9th Biology Chapter7 Bioenergetics

Question 1. Explain Oxidation-Reduction Reactions in Biological Systems.
Answer:

Oxidation-reduction (redox) reactions involve the transfer of electrons between reactants. Oxidation refers to the loss of electrons by a molecule, while reduction refers to the gain of electrons. These reactions play crucial roles in cellular respiration, photosynthesis, and other metabolic pathways, where they transfer energy and drive biochemical processes.

Question 2. Explain the Mechanism of Photosynthesis.
Answer:

Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). During the light-dependent reactions, light energy is converted into chemical energy in the form of ATP and NADPH. In the light-independent reactions, ATP and NADPH are used to fix carbon dioxide into organic molecules, ultimately producing glucose.

Question 3. What are Limiting Factors in Photosynthesis?
Answer:

Limiting factors are environmental factors that directly affect the rate of photosynthesis by limiting the availability of resources or the efficiency of the process. The three main limiting factors in photosynthesis are light intensity, carbon dioxide concentration, and temperature.

Question 4. What is the Major Role of ATP in Cells?
Answer:

ATP, or adenosine triphosphate, serves as the primary energy currency of cells. Its major role is to store and transfer energy for cellular processes, including metabolism, biosynthesis, active transport, and muscle contraction.

Question 5. What is Respiration and Why is it Important for Living Organisms?
Answer:

Respiration is the process by which organisms obtain energy from organic molecules, such as glucose, through the breakdown of these molecules in the presence of oxygen. This process produces ATP, the energy currency of cells, which is used for various cellular activities. Respiration is essential for providing energy to carry out life-sustaining processes and maintaining cellular functions.

Question 6. Describe the Krebs Cycle (Citric Acid Cycle) and its Role in Aerobic Respiration.
Answer:

The Krebs cycle is the second stage of aerobic respiration that occurs in the mitochondrial matrix. It involves a series of enzyme-catalyzed reactions that oxidize acetyl-CoA, produced from pyruvate, to carbon dioxide. The Krebs cycle generates ATP, NADH, and FADH2, which carry high-energy electrons to the electron transport chain.

Question 7. Describe the Intake of Water by Plants.
Answer:

Plants absorb water from the soil through their roots. Specialized structures called root hairs increase the surface area for water absorption. Water travels upward through the plant’s vascular system to reach the leaves, where it is used during photosynthesis.

Question 8. What is Photosynthesis and Why is it Important for Plants and Other Organisms?
Answer:

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, while releasing oxygen as a byproduct. It is essential for producing food and oxygen, supporting life on Earth.

Question 9. How Does Temperature Affect Photosynthesis?
Answer:

Temperature affects the rate of photosynthesis by influencing the activity of enzymes involved in the process. Photosynthesis is an enzyme-catalyzed reaction, and enzymes have optimal temperature ranges at which they function most efficiently. As temperature increases within this range, the rate of photosynthesis increases. However, beyond the optimal temperature range, enzyme activity decreases, and photosynthesis is inhibited.

Question 10. Describe the Light-Dependent Reactions of Photosynthesis.
Answer:

The light-dependent reactions occur in the thylakoid membranes of chloroplasts. Light energy is absorbed by chlorophyll, which triggers the splitting of water molecules into oxygen, protons, and electrons. The energy from the electrons is used to generate ATP and NADPH, which are then used to power the light-independent reactions.

Question 11. Explain the Role of Carbon Dioxide and Water in Photosynthesis.
Answer:

Carbon dioxide (CO2) and water (H2O) are the raw materials used by plants during photosynthesis. Carbon dioxide is absorbed from the atmosphere through tiny pores called stomata on the leaves, while water is absorbed from the soil through the roots.

Question 12. Explain Anaerobic Respiration and its Types: Alcoholic Fermentation and Lactic Acid Fermentation.
Answer:

Anaerobic respiration is a type of cellular respiration that occurs in the absence of oxygen. In alcoholic fermentation, pyruvate is converted into ethanol and carbon dioxide, while in lactic acid fermentation, pyruvate is converted into lactic acid. These processes regenerate NAD+ from NADH, allowing glycolysis to continue producing ATP in the absence of oxygen.

Question 13. Explain the Role of Carbon Dioxide Concentration in Photosynthesis.
Answer:

Carbon dioxide concentration affects the rate of photosynthesis because it is one of the reactants used by plants to produce glucose. When carbon dioxide concentration is low, the rate of photosynthesis is limited, but as carbon dioxide concentration increases, the rate of photosynthesis also increases until it reaches a point of saturation.

Question 14. Compare Aerobic and Anaerobic Respiration.
Answer:

Aerobic respiration occurs in the presence of oxygen and results in the complete oxidation of glucose to carbon dioxide and water, producing a large amount of ATP. Anaerobic respiration occurs in the absence of oxygen and involves incomplete oxidation of glucose, leading to the production of ATP and metabolic byproducts such as ethanol or lactic acid. Aerobic respiration produces more ATP per glucose molecule compared to anaerobic respiration.

Question 15. Why is ATP Often Referred to as the Energy Currency of the Cell?
Answer:

ATP is often referred to as the energy currency of the cell because it provides the energy needed for various cellular activities. When ATP is hydrolyzed to ADP (adenosine diphosphate) and inorganic phosphate (Pi), energy is released, which can be used to drive endergonic (energy-requiring) reactions within the cell.

Question 16. How Does Light Intensity Affect Photosynthesis?
Answer:

Light intensity directly influences the rate of photosynthesis, as it determines the amount of light energy available for chlorophyll to absorb. At low light intensities, the rate of photosynthesis is limited, but as light intensity increases, the rate of photosynthesis also increases, up to a certain point where it plateaus and becomes saturated.

Question 17. Describe Aerobic Respiration and its Mechanism.
Answer:

Aerobic respiration is the process of cellular respiration that occurs in the presence of oxygen. It consists of three main stages: glycolysis, the Krebs cycle (citric acid cycle), and the electron transport chain. During aerobic respiration, glucose is completely oxidized to carbon dioxide and water, producing a large amount of ATP through oxidative phosphorylation.

Question 18. What is the Importance of Anaerobic Respiration?
Answer:

Anaerobic respiration is important for organisms that live in environments with low oxygen availability, such as certain bacteria, yeast, and muscle cells during intense physical activity. It allows these organisms to produce ATP and continue metabolic processes even when oxygen is scarce.

Question 19. Explain the Electron Transport Chain and its Role in Aerobic Respiration.
Answer:

The electron transport chain is the final stage of aerobic respiration that occurs in the inner mitochondrial membrane. It consists of a series of protein complexes and electron carriers that transfer high-energy electrons from NADH and FADH2 to molecular oxygen. This transfer of electrons drives the pumping of protons across the inner mitochondrial membrane, generating a proton gradient that powers ATP synthesis through oxidative phosphorylation.

Question 20. Differentiate Between Anaerobic and Aerobic Respiration.
Answer:

Anaerobic respiration occurs in the absence of oxygen and involves incomplete breakdown of glucose, leading to the production of energy and metabolic byproducts such as ethanol or lactic acid. Aerobic respiration occurs in the presence of oxygen and involves the complete breakdown of glucose into carbon dioxide and water, producing a large amount of ATP.

Question 21. Why is Photosynthesis Essential for All Life Forms?
Answer:

Photosynthesis is essential for all life forms because it is the primary process by which green plants, algae, and some bacteria produce organic molecules (such as glucose) using light energy, carbon dioxide, and water. These organic molecules serve as food and energy sources for all other organisms in the ecosystem, directly or indirectly supporting the survival and growth of all life forms on Earth. Without photosynthesis, there would be no food, oxygen, or energy available for sustaining life.

Question 22. What is the Role of Light and Chlorophyll in Photosynthesis?
Answer:

Light and chlorophyll are essential components of photosynthesis:

– Light energy is absorbed by chlorophyll molecules located in chloroplasts within plant cells. This light energy is used to power the chemical reactions of photosynthesis.

– Chlorophyll is a green pigment found in chloroplasts that captures light energy and initiates the conversion of carbon dioxide and water into glucose and oxygen.

Question 23. Describe the Structure of ATP.
Answer:

ATP is composed of three components:

– Adenine: A nitrogenous base derived from purine.

– Ribose: A five-carbon sugar that forms the backbone of the ATP molecule.

– Triphosphate tail: Consists of three phosphate groups (hence the name adenosine triphosphate). These phosphate groups are attached to the ribose sugar and are the primary source of energy stored in ATP.

Question 24. Explain the Light-Independent Reactions (Calvin Cycle) of Photosynthesis.
Answer:

The light-independent reactions, also known as the Calvin cycle, occur in the stroma of chloroplasts. During this stage, carbon dioxide is fixed into organic molecules using the ATP and NADPH generated during the light-dependent reactions. These organic molecules are then used to synthesize glucose and other carbohydrates.

Question 25. Compare Respiration and Photosynthesis.
Answer:

Respiration is the process by which organisms obtain energy from organic molecules, such as glucose, through the breakdown of these molecules in the presence of oxygen, while photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose, while releasing oxygen as a byproduct. Respiration occurs in all living organisms, while photosynthesis occurs only in autotrophic organisms. Respiration consumes oxygen and produces carbon dioxide, while photosynthesis consumes carbon dioxide and produces oxygen. Both processes are complementary and are vital for the cycling of energy and matter in ecosystems.

Question 26. Explain Glycolysis and its Role in Aerobic Respiration.
Answer:

Glycolysis is the first stage of aerobic respiration that occurs in the cytoplasm of cells. It involves the breakdown of glucose into two molecules of pyruvate, along with the production of ATP and NADH. Glycolysis does not require oxygen and can occur under both aerobic and anaerobic conditions.

Question 27. How do Plants Intake Carbon Dioxide?
Answer:

Plants intake carbon dioxide from the atmosphere through small pores called stomata, which are primarily located on the undersides of leaves. The stomata open to allow carbon dioxide to enter the leaf tissue and close to prevent excessive water loss.