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Reproduction in plants Class 7 Notes




Introduction to reproduction in plants

All Living things produce more of their own kind The process through which a living thing (organism) produces new living things (young ones) like itself is called ​reproduction​.

Why is reproduction important?

Reproduction allows living organisms to continue to live on the earth from one generation to the other.

Types of reproduction in plants

Reproduction in plants occurs in two ways:

  1. Asexual : Plants can give rise to new plants without seeds.
  2. Sexual reproduction : New plants are obtained from seeds.

Asexual reproduction in plants

Fragmentation, budding, spore formation and vegetative propagation are some of the different type of asexual reproduction.

Fragmentation​:

In this method the body of parent organism breaks into 'fragments' and each fragment can grow to function as a new individual. For example; Algae like Oscillatoria and Spirogyra are reproduced by fragmentation.

Budding:

reproduction in plants class 7
Reproduction in yeast by budding
Some simple organisms reproduce by producing small outgrowths from their body. These outgrowths,called Buds. The buds gradually grow and get detached from the parent cell and forms new organism. For example, Yeast.

Spore formation:

Spores are tiny, spherical unicellular bodies protected by a thick wall to withstand to unfavorable conditions When the conditions are favorable, these spores germinate into new individuals. Mosses, ferns, fungi, etc. reproduce by this method.

reproduction through spore formation in fungus class 7
Reproduction through spore formation in fungus

Vegetative propagation:

In some plants, any vegetative part of a plant such as the root, stem or leaf can give rise to new plant. This type of asexual reproduction is called vegetative propagation. Vegetative propagation can take place naturally and can also be carried out by artificial means.

Vegetative propagation by natural means:

From stem: New plants can grow either from horizontal stem or from underground stem.

From Horizontal stems:

Runner Slender branch that creeps some distance away from
the mother plant on the ground, root itself at the
nodes and grows into a new plant.
Ex. Wood sorrel and grass.
Stolons that arise from the base of
the stem, root at the
nodes, producing buds that
soon grow into daughter plants.
Ex. White, strawberry and peppermint
Offset Water lettuce
Suckers Chrysanthemum

Underground stem

Bulbs Bulbs are underground stems
with thick fleshy scaly
leaves that store
food around the bud.
Ex. Onion Garlic, Lily and Tulip.
Rhizome Rhizomes are underground
stems that have scaly
leaves at their nodes.

The axil of the scaly
leaf has buds that grow into new
shoots upward.
Ex. Ginger asparagus and water lily.
Tubers Potato is a modified
stem and has buds.
It is called a tuber.
When a piece of potato
containing a bud is
planted into the soil,
it can grow into a
new potato plant.

Vegetative propagation From root:

Some plants like sweet potato and dahlia have swollen roots without any shape. These roots are called tuberous roots. These roots have small buds which give rise to a new plant when they are planted into the soil.

Vegetative propagation From leaves:

Plants like Bryophyllum produce buds from the margin of the leaves. These buds drop off from the leaves and fix themselves to the ground and later grow into new plants.

Vegetative propagation by artificial means:

  1. Cutting: Plants such as Rose, cactus and bougainvillea can be propagated through cutting from their stem. The cut stem is planted in a moist soil, which eventually developed roots and shoots and grows into a new plant.
    Vegetative propagation by cutting
  2. Grafting: Grafting involves two plants of the same species. A bud or a stem cutting from one plant called scion is inserted into a groove of second plant called stock which is rooted to the ground. The stock and scion join together to form one plant. Varieties of fruit bearing trees developed by grafting.
  3. Layering: In plants such as Jasmine and grapevine, the lower branch of the plant is bent down and covered with moist soil after removing a ring of bark from the stem. After a few weeks, new roots develop and the plant is separated from the mother plant

Advantages of vegetative propagation:

  • Vegetative propagation is very useful for plant growers as they can get large quantities of new plants in a short time
  • The newly reproduced plant have the exact characters as that of their parent plant.
  • Fruit without seed, disease and drought resistant plants can be produced using these methods.
  • It is easy to produce new varieties of plants with the required characteristics.
  • Vegetative plants grow faster than the plants grown from seeds and needs less attention during early stages of growth.

Tissue culture:

In this method, the growing tips of plants are cut and planted in an artificial medium kept inside a conical flask or a test tube. The medium provides all the necessary nutrients and plant hormones for plant growth. Once the roots develop, they are planted in suitable soil. From here, they grow into whole new plants.

Sexual reproduction

In sexual reproduction, in male cell (gamete) produced by the male part of the flower fuses with female cell (gamete) produced by the female part of the flower. The fusion of the male and female gametes known as fertilization, leads to the formation of single cell called the zygote. This cell divides and redivides and slowly give rise to a new individual.

Picture of a typical flower: Flower is the reproductive part of flowering plant. A typical flower has four parts- sepals, petals, stamens and a carpel.

  1. Sepals: Sepals are green and they protect the other part of a flower before it blooms.
  2. Petals: Petals are either colored or white and are seen as the flower blooms. They usually attract insects. The sepals and petals do not directly take part in reproduction.
  3. Stamen: Stamen is the male part of the flower, that has a long filament with an elongated sac like structure at its tip called the anther. Anthers produce pollen grains.
  4. Pistil: The pistil or carpel is the female reproductive organ of the flower. The carpel has a stalk-like style with a sticky tape called the stigma and a swollen base, called the ovary. Ovary contains one or more ovules. Ovules contain the egg cells, the female gamete of the plant.
reproduction in plants

Flowers are of two types:

  1. Unisexual flowers
  2. Bisexual flowers

Unisexual flowers Bisexual flowers
Flowers with only the male or the female reproductive part are called unisexual flower. They are also called incomplete flowers. Flowers having both stamens and pistils are called bisexual flowers. They are also called complete flowers.
For example: Watermelon, cucumber, papaya For example: hibiscus, wild rose.

Reproduction in plants:

Pollination

The transfer of pollen grains from the anther to the stigma of the same kind of flower is called pollination. Pollination is of two types:

  • Self pollination
  • Cross pollination
pollination in flower
pollination types
Pollinating agents: Birds insects, bats and wind carry pollen Grain from flower to flower. Flowers of these plants have special features that attract their pollinating agents. Different plants have different pollinating agents.
pollinating agents

Fertilization

When a pollen grain falls on the stigma of a flower of the same kind, it develops a long tube called Pollen tube. The Pollen tube grows downwards through the style towards the ovary. The male gametes are inside the pollen tube. Once inside the ovary, it enters the ovule. The male gamete fuses with the female gamete and form zygote. The process of fusion of the male and female gamete is known as fertilization. The fertilized cell is known as the zygote. The ovule develops into a seed and the ovary into the fruit after fertilization.

fertilisation zygote formation

What are Seeds:

The fertilized egg begins to divide inside the ovule and develops into an embryo. The ovule develops into a seed. The embryo has a radical and plumule. It is attached to one or two cotyledons. Upon germination the radicle will develop into the root system, while the plumule will develop into the shoot system. The cotyledon have a store of food which is used by the seedling.

Fertilization by Seed dispersal:

Once the seeds dry, they get dispersed. Seed dispersal in the scattering of seeds over a large area by various means. The different means of seed dispersal are wind, water,animals and explosion of fruits. Different means of seed dispersal help the plants as it helps the seeds to reach a suitable medium for germination, far away from the parent plant.

Fertilization By the wind:

Some plants like drumsticks and maple have winged seeds, which are carried by the wind. The seeds of other plants, like milkweed silk cotton and Devil's tree have tufts of hair which help them ride on the wind.

Fertilization By water:

Seeds that are dispersed by water have a spongy coat or a layer of fiber that make them light. This property help them to float on water. The flowing water then carries them too far off places for example coconut.

Fertilization By animals:

Birds, monkeys and other animals eat the fruit of many plants and throw away the seeds. Some plants have fruit or seeds with hooks, bristles, or spines. These get attached to the fur of animals or to our clothes. They are carried a long way before they fall off or are brushed off. By exploding fruits: The fruits of the rubber tree, balsam, lady finger, and night jasmine explode when they ripen. The sudden bursting of the fruit scatter the seeds away from the parent plant.

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Also Read



Reference Books for class 7 Science

Given below are the links of some of the reference books for class 7 math.

  1. Science for Class 7 by Lakhmir Singh
  2. Science Foundation Course For JEE/NEET/NSO/Olympiad - Class 7
  3. CBSE All In One Science Class 7 by Arihant Experts (Author)
  4. IIT Foundation Physics, Chemistry & Maths for Class 7

You can use above books for extra knowledge and practicing different questions.



Class 7 Maths Class 7 Science





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