OBJECT To study homologous and analogous organs in various plants and animals and comment on them. Vertebrate Forelimbs (Homologous organs) Homologous organ among plant, wings or flying animal (analogous organs)

• EXPERIMENT 7

OBJECT

To study homologous and analogous organs in various plants and animals and comment on them. 

Vertebrate Forelimbs (Homologous organs)

Comments:-

1.The forelimbs of frog, lizard, pigeon, mole, bat, whale horse and human have the same basic structural plan.

2. In each case the fore limb consists of an upper arm,fore arm, wrist, palm and fingers.

3. The upper arm is always made up of humerus, the fore-arm composed of radio-ulna the wrist consists of carpals and the palm containing metacarpals and digits.

4. The skeletal parts of the forelimbs of all vertebrates are similar in structure and arrangement. But the fore-limbs of these animals have different shape sand functions.

5. In frog they are used for leaping, in lizard for creep-ing, in pigeon for flying, in mole for digging, in bat for flying, in whale for swimming, in horse for run-ning and in human for grasping.

Therefore, the above organs offer an example of homologous organs.

Homologous Organs Among Plants

Comments

1. In plants the homologous organs may be a thorn in Bongainvillea or a tendril of cucurbita, both arising in the axillary position.

2. The leaves of higher plants arise from nodes possess, axillary buds and produce a gap in the vascular supply of the stem.

3. In form the leaves may be sessile petiolate, simple or compound, reduced to scales, modified into spine for protection and tendril's for climbing.

4. These modifications indicate the evolution of the organs to suit different functions.

Wings or Flying Animals (Analogous organs)

Comments

1. The wings of an insect are analogous to wings of Pterodactyl (extinct flying reptile), of a bird and of a bat.

2. It is due to the fact that the basic structure of the wings of the insects is different from the wings of Pterodactyl, a bird a bat. However, their function is similar.

Photosynthetic organs in some plants

Comments

1. Leaves are the plant organs specialized for photosynthesis. However, there are plants, where the leaves are modified or reduced in response to a particular environment or requirement.

2. The function of leaves is then taken over by other organs like stipules (e.g. Lathyrus aphaca), petiole(e.g. Acacia auriculiformis) and stem branches (e.g. Ruscus, Asparagus).

3. Similarly plant tendrils are meant for climbing. They can be desired from stem branches (e.g. Passiflora),leaves (e.g. Lathyrus aphaca) leaf apex (e.g. Gloriosa) petiole (e.g. Garden nasturtium) or stipules(e.g., Smilax).

4. They are the analogous organs amongst them.

5.The presence of analogous organs indicate a similar adaptation by unrelated groups though modification or evolution of different parts.