Evolution : Grade 9

 EVOLUTION

1. What is evolution?

Ans: Evolution is the gradual change in organisms over generations leading to the development of new species.

2. What is organic evolution?

Ans:  Organic evolution is the process of gradual change in living organisms over time from simple to complex forms.

3. State the different evidences in support of organic evolution.

Ans: Evidences include fossil records, comparative anatomy, embryology, molecular biology, and geographical distribution.

4. What are homologous organs?

Ans: Homologous organs are organs that have similar structure but different functions, showing common ancestry.

5. What is the major contribution of Charles Darwin?

Ans: Charles Darwin proposed the theory of natural selection as the mechanism of evolution. This is the major contribution of Charlse Darwin.

6. Name two fossils of animals.

The name of two fossils of animals are: Archaeopteryx and Trilobite.

7. Which organ of man is homologous to the wings of birds?

Ans: The human arm is homologous to the wings of birds.

8. Which is the connecting link between reptiles and birds?

Ans: Archaeopteryx is the connecting link between reptiles and birds.

9. What causes origin of new species according to Hugo de Vries?

Ans: Mutation causes origin of new species according to Hugo de Vries .

10. Name some homologous organs in the vertebrates.

Ans: Homologous organs in vertebrates are: Forelimbs of human, patagium of bat, flippers of whale, and wings of bird.

11. What are vestigial organs?

Ans: Vestigial organs are body parts that have lost their original function through evolution.

12. Name a few vestigial organs in human body.

Ans: A few vestigial organs in human body are: Vermiform Appendix, wisdom teeth, tailbone (coccyx), and muscles of the ear (Pinnae).

C. Short answer type questions.

1. What is the main idea of the theory of specials creation?

The main idea of the theory of special creation is that the god, a supernatural power has created all the creature on the earth.

2. State the different evidences in support of organic evolution.

Different evidences in support of organic evolution are:

o   Fossil records showing gradual changes over time

o   Comparative anatomy (homologous and analogous structures)

o   Embryological similarities

o   Molecular biology and genetics

o   Biogeography (distribution of species across the globe)

3. Which of the fossils are the oldest and which one are more recent?

The fossils which are Simple, microscopic organisms like bacteria and algae from Precambrian times are oldest and complex plants and animals from later geological periods like the Cenozoic era are more recent.

4. What are the different aspects of struggle for existence?

Different aspects of struggle for existence:

• Competition for food and resources
• Competition for mates
• Predation and defence against predators
• Survival against environmental conditions

5. How do the fossils evidences support the theory of natural selection?

Ans: Fossils show gradual changes in species over time, showing that the traits favourable for survival become more common, and unfavourable traits (characters) are less common. This supporting the idea of natural selection shaping species.

6. Write any two proofs supporting Darwin’s theory of natural selection.

Ans: Two proofs supporting Darwin’s theory of natural selection:

• Variation exists within populations, providing material for selection
• Organisms produce more offspring than can survive, leading to competition and survival of the fittest

7. Write two differences between mutation theory of Hugo de Vries and Darwin’s theory of natural selection.

Ans: Two differences between mutation theory (Hugo de Vries) and Darwin’s theory:

o   Mutation theory emphasizes sudden, large changes (mutations) as the source of new species where as Darwin’s theory emphasizes gradual selection of small variations

o   Mutation theory focuses on genetic changes as primary cause but Darwin’s theory focuses on environmental selection pressures

8. What do you conclude from the study of embryos?

From the study of embryos we conclude that:
Embryos of different species show similar stages in early development, indicating common ancestry and evolutionary relationships.

9. Why is fossil record incomplete?

fossil record is incomplete because:
Because fossilization requires specific conditions, many organisms never fossilized; also, some fossils are destroyed by geological processes or remain undiscovered.

10. What do we deduce from fossil record? Write any two points.

we deduce following two points from fossil record.

• Life on Earth has changed gradually over millions of years
• Species have appeared, evolved, and gone extinct through geological time.

 

Long answer questions:

1.      How can you explain the close similarities between the embryos of different vertebrates?

The close similarities between the embryos of different vertebrates can be explained by their common ancestry.

During early stages of development, embryos of fish, amphibians, reptiles, birds, and mammals show close similarities — such as having gill slits, tail structures, and a similar body plan — even though they grow into very different adult forms.

These similarities suggest that all vertebrates have evolved from a common ancestor, and the early embryonic development has been conserved as evidence of evolution.

2.      How are fossils helpful in support of organic evolution.

Fossils support organic evolution by providing direct evidence of organisms that lived in the past and showing how species have changed over time.

They help in the following ways:

·       Fossils reveal how simple organisms evolved into more complex forms.

·       Some fossils like  Archaeopteryx show characteristics of two different groups, like reptiles and birds which is also evidence that organisms have been evolved from simple to complex.

·       Fossils of organisms that no longer exist show that species can arise and disappear, supporting the idea of evolution.

·       Fossils found in different layers of rock help trace evolutionary history in a time sequence.

3.      How are fossils formed? Explain.

Fossils are created through various processes, but they generally involve the remains of an organism being preserved over a long period. Here's a breakdown:

When a plant or animal dies, the organisms is buried by the  Sediment, such as mud, sand, or volcanic ash, covers the organism. The  minerals in groundwater seep into the remains of buried organisms. These minerals fill the pores and empty spaces within the bone or other tissue. Over time, the minerals harden and turn the remains into rock. Sometimes instead of filling the spaces, the original material of the organism dissolves and is replaced by minerals. The replacing mineral replicates the structure of the original organism. In some cases If an organism completely dissolves, it can leave an empty space in the rock called a mold. If that space then fills with sediment or minerals, it forms a cast, which is a replica of the original organism.

4.      How will you find the age of fossils?

To find the age of fossils, scientists primarily use these methods:

·       Radiometric Dating: In this method,  the amount of the original isotope and its decay product is measured and then the time elapsed since the material formed can be determined. For example, carbon-14 dating is useful for dating organic material up to around 50,000 years old. For older fossils, isotopes with longer half-lives, like uranium-238 or potassium-40, are used.

·       Relative Dating It's based on the principle that older layers are generally found deeper in the Earth than younger layers. By comparing the position of a fossil within these layers, its relative age can be estimated.

5.      How are evidences from homologous organs helpful in support of organic evolution?

Evidences from homologous organs are very helpful in supporting organic evolution because of the following reasons.

1.      Homologous organs have a similar basic structure but perform different functions in different species (e.g., the forelimbs of humans, bats, whales, and cats). This suggests that these species evolved from a common ancestor that had a basic limb structure.

2.      The presence of homologous organs indicates that organisms have inherited these structures from a common ancestor, supporting the idea of descent with modification.

3.      Over time, these organs have adapted to different environments and needs, showing how species evolve by modifying existing structures rather than creating entirely new ones.

6. How are evidences from vestigial organs helpful in support of organic evolution?

Evidences from vestigial organs support organic evolution by showing remnants of structures that were functional in ancestors but are now reduced or useless in modern organisms. Here’s how they help in organic evolution:

Vestigial organs, like the human appendix or whale pelvic bones, indicate that organisms have inherited these structures from ancestors in which they were useful. These organs are still functional in other animals. The reduction or loss of function in these organs demonstrates how species change over time, losing traits that are no longer needed due to changes in lifestyle or environment. The presence of vestigial organs aligns with the idea that natural selection favors traits that increase survival and reproduction, while unused organs may shrink or disappear.

7. Explain the use and disuse of organs with suitable example.

The theory of use and disuse of organs was proposed by Jean-Baptiste Lamarck to explain how organisms evolve traits during their lifetime. If an organism frequently uses a particular organ or body part, that organ becomes more developed and stronger. If an organ is rarely or never used, it becomes weaker and may eventually disappear over generations.

Example:

• Use: The neck of a giraffe – According to Lamarck, giraffes stretched their necks to reach higher leaves. Because they used their necks so much, their necks became longer and stronger over generations.
• Disuse: The eyes of cave-dwelling animals – Animals living in complete darkness, like cave fish, don’t use their eyes. Over time, their eyes become reduced or non-functional.

8. Explain the salient features of Hugo de Vries theory of mutation.

Here are the salient features of Hugo de Vries' theory of mutation:

a)      Sudden Changes: Mutations are sudden, spontaneous, and heritable changes in the genetic material that can produce new variations in organisms.

b)     Source of Variation: Mutations are the main source of genetic variation, which is essential for evolution.

c)      Discontinuous Variation: Mutation leads to discontinuous or saltational variations—large changes that differ markedly from the parent, rather than small gradual changes.

d)     Mutation is Random: Mutations occur randomly and are not influenced by the environment or the organism’s needs.

e)      Mutations Can Be Beneficial, Neutral, or Harmful: Some mutations can lead to advantageous traits that may be passed on to future generations, while others can be neutral or harmful.

f)        Mutations are Heritable: Once a mutation occurs, it can be passed on to offspring, contributing to evolutionary change.

g)      Evolution by Mutation: According to de Vries, mutation alone can drive evolution by producing new species through the accumulation of mutations.

9. According to Darwin theory of evolution, how does a new species evolve? Explain.

According to Darwin’s theory of evolution, a new species evolves through the process of natural selection acting on variation within a population. Here’s how it works:

a.      Variation: Individuals in a population show natural variations in traits (e.g., size, colour, behaviour).

2. Overproduction: Organisms produce more offspring than can survive, leading to competition for resources.
3. Struggle for Existence: Due to limited resources, individuals compete, and only some survive.
4. Survival of the Fittest: Individuals with traits better suited to the environment are more likely to survive and reproduce. These advantageous traits are called adaptations.
5. Inheritance: The favourable traits are passed on to the next generation.
6. Accumulation of Changes: Over many generations, these small changes accumulate, causing populations to gradually diverge.
7. Formation of New Species: When populations become so different that they can no longer interbreed and produce fertile offspring, a new species is formed.

 

 

 

10. How does variation help in evolution?

Individuals are not identical:  Within any species, there are differences in traits — such as size, color, disease resistance, speed, etc. These differences arise due to genetic variation and sometimes environmental factors.

Some variations are advantageous: In a given environment, certain traits make survival or reproduction easier.

Natural selection favors the beneficial traits: Individuals with favorable variations are more likely to survive and produce offspring. Over generations, the genes for those advantageous traits become more common in the population.

Adaptation to changing environments: If the environment changes — say, climate shifts or predators appear — variation means that some individuals might already have traits suited to the new conditions, giving the species a better chance to survive.

Long-term effect: evolution
Over many generations, the accumulation of selected variations can lead to the emergence of entirely new species — that’s evolution in action.

 

1.      Briefly explain how a new species is formed by natural selection.

 new species is formed by natural selection through the following process:

1.      Variation: Within a population, individuals have genetic differences or variations in traits, some of which may be inherited.

2.      Overproduction and Struggle for Existence: Organisms produce more offspring than can survive, creating competition for resources like food, space, and mates.

3.      Differential Survival and Reproduction: Individuals with traits better suited to their environment (adaptations) are more likely to survive and reproduce, passing those advantageous traits to their offspring.

4.      Accumulation of Changes: Over many generations, these advantageous traits become more common in the population.

5.      Reproductive Isolation and Speciation: Over long periods, populations may become so different genetically and adaptively (often due to geographic or reproductive barriers) that they can no longer interbreed, resulting in the formation of a new species.

 

2.      How can you say that complex forms have been evolved from simple ones?

You can say complex forms have evolved from simple ones based on multiple lines of scientific evidence:

1.      Fossil Record: Fossils show a clear progression from simple to more complex organisms over billions of years.

2.      Cellular Evolution: Scientific research indicates that complex eukaryotic cells evolved from simpler prokaryotic cells.

3.      Molecular Evidence: The genetic code and many biochemical systems are shared across all living organisms, suggesting common ancestry with increasing complexity.

4.      Examples of Gradual Complexity: Complex organs like eyes evolved through many intermediate stages, from simple light-sensitive patches in some flatworms to the sophisticated eyes found in vertebrates.

5.      Phylogenetic Relationships: Comparative anatomy and molecular biology reveal homologous structures and shared genes linking simple and complex organisms in an evolutionary tree, supporting the idea of descent with modification from simpler forms.