Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic B6.1 — Photosynthesis (Parts (a)(i), (a)(ii))
• Topic B5.1 — Enzymes (Parts (b)(i), (b)(ii))
• Topic B2.1 — Cell structure (Parts (c)(i), (c)(ii), (c)(iii))
• Topic B3.3 — Transport in plants (Part (c)(iv))
(a)(i) Oxygen
Photosynthesis produces glucose and oxygen as products.
The bubbles collected from the aquatic plant are oxygen gas.
This oxygen is released as a by-product of the light-dependent reactions.
(a)(ii) Light is needed for photosynthesis
Removing the filament lamp removes the light source.
Light provides the energy needed to drive photosynthesis.
Without light, the rate of photosynthesis (and therefore oxygen production) decreases sharply.
(b)(i) Protein that acts as a biological catalyst
An enzyme is a protein molecule.
It speeds up the rate of a specific chemical reaction.
It is not used up or changed permanently during the reaction.
(b)(ii) Enzymes stop working / enzyme activity slows down
A hot lamp placed too close raises the water temperature above the enzyme’s optimum.
Excess heat causes the enzyme’s shape (active site) to change, known as denaturation.
A denatured enzyme can no longer catalyse the reactions of photosynthesis, so bubble production stops.
(c)(i) Chloroplast
The photomicrograph shows small green organelles within the cell.
These structures labelled X are chloroplasts.
Chloroplasts contain chlorophyll and are the site of photosynthesis.
(c)(ii) Cell membrane, cytoplasm, nucleus
The cell membrane controls the movement of substances into and out of the cell.
The cytoplasm is the jelly-like substance where many cell reactions occur.
The nucleus contains the cell’s genetic material (DNA) and controls cell activities.
(c)(iii) Elongated shape; contains no chloroplasts
Root hair cells have a long, thin extension that increases surface area for absorption.
Unlike the Elodea leaf cells, root hair cells live underground and receive no light.
Because they carry out no photosynthesis, they contain no chloroplasts.
(c)(iv) Absorb water and mineral ions
Root hair cells are specialised cells found on the surface of plant roots.
Their large surface area allows efficient uptake of water and dissolved mineral ions from the soil.
These substances are then transported to other parts of the plant via the xylem.
