Home / IB DP Biology- C1.3 Photosynthesis IB Style Questions For HL Paper 1A

IB DP Biology- C1.3 Photosynthesis IB Style Questions For HL Paper 1A-New Syllabus

IBDP Biology HL Paper 1 -FA 2025- All Chapters

Question

What occurs in photosynthesis?

(A) Photolysis occurs in photosystem I.
(B) Electron transport chain synthesises ATP in the outer membrane of the chloroplast.
(C) Oxidation of NADP occurs in photosystem I.
(D) Photosystems I and II emit excited electrons.
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{D}} \)

During the light-dependent stage of photosynthesis, both Photosystem II and Photosystem I absorb light energy, causing their chlorophyll molecules to release excited electrons. These electrons pass through the electron transport chain, providing the energy needed for ATP formation and the production of reduced NADP.

Question

Which of the following groups release oxygen as a by-product of photosynthesis?

I.  Algae

II.  Cyanobacteria

III.  Fungi

A.  I only

B.  I and II only

C.  II and III only

D.  I, II and III

▶️ Answer/Explanation
Algae and cyanobacteria both carry out oxygen-producing photosynthesis. Fungi do not photosynthesize, so they do not release oxygen.
✅ Answer: (B)

Question

The diagram shows a chromatogram of the pigments in a leaf. Substance Z is known to have an \( R_f \) of 0.5.

PigmentColour\( R_f \)
CaroteneYellow0.95
PhaeophytinYellow-grey0.83
Chlorophyll aBlue-green0.65
Chlorophyll bGreen0.45

What are pigments X and Y?

OptionXY
AChlorophyll aPhaeophytin
BChlorophyll aCarotene
CChlorophyll bCarotene
DChlorophyll bChlorophyll a
▶️ Answer/Explanation
Substance Z has an \( R_f \) of 0.5, which matches closely with chlorophyll b (\( R_f = 0.45 \)). The pigment X, located higher on the chromatogram, has an \( R_f \) of about 0.65 and matches chlorophyll a. Pigment Y, near the top, corresponds to a pigment with an \( R_f \) higher than 0.8, likely chlorophyll a’s neighbor in mobility.
✅ Answer: (D)
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