Comparing Photosynthesis & Respiration — Drills · Grade 10 Science

Chapter: Matter & Energy in Living Systems

What these drills covers

By the end of Comparing Photosynthesis & Respiration you should be able to:

7 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: matter cycling, energy transfer, carbon cycle, conservation of energy.

Problem 1

Why are net equations insufficient to show the steps of a biological pathway?
Answer and explanation

They account for overall changes but omit intermediate reactions, locations, regulation, and coupling.

Problem 2

Photosynthesis and respiration are related in that
  1. each is the exact reverse reaction of the other
  2. the products of one are the reactants of the other, though the pathways differ
  3. both occur only in plants
  4. both release oxygen
Answer and explanation

the products of one are the reactants of the other, though the pathways differ

The overall reactants and products are complementary, but the two processes use different pathways, enzymes, and locations, so neither is the literal reverse of the other.

Problem 3

Which organisms carry out cellular respiration?
  1. Only animals
  2. Only plants
  3. Both plants and animals
  4. Only decomposers
Answer and explanation

Both plants and animals

All cells respire to generate ATP, including plant cells, which respire day and night while photosynthesizing only in the light.

Problem 4

A plant produces 30 units of oxygen by photosynthesis and consumes 12 units by respiration in the same hour. What is the net oxygen released?
Answer and explanation

18 units

30 − 12 = 18 units. Measured gas exchange gives the net value, so gross photosynthesis is larger than it appears.

Problem 5

In the dark a plant consumes 12 units of oxygen per hour. In the light the same plant shows a net release of 18 units per hour. What is its gross photosynthetic oxygen production per hour?
Answer and explanation

30 units

Gross production = net release + respiratory consumption = 18 + 12 = 30 units, assuming respiration continues at the same rate in the light.

Problem 6

In a plant cell, photosynthesis and respiration occur respectively in the
  1. chloroplast and mitochondrion
  2. mitochondrion and chloroplast
  3. nucleus and cytoplasm
  4. cell wall and vacuole
Answer and explanation

chloroplast and mitochondrion

Photosynthesis takes place in chloroplasts and respiration mainly in mitochondria, so a plant cell needs both organelles.

Problem 7

Explain why describing respiration as "photosynthesis run backwards" is inaccurate even though the equations look reversed.
Answer and explanation

The summary equations are complementary, but the two processes run through different sequences of reactions, use different enzymes and electron carriers, and occur in different organelles. Photosynthesis splits water and fixes carbon dioxide in the chloroplast; respiration oxidizes glucose and reduces oxygen to water in the cytoplasm and mitochondrion. Neither is the reverse pathway of the other, and both release some energy as heat, so a cycle running one process backwards into the other would not conserve usable energy.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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