Question

A. What are the characteristics of an animal?

B. What are the four key evolutionary branch points in evolution of animals? Describe each branch point in detail including the animals that display those characteristics, the structural features that evolved as a result of the characteristic and the importance of this feature in the slow evolution of animals.

C. Compare and Contrast protostome and deuterostome development.

Answer 1

Answer:---

A- Organism which shows heterotrophic mode of nutrition with locomotion called animal.

Basic character of animals-

• Growth
• Definite shape and size
• Consumer
• Heterotrophic mode of nutrition
• Presence of notochord
• Conceousness
• Sensitivity
• Reproduction etc.

B- Level of organization, body symmetry, body plan and body cavity are four key evolutionary branch point of evolution in animals.

Level of organization - it is first key evolutionary branch point of animals it is following type

• Cellular level
• Tissue level
• Organ level
• Organ system level

Evolution point of view level of organisation indicate gradual development of complexity of body.

Body plan- arrangement of level of organisation in body calles body plan. Animals have following type of body plan .....

• Cell aggregate
• Blind sac
• Tube with in a tube

Body symmetry - Animals have following type of body symmetry.....

• Asymmetry
• Radial symmetry
• Bilateral symmetry

Symmetry plays important role in maintenance of body balance, locomotion, protection etc.

Body cavity - fluid filled space present between body wall and gut wall called body cavity or body coelom. Animals have following type of body cavity...

• Acoelom
• Pseudocoelom
• True coelom

Body cavity allows compartmentalization of body so the different type organ system can evolve and easily transport nutrients to other parts of body.

C - The body has two tubes, one formed by the body wall and second formed with in it by the digestive tract. Tube with in a tube body plan developed in animal by two ways ---

i - Protostomes

The mouth of the digestive tract develops first in the embryo and asshole is formed later. The animals which have this type body plan called protostomes. For example roundworms, annelids, molluscs, and arthropods.

Ii - Deuterostomes

The asshole of the digestive tract develops first in the embryo and mouth is formed later. The animals which posses this body plan are called deuterostomes. For example echinoderms, hemichordates and chordates.