Photosynthesis — Practice · Grade 10 Science

Chapter: Matter & Energy in Living Systems

What this practice covers

By the end of Photosynthesis you should be able to:

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

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

Problem 1

Which pair are the reactants (starting materials) of photosynthesis?
  1. Carbon dioxide and water
  2. Glucose and oxygen
  3. ATP and NADPH
  4. Nitrogen and sunlight
Answer and explanation

Carbon dioxide and water

Photosynthesis uses carbon dioxide and water (plus light energy) to build glucose and release oxygen. Glucose and oxygen are the products, not the reactants.

Problem 2

In which organelle does photosynthesis take place?
  1. The ribosome
  2. The chloroplast
  3. The mitochondrion
  4. The nucleus
Answer and explanation

The chloroplast

Photosynthesis happens in the chloroplast, whose thylakoid membranes hold the chlorophyll that captures light.

Problem 3

According to the balanced equation, how many oxygen (O2) molecules are released for each glucose molecule made?
Answer and explanation

6 O2 molecules

The equation 6 CO2 + 6 H2O → C6H12O6 + 6 O2 shows 6 molecules of O2 released per glucose.

Problem 4

The oxygen released by photosynthesis comes from splitting one of the reactants. Which reactant is split, and in which stage does this happen?
Answer and explanation

The oxygen comes from splitting water (H2O). This happens in the light-dependent reactions, in the thylakoid membranes, where light energy is used to break water apart.

Problem 5

Leaves look green because chlorophyll
  1. produces a green-colored sugar
  2. reflects every color of light equally
  3. absorbs red and blue light and reflects green light
  4. absorbs green light and reflects red light
Answer and explanation

absorbs red and blue light and reflects green light

Chlorophyll absorbs mostly red and blue wavelengths to power photosynthesis and reflects green light back to our eyes, which is why plants look green.

Problem 6

A plant gains organic carbon while lit. Identify a major carbon source and distinguish it from released oxygen's source. Explain the reasoning in your own words.
Answer and explanation

CO₂ supplies carbon; water supplies the oxygen atoms released as O₂.

Carbon is incorporated from CO₂.

In oxygenic photosynthesis, released O₂ comes from water.

Response criteria

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

Problem 7

What is one role of water in oxygenic photosynthesis? Show the reasoning, not just the conclusion.
Hints

Light supplies energy; it is not a source of carbon atoms.

Answer and explanation

Water supplies electrons and hydrogen in light reactions; released O₂ originates from water.

Problem 8

Can a photosynthetic plant also respire during daylight?
Hints

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

Answer and explanation

Yes. Cellular respiration can continue while photosynthesis occurs.

Problem 9

A pigment absorbs some wavelengths more strongly than othersA pigment absorbs some wavelengths more strongly than othersRelative absorption (model units)04812400450500550600650700Wavelength (nm)Absorption is not identical to a whole-leaf photosynthetic rate.
Original illustrative pigment-absorption pattern, not a measured spectrum of one chlorophyll type or a calibrated leaf action spectrum.
Interpret the supplied visual. Why should an absorption curve and a photosynthesis-rate curve have different axis labels?
Answer and explanation

They measure different quantities; relating them requires controlled biological and optical conditions.

A pigment interacts with light at particular wavelengths. An absorption spectrum shows absorption versus wavelength, while an action spectrum shows a measured biological process versus wavelength under controlled conditions. Pigments and associated structures can broaden useful light capture, but absorbed light is not all converted into organic production. Leaf thickness, other pigments, light intensity and physiological conditions influence the outcome. A leaf’s visible color reflects light reaching the observer, not proof that the other wavelengths never interact.

They measure different quantities; relating them requires controlled biological and optical conditions.

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

A lit plant’s gross photosynthetic oxygen production is 14 units/h and its oxygen consumption is 5 units/h under the supplied model. Find net output and explain the oxygen-atom source in oxygenic photosynthesis.
Answer and explanation

Net output is 14−5 = 9 units/h. The released photosynthetic O₂ is traced to water; plants also consume oxygen, and a net gas measurement alone is not gross production.

Net output is 14−5 = 9 units/h. The released photosynthetic O₂ is traced to water; plants also consume oxygen, and a net gas measurement alone is not gross production.

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