How Do Organisms Reproduce?

Notes

Chapter Overview

Reproduction

Reproduction is the biological process through which organisms produce offspring of their own kind.

Importance

Maintains continuity of species.

Transfers hereditary characters.

Produces variations.

Helps evolution.

Important Board Line

Reproduction is essential for the survival of the species but not for the survival of an individual.

DNA Copying

During reproduction, DNA is copied.

DNA copying is never completely accurate.

This causes:

Small variations

Diversity among organisms

Better adaptation

Board Question

Why are variations important?

Answer

Variations help organisms survive changing environmental conditions and are the basis of evolution.

Types of Reproduction

1. Asexual Reproduction

Only one parent is involved.

No fusion of gametes.

Offspring are genetically identical (clones).

Characteristics

One parent

Fast process

No fertilization

Less variation

Methods of Asexual Reproduction

(A) Binary Fission

One organism divides into two.

Examples

Amoeba

Paramecium

Diagram

Amoeba

O

↓

O O

(B) Multiple Fission

One parent divides into many offspring.

Example

Plasmodium

(C) Budding

A small bud develops on parent.

Examples

Hydra

Yeast

Diagram

Hydra

|

( )

|

( )

(D) Fragmentation

Body breaks into fragments.

Each fragment forms a new organism.

Example

Spirogyra

(E) Regeneration

Lost body parts regenerate into complete organisms.

Examples

Planaria

Hydra

(F) Spore Formation

Spores are produced inside sporangia.

Example

Rhizopus (Bread mould)

(G) Vegetative Propagation

New plants develop from roots, stems or leaves.

Examples

Plant Vegetative Part

Potato Stem

Ginger Stem

Onion Stem

Bryophyllum Leaf

Sweet Potato Root

Advantages

Faster reproduction

Seedless plants produced

Desired characters retained

Sexual Reproduction

Two parents participate.

Fusion of male and female gametes forms a zygote.

Produces greater variation.

Sexual Reproduction in Flowering Plants

Parts of Flower

Male Part

Stamen

Anther

Filament

Produces pollen grains.

Female Part

Pistil (Carpel)

Stigma

Style

Ovary

Ovule

Pollination

Transfer of pollen from anther to stigma.

Types

Self Pollination

Same flower or same plant.

Cross Pollination

Different plants of same species.

Fertilization

Fusion of male and female gametes.

Produces

Zygote

Embryo

Seed

…