What is co-evolution? Explain, with the help of an example.
The term co-evolution was coined by Paul R. Ehrlich and Peter H. Raven in 1964. It refers to the process in which two or more species exert selective pressures on others, thus affecting their evolution. Thus there can be a reciprocal influence which may lead to evolution of the organisms in a complementary way. Co-evolution may involve ecological interactions like mutual-ism, parasitism etc. For-example, the loss of digestive organs in parasites has resulted due to their obligate relationship with the host, so that they can take advantage of the nutrients given by the host directly. Flowering plants and insects as pollinators show co-evolution.
How does variation lead to evolution? How can variation arise in case of asexual reproduction?
Variation refers to change in traits of an organism. Variation helps the organism to adapt towards changes in environment. It arises either due to error in DNA copying (asexual reproduction) or during the process of gamete formation. Favorable variations are selected by nature, which leads to differential survival. The organisms with variations which make them better adapt towards the change in the environment, are able to reproduce more and leave more progeny. This is defined as reproductive success. Variations, when accumulated over a period of time may lead to speciation. Thus, variations play a crucial role in the process of evolution. In case of asexual reproduction, only one parent is involved. The DNA of the parent cell undergoes replication process to double itself. The process of DNA copying is not an accurate process. Errors do arise during the process of DNA replication despite of proofreading activity of the DNA polymerase enzyme which synthesizes DNA. These errors lead to the variations in the progeny.
Describe the structure of a flower of an angiosperm. Mention the botanical terms involved.
The flower of an angiosperm typically consists of the male and female reproductive parts and the accessory whorls. The stalk of the flower, attached to the plant body is called thalamus. If leaves like structures are present at the tip of the thalamus, these are called bracteoles. Sepals are the accessory whorl of leaf like structures which protect the flower during the budding stage. Petals are the large, colourful structures which are meant for protection and for attracting the pollinators for the process of transfer of pollen grains. The male reproductive part is called stamen, consisting of anther and filament. Anther is bi-lobed and each lobe contains two theca (compartments). The process of formation of pollen grains occurs in each of these two compartments. This process is called microsporogenesis. The female reproductive part is called carpel or pistil. It further contains a sticky portion called stigma, a long tube called style and a swollen part containing ovule, called ovary. Egg formation and endosperm development occurs in the ovule present inside the ovary. Micropyle is the opening in the ovule from where the pollen tube enters. The whorl of sepals is called calyx and the whorl of petals is called corolla. Androecium and Gynoecium form the male and female parts respectively.