Focus on the unusual flowering behavior of certain perennial plant species:
(a) Bamboo species flower only once in their life, generally after 50–100 years, produce large numbers of fruits, and die. (b) Strobilanthus kunthiana (Neelakuranji) flowers once every 12 years. (c) The mass flowering of Neelakuranji turns hilly areas of Kerala, Karnataka, and Tamil Nadu into blue stretches.
Which of these statements are accurate?
All the statements are correct according to NCERT. Bamboo flowers only once after several decades and dies, while Neelakuranji blooms once every 12 years, covering the hills with blue flowers.
Question 12 of 100
📘 CLASS XII
Analyze the cyclic changes occurring in female placental mammals:
(p) Non-primate mammals show cyclic changes during the breeding phase known as the oestrus cycle. (q) Primate mammals (monkeys, apes, humans) exhibit cyclic changes during the reproductive phase called the menstrual cycle. (r) Both oestrus and menstrual cycles continue without pause even during pregnancy and lactation phases.
Choose the correct option.
Non-primate mammals exhibit the oestrus cycle, whereas primates exhibit the menstrual cycle. These cycles are interrupted during pregnancy and are hormonally regulated. Hence statement (r) is incorrect.
Question 13 of 100
📘 CLASS XII
Differentiate between seasonal and continuous breeders from the statements below:
(i) Seasonal breeders exhibit cyclic changes in ovary activity only during favorable seasons in their reproductive phase. (ii) Continuous breeders are reproductively active throughout their reproductive phase. (iii) Captive birds in poultry farms are seasonal breeders that lay eggs only in winter.
Choose the correct option.
Seasonal breeders reproduce only during favourable seasons, whereas continuous breeders remain reproductively active throughout the reproductive phase. Poultry birds in captivity are induced to lay eggs throughout the year, making statement (iii) incorrect.
Question 14 of 100
📘 CLASS XII
Read the statements on senescence and transitional regulation:
(1) The end of the reproductive phase is recognized as one of the key parameters of senescence or old age. (2) During senescence, there is a slowing of metabolism and other physiological processes in the body. (3) Environmental factors alone, with no hormonal involvement, regulate transitions between juvenile, reproductive, and senescent phases.
Choose the correct option.
The end of the reproductive phase marks the onset of senescence, during which metabolism and physiological activities slow down. Transitions between juvenile, reproductive and senescent phases are regulated by interactions between hormones and environmental factors. Hence statement (3) is incorrect.
Question 15 of 100
📘 CLASS XII
Assess these statements regarding gametes and sexuality:
(I) Gametes are always haploid cells, irrespective of whether the parental body is haploid or diploid. (II) Homogametes (isogametes) are morphologically identical and are common in human beings. (III) Heterogametes consist of a motile male gamete (sperm/antherozoid) and a stationary female gamete (egg/ovum).
Which of the statements are correct?
Gametes are always haploid. Humans possess heterogametes (sperm and ovum), whereas isogametes occur in certain algae such as Cladophora. Hence statement (II) is incorrect.
Question 16 of 100
📘 CLASS XII
Match sexuality terminology in plants and fungi with their descriptions:
(a) Bisexual conditions are denoted by the terms homothallic and monoecious. (b) Unisexual conditions are denoted by heterothallic and dioecious. (c) Papaya and date palm are excellent examples of monoecious plants. (d) Cucurbits and coconuts are classic examples of dioecious plants.
Which of the statements are true?
Papaya and date palm are dioecious plants, whereas cucurbits and coconuts are monoecious. Therefore statements (c) and (d) are incorrect.
Question 17 of 100
📘 CLASS XII
Study the distribution of sex organs in animals based on these statements:
(x) Earthworms, sponges, tapeworms, and leeches possess both male and female reproductive organs in a single individual. (y) Organisms with both male and female sex organs in one individual are termed hermaphrodites. (z) Cockroach is a bisexual animal containing both functional testes and ovaries.
Choose the correct option.
Earthworms, sponges, tapeworms and leeches are hermaphrodites. Cockroaches are unisexual animals with separate male and female individuals. Hence statement (z) is incorrect.
Question 18 of 100
📘 CLASS XII
Evaluate the chromosome counts of meiocytes (2n) and gametes (n) from NCERT Table 1.1:
(1) In Ophioglossum (a fern), the chromosome number in the gamete (n) is 630. (2) In a butterfly, the meiocyte chromosome number (2n) is 380. (3) In a fruit fly, the meiocyte (2n) contains 8 chromosomes, while the gamete (n) contains 4. (4) In humans, the gamete (n) contains 46 chromosomes.
Which combination is correct?
Human gametes contain 23 chromosomes (n = 23), whereas human meiocytes contain 46 chromosomes (2n = 46). Therefore statement (4) is incorrect.
Question 19 of 100
📘 CLASS XII
Choose the correct statement combination concerning gamete transfer in simple plants:
(i) In a majority of organisms, the male gamete is stationary and the female gamete is motile. (ii) Simple plants like algae, bryophytes, and pteridophytes utilize water as a medium for gamete transfer. (iii) Since a large number of male gametes fail to reach the female gametes, male gametes are produced in several thousand times the number of female gametes.
Choose the correct option.
In most organisms, the male gamete is motile whereas the female gamete is non-motile. Water serves as the medium for gamete transfer in algae, bryophytes and pteridophytes, and numerous male gametes are produced because many fail to reach the female gamete.
Question 20 of 100
📘 CLASS XII
Analyze these statements regarding pollen grain transfer in angiosperms:
(a) Pollen grains are the carriers of male gametes and are produced in the anthers. (b) In self-fertilizing plants like peas, pollination is relatively easy because the anther and stigma are located very close to each other. (c) Dioecious plants require specialized pollination mechanisms to facilitate gamete transfer.
Which of the following statements are correct?
All three statements are correct. Pollen grains carry the male gametes, self-pollinating plants such as pea have closely placed anthers and stigma, and dioecious plants require pollination mechanisms to transfer pollen between separate male and female plants.
