This biology question covers important biological concepts and processes. The step-by-step explanation below helps you understand the underlying mechanisms and reasoning.
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You're on a roll — here are the answers to your questions: 7. (a) What is natural selection? Natural selection is the process by which organisms better adapted to their environment tend to survive and produce more offspring. It is a key mechanism of evolution, driving changes in populations over time based on differential survival and reproduction. 7. (b) State two advantages of natural selection to organisms. • It leads to the adaptation of organisms to their specific environments, increasing their chances of survival and reproduction. • It drives the evolution of new species (speciation) over long periods, increasing biodiversity. • It helps to remove less fit individuals from a population, strengthening the gene pool. 8. The illustrations below explain the two mechanisms of evolution according to Lamarck (first illustration) and Darwin (second illustration). Explain the Mechanisms: 8. (a) (i) First illustration (Lamarck's theory) This illustration depicts Lamarck's theory of inheritance of acquired characteristics. It suggests that giraffes originally had short necks. As they stretched their necks to reach higher leaves on trees (use), their necks gradually elongated during their lifetime. This acquired trait (longer neck) was then passed on to their offspring, leading to progressively longer-necked generations. 8. (a) (ii) Second illustration (Darwin's theory) This illustration depicts Darwin's theory of natural selection. It suggests that within a population of giraffes, there was natural variation in neck length (some had slightly longer necks, some shorter). In an environment where food was scarce at lower levels, giraffes with naturally longer necks had an advantage, as they could reach more food. These longer-necked giraffes were more likely to survive, reproduce, and pass on their long-neck genes to their offspring. Over many generations, the proportion of long-necked giraffes in the population increased. 8. (b) Explain the following terms giving examples in each case: 8. (b) (i) Struggle for existence Struggle for existence refers to the competition among organisms for limited resources (like food, water, shelter, mates) and against environmental challenges (like predators, diseases, harsh climate). This competition determines which individuals survive and reproduce. Example: In a forest, many seedlings sprout, but only a few will grow into mature trees due to competition for sunlight, water, and nutrients. 8. (b) (ii) Survival of the fittest Survival of the fittest is the outcome of the struggle for existence, where individuals with traits that are best suited or "fittest" for their environment are more likely to survive, reproduce, and pass on those advantageous traits to the next generation. Example: In a population of deer, those with faster running speeds are more likely to escape predators and survive to reproduce, thus demonstrating "survival of the fittest." 9. (a) Name three evidences which suggests that evolution is still taking place. • Development of antibiotic resistance in bacteria. • Development of pesticide resistance in insects. • Changes in beak size of finches in response to food availability. • Industrial melanism in peppered moths. • Evolution of drug resistance in viruses (e.g., HIV). 9. (b) The figure below shows two variants of a beetle species. Using Darwin's theory of natural selection, explain how one of the variants may eventually become extinct in this habitat. The figure shows light-colored beetles and dark-colored beetles. If this habitat has a dark-colored background (e.g., dark soil or tree bark), the light-colored beetles would be more conspicuous to predators (like birds). Predators would easily spot and consume the light-colored beetles, reducing their numbers. The dark-colored beetles, being camouflaged against the dark background, would be less visible to predators, increasing their chances of survival and reproduction. Over successive generations, the dark-colored beetles would pass on their genes, while the light-colored beetles would be selected against, leading to a decline in their population and eventual extinction in that specific habitat. 10. (a) 10 years ago, chloroquine was an effective anti-malarial drug. Recently this has been banned in the market. Explain why certain drugs become ineffective in curing diseases after many years. Drugs become ineffective due to the evolution of drug resistance in the disease-causing organisms (e.g., malaria parasites, bacteria). Within a population of pathogens, there are naturally occurring genetic variations, some of which confer resistance to a particular drug. When the drug is administered, it acts as a selective pressure, killing off the susceptible pathogens. The resistant pathogens survive, reproduce, and pass on their resistance genes to their offspring. Over time, the resistant strain becomes dominant in the population, rendering the drug ineffective. 10. (b) What biological process has occurred in this situation? The biological process that has occurred is natural selection (specifically, drug resistance or evolutionary adaptation). 10. (c) Suggest resultant effect of the biological process mentioned above after long period of time. The resultant effect is the emergence of superbugs or highly resistant strains of pathogens, leading to increased difficulty in treating diseases, higher mortality rates, and the need for continuous development of new drugs. 11. Briefly describe how industrial melanism can be used to provide evidence for evolution. Industrial melanism in peppered moths (Biston betularia) provides a classic example of evolution by natural selection. Before the Industrial Revolution, light-colored moths were prevalent because they were camouflaged against light-colored lichen-covered trees. Dark-colored moths were rare. With industrial pollution, soot darkened tree trunks and killed lichens, making the light-colored moths conspicuous to predators. The dark-colored moths, however, became camouflaged. As a result, predators selectively ate the light moths, leading to an increase in the population of dark moths. This shift in moth coloration demonstrates how environmental changes can drive rapid evolutionary adaptation through natural selection. 12. Compare and contrast Lamarck's and Darwin's theories of evolution. Comparison (Similarities): • Both theories propose that species change over time (evolution occurs). • Both acknowledge that organisms adapt to their environment. • Both suggest that environmental factors play a role in shaping organisms. Contrast (Differences): • Lamarck's theory (inheritance of acquired characteristics) proposed that traits acquired during an organism's lifetime through use or disuse could be passed to offspring. Darwin's theory (natural selection) proposed that individuals with pre-existing, heritable variations that are advantageous in a given environment are more likely to survive and reproduce, passing those traits to offspring. • Lamarck suggested that individual organisms change in response to their environment and pass on those changes. Darwin suggested that populations change over generations due to differential survival and reproduction of individuals with advantageous inherited traits. • Lamarck's mechanism involved a purposeful striving or internal drive for perfection. Darwin's mechanism was random variation acted upon by natural selection, with no inherent direction or purpose. 13. Explain the role played by mutations in evolution. Mutations are random, heritable changes in the DNA sequence of an organism. They are the ultimate source of all new genetic variation within a population. While many mutations are neutral or harmful, some can be beneficial, providing new traits that might enhance an organism's survival or reproductive success in a particular environment. This new variation is the raw material upon which natural selection acts, allowing populations to adapt and evolve over time. Without mutations, there would be no new traits for selection to favor, and evolution would cease. 14. Explain how microorganisms become resistant to drugs. Microorganisms become resistant to drugs through a process driven by natural selection. Within a large population of microorganisms, random mutations occur in their genetic material. Some of these mutations may confer a slight advantage, such as the ability to neutralize a drug or pump it out of the cell. When a drug is introduced, it acts as a strong selective pressure, killing off the vast majority of susceptible microorganisms. The few individuals that possess the resistance-conferring mutation survive. These resistant microorganisms then reproduce rapidly, passing on their resistance genes to their offspring. Over time, the population becomes dominated by drug-resistant strains, rendering the drug ineffective. 15. Explain the emergent of webbed feet of ducks using Lamarck's theory. According to Lamarck's theory, the webbed feet of ducks would have emerged through the principle of use and disuse and the inheritance of acquired characteristics. Ancestral ducks, needing to swim to find food or escape predators, would have repeatedly stretched the skin between their toes (use) to propel themselves more efficiently through water. This continuous stretching would have caused the skin between their toes to gradually enlarge and become webbed during their lifetime. This acquired trait (webbed feet) would then be passed on to their offspring. Over many generations, this continuous use and inheritance of the acquired webbed feet would lead to the fully webbed feet observed in modern ducks. Last one for today! Got more? Send 'em.