Lab Manual: Homology and Analogy of Plants and Animals | Lab Manuals for Class 10 PDF Download

Objective

• Specimens required for homology in animals are:
  Charts or model or preserved specimen of forelimb of bird, bat, man, seal, etc.
• Specimens required for homology in plants are:
  Preserved or fresh specimen of thorn of Bougainvillea and tendril of Cucurbita.
• Specimens/charts required for analogy in animal are:
  • Preserved forelimb of bat/bird.
  • Preserved wings of insects.
• Specimens/charts required for analogy in plants are:
  Preserved or fresh specimen of stem tendril in Passiflora and leaflet tendril in Pea.

Theory/Principle

• The organs or features which have common or similar fundamental structures but are involved in different functions in different species are referred to as analogous organs and their study is called as analogy. These similarities arise due to the adaptive convergence of the different organs to be used in similar environment, e.g. wings of bat and wings of an insect are analogous organs.
• Homology (similarities in traits of two different organisms) and analogy (similarities in functions of two different organisms) are common in occurrence in both plant and animal species. During the course of evolution, the organism adapts/recieves these organs or features from their ancestors.

Procedure

• The specimens of the limbs of both animals and plants are studied closely.
• Note the characteristic shape, structure, similarities, if any.
• Select the charts/figures of different animals and plants and study the details about homologous and analogous organs or features.
• Make a thorough observation of external and internal features and find out the similarity and dissimilarities (in structure and function) between them, then record your observations carefully in your notebook.

Observation
(i) Homology/Homologous Organs

• The structures depict the forelimbs of a man, cheetah, whale and bat (see Fig. 1) in the case of animals.
  
• The hand of a man, limb of cheetah, flipper of a whale and the wings of a bat have common set of bones but all of these structures though appears similar but are involved in different functions like grasping, running, swimming and flying respectively.
• The structures depict Bougainvillea (thorn) and Cucurbita (tendrils) (see Fig. 2) in the case of plants.

• The leaves of the plant Bougainvillea have been modified into the thorns for protection while leaves in Cucurbita are made into tendrils for providing support in climbers.
• These structures of animals and plants under study show homology, i.e. similarity in the fundamental (basic) structures due to shared or common embryonic origin but all of these organs/features performs different functions.

(ii) Analogy/Analogous Organs

• The structures depict the wings of a bat and wings of an insect (see Fig. 3) in case of animals.
  
• The forelimbs of bats, birds and wings of insects are used for flying by these animals however, they are structurally very different from each other.
• The structures depict Passiflora (stem tendril) and pea (leaflet tendril) (see Fig. 4) in case of plants.

• The Passiflora and pea have leaves modified into tendrils which support the plant during climbing whereas they do not share any structural similarities.
• The above structures of animals and plants under study shows analogy, i.e. they perform similar functions in different organisms but do not share same structure on the basis of origin.

Result
The observations made on the above given structures reveals that during course of evolution, some organs of same origin in different organisms have taken up different functions, such organs are called as homologous organs, e.g. forelimbs of vertebrates and leaves in plants.
Some organs, in contrary, have evolved to perform the same function but their origin is not same and they do not resemble or are not similar to each other, such organs are called as analogous organs, e.g. wings of insects and birds.

Precautions

• Handle the specimens carefully.
• Observe the similarities and dissimilarities (structural and functional) in both animals and plants; and note down carefully.