CXC - Caribbean Examinations Council Biology: Photosynthesis and Respiration Questions and Answers — Questions and Answers
Question 1: Which of the following is the correct balanced chemical equation for photosynthesis?
- C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
- 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (Correct answer)
- C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
- 6O₂ + C₆H₁₂O₆ → 6H₂O + 6CO₂
Correct answer: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Photosynthesis uses carbon dioxide (CO₂) and water (H₂O) in the presence of light energy to produce glucose (C₆H₁₂O₆) and oxygen (O₂). The balanced equation requires 6 molecules of CO₂ and 6 molecules of H₂O to produce 1 molecule of glucose and 6 molecules of oxygen.
Question 2: A student places a destarched plant in a sealed, transparent container under a bright light. After several hours, which TWO gases would be expected to show a net change in concentration inside the container?
- Nitrogen increases, Oxygen decreases
- Carbon dioxide increases, Oxygen increases
- Carbon dioxide decreases, Oxygen increases (Correct answer)
- Nitrogen decreases, Carbon dioxide increases
Correct answer: Carbon dioxide decreases, Oxygen increases
Under a bright light, the rate of photosynthesis is significantly higher than the rate of respiration. Photosynthesis consumes carbon dioxide from the container's atmosphere and releases oxygen as a by-product. Therefore, the concentration of carbon dioxide will decrease while the concentration of oxygen will increase.
Question 3: Which of the following statements correctly distinguishes between aerobic respiration and photosynthesis?
- Respiration occurs only in animals, while photosynthesis occurs only in plants.
- Respiration releases energy from glucose, while photosynthesis stores energy in glucose. (Correct answer)
- Respiration produces oxygen, while photosynthesis consumes oxygen.
- Respiration occurs only in the dark, while photosynthesis occurs only in the light.
Correct answer: Respiration releases energy from glucose, while photosynthesis stores energy in glucose.
The fundamental purpose of aerobic respiration is to break down glucose to release chemical energy (ATP) for cellular activities. In contrast, photosynthesis captures light energy and converts it into chemical energy stored in the bonds of glucose molecules. Plants perform both photosynthesis and respiration. Respiration is a continuous process in most living cells, occurring day and night.
Question 4: In the absence of oxygen, yeast cells undergo anaerobic respiration. What are the main products of this process?
- Lactic acid and ATP
- Carbon dioxide and water
- Ethanol and carbon dioxide (Correct answer)
- Glucose and oxygen
Correct answer: Ethanol and carbon dioxide
Anaerobic respiration in yeast, also known as alcoholic fermentation, breaks down glucose into ethanol and carbon dioxide, releasing a small amount of energy (ATP). This process is utilized in baking, where the CO₂ causes bread to rise, and in brewing to produce alcoholic beverages. Lactic acid is the product of anaerobic respiration in animal muscle cells.
Question 5: A scientist is growing a water plant in a beaker of water with hydrogencarbonate indicator. The setup is placed under a lamp. Initially, the indicator is red. After one hour, it turns purple. What is the MOST likely limiting factor for photosynthesis at this point? (Indicator colours: Yellow = high CO₂, Red = normal CO₂, Purple = low CO₂)
- Light intensity
- Water availability
- Carbon dioxide concentration (Correct answer)
- Temperature
Correct answer: Carbon dioxide concentration
Hydrogencarbonate indicator changes colour based on the concentration of CO₂. A purple colour indicates a low concentration of CO₂. This means the plant has actively used up the available carbon dioxide for photosynthesis. Since the CO₂ level is now depleted, it has become the factor that is limiting the rate of photosynthesis, even if light and temperature are optimal.
Question 6: In which organelles do photosynthesis and aerobic respiration primarily occur within a typical plant cell, respectively?
- Mitochondria; Chloroplast
- Cytoplasm; Mitochondria
- Nucleus; Chloroplast
- Chloroplast; Mitochondria (Correct answer)
Correct answer: Chloroplast; Mitochondria
Photosynthesis takes place within the chloroplasts, which contain the chlorophyll needed to capture light energy. Aerobic respiration, the process of releasing energy from food, primarily occurs in the mitochondria, often referred to as the 'powerhouses' of the cell.
CXC - Caribbean Examinations Council Biology: Photosynthesis and Respiration Questions and Answers
Which of the following is the correct balanced chemical equation for photosynthesis?