CBSE 2024 · Region 4 · Set 3 · Q33 · 5 marks
(i)State the objective of adopting artificial hybridisation programme in plants.(ii)Describe the steps followed in this technique.(i)Describe the development of placenta during pregnancy in a human female.(ii)Explain its role.
(i)
State the objective of adopting artificial hybridisation programme in plants.
(ii)
Describe the steps followed in this technique.
(i)
Describe the development of placenta during pregnancy in a human female.
(ii)
Explain its role.
Marking-scheme solution
(i)
To combine desirable characters from two different varieties , so as to
obtain improved/ superior variety
(ii)
If the female parent plant bears bisexual flowers, it is necessary to
remove the anthers from the flower before its dehiscence. which is called emasculation , such flowers are then bagged , (with butter paper bags of suitable size) to prevent contamination of its stigma. which is called bagging
, When the stigma of bagged flower attains receptivity, mature pollen collected from anthers of the male parent are dusted on the stigma , and flower is rebagged and fruit is allowed to develop.
(i)
After implantation, finger-like projections appear on the trophoblast
called chorionic villi , which are surrounded by uterine tissue and maternal blood , The chorionic villi and uterine tissue become interdigitated with each other , and jointly form a structural and functional unit between developing embryo and maternal body called placenta.
(ii)
Placenta facilitates supply of O2 and nutrition to the embryo , and
removal of CO2 and waste from foetus , Placenta also acts as endocrine tissue and produces several hormones hCG hPL estrogen progesterogen essential for maintaining pregnancy.
Human ReproductionPregnancy and Embryonic DevelopmentApplylong_answermedium
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CBSE Class 12 Biology past-paper question from the 2024board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.