NCERT Sexual Reproduction in flowering plants class 12 chapter 2 Explanation Question and Answer
Sexual Reproduction in flowering plants class 12 taken from NCERT Book In this we are all the concepts. are covered and very easy understand to students chapter 2 Read this and clear and All the doubts .
Sexual Reproduction in flowering class 12 Intoduction
Sexual reproduction in flowering plants is a crucial and fascinating process centered around the flower. Flowers, with their unique structures, facilitate the transfer of pollen (containing male gametes) to the stigma. This pollination leads to the formation of seeds through the fusion of male and female gametes inside the ovule, housed in the ovary. After fertilization, the ovary transforms into a fruit, protecting the seeds. This process not only ensures the continuation of plant
Sexual Reproduction in flowering class 12 key features (Important Notes)
- Flower Structure:
- Sexual reproduction in flowering plants centers around the flower, the specialized reproductive organ. Flowers typically consist of sepals, petals, stamens (male reproductive organs), and carpels (female reproductive organs).
- Pollination is the transfer of pollen grains (containing male gametes or sperm cells) from the anther to the stigma. This can occur through various agents such as wind, insects, birds, or animals.
- After successful pollination, the pollen tube grows down the style and enters the ovule in the ovary. Fertilization involves the fusion of the male gamete (sperm) with the female gamete (egg) inside the ovule.
- Seed Formation:
- Fertilization results in the formation of a zygote, which develops into an embryo. The ovule transforms into a seed, containing the embryonic plant, stored food, and a protective seed coat.
- Fruit Development:
- The ovary surrounding the ovule develops into a fruit, protecting the seeds and aiding in their dispersal. Fruits can be fleshy, dry, or specialized structures adapted for dispersal by various means.
Sexual Reproduction in flowering class 12 definition
Sexual reproduction in flowering plants involves the fusion of male and female gametes through pollination and fertilization, leading to seed and fruit formation, ensuring genetic diversity and species propagation.
Sexual Reproduction in flowering class 12 Explanation
are we not lucky that plants reproduce sexually? the myriads of flowers that we enjoy gazing at the scents and the perfumes that we swoon over. the rich colours that attract us. are all there as an aid to sexual repruduction. flowers do not exist only for us to be used for our ownn selfishness. all flowering plants show sexual reproduction. a look at the diversity of structures of the inflorescences, flowers and floral parts shows an amazing range of adaptaions to ensure formation of the end products of sexual reproduction, the fruits and seeds, In this chapter.let us understand the morphology, structure and the processes of sexual reproduction in flowering plants (angiosperms)
FLOWER – A FASCINATING ORGAN OF ANGIOSPERMS
Human beings have had an intimate relationship with flowers since time immemorial, flowers are objects of aesthetic, ornamental, social, religious and cultural value they have always been used as symbols for conveying important human feelings such as love, affection, happiness, grief mouring, etc list at least five flowers of ornamental value that are commonly cultivated at
homes and in garden, find out the names of five more flowers that are used in social and cultural celebration in your family. have you heard of floriculture -what does it refer to ?
To a biologist, flowers are morphological and embryological marvels and the sites of sexuall reproduction. In class XI you have read the various parts of a flower. figure 2.1 will help you recall the parts of a typical flower.can you name the two parts in a flower in which the two most important units of sexual reproduction develop?
PRE-FERTILISATION: STRUCTURES AND EVENTS
Much before the actual flower is seen on a plant, the decision that the plant is going to flower has taken place. several hormonal and structural changes are initiated which lead to the differenciation and further development of the floral primordium. inflorecences are formed which bear the floral buds and then the flowers.
IMeaning of this word inflorecences : nflorescences refer to the arrangement of flowers on a plant’s stem, describing how they are organized into clusters or groups.
In the flower the male and female reproductive structures. the androecium and the gynoecium differentiate and develop. you would recollect that the androecium consists of a whorl of stamens representing the male reproductive organ and the gynoecium represents the female reproductive organ.
Figure. 2.2 shows the two parts of a typical stamen the long and slender stalk called the filament, and the terminal generally bilobed structure called the another. the proximal end of the filament is attached to the thalamus or the petal of the flower.
the number and length of stamens are variable in flowers different species, if you were to collect a stamen each from ten flowers (each from different species ) and arrange them on a slide, you would be able to appreciate the large variation in size seen in nature.
careful observation of each stamen under a dissecting microscope and making neat diagrams would elucidate the range in shape and attachement of anthers in different flowers. a typical angiosperm anther is bilobed with each lobe having two theca, i:e they are dithecous figure. 2.2 often a longitudinal groove runs lengthwise separating the theca.
Let us understand the various types of tissues and their organisation in the transverse section of an anther figure. 2.3 the bilobed nature of an anther is very distinct in the transverse section of the .the anther is a four sided (tetragonal ) structure consisting of four microsporangia located at the corners, two in each lobe.
The microsporangia develop further and become pollen sacs. they extend longitudinally all through the length of an anther and are packed with pollen grains. structure of microsporangium: in transverse section, a typical microsporangium appears near circular in outline, it is generally surrounded by four wall layers figure 2.3 the epidermis, endothecium, middle layers and the tapetum. the outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
Meaning of this word longitudinally : Longitudinally refers to the direction aligned with the length of an object or organism.
The innermost wall layer is the possess dense cytoplasm and generally have more than one nucleus. can you think of how tapetal cells could become bi-nucleate? when the anther is young. a group of compacity arranged homogenous cells called the sporogenous tissue occupies the centre of each microsporangium.
As each cell the sporogenous tissue is capable of giving rise to a microspore tetrad. each one is a potential pollen or microspore mother cell (PMC) the process of formation of microspores from a pollen mother cell through meiosis is called microsporogenesis. the microspores, as they are formed. are arranged in a cluster of four cells-the microspore tetrad figure. 2.3 as the anthers mature and dehydrate. the microspores dissociate from each other and develop into pollen grains figure. 2.3 inside each microsporangium several thousands microspores or pollen grains are formed that are released with the dehiscence of anther figure. 2.3
Meaning of this word microsporogenesis: Microsporogenesis is the process of formation and development of microspores within the microsporangia of a plant, leading to the production of male gametophytes.
pollen grain: the pollen grains represents tha male gametophytes. if you touch the opened anthers of hibiscus or any other flower you would find deposition of yellowish powdery pollen grains on your fingers. sprinkle these grains on a drop water taken on a glass slide and observe under
a microscope. you will really be amazed at the variety of architecture -sizes, shapes colours, designs-seen on the pollen grains from different species figure. 2,4 pollen grains are generally spherical measuring about 25-50 micrometers diameter. it has prominent two-layered wall the hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic material known. it can withstand high temperature and strong acids and alkali.
No enzyme that degrades sporopollenin is so far known. pollen grain exine has prominent apertures called germpores where sporopollenin is absent. pollen grains are welll presevred as fossils because of the presence of sporopollenin. the exine exhibits a fascinating array of patterns and designs. why do you think exine should be hard? what is the function of germ pore? the inner wall of the pollen grain is called the intine. it is a thin and continuous layer made up of cellulose and pectin. the cytoplasm of pollen grain is surrounded by a plasma membrane.
when the pollen grains is nature it contains two cells, the vegetative cell and generative cell figure. 2.5b the vegetative cell is bigger, has aboundant food reserve and a large irregulary shaped nucleus. the generative cell is small and floats in the cytoplasm of the vegetative cell. it is spindle shaped with dense cytoplasm and a nucleus. In over 60 percent if angiosperm,
pollen grains are shed at this 2 celled stage. In the remaining spacies. the generative cell divideds mitotically to give rise to the two male gametes before pollen grains are shed 3 celled stage.
pollen grains are rich in nutrients, it has become a fashion in recent years to use pollen tablets as food supplements. In western countries, a large number of pollen products in the form of tablets and syrups are available in the marker. pollen consumption has been claimed to increase the performance of anthletes and race horses figure. 2.6
when once they are shed. pollen grains have to land on the stigma before they lose viability if they have to bring about fertilsation how long do you think the pollen grains retain viability ? the period for which pollen grains remain viable is highly variable and to some extend depends on the prevailing temperature and humidity. In some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release,
And in some members of Rosaceae, Leguminoseae and solanceae, they maintain viability for months, you may have heard of storing semen/sperms of many animals including humans for artificial insemination.it is possible to store pollen grains of a large number of species for year in liquid nitrogen -196oC such stored pollen can be used as pollen banks, similar to seed banks, in crop breeding programmers.
Class XI arising from the placenta are the megasporangia, commonly called ovules, the number of ovules in an ovary may be one wheat, paddy, mango to many (papaya, water melon, orchids)
The Megasporangium ovule: let us familiarise ourselves with the structure of a typical angiosperm ovule figure. 2.7d the ovule is a small structure attached to the placenta by means of a stalk called funicle. the body the ovule fuses with funicle in the region called hilum. thus hilum represents the junction between ovule and funcicle each ovule has one or two protective envelopes called integuments, Integuments encircle the ovule except at the tip where a small opening called the micropyle is organised.
opposite the micropylar end,is the chalaza, representing the basal part of the ovule. Enclosed within the Integuments is a mass of cells called. the nucellus. cells of the nucellus have abundant reserve food materials, located in the nucellus is the embyro sac or female gametophyte. an ovule generally has a single
embyro sac formed from a megaspore through reduction dividion. megasporangenesis :the process of formation of megaspores from the megaspore mother cell is called megasporogenesis. ovules generally differenciate a single megaspore mother cell MMC in the micryoplyar region .
of the nucellus, it is a large cell containing dense cytoplasm and a prominent nucleus. the MMC undergoes meiotic dividion. what is the importance of the MMC undergoing meiosis? meiosis results in the production of four megaspores
Female gametophyte: In a majority of flowering plants. one of the megaspores is functional while the other three degenerate. only the functional megaspore develops into the female gametophyte embryo monosporic development. what will be the ploidy of the cell of the nucellus. MMC the functional megaspore and female gametophyte?
Sexual Reproduction in flowering class 12 summary
Sexual reproduction in flowering plants is a complex process crucial for the perpetuation of species. It begins with pollination, where pollen grains containing male gametes are transferred to the stigma of a flower. The subsequent process of fertilization involves the fusion of male and female gametes, resulting in the formation of a zygote within the ovule. The ovule transforms into a seed, encapsulated within a mature ovary that develops into a fruit. This cycle ensures the production of offspring with genetic diversity, contributing to the adaptation and survival of plant species.
Hormones play a pivotal role in regulating various stages of sexual reproduction, orchestrating the growth and development of floral organs. Overall, sexual reproduction in flowering plants is a finely orchestrated biological dance that encompasses pollination, fertilization, and seed dispersal, essential for the sustainability of plant life.
Sexual Reproduction in flowering class 12 Question and Answer
Q1: Define sexual reproduction in flowering plants.
A1: Sexual reproduction in flowering plants involves the formation of seeds through the fusion of male and female gametes. It includes the processes of pollination, fertilization, and seed development.
Q2: Explain the process of pollination.
A2: Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same or a different flower. It can occur through various agents such as wind, water, insects, birds, or animals.
Q3: Differentiate between self-pollination and cross-pollination.
A3: Self-pollination occurs when pollen is transferred from the anther to the stigma of the same flower or another flower on the same plant. Cross-pollination involves the transfer of pollen from the anther of a flower on one plant to the stigma of a flower on another plant.
Q4: Describe the structure and function of male and female reproductive organs in a flower.
A4: The male reproductive organ is the stamen, consisting of anther and filament. The anther produces pollen containing male gametes. The female reproductive organ is the pistil, consisting of stigma, style, and ovary. The stigma receives pollen, and the ovary contains ovules with female gametes.
Q5: What is fertilization in flowering plants?
A5: Fertilization is the fusion of a male gamete (from pollen) with a female gamete (in an ovule) to form a zygote. This process leads to the formation of a seed within the ovary.
Q6: Explain the significance of fruits in the process of seed dispersal.
A6: Fruits develop from fertilized ovaries and aid in the dispersal of seeds. They attract animals with their sweet or nutritious flesh, encouraging them to consume the fruit and disperse the seeds in different locations through excretion.
Q7: Discuss the role of hormones in the process of flowering.
A7: Plant hormones like auxins, gibberellins, and cytokinins play crucial roles in the initiation and regulation of flowering. They influence the growth of floral organs and coordinate various developmental processes during flowering.
Sexual Reproduction in flowering class 12 MCQ
Question:1 What is the primary purpose of flowers in plants?
- a. Photosynthesis
- b. Sexual reproduction
- c. Water absorption
- d. Root development
Question:2 Which part of the flower produces pollen?
- a. Stigma
- b. Anther
- c. Ovary
- d. Petal
Question:3 The transfer of pollen from the anther to the stigma of the same flower is known as
- a. Cross-pollination
- b. Fertilization
- c. Self-pollination
- d. Germination
Question:4 What is the main purpose of pollination in plants?
- a. Seed dispersal
- b. Seed formation
- c. Gamete fusion
- d. Root development
Question:5 Which plant hormone is associated with the promotion of flowering?
- a. Gibberellins
- b. Auxins
- c. Cytokinins
- d. Abscisic acid
Question:6 The female reproductive organ in a flower is called
- a. Stamen
- b. Ovule
- c. Pistil
- d. Filament
Question:7 What is the process by which pollen grains reach the stigma of a flower?
- a. Germination
- b. Fertilization
- c. Pollination
- d. Ovulation
Question:8 Where does fertilization in flowering plants occur?
- a. Stigma
- b. Ovary
- c. Anther
- d. Petal
Question:9 Which of the following is a result of fertilization in flowering plants?
- a. Formation of fruit
- b. Formation of pollen
- c. Initiation of germination
- d. Development of roots
Question:10 What is the role of fruits in seed dispersal?
- a. Protecting seeds
- b. Attracting pollinators
- c. Attracting herbivores
- d. Aiding in seed dispersal
In conclusion, sexual reproduction in flowering plants encompasses the processes of pollination, fertilization, and seed development, ensuring genetic diversity and the continuity of plant species.
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