CBSE Class 12 Biology Reproduction In Flowering Plants Worksheet Set B

Very Short Answer Questions

Question. Name a plant in which dichogamy is found.
Answer. Magnolia

Question. Why do pollen grains of some flowers trigger ‘sneezing’ in some people?
Answer. They result in an allergic reaction.

Question. What is nucellus?
Answer. The body of the ovule consists of a mass of parenchymatous cells rich in reserve food material which is called nucellus.

Question. Who discovered double fertilisation in angiosperms?
Answer. S. G. Nawaschin (1897) discovered double fertilisation in angiosperms.

Question. State the function of filiform apparatus found in mature embryo sac of an angiosperm.
Answer. The filiform apparatus guides the pollen tube into the synergid.

Question. Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
Answer. False fruits are those fruits in which accessory floral parts also contribute to fruit formation. In apple, the thalamus also contributes to fruit formation. Therefore, it is called a false fruit. The fruit develops from the ovary of the flower.

Question. How many cells are found in a typical embryo sac?
Answer. There are seven cells in a typical embryo sac. These are one egg cell, two synergids, three antipodal cells and a central cell.

Question. How many germ pores are there in the pollen grains of monocots and dicots?
Answer. There are three germ pores in dicots and one in monocots.

Question. Name the tissue present in the fertilised ovules of angiospermic plants that supplies food and nourishment to the developing embryo.
Answer. Endosperm

Question. What is funiculus?
Answer. Funiculus is the stalk of ovule that attaches it to the placenta.

Question. What is bagging technique? How is it useful in a plant breeding programme?

Answer. It is the covering of female plant with butter paper germ to avoid their contamination from foreign pollens during breeding programme.

Question. Mention two strategies evolved to prevent self-pollination in flowers.
Answer. The two strategies evolved to prevent self-pollination in flowers are:
(i) Maturation of anthers and stigma at different time periods in a bisexual flower prevents selfpollination (dichogamy).
(ii) Production of unisexual flowers.

 Short Answer Questions

Question. How does the Mediterranean orchid Ophrys ensures its pollination by bees? 
Answer. The petals of the Ophrys resemble the female of a bee species in size, colour and odour. Male bee mistakes the Ophrys for female bee and tries to copulate. Few pollen grains adhered to the body of the male bee fall over stigma of the flower thereby leading to pollination showing sexual deceit.

Question. Why should a bisexual flower be emasculated and bagged prior to artificial pollination?
Answer. A bisexual flower is emasculated to prevent self-pollination in the flower and it is bagged after emasculation to prevent contact of unwanted pollen grain with the stigma of the flower.

Question. Write the cellular contents carried by the pollen tube. How does the pollen tube gain its entry into the embryo sac? 
Answer. Pollen tube carries two male gametes.
Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus which guides the entry of pollen tube into egg cell.

Question. If you squeeze a seed of orange you might observe many embryos of different sizes? How is it possible? Explain. 
Answer. In orange, the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into a number of embryos of different sizes.

Question. Double fertilisation is reported in plants of both, castor and groundnut. However, the mature seeds of groundnut are non-albuminous and castor are albuminous. Explain the postfertilisation events that are responsible for it. 
Answer. The development of endosperm (preceding the embryo) takes place from primary endosperm nucleus (PEN) in both, castor and groundnut.
The developing embryo derives nutrition from endosperm.
PEN undergoes repeated division to give free nuclei. Subsequently cell wall is formed and endosperm becomes cellular. At this stage endosperm is retained in castor or is not fully consumed but in groundnut endosperm is consumed by growing embryo.

Question. In a flowering plant a microspore mother cell produce four male gametophytes while a megaspore mother cell form only one female gametophyte. Explain. 
Answer. Male gametophytes are formed by meiosis of single microspore mother cell whereas female gametophytes are formed by meiosis of single megaspore mother cell to produce 4 megaspores, out of which 3 degenerate and only one survives. The surviving megaspore undergoes mitotic division to form the female gametophyte.

Question. Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm. 
Answer.  

S.No. Vegetative cell Generative cell
(i) It is bigger in size. It is smaller and floats in the cytoplasm of vegetative cell.
(ii) It has food reserves. It gives rise to two male gametes.

Question. What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer. Triple fusion is fusion of one male gamete and two polar nuclei (or secondary nucleus; if the two have already fused) in the central cell of embryo sac to form primary endosperm nucleus. 
It takes place in the central cell of an embryo sac. Three nuclei are involved in triple fusion, i.e., one male nucleus and two polar nuclei in the central cell.

Question. Explain any two devices by which autogamy is prevented in flowering plants.
Answer.  (i) Male and female flowers are present on different plants.
(ii) The stamens and stigma of a bisexual flower mature at different times.
(a) Anthers mature earlier than the stigma and release pollens.
(b) The stigma matures earlier than the anther.
(iii) Flowers are self-sterile or self-incompatible.
(iv) Chasmogamous flowers are present with exposed stamens and stigma which facilitate crosspollination.
(Any two)

Question. Geitonogamous flowering plants are genetically autogamous but functionally cross-pollinated.
Justify. Give similarity of geitonogamy with autogamy and xenogamy. 
Answer. Geitonogamous flowers are genetically autogamous because both male and female flowers are borne on the same plant. They are functionally cross-pollinated because the pollen from one flower is transferred to the stigma of a different flower.

Question. Banana is a parthenocarpic fruit whereas oranges show polyembryony. How are they different from each other with respect to seeds?
Answer. Banana develops from an ovary without fertilisation having non-viable seeds so it is called parthenocarpic fruit. An orange contain seeds with more than one embryo thus, it shows polyembryony.

Question. (a) You are given castor and bean seeds. Which one of the two would you select to observe the endosperm?
(b) The development of endosperm precedes that of embryo in plants. Justify.
Answer. (a) Castor
(b) Endosperm stores reserve food materials. It provides nutrition to the developing embryo, therefore its development precedes that of embryo.

Long Answer Questions

Question. What will be the ploidy of the cells of the nucellus, microspore mother cell, the functional megaspore and female gametophyte? 
Answer. Nucellus : Diploid
Microspore mother cell : Diploid
The functional megaspore : Haploid
Female gametophyte : Haploid

Question. Why are angiosperm anthers called dithecous? Describe the structure of its microsporangium.
Answer. The anthers of angiosperms are called dithecous because they are bilobed and each lobe of anther has two theca.
Microsporangium is surrounded by four wall layers named as epidermis, endothecium, middle layer and tapetum. In young anther, a group of compactly arranged homogenous cells called sporogenous tissue occupies the centre of each microsporangium which produce microspores or pollen grains.

Question. The generative cell of a 2-celled pollen divides in the pollen tube but not in a 3-celled pollen. Give reasons. 
Answer. In a 3-celled pollen, the generative cell has already divided and formed 2 male gametes. Hence, it will not divide again in the pollen tube. As the generative cell has not divided in a 2-celled pollen, it divides in the pollen tube.

Question. Write the differences between wind-pollinated and insect-pollinated flowers. Give an example of each type.
Answer.  

S.No. Wind-pollinated flowers Insect-pollinated flowers
(i) These produce large numbers of pollen grains. These produce less number of pollen grains.
(ii) These are dull, nectarless and scentless. These are bright, scented and have nectar.
(iii) Stamens are long and protrude above petals. Stamens lie within the corolla tube.
(iv) The pollen grains are dry, light, small and smooth.For example, ragweed. The pollen grains are larger, heavier with appendages like hooks and barbs. For example, rose, sweet pea.

Question. (a) Name the organic material exine of the pollen grain is made up of. How is this material advantageous to pollen grain?
(b) Still it is observed that it does not form a continuous layer around the pollen grain. Give reason.
(c) How are ‘pollen banks’ useful? 
Answer.  (a) Sporopollenin
It is most resistant material to high temperature, strong acids on alkali and no enzymes can degrade it.
(b) Germs pores are present to allow pollen tube to emerge out for pollen germination.
(c) Pollen banks help in storing pollen grains for years for crop breeding programmes.

Question. (i) Write the characteristic features of anther, pollen and stigma of wind-pollinated flowers.
(ii) How do flowers reward their insect pollinators? Explain.
Answer. (i) The characteristics of wind-pollinated flowers are:
(a) Pollen grains are light in weight, non-sticky, dry and winged, so that they can be easily transported.
(b) Well-exposed stamens for easy dispersal of pollen grains in the wind.
(c) The stigma is sticky, large, feathery to trap pollen grains in air.
(d) Numerous flower are packed together to form inflorescence.
(d) The flowers are small and inconspicuous.
(ii) Insect pollinators are rewarded in following ways:
(a) The flowers offer floral reward like nectar and pollen grain.
(b) In some species floral reward provides safe place to lay eggs.

Question. When and where do tapetum and synergids develop in flowering plants? Mention their functions. 
Answer. Tapetum develop during microsporogenesis in the microsporangium (anther). It nourishes the developing pollen grains.
Synergids develop during megasporogenesis in the megasporangium (ovule). Synergids have filiform apparatus to guide the pollen tube into it.

Question. Explain the process of artificial hybridisation to get improved crop variety in (i) plants bearing bisexual flowers (ii) female parent producing unisexual flowers.
Answer. (i) In plants bearing bisexual flowers, the anthers are removed from the flower before they dehisce. This is called emasculation. The emasculated flowers are covered with a bag of butter paper to prevent contamination of stigma with unwanted pollen. This process is called bagging. When this stigma attains receptivity, mature pollen grains are dusted on the stigma and the flowers are rebagged to allow the fruits to develop.

Question. Where are the following structures present in a male gametophyte of an angiosperm? Mention the function of each one of them.
(a) Germ pore (b) Sporopollenin (c) Generative cell 
Answer.  (a) Germ pore: Exine of pollen grain. It is the site from where pollen tube emerges.
(b) Sporopollenin: Exine of pollen grains. It protects the pollen grains from high temperature, strong acids and alkali, enzymes and adverse conditions.
(c) Generative Cells: These are present in pollen grains. These give rise to two male gametes.

Question. Given below are the events that are observed in artificial hybridisation programme. Arrange them in the correct sequential order in which they are followed in the hybridisation programme.
(a) re-bagging; (b) selection of parents;
(c) bagging; (d) dusting the pollen on stigma;
(e) emasculation; (f) collection of pollen from male parent.
Answer. (b); e(); c(); f)(; d(); a().

Question. (a) Seeds offer several advantages to angiosperms. Describe any three such advantages.
(b) Why is banana called a parthenocarpic fruit? Would you call banana a true fruit? Give reason in support of your answer.
Answer. (a) Reproductive processes such as pollination and fertilisation are independent of water.
Following are their advantages:
(i) Better adaptive strategies for dispersal to new habitats.
(ii) Hard seed coat provides protection to young embryo .
(iii) Sexual reproduction—new genetic combinations.
(iv) Sufficient food reserves for the seedling.
(v) Basis of agriculture–storage of seeds can occur due to seed habit-dehydration and dormancy. (Any three)
(b) Banana fruit develops without fertilisation therefore, it is called parthenocarpic fruit. Yes, it is a true fruit because it develoryp.