Tag: Science

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 Genetic recombination results from crossing over during gamete development. Different chromosome combinations in gametes are formed by independentcollections of chromosomes. The process of fertilization in which one of the countless sperms’ fuses with an egg. A mutation in the gamete-forming germ cells. 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