Pollination and Fertilization

1. Pollination is the process of transfer of pollen grains.
2. The two kinds of pollination are self-pollination and cross-pollination.
3. For self-pollination, the flowers need not be large and showy.
4. For self-pollination, anthers and stigma must mature at the same time.
5. Self-pollination does not yield new varieties.
6. In cross pollination, there is much wastage of pollen grains.

1. False
   Corrected Statement — Exine is the outer wall of pollen grain.
2. True
3. True
4. False
   Corrected Statement — Ovule becomes seed.
5. True

Pollen grain

Reason — The outer wall of the pollen grain is known as exine and the inner wall is known as intine.
Embryo sac contains the female gametophyte. Stigma is a part of the pistil. Seed contains embryo, seed coat.

Stigma and anthers mature at the same time

Reason — Homogamy, i.e., maturation of stigma and anthers at the same time, is necessary for self-pollination.
Large and showy flowers are generally a feature of cross-pollinated plants. Flowers that remain closed and do not open show cleistogamy, which is a special condition favouring self-pollination but not a general characteristic of all self-pollinated flowers. Pollen produced in very large quantities is a feature of many cross-pollinated plants, especially wind-pollinated plants.

Autogamy

Reason — Autogamy refers to pollination in which the pollen grain is transferred from anther to stigma of the same flower.
Geitonogamy is the pollen transfer between different flowers of the same plant. Homogamy is a condition where anthers and stigma mature at the same time. Allogamy is pollen transfer between different plants.

Homogamy

Reason — In homogamy anther and stigma of a flower mature at the same time, favouring self-pollination.
Herkogamy is a physical barrier or separation between anthers and stigma. So, it prevents self-pollination and promotes cross-pollination. Dichogamy is anthers and stigma mature at different times. So, it prevents self-pollination.

Ornithophily

Reason — Ornithophily refers to pollination where pollinating agent are birds.
Entomophily is pollination by insects. Anemophily is pollination by wind. Elephophily refers to pollination by elephants, which is not a standard biological type for pollination.

Bignonia

Reason — Bignonia flower is pollinated by birds.
Bougainvillea is mainly insect-pollinated. Vallisneria is water pollinated plant. Rafflesia is pollinated by insects.

Insects

Reason — Bright, showy and nectar producing flowers attract insects.
Wind-pollinated flowers are small, non-attractive, without nectar. Water-pollinated flowers are non-attractive, lack nectar. Elephants may rarely act as pollinating agents in flowers such as Rafflesia, but bright, showy and nectar-producing flowers are typically insect-pollinated.

Tassel

Reason — Tassel is the male inflorescence of maize plant.
The cob is the female inflorescence of maize. Ear is another name for the female inflorescence in maize. Silk refers to the long, thread-like styles of the female flower.

Pea plants

Reason — Wing and keel petals of pea plant help in pollination by insects.
Vallisneria flowers are small and lack such specialized petal types. Maize plant flowers are not showy and do not have wing or keel petals. Dahlia petals are uniform, not differentiated into wing and keel types.

Generative nucleus

Reason — Embryo sac contains one egg cell, two synergids, three antipodal cells, one large central cell. Generative nucleus is present in pollen grain.
Antipodal cells are present in the embryo sac, located at the chalazal end. Polar nuclei are found in the central cell of the embryo sac. Synergids are located near the egg cell.

Herkogamy and Heterostyly

Reason — In herkogamy, a structural barrier or the relative position of anthers and stigma prevents self-pollination and promotes cross-pollination. In heterostyly, the style and stamens are of different lengths in different flowers, which promotes cross-pollination.
In homogamy, anthers and stigma mature at the same time. So, it favours self-pollination, not cross-pollination.

P — Entomophily, Q — Hydrophily, R — Anemophily

Reason — Flowers of Hibiscus are large, colourful and scented which attracts insects, hence pollination is by insects (Entomophily).
Hydrilla is an aquatic plant so pollination happens via water (Hydrophily).
Flowers of wheat are small, non-showy hence pollen grains are carried by wind (Anemophily).
Ornithophily is pollination by birds. So, flowers are bright, showy colours, have nectar. Elephophily, also called blepophily, refers to pollination by elephants.

Each ovule has one or two protective coverings, the integuments. The integuments leave a small opening called the Micropyle at one end. Enclosed by the integuments is the Nucellus (a mass of food laden cells), and further inside it, is the embryo sac. Embryo sac contains one Egg cell and two Synergids at one end. Three Antipodal cells are found at the opposite end of embryo sac.

1. butterflies
2. wind
3. water

1. Transfer of pollen grains from anthers to stigma of the same flower is called autogamy.
2. Different timings for maturation of gynoecium and androecium, is called dichogamy.
3. Vallisneria is a water-pollinated flower.

(a) Seed — Ovule
(b) Fruit — Ovary
(c) Fruit wall — Ovary wall (Pericarp)

1. Bisexual flower

2. Inflorescence

3. Self-pollination/Autogamy

4. Dichogamy

5. Heterostyly

6. Entomophily

7. Ornithophily

1. The process of pollination carried out by birds is known as ornithophily.

2. The process of pollination carried out by elephants is known as elephophily/blepophily.

3. The process in which pollen grains are transferred to the stigma manually by human beings is called artificial pollination.

1. Pollination is the process of transfer of pollen grains from the anther to the stigma.
2. Herkogamy is the condition of flower favouring cross-pollination, in which a structural barrier around the stigma prevents self-pollination.
3. Cleistogamy is a condition favouring self-pollination, in which the flower remains closed even at maturity, and the anthers and stigma remain hidden close to each other.
4. Emasculation is the process of removal of anthers from a young flower for ensuring artificial pollination.
5. The process of fusion or union of the nuclei of male and female gametes is called fertilisation.

1. Ovules — Ovules become seeds after fertilization.
2. Calyx — After fertilization, the calyx sheds or falls off or remains intact in a shriveled and dried form.
3. Petals — After fertilization, the petals wither and generally fall off.
4. Stamens — After fertilization, the stamens wither and generally fall off.

Contrivances in flowers which favour cross-pollination:

1. Unisexuality

2. Different timings of maturation of androecium and gynoecium

3. Self-sterility

4. Structural barriers

(a) Difference between Autogamy and Geitonogamy:

(b) Difference between Homogamy and Dichogamy:

(c) Difference between Protandry and Protogyny:

(d) Difference between Entomophilous and Anemophilous flowers:

(e) Difference between advantages of self and cross-pollination:

1. Long and feathery stigma — Helps to trap pollen grains in wind-pollination.

2. Brightly coloured petals — Attracts insects for cross-pollination.

3. Smooth and light pollen — It is easily carried by wind, enabling cross-pollination.

4. Protruding and easily movable anthers — Even the slightest wind can move them.

5. Fragrant nectar — Attracts insects for pollination.

Advantages of cross-pollination:

1. The offspring are healthier.

2. The seeds produced are abundant and viable.

3. New varieties may be produced by cross-pollinating two different varieties of the same species.

Disadvantages of cross-pollination:

1. Pollination is not always certain.

2. The pollen has to be produced in large quantity.

3. The process is uneconomical for the plant because the flowers have to be large, coloured, scented and have to produce nectar for attracting pollinating agents.

The function of the pollen tube is to carry the male gametes/sperm nuclei from the pollen grain to the embryo sac inside the ovule for fertilization.

The pollen tube grows out of the pollen grain by breaking through its exine. It grows through the stigma and style by dissolving these tissues with the help of enzymes and reaches the ovary, where it enters the ovule through a minute pore called the micropyle.

(a) The process is Cross-Pollination. It is defined as the transfer of pollen grains from the anthers of one flower to stigma of another flower of a different plant of the same species.

(b) Allogamy

(c) Oxalis, Hibiscus

(d) Advantage — The offspring are healthier and can adapt to environmental changes.
Disadvantage — The pollination is not always certain because some pollinating agent is always needed which may or may not be available at the proper time.

(e) Insects, Wind

(a) The parts labelled 1, 2, 3, 4 and 5 are:

• 1 → Exine
• 2 → Intine
• 3 → Pollen tube
• 4 → Tube nucleus
• 5 → Generative nucleus

(b) Germination of the pollen grain takes place only after it falls on the stigma of the same plant species. The pollen grain is stimulated to germinate due to the secretion of sugars by the stigma.

(c) The function of part '4' (tube nucleus) is to direct the growth of the pollen tube towards the ovary.

(d) During germination of the pollen grain, part '5' (generative nucleus) present at the tip of the pollen tube divides into two sperm nuclei. The pollen tube enters one of the synergids and releases its two sperm nuclei. Of these, one sperm nucleus enters the egg cell and fuses with its nucleus, while the other sperm nucleus moves towards the two polar nuclei in the central cell and fuses with them.

(a) The parts labelled 1, 2, 3, 4, 5 and 6 are:

• 1 → Style
• 2 → Pollen tube
• 3 → Polar nuclei
• 4 → Embryo sac
• 5 → Antipodal cells
• 6 → Micropyle

(b) After fertilization, the ovary enlarges to form the fruit and the ovarian wall forms the fruit wall. The ovule becomes the seed.

(c) Synergids help guide the pollen tube towards the egg cell and assist in the entry and release of the male gametes into the embryo sac.

(d) Pollen grain is transferred to the stigma during pollination. Germination of pollen grain takes place only if it falls on the stigma. After germination, the pollen tube grows through the stigma and reaches the ovary for the fertilization of the egg cell.

(a) Diadelphous

(b) The standard (1), the wings (2) and the keel (formed by fusion of 2 petals).

(c) Entomophily (pollination by insects). The flowers pollinated by insects are brightly coloured and produce nectar.

A is false but R is true.

Reason — A is false because autogamy is self-pollination, while allogamy is cross-pollination. Self-pollination includes autogamy, which occurs within the same flower, and geitonogamy, which occurs between two flowers of the same plant. Hence, R is true.

Therefore, A is false but R is true is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as herkogamy refers to the presence of a physical or structural barrier between the anthers and stigma in a flower. This adaptation prevents self-pollination and favours cross-pollination. R is true because in Pansy, the stigma is covered by a hood-like structure, making it an example of herkogamy.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true because entomophilous flowers are pollinated by insects. They are usually brightly coloured, scented, and often produce nectar to attract insects.
R is true because entomophily involves insects as pollinators. So, entomophilous flowers are brightly coloured.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

A is false but R is true.

Reason — A is false because one male gamete fuses with the two polar nuclei to form the endosperm nucleus. The other male gamete fuses with the egg cell to form the zygote. R is true because the large central cell contains two polar nuclei, which fuse with one male gamete. This fusion is called triple fusion.

Therefore, A is false but R is true is the correct option.

Both A and R are true and R is the correct explanation of A.

Reason — A is true as emasculation is the process of removing anthers from a young flower to prevent self-pollination.
R is true as it is an important step in artificial hybridization, where the emasculated flowers are manually pollinated with pollen from a selected plant to develop desired varieties.

Therefore, Both A and R are true and R is the correct explanation of A is the correct option.

(a) Yes, pollination is a necessary event before fertilization in flowering plants. Pollen grains must first reach the stigma so that the pollen tube can form and carry the male gametes to the ovule for fertilization.

(b) Pea: No external pollinating agent required because self-pollination occurs.
     Maize: Wind

(c) The scientific term for pollination in pea flower is entomophily and for maize flower is anemophily.

(d) The technical term for the specific condition of stamens in pea flower is diadelphous.

(e) The two advantages of cross-pollination are:

1. It produces genetic variation in offspring.

2. It results in healthier and more vigorous plants.