CBSE 2025 · Region 1 · Set 1 · Q32 · 5 marks
Student to attempt either option-(A) or (B) :(A)Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm.(b)Study the diagram given below showing the modes of pollination. Answer the questions that follow.
(i)The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods '$\displaystyle 1$', '$\displaystyle 2$' and '$\displaystyle 3$'.(ii)How do the following plants achieve pollination successfully ?Water lily(b)Vallisneria(iii)Write advantages of pollen transfer in method '$\displaystyle 3$'.Given below is the diagram of human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follows :
(i)Compare the fate of sperms 'P', 'Q' and 'R' shown in the diagram.(ii)Write the role of Zona pellucida in this process.(iii)Analyse the changes occurring in the ovum after the entry of sperm.(iv)How acrosome and middle piece of a human sperm are able to play an important role in human fertilization ?
Student to attempt either option-(A) or (B) :
(A)
Distinguish between the two cells enclosed in a mature male gametophyte of an angiosperm.
(b)
Study the diagram given below showing the modes of pollination. Answer the questions that follow.
(i)
The given diagram shows three methods of pollen transfer in plants. Examine them carefully and write the technical terms used for pollen transfer methods '$\displaystyle 1$', '$\displaystyle 2$' and '$\displaystyle 3$'.
(ii)
How do the following plants achieve pollination successfully ?
Water lily
(b)
Vallisneria
(iii)
Write advantages of pollen transfer in method '$\displaystyle 3$'.
Given below is the diagram of human ovum surrounded by a few sperms. Observe the diagram and answer the questions that follows :
(i)
Compare the fate of sperms 'P', 'Q' and 'R' shown in the diagram.
(ii)
Write the role of Zona pellucida in this process.
(iii)
Analyse the changes occurring in the ovum after the entry of sperm.
(iv)
How acrosome and middle piece of a human sperm are able to play an important role in human fertilization ?
Marking-scheme solution
(a)
| Vegetative cell | Generative cell |
| It is big with abundant food reserve and an irregular shaped nucleus | Generative cell is small, floats in the cytoplasm of the vegetative cell |
| Helps in the formation of pollen tube | Forms two male gametes |
(b)(i)
$\displaystyle 1$ = Autogamy
$\displaystyle 2$ = Geitonogamy
$\displaystyle 3$ = Xenogamy
(ii)
a = by Insects or wind
b = by Water
(iii)
Genetic variation, Healthier offspring,Elimination of recessive traits, Disease resistance ,Evolution, no inbreeding depression, promotes heterosis
(i)
P is able to penetrate or fertilise the ovum ,whereas Q and R are unable to penetrate or fertilise.
(ii)
When a sperm comes in contact with the zona pellucida layer of the ovum it induces changes in the membrane that blocks the entry of additional sperms.
(iii)
Entry of sperm induces completion of meiotic division of the secondary oocyte and formation of second polar body and a haploid ovum (ootid)
(iv)
Acrosome : It is filled with the enzyme which helps the sperm to enter into the cytoplasm of the ovum
Middle piece : It has numerous mitochondria which produce energy for the movement of tail that facilitate sperm motility for fertilisation
Sexual Reproduction in Flowering PlantsPre-fertilisation: Structures and EventsAnalyselong_answerhard
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CBSE Class 12 Biology past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.