1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers
with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
2. An example of homologous organs is
(a) our arm and a dog’s foreleg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.
3. In evolutionary terms, we have more in common with
(a) a Chinese school boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
5. How are the areas of study - evolution and classification - interlinked?
6. Explain the terms - analogous and homologous organs - with examples.
7. Outline a project which aims to find the dominant coat colour in dogs.
8. Explain the importance of fossils in deciding evolutionary relationships.
9. What evidence do we have for the origin of life from inanimate matter?
10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answers to NCERT solution exercises
1. Option (c)
TtWW represents the genetic make-up of the tall parent. TtWW could be the tall parent's genetic structure. Because half of the plantlets are short, this means that the parent plant has several short genes as well. Also, all offspring produced violet flowers, indicating that violet colour is dominant over white.
2. Option (d) All of the above is the right answer.
Homologous organs have the same origin as the previous organs but perform distinct roles. Homologous organs are organs from different species with a similar fundamental structure but diverse functions.
3. The option (a) Chinese schoolboy is correct.
In terms of evolution, we are more similar to a Chinese schoolboy because we are both members of the same species - Homo sapiens.
4. To determine whether a trait is dominant or recessive, you must have access to information about at least three generations. As a result, determining whether a character is dominant or recessive is not possible in this case.
5. Organisms are classified according to their relative similarities and differences. The similarities between species are attributable to a common ancestor, while the variances are due to adaptations to different environments. The fact that creatures may be classified in increasing complexity points to evolution. Organisms with similar traits are often grouped together whereas those with different qualities are classed or categorised differently. A collection of traits determines the level of evolution of an organism.
6. Homologous organs share the same fundamental structural architecture and origin but perform distinct roles. For example, the limbs of mammals and reptiles.
Organs that serve comparable functions but have a unique structural architecture and origin are analogous organs. For example, the wings of birds and the wings of bats.
7. The coat colour in dogs is decided based on the dominant gene in the offspring. Assume a homozygous black male and a brown homozygous female have copulated. If all the puppies are black, black is the dominant coat colour.
The presence of the dominant black gene will result in the black colour of the coat in all the offspring.
8. The following are some of the things we may discover from fossils:
- Fossils aid in the tracing of species' history
- They aid in the measurement of geological time
- Older fossils are found deeper in the ground, while newer fossils are found closer to the surface. Complex creatures are found at the top, whereas simple organisms are found at the bottom.
- Fossils such as Archaeopteryx demonstrate the relationship between two kinds of species.
9. In 1953, Miller and Urey created an atmosphere that resembled what was assumed to exist during the early era (with gases such as ammonia, methane, and hydrogen sulphide). Sparks were transmitted through the combination of gases to imitate illumination, which was kept at a temperature slightly below 100°C. After a week, 15 percent of the carbon (from methane) had been transformed into simple carbon compounds, such as amino acids, which are the building blocks of protein molecules. The presence of a protein cell membrane coincided with the results of the previous experiment. This demonstrated that life sprang from inanimate substances.
10. There occurs chromosomal 'crossing over' during sexual reproduction, which results in variations. These variations are hereditary and boost an organism's likelihood of living.
- Variations in sexual reproduction may develop as a result of DNA copying errors.
- Variations may occur as a result of the interchange of homologous chromosomes that occurs when male and female chromosomes cross over.
- It is not specified which gamete will unite with another gamete during sexual reproduction. It is entirely dependent on chance. It's also a source of variation.
These changes allow organisms to adapt to changing environments and contribute to the emergence of new species.
11. For most species, genetic material is organised into sets of chromosomes. Inheritance of the same number of chromosomes from each parent ensures equal genetic contribution of male and female parents in children.
12. The statement - Only variations that confer an advantage to an individual organism will survive in a population - is true. Individuals having a higher chance of surviving, reproduce within the population and transfer the advantageous mutation to their offspring. Natural selection is responsible for the evolution that takes place within organisms.