UK K12 GCSE A-Level Year 9 KS3Pre-GCSE Science Photosynthesis and Cellular Respiration

Learning Objectives

By the end of this topic, students will be able to:

• Explain the processes of photosynthesis and cellular respiration, including the reactants, products, and overall energy transformations.
• Describe the roles of light, water, carbon dioxide, and chlorophyll in photosynthesis.
• Explain the importance of glucose and oxygen in cellular respiration.
• Describe the differences between aerobic and anaerobic respiration.
• Evaluate the significance of photosynthesis and cellular respiration in maintaining the balance of the Earth's ecosystem.

Core Concepts

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy from the sun into chemical energy in the form of glucose. This process occurs in specialized organelles called chloroplasts, which contain the pigment chlorophyll. Chlorophyll absorbs light energy and transfers it to a molecule called ATP (adenosine triphosphate), which is then used to convert carbon dioxide and water into glucose and oxygen.

The overall equation for photosynthesis is:

6 CO2 + 6 H2O + light energy → C6H12O6 (glucose) + 6 O2

Cellular respiration is the process by which cells break down glucose to produce energy in the form of ATP. This process occurs in the mitochondria and involves the transfer of electrons through a series of electron transport chains, ultimately resulting in the production of ATP.

The overall equation for cellular respiration is:

C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O + ATP (energy)

Worked Examples

Example 1: Photosynthesis

A plant absorbs 12 moles of carbon dioxide and 12 moles of water during photosynthesis. If the plant produces 6 moles of glucose and 12 moles of oxygen, what is the efficiency of the photosynthesis process?

To solve this problem, we need to calculate the energy released from the light energy absorbed by the plant. The energy released from the light energy is equal to the energy stored in the glucose produced.

The energy stored in 6 moles of glucose is:

6 mol C6H12O6 × 686 kJ/mol = 4116 kJ

The energy absorbed from the light energy is equal to the energy stored in the glucose produced, which is 4116 kJ.

The efficiency of the photosynthesis process is the ratio of the energy stored in the glucose produced to the energy absorbed from the light energy:

Efficiency = (4116 kJ) / (4116 kJ) = 100%

Example 2: Cellular Respiration

A cell breaks down 12 moles of glucose to produce 24 moles of ATP. If the cell uses 12 moles of oxygen during cellular respiration, what is the efficiency of the process?

To solve this problem, we need to calculate the energy released from the glucose broken down by the cell. The energy released from the glucose is equal to the energy stored in the ATP produced.

The energy stored in 24 moles of ATP is:

24 mol ATP × 30.5 kJ/mol = 732 kJ

The energy released from the glucose broken down by the cell is equal to the energy stored in the ATP produced, which is 732 kJ.

The efficiency of the cellular respiration process is the ratio of the energy stored in the ATP produced to the energy released from the glucose broken down:

Efficiency = (732 kJ) / (732 kJ) = 100%

Common Misconceptions

• Photosynthesis is the process by which plants produce oxygen. While it is true that plants produce oxygen during photosynthesis, this is not the primary function of the process. The primary function of photosynthesis is to convert light energy into chemical energy in the form of glucose.
• Cellular respiration is the process by which cells produce glucose. This is incorrect. Cellular respiration is the process by which cells break down glucose to produce energy in the form of ATP.

Exam Tips

• Make sure to understand the overall equations for photosynthesis and cellular respiration.
• Be able to describe the roles of light, water, carbon dioxide, and chlorophyll in photosynthesis.
• Be able to explain the importance of glucose and oxygen in cellular respiration.
• Be able to describe the differences between aerobic and anaerobic respiration.
• Make sure to evaluate the significance of photosynthesis and cellular respiration in maintaining the balance of the Earth's ecosystem.

MCQs with Explanations

MCQ 1 [F]

What is the primary function of photosynthesis?

A) To produce oxygen B) To convert light energy into chemical energy in the form of glucose C) To break down glucose to produce energy D) To produce ATP

Correct answer: B) To convert light energy into chemical energy in the form of glucose

Why the distractors fail: A) While it is true that plants produce oxygen during photosynthesis, this is not the primary function of the process.
C) This is the function of cellular respiration, not photosynthesis.
D) This is the function of cellular respiration, not photosynthesis.

MCQ 2 [H]

What is the overall equation for cellular respiration?

A) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP B) C6H12O6 + 6 CO2 → 6 O2 + 6 H2O + ATP C) 6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2 D) 6 CO2 + 6 H2O → C6H12O6 + 6 O2

Correct answer: A) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP

Why the distractors fail: B) This is the equation for photosynthesis, not cellular respiration.
C) This is the equation for photosynthesis, not cellular respiration.
D) This is the equation for photosynthesis, not cellular respiration.

MCQ 3 [F]

What is the role of chlorophyll in photosynthesis?

A) To absorb light energy B) To break down glucose to produce energy C) To produce oxygen D) To produce ATP

Correct answer: A) To absorb light energy

Why the distractors fail: B) This is the function of cellular respiration, not photosynthesis.
C) While it is true that plants produce oxygen during photosynthesis, this is not the primary function of the process.
D) This is the function of cellular respiration, not photosynthesis.

MCQ 4 [H]

What is the difference between aerobic and anaerobic respiration?

A) Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen.
B) Aerobic respiration occurs in the absence of oxygen, while anaerobic respiration occurs in the presence of oxygen.
C) Aerobic respiration produces more ATP than anaerobic respiration.
D) Anaerobic respiration produces more ATP than aerobic respiration.

Correct answer: A) Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen.

Why the distractors fail: B) This is the opposite of the correct answer.
C) While it is true that aerobic respiration produces more ATP than anaerobic respiration, this is not the primary difference between the two processes.
D) This is the opposite of the correct answer.

MCQ 5 [H]

What is the significance of photosynthesis and cellular respiration in maintaining the balance of the Earth's ecosystem?

A) They produce oxygen and glucose, but do not affect the balance of the ecosystem.
B) They produce oxygen and glucose, and help to regulate the Earth's temperature.
C) They produce oxygen and glucose, and help to maintain the balance of the ecosystem by providing energy for living organisms.
D) They produce oxygen and glucose, and help to regulate the Earth's water cycle.

Correct answer: C) They produce oxygen and glucose, and help to maintain the balance of the ecosystem by providing energy for living organisms.

Why the distractors fail: A) This is an oversimplification of the role of photosynthesis and cellular respiration in the ecosystem.
B) While it is true that photosynthesis and cellular respiration help to regulate the Earth's temperature, this is not their primary significance in the ecosystem.
D) This is not the primary significance of photosynthesis and cellular respiration in the ecosystem.

Short-answer questions

1. Describe the overall equation for photosynthesis and explain the importance of light, water, carbon dioxide, and chlorophyll in the process.

Answer: The overall equation for photosynthesis is:

6 CO2 + 6 H2O + light energy → C6H12O6 (glucose) + 6 O2

Light energy is absorbed by chlorophyll, which is a pigment found in chloroplasts. Water is absorbed by the plant through its roots and is transported to the chloroplasts. Carbon dioxide is absorbed by the plant through its leaves and is transported to the chloroplasts. Chlorophyll plays a crucial role in photosynthesis by absorbing light energy and transferring it to a molecule called ATP, which is then used to convert carbon dioxide and water into glucose and oxygen.

1. Describe the overall equation for cellular respiration and explain the importance of glucose and oxygen in the process.

Answer: The overall equation for cellular respiration is:

C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O + ATP (energy)

Glucose is broken down by cells to produce energy in the form of ATP. Oxygen is used as a reactant in cellular respiration to produce ATP. The importance of glucose and oxygen in cellular respiration is that they provide the energy and reactants necessary for the process to occur.

1. Describe the differences between aerobic and anaerobic respiration and explain the significance of each process in the ecosystem.

Answer: Aerobic respiration occurs in the presence of oxygen and produces more ATP than anaerobic respiration. Anaerobic respiration occurs in the absence of oxygen and produces less ATP than aerobic respiration. The significance of aerobic and anaerobic respiration in the ecosystem is that they provide energy for living organisms and help to maintain the balance of the ecosystem. Aerobic respiration is the primary source of energy for most living organisms, while anaerobic respiration is used by some microorganisms to produce energy in the absence of oxygen.