Class 8 Science Chapter 5 Life Processes

Life processes → The basic functions essential for the survival of living organisms.

• Include: nutrition, respiration, transportation, excretion, and reproduction.
• Reproduction → Biological process by which living organisms produce new individuals of their own kind.

Exam Tip: Life processes are indicators of living beings (growth, metabolism, reproduction, response to stimuli).

Reproduction

  Definition: Biological process by which living organisms produce new individuals of their own kind.  Ensures continuity of life and prevents extinction.

Significance of Reproduction (4 points)

1. Continuity of life by producing offspring.
2. Maintains population of a species.
3. Ensures transfer of genetic information.
4. Enables variation → evolution and adaptation.

 Types of Reproduction

a. Asexual Reproduction

• Definition: Production of offspring by a single parent, without gamete fusion. Offspring are genetically identical (clones).

Methods:
i. Binary fission → Cell divides into two (e.g., Amoeba, Bacteria).
ii. Budding → New organism develops from a bud on parent (e.g., Hydra, Yeast).
iii. Regeneration → Lost body parts regenerate into new organism (e.g., Planaria, Starfish).
iv. Vegetative propagation → New plants from roots, stems, leaves (e.g., potato, onion, Bryophyllum).

Basic features of asexual reproduction:

1. Single parent involved.
2. No gametes or fertilization.
3. Offspring are clones (no variation).
4. Rapid and simple process.
5. Occurs commonly in lower organisms and some plants.

b. Sexual Reproduction

• Definition: Production of offspring by fusion of male and female gametes.
• Involves meiosis and fertilization → genetic variation.

Examples:

• Humans and most animals.
• Flowering plants (angiosperms).

Basic features of sexual reproduction (5 points):

1. Involves two parents.
2. Formation and fusion of gametes.
3. Offspring show variation.
4. Slower and complex process.
5. Occurs in higher plants and animals.

Asexual Reproduction in Plants and Animals

Definition: Mode of reproduction where offspring arise from a single parent without gamete fusion.

Methods:

i. Fission

• Binary fission: Parent splits into two equal halves (Amoeba, Paramecium, Bacteria).
• Multiple fission: Parent divides into many daughter cells simultaneously (Plasmodium, Algae).

ii. Budding

• New bud forms on parent body and detaches (Hydra, Yeast).

iii. Sporulation

• Spores (tiny, resistant cells) germinate into new organism (Fungi → Rhizopus, Mucor).

iv. Fragmentation

• Parent body splits into fragments; each fragment grows into new organism (Spirogyra, some annelids).

v. Regeneration

• Regrowth of lost body parts into complete organism (Planaria, Starfish).

vi. Parthenogenesis

• Development of unfertilized egg into new organism (Honeybee drones, some reptiles like whiptail lizards).

vii. Vegetative Propagation in Plants

• New plants grow from vegetative parts (root, stem, leaf).

Natural Methods of Vegetative Propagation

i. By Roots → e.g., Sweet potato, Dahlia.

ii. By Underground Stems (Storage organs; allow survival and propagation):

• Rhizomes → Horizontal underground stems (Ginger, Turmeric).
• Tubers → Swollen underground stems storing food (Potato).
• Corms → Short, vertical swollen stems (Gladiolus, Colocasia).
• Bulbs → Modified stem with fleshy leaves (Onion, Garlic).
• Stolons/Runners → Creeping horizontal stems (Strawberry, Grass).

iii. By Aerial Stem → Offshoots/buds on aerial stems form new plants (Chrysanthemum, Pineapple).

iv. Bulbil → Special swollen bud-like structures develop into new plant (Agave, Dioscorea).

v. By Leaves → Adventitious buds on leaf margins give rise to new plants (Bryophyllum, Begonia).

Artificial Methods of Vegetative Propagation

1. Cutting → Portion of root/stem/leaf cut and planted (Rose, Sugarcane).
2. Grafting → Joining of two plant parts (stock + scion) (Mango, Apple).
3. Layering → Branch bent and covered with soil develops roots (Jasmine, Strawberry).
4. Gootee (Air layering) → Stem girdled, wrapped with moist soil/moss until roots form (Guava, Litchi).
5. Tissue Culture → Plant grown from single cell or tissue under sterile lab conditions (Orchid, Banana).

Interesting Facts

• Parthenogenesis in honeybees → fertilized eggs → females (queen, worker); unfertilized eggs → males (drones).
• Potato is a stem tuber, not a root.
• Bryophyllum is famous as the “plant that grows from leaves.”

Mnemonics / Memory Aids

• Binary, Budding, Fragmentation, Regeneration, Sporulation → “Big Boys Fight Really Strong.”
• Underground stem types → “Really Tough Cows Bite Slowly” → Rhizome, Tuber, Corm, Bulb, Stolon.

 Sexual Reproduction in Plants

• Definition: Process of producing offspring by fusion of male (pollen) and female (ovule) gametes in flowering plants.
• Steps → Pollination → Fertilization → Embryo formation → Seed & Fruit development.

a. Pollination

• Pollination: Transfer of pollen grains from anther (male part) to stigma (female part).

Types:

1. Self-pollination → Pollen from the same flower/plant falls on its own stigma (e.g., Pea, Rice).
2. Cross-pollination → Pollen transferred between two different flowers/plants of same species (e.g., Apple, Mustard).

Advantages of Pollination (3):

1. Ensures reproduction in plants.
2. Cross-pollination introduces variation → adaptation & evolution.
3. Maintains biodiversity of plants.

Disadvantages of Pollination (3):

1. Self-pollination → weak offspring (no variation).
2. Cross-pollination depends on external agents (wind, insects, water).
3. Cross-pollination is less reliable and energy-consuming.

b. Fertilization

• Definition: Fusion of male gamete (from pollen tube) with female gamete (ovum in ovule).
• In angiosperms → Double fertilization occurs:
  • One male gamete + egg cell → zygote (embryo).
  • Other male gamete + polar nuclei → endosperm (nutritive tissue).
• Result → Formation of seed (embryo inside) and fruit (developed ovary).

 Sexual Reproduction in Animals

Steps:

1. Mating & Gamete Formation
   • Males produce sperm (testes).
   • Females produce egg/ova (ovaries).
   • Example: Humans, mammals, birds, reptiles.
2. Fertilization
   • External fertilization → gametes fuse outside body (e.g., Fish, Amphibians).
   • Internal fertilization → gametes fuse inside female body (e.g., Humans, Reptiles, Birds).
3. Embryo Development & Birth
   • Fertilized egg (zygote) undergoes cell division → embryo.
   • Embryo attaches to uterus wall (in mammals) → develops into foetus.
   • Birth → young one delivered after gestation (e.g., 9 months in humans).
   • In oviparous animals (birds, reptiles) → zygote develops inside egg outside mother’s body.

Seed

 What is a Seed?

• Seed → Fertilized mature ovule containing embryo, capable of developing into a new plant.

 Structure of a Seed (Brief Overview)

a. Seed Coat

• Outer protective covering.
• Functions: prevents damage, drying, and infection.

b. Embryo

• Baby plant inside seed.
• Has radicle (root), plumule (shoot), and cotyledons (seed leaves).

c. Endosperm

• Food storage tissue (starch, protein, oil).
• Provides nourishment during germination.

 Germination of Seed

• Definition: Process by which dormant seed resumes growth → embryo develops into seedling.

Factors affecting germination:
a. Water → activates enzymes, softens seed coat.
b. Air (oxygen) → required for respiration.
c. Temperature → suitable warmth activates metabolism.
d. Sunlight → necessary for seedling growth (not always for initial germination).

Importance of seed germination (4 points):

1. Ensures reproduction of plant species.
2. Helps in agriculture and food production.
3. Maintains biodiversity of plants.
4. Enables dispersal and survival of species.

 Dispersal of Seeds

• Definition: Process of scattering seeds away from parent plant to avoid overcrowding and competition.

Methods & Examples:

a. By Wind → Lightweight, winged, hairy seeds (e.g., Cotton, Dandelion, Maple).
b. By Explosion (Autochory) → Fruit bursts open and throws seeds (e.g., Pea, Balsam, Mustard).
c. By Water → Seeds with spongy or fibrous coats float on water (e.g., Coconut, Lotus).
d. By Animals →

• Edible fruits eaten → seeds excreted (e.g., Mango, Tomato).
• Hooked/spiny seeds attach to fur (e.g., Xanthium, Burdock).
  e. By Gravity → Heavy fruits fall near parent plant (e.g., Apple, Mango, Coconut).

Interesting Facts

• Orchid seeds are the smallest in size; coconut seed is one of the largest.
• In angiosperms, double fertilisation is unique.
• Some seeds (e.g., Lotus, Date palm) can remain viable for hundreds of years.

Mnemonics / Memory Aids

• Agents of pollination → “WABI” → Wind, Animals, Birds, Insects.
• Factors for germination → “WATS” → Water, Air, Temperature, Sunlight.
• Seed dispersal → “WEWAG” → Wind, Explosion, Water, Animals, Gravity.

Summary / Quick Revision

• Life processes include reproduction.
• Asexual reproduction → single parent, no gametes, offspring are clones, rapid.
• Sexual reproduction → two parents, gamete fusion, offspring show variation.
• Asexual methods: fission, budding, sporulation, fragmentation, regeneration, parthenogenesis, vegetative propagation.

Vegetative propagation can be natural (roots, stems, leaves) or artificial (cutting, grafting

• Sexual reproduction in plants: Pollination (self/cross), Fertilisation (double fertilisation).
• Sexual reproduction in animals: gamete formation, fertilisation (external/internal), embryo & birth.
• Seed: fertilized ovule with seed coat, embryo, endosperm.
• Germination requires water, air, temperature, sunlight.
• Seed dispersal methods: wind, explosion, water, animals, gravity.

Also Check Out :- Chapter 1 , chapter 2 , chapter 3 , chapter 4