Section II: Short Answer Questions

Explain the homologous structures in plants.
Ans; Homologous structures are organs that have a similar structure but different functions. These structures are similar anatomically because they were inherited from a common ancestor. The cactus has modified its leaves into small needle-like structures to reduce water loss in dry areas with high temperatures and to protect itself from herbivores (animals that feed on plants).

Why the theory of evolution was attributed to Darwin?
Ans; Evolution had been proposed before, but Darwin’s really new idea was natural selection. Darwin formulated the theory of natural selection, which provides a mechanism for evolution. He proposed that organisms with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits to the next generation. His many books provided thorough, detailed, and compelling arguments for natural selection and evolution.

What is meant by descent with modification?
Ans; It is an important postulate of Darwin theory of Natural selection. According to Darwin species change over time, give rise to new species and share an ancestor is known as “descent with modification,”. In simple words, “descent with modification,” means the descendants produced from ancestor will always be different/modified.

Which variety was more common when there was more air pollution? Give a reason as well.
In England 90% of the peppered moth during the industrial era of pollution was black. This is because Sulphur dioxide from coal burning blackened tree trunks and walls. This made the light-colored peppered moth more visible to predator birds, while the black form was better camouflaged. Over time, black moths became more common.

Which variety is more common in England nowadays? Give a reason as well.
After the 1950s, England industrial pollution was reduced and as a result the number of light-colored peppered moths became more common again. This is because the tree trunks became cleaner and lichen growth increased, making the light-colored peppered moth better camouflaged.

Define/Describe/Explain briefly:
evolution, homologous organs, speciation, natural selection, artificial selection, industrial melanism, paleontology, comparative anatomy, vestigial organs, selective breeding,

Evolution
The slow change in living things over time, leads to new species. It happens as organisms adapt to their environment and pass on traits to their offspring.
Homologous Organs
Body parts in different animals or plants that have a similar structure but do different jobs. Example: A bat’s wing and a human’s arm are homologous because they have the same bone structure but different functions.
Speciation
The process by which new species are formed. This happens when groups of the same species become so different that they can no longer reproduce together.
Natural Selection
A process where organisms with traits that help them survive (like better camouflage) are more likely to reproduce and pass those traits to their offspring.
Artificial Selection
When humans choose specific traits in plants or animals and breed them to produce offspring with those traits. Example: Breeding dogs for size or farming crops for sweetness.
Industrial Melanism
A change in the color of species (like moths) due to industrial pollution. Example: Dark-colored moths became more common during the Industrial Revolution because they were harder for predators to see on polluted, dark trees.
Palaeontology
The study of fossils (remains of extinct plants and animals) to learn about life from the past and how it has changed over time.
Comparative Anatomy
Comparing the body structures of different animals to understand how they are related. Example: Similar bone patterns in a human arm, a dogs leg, and a whale’s flipper show they share a common ancestor.
Vestigial Organs
Body parts that no longer have a use but were useful to ancestors. Example: The human appendix, wings of flightless birds, leaves of cacti.
Selective Breeding
When humans choose certain plants or animals with specific traits to breed, creating new varieties or breeds over time. Example: Growing bigger fruits or breeding cows for more milk.

Differentiate between natural and artificial selection.

Natural Selection	Artificial selection
Selection occurs when natural environmental conditions changes.	It is selected by man.
Varieties are produced by mutations.	Varieties are produced by selective breeding.
It operates in a natural population.	It operates in a domesticated population.
It is a slow process and takes thousands to millions of years.	It is a fast process, and results are immediate (in the next generation).
It is responsible for the great biological diversity.	It is responsible for new varieties different from starting generation.

Section III: Extensive Answer Questions

What is variation? Explain the sources of variation.
Ans; The term variation refers to the differences in traits displayed by members of the same species. For instance, although all domestic cats are members of the same species, they differ greatly in terms of size, coat colour, eye colour, hair length, and other characteristics.
Sources of variations

1. Genetic recombination results from crossing over during gamete development.
2. Different chromosome combinations in gametes are formed by independentcollections of chromosomes.
3. The process of fertilization in which one of the countless sperms’ fuses with an egg.
4. A mutation in the gamete-forming germ cells.
5. Gene flow, or the transfer of genes from one population of a species to another.

Assess selection as a possible means of evolution.
Selection is one of the main ways evolution happens. It decides which traits get passed on to the next generation. There are two main types of selection: natural selection and artificial selection.

Natural Selection
In nature, some organisms have traits that help them survive better in their environment. These organisms are more likely to survive, reproduce, and pass on those helpful traits to their offspring. Over many generations, these traits become more common, and the species evolves.

Artificial Selection
Humans choose which traits they want in plants or animals and breed only those with those traits. This changes the species over time, but it’s guided by humans, not nature.

Explain the theory of evolution by natural selection with examples.
Theory Natural Selection
Natural selection is the process through which organisms who possess traits that are helpful for reproduction in a certain environment produce more children in the following generation. As a result, they gradually expand the population’s genetic diversity. Natural selection theory is based on:

1. Overproduction: All living creatures are very fertile so that their populations could grow quickly to produce large number of offspring.
2. Competition: We can observe that population sizes do not rise to a very high level even after overproduction. The numbers stay constant. This is because food supplies and other resources are scarce. As a result, there is competition for resources and food.
3. Variations: No two organisms are the same. They will not have the same opportunities to survive and reproduce as others. A large portion of this diversity is heritable. Such qualities are inherited from parents through the genes of the offspring.
4. Natural selection: Only those organisms who live and reproduce can give rise to the next generation. And only those organisms with the desirable variations will live till reproductive age. The population will have more advantageous genetic variations and fewer harmful ones after many generations. Natural selection is essentially an elimination process. Only fittest organisms will survive.

 Real-Life Example:
Peppered Moths: During the Industrial Revolution in England, trees became darkened by soot. Light-colored moths, which were once camouflaged, became easy targets for predators, while dark-colored moths were harder to spot. Over time, the population shifted to mostly dark-colored moths. When pollution decreased and trees became lighter again, the moth population shifted back to being mostly light-colored.
This process of natural selection explains how species evolve and adapt to their environments over time

Discuss briefly the observations Darwin made during his voyage on HMS Beagle.
Ans; Charles Darwin’s voyage on the HMS Beagle was crucial in shaping his ideas about evolution and natural selection. During the journey, he made several key observations:

1. Diversity of Life: Darwin noticed the variety of plants and animals in different regions. He observed how species in similar climates, such as in South America and Africa, were not identical but still shared some similarities.
2. Fossil Evidence: In South America, he discovered fossils of extinct animals, which resembled but were different from living species. This made him wonder about how species changed over time.
3. Galápagos Islands: In the Galápagos, Darwin observed unique animals like finches that varied from one island to another. For example, the finches had different beak shapes depending on their food sources, suggesting adaptation to their environment.

Describe speciation.

Ans; The evolutionary process by which new biological species arise is called speciation. Two groups that originate from the same ancestor can become very different over time if they live in different places. When a species gets split into two geographical regions, the process of speciation starts. Each adapts to its own environmental conditions. After a while, individuals from one group can no longer reproduce with the other group. Ultimately, two new species have evolved from one.

Describe the evidence of evolution according to palaeontology.
Palaeontology is the study of fossils (the remains of ancient plants and animals). It gives strong evidence for evolution because fossils show how life on Earth has changed over millions of years.

How Fossils Prove Evolution:
By studying fossils, scientists can see what ancient plants and animals looked like and compare them to modern species. Fossils also show “in-between” species that connect ancient organisms to modern ones. Fossils of animals like dinosaurs show that some species no longer exist. This shows how species evolve or die out when they can’t adapt. Fossils of ancient horses show they were small, had multiple toes, and lived in forests. Over millions of years, horse fossils show they became larger, developed a single toe (hoof), and adapted to grasslands.

How comparative anatomy proves evolution?
Comparative anatomy is the study of similarities and differences in the body structures of different organisms. It provides strong evidence for evolution by showing how different species are related and have evolved from a common ancestor.
How It Proves Evolution:
a) Homologous Structures
These are body parts in different species that have a similar structure but may perform different functions. For example: A human arm, a bird’s wing, a dog’s leg, and a whale’s flipper all have the same bone structure but are used for different functions. This shows they all evolved from a common ancestor and adapted to different environments over time.
b) Vestigial Organs
These are body parts that no longer have a use but were functional in ancestors. For example: The human appendix, wings of flightless birds. This shows how species have changed over time, keeping structures, they no longer need.

Describe the evidence of evolution according to Selective breeding.
Selective breeding (also called artificial selection) is when humans choose specific traits in plants or animals and breed them to produce offspring with those traits. It provides evidence for evolution because it shows how living things can change over time when certain traits are favored.

How It Proves Evolution:
a) Humans act like nature: In natural selection, the environment “chooses” traits that help organisms survive. In selective breeding, humans choose the traits they want. Both processes cause changes in species over time.
b) Changes over generations: Selective breeding shows that species can change dramatically in a short time when certain traits are consistently selected.

For Examples:
a) Dogs: All dog breeds were bred from wolves. Humans selected traits like size, fur color, and behavior to create different breeds.
b) Crops: Modern corn was bred from a wild grass called teosinte. By selecting plants with bigger seeds and better taste, humans created the corn we eat today.

A species of snail may have a yellow, pink or brown shell. Each color shell may have dark bands or have no bands. The snails are eaten by birds. The following observations were made:
• Most snails living on a plain background have no bands.
• Most snails living on green background are yellow.
• Most snails living on rough background have bands.
(a) Suggest an explanation or these observations.
(b) Predict the colour of snails living on dead leaves.
(c) Suggest which colour snails will be in summer and autumn.

 (a) Explanation of the Observations:
The variation in snail shell colors and patterns is an example of natural selection. Birds are the predators, and snails that blend in with their environment are less likely to be seen and eaten. Over time, the snails that are best camouflaged in their specific surroundings survive and reproduce, passing on their traits.

• Plain background: Snails with no bands are harder to spot on a plain background, so they are more likely to survive.
• Green background: Yellow snails blend in better with the green surroundings, making them less visible to birds.
• Rough background: Snails with bands mimic the rough, textured patterns of their environment, giving them better camouflage.

(b) Predict the Color of Snails Living on Dead Leaves:

Snails living on dead leaves are likely to be brown because this color blends well with the earthy tones of dead leaves, offering better camouflage.

(c) Predict the Color of Snails in Summer and Autumn:

• Summer: In summer, with lush green vegetation, yellow snails are likely to be more common because they blend with green surroundings.
• Autumn: In autumn, as leaves turn brown, brown snails will be more common because they match the color of the fallen leaves.

 Many small volcanic islands are located near South America; these are called
Galapagos islands. There is only one species of finches on South America continent but there are 14 species of finches on Galapagos islands. Why are there more species on Galapagos islands as compared to mainland?

The Galápagos Islands have more species of finches compared to mainland South America because of a process called adaptive radiation. This happens when a single species evolves into many different species to adapt to different environments.
How it Happened:
A long time ago, one species of finch from South America flew to the Galápagos Islands. The islands had many different habitats, like forests, dry areas, and rocky regions. Each habitat had different types of food, like seeds, insects, or fruits. The finches adapted to these different environments by developing specialized beaks suited for the type of food they ate:

1. Finches that ate seeds developed strong, thick beaks.
2. Finches that ate insects developed long, pointed beaks.

Over time, these groups of finches became so different from each other that they turned into separate species.

Why It’s Different from the Mainland:
On the mainland, there’s more competition, and the environment is more uniform. This didn’t push the finches to evolve into many different species like it did on the islands, where there were fewer competitors and a variety of environments.In conclusion, The Galápagos Islands have more finch species because they provided many different environments. The finches adapted to these environments, leading to the evolution of 14 different species. This is an example of how organisms evolve to fit their surroundings.