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Biology · 2024 · 5 marks
CBSE 2024 · Region 1 · Set 3 · Q31
(a) (i) Draw a labelled diagram of the embryonic stage that gets implanted in the human female leading to pregnancy. 1 1/2 (ii) Explain the changes…
(i)
Draw a labelled diagram of the embryonic stage that gets implanted in the human female leading to pregnancy. $\displaystyle 1 \frac{1}{2}$
(ii)
Explain the changes that the different parts of the embryo undergo after implantation up till ($\displaystyle 1$) Placenta formation and
(2)
formation of three germ layers. $\displaystyle 2$
(iii)
Mention the role of the following : $\displaystyle 1 \frac{1}{2}$
(1)
Placenta
(2)
Three germ layers
(i)
Why do plants like Viola and Oxalis give assured seed sets even in the absence of pollinators ? When an orange seed is squeezed, many embryos of different shapes and sizes are observed. Why ? $\displaystyle 1$
(ii)
Mention four advantages of seed formation to angiosperms. $\displaystyle 2$
(iii)
Draw a diagram of a fertilized embryo sac of an angiosperm and label any four parts.
Marking-scheme solution
(i)
Blastocyst
j
(ii)
(1) After implantation
– finger-like projections appear on the trophoblast called chorionic villi which are surrounded by uterine tissue and maternal blood, 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.
(2)
Inner Cell Mass differentiates into three germ layers ( outer Ectoderm,middle mesoderm
,inner endoderm)
(iii)(1)
Role of Placenta- It facilitates the supply of oxygen and nutrients to the embryo, it help in removal of CO2 and excretory waste materials produced by the embryo, it acts as an endocrine tissue and produces hormones hCG or hPL or estrogens .
(2)Role of three germ layers: They give rise to all tissues/ organs in adults
(b)
• They are cleistogamous or closed flowers and hence autogamous so no need of
pollinators.
• Because some of nucellar cells surrounding the embryo sac start dividing protrude
into embryo sac and develop into embryos.
(ii)
-No need of water for pollination or fertilization so seed formation is more dependable
Seeds have better adaptive strategies for dispersal to new habitats.
They have sufficient food reserve so nourish the young seedlings until they are capable of
photosynthesis on their own.
They have hard seed coat to protect the young embryos.
Being product of sexual reproduction they generate new genetic combinations causing
variations .
(iii)
All Human Reproduction questions2024 question paperNCERT solutions: Human ReproductionPractice Human Reproduction →
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CBSE Class 12 Biology past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.