Photosynthesis — Drills · Grade 10 Science

Chapter: Matter & Energy in Living Systems

What these drills covers

By the end of Photosynthesis you should be able to:

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

Vocabulary used: photosynthesis, chloroplast, chlorophyll, light-dependent reactions, Calvin cycle.

Problem 1

The overall reactants of photosynthesis are
  1. glucose and oxygen
  2. carbon dioxide and water
  3. ATP and NADPH
  4. oxygen and water only
Answer and explanation

carbon dioxide and water

Carbon dioxide and water are the raw materials; glucose and oxygen are the products. ATP and NADPH are intermediates made and used within the process.

Problem 2

The oxygen released by photosynthesis comes from
  1. carbon dioxide
  2. water
  3. glucose
  4. chlorophyll
Answer and explanation

water

Water is split in the light-dependent reactions, releasing oxygen. Carbon dioxide supplies the carbon and oxygen that end up in sugar.

Problem 3

Leaves appear green because chlorophyll
  1. absorbs green light strongly
  2. reflects green light while absorbing red and blue
  3. converts all light to green
  4. contains green carbon
Answer and explanation

reflects green light while absorbing red and blue

Chlorophyll absorbs red and blue wavelengths efficiently and reflects green, which is why green is the colour that reaches our eyes.

Problem 4

In the overall equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, how many carbon atoms are in the glucose produced from 6 molecules of carbon dioxide?
Answer and explanation

6

Each carbon dioxide supplies one carbon atom, and glucose contains six, so six molecules are required.

Problem 5

A plant produces 48 bubbles of oxygen in 4.0 minutes at a given light intensity. Report the rate in bubbles per minute.
Answer and explanation

12 bubbles/min

48 / 4.0 = 12 bubbles per minute. Bubble counts are a proxy for oxygen production and assume uniform bubble size.

Problem 6

Explain why increasing light intensity raises the rate of photosynthesis up to a point and then stops raising it.
Answer and explanation

At low intensity, light is the factor in shortest supply, so adding light increases the rate of the light-dependent reactions and therefore the overall rate. Beyond a certain intensity something else becomes limiting — usually carbon dioxide concentration, temperature, or the capacity of the enzymes that fix carbon — so additional light cannot increase the rate. The plateau identifies a change in which factor is limiting, not a failure of the light reactions.

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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