CBSE 2026 · Region 2 · Set 1 · Q31 · 5 marks
(i)Explain the role of stigma in pollen pistil interaction.(ii)Describe the post pollination events leading to double fertilization in angiosperms starting with $\displaystyle 2$-celled pollen grain.(i)Explain menstrual phase in the menstrual cycle of human female.(ii)Why is follicular phase also called proliferative phase?(iii)Explain the events that occur in Graafian follicle at the time of ovulation and thereafter.(iv)Draw a Graafian follicle and label – Antrum and secondary oocyte.
(i)
Explain the role of stigma in pollen pistil interaction.
(ii)
Describe the post pollination events leading to double fertilization in angiosperms starting with $\displaystyle 2$-celled pollen grain.
(i)
Explain menstrual phase in the menstrual cycle of human female.
(ii)
Why is follicular phase also called proliferative phase?
(iii)
Explain the events that occur in Graafian follicle at the time of ovulation and thereafter.
(iv)
Draw a Graafian follicle and label – Antrum and secondary oocyte.
Marking-scheme solution
(i)
Stigma has the ability to recognise the right or compatible and wrong or
incompatible type of pollen
(ii)
Compatible pollen grain germinates on the stigma to produce pollen tube that grows through the tissues of stigma and style and reaches to the ovary
Generative cell divides into two male gametes while moving through style and Pollen tube enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus
The pollen tube releases the two male gametes in the cytoplasm of Synergid and one male gamete moves towards the egg cell and fuses with its nucleus forming a zygote (syngamy)
The other male gamete moves towards the two polar nuclei present in the central cell and fuses with them to form Primary Endosperm Nucleus / PEN
(triple fusion).
(Since syngamy and triple fusion both occur in embryo sac so it is termed as
Double Fertilization)
(i)
During menstrual phase in the menstrual cycle of human female endometrium lining of the uterus and its blood vessels which forms liquid comes out through vagina and flow lasts for $\displaystyle 3$-$\displaystyle 5$ days.
(ii)
As the regeneration of endometrium through proliferation takes place.
(iii)
Graafian follicle ruptures to release secondary oocyte, remaining part of graafian follicle transforms into corpus luteum
(iv)
Sexual Reproduction in Flowering PlantsPre-fertilisation: Structures and EventsUnderstandlong_answerhard
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CBSE Class 12 Biology past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.