CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals

BASIC BUILDING CONCEPTS
The organs which have similar basic structure but perform different functions in different species are called homologous organs. For example, tendrils of pea plant and spines of Barberry. Both tendril of pea and spines of Barberry are modified leaves. So, structurally they are same. But due to different adaptations leaves in pea and Barberry are modified into different structures.
CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 1
The organs which are quiet different in fundamental structure but perform same function and superficially look alike in different species are called analogous organs. For example, tendril of pea and tendril of cucurbits. The tendril of pea is modified leaf but the tendril of cucurbits is modified stem. It means both tendril of pea and cucurbits are structurally different. But in both the plants they are adapted to perform same function, i.e., to climb a support.
CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 2

AIM
To study homology and analogy with the help of models/charts of animals and models/charts/ specimens of plants.

MATERIALS REQUIRED
Plant specimens such as Bougainvillea, cucurbits, potato and sweet potato. Animal models like bird, butterfly, forelimb of frog.

THEORY
Homologous organs: The organs which perform different functions in different species but have similar basic structure and similar embryonic origin are called homologous organs.
Analogous organs: The organs which are quiet different in fundamental structure and embryonic origin but perform same function and may superficially look alike in entirely different species are called analogous organs.

PROCEDURE

  1. Take the specimens/models/charts and observe them carefully.
  2. Record the structure and function of each specimen.
  3. Draw their neat and labelled diagrams.

OBSERVATIONS
A. Tendrils of cucurbits and spines of Bougainvillea

  1. Tendrils of cucurbits are modified stem which are used to climb a support.
  2. Spines of Bougainvillea are modified stem which are meant for protection.
  3. Both tendril of cucurbits and spines of Bougainvillea have same basic structural design but perform different functions. So, they are homologous organs.
    CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 3

B. Forelimb of frog and forelimb of bird

  1. The forelimb of frog consists of upper arm, fore arm, wrist, palm and five fingers. The upper arm is having humerus, fore arm with radius and ulna, wrist with carpels, palm have metacarpels and fingers have phalanges. The forelimb of frog helps the animal to prop up the front end of the body at rest and acts as a shock absorber when the animal lands on the ground after a leap.
  2. The forelimb of birds also has same basic plan of structure with an upper arm having humerus, a fore arm with radius and ulna, a wrist with carpels, a palm with metacarpels and five fingers with phalanges. The forelimb of the bird helps in flying.
  3. Both forelimbs of frog and bird show similarity in basic structure but perform entirely different function. So, they are homologous organs.
    CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 4

C. Potato and sweet potato

  1. In potato, eyes are present which are actually nodes. .
  2. Potato is a modified stem which is adapted to store the food.
  3. Sweet potato is a modified root which is meant for storage of food.
  4. Both potato and sweet potato are structurally different but they perform the same function, i.e., storage of food. So, they are analogous organs.
    CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 5

D. Wings of butterfly and wings of bird.

  1. The wings of butterfly are extensions of integuments which are supported by a few muscles and used for flying in the air.
  2. The wings of birds are formed of limb bones covered with flesh, skin and feathers. Birds also use their wings for flying.
  3. Both wings of butterfly and wings of birds are structurally different but they perform the same function. So, they are analogous organs.
    CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 6

RESULT AND DISCUSSION

  1. Homologous organs have same structure but are functionally different.
  2. Analogous organs have same function but are structurally different.

PRECAUTIONS
The specimens should be fresh and clean.

INTERACTIVE SESSION

Question 1.
What is the evidence of evolution?
Answer:
The fossil records, homologous organs, analogous organs, vestigial organs provide evidence for evolution.

Question 2.
What is the evidence of common ancestry?
Answer:
Homologous organs, vestigial structures, embryonic development provide evidence for common ancestry.

Question 3.
What do you understand by homology?
Answer:
Similarity in structure due to relatedness are known as homologies.

Question 4.
Give an example of homologous leaves.
Answer:
Pitcher of pitcher plant and spines of Opuntia.

Question 5.
Give an example of plant analogies.
Answer:
Tendril of cucurbits and tendril of pea.

Question 6.
Give an example of animal analogies.
Answer:
Wings of a bird and wings of a bat.

Question 7.
Give an example of animal homologies.
Answer:
Forelimb of frog, lizard, bird and human.

Question 8.
Why are thorn of Bougainvillea and tendril of Passiflora plant considered homologous organs?
Answer:
Both are structurally similar (modified stem) but perform different function.

Question 9.
How do embryological studies provide evidences for evolution?
Answer:
Embryological studies refer to study of development of an embryo of an organism from the fertilized egg to young one. This study shows that early embryos of fish, salamander, tortoise, chick, rabbit and human resemble in shape and structure. This similarity indicates that all vertebrates have evolved from a common ancestor.

PRACTICAL BASED QUESTIONS

Multiple Choice Questions/VSA (1 Mark)

Question 1.
The difference between homologous and analogous organs is that
(a) homologous organs have same design and function whereas analogous organs have different design and function.
(b) homologous organs have different design and function whereas analogous organs have same design and functions.
(c) homologous organs have same design but different functions whereas analogous organs have different design but similar function.
(d) homologous organs have different design but similar functions whereas analogous organs have same design but different functions.

Question 2.
One of the examples of analogous organs can be the wing of parrot and
(a) flipper of whale
(b) foreleg of horse
(c) front leg of frog
(d) wings of housefly

Question 3.
Which of the following pairs of organs is analogous to each other?
(a) Leaf spines and leaf tendrils
(b) Flipper of a whale and leg of a horse
(c) Wings of an insect and wings of a bat
(d) Forelimbs of a frog and human hand

Question 4.
The three long bones in your arm and in the wing of a bird are
(a) homoplastic structures
(b) homologous structures
(c) analogous structures
(d) all of the above

Question 5.
Thorns of Bougainvillea plant and tendril of cucurbits are
(a) homologous organs
(b) paralogous organs
(c) analogous organs
(d) orthologous organs

Question 6.
The similarity in bone structure in the forelimbs of many vertebrates is an example of
(a) analogy
(b) homology
(c) digitality
(d) convergence

Question 7.
An example of homologous organs is
(a) man’s arm and cat’s foreleg
(b) man’s teeth and elephant’s tusk
(c) potato and pumpkin
(d) all of the above

Question 8.
A student wants to collect analogous organs for his project. Which one of the following pairs would you suggest? [Foreign 2013]
(a) Forelimbs of frog and birds
(b) Thorn of bougainvillea and a tendril in cucurbits
(c) Wings of an insect and wings of a bird
(d) Forelimbs of horse and human arm.

Question 9.
Which of the following statements is true?
(a) Tendril of cucurbits and phylloclade of Opuntia are homologous.
(b) Tendril of cucurbits and phylloclade of Opuntia are analogous.
(c) Wings of birds and limbs of lizards are analogous.
(d) Wings of birds and wings of bat are homologous.

Question 10.
A basket of vegetables contain carrot, potato, radish and tomato. Which of them represent the correct analogous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) All of the above

Question 11.
Choose the right pair of analogous organs
(a) Forelegs of rabbit and frog
(b) Spines of cacti and Euphorbia
(c) Fins of fish and forelegs of lizard
(d) Fruits of apple and orange

Question 12.
Analogous pair of a sweet potato is
(a) onion
(b) ginger
(c) potato
(d) all of the above

Question 13.
Which of the following is correct?
(a) Homologous organs are structurally same.
(b) Analogous organs are structurally same.
(c) Homologous organs are functionally same.
(d) Analogous organs are functionally not same.

Question 14.
Which of the following are the examples of homologous organs?
(a) Venus fly trap and spines of cactus
(b) Tendrils of cucurbits and Venus fly trap
(c) Spines of Barberry and fruit of lemon
(d) Venus fly trap and pitcher plant.

Question 15.
When two organs have same structures but different functions they are
(a) homologous organs
(b) analogous organs
(c) vestigial organs
(d) none of the above

ANSWER KEY

  1. (c)
  2. (d)
  3. (c)
  4. (b)
  5. (a)
  6. (b)
  7. (a)
  8. (c)
  9. (a)
  10. (a)
  11. (b)
  12. (d)
  13. (a)
  14. (a)
  15. (a)

Short Answer Questions (2 Marks)

Question 1.
Giving an example explain what are homologous organs.
Answer:
The organs which have similar basic structures but perform different functions in different species are called homologous organs. For example, tendril of pea plant and spines of Barberry. Both tendril of pea plant and spines of Barberry are modified leaves. So, structurally they are same. But due to different adaptations, leaves in Barberry and pea are modified into different structures.

Question 2.
What are analogous organs? Give any two examples.
Answer:
The organs which are quite different in fundamental structure and embryonic origin but perform the same function and may superficially look alike in entirely different species are called analogous organs.
Examples:

  1. Wings of a butterfly and wings of a bird.
  2. Potato and sweet potato.

Question 3.
Out of potato, carrot, spines of cacti, spinach

  1. which two are homologous organs?
  2. which two are analogous organs?

Answer:

  1. Spines of cacti and spinach are leaf so structurally they both are same. But they perform different functions therefore, they are homologous organs.
  2. Potato is a underground stem and carrot is a root. Structurally they both are different but they are modified to perform the same function which is storage of food. Therefore, potato and carrot are analogous organs.

Question 4.
Differentiate between homologous and analogous organs.
Answer:
CBSE Class 10 Science Practical Skills – Homology and Analogy of Plants and Animals 7

Question 5.
Tendrils of cucurbits and spines of bougainvillea are homologous organs. Why?
Answer:
Tendril of cucurbits are modified stem which are used to climb a support. Spines of Bougainvillea are modified stem which are meant for protection. Both the organs have same basic structural design but perform different functions. So, they are homologous organs.

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