• In contrast, true fruits develop only from the ovary. • In few species, fruits develop without fertilisation. Such fruits are called parthenocarpic fruits. Banana is an example of parthenocarpic fruit.
Albuminous and non-albuminous seed
• Mature seeds may be albuminous or non-albuminous. Albuminous seeds retain a part of endosperm as it is not completely used up during embryo development (e.g., wheat, maize, barley, castor, sunflower). Non-albuminous seeds have no residual endosperm as it is completely consumed during embryo development (e.g., pea, groundnut). Occasionally, in some seeds such as black pepper remnants of nucellus are also persistent. This residual persistent nucellus is the perisperm.
APOMIXIS AND POLYEMBRYONY
• A few flowering plants such as some species of Asteraceae and grasses have evolved a mechanism to produce seeds without fertilisation called apomixis. • There are several methods of apomictic development in seeds, two common methods are recurrent agamospermy and adventive embryony. • Agamospermy is the formation of seed that has an embryo formed without meiosis and syngamy.
Agamospermy Non-recurrent agamospermy • The embryo is haploid and therefore the seed having it is nonviable.
Recurrent agamospermy
• All the cells of the embryo sac are diploid as it is formed directly either from a nucellar cell (apospory) or diploid megaspore mother cell (diplospory).
• The diploid egg as well as other diploid cells of embryo sac can grow into normal embryos.
• Formation of embryo directly from diploid egg without fertilisation is called diploid parthenogenesis, e.g., apple, Poa. • Adventive embryony - An embryo develops directly from a diploid cell other than egg like that of nucellus and integument, e.g., Citrus, Opuntia. It gives rise to a condition called polyembryony or the phenomenon of having more than one embryo. In gymnosperms, polyembryony can also occur due to cleavage of growing embryo. It is called cleavage polyembryony. Occurrence of polyembryony due to fertilisation of more than one egg is called simple polyembryony while formation of extra embryos through sporophytic budding is called adventive polyembryony. • Polyembryony is common in onion, groundnut, mango, lemon, orange.
3. 4.
What type of outbreeding contrivance is found in Primula? What is the advantage of recurrent agamospermy over non-recurrent agamospermy?
APRIL 2018 1-c- OPSONIN
2-d- EPHYRA
3-f- TURION
4-a- PITUICYTES
5-g- RIBOPHORIN
6-h- PUTREFACTION
7-j- BLEPHAROPLAST
8-i- GRISEOFULVIN
9-e-BICOLLATERAL
10-b- POLLINIUM
Winner : Aswini Mura (West Bengal)
To easily remember the characteristics of monocots, the mnemonic “Many Smart People Take French” can be used as follows: Many
:
Monocots
Smart
:
Scattered vascular bundles
People
:
Parallel leaf venation
Take
:
Threes (units of floral parts)
French
:
Fibrous roots MT BIOLOGY
TODAY | MAY ‘18
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