Question 1

A student placed a green leaf in the dark for 48 hours (destarched). It was then illuminated for 6 hours. The leaf was tested for starch using iodine solution.
(i) What result would you expect and why?
(ii) Write the word equation for photosynthesis.
(iii) Name TWO factors that limit the rate of photosynthesis in a plant kept indoors.

Accepted Answer

(i) The iodine solution turns BLUE-BLACK where starch is present — expected in the illuminated leaf because the plant performed photosynthesis during the 6 hours of light, producing and storing starch.
(ii) Carbon dioxide + Water → (light energy) → Glucose + Oxygen
(iii) Low light intensity; low carbon dioxide concentration (temperature could also be limiting if indoor temp is low).

Question 2

Three resistors of 4 Ω, 6 Ω and 12 Ω are connected in parallel to a 12 V battery.
(i) Draw the circuit diagram.
(ii) Calculate the total resistance of the combination.
(iii) Calculate the total current drawn from the battery.
(iv) State Ohm's Law.

Accepted Answer

(ii) 1/R_total = 1/4 + 1/6 + 1/12 = 3/12 + 2/12 + 1/12 = 6/12 → R_total = 2 Ω
(iii) I = V / R = 12 / 2 = 6 A
(iv) Ohm's Law: the current through a conductor is directly proportional to the potential difference across it, provided the temperature remains constant (V = IR).

Question 3

The diagram shows a nephron (kidney tubule).
(i) State the two main functions of the kidney.
(ii) Describe what happens during filtration in the glomerulus.
(iii) Name TWO substances that are selectively reabsorbed in the proximal convoluted tubule.
(iv) Name the hormone that controls the amount of water reabsorbed by the kidney.

Accepted Answer

(i) Excretion of nitrogenous waste (urea); Osmoregulation (control of water balance in blood).
(ii) High blood pressure in the glomerulus forces small molecules (water, glucose, urea, salts) out of the capillaries into the Bowman's capsule. Large molecules (proteins, blood cells) remain in the blood.
(iii) Glucose and amino acids (also accept water, Na⁺).
(iv) ADH (Antidiuretic hormone / Vasopressin).

Question 4

Q31: Which of the following is NOT a greenhouse gas?
   A. Methane   B. Nitrogen   C. Carbon dioxide   D. Nitrous oxide

Q42: A student mixes copper sulphate solution with iron nails. The blue colour fades and iron becomes coated. This reaction is best described as:
   A. Combination   B. Decomposition   C. Displacement   D. Neutralisation

Accepted Answer

Q31: Answer B — Nitrogen (N₂). Methane, CO₂ and N₂O are greenhouse gases; nitrogen makes up ~78% of the atmosphere but does NOT trap heat significantly.

Q42: Answer C — Displacement. Iron is more reactive than copper, so it displaces copper from copper sulphate solution: Fe + CuSO₄ → FeSO₄ + Cu. The blue colour fades as copper ions are removed; red/brown copper coats the iron nail.

Science 2023