Honeybees produce their young ones only by sexual reproduction. Inspite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.
(i) Sterile diploid females as workers
(ii) One fertile diploid female as queen
(iii) Fertile haploid males as drones.
In case of honeybees, both haploid and diploid individuals formad as a result of incomplete (cyclic) parthenogenesis, i.e., both sexual reproduction and parthenogenesis. Fertilised eggs (zygote) give rise to queen and workers (both are females) by the process of sexual reproduction and unfertilised eggs (ova) develop into drones (males) by the process of parthenogenesis.
With which type of reproduction do we associate the reduction division? Analyse the reasons for it.
Reduction division (meiosis) is associated with sexual reproduction. The reasons are
(i) Since, sexual reproduction involves the fusion of two types of gametes male and female), they must have haploid number of chromosomes.
(ii) The cell (meiocyte) which gives rise to gametes often has diploid number of chromosomes and it is only by reducing the number by half that we can get haploid gametes.
(iii) Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.
Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger, etc., as a type of asexual reproduction? Give two/three reasons.
The formation of new plants from vegetative units (vegetative propagules) such as buds, tubers, rhizomes. etc., is called vegetative propagation (vegetative reproduction). It can be considered as a type of asexual reproduction as it involves the production of new individuals.
(i) by a single parent
(ii) without the formation and fusion of gametes
(iii) without resulting in any genetic or morphological variations.
'Fertilisation is not an obligatory event for fruit production in certain plants'. Explain the statement.
Fertilisation is not an obligatory event for fruit production in certain plants. Some fruits are developed from unfertilised ovary called parthenocarpic fruits.
These are seedless fruits, such as pomegranate, grapes, etc. Flowers of these plants are sprayed by a growth hormone that induces fruit development even though fertilisation has not occurred. The ovules of such fruits, however, fail to develop into seeds.
In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
Cell divisions increase the number of cells in the developing embryo, while cell differentiation helps group of cells to undergo certain modifications to form specialised tissues and organs to form an organism.
At many stages of embryogenesis, if cell differentiation does not occur, the embryo cannot develop into a new organism. It will only remain as a mass of cells.