Sexual Reproduction in Flowering Plants

1. Among the terms listed below, those that are not technically correct names for a floral whorl are:

i. Androecium ii. Carpel iii. Corolla iv. Sepal

(a) i and iv

(b) ii and iii

(c) ii and iv

(d) i and ii

Key Answer: (c) ii and iv

Explanation: The four floral whorls are calyx, corolla, androecium, and gynoecium. Sepals and carpels are individual units that make up the calyx and gynoecium whorls, respectively, not whorls themselves.

2. Embryo sac is to ovule as ______ is to anther.

a. Stamen

b. Filament

c. Pollen grain

d. Androecium

Key Answer: c. Pollen grain

Explanation: The embryo sac is the female gametophyte located inside the ovule. Analogously, the pollen grain is the male gametophyte which develops inside the anther.

3. In a typical complete, bisexual and hypogynous flower the arrangement of floral whorls on the thalamus from the outermost to the innermost is:

a. Calyx, corolla, androecium and gynoecium

b. Calyx, corolla, gynoecium and androecium

c. Gynoecium, androecium, corolla and calyx

d. Androecium, gynoecium, corolla and calyx

Key Answer: a. Calyx, corolla, androecium and gynoecium

Explanation: A typical flower consists of four concentric whorls starting from the outside: calyx (sepals), corolla (petals), androecium (male reproductive organs), and the innermost gynoecium (female reproductive organs).

4. A dicotyledonous plant bears flowers but never produces fruits and seeds. The most probable cause for the above situation is:

a. Plant is dioecious and bears only pistillate flowers

b. Plant is dioecious and bears both pistillate and staminate flowers

c. Plant is monoecious

d. Plant is dioecious and bears only staminate flowers.

Key Answer: d. Plant is dioecious and bears only staminate flowers.

Explanation: Staminate flowers contain only male reproductive organs (stamens) and lack female organs (carpels). Without an ovary to develop into a fruit and ovules to develop into seeds, the plant cannot produce them.

5. The outermost and innermost wall layers of microsporangium in an anther are respectively:

a. Endothecium and tapetum

b. Epidermis and endodermis

c. Epidermis and middle layer

d. Epidermis and tapetum

Key Answer: d. Epidermis and tapetum

Explanation: A typical microsporangium is surrounded by four wall layers: the epidermis (outermost), endothecium, middle layers, and the tapetum (innermost layer which nourishes the developing pollen grains).

6. During microsporogenesis, meiosis occurs in:

a. Endothecium

b. Microspore mother cells

c. Microspore tetrads

d. Pollen grains.

Key Answer: b. Microspore mother cells

Explanation: Microspore mother cells (pollen mother cells) are diploid cells that undergo meiotic division to form a cluster of four haploid microspores, known as a microspore tetrad.

7. From among the sets of terms given below, identify those that are associated with the gynoecium.

a. Stigma, ovule, embryo sac, placenta

b. Thalamus, pistil, style, ovule

c. Ovule, ovary, embryo sac, tapetum

d. Ovule, stamen, ovary, embryo sac

Key Answer: a. Stigma, ovule, embryo sac, placenta

Explanation: The gynoecium is the female reproductive part containing the stigma, style, ovary, placenta, and ovule (which houses the embryo sac). Terms like tapetum and stamen belong to the male androecium.

8. Starting from the innermost part, the correct sequence of parts in an ovule are,

a. egg, nucellus, embryo sac, integument

b. egg, embryo sac, nucellus, integument

c. embryo sac, nucellus, integument, egg

d. egg, integument, embryo sac, nucellus.

Key Answer: b. egg, embryo sac, nucellus, integument

Explanation: The egg is located inside the embryo sac, which is surrounded by the mass of cells called the nucellus. The nucellus is enclosed by protective envelopes known as integuments on the outside.

9. From the statements given below choose the option that are true for a typical female gametophyte of a flowering plant:

i. It is 8-nucleate and 7-celled at maturity

ii. It is free-nuclear during the development

iii. It is situated inside the integument but outside the nucellus

iv. It has an egg apparatus situated at the chalazal end

(a) i and iv

(b) ii and iii

(c) i and ii

(d) ii and iv

Key Answer: (c) i and ii

Explanation: A typical angiosperm embryo sac is 8-nucleate and 7-celled, and its mitotic divisions are strictly free-nuclear initially. Statement iii is false because it's inside the nucellus, and statement iv is false because the egg apparatus is at the micropylar end.

10. Autogamy can occur in a chasmogamous flower if:

a. Pollen matures before maturity of ovule

b. Ovules mature before maturity of pollen

c. Both pollen and ovules mature simultaneously

d. Both anther and stigma are of equal lengths.

Key Answer: c. Both pollen and ovules mature simultaneously

Explanation: Chasmogamous flowers are open flowers. For autogamy (self-pollination within the same flower) to occur, synchrony in pollen release and stigma receptivity is absolutely essential.

11. Choose the correct statement from the following:

a. Cleistogamous flowers always exhibit autogamy

b. Chasmogamous flowers always exhibit geitonogamy

c. Cleistogamous flowers exhibit both autogamy and geitonogamy

d. Chasmogamous flowers never exhibit autogamy

Key Answer: a. Cleistogamous flowers always exhibit autogamy

Explanation: Cleistogamous flowers do not open at all. Therefore, there is no chance of cross-pollen landing on the stigma, making them obligate autogamous (strictly self-pollinating).

12. A particular species of plant produces light, non-sticky pollen in large numbers and its stigmas are long and feathery. These modifications facilitate pollination by:

a. Insects

b. Water

c. Wind

d. Animals.

Key Answer: c. Wind

Explanation: Wind pollination (anemophily) requires light and non-sticky pollen so they can be transported by air currents, and large, feathery stigmas to easily catch the airborne pollen.

13. From among the situations given below, choose the one that prevents both autogamy and geitonogamy.

a. Monoecious plant bearing unisexual flowers

b. Dioecious plant bearing only male or female flowers

c. Monoecious plant with bisexual flowers

d. Dioecious plant with bisexual flowers

Key Answer: b. Dioecious plant bearing only male or female flowers

Explanation: In dioecious plants, male and female flowers are on completely separate plants. This physical separation prevents both autogamy (same flower) and geitonogamy (different flower, same plant).

14. In a fertilised embryo sac, the haploid, diploid and triploid structures are:

a. Synergid, zygote and primary endosperm nucleus

b. Synergid, antipodal and polar nuclei

c. Antipodal, synergid and primary endosperm nucleus

d. Synergid, polar nuclei and zygote.

Key Answer: a. Synergid, zygote and primary endosperm nucleus

Explanation: Synergids are haploid (n) cells of the egg apparatus. The zygote is formed by syngamy and is diploid (2n). The Primary Endosperm Nucleus (PEN) is formed by triple fusion, making it triploid (3n).

15. In an embryo sac, the cells that degenerate after fertilisation are:

a. Synergids and primary endosperm cell

b. Synergids and antipodals

c. Antipodals and primary endosperm cell

d. Egg and antipodals.

Key Answer: b. Synergids and antipodals

Explanation: After fertilization, the zygote develops into an embryo and the central cell develops into the endosperm. The remaining cells—synergids at the micropylar end and antipodals at the chalazal end—degenerate.

16. While planning for an artificial hybridization programme involving dioecious plants, which of the following steps would not be relevant:

a. Dusting of pollen on stigma

b. Bagging of female flower

c. Collection of pollen

d. Emasculation

Key Answer: d. Emasculation

Explanation: Emasculation is the removal of anthers from a bisexual flower to prevent self-pollination. Since dioecious plants produce unisexual female flowers, there are no anthers to remove, making this step irrelevant.

17. In the embryos of a typical dicot and a grass, true homologous structures are:

a. Coleorhiza and coleoptile

b. Coleoptile and scutellum

c. Cotyledons and scutellum

d. Hypocotyl and radicle.

Key Answer: c. Cotyledons and scutellum

Explanation: The scutellum is the name given to the single, large, shield-shaped cotyledon found in grass (monocot) embryos. Therefore, it is biologically homologous to the two cotyledons found in a dicot embryo.

18. The phenomenon observed in some plants wherein parts of the sexual apparatus is used for forming embryos without fertilisation is called:

a. Parthenocarpy

b. Apomixis

c. Vegetative propagation

d. Sexual reproduction.

Key Answer: b. Apomixis

Explanation: Apomixis is a form of asexual reproduction that mimics sexual reproduction, where seeds (and embryos within them) are formed without the fusion of gametes (fertilization).

19. In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be:

a. Haploid

b. Diploid

c. A few haploid and a few diploid

d. With varying ploidy.

Key Answer: b. Diploid

Explanation: A megaspore mother cell is originally diploid (2n). If it bypasses meiosis during development, there is no reduction division, resulting in an embryo sac where all nuclei remain diploid.

20. The phenomenon wherein, ovary develops into a fruit without fertilisation is called:

a. Parthenocarpy

b. Apomixis

c. Asexual reproduction

d. Sexual reproduction

Key Answer: a. Parthenocarpy

Explanation: Parthenocarpy refers specifically to the development of a fruit without prior fertilization of the ovules. Such fruits are typically seedless (e.g., commercial bananas).