Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants
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Selina Concise ICSE Solutions for Class 8 Biology Chapter 2 Reproduction in Plants
Multiple Choice Questions:
1. Put a tick mark (✓) against the correct alternative in the following statements
(a) Pollen is produced in the:
(b) Reproductive whorls of a flower are:
- Stamens and carpels
- Sepals and petals
- Sepals and stamens
- Petals and carpels
(c) Grafting is a method of:
- Artificial vegetative propagation
- Sexual reproduction
- Artificial pollination
(d) Which one of the following is a false fruit ?
Short Answer Questions:
Write two ways in which pollination may occur in plants.
The two ways in which pollination may occur in plants are:
Name the three agents of pollination.
The three agents of pollination are:
Give two features of flowers which favour pollination by insects.
Specialities of insect-pollinated flowers:
(a) These flowers are large with coloured petals to attract insects.
(b) These are scented so that insects locate the flowers by smell.
Name two characteristics of flowers in which pollination occur by wind.
Special features of wind-pollinated flowers:
(a) They produce light pollen so that it is easily carried away.
(b) They produce a large quantity of pollen.
What is a “false fruit” ? Give one example:
In false fruits the base of the flowers (thalamus) becomes the main fleshy part of the fruit, while the ovary remains a small central part containing seeds. Example: Apple and Pear.
Name any three agencies for dispersal of seeds.
c. Man and animals, birds, bats, squirrels.
Fill in the blanks by selecting suitable words:
(unisexual, fertilisation, fruit, stamen, anther, bisexual, pollination, seed, ovary)
a. A flower that bears both the male and the female parts is known as bisexual flower.
b. A flower bearing only male or female parts is known as unisexual flower.
c. Transfer of pollen grains from the anther to the stigma is known as pollination.
d. Fusion of male cell with the female cell is called fertilisation.
e. The ovule develops into a seed.
f. The ovary of the flower develops into a fruit.
Long Answer Questions:
What is vegetative reproduction?
Vegetative reproduction: In this method, new plants are produced by the vegetative parts of the plants. The vegetative part mean the leaf, stem and root. Potato, mint, ginger, banana etc. are reproduced by this method.
Vegetative propagation can occur by natural methods as well as by artificial methods.
Natural method includes reproduction by stem, by roots and by leaves.
Artificial method include reproduction by cutting, layering, grafting and tissue culture.
Briefly explain why a gardener prefers to grow certain plants vegetatively?
Gardener prefer to grow certain plants by vegetative method. The advantages in doing so are as follows:
- Reproduction by vegetative parts takes place in a shorter time.
- New plants, thus produced, spread very fast in a small area.
- It is a surer method.
- All the characters of the mother plant are retained by the daughter plants.
Why is it disadvantageous to grow plants vegetatively?
It is disadvantageous to grow plants vegetatively because of following:
- As all plants developed by vegetative propagation are identical, they are likely to be affected simultaneously if a disease spreads in the farm.
- Dispersal of plants does not take place on its own. Daughter plants, so developed, tend to remain nearby and are restricted to a particular area leading to competition for resources.
What is meant by pollination? Explain the structure of germinating pollen grain with the help of a labelled diagram.
Pollination: Pollination is the process in which the pollen grains from the anthers are transferred to the stigma.
Structure of the pollen grain: After pollination pollen grains are deposited on the stigma of the carpel. Under suitable conditions pollen grains produce a tube known as pollen tube. This tube grows down through the stigma and style towards the ovary.
The nucleus of the pollen grains divides by mitosis and forms two male gametes. The tip of the pollen tube after entering ovary discharges the two male gametes into the embryo sac.
One of the male gametes fuses with the egg to form the zygote. This fusion is called fertilization. Another male gamete fuses with the diploid secondary nucleus and forms the endosperm, a food storing tissue.
Imagine all the seeds produced by a plant happen to fall under the same plant and sprout into new plants. Mention any two problems that will be faced by the new plants. –
If all the seeds produced by a plant happen to fall under the same plant and sprout into new plants then in this situation plants will face the following problems:
- A large number of plants will grow in a small limited space. The water and the minerals available to them in the soil will be limited.
- The air surrounding them will not be enough and less sunshine will be available to them. As a result, most of these sprouted plants will die.
What is a flower ? Draw a neat labelled diagram showing the L.S. of a typical flower.
A flower is a reproductive part of a plant. It helps in sexual reproduction as it has male parts and female parts. A fully opened flower has the following parts:
Stalk—A flower is attached to the shoot by means of stalk or pedicel stalk. The tip of the stalk is swollen or flattened. This is called torus or thalamus or receptacle.
The different parts of a flower are inserted on the thalamus. There are usually four whorls as
Gynoecium (Carpels) Present on the thalamus
- Sepals (Calyx): These are the outermost part of the flower. These are leaf like and green in colour. This is the outer covering of the flower and form outer whorl in a flower. The Calyx (sepals) enclose the inner parts of the flower when it is a bud. It is protective in function.
- Corolla (Petals): Petals form the second whorl inner to the sepals. These are usually coloured, gaudy, or white in colour and scented and give sweet smell. The value of a flower is due to the attractive colour of the petals. These attract the insects for pollination.
- Stamens (Androecium): The third whorls inner to the petals are stamens. This third whorl is called Androecium. These are the male parts of the flower. Each stamen is formed of a long narrow, hair like structure called filament. On its tip it bears, a rounded broad sac like structure called anther. Each anther has two anther lobes. Each anther lobe has two pollen sacs which have powdery mass called pollen grains.
- Carpels (Gynoecium): Carpels are the inner most or fourth whorl in a flower. It is lodged on the thalamus and forms the female part of a flower. This whorl of carpels is called gynoecium. Each carpel or pistil has three parts.
(a) The lower most, swollen part is ovary. It is attached to the thalamus.
(b) The middle part is style which is narrow, thread like.
(c) Stigma: The style ends in a knob like, rounded structure which is sticky in nature to receive the pollen grains.
The ovaries contain ovules which later turn into seeds after fertilization and the ovary wall forms the fruit sometimes the thalamus also becomes a part of the fruit as in apple.
Write short notes on the following:
(a) Micro propagation
(c) Vegetative reproduction
(a) Micro propagation: This is the propagation of plants involving cell and tissue culture. If vegetative propagation is not possible in a crop, then buds, shoot apex or any other part of the plant can be used as explant for micropropagation.
- The explants are treated with sterilisation chemicals to prevent microbial growth, and then cultured in a particular nutrient medium.
- Cells grow and divide to form a cell mass called callus Some growth regulators (Plant hormones) are added.
- The callus differentiates into plant parts looking like plant (plantlet). After 4-6 weeks the plantlets transferred to the soil.
(b) Bryophyllum: It is a beautiful plant grown in gar xerophyte plant and can grow in any type soil or container. It requires sun and watering time to time. We can grow it vegetatively.
When a leaf is put on the soil or falls off accidentally from the parent plant. It starts giving out buds in the notches of the leaves. These buds start growing when in touch with soil having moisture. They give out adventitious roots which go into the soil and small aerial shoots which go into the air. So these adventitious buds form many plants from a single plant. Thus we can get many plants from a single leaf. We can grow these tiny plants into separate pots to get independent plants. This is one of the vegetative mode of reproduction.
(c) Vegetative reproduction: This is method of producing new plants from the vegetative parts of the plants. The vegetative part means the leaf, stem, root. As potato, mint, ginger, banana, sugar beet, gul-e-daudi, asparagus, sugar cane, are produced by this method.
(d) Grafting: In plants like mango, zizyphus (ber), guava apples, fruits, roses, a small bud is fixed on the stem. Many types of apples on a single plant thus a small orchard on a single plant. So we can have different types of roses and chrysanthemums on a single plant.
How artificial pollination is useful to plant breeders ? Discuss briefly.
Artificial pollination means transfer of pollen to the stigma artificially. In ancient times, it was a common practice to sprinkle “male flowers of palms on the “female flowers”. However, in modem era, plant breeders use artificial pollination for developing new varieties. The breeders remove the anthers in young flowers and cover such flowers by plastic bags. Such flowers are then pollinated with pollen from the plants of the desired variety.
With the help of suitable diagrams, describe
(a) Binary fission in plants
(b) Budding in yeast cell
(a) Binary fission: This is one of the asexual mean of reproduction. In lower plants like bacteria reproduction takes place by this process. In this process the nucleus of the cell divides into two. Then the cell wall splits across the middle of the cell. Thus each part has a nucleus. Thus each part is an independent bacterium.
Later on these two parts of the cell get separated from each other and form two independent individuals called daughter cells and lead independent life.
(b) Budding in yeast cell: Budding is the most common method in yeast. The Parent cell produces an outgrowth called a bud. The bud grows, and then gets detached from the parent body to lead an independent life.