What photosynthesis makes — questions

1. identify

Which statement describes photosynthesis?

Circle one answer.

• Plants build carbohydrates from carbon dioxide and water, using energy from light.
• Plants break down glucose to release energy for their cells.
• Plants take in food from the soil through their roots.
• Plants turn light into glucose, using carbon dioxide from the soil.

Nudge (only if you are stuck): Look for the statement with the right raw materials, the right product and the right source of energy.

2. classify

Photosynthesis needs or makes each of these. Match each one to its place in the word equation.

Write the number of the matching option.

1. a raw material
2. a product
3. needed, but not a raw material

• carbon dioxide: ______
• water: ______
• glucose: ______
• oxygen: ______
• light: ______
• chlorophyll: ______

Nudge (only if you are stuck): Raw materials go on the left of the arrow and products on the right. Which two are needed but give no atoms to the glucose?

3. complete

Complete the word equation for photosynthesis.

carbon dioxide + … →

→ … + oxygen

in the presence of … and chlorophyll

Nudge (only if you are stuck): One raw material comes from the air and one from the soil; one product is a sugar.

4. state / describe

A leaf needs two raw materials for photosynthesis. For each one, state where it comes from and how it reaches the leaf.

(a) Carbon dioxide

(b) Water

Nudge (only if you are stuck): One comes from the air and one from the soil. How does each one get into the leaf?

5. identify

Which statements about chlorophyll are correct? Choose all that apply.

Tick every correct statement.

• It is a green pigment.
• It is found in chloroplasts.
• It transfers energy from light into energy in chemicals.
• Its atoms become part of the glucose that is made.
• It is found in every cell of a plant, including root cells.
• It absorbs mostly green light.

Nudge (only if you are stuck): Think about what chlorophyll is, where it is, and whether it is used up.

6. explain

A student writes: "Photosynthesis turns light into glucose." Explain what is wrong with this, using the words chlorophyll and energy.

Nudge (only if you are stuck): Is light a substance? Where do the atoms of glucose come from, and where does the energy end up?

7. explain

Over five years, a willow tree in a tub of dried soil gained about 74 kg, while the soil lost less than 100 g. The tree was given only water. Explain where most of the tree's new mass came from.

Nudge (only if you are stuck): Which raw material comes from the air? What does the plant build from glucose?

8. complete

Supplement. Build the balanced equation for photosynthesis, starting from one molecule of glucose, C₆H₁₂O₆. Complete the sentences.

Glucose has 6 carbon atoms, and one CO₂ molecule brings 1, so the number in front of CO₂ is …

Glucose has 12 hydrogen atoms, and one H₂O molecule brings 2, so the number in front of H₂O is …

A big number in front of a formula tells you the number of …

A small number written low tells you the number of … of the element just before it, in one molecule.

Nudge (only if you are stuck): Start from glucose: count its carbon atoms and its hydrogen atoms. Each CO₂ brings one carbon atom; each H₂O brings two hydrogen atoms.

9. balance / explain

Supplement. Balance the chemical equation for photosynthesis: carbon dioxide and water make glucose and oxygen.

Write a number in front of each formula. Leave it blank for 1.

____ CO₂ + ____ H₂O → ____ C₆H₁₂O₆ + ____ O₂

Why may you change only the numbers in front of the formulas?

Nudge (only if you are stuck): Glucose has 6 carbon atoms, so start with the carbon. Count oxygen last: it is in every substance.

10. calculate

Supplement. In the balanced equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, count the oxygen atoms on each side.

Oxygen atoms on the left: ______________ unit ________

Oxygen atoms on the right: ______________ unit ________

Nudge (only if you are stuck): Multiply the atoms in one molecule by the number of molecules, then add up for each substance on that side.

11. explain

A pumpkin plant grows in a garden bed. In one summer it makes a pumpkin of 8 kg, and the soil in the bed hardly changes. A visitor says: "All that pumpkin was sucked up out of the soil." Explain where the material of the pumpkin really came from.

Nudge (only if you are stuck): What does a plant build its carbohydrates from, and where does each raw material come from?

12. suggest / explain

A copper beech tree has dark red-purple leaves, not green ones, yet its leaves photosynthesise. Suggest how this is possible.

Nudge (only if you are stuck): Can a leaf contain more than one pigment? Which pigment is needed to absorb light for photosynthesis?

13. explain

Euglena is a single-celled organism that swims in ponds. It has chloroplasts. In the light it makes its own food; kept in the dark for some days, it survives only if there is food dissolved in the water for it to absorb. Explain why.

Nudge (only if you are stuck): What do chloroplasts contain, and what does that substance need to make carbohydrates?

14. calculate

Supplement. A leaf makes 3 molecules of glucose by photosynthesis. Use the balanced equation to work out how many molecules of carbon dioxide it takes in and how many molecules of oxygen it gives out.

Molecules of carbon dioxide taken in: ______________ unit ________

Molecules of oxygen given out: ______________ unit ________

Nudge (only if you are stuck): The balanced equation is for one molecule of glucose. What happens to every number when there are 3?