Describe the Oparin Haldane theory of Origin of life.

Life has originated on earth around 4.5 million years ago. Oparin and Haldane proposed that the formation of life was preceded by chemical evolution. There must be a gradual chemical evolution of carbon-based molecules in a 'primordial soup' and different organic molecules were formed from inorganic constituents during the course of chemical evolution. They suggested that: Spontaneous generation of life under present circumstances is not possible and the Earth's previous atmosphere was reducing. The first life arose due to a progressive series of chemical reactions that formed complex organic molecules. Heat and lightning provided energy for these chemical reactions to occur.

Explain the evolution of long neck of giraffe according to Charles Darwin.

According to Darwin, the organisms which have favourable variations to adapt to the environmental conditions would survive. The struggle for existence results in the survival of the fittest. For example, both long-necked and short-necked giraffes were present, but due to scarcity of food, the short-necked giraffes could not survive. The individuals with long-necked ones had easy access for foraging because they could reach higher branches and leaves on the top of the trees. They can survive and shows reproductive fitness, with their offspring inheriting their long necks. Hence, the long-necked giraffe is selected over a short-necked one and passed on to the next generation. It is an example of Darwin's theory of evolution through natural selection.

Give one example of homologous organs and one example of analogous organs found in plants.

Homologous organs in plants: The leaves of a pitcher plant, a Venus flytrap, a cactus and a poinsettia are all examples of homology. They are homologous structures because, although they have different shapes and different functions today, they all share a common ancestor. Analogous organs in plants are: Potato is a stem while the sweet potato is a root; both perform storage and vegetative propagation. Analogous organs are those that are different in their origin and structures but execute a similar function in two dissimilar species.

Write two differences between homologous organs and analogous organs.

Features Homologous organs Analogous organs Definition These have similarity of structure, physiology, or development of different species of organisms based upon their descent from a common evolutionary ancestor. These are with different structural plans performing common functions. Features Homologous organs Analogous organs Type of evolution Result of divergent evolution Result of convergent evolution