Question 1

Explain the different types of calyx.

Accepted Answer

Different types of calyx are as follows,. Persistent calyx: the calyx does not wither off after fertilization or during fruit development  but is present attached to the fruitExample: Brinjal, Solanum nigrum etc. Caducous: deciduous, the calyx withers off much before the formation of fruit example, poppy. Pappus calyx: feathery calyx, non green in color Example: members of family Asteraceae. Petalloid calyx: The sepal are non-green usually of a different color, appearing like petals. Example: Michelia (sepals are yellow in color)

Question 2

The perianth term used when

Accepted Answer

The perianth term used when calyx and corolla are similar. The perianth is the non-reproductive part of the flower and structure that forms an envelope surrounding the sexual organs, consisting of the calyx (sepals) and the corolla (petals).

Question 3

Ligulate/strap-shaped corolla occurs in sunflower in

Accepted Answer

Ligula means strap-shaped. In members of Compositae (sunflower), a ligule is the strap-shaped, an elongated tongue of the corolla of a ray floret or ligulate flower. Lingule is the hairy outgrowth at the junction of the ray of florets formed by the fusion of petals in a strap-shaped structure towards the upper end.

Question 4

Obdiplostemonous condition is that in which the stamens are in two whorls and

Accepted Answer

Obdiplostemonous condition of stamens occurs when stamens of the outer whorl are opposite the petals and those of the second whorl alternate with the members of the first whorl. The flowers have twice as many stamens as petals, those of the outer set being opposite the petals.

Question 5

Corolla in a China rose are

Accepted Answer

Hibiscus rosa-sinensis or China rose is a species from the family Malvaceae. The flowers of this plant are bisexual, actinomorphic, pentamerous, hypogynous and solitary. The corolla is made up of five petals, polypetalous but fused at the base.

Question 6

Anthers are fused and filaments are free in

Accepted Answer

Syngenesious is the condition in which the anthers of the stamens are fused while the filaments remain free. it is a characteristic feature of the family Asteraceae and can be seen in the flowers belonging to the family like sunflower (Helianthus) and Tridax. A. Sunflower shows syngenesious condition.B. Gossypium shows Polyadelphous condition.C. Murraya shows polyadelphous condition. D. Petunia shows epipetalous condition.Hence, the correct answer is 'Sunflower'

Question 7

Differentiate:Sycarpous & apocarpous condition

Accepted Answer

Apocarpous ovary: The flowers with apocarpus ovary have more than one carpel. These carpels are free. Eg: lotus and rose flowers.Syncarpous ovary: The flowers with syncarpous ovary have more than one carpel. However, these carpels are fused. Eg: flowers of tomato and mustard.

Question 8

250 microsporocytes will give rise to ........... microspores.

Accepted Answer

The microsporangia produce the microsporocyte which is also known as the microspore mother cell, which then creates four microspores through meiosis. The microspores divide to create pollen grains. Therefore, 250 microsporocytes will give rise to 250 x 4 = 1000 microspores.

Question 9

The number of meiotic divisions required to produce 400 seeds in a pea plant is

Accepted Answer

During sexual reproduction in angiosperms, meiosis occurs in microspore and megaspore mother cells. For the formation of 400 seeds in the pea plant, we require 400 male and 400 female gametes. In one meiotic division, one microspore mother cell in the anther forms 4 microspores, each of which develops as a pollen grain. For the production of 400 male gametes, the number of meiotic division is 400/4= 100. In one meiotic division, one megaspore mother cell produces one female gamete (4 produce, 3 degenerated). For the production of 400 female gametes, the number of meiotic division is 400.So, the total number of meiotic divisions are 100+400=500.

Question 10

Tapetal cells show

Accepted Answer

Tapetum is the innermost layer of anther wall. It is single layered and the cells have dense cytoplasm and prominent nuclei. A very common feature of the Tapetum is that total DNA content increases enormously in the meiotic prophase. This may arise due to many reasons one of which is endomitosis. Endomitosis is also known as Endopolyploidy. It is a type of mitosis in which there is chromosome duplication and the chromatids separation take place within the intact nuclear membrane because there is no spindle formation. This results in large polyploid nucleus.

Question 11

Explain sexual reproduction in plants.

Accepted Answer

1. Pollen grains are produced inside the anther through the process of meiosis in microspores mother cells (microsporogenesis). Pollen grains are also called the male gametophyte and they contain a tube nucleus and two male gametes. 2. Inside the ovule, megaspore mother cell undergoes meiosis to make a 7-celled-8-nucleated female gametophyte. It has two synergids, one egg cell, one central cell with two polar nuclei and three antipodals.3. During pollination, pollen grain is transferred to the stigma from the anther.4. Pollen grain germinates to produce the pollen tube which carries the two male gametes to the female gametophyte via the style.5. The two male gametes are released in one of the synergids.6. One of the male gametes fuses with the egg cell and forms the zygote. This is called syngamy.7. The other male gamete fuses with the polar nuclei of central cell and forms triploid primary endosperm nucleus. This is called triple fusion.8. The event of triple fusion and syngamy is called double fertilization.9.  The zygote develops into an embryo and the primary endosperm nucleus forms the endosperm.

Question 12

How many meiotic and mitotic division are required for the formation of fully mature male gametophyte from microspore mother cell in angiosperm?

Accepted Answer

. Microspore mother cell undergoes one meiotic division and gives four microspores.. Then, the nucleus within the microspore divides mitotically to form one big vegetative nuclei and one small generative nuclei.. After pollination, the generative cell after entering into the pollen tube divide mitotically to form two non-motile male gametes.. Hence, one meiotic division and two mitotic division are required for the formation of fully mature male gametophyte from microspore mother cell in angiosperm.So, the correct answer is '1, 2'.

Question 13

Describe the development of the male gametophyte from the microspore mother cell to the production of sperm.

Accepted Answer

Formation of the male gametophyte in flowering plants takes place within specialized male reproductive organs called the stamens. During microsporogenesis, diploid pollen mother cells undergo meiotic division to produce tetrads of haploid microspores. This stage is completed when distinct unicellular microspores are released from the tetrad by the activity of a mixture of enzymes secreted by the tapetum, the inner nutritive layer of the stamen. This results into production of the sperm cell.

Question 14

How tapetal cells could become bi-nucleate?

Accepted Answer

Tapetal cells are very large cells with more than one nucleus. They assist with pollen grain growth and development. Tapetal cells undergo endomitosis where the nucleus in the nuclear membrane splits, but cytokinesis does not happen. They become bi / multi nucleate because of this. Usually the cells are larger and have more than one nucleus per cell. The nuclei of tapetal cells also split as the sporogenous cells undergo mitosis. Sometimes, this mitosis is not normal due to which many cells of mature tapetum become multinucleate. It is also possible to see polyploidy and polyteny at times.

Question 15

Microsporogenesis : As the anther develops, the cells of the sporogenous tissue undengo meiotic division to form microspore tetrade. What would be the ploidy of the cells of the tetrad?

Accepted Answer

Formation of microspores inside the microsporangia of seed plants, Diploid cell in microsporangium undergoes meiosis and gives rise to four haploid microspores. Four nuclei are arranged tetrahedrally are soon invested with cell walls. Each and every cell in a microspore tetrad is haploid!! Tetrad just means there are four cells all of which are haploid in nature and are formed by reduction division or meiosis in microspore mother cells.

Question 16

A fertilised egg of a plant has 40 chromosomes. The number of chromosomes present in the microscope mother cell is?

Accepted Answer

Fertilization in plant occurs when haploid gametes meet to create a diploid zygote, which develops into an embryo. So if the fertilized egg of a plant has 40 chromosomes, it must be the combination of its parent's chromosomes, half from microspore and half from megaspore mother cell.So the correct answer is '20'.

Question 17

Explain the structure of microsporangium and write the functions of its different layers.

Accepted Answer

Microsporangium is the sporangial structure which contains microspores which are the pollen sacs giving rise to male gametes in an angiosperm. A microsporangium is circular in outline in transverse section and is usually surrounded by four wall layers. The outermost is the single layer of the epidermis. The second layer is endothecium, where cells develop thickenings. The middle layer is made up of 2-4 cells. The innermost layer is tapetum, which provides nutrition to the developing pollen cells. The cells of tapetum may be multinucleate. The outer three layers are protective in function. They also help in dispersal of pollens by dehiscing themselves. There are four pollen sacs present inside. The centre of the microsporangium comprises of compact sporogenous tissue. These tissues undergo meiotic divisions to form microspore tetrads, that further divide to form pollen grains.

Question 18

Explain the transverse section of young anther with a labelled diagram.

Accepted Answer

Male reproductive part of a plant consists of an anther and the filament. Anther is bilobed containing 4 microsporangia in angiosperms so it is known as dithecous anther. Each microsporangium contains spores that produce male gametes. It has following layers:. The outermost layer is known as the epidermis.. Inner to the epidermis is the layer of endothecium.. Inner to endothecium, there are 2-3 cell middle layers that usually disintegrate during anther maturation.. The innermost layer is known as tapetum.Inner to the tapetum are the microspore mother cells which give rise to pollen grains through meiotic division.

Question 19

Explain the structure of male gametophyte of angiosperms with the help of a suitable diagram?

Accepted Answer

Microspore or the pollen grain represents the initial cell of male gametophyte. During germination, the cytoplasm of the pollen grain comes out in the form of a tube like structure called pollen tube through the germ pore. The pollen tube carries the tube nucleus cytoplasm and generative cell. The pollen tube grows through the style towards the ovule due to some chemical stimulus inside the ovary. The generative cell of the pollen grain divides by mitosis and forms two haploid non motile gametes. Pollen tube consisting of the two male gametes and a degenerating tube nucleus represents the male gametophyte.

Question 20

Function of obturator for any ovular structure is to

Accepted Answer

Any ovular structure which helps in directing the growth of pollen tube towards the micropyle is generally referred to as obturator. Obturators exhibit great variation in their origin, morphology, anatomy and extent of development. They may originate from placenta or funiculus or both. The most common type of obturator is one formed by local swelling of the funiculus as in families Acanthaceae, Anacardiaceae, Lamiaceae, Magnoliaceae etc.

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Solution for Class 12, Biology, Sexual Reproduction in Flowering Plants

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