SEXUAL REPRODUCTION IN FLOWERING PLANTS | PART – C | 3 MARKS QUESTION WITH ANSWERS | CLASS 12 | PUC 2 YEAR
Before you begin, Read and revise notes here: SEXUAL REPRODUCTION IN FLOWERING PLANTS – Notes
1. Draw a labelled diagram of transverse section of a young anther.
Answer:
2. Describe the structure of microsporangium.
Answer: In a transverse section, a typical microsporangium appears near-circular in outline. It is generally surrounded by four wall layers:
- Epidermis: The outermost protective layer.
- Endothecium: Helps in protection and the dehiscence of the anther to release pollen.
- Middle layers: 2 to 3 layers that perform the function of protection and help in dehiscence.
- Tapetum: The innermost wall layer. It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus. When the anther is young, a group of compactly arranged homogenous cells called sporogenous tissue occupies the centre of each microsporangium.
3. Write any two commercial uses of pollen grains and mention the viability period of pollen grains of Solanaceae members.
Answer: Pollen grains are extremely rich in nutrients.
- Because of this nutritional value, it has become a popular fashion in recent years to use pollen tablets as daily food supplements.
- In western countries, a large variety of pollen products are widely available in the market in the form of both tablets and syrups.
- The consumption of pollen products has been claimed to significantly increase the physical performance of athletes and racehorses.
4. Draw a neat labeled diagram of a typical anatropous ovule.
Answer: Typical anatropous ovule:
5. Describe the structure of megasporangium.
Answer: The ovules arise from the placenta.
- Funicle: A small stalk that attaches the ovule to the placenta.
- Hilum: The region where the body of the ovule fuses with the funicle. It represents the junction between the ovule and the funicle.
- Integuments: One or two protective envelopes that encircle the ovule.
- Micropyle: A small opening at the tip of the ovule where the integuments are absent.
- Chalaza: Located opposite the micropylar end, representing the basal part of the ovule.
- Nucellus: A mass of cells enclosed within the integuments containing abundant reserve food materials.
- Embryo Sac (Female Gametophyte): Located inside the nucellus. Generally, an ovule has a single embryo sac formed from a megaspore.
6. Explain the structure of a mature female gametophyte in flowering plants.
Answer: A typical mature angiosperm embryo sac is 8-nucleate but 7-celled.
- Egg Apparatus: Three cells grouped at the micropylar end, consisting of two synergids and one egg cell.
- Filiform Apparatus: Special cellular thickenings at the micropylar tip of the synergids that play a crucial role in guiding pollen tubes into the synergid.
- Antipodals: Three cells situated at the chalazal end.
- Central Cell: The large central space containing two polar nuclei.
7. Draw a neat labeled diagram of a mature embryo sac.
Answer: mature embryo sac:
8. List the characters of insect pollinated flowers.
Answer: Characters of insect pollinated flowers:
- Flowers are usually large and colourful.
- Flowers are fragrant to attract insects.
- Flowers are rich in nectar.
- They provide floral rewards like nectar and pollen.
- Some flowers also provide safe places for insects to lay eggs.
9. What is artificial hybridization? Name the techniques that are employed to achieve this?
Answer: Artificial hybridisation is one of the major approaches in crop improvement programmes. Artificial hybridization is achieved by emasculation and bagging.
- Emasculation: Removal of anthers from a bisexual flower bud before dehiscence of anther is called emasculation. It is done by using a pair of forceps. It is to prevent self pollination. In unisexual female flowers there is no need for emasculation.
- Bagging: It is the process of covering emasculated flower by polythene bag / butter paper. It is to prevent contamination of stigma of emasculated flower with unwanted pollen. Small pores should be made in the polythene bag for aeration.
- Crossing (Hand pollination): It is the transfer of desired pollen grains onto the stigma of emasculated flower. After crossing the flower is re-bagged and allowed for seeds and fruit setting.
- Labeling: It involves the tagging of a label to emasculate flower. Label should contain the details like date of crossing, nature of male & female plant etc.
10. What is triple fusion? Where does it take place in the megasporangium? Name the nuclei involved in triple fusion.
Answer: It is the fusion of one male gamete with two polar nuclei in the central cell of the embryo sac to produce a triploid primary endosperm nucleus (PEN). It takes place in the large central cell of the embryo sac. The nuclei involved are one male gamete and two polar nuclei.
11. Draw a labeled diagram of the fertilized female gametophyte and mention the ploidy of any one of the products of double fertilization.
Answer:
Ploidy of the products: Zygote = Diploid (2n), Primary Endosperm Nucleus (PEN) = Triploid (3n).
12. Name the product of fertilization that forms the kernel of coconut. How does the kernel differ from coconut water?
Answer:
- The primary endosperm nucleus (PEN) develops into the endosperm.
- The white kernel surrounding the coconut water is the cellular endosperm.
- The coconut water from tender coconut is made up of thousands of free nuclei (free-nuclear endosperm).
13. Draw a L.S. of grass embryo diagram and label the following parts: a) Scutellum b) Coleoptile c) Shoot apex d) Radicle e) Root cap f) Coleorrhiza
Answer:
14. Draw a neat labeled diagram of a monocot seed.
Answer:
Monocot seed
15. ‘Fertilization is not an obligatory event for fruit production in certain plants’. Justify the statement.
Answer:
- In some plants, fruits develop without fertilization. Such fruits are called parthenocarpic fruits. These fruits are seedless.
- Parthenocarpy can occur naturally or be induced by the application of growth hormones.
- Example: Banana.
16. Explain any three advantages the seeds offer to angiosperms.
Answer:
- Water Independence: Reproductive processes such as pollination and fertilisation are independent of water, making seed formation more dependable.
- Dispersal Strategies: Seeds have better adaptive strategies for dispersal to new habitats, helping the species to colonise other areas.
- Nourishment: Sufficient food reserves nourish young seedlings until they are capable of photosynthesis on their own. Protection: The hard seed coat provides protection to the young embryo.
- Genetic Variation: Being products of sexual reproduction, seeds generate new genetic combinations leading to variations.
17. Why are some seeds referred to as apomictic seeds? Mention its advantages to a farmer who uses them.
Answer:
- Apomixis is a mechanism to produce seeds without fertilization, mimicking sexual reproduction.
- Hybrid seeds increase productivity but the production of hybrid seeds is costly.
- If hybrids are made into apomicts, there is no segregation of characters, and farmers can keep using the hybrid seeds year after year.
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