Pollination and Fertilization

Match the following in Column I with those in Column II

Answer

Complete the following statements

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

Answer

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.

Mention if the following statements are true.

1. Intine is the outer wall of pollen grain.
2. Pollen tube enters ovule through micropyle.
3. Zygote gives rise to embryo.
4. Ovule becomes fruit.
5. Dry sepals may persist in some fruits.

Answer

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

Exine and intine are the parts of:

1. Embryo sac
2. Pollen grain
3. Stigma
4. Seed

Answer

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.

Which one of the following is one of the characteristics of self-pollinated flowers?

1. Flowers are large and showy
2. Flowers remain closed and do not open
3. Stigma and anthers mature at the same time
4. Pollen is produced in very large quantities

Answer

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.

The kind of pollination in which the pollen of the same flower falls on its stigma is termed as:

1. Geitonogamy
2. Autogamy
3. Homogamy
4. Allogamy

Answer

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.

Which of the following conditions favours self-pollination?

1. Homogamy
2. Herkogamy
3. Dichogamy
4. None of these

Answer

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.

Pollination by birds is termed as :

1. Entomophily
2. Anemophily
3. Ornithophily
4. Elephophily

Answer

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.

Which of the following is an example of an ornithophilous flower ?

1. Bougainvillea
2. Vallisneria
3. Bignonia
4. Rafflesia

Answer

Bignonia

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

Bright, showy and nectar producing flowers are needed for pollination to occur by:

1. Wind
2. Water
3. Insects
4. Elephant

Answer

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.

The male inflorescence of maize plant is termed as:

1. Cob
2. Ear
3. Tassel
4. Silk

Answer

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.

Wing and keel petals are found in the flowers of:

1. Pea plants
2. Vallisneria
3. Maize plants
4. Dahlia

Answer

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.

Which of these does not belong to the embryo sac of a flower?

1. Generative nucleus
2. Antipodal cells
3. Polar Nuclei
4. Synergids

Answer

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.

The given figures A and B show ............... and ............... conditions which favour cross-pollination.

1. Herkogamy and Heterostyly
2. Heterostyly and Herkogamy
3. Herkogamy and Homogamy
4. Heterostyly and Homogamy

Answer

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.

Look at the table given below and identify the kind of pollination that usually occurs in the flower mentioned.

1. P — Entomophily, Q — Hydrophily, R — Anemophily
2. P — Hydrophily, Q — Elephophily, R — Anemophily
3. P — Ornithophily, Q — Anemophily, R — Elephophily
4. P — Ornithophily, Q — Hydrophily, R — Entomophily

Answer

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.

Given below is the internal structure of an ovule. Read the information below the diagram and fill in the blanks:

Ovule is located in the inner part of the ovary. It is destined to become the seed and the ovary to become the fruit. The number of ovules in the ovary vary from species to species. It can be one or more.

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

Answer

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.

State the name of the chief pollinating agent against the corresponding plant by choosing from those given in brackets.

1. Dahlia......(Crow, butterflies, mosquito).
2. Maize.......(Bees, locusts, rain, wind).
3. Vallisneria.........(Wind, water, ants, rabbits).

Answer

1. butterflies
2. wind
3. water

Fill in the blanks with suitable words.

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

Answer

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.

Name the parts of ovary which give rise to:

(a) Seed ...............
(b) Fruit ...............
(c) Fruit wall ...............

Answer

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

Give one word/term for the following:

1. A flower containing both male and female parts.
2. Arrangement of flowers on a twig/stem.
3. When pollen grains of a flower reach the stigma of the same flower.
4. When maturation time of reproductive parts in a flower is different.
5. When stigma and anthers do not grow up to same height, what favours only cross-pollination?.
6. Pollination of flowers by insects.
7. Pollination of flowers by birds.

Answer

1. Bisexual flower

2. Inflorescence

3. Self-pollination/Autogamy

4. Dichogamy

5. Heterostyly

6. Entomophily

7. Ornithophily

Match the items in Column A with those in Column B.

Answer

Explain the following terms:

1. Ornithophily
2. Elephophily
3. Artificial pollination

Answer

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.

Define:

1. Pollination
2. Herkogamy
3. Cleistogamy
4. Emasculation
5. Fertilization

Answer

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.

What happens to the following after fertilization?

1. Ovules
2. Calyx
3. Petals
4. Stamens

Answer

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.

Mention any two contrivances in flowers which favour cross-pollination.

Answer

Contrivances in flowers which favour cross-pollination:

1. Unisexuality

2. Different timings of maturation of androecium and gynoecium

3. Self-sterility

4. Structural barriers

Distinguish between the following pairs:

(a) Autogamy and Geitonogamy

(b) Homogamy and Dichogamy

(c) Protandry and Protogyny

(d) Entomophilous and Anemophilous flowers

(e) Advantages of self and cross-pollination

Answer

(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:

What are the advantages of the following in the flower to the plant concerned?

1. Long and feathery stigma
2. Brightly coloured petals
3. Smooth and light pollen
4. Protruding and easily movable anthers
5. Fragrant nectar

Answer

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.

Describe the advantages and disadvantages of cross-pollination to the plant.

Answer

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.

What is the function of the pollen tube? Explain it with the help of a diagram.

Answer

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.

The figure shown below represents a process in flowers. Study the same and answer the following questions.

(a) Name and define the process.

(b) Write the technical term of the above mentioned process.

(c) Give two examples of plants in which this process occurs.

(d) Write one advantage and one disadvantage of the process shown.

(e) Name two agents that participate in this process.

Answer

(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

Given alongside is a diagrammatic sketch of the sectional view of a germinating pollen grain. Study the same and then answer the questions that follow:

(a) Name the parts labelled 1, 2, 3, 4 and 5.

(b) Where does the germination of the pollen grain take place and how?

(c) What is the function of the part labelled '4'?

(d) What happens to the part labelled '5' during the process?

Answer

(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.

Given below is a diagrammatic representation of the process of fertilization. Study the same and then answer the questions that follow:

(a) Name the parts labelled 1, 2, 3, 4, 5 and 6.

(b) What happens to (i) Ovary (ii) Ovule after fertilization?

(c) What is the function of the synergids?

(d) What part does the stigma play in the process of fertilization?

Answer

(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.

Shivam dissected a flower of sweet pea and removed all the petals. He observed the reproductive parts of the flower (both male and female), arranged in a specific manner as shown in the diagram given below.

(a) Mention the kind of arrangement of the stamens as shown in the figure.

(b) What are the three kinds of petals that Shivam removed from the flower? Name them.

(c) Name the kind of pollination (on the basis of pollinating agent) with one specific feature of the flower which favours it.

Answer

(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.

Assertion (A): Autogamy and allogamy are the two kinds of self-pollination.

Reason (R): Self-pollination occurs within the same flower or two flowers of the same plant.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

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.

Assertion (A): Herkogamous flowers favour cross-pollination as these flowers have a structural barrier between the male and female reproductive parts.

Reason (R): Pansy is an example of a herkogamous flower which has a hood covering the stigma.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

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.

Assertion (A): Entomophilous flowers are brightly coloured and often scented.

Reason (R): The pollinating agents of entomophilous flowers are insects which usually get attracted towards the bright colours or scents of the flowers.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

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.

Assertion (A): One polar nucleus fuses with two sperm nuclei of a flower and develop into an endosperm during the process of fertilization.

Reason (R): The large central cell of the embryo sac contains two polar nuclei, which fuse with one male nucleus. This process is termed as 'triple fusion'.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

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.

Assertion (A): The process of removal of anthers in young flowers is termed as 'emasculation'.

Reason (R): Emasculation is mainly performed during artificial pollination to produce the desired variety of the plants.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Answer

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.

Shaista is working on her school project about plant reproduction. Her teacher Mrs. Aggrawal gave her the task of investigating pollination in pea flower, a common garden plant. Shaista is curious to know how pollination in pea flower and maize flower differs from each other.

(a) Is pollination a necessary event before fertilization for reproduction in plants? Explain.

(b) What are the pollinating agents for pea and maize flowers respectively?

(c) Write scientific terms for the kind of pollination found in pea flower and maize flower on the basis of pollinating agents.

(d) Mention the technical term for the specific condition of stamens in pea flower.

(e) What are the two advantages of cross-pollination?

Answer

(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.