CBSE Class 12 Biology Sexual Reproduction In Flowering Plants Worksheet Set A Solved

• The cells of sporogenous tissues undergo meiotic division to form microspore tetrad. As the anther mature and dehydrate, the microspore dissociate and develops into pollen grains.

Very Short Answer Questions

Question. How many microsporangia are present in a typical anther of an angiosperm? 
Answer. Four

Question. Pea flowers produce assured seed sets. Give a reason.
Answer. Pea flowers are cleistogamous, i.e., anther and stigma lie close to each other in closed flowers. So when anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Thus, assured seeds are produced in pea.

Question. Write the function of scutellum. 
Answer. It provides nourishment and protection to the developing embryo.

Question. Name the part of gynoecium that determines the compatible nature of pollen grain.
Answer. Stigma

Question. Name the common function that cotyledons and nucellus perform. 
Answer. Cotyledons and nucellus provide nourishment.

Question. Which are the three cells found in a pollen grain when it is shed at the three-celled stage?
Answer. One vegetative cell and two male gametes.

Question. How is it possible in Oxalis and Viola plants to produce assured seed-sets even in the absence of pollinators? 
Answer. By presence of cleistogamous flowers. 

Question. How do flowers of Vallisneria get pollinated? 
Answer. In Vallisneria, the female flower stalk is long to reach the water surface to receive the pollen grains carried by water currents and then it gets coiled after pollination.

Question. What features of flowers facilitate pollination by birds?
Answer. Presence of a large quantity of nectar, bright colours of petal, fragrance and large flowers attract
birds from long distances.

Short Answer Questions

Question. Explain the function of each of the following:
(a) Coleorhiza
(b) Germ pores 
Answer. (a) Coleorhiza protects the radical of (monocot) embryo.
(b) Germ pores allow germination of pollen grain and formation of pollen tubes.

Question. Mention the reasons for difference in ploidy of zygote and primary endosperm nucleus in an angiosperm. 
                                                                          OR
In angiosperms, zygote is diploid while primary endosperm cell is triploid. Explain.
Answer. A zygote is formed by the fusion of haploid male gamete with the haploid egg to form a diploid cell; whereas, primary endosperm nucleus (PEN) is formed by the fusion of haploid male gamete with two haploid polar nuclei, forming a triploid nucleus.

Question. Some angiosperm seeds are said to be ‘albuminous’, whereas few others are said to have a perisperm. Explain each with the help of an example.
Answer. Albuminous seeds are those which retain a part of endosperm as it is not completely used up during embryo development. For example, in wheat and maize. In some seeds remnants of nucellus are also persistent. This residual, persistent nucleus is the perisperm. For example, in black pepper and beet.

Question. (a) Mature seeds of legumes are non-albuminous. Then, can it be assumed that double fertilisation does not occur in legumes? Explain your answer.
(b) List the differences between the embryos of dicot (pea) and monocot (grass family).
Answer. (a) No it cannot be assumed so because fertilisation does takes place but the endosperm is consumed during embryo development
(b)

Question. Draw a sectional view of an apple and label the different parts of an ovary in it. Fruits develop from an ovary. Then why is apple referred to as a false fruit? 
Answer. In apple, the thalamus also contributes to fruit formation. Therefore, it is called a false fruit.

Question. What is pericarp? Mention its functions.
Answer. The wall of the ovary that develops into wall of the fruit is called pericarp.
Functions: (i) Protects the seed till its maturity.
(ii) Helps in seed dispersal.

Question. A non-biology person is quite shocked to know that apple is a false fruit, mango is a true fruit and banana is a seedless fruit. As a biology student how would you satisfy this person?
Answer. In apple only the thalamus (along with ovary) portion contributes to fruit formation. Therefore, it is a false fruit. Mango develops only from the ovary, therefore it is a true fruit.
Banana develops from ovary but without fertilisation. The method is known as parthenocarpy.
Since there is no fertilisation, no seeds are formed in banana.

Question. Why are some seeds referred to as apomictic seeds? Mention one advantage and one disadvantage to a farmer who uses them. 
Answer. Seeds that are produced without fertilisation are referred to as apomictic.
Advantage: Desired characters are retained in offspring (progeny) as there is no segregation of characters in offspring (progeny). Seed production is assured even Apomictic seeds are economical as they can be used to Disadvantage: Cannot control accumulation of deleterious genetic mutation. These are usually
restricted to narrow ecological niches and lack ability to adapt Q. 42. Explain any two ways by which apomictic seeds get developed. 
Ans. Ways by which apomictic seeds develop are:
(i) A diploid egg is formed without reduction division which develops into embryo without fertilisation.
(ii) Some cells of the nucellus, which are diploid in nature, start dividing and without fertilisation develop into embryo.

Question. List the two steps that are essential for carrying out artificial hybridisation in crop plants and why. 
Answer. (a) Selection of parents: Only those plants should be selected which have desired traits.
Emasculation: Removal of anthers from flower before they are mature and dehisce.
(b) Crossing over: Pollen grains from selected male plant is collected and transferred to the female plant after which it is bagged.

Question. Explain the steps that ensure cross pollination in an autogamous flower. 
Answer. A bisexual flower is emasculated at unopened stage 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. Artificial pollination is then performed when the stigma is ready and the flower is rebagged.

Question. (a) How are parthenocarpic fruits produced by some plants and apomictic seeds by some others? Explain.
(b) When do farmers prefer using apomictic seeds? 
Answer. (a) Parthenocarpic fruits are formed when ovary develops into fruit without fertilisation.
Apomictic seeds are formed when formation of seeds take place without fertilisation.
(b) To maintain hybrid characters (year after year in a desired plant) and to avoid buying hybrid seeds every year (expensive seeds) farmers prefer using apomictic seeds. 

Question. What is agamospermy? How is agamospermy different from parthenogenesis and parthenocarpy?
Answer. The phenomenon of asexual reproduction that mimics sexual reproduction as it forms seed without fertilisation is called agamospermy.
Parthenogenesis refers to the development of unfertilised egg into an adult individual. On the other hand, parthenocarpy is the phenomenon of formation of fruits without fertilisation of an ovary.

Question. Name the part of the flower which the tassels of the corn-cob represent. 
Answer. Tassels of corn cob represent staminate inflorescence (cluster of male flowers), so they represent androecium  (male reproductive part) of the flower.

Question. Give an example of a plant which came into India as a contaminant and is a cause of pollen allergy. 
Answer. Parthenium or carrot grass is an example of a plant which came to India as a contaminant and is a major contributor to pollen allergy.

Question. What is pollen-pistil interaction and how is it mediated? 
Answer.  Pollen-pistil interaction is the group of events that occur from the time of pollen deposition over the stigma to the time of pollen tube entry into ovule. The dialogue between pollen grain and the pistil is mediated by chemical components  of the pollen interacting with those of the pistil. The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). This is followed by its acceptance or rejection.

Question. State the function of filiform apparatus found in mature embryo sac of an angiosperm.
Answer. Filiform apparatus refers finger-like projections which arise from cell wall of the synergid and penetrate into the cytoplasm of the central cell. These are present at the micropylar tip of synergids. They play an important role in distribution of nutrients in the embryo sac, secretion of substances that attract pollen tube thereby guiding the pollen tube into synergid and also provide mechanical strength to synergids.

Question. Differentiate between xenogamy and geitono- gamy.
Answer. 

Question. Explain the function of germ pores.
Answer.  Germ   pores   are   prominent    apertures   of pollen grain where exine is thin or absent hence, sporopollenin is absent and intine is thickened. These are the regions where intine  comes out  to form a pollen tube after pollination.

Question. Write the characteristic features of anemo- philous flowers. 
Answer.  The characteristic features of anemophilous flowers are well exposed stamens light, small, winged or dusty pollen grains and large, often-feathery and exposed stigma to trap air-borne pollen grains.

Question. Give reason why anthers of angiosperm flowers are described as dithecous.
Answer. Anthers  of most  angiosperms  (flowering plants) contain two anther lobes, hence are called dithecous.

Question. Mention any one application of a pollen bank.
Answer. Pollen banks are used to store pollen grains for long time, which can be used in plant breeding programmes. In pollen banks, pollens are stored in liquid nitrogen at a temperature of –196°C.

Question. All papaya plants bear flowers but fruits are seen in some. Explain.
Answer. Papaya plant is dioecious plant and bears male and female flowers on different plants i.e., male plant and female plant. Fruit is formed by the female part of the  flower after fertilisation. Following double fertilisation, i.e., fusion of one male gamete with egg cell and the other male gamete with secondary nucleus. Ovules turn into seeds and ovary turns into fruits.
As these female structures are found only on female papaya  plants  hence  fruits  are  present  only  on female papaya plant whereas male papaya plant only produces gametophytes, i.e., pollen grains which bear male gametes.

Question. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain.
Answer. Pea plant is monoecious plant i.e., bearing both male and female flowers on same plant. Thus, a single pea plant can produce viable seeds after pollination and fertilisation. However, a papaya plant is dioecious plant i.e., bearing male and female flowers on different plants and requires cross pollination for production of viable seeds. Thus, in absence of either stamens or pistils, fertilisation will not take place and hence viable seeds will not be produced.

Question. Gynoecium of a flower may be apocarpous or syncarpous. Explain with the help of an example each. 
Answer. Gynoecium represents the female reproductive part of a flower. Gynoecium is called apocarpous if the carpels are free, e.g., Michelia. It is called syncarpous if the carpels are fused, e.g., Papaver (poppy).

Question. Why do hermaphrodite angiosperms develop outbreeding devices? Explain any two such devices with the help of examples.
Answer. Hermaphrodite angiosperms develop out breeding devices to avoid self pollination and encourage cross pollination. Two outbreeding devices which ensure cross pollination are as follows:
(i) Dichogamy : Anthers and stigmas mature at different times in a bisexual flower. It is of two types: (a) Protandry : Anthers mature earlier than stigma of the same flower. Their pollen grains become available to stigmas of the older flowers, e.g., Sunflower, Salvia. (b) Protogyny : Stigmas mature earlier so that they get pollinated before the anthers of the same flower develop pollen grains, e.g., Mirabilis jalapa, Gloriosa, Plantago.
(ii) Self sterility (Self incompatibility) : Pollen grains of a flower do not germinate on the stigma of the same flower due to presence of similar self sterile gene (S1S3 in pistil and S1 or S3 in pollen grain) e.g., tobacco, potato, crucifers.

Question. What is the role of endothecium and tapetum in an anther? 
Answer. Endothecium performs the function of protection in the young anther and is involved in dehiscence of the mature anther.
Role of tapetum in an anther is as follows:
(i) Nourishment of the developing microspore mother cells and pollen grains.
(ii) It produces lipid rich ubisch granules containing sporopollenin for exine formation, pollenkitt in case of entomophilous plants, special proteins for the pollen grains to recognise compatibility and hormone IAA.
(iii) It secretes enzyme callase responsible for the degradation of callose wall around pollen tetrad.

Question. Differentiate between autogamy, geitonogamy and xenogamy. 
Answer. 

Question. Why does a breeder need to emasculate a bisexual flower? Mention a condition in a flower where emasculation is not necessary.
Answer. Emasculation is removal of stamens from the floral buds of female parent. A breeder needs to emasculate a bisexual flower to eliminate the chances of self pollination. Emasculation is not required if the flowers are unisexual. However, flowers must be kept covered by bags to protect them from contamination by unwanted pollen grains.

Question. (a) Mention any four strategies adopted by flowering plants to prevent self-pollination.
(b) Why is geitonogamy also referred to as genetical autogamy? 
Answer. (a) In self pollination, the pollen grains are transferred from the anther of a flower to the stigma of either the same or genetically similar flower. In this process the parental characters are sustained and new useful characters are seldom introduced in next generation. So, to prevent this, some strategies are adopted by the flowering plants. These are as follows:
– Dichogamy : Male and female sex organs of a bisexual flower mature at different times.
– Self sterility : The pollen of a flower has no fertilising effect on the stigma of the same flower.
– Pollen prepotency : In some plants when the stigma receives pollen from the same flower as well as from the other flower simultaneously the foreign pollen germinates quickly and fertilises the ovule.
– Herkogamy : It is the presence of natural and physical barriers between androecium and gynoecium which help in avoiding self pollination.
(b) In geitonogamy pollen grains of one flower are transferred to the stigma of another flower belonging to either the same plant or genetically similar plant. Thus, geitonogamy is also referred to as genetical autogamy.

Please click on below link to download CBSE Class 12 Biology Sexual Reproduction In Flowering Plants Worksheet Set A Solved