1. Reproduction-
ü The process by which living organism produce their own kind is called as reproduction.
ü Reproduction is divided in two broad categories viz - Asexual reproduction and sexual reproduction.
a) Asexual Reproduction-
ü The reproduction process in which only one parent is involved in the production of new individual(s) of the same kind is called asexual reproduction.
ü In plants asexual reproduction results in the formation of off springs or new plants without involving seeds or spores.
ü Asexual reproduction in plants mostly occurs through the following methods: Vegetative propagation, Budding, Fragmentation and Spore formation.
(i) Vegetative Propagation-
n It is the formation of new plants from vegetative units of adult plant for example bud, stem, etc.
n These vegetative units are called propagules.
n The stems or branches of the plant normally bear buds in the axial. The buds that are present in the axial develops into the shoot. These are called vegetative buds.
n The vegetative buds can give rise to a new plant. These buds consist of a short stem around which immature overlapping leaves are folded. These can produce a new plant by vegetative propagation.
Figure 01- Cutting method
n Cutting- New plants are obtained from the stem by the cutting method. In this method, the small part of stem is removed by making a cut with a sharp knife. The stem cutting must have some buds on it. Now the lower end of stem cutting is buried in the moist soil. The upper part of cutting having bud on it, is kept above the soil. After few days, this cutting develops new roots. The bud grows and produces a shoot
n Layering- In this method, a mature branch of parent plant is bent down and covered with soil. The tip of the plant is kept above the ground. The root develops from the branches and grows into a new plant. Layering method is usually done in the plants that have long and slender branches, e.g. jasmine.
n Grafting- In this new plants of desired qualities is developed from two different plants. The part that has shoot part is called scion and part having root is called stock. Scion is attached to the stock which provides support and basic requirement for the development of plant, e.g. apple, mango, rose, etc.
n When the leaf of some plants are hurried into the moist soil, the cut edges or margins of leaves develop a new plants that resemble to the parent, for example Bryopbyllum or sprout leaf plant.
Figure 02- Growth from eye buds
n In some plants like sweet potato, dahlia, etc, a new plant develops through their roots and bulbs.
(ii) Budding -
Figure 03- Budding
n In this process, a daughter individual is formed from a small projection on parent body called a bud. Most of the fungi-like, yeast reproduce by budding.
n Yeast grow and multiply in every few hours, if provided with sufficient nutrients and favourable condition.
(iii) Fragmentation-
Figure 04- Fragmentation
n Some algae (Spirogyra) that are present in waterbodies reproduce by fragmentation. In this- method, the body of the parent breaks into small pieces called fragments and each fragment grows up to become a new plant.
n Fragmentation of parent body occurs when they are matured.
n If water and nutrient are available, the algae will grow and multiply rapidly by fragmentation.
n If this process continues, it will cover a large area in a very short period of time.
(iv) Spore Formation-
Figure 05- Spore formation
n Some fungus like bread mould reproduces asexually by spore formation.
n Spores are the small spherical bodies, having a thick protective wall that protects them from unfavourable conditions.
n When favourable conditions arrive the spores burst and germinate to develop into new plants.
n Spores are very light asexually reproducing bodies which can be carried over a long distance by air or wind.
n Some other plants like mosses and ferns also reproduce by spore formation in the underside of their leaves.
(b) Sexual Reproduction-
n Flowers are the reproductive part of a plant.
n They help the plants in sexual reproduction and producing fruits and seeds.
n In sexual reproduction, a male cell is produced by the male part of a flower which fuses with a female cell produced by the female part of the flower.
n These cells are called gametes, which when combined form a zygote by the process called fertilization.
2. Flower-
(i) Parts Of Flower-
Figure 06- Reproductive parts of flower
ü Sepals- These are the green leaf-like outermost circle of the flower. All the sepals are together referred to as calyx. The function of the calyx is to protect the flower when it is in bud form.
ü Petals- These are the colourful and most attractive part of the flower. These lie inside the sepals. All the petals are together referred to as corolla. These are scented and attract insects for pollination.
ü Stamen- It is a male reproductive organ of a plant. These are the little stalks with swollen top and lies inside the ring of petals. The stamen is made up of two parts, i.e. filament and another. The stalk of stamen is called filament and the swollen top of stamen is called anther.
ü The Anther- It contains the pollen grain which have male gamete in it. Pollen grains are exposed when the anther ripens and splits. These appear as the yellow powder like substance which is sticky in nature. Flowers usually have a number of stamens in it.
ü Pistil- It is the female reproductive part of a flower that lies in the centre of a flower. These are a flask-shaped structure which is made up of three parts, i.e. stigma, style and ovary.
3. Pollination-
ü Unisexual flower- The flower which contains only one reproductive organ (i.e. either male or female) are called unisexual flowers. These are also called as an incomplete flower, e.g. papaya, watermelon, corn, cucumber, etc.
ü Bisexual flower- The flower that contains both reproductive parts (i.e. male and female) in a single flower are called a bisexual flower. These are also termed as hermaphrodites or complete flower, e.g. rose, mustard, Hibiscus, etc.
ü The transfer of pollen grains from the anther of a stamen to the stigma of a pistil is called pollination. Pollination takes place in two different ways
Figure 07- Self and cross pollination
n Self-pollination- When the pollen grain from the anther of one flower reaches to the stigma of the same flower, it is called self-pollination. Self-pollination generally occurs in a bisexual flower.
n Cross-pollination- When the pollen grains from the anther of a flower or of a plant are transferred to the stigma of a flower of the same plant or that of a different plant of the same kind the process is called cross-pollination. This transfer to another plant is mediated by insects, wind, water, animals, birds, etc.
ü The process of pollination is carried out by some external agencies like wind, water, insects, birds, etc. These are called agents of pollination.
4. Fertilization-
Figure 08- Fertilization
ü The process in which the male gamete fuses with the female gamete to form a new cell (called zygote) is called fertilization.
ü When the pollen are deposited on the stigma of the pistol, it begins to germinate.
ü After some time, a long pollen tube is developed from the pollen grain which passes through the style towards the female gametes in the ovary.
ü The male gametes move down the pollen tube and the tube enters the ovule present inside the ovary.
ü The tip of pollen tube bursts and the male gamete comes out of the pollen tube. Inside the ovary, the male gametes fuse with the female gametes present in the ovule to form a fertilized egg cell which is called zygote.
ü The zygote develops into an embryo which is a part of a seed that develops into a new plant.
5. Fruit And Seed Formation-
Figure 09- Fruit and seed
ü After the fertilization, the ovary grows into the fruit and the ovule develops into the seeds.
ü The outer parts of the flower, i.e. petals, sepals and stamen become dry and fall off. Stigma and style also fall off leaving ovary on the receptacle.
ü The zygote inside the ovary gets its food from the ovule and grows by cell division to form an embryo. Parts of the ovule develop into the seed covering or seed coat.
ü Fruits are the ripened ovary of a flower. Which protect the seed. Some fruits are fleshy and juicy, e.g. mango, apple and orange, while some are hard like almonds and walnuts.
6. Dispersal Of Seeds-
(i) Dispersal by Wind or Air - The seeds that are very light and have wing or hair-like structure on them, are easily carried away by the blowing wind, e.g. seeds of maple, drumstick have wings, seeds of Madar or oak have hairs on them, cottonseed also possess hairs on them, while seeds of grasses, orchids, begonia are very small and light. These seeds can be easily carried away by the wind and dispersed away from their natural habitat.
(ii) Dispersal by Water- The seeds of some plants that have an outer fibrous or spongy covering are dispersed through water. They have the ability to float in the water and drift along with its flow, e.g. seeds of water lily, lotus, chestnut (singhara) and coconut are dispersed through water. The coconut fruits have a fibrous outer coat which enables them to float in water and carried away by flowing water to far off places.
(iii) Dispersal by Birds- The birds eat fruits along with the seeds. These seeds have hard outer covering. The seeds are dispersed to some other place through the bird’s faeces. The digestive enzymes present in the digestive system of birds helps in dissolving the hard seed coat and when they are released or excreted along with the faeces, they germinate, e.g. neem seeds are dispersed by the bird’s faeces.
(iv) Dispersal by Animals- Some seeds have hooks or spines which get attached to the fur or body of the grazing animals. When these animals move to a distant place, the seeds get dispersed (while animal rub their body surface), e.g. fruit of Xantbium and Urena plants are covered by numerous hooks which attach to the animal’s fur and are dispersed with them. Along with the fruits, the seeds also get dispersed.
(v) Dispersal by Explosion or Bursting of Fruits- Sometimes fruits mature and a strain is produced in their walls. This produces a sudden jerk causing fruits to break open, thus allowing the seeds to scatter far away from their parent plants. Due to the explosion of fruit, the seeds are thrown away from the plant with a great force in all direction, e.g. castor plant burst suddenly with a jerk and scatter the seeds far away from the parent plant. Similarly, fruit of balsam is also dispersed through the explosion mechanism.
(vi) Benefits of Seed Dispersal-
ü Seed dispersal avoids overcrowding of young plants around their parent plants.
ü It helps in preventing competition between the plants and its own seedlings for sunlight, water and minerals.
ü One of the benefits of seed dispersal is that it enables the plant to grow into new habitats for wider distribution and provides them with a better chance of survival.
NCERT PRACTICE QUESTIONS
Q.1.Fill in the blanks:
(a) Production of new individuals from the vegetative part of parent is called ___________.
(b) A flower may have either male or female reproductive parts. Such a flower is called _______.
(c) The transfer of pollen grains from the anther to the stigma of the same or of another flower of the same kind is known as __________.
(d) The fusion of male and female gametes is termed as ____________ .
(e) Seed dispersal takes place by means of ________ and __________.
Ans. (a) vegetative reproduction (b) unisexual flower (c) pollination (d) fertilization (e) wind, water
Q.2. Describe the different methods of asexual reproduction. Give examples.
Ans.
(a) Binary Fission- This process takes place in unicellular organisms. Parent cell elongates and gets divided into two identical daughter cells. Each daughter cell grows into an independent adult.
(b) Endospore Formation- In this method the spore wall is formed around a bacterial cell to form an endospore. This endospore germinates to form an active bacterium under favourable conditions.
(c) Fragmentation- In this process, body of the organism breaks up into two parts. Then each part grows into a new filament thus forming two organisms from a single one.
(d) Spore Formation- The spores are tiny spherical unicellular structures protected by thick wall. The spores are stored in a hard outer covering and this is called sporangium. Under favourable conditions the hard cover breaks and spores spread for germination.
(e) Budding- In yeast, new organisms are produced by the bud formation from the parent organism. After growing to full size, the bud gets detached and forms a new independent individual.
(f) Vegetative propagation- When vegetative parts of a plant like stems, leaves and root etc., give rise to new ones, it is.called vegetative propagation.
Q.3. Explain what you understand by sexual reproduction.
Ans. Sexual reproduction means involvement of two parents in the process of reproduction. It is found mainly in higher plants where male gamete and female gamete fuse to form a zygote. These zygotes develop into individuals which are not identical. Off-springs inherit the characteristics of both the parents. In sexual reproduction both parents survive after the process of reproduction.
Q.4. State the main difference between asexual and sexual reproduction.
Q.5.Sketch the reproductive parts of a flower.
Q.6.Explain the difference between self-pollination and cross-pollination.
Q.7.How does the process of fertilization take place in flowers?
Ans.When the pollen grain reaches the stigma of a same species flower, it starts growing out into the pollen tube of the stigma. This tube continues to grow inside the style till it reaches the ovule. Male cells are released into the ovule for the fertilization with the female egg cell and thus the zygote is formed. After this process of fertilization, the ovary develops into fruit and ovule into seeds.
Q.8.Describe the various ways by which seeds are dispersed.
Ans. Following are the ways in which the seeds are dispersed:
(i) Some light seeds like that of madar, which are hairy, dry and small are carried away by the wind to different places.
(ii) Spiny seeds and fruits like that of xanthium and urena, stick to the clothes of passers by and animals. These seeds are carried away by these agents to different places.
(iii) In some plants having heavy seeds like that of coconut, water acts as the dispersing agents.
(iv) Some seeds are dispersed with the fruit burst like in case of balsam and castor.
Q.9.Match items in Column I with those in Column II.
Q.10. Tick the correct answer-
(a) The reproductive part of a plant is the
(i) leaf (ii) stem (iii) root (iv) flower
(b) The process of fusion of the male and the female gametes is called
(i) fertilization (ii) pollination (iii) reproduction (iv) seed formation
c) Mature ovary forms the
(i) seed (ii) stamen (iii) pistil (iv) fruit
(d) A spore producing plant is
(i) rose (ii) bread mould (iii) potato (iv) ginger
(e) Bryophyllum can be reproduced by its
(i) stem (ii) leaves (iii) roots (iv) flower
Ans.(a) (iv) flower (b) (i) fertilization (c) (iv) fruit (d) (ii) bread mould (e) (ii) leaves
Junior Science Topic - Reproduction In Plants. Chapter notes, video lectures, power point presentation and NCERT exercise solution. (Class 7, CBSE syllabus, chapter 12)
By - EduPorm India - The Educational Platform
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