Class 12 Biology - Evolution

Activity 6.1: Study of Homologous and Analogous Organs

Aim: To identify and differentiate between homologous and analogous organs in plants and animals to understand divergent and convergent evolution.

Materials Required:

Specimens or Models:
- Homologous (Animals): Forelimbs of Man, Cheetah, Whale, and Bat.
- Homologous (Plants): Thorns of Bougainvillea and Tendrils of Cucurbita.
- Analogous (Animals): Wings of Butterfly and Wings of Birds.
- Analogous (Plants): Sweet Potato (Root tuber) and Potato (Stem tuber).
Dissecting microscope or magnifying lens

Procedure:

Examine the structural components of the forelimbs in mammals. Note the presence of the humerus, radius-ulna, carpals, metacarpals, and phalanges across all specimens.
Compare the origin of thorns in Bougainvillea and tendrils in Cucurbita (both arise from the axillary position).
Observe the structural differences between butterfly wings (integumentary folds) and bird wings (feathers covering the forelimb bony structure).
Analyze the storage organs of Potato and Sweet Potato.

Scientific Note Homology indicates common ancestry (Divergent Evolution). Despite performing different functions (grasping, running, swimming, flying), the underlying skeletal plan is identical. Analogy indicates similar environmental pressures (Convergent Evolution) leading to similar functional adaptations in phylogenetically unrelated organisms.

Observation:

Homologous Organs: Share a similar anatomical blueprint but different functions.
Analogous Organs: Different anatomical origins but perform identical functions.

Lab Best Practice When observing plant specimens, look specifically at the axillary bud position. If both structures arise from the same position, they are likely homologous regardless of their final appearance.

Activity 6.2: Simulating Natural Selection (The "Bead" Model)

Aim: To demonstrate how environmental pressure leads to changes in allele frequencies over generations (Microevolution).

Materials Required:

100 white beads and 100 black beads (representing two alleles)
A large container (Gene pool)
Tweezers (Environmental "Predator")
Stopwatch

Procedure:

Place 50 white and 50 black beads in the container.
Set a timer for 30 seconds. A "predator" (using tweezers) must pick as many white beads as possible (simulating a dark environment where white prey is easily spotted).
Record the number of surviving beads of each color.
"Reproduce" the survivors by adding an equal number of beads of the same color to the container for the next generation.
Repeat for 5 generations and plot a graph of Allele Frequency vs. Generation.

Scientific Note This is a simplified simulation of Industrial Melanism observed in the peppered moth (Biston betularia). Natural selection acts on the phenotype, but the resulting change is seen in the genotype frequency of the population.

Safety First Small beads can be a choking hazard. Ensure all materials are accounted for and stored properly after the activity.

Activity 6.1: Study of Homologous and Analogous Organs

Aim: To identify and differentiate between homologous and analogous organs in plants and animals to understand divergent and convergent evolution.

Materials Required:

Specimens or Models:

Homologous (Animals): Forelimbs of Man, Cheetah, Whale, and Bat.
Homologous (Plants): Thorns of Bougainvillea and Tendrils of Cucurbita.
Analogous (Animals): Wings of Butterfly and Wings of Birds.
Analogous (Plants): Sweet Potato (Root tuber) and Potato (Stem tuber).

Dissecting microscope or magnifying lens

Procedure:

Examine the structural components of the forelimbs in mammals. Note the presence of the humerus, radius-ulna, carpals, metacarpals, and phalanges across all specimens.

Compare the origin of thorns in Bougainvillea and tendrils in Cucurbita (both arise from the axillary position).

Observe the structural differences between butterfly wings (integumentary folds) and bird wings (feathers covering the forelimb bony structure).

Analyze the storage organs of Potato and Sweet Potato.

Observation:

Homologous Organs: Share a similar anatomical blueprint but different functions.

Analogous Organs: Different anatomical origins but perform identical functions.

Activity 6.2: Simulating Natural Selection (The "Bead" Model)

Aim: To demonstrate how environmental pressure leads to changes in allele frequencies over generations (Microevolution).

Materials Required:

100 white beads and 100 black beads (representing two alleles)

A large container (Gene pool)

Tweezers (Environmental "Predator")

Stopwatch

Procedure:

Place 50 white and 50 black beads in the container.

Set a timer for 30 seconds. A "predator" (using tweezers) must pick as many white beads as possible (simulating a dark environment where white prey is easily spotted).

Record the number of surviving beads of each color.

"Reproduce" the survivors by adding an equal number of beads of the same color to the container for the next generation.

Repeat for 5 generations and plot a graph of Allele Frequency vs. Generation.

Safety First Small beads can be a choking hazard. Ensure all materials are accounted for and stored properly after the activity.

Class 12 Biology - Evolution (Activities)

Class 12 Biology - Evolution

Activity 6.1: Study of Homologous and Analogous Organs

Activity 6.2: Simulating Natural Selection (The "Bead" Model)

On this page

Class 12 Biology - Evolution (Activities)

Class 12 Biology - Evolution

Activity 6.1: Study of Homologous and Analogous Organs

Activity 6.2: Simulating Natural Selection (The "Bead" Model)

On this page