Comparing Photosynthesis & Respiration — Practice · Grade 10 Science

Chapter: Matter & Energy in Living Systems

What this practice covers

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

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

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

Problem 1

How are photosynthesis and cellular respiration related?
  1. The products of one are the reactants of the other
  2. They are the exact same reaction with the same name
  3. Both processes occur only in animals
  4. Both processes release oxygen
Answer and explanation

The products of one are the reactants of the other

Their simplified net equations connect reactants and products, but their biochemical pathways differ.

Problem 2

In an ecosystem, matter (atoms) ___ and energy ___.
  1. flows one way; flows one way
  2. cycles; flows one way
  3. flows one way; cycles
  4. cycles; cycles
Answer and explanation

cycles; flows one way

The same atoms are reused over and over (matter cycles), but energy enters as sunlight and is lost as heat at each step (energy flows one way and must be resupplied).

Problem 3

Why does cycling carbon in a forest not eliminate the need for a continuing usable energy input?
Answer and explanation

Carbon atoms can be reused; energy is transferred and dispersed as heat. Biological work needs usable input, and matter also crosses real forest boundaries.

Problem 4

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

Both plants and animals commonly carry out aerobic respiration

Plants and animals commonly use aerobic respiration; some specialized cells and other organisms use different pathways.

Problem 5

If a plant's cells fully respire 4 glucose molecules using C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, how many CO2 molecules are released in total?
Answer and explanation

24 CO2 molecules

Each glucose respired releases 6 CO2, so 4 × 6 = 24 CO2 molecules.

Problem 6

Why can a green plant consume oxygen in darkness? Explain the reasoning in your own words.
Answer and explanation

Respiration continues even when light-dependent photosynthesis stops.

Cells still need ATP for maintenance and work.

Aerobic respiration can continue using stored organic molecules when photosynthesis is not occurring.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

If photosynthesis uses 12 units of CO₂ and respiration releases 5 in a period, find net CO₂ uptake. Show the reasoning, not just the conclusion.
Hints

Measure net flux rather than treating it as one process.

Answer and explanation

12−5=7 units, under the stated boundary.

Problem 8

Why do photosynthesis and respiration not form a perfectly closed energy cycle?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Matter can cycle, but energy inputs and thermal losses require ongoing external energy.

Problem 9

Net exchange subtracts simultaneous opposing processesNet exchange subtracts simultaneous opposing processesSupplied rates (units/h)Gross O₂ production12O₂ consumption4Net O₂ release8Net = gross production − consumption; here 12 − 4 = 8.
Original oxygen-rate account, not a direct conversion to a measured carbon or biomass rate.
Interpret the supplied visual. If net oxygen output is zero, must both processes have stopped?
Answer and explanation

No. Equal production and consumption can balance to zero while both continue.

Gross production refers to production before a specified subtraction; net exchange is the signed balance of inflows/outflows or production/consumption at the stated boundary. In this oxygen model, production is 12 units/h and consumption four, so net release is eight. A zero net rate can therefore coexist with active production and consumption. Definitions must identify the variable: ecosystem net carbon production, leaf oxygen exchange and biomass growth are related but different accounts. Changing a light level may alter more than one process.

No. Equal production and consumption can balance to zero while both continue.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

For six hours a model produces 10 oxygen units/h and consumes 3. For the remaining 18 hours production is zero and consumption remains 3. Find the day’s net change.
Answer and explanation

Net daytime gain is 6×(10−3)=42 units; later loss is 18×3=54. The day’s net change is −12 units despite positive daytime release under the stated simplified conditions.

Net daytime gain is 6×(10−3)=42 units; later loss is 18×3=54. The day’s net change is −12 units despite positive daytime release under the stated simplified conditions.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses