:
- Produces
more variations
- Increases
survival chances
- Creates
new combinations of genes
MEIOSIS
Cell division that produces cells having half the
chromosome number.
Importance:
Maintains chromosome number after fertilisation.
GAMETES
Special reproductive cells.
Types:
|
Male Gamete |
Female Gamete |
|
Small and motile |
Large and contains food |
SEXUAL REPRODUCTION IN FLOWERING PLANTS
Reproductive organs are present in flowers.
Flower Parts
|
Part |
Function |
|
Sepals |
Protect flower bud |
|
Petals |
Attract insects |
|
Stamens |
Male reproductive organ |
|
Pistil |
Female reproductive organ |
Examples from textbook
Unisexual flowers
- Papaya
- Watermelon
Bisexual flowers
- Hibiscus
- Mustard
STAMEN
Male reproductive part.
Produces:
Pollen grains
PISTIL
Female reproductive part.
Parts:
- Stigma
- Style
- Ovary
Ovary contains:
Ovules
Each ovule contains:
Egg cell
POLLINATION
Transfer of pollen grains from anther to stigma.
Types:
Self-pollination
Pollen reaches same flower.
Cross-pollination
Pollen reaches another flower.
Agents:
- Wind
- Water
- Animals
FERTILISATION
Fusion of male and female gametes.
Result:
Zygote formation
AFTER FERTILISATION
Changes:
- Zygote
→ Embryo
- Ovule
→ Seed
- Ovary
→ Fruit
Seed germinates and forms seedling.
Activity 7.7 — Bengal Gram Experiment
Observation:
Parts observed:
- Cotyledon
- Plumule
- Radicle
REPRODUCTION IN HUMAN BEINGS
Humans reproduce sexually.
PUBERTY
The stage when reproductive organs become mature.
Changes common in boys and girls:
✔ Hair growth in armpits
✔ Hair growth near genital region
✔ Oily skin
✔ Pimples
Changes in Girls
✔ Increase in breast size
✔ Menstruation begins
Changes in Boys
✔ Facial hair appears
✔ Voice cracks
✔ Penis enlarges
MALE REPRODUCTIVE SYSTEM
Parts:
- Testes
- Scrotum
- Vas
deferens
- Seminal
vesicles
- Prostate
gland
- Urethra
- Penis
Functions:
Testes
- Produce
sperms
- Produce
testosterone hormone
Seminal Vesicles and Prostate Gland
- Provide
nourishment
- Help
sperm transport
FEMALE REPRODUCTIVE SYSTEM
Parts:
- Ovaries
- Fallopian
tubes
- Uterus
- Cervix
- Vagina
Functions:
Ovaries
- Produce
eggs
- Produce
hormones
Uterus
- Development
of embryo
FERTILISATION IN HUMANS
Steps:
- Sperm
enters vagina
- Travels
to oviduct
- Meets
egg
- Fertilisation
occurs
- Zygote
forms
- Embryo
develops
- Foetus
forms
PLACENTA
A special tissue connecting mother and embryo.
Functions:
✔ Provides oxygen
✔ Provides glucose and nutrients
✔ Removes waste materials
GESTATION PERIOD
Time for development of baby inside mother:
Approximately 9 months
MENSTRUATION
If fertilisation does not occur:
- Egg
dies
- Uterine
lining breaks
- Blood
and mucus released
Duration:
About 2–8 days
REPRODUCTIVE HEALTH
Sexually transmitted diseases:
Bacterial diseases
- Gonorrhoea
- Syphilis
Viral diseases
- Warts
- HIV/AIDS
CONTRACEPTIVE METHODS
Mechanical methods
- Condoms
Hormonal methods
- Oral
pills
Devices
- Copper-T
- Loop
Surgical methods
- Blocking
vas deferens
- Blocking
fallopian tubes
IMPORTANT DIFFERENCES
|
Asexual Reproduction |
Sexual Reproduction |
|
One parent |
Two parents |
|
No gamete formation |
Gamete formation |
|
Less variation |
More variation |
|
Fast |
Slow |
