A-Level Biology Paper 2 (7402) - Updated Version 2024, Exams of Biology

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A-Level (7 402 )

Biology

Paper 2 Updated Version 2024

QNS & ANS

1. Question: Describe how the process of photosynthesis in plants contributes to energy transfer in ecosystems. Answer : Photosynthesis converts solar energy into chemical energy by synthesizing glucose from carbon dioxide and water using chlorophyll, forming the base for energy transfer to consumers in the ecosystem.
2. Question: Name one adaptation of ectotherms that helps them survive in fluctuating temperatures. Answer : Ectotherms, like reptiles, often bask in the sun to absorb heat which raises their body temperature, allowing their metabolic processes to function adequately.
3. Question: Explain the significance of the Hardy-Weinberg principle in population genetics. Answer : The Hardy-Weinberg principle provides a mathematical model that describes how allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences.
4. Question: What is the role of operons in prokaryotic gene regulation? Answer : Operons are clusters of genes transcribed together under the control of a single promoter, enabling

coordinated regulation of gene expression in response to environmental changes.

5. Question: Give two examples of internal environments an organism might respond to and the corresponding response mechanism. Answer : 1) Internal pH levels: organisms can regulate enzyme activity to maintain optimal pH. 2) Blood glucose levels: organisms utilize insulin to lower blood glucose when levels are high.
6. Question: List the three main components of the cell theory. Answer : 1) All living organisms are composed of cells. 2) Cells are the basic unit of life. 3) All cells arise from pre-existing cells.
7. Question: What is the effect of temperature on enzyme activity? Answer : Temperature affects the kinetic energy of molecules; as temperature increases, enzyme activity typically increases until an optimum is reached, after which denaturation occurs.
8. Question: Describe the difference between mutations and polymorphisms. Answer : Mutations are changes in DNA sequences that can lead to variations in traits, while polymorphisms refer to variations in a population that are common and may not affect fitness.
9. Question: Explain the concept of ecological succession. Answer : Ecological succession is the process where one community replaces another over time, often after a disturbance, leading to a more stable ecosystem.
10. Question: What is the function of RNA polymerase in transcription? Answer : RNA polymerase synthesizes RNA by unwinding the DNA and adding complementary RNA nucleotides to form a primary transcript.

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Long Answer Questions

11. Question: Discuss the impact of climate change on energy transfer within an ecosystem, referencing specific examples. Answer : Climate change can disrupt energy transfer by altering plant growth patterns, leading to reduced photosynthesis and nutrient availability. For instance, rising temperatures can shift species distributions, affecting predator- prey dynamics. Additionally, increased CO2 levels may enhance plant growth initially (carbon fertilization), but extreme weather can lead to habitat loss, thus reducing the biomass and energy flow through food webs.
12. Question: Analyze the mechanisms of gene expression control in eukaryotic cells, including the roles of transcription factors and epigenetic modifications. Answer : In eukaryotic cells, gene expression is controlled at multiple levels. Transcription factors bind to specific DNA sequences to activate or repress transcription. Additionally, epigenetic modifications, such as DNA methylation and histone acetylation, alter chromatin structure, influencing gene accessibility. These mechanisms allow cells to respond to internal signals or environmental cues, ultimately directing development and adaptation.
13. Question: Evaluate the role of essential nutrients in energy transfers within living organisms, emphasizing ATP synthesis. Answer : Essential nutrients, such as carbohydrates, lipids, and proteins, serve as substrates for ATP synthesis. In cellular respiration, glucose is broken down through glycolysis and the Krebs cycle, producing intermediates that feed into the electron transport chain, ultimately leading to ATP production. Macromolecules also play roles in energy storage and transfer (e.g., fats store more energy per gram than carbohydrates), facilitating metabolic processes across the body's systems.
14. Question: Compare and contrast natural selection and genetic drift as mechanisms of evolution, providing examples of

each. Answer : Natural selection operates when individuals with advantageous traits reproduce more successfully in a given environment, leading to adaptive evolution (e.g., antibiotic resistance in bacteria). In contrast, genetic drift is a random process affecting allele frequencies, especially in small populations, leading to loss of genetic variation (e.g., the bottleneck effect after a disaster reduces genetic diversity). Both contribute to evolutionary change, but via different mechanisms and scales.

15. Question: Discuss how organisms adapt to both biotic and abiotic changes in their environments, with specific references to evolutionary mechanisms. Answer : Organisms adapt through evolutionary mechanisms like natural selection, where traits beneficial for survival in a changing environment become more common over generations. Biotic changes (e.g., competition, predation) might lead to behaviors like camouflage or social structures. Abiotic changes (e.g., climate, temperature fluctuations) might result in physiological adaptations like antifreeze proteins in polar fish. These adaptations stem from genetic variations that confer survival advantages, shaping populations over time.
16. Question: Describe the role of feedback mechanisms in maintaining homeostasis in organisms, providing examples relevant to temperature regulation and osmoregulation. Answer : Feedback mechanisms maintain homeostasis through negative and positive feedback loops. For temperature regulation (e.g., thermoregulation), when body temperature rises, mechanisms such as vasodilation and sweating activate to dissipate heat. In osmoregulation, when blood osmolarity increases, the body releases antidiuretic hormone (ADH) which promotes water reabsorption in kidneys, lowering osmolarity. These feedback systems ensure internal conditions remain stable despite external fluctuations.
17. Question: Explain the significance of the gene regulatory network in development and differentiation in multicellular organisms. Answer : Gene regulatory networks consist of interactions between various genes and the proteins they produce, which

coordinate the expression of genes required for development and differentiation. For example, during embryonic development, specific transcription factors activate genes necessary for forming different tissues and organs. Disruption of these networks can lead to developmental disorders or cancer, highlighting their critical role in proper organismal development.

18. Question: Examine the concept of carrying capacity and its implications for population dynamics within an ecosystem. Answer : Carrying capacity is the maximum population size that an environment can sustain indefinitely without degrading. When a population exceeds its carrying capacity, resources can become scarce, leading to increased mortality, decreased birth rates, and eventual population decline. These dynamics create fluctuations in population sizes, influencing biodiversity and ecosystem stability, as species compete for limited resources.
19. Question: Illustrate how epigenetic factors influence gene expression and how this can affect an organism’s phenotype without altering DNA sequences. Answer : Epigenetic factors, such as DNA methylation and histone modification, can silence or activate genes without changing the underlying DNA sequence. For example, the Agouti gene in mice can be epigenetically modified, resulting in coat color variations despite identical genetic sequences. Environmental influences like diet can trigger these epigenetic changes, leading to phenotypic variations that can sometimes be inherited, demonstrating that phenotype can be shaped by factors beyond the genetic code.
20. Question: Discuss the interrelationship between genetic variation, environmental pressures, and the process of evolution. Answer : Genetic variation arises from mutations, recombination, and gene flow, providing the raw material for evolution. Environmental pressures, such as changes in climate, habitat loss, or the introduction of new predators, exert selective pressure on populations. Individuals with advantageous traits are more likely to survive and reproduce, gradually leading to the evolution of those traits within the population. This interplay drives adaptation and biodiversity

over time.

Additional Questions (Short and Long)

21. Short Answer Question: What is the role of chlorophyll in photosynthesis? Answer : Chlorophyll absorbs light energy, primarily in the blue and red wavelengths, which is then used to convert carbon dioxide and water into glucose during photosynthesis.
22. Long Answer Question: Explain the impact of habitat fragmentation on genetic diversity within populations. Answer : Habitat fragmentation isolates populations, leading to smaller, more inbred groups with reduced genetic diversity. This can result in increased susceptibility to disease, reduced adaptability to environmental changes, and potential extinction, as genetic drift may lead to the loss of beneficial alleles over time.
23. Short Answer Question: Describe the function of ribosomes in protein synthesis. Answer : Ribosomes are the cellular machinery that translates mRNA into polypeptides by assembling amino acids in the sequence dictated by the mRNA transcript during the process of translation.
24. Long Answer Question: Analyze the effects of bioremediation on ecosystems, focusing on its mechanisms and implications for environmental health. Answer : Bioremediation employs microorganisms or plants to degrade or accumulate pollutants from the environment, effectively cleaning contaminated ecosystems. By breaking down harmful substances, such as oil spills or heavy metals, bioremediation can restore ecological balance, improve soil health, and enhance biodiversity. However, careful management is required to avoid introducing non-native species or unintended consequences.
25. Short Answer Question: What are plasmids, and how are they utilized in genetic engineering?

Answer : Plasmids are small, circular DNA molecules found in bacteria that can replicate independently. In genetic engineering, they are used as vectors to introduce foreign genes into host cells for various applications, including gene therapy and the production of recombinant proteins.

26. Long Answer Question: Discuss the implications of selective breeding on genetic diversity and traits in domesticated species. Answer : Selective breeding can enhance desirable traits in domesticated species, such as disease resistance or higher yield. However, this practice often reduces genetic diversity by favoring a narrow gene pool. Reduced diversity can lead to increased vulnerability to diseases, environmental changes, and unintended health issues due to inbreeding. The long-term sustainability of selectively bred species may be compromised without genetic variation.
27. Short Answer Question: Identify the process by which allele frequencies change due to random sampling effects in a population. Answer : The process is known as genetic drift, which can lead to significant changes in allele frequencies, especially in small populations.
28. Long Answer Question: Evaluate the role of symbiotic relationships in ecosystems, providing examples of mutualism, commensalism, and parasitism. Answer : Symbiotic relationships are interactions between different species that coexist in close proximity, and they play critical roles in ecosystem dynamics. In mutualism, both species benefit (e.g., bees and flowering plants), enhancing reproductive success and food availability. Commensalism benefits one species while the other is neither helped nor harmed (e.g., barnacles on whales). Parasitism benefits the parasite at the expense of the host (e.g., tapeworms in animals), potentially impacting the host's health and the ecosystem's stability by stressing the host population.
29. Short Answer Question: What is the principal function of the mitochondria in eukaryotic cells? Answer : Mitochondria are responsible for ATP production

through aerobic respiration, providing energy for various cellular processes.

1. Explain the role of ATP in energy transfers within cells. Provide an example of a process that requires ATP. Answer : ATP acts as the main energy currency in cells, transferring energy for cellular processes. An example is the sodium-potassium pump which requires ATP to maintain the membrane potential in neurons.
2. Describe the process of chemiosmosis in mitochondria and its importance in ATP synthesis. Answer : Chemiosmosis involves the movement of protons across the mitochondrial membrane, driving the synthesis of ATP via ATP synthase. It's crucial for energy production in cells.
3. Discuss how organisms utilize energy from the environment to maintain homeostasis. Answer : Organisms convert energy from their environment, such as sunlight or food, into usable forms like ATP, to drive processes that maintain a stable internal environment.
4. Compare and contrast the light-dependent and light- independent reactions of photosynthesis. Answer : The light-dependent reactions convert light energy into chemical energy (ATP and NADPH), while the light- independent reactions use these to fix carbon dioxide into glucose.
5. Evaluate the impact of temperature on enzyme activity in ectothermic and endothermic organisms. Answer : In ectotherms, enzyme activity increases with temperature up to a point, then rapidly decreases. Endotherms maintain a constant internal temperature, so enzyme activity remains stable.
6. How do guard cells regulate gas exchange and water loss in plants? Answer : Guard cells control the opening and closing of stomata, regulating gas exchange and transpiration by responding to environmental cues like light and humidity.

7. Define gene expression and outline the steps involved in going from a gene to a functional protein. Answer : Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein. It involves transcription and translation.
8. What is the significance of meiosis in genetic diversity? Answer : Meiosis introduces genetic diversity through independent assortment and crossing over, leading to unique combinations of genes in gametes.
9. Analyze the role of natural selection in shaping populations. Answer : Natural selection drives evolution by favoring individuals with advantageous traits, leading to changes in the genetic makeup of populations over time.
10. Discuss the concept of genetic drift and its potential effects on small populations. Answer : Genetic drift is the random change in allele frequencies, which can lead to significant genetic variation or loss of alleles in small populations.
11. Explain the Hardy-Weinberg principle and its conditions. Answer : The Hardy-Weinberg principle describes a population in genetic equilibrium. Its conditions include a large breeding population, random mating, no mutation, no migration, and no selection.
12. Describe the process of gene regulation in prokaryotes, using the lac operon as an example. Answer : In prokaryotes, gene regulation often occurs at the transcriptional level. The lac operon is regulated by the presence or absence of lactose, which controls the expression of genes involved in lactose metabolism.
13. How do epigenetic factors influence gene expression? Answer : Epigenetic factors, such as DNA methylation and histone modification, can alter gene expression without changing the DNA sequence, affecting how genes are turned on or off.

14. Outline the process of transcriptional regulation in eukaryotes. Answer : Transcriptional regulation in eukaryotes involves multiple levels of control, including promoter regions, enhancers, silencers, and transcription factors that interact to modulate gene expression.
15. Discuss the role of non-coding RNAs in gene regulation. Answer : Non-coding RNAs, like miRNAs and lncRNAs, play roles in gene silencing, regulation of transcription, and post- transcriptional modifications, influencing gene expression.
16. Explain how a signal transduction pathway leads to a cellular response. Answer : A signal transduction pathway involves the transmission of a molecular signal through a series of molecular changes, leading to a specific cellular response, such as gene expression or cell division.
17. Describe the feedback mechanisms involved in the regulation of blood glucose levels. Answer : Blood glucose levels are regulated by negative feedback mechanisms involving insulin and glucagon, which decrease or increase blood glucose levels, respectively.
18. How do mutations affect gene expression and potentially lead to disease? Answer : Mutations can alter gene expression by changing gene structure, regulatory elements, or protein function, potentially leading to diseases if they disrupt normal cellular processes.
19. Compare the roles of selective breeding and genetic engineering in altering the genetic makeup of organisms. Answer : Selective breeding involves choosing specific traits to propagate, while genetic engineering directly modifies the DNA to introduce desired traits.
20. Evaluate the ethical considerations of using CRISPR technology in gene editing. Answer : Ethical considerations include potential off-target effects, long-term impacts on the gene pool, and the

implications of editing human embryos or germline cells. <[assistant]> Short Answer Question: Describe the process of photosynthesis and its significance in energy transfer within ecosystems. Answer : Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose. This process involves the absorption of sunlight by chlorophyll, leading to the conversion of carbon dioxide and water into glucose and oxygen. Photosynthesis is significant as it forms the primary energy source for most ecosystems, supporting food chains and influencing energy transfer between organisms. Long Answer Question: Discuss how interspecific competition affects energy transfer between species in an ecosystem. Answer : Interspecific competition occurs when different species compete for the same resources, such as food, space, or light. This competition can impact energy transfer as species may alter their feeding habits or habitat use to reduce overlap. The outcome of such competition often influences population dynamics, species diversity, and overall ecosystem health. Energy transfer efficiency may decrease if dominant species monopolize resources, leading to reduced access for others and potentially lowering the overall productivity of the ecosystem. Short Answer Question: What role do enzymes play in metabolic pathways of organisms? Answer : Enzymes are biological catalysts that speed up chemical reactions in metabolic pathways by lowering the activation energy required for the reactions to occur. They are crucial for processes such as respiration and photosynthesis, allowing organisms to efficiently convert energy stored in nutrients into usable forms. Long Answer Question: Explain how organisms maintain homeostasis in response to external environmental changes. Answer : Organisms maintain homeostasis through various physiological and behavioral mechanisms that regulate internal conditions, such as temperature, pH, and ion concentrations.

For example, in response to rising external temperatures, mammals may sweat to promote evaporative cooling, while plants may close their stomata to conserve water. Feedback mechanisms, involving receptors, effectors, and control centers, are vital in detecting changes and initiating appropriate responses to restore balance. Short Answer Question: Define genetic drift and its impact on small populations. Answer : Genetic drift is a mechanism of evolution that refers to random changes in allele frequencies within a population, particularly affecting small populations. It can lead to reduced genetic variation and increased susceptibility to extinction as certain alleles may become fixed or lost purely by chance. Long Answer Question: Analyze the process of natural selection and its role in evolution. Answer : Natural selection is a key mechanism of evolution where individuals with advantageous traits are more likely to survive and reproduce in a given environment. Over time, these traits become more common in the population, leading to evolutionary changes. Factors such as variation, competition, and environmental pressures facilitate this process, resulting in adaptation and speciation. Short Answer Question: What is the significance of the Hardy- Weinberg principle in population genetics? Answer : The Hardy-Weinberg principle provides a mathematical framework for understanding genetic variation in a population at equilibrium. It states that allele frequencies will remain constant from generation to generation in the absence of evolutionary influences. This principle is significant as it serves as a null hypothesis for detecting evolutionary changes. Long Answer Question: Discuss the mechanisms of gene expression regulation in eukaryotic cells. Answer : Gene expression in eukaryotic cells is regulated at multiple levels, including transcriptional, post-transcriptional, translational, and post-translational stages. Transcription factors bind to specific DNA sequences to enhance or inhibit transcription. Additionally, RNA processing, such as splicing and the addition of a poly-A tail, influences mRNA stability and

translation efficiency. Epigenetic modifications, such as DNA methylation and histone acetylation, also play crucial roles in regulating gene expression, allowing cells to respond to environmental changes dynamically. Short Answer Question: Describe the significance of ATP in cellular energy transfer. Answer : ATP (adenosine triphosphate) is the primary energy currency of cells. It stores and transports chemical energy within cells, allowing for various biological processes, including muscle contraction, nerve impulse propagation, and biosynthesis. The hydrolysis of ATP releases energy, which is utilized by enzymes and other proteins to perform work. Long Answer Question: Evaluate the role of the electron transport chain in cellular respiration. Answer : The electron transport chain (ETC) is a series of protein complexes located in the inner mitochondrial membrane that plays a critical role in cellular respiration. Electrons derived from NADH and FADH2 are transferred through the chain, releasing energy used to pump protons across the membrane, creating a proton gradient. This gradient drives ATP synthesis via ATP synthase through chemiosmosis. The final electron acceptor, oxygen, combines with electrons and protons to form water, highlighting the chain's essential role in aerobic respiration and energy production. Short Answer Question: Explain the concept of ecological succession and its stages. Answer : Ecological succession is the process by which ecosystems change and develop over time. It occurs in two main stages: primary succession, which begins on bare substrates without soil (e.g., after a volcanic eruption), and secondary succession, which follows a disturbance in an existing ecosystem (e.g., after a forest fire). The stages involve pioneer species colonizing the area, leading to increased biodiversity and changes in community structure until a stable climax community is established. Long Answer Question: Analyze the relationship between genotype and phenotype with examples. Answer : The genotype refers to the genetic makeup of an

organism, while the phenotype is the observable characteristics resulting from the interaction of the genotype with the environment. For example, in pea plants, the genotype for flower color may be homozygous for purple (PP) or heterozygous (Pp), resulting in a purple phenotype due to the dominance of the purple allele. Environmental factors, such as soil pH or temperature, can also influence phenotypic expression, illustrating the complex interplay between genetics and the environment. Short Answer Question: What is the role of ribosomes in protein synthesis? Answer : Ribosomes are cellular structures that facilitate the synthesis of proteins by translating messenger RNA (mRNA) sequences into polypeptide chains. They consist of ribosomal RNA (rRNA) and proteins, and their function is crucial for decoding genetic information and assembling amino acids in the correct order to form proteins. Long Answer Question: Discuss the impact of human activities on genetic diversity in natural populations. Answer : Human activities, such as habitat destruction, pollution, and overexploitation of resources, significantly impact genetic diversity in natural populations. Habitat fragmentation reduces gene flow between populations, leading to inbreeding and loss of genetic variation. Additionally, pollution can introduce harmful substances that affect reproductive success and survival. Conservation efforts aimed at preserving habitats and promoting genetic diversity are essential for maintaining resilient ecosystems. Short Answer Question: Define and differentiate between the terms "haploid" and "diploid." Answer : Haploid refers to cells that contain a single set of chromosomes (n), such as gametes (sperm and egg cells). Diploid refers to cells that contain two sets of chromosomes (2n), typical of somatic cells in organisms. The haploid condition is crucial for sexual reproduction, ensuring that offspring receive genetic material from both parents. Long Answer Question: Evaluate how genetic mutations can lead to evolutionary changes within populations.

Answer : Genetic mutations are changes in the DNA sequence that can introduce new alleles into a population's gene pool. While many mutations are neutral or deleterious, beneficial mutations can confer advantages that enhance survival and reproduction. Over time, such advantageous mutations may become more prevalent through natural selection, contributing to evolutionary changes within populations. This process highlights the role of genetic variation in adaptation and the dynamics of evolution. Short Answer Question: What is the role of the nervous system in organism responses to stimuli? Answer : The nervous system plays a crucial role in detecting and responding to stimuli from the environment. It processes sensory information, coordinates responses, and facilitates communication between different body parts. Neurons transmit signals rapidly, allowing for quick reactions, essential for survival. Long Answer Question: Analyze the importance of biodiversity in ecosystem stability and resilience. Answer : Biodiversity is vital for ecosystem stability and resilience, as it enhances ecosystem functions and services, such as nutrient cycling, pollination, and disease regulation. Diverse ecosystems are better equipped to withstand environmental changes and disturbances, as a variety of species can fulfill different roles and provide redundancy. Loss of biodiversity can lead to decreased ecosystem functionality and increased vulnerability to stressors, highlighting the importance of conservation efforts. Short Answer Question: Describe the impact of climate change on species distribution and adaptation. Answer : Climate change significantly impacts species distribution as shifting temperatures and altered precipitation patterns can render habitats unsuitable. Species may migrate to more favorable conditions or adapt through evolutionary changes, such as phenotypic plasticity or genetic adaptation. However, not all species can adapt or migrate quickly enough, leading to potential declines in populations or extinctions. Long Answer Question: Discuss the ethical implications of

genetic engineering and gene editing technologies in modern biology. Answer : Genetic engineering and gene editing technologies, such as CRISPR, present significant ethical implications in modern biology. These technologies raise questions about the manipulation of genetic material, the potential for unintended consequences, and the long-term impact on biodiversity and ecosystems. Ethical considerations include the risks of creating genetically modified organisms (GMOs), the consequences of gene editing in humans, and the moral obligations to future generations. The balance between scientific advancement and ethical responsibility remains a critical discussion in the field of genetics and biotechnology.