CXC - Caribbean Examinations Council Biology: Photosynthesis and Respiration Questions and Answers

Question 1

Which of the following is the correct balanced chemical equation for photosynthesis?

Accepted Answer

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Answer

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?

Accepted Answer

Carbon dioxide decreases, Oxygen increases

Answer

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?

Accepted Answer

Respiration releases energy from glucose, while photosynthesis stores energy in glucose.

Answer

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?

Accepted Answer

Ethanol and carbon dioxide

Answer

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)

Accepted Answer

Carbon dioxide concentration

Answer

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.

CXC - Caribbean Examinations Council Practice Test

CXC - Caribbean Examinations Council Practice Test

CXC - Caribbean Examinations Council Biology: Photosynthesis and Respiration Questions and Answers