Sexual Reproduction in Flowering Plants
Short questions and answers
One mark questions with answers
1. What are the two characteristics of sexual reproduction?
Answer: Meiosis and syngamy
2. What process in sexual reproduction makes the offspring look different from parents?
3. At what stage the pollen grains are generally liberated from the anther?
Answer: 2-celled stage
4. What is the alternative name of the embryo sac?
Answer: Female gametophyte
5. Why is grafting not possible in monocotyledons?
Answer: Monocots lack cambium, meristematic cells of the cambium play an important role in callus formation in grafting.
6. What is sporopollenin?
Answer: It is one of the components of outer spore wall (exine); it is a very hard substance and is resistant to physical and chemical disintegration.
7. Which layer of anther wall provides nutrition to the developing microspores?
8. What does the aril of litchi represent?
Answer: Aril represents to the third integument which develops from the base of the ovule.
9. Why the endosperm is haploid in gymnosperms and triploid in angiosperms?
Answer: In gymnosperms endosperm develops before fertilization by repeated divisions of the functional megaspore whereas in angiosperms it is formed as a result of triple fusion.
10. Which three nuclei take part in triple fusion?
Answer: One male gamete and two polar nuclei.
11. Which structure develops into fruit wall after pollination and fertilization?
Answer: Ovary wall
12. What is scutellum?
Answer: Cotyledon of the monocotyledonous embryo
13. What is the role of integuments of ovule after fertilization?
Answer: Integuments of ovule develop into seed coat
14. Which is the most common type of ovule found in angiosperms?
15. What is apomixis?
Answer: It is the substitution of sexual process by any such method which does not involve meiosis and syngamy.
Give one word technical term for the following:
1.Transfer of pollen grains from the anthers of a flower to the stigma of another flower born on the same plant.
Answer: Geitonogamy (self pollination)
2. Maturation of stamens and gynoecium at the same time
3. Flowers which always remain closed
4. Pollination of flowers by animals
5. The condition when plants bear unisexual flowers
6. The condition when gynoecium matures earlier than anthers
7. Formation of pollen grains from pollen mother cells
8. Development of embryo sac from megaspore
9. Innermost layer of the anther wall that provides nutrition to the microscopes
10. Cytokinesis where wall formation occurs once after meiosis I and again after meiosis II
Answer: Successive cytokinesis
11. An ovule in which functional megaspore is situated deep in the nucellar tissue
12. Development of gametopyte from sporophyte without meiosis.
13. Development of egg into embryo without fertilization
14. Normal process of sexual reproduction involving meiosis and fertilization
15. Development of sporophyte from the cells of gametophyte without fertilization
Two marks questions with answers
1. Differentiate between asexual reproduction and sexual reproduction.
Answer: In asexual reproduction new individuals are derived from a single parent, whereas in sexual reproduction two parents male and female are involved in the formation of new individuals. In case of asexual reproduction any vegetative part of plant such a stem, root or even few meristematic cells are capable of giving rise to new individual whereas in case of sexual reproduction vegetative parts has no role in sexual reproduction, fusion of male and female gametes results in the development of new individual.
2. What are antipodals?
Answer: The three cells situated at the chalaza end are called the antipodals. They are vegetative cells of the embyo sac. These cells generally degenerate soon after fertilization. Internally the antipodals are connected with the central cell by means of plasmodesmata.
3. A mature monosporic polygonum type of embryo sac is how many celled?
Answer: A mature monosporic polygonum type of embryo sac at the time of fertilization is seven celled and eight nucleate. Three cells at micropylar end which consists of two synergids and one egg cell. A single central cell with a diploid secondary nucleus in the middle part and. Three antipodals at the chalazal end.
4. What is a tetrasporic embryo sac?
Answer: An embryo sac is said to be bisporic when it develops from one of the two dyads formed as a result of first meiotic division of the megaspore mother cell, the other dyad degenerates. Sometimes, meiotic division of the megaspore mother cell is not accompanied by wall formation and as such, all the four nuclei take part in the development of the embryo sac. Such embryo sac is known as tetrasporic.
5. What is pollenkitt?
Answer: In insect pollinated flowers, the exine of the pollen grain is covered with a yellowish viscous and sticky substance called pollenkitt. This is a protective envelop which sticks to the body of the insect and helps in pollination
Three marks questions with answers
1. Explain briefly the structure of egg-apparatus.
Answer: This is a group of three cells situated at the micropylar end. The three micropylar cells are collectively known as egg-apparatus. They are pyriform in outline and are arranged in a triangular fashion. The centrally located cell is called the egg cell or oosphere. It bears peculiar wall thickenings called filiform apparatus towards the embryo sac membrane, a central or micropylar vacuole and a nucleus towards the chalazal end. The remaining two cells are called synergids or helper cells. The synergids show a filiform-apparatus attached to their upper wall, which is known to attract and guide the pollen tube. The synergids help in obtaining nourishment from the outer nucellar cells, and function as shock absorbers during the penetration of pollen tube into the embryo sac.
2. What is microgametogenesis?
Answer: It is the process of formation of male gametophyte from a pollen grain or microspore. The nucleus of a pollen grain divides mitotically to form a vegetative nucleus (tube nucleus) and a generative nucleus. The generative nucleus gets surrounded by cytoplasm to become generative cell. At this stage, pollen grain is two celled – a large vegetative cell and a small lenticular generative cell. The pollen grain may be discharged from the anther at this stage (two-celled stage). In most of the plants, three-celled condition is formed after pollen grain has been shed. The liberated pollen grain germinates on the stigma and produces a pollen tube. The pollen tube is covered by intine. It secretes pectinases and other hydrolytic enzymes to create a passage for it in the style. The pollen tube absorbs nourishment from the cells of the style for its growth. The tube nucleus descends to the tip of the pollen tube. The generative cell also passes into it and divides inside the pollen tube to form two male gametes.
3. Explain in brief the structure of pollen grain.
Answer: The wall or covering of pollen grain is called sporoderm. It is made of two layers. The outer layer is called exine. It is thick and ornamented. The exine is made of fatty substance called sporopollenin. It is biologically the most resistant substance and can withstand high temperature and strong acids and alkali.
The inner layer, called intine, is thin and uniform. It is made of pecto-cellulose. At the time of pollen germination, intine comes out of the germ pores in the form of a pollen tube.
The cytoplasm of pollen grain is rich in nutrients. The size and form of pollen grain and ornamentation of exine are characteristic of a plant.
4. What is tapetum? Mention the two types of tapetum and their functions.
Answer: Tapetum is the innermost layer of the wall made of multinucleate densely cytoplasmic cells. Two types of tapetum has been distinguished; secretary or granular tapetum( the cells of this type of tapetum remain in contact with the anther wall throughout) and amoeboid or plasmodial tapetum (the cells of amoeboid tapetum separate from the wall and move freely in the pollen chamber).
Functions of tapetum:
(1). It nourishes the developing microspore mother cell and pollen grains.
(2). It secretes enzymes and hormones
(3). Tapetum produces Ubisch granules for forming exine of pollen grain
(4). It secretes pollenkitt
(5). Secretes special proteins for the pollen grains to recognise compatibility.
5. What do you mean by incompatibility?
Answer: In the normal process of sexual reproduction the pollen grains after reaching the stigmatic surface germinate, form one or more pollen tubes through which male gametes are transported to the embryo sac. In the embryo sac one of the male gametes fertilizes the egg. Fertilization is followed by fruit and seed development. In many plants with perfect flowers fertilization and fruit and seed formation proceed normally after self pollination. This condition is known as self compatibility.
In other plants with perfect flowers, fertilization does not occur when the stigma is pollinated by pollens of the same flower. Even pollens from another flower of the same plant of from flowers of other plants of like genetic constitution with not result in fertilization. This is due to the failure of one or more post pollination events. This condition is referred to as incompatibility.