PLANT REPRODUCTION SYSTEMS

Question 1

Asexual Reproduction

Apomixis

Answer 1

A sexual reproduction does not involve fusion of male and female gametes
New plants may develop from vegetative parts of the plant (vegetative reproduction) or may arise from embryos that develop without fertilization (apomixis)

Apomixis
Apomixis(asexual seed formation) is the result of a plant gaining the ability to bypass the most fundamental aspects of sexual reproduction: meiosis and fertilization
Without the need for male fertilization, the resulting seed develops as a maternal clone.

Question 2

Vegetative Reproduction

Underground Stems

Answer 2

In nature, a new plant develops from a portion of the plant body
This may occur through modified underground and sub-aerial stems, and through bulbils

Underground Stems
The underground modifications of stem generally serve as storage organs and contain many buds
These buds develop into shoots and produce plants after rooting. Examples of such modifications are:
Tuber: Potato
Bulb : Onion, Garlic ,Ginger, Turmeric

Sub-aerial Stems
These modifications include runner, stolon
Bulbils
Bulbils are modified flowers that develop into plants directly without formation of seeds
These are tiny secondary bulbsthat form in the angle between a leaf andstem or in place of flowers on certain plants. E.g. Onion, lily
These are vegetative bodies; their development does not involve fertilization and seed formation

Question 3

Vegetative Reproduction

Answer 3

It is commonly used for the propagation of many crop species, although it may not occur naturally in those species
Stem cuttings are commercially used for the propagation of sugarcane, grapes, roses, etc.
Layering, budding and grafting are commonly used for the propagation of fruit trees and ornamental shrubs.

Question 4

SEXUAL REPRODUCTION

Answer 4

Sexual reproduction involves fusion of male and female gametes to form a zygote, which develops in to an embryo
In crop plants, male and female gametes are produced in specialized structures known as flowers
A flower usually consists of sepals, petals (or their modifications), stamens and/or pistil
A flower containing both stamens and pistil is a perfect or hermaphrodite flower.

Question 5

1. If a plant contains stamens, but not pistil, it is known as …………., while a pistillate flower contains pistil but not stamens
2. Staminate and pistillate flowers occur on the same plant in a ……………species, such as maize, Colocasia, coconut, etc
3. But in ………………. species, staminate and pistillate flowers occur on different plants, e.g., papaya, date palm.
4. …………………can be classified as annuals, biennials and perennials depending upon the time they take to complete the life cycle and flowering.

Answer 5

1. staminate
2. monoecious
3. dioecious
4. Angiosperms (flowering plants)

Question 6

Annuals , Biennials, Perennials, Monocarpic and perennials

Answer 6

Annuals : Plants live for one year. The plants which produce flowers and seeds within one season are called annuals eg. Pea
Biennials : Plants which complete their life cycle in two seasons are called biennials. In the first year, the plants remain in the vegetative state. In the second year, they produce flowers, fruits, and seeds and then die e.g. radish.

Perennials : Plants which live for several years are termed perennials
Their vegetative stage may last from one to a few years after which they produce flowers, fruits, and seeds every year e.g. mango, peepal, neem etc.

Monocarpic : Some perennial plants reproduce only once in their life-time and then die. Such plants are called Monocarpic e.g. bamboo

Question 7

Factors Affecting Flowering

Answer 7

Flowering in a plant is affected by temperature (vernalisation) and light (photoperiodism)
Vernalisation : Low temperature treatment which stimulates early flower formation is called vernalisation. E.g winter wheat
Photoperiodism : It is the response in growth and flowering of a plant to the duration of light and dark period per day.

Question 8

MODES OF POLLINATION

Answer 8

Pollination refers to the transfer of pollen grains from anthers to stigmas
Pollen from an anther may fall on to the stigma of the same flower leading to self- pollination or Autogamy

When pollen from flowers of one plant are transmitted to the stigmas of flowers of another plant, it is known as cross-pollination or Allogamy

A third situation, Geitonogamy, results when pollen from a flower of one plant falls on the stigmas of other flowers of the same plant, e.g., in Maize
However, maize is cross-pollinated and there are various mechanisms to avoid geitonogamy. Some examples are:
Stamens and pistils of hermaphrodite flowers may mature at different times facilitating cross - pollination.
Protogyny: Bajra
Protandry: Maize

Question 9

Some Adaptations to Promote Cross Pollination

Answer 9

Unisexuality : Flowers may be only male or female, borne on different plants e.g. papaya, palm.

Dichogamy : Male and female sex organs mature at different times. In sweet pea, anther matures earlier than the stigma and in custard apple stigma matures earlier than the anther.

Self Sterility : Pollen grains are incapable of affecting fertilization even after being placed on the stigma of the same flower e.g. petunia, apple.

Cleistogamy
In this case, flowers do not open at all. This ensures complete self-pollination since foreign pollen cannot reach the stigma of a closed flower, e.g. Groundnut
In some species, the flowers open, but only after pollination has taken place. Since the flower does open, some cross-pollination may occur.
In some species, flowers open but the stamens and the sigma are hidden by other floral organs. In several legumes, stamens and the stigma are enclosed by the two petals forming a keel, example Pea.

Question 10

Importance of pollination

Answer 10

Importance of Pollination :
It results in fertilization and ovule is converted into seed
New varieties of plants are formed through new combination of genes in case of cross pollination
It is the basis for genetic diversity in plants
Cross pollination is brought about by various external agencies such as, wind, insects, water, birds and other animals.

Question 11

types of pollination

Answer 11

Pollination by wind (Anemophily)
Flowers are small, without colour, nectar and scent
Flowers produce a large number of pollen grains to allow for wastage when carried with wind to another flower
The pollen grains are small, light and sometimes provided with ‘Wings’
The stigmas are comparatively large, protruding and some times hairy to trap pollen grains. Example: grasses and some cacti.

Pollination by insects (Entomophily)
Flowers are usually large, coloured and showy to attract insects
Some of these flowers secrete nectar to attract insects
Salvia flowers show special adaptations for pollination by bees.

Pollination by Water (Hydrophily)
This takes place in aquatic plants
Pollen grains are produced in large numbers
Pollen grains float on surface of water till they land on the stigma of female flowers e.g. Hydrilla

Pollination by Animals (Zoophily)
Flowers of such plants attract animals by their bright colour, size, scent etc.
For example, sun bird pollinates flowers of Canna, gladioli etc.
Squirrels pollinate flowers of silk cotton tree.