Variation

Variation is all the difference (in terms of physical characteristics) that exists between the members of the same species.

There are two types of variation:

  1. Continuous variation (affected by genes and the environment)
  2. Discontinuous variation (affected only by genes)

Continuous variation:

  • Differences in the features of a group of organisms, in which there are no definite categories; each individual’s characteristics can lie anywhere between two extremes.

Example:

  1. Height
  2. Weight
  3. Finger length
  4. Leaf length
  5. Heart beat rate

Discontinuous variation:

  • Differences in the features of a group of organisms, where each individual fits into one of a few clearly defined categories.
  • For example, blood group. Every person has a specific blood group and there are no exceptions to it; Blood groups always have specific categories such as A, B, O, and AB.

Genetic variation: where the genes affect an organism’s genotype and thus its phenotype.

Environmental variation: where the environment is responsible in interfering with the organism’s phenotype; For example, a pine tree has a genotype to grow tall. But it will not realize this until it has got enough space to grow. It may remain stunted for life!

Causes of variation

Cause Notes
Mutation Mutation is the change in the base sequence in the DNA.
Meiosis In meiosis, homologous chromosomes exchange genes and separate from one another.

Thus the genes formed are not exactly the same.

Fertilization When two haploid gametes fuse together and form a zygote, an organism that is completely different from its parents (in terms of genotype) is born.

This is why every person born is genetically unique! (I am sure you are as well unless you have a twin!)

Adaptation

  • Nature has an amazing rule- ‘survival of the fittest’. It means that an organism is much more likely to survive if it is well adapted.
  • The ‘fitness’ of an organism is the probability that it survives in the environment where it is found.
  • An adaptive feature is the inherited functional feature that increases an organism’s fitness.

Let us see how organisms are adapted to their environments:

Xerophytes :plants living in habitats where there is water scarcity
Adaptation How it increases the plant’s fitness
Closing Stomata Plants loose most water through the stomata by transpiration.

Stomata close when:

It is very hot and arid

Photosynthesis is not possible (at night!)

This helps conserve water by restricting plant growth (as photosynthesis is rarely possible.

Waxy cuticle The wax makes the leaf waterproof

It cuts down transpiration rates

Hairy leaves Some plants have thick growing hair present on their leaves.

These help to trap a layer of moist air next to the leaf.

Stomata on underside of leaves (or less stomata) Lower part of the leaf is usually cooler than the upper part

Less stoma means less transpiration, hence less growth.

Thus stomata are usually located in deep pits,

Leaves with lower surface area Cuts down transpiration rate (with a compromise on photosynthetic rates)

Hence conserves water

Have deep or spreading roots Deep roots can access water underground

Spreading roots can access water over a large area

 

Hydrophytes-Plants that live in very wet places and in water as well!
Adaptation How it increases the plant’s fitness
Roots not attached to riverbed Help the plant to float freely without the need of anchorage
Leaf stalks and stem have hollow air spaces To help plant float above water

For buoyancy

Get plenty of light for photosynthesis as they float above water

Stomata on both surfaces Helps absorb carbon dioxide for photosynthesis
Thin or no cuticle As there is no need of conserving water, a cuticle is not needed.

 

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