SS3 Biology Lesson Note on Evolution

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TOPIC: EVOLUTION        

CONTENT:

1. Progressive change in structure and anatomy of organisms.
2. Structural adaptation: Adaptive colouration
3. Structural adaptation: For obtaining food.
4. Different castes of termites.
5. Different castes of bees.

 

SUB-TOPIC 1: PROGRESSIVE CHANGE IN STRUCTURE AND ANATOMY OF ORGANISMS.

Definition of Evolution

Organic evolution is the sum total of adaptive changes that have taken place over a long period of time in the life history of an organism. This process usually leads to the development of new species from pre- existing ones.

Organic evolution suggests that all living things have arisen from pre-existing ones by a gradual process of change over a long period of time.

Evolution proposes that life started in water; from marine water to fresh water to land and then to air. Progressive changes in the structure and anatomy of organisms have been going on as they inhabited these habitats at one time or the other. These changes enabled the organisms to be well adapted to the various habitats.

Organisms that live in water environment have streamlined body shape, soft and moist skin, water dependent reproductive system, efficient osmoregulator and other structural and anatomical adaptations.

The fore limbs of aquatic animals are also modified for swimming and orientation in water. These fore limbs in the course of progressive evolution changes are modified into crawling and hopping as in amphibians; running in reptiles; flight for birds and bat; climbing and swinging as in monkeys and walking and grasping as in humans and chimpanzees respectively.

All these animals have the same anatomical pattern of forelimbs but diversified structures for various adaptations in their respective habitats.

Similar structures that perform similar functions are called homologous structures. Dissimilar structures that perform similar functions are said to be analogous.

In the process of their evolution from water to land, Organisms progressively changed by possessing;

1. complex body posture to withstand gravity,
2. dry skin to prevent desiccation (drying up),
3. internal fertilization mechanism to ensure reproduction on land and
4. a modified osmo-regulator to conserve water on land.

EVALUATION

1. Describe how organisms evolved from one habitat to another.
2. State the changes that occurred in limb structure as organisms progressively evolved from one habitat to another.

SUB-TOPIC 2: STRUCTURAL ADAPTATIONS

To survive in their environments, organisms show different adaptations in their form and function. The following are some of the special adaptations shown by organisms for survival:

Adaptive Colouration: Many organisms posses bright, attractive colour with special markings on their bodies to help them obtain food, escape or hide from enemies and to secure mates. Some flowering plants have brightly coloured flowers which attract animal pollinators.

Warning Colouration: Many vulnerable preys develop bright colours and are bitter and unpalatable to their vertebrate predators. Distasteful insects are brightly coloured and conspicuous with contrasting pattern of different colour bands. Examples are lady bird beetles, wasps and butterflies. Even insects with nice taste but with colours like that of the unpalatable ones also survive.

Mimicry: This is the close resemblance of an animal called a mimic to another different object referred to as a model in order to increase its chances of survival. A harmless organism is usually protected from its predator by mimicking a dangerous species. A mimic and a model are naturally unrelated. For good success a mimic must also behave like the model in some ways.

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