Before starting with Class 7 Science Chapter 8 i.e. ‘Reproduction in Plants’, I am hoping that you have completed Chapter 7 of the 7th class. If not, then you can go through its Notes and NCERT Exercise Solutions whose links have been provided below. ⤵️
Table of Content
Introduction
In the 6th class, we have learnt about the various characteristics that are possessed by the majority of living organisms. Reproduction is one such characteristic that is possessed by the living organisms.
Reproduction is a process by which living organisms (parents) produce new living organisms (children) like themselves.
In this chapter, we are going to learn about the various modes of reproduction in plants.
Modes of Reproduction
In the 4th chapter of the 6th class, we have learnt about the various parts of a flowering plant.
The root(s), stem, branches, leaves axial buds, etc. of a plant are called the vegetative parts.
Whereas, the flower of a plant is called the reproductive part. It is these flowers that give rise to the seeds and fruits.
There are mainly two different modes by which plants reproduce:
- Sexual mode of reproduction: The new plants are obtained from the seeds.
2. Asexual mode of reproduction: The plant can give rise to a new plant without seeds. This mode of reproduction mainly involves the vegetative parts of a plant.
Asexual/Vegetative Reproduction in Plants
New plants are produced from the vegetative parts of a plant like roots, stems, leaves, buds, etc.
There are various vegetative methods and techniques by which we can vegetatively grow new plants.
Some of the common examples of vegetative reproduction in plants are:
1. Stem Cutting
In this method of vegetative reproduction, a new plant grows from a cutting (a piece of branch) that has a node and has been buried in the soil.
A node is a part of a stem/branch at which a leaf arises.
Plants like Champa and rose can be grown using the cutting method.
Buds
A bud consists of a short stem around which immature overlapping leaves are present.
A flower bud or a floral bud develops into a flower. There are other types of buds that are present in a plant other than the floral buds.
AXILLARY BUD or LATERAL BUD:
It is a bud that is located in the axil (point of attachment of a leaf at the node) of a leaf and it grows into a shoot.
These buds are also called vegetative buds as they mainly give rise to the vegetative parts of a plant. These buds can also give rise to new plants as well.
2. Potato Eyes
Potatoes have small scars present on their surface called the eyes.
You can grow a potato vegetatively by cutting the potato into small pieces with each piece containing an eye at least and then burying it in soil and watering it regularly.
Ginger and turmeric can also be grown in the same way as they also have sprouting growth on them.
These are examples of vegetative reproduction by stem.
3. Bryophyllum Leaf Buds
It is also known as the sprout leaf plant. It has buds present in the margins of leaves.
If a leaf of this plant falls on moist soil then each bud can give rise to a new plant.
This is an example of vegetative reproduction by a leaf.
4. Vegetative Reproduction by Roots
Roots of some plants like sweet potato and dahlia can give rise to a new plant.
5. Vegetative Reproduction in Cacti
When their parts (offshoots) get detached from the main plant body and land on the surface they grow into a new plant.
Benefits of Vegetative Propagation/Reproduction
- Plants produced by this method take less time to grow and bear flowers and fruits earlier than those produced from the seeds.
- The new plants are the exact copies of the parent plant, as they are produced from a single parent. So, the benefit of this is that the progeny of the parent plant will bear the same characteristics as that of a parent e.g. the progeny of a plant that produces good quality fruits will also produce the same good quality fruits, etc.
Budding
A bud is a small bulb-like projection coming out of the parent cell or body.
Organisms like yeasts undergo reproduction by budding. They are single-celled organisms. These bud(s) gradually grow get detached from the parent’s body and form a new yeast cell.
And, this cycle of cell growth, maturation and production of more yeast cells continues.
Sometimes, another bud arises from the bud forming a chain of buds and if this continues, a large number of yeast cells are produced in a short time.
Fragmentation
Mainly the algae reproduces by this method. Algae are the slimy green patches seen in ponds and other stagnant water bodies.
Algae grow rapidly by fragmentation when water and nutrients are available to it. e.g. Spirogyra, Ulothrix, etc.
In the fragmentation method of reproduction, an algae breaks up into two or more fragments. Then each of these fragments grows into a new individual. This process continues till the algae covers the whole surface of the water body.
Reproduction by Spores
Reproduction by spore formation mainly takes place in fungi and plants like moss, ferns, etc.
You can observe the spores in the bread mould’s cotton-like mesh. They are very lightweight, so they keep on floating in the air and can cover very large distances.
Spores are asexual reproductive bodies. Each spore is covered by a hard protective coat to withstand unfavourable conditions such as high temperature and low humidity.
Under favourable conditions (warm and damp places), these spores germinate and develop into a new individual.
Sexual Reproduction in Plants
In our 6th class, we have studied about the flower and its parts, you can refer to it.
The prominent parts of a flower are:
- Stamen is the male reproductive part of a flower.
- The carpel or pistil is the female reproductive part of a flower.
UNISEXUAL FLOWERS:
These flowers only contain either stamen or carpel. E.g. papaya, corn, cucumber, etc. The male and female unisexual flowers may be present in the same plant or in a different plant.
BISEXUAL FLOWERS:
These flowers contain both the stamen and carpel. E.g. mustard, rose, china rose, petunia, etc.
Stamen
When you observe inside the flower you will see some filamentous structures with a small hammer-like structure present at the top well those two structures together are known as stamen.
- Filament: is a thread or stalk-like structure that connects the anther to the flower.
- Anther: A small hammer-like structure that is present at the top of the filament and it carries the pollen grains which produce the male gametes.
Carpel or Pistil
This is the innermost part of a flower.
It mainly consists of 3 parts:
- Stigma: This is the topmost part of a pistil which is sticky and flat in nature.
- Style: This is the middle part of a pistil which is tubular in nature and connects the stigma with the ovary.
- Ovary: This part is present in the core of the flower. It ripes into a fruit. Each ovary consists of one or more ovules.
Ovules
They are small beads-like structures that are present inside an ovary and when they mature they form seeds.
The female gamete or egg is formed in an ovule.
In sexual reproduction, the male and the female gametes fuse to form a zygote.
Pollination
This process or phenomenon answers your question, how do pollen grains reach the female gametes present inside the ovule?
The transfer of pollen from the anther to the stigma of a flower is called pollination.
Pollen grains are very lightweight and have a tough protective coat which prevents them from damaging and drying up. These pollen grains can easily be carried by the wind, water and insects to the stigma of a flower.
POLLINATORS:
A pollinator is an animal or other entity that helps move pollen from a flower’s male part (stamen) to its female part (stigma).
SELF-POLLINATION:
It is the transfer of pollen grain(s) from the anther to the stigma of the same flower or another flower of the same plant.
CROSS-POLLINATION:
It is the transfer of pollen grain(s) from the anther to the stigma of a flower of a different plant of the same kind.
When the pollen grain lands on the stigma it starts to develop a pollen tube and this tube reaches to the ovary and then ultimately to the ovule(s).
Fertilisation
It is the fusion of male gametes (carried by the pollen tube) with the female gamete or egg cell present in the ovule leading to the formation zygote.
Then this zygote develops into an embryo.
Fruits & Seeds Formation
Afer the fertilisation,
- The ovary grows into a fruit and the rest of the parts of a flower (leaves, anther, sepal, etc.) fall off.
- The ovules mature into the seeds. Each seed contains an embryo enclosed in a protective seed coat.
There are a vast variety of fruits that are present in nature. Some are juicy and fleshy like mangoes and oranges whereas some are hard like almonds and walnuts.
Seed Dispersal
Just like the pollen grains are transferred from the anther to the stigma by various means (pollinators), the seeds of a plant are also dispersed over a large area by various entities like:
SEED DISPERSAL BY AIR (ANEMOCHORY):
Examples:
- Winged seeds of maple and drumstick.
- Light seeds of grasses.
- Hairy seeds of aak or madar.
- Hairy fruit of sunflower.
Such seeds or fruits enclosing the seeds get blown off by wind to far away places.
SEED DISPERSAL BY WATER (HYDROCHORY):
These seeds or fruits enclosing the seeds develop floating ability in the form of a spongy or fibrous outer coat as in coconut.
SEED DISPERSAL BY ANIMALS (ZOOCHORY):
Seeds that are spiny and have hooks get attached to the bodies of animals and are carried to distant places.
- E.g. Xanthium (Cockleburs) and Urena
Special Mechanism of Seed Dispersal (BALLISTIC DISPERSAL):
In plants like castor and balsam, the fruits burst open with a sudden jerk spilling their seeds over large distances.
In nature, you can find the same kind of plants growing in different places. This all happens because of the dispersal of seeds to different places.
Why do seeds need to be dispersed?
If the seeds are not dispersed then they all will fall in the same place (near the plant) and start to grow there, but there will be heavy competition among the seedlings for essential resources like sunlight, water, minerals, space etc. reducing the chances of survival and the proper growth of the seedlings.
This unhealthy competition is prevented by the plant by the dispersal of its seeds over a long distance. It also enables the plants to invade the new habitats for wider distribution.
Conclusion
The plants that are produced by sexual reproduction have the characteristics of both the male and the female parent plants, unlike the plants that are produced by vegetative propagation.
Both modes of reproduction have their own benefits and lackings, we’ll learn about these in detail in the higher classes.
Credits & References
- Class 7th Science NCERT Textbook
- Image by WikimediaImages from Pixabay
- Image by brgfx on Freepik
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- Image by Myriams-Fotos from Pixabay
- https://www.nps.gov/subjects/pollinators/what-is-a-pollinator.htm
- Image by brgfx on Freepik
- Image by brgfx on Freepik
- Image by romanov from Pixabay
- Image by Hans from Pixabay
- Image by Daina Krumins from Pixabay
- Image by JamesDeMers from Pixabay
- Image by Heike Tönnemann from Pixabay
- Image by hartono subagio from Pixabay
- Image by David Ehret from Pixabay
- Image by Teodor Buhl from Pixabay
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