Sample 1Easy
The occurrence of more than one embryo in a seed is commonly seen in
- A
wheat
- B
pea
- C
maize
- D
citrus
Show the answer
The answer is D.Occurrence of more than one embryo in a seed is called polyembryony. Many citrus and mango varieties show it because some nucellar cells divide and develop into embryos.
- A.
Wheat seeds normally carry a single embryo.
- B.
Pea seeds normally carry a single embryo.
- C.
Maize grains normally carry a single embryo.
NCERT: Class 12 Biology, Chapter 1 (Sexual Reproduction in Flowering Plants), Apomixis and Polyembryony
Sample 2Medium
A sketch of a cut Citrus seed shows several embryos in one ovule. One lies within the embryo sac and has developed from the zygote. The others bulge into the embryo sac from the surrounding nucellus. Which statement about these extra embryos is correct?
- A
They are haploid because they develop from synergids
- B
They are triploid because they develop from the endosperm
- C
They result from several eggs each fertilised by a separate male gamete
- D
They arise from nucellar cells without fertilisation, so they are genetically like the mother plant, and the seed shows polyembryony
Show the answer
The answer is D.In Citrus and mango, some nucellar cells around the embryo sac divide, protrude into it and develop into embryos without fertilisation. More than one embryo in a seed is polyembryony, and such apomictic embryos are clones of the parent.
- A.
The figure shows them arising from the diploid nucellus, not from synergids.
- B.
Embryos do not arise from endosperm; these come from nucellar cells.
- C.
They develop without fertilisation from nucellar cells, a form of apomixis.
NCERT: Class 12 Biology, Chapter 1, 1.5