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MODEL PAPER 4 — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMODEL PAPER 44 Marks
Question
i. Double fertilisation is an event unique to all flowering plants. Explain the process.
ii. Give a reason for the following:
a. A seed of an orange has many embryos.
b. Cashew is a false fruit but Guava is a true fruit.
✓

Answer

i. All angiosperms are characterised by a unique process called double fertilisation.
Double fertilisation is the occurrence of two types of fusion syngamy and triple fusion in an embryo sac of the angiosperm.
Syngamy- Fusion of one of the male gamete and the egg cell resulting in formation of a zygote (diploid).
Triple fusion- Fusion of another male gamete with two haploid polar nuclei to produce a (triploid) primary endosperm nucleus.
ii. a. The fruit of orange is an example of polyembryony. The egg is fertilized and leads to the formation of multiple embryos. This phenomenon is known as polyembryony. There are many embryos produced from the single fertilized egg of ovule.
b. In case of Cashew thalamus also contribute in fruit formation along with ovary/development of fruit after fertilisation from the part other than ovary, Guava fruit develops only from the ovary after fertilisation therefore it is true fruit.

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