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How are the areas of study – evolution and classification – interlinked?

The cell is the basic unit of life in all organisms. The characteristics in the next level of classification would be shared by most, but not all organisms. A basic characteristic of cell design that differs among different organisms is whether the cell has a nucleus. Bacterial cells do not, while the cells of most other organisms do. Among organisms with nucleated cells, which ones are unicellular and which ones multi-cellular? That property marks a very basic difference in body design, because of specialisation of cell types and tissues. Among multi-cellular organisms, whether they can undertake photosynthesis or not will provide the next level of classification. Among the multi-cellular organisms that cannot do photosynthesis, whether the skeleton is inside the body or around the body will mark another fundamental design difference. We can see that, even in these few questions that we have asked, a hierarchy is developing that allows us to make classification groups.


Explain the terms analogous and homologous organs with examples.

Homologous Organ
Those organs which have same basic structure but have different functions are known as homologous organs. E.g. The forelimbs of different animals have different functions. In humans they are used for grasping or holding things. In frogs they are used for leaping, in a horse they are used for running, in a lizard for creeping, in brids for flying, swimming in whale. Basic structure of forelimbs is same. This suggests that all vertebrates have evolved from a common ancestor.


Analogous Organs
Those organs which have different origin and structural plan, but appear similar and perform similar functions, are called analogous organs e.g., Plants tendrils help in climbing but they can be modified leaves as in Lathyrus aphaca or modified leaf apex as in gloriosa or modified petiole as in Garden Nasturtium or modified stipules as in Smilax. So all these are modified from different parts but performing the same function.


a. Leaf Tendril

b. Petiole tendril


Explain the importance of fossils in deciding evolutionary relationships.

A broad historical sequence of biological evolution can be built up.

Habits and behaviour of extinct species can be inferred.

Fossils provide direct evidence of past life.

These provide convincing proof of organic evolution.


What evidence do we have for the origin of life from inanimate matter?

There is no natural discontinuity between life and the rest of creation. Scientific conclusions that include discontinuity in the operation of the universe are representative of theoretical error. This is true for gaps existing within mechanical theory, and it is true for the gap between mechanical theory and life. The universe includes mechanics, life and intelligence, all of which had the same origin. The universe gave birth to life. We are formed from its substance and are a part of its nature. Our particles of matter existed for eons as part of the inanimate universe before they joined together and became us. Our insignificant amount of common matter did not change its nature when it became us. It is still a part of the nature of the full universe. It will return again to the inanimate universe and be indistinguishable.


Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?

In asexual reproduction, organisms raised are the exact copies of their parents and are known as clones. Due to their identical set of chromosomes, they exhibit no or very little variations. These variations may be either due to some environmental factors like light, scarcity of food, abundance of food, temperature etc. or mutations that are sudden changes in genes. Out of these two factors, only mutations are heritable.


In sexual reproduction, two parents are involved and there is formation and fusion of gametes. Due to crossing over and exchange of gene segments, offspring show variations from their parents. They are not the carbon copies of their parents. Due to recombination of parental genes, variations occur which are heritable.


How is the equal genetic contribution of male and female parents ensured in the progeny?

During gametogenesis meiotic division results in haploid set of chromosomes in the gametes. These gametes ( egg and sperm) when fuses or fertilization process occurs, half of the chromosome of the zygote consists of paternal genes and half maternal genes.

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