Home / iGCSE Biology (0610)-6.1 Photosynthesis – iGCSE Style Questions Paper 3

iGCSE Biology (0610)-6.1 Photosynthesis – iGCSE Style Questions Paper 3

IGCSE Biology (0610) Practice Questions Paper 3 - All Chapters

Question

(a) State the word equation for photosynthesis.
(b) Fig. 4.1 is a diagram of leaves from two plants of the same species.
One plant has variegated leaves with green and white areas.
The other plant has leaves that are only green.
(i) State the name of the structure in plant cells where photosynthesis occurs.
(ii) State the name of the pigment which is present in the green parts of the leaf but is not present in the white parts of the leaf.
(c) A student investigated the effect of light intensity on photosynthesis.
Fig. 4.2 is a diagram of the apparatus used.
The investigation was done in a room where the lamp was the only source of light.
A lamp was placed \(5 \, \text{cm}\) from the aquatic plant.
The number of gas bubbles produced in one minute was recorded.
The distance of the lamp was changed and the investigation was repeated.
The results are shown in Table 4.1.
(i) Calculate the percentage decrease in the number of gas bubbles produced in one minute, when the distance of the lamp changed from \(15 \, \text{cm}\) to \(30 \, \text{cm}\). [cite_start]Give your answer as a whole number.
(ii) Describe and explain the results shown in Table 4.1.
▶️ Answer/Explanation
Detailed solution

(a) Word equation for photosynthesis:
\[\text{carbon dioxide} + \text{water} \xrightarrow{\text{light, chlorophyll}} \text{glucose} + \text{oxygen}\]
Note: The arrow typically signifies the presence of light energy and chlorophyll, which are required for the reaction but are not reactants themselves. [cite: 335]

(b)(i) Structure for photosynthesis:
Chloroplasts. [cite_start]These are the organelles within plant cells that contain the machinery necessary for photosynthesis. [cite: 250, 335]

(b)(ii) Pigment name:
Chlorophyll. This is the green pigment responsible for absorbing light energy. [cite_start]It is absent in the white areas of a variegated leaf. [cite: 335]

(c)(i) Percentage decrease calculation:
First, identify the number of bubbles at the two specified distances from Table 4.1:

  • At \(15 \, \text{cm}\): \(13\) bubbles
  • At \(30 \, \text{cm}\): \(3\) bubbles

Calculate the decrease in the number of bubbles: \[\text{Decrease} = 13 – 3 = 10\] Calculate the percentage decrease relative to the starting value (\(15 \, \text{cm}\)): \[\text{Percentage Decrease} = \frac{\text{Decrease}}{\text{Original Value}} \times 100\] \[= \frac{10}{13} \times 100 \approx 76.92\%\] Rounded to a whole number: 77%.

(c)(ii) Describe and explain the results:
Description (What the data shows):

  • There is a negative correlation between distance and the rate of bubbling. [cite_start]As the distance of the lamp from the plant increases, the number of gas bubbles produced per minute decreases. [cite: 351]
  • For example, at \(5 \, \text{cm}\) there are \(31\) bubbles, dropping to only \(3\) bubbles at \(30 \, \text{cm}\).

Explanation (Why it happens):

  • Light Intensity: Light is a limiting factor for photosynthesis. [cite_start]As the lamp moves further away, the light intensity reaching the plant decreases (following the inverse square law). [cite: 351][cite_start]
  • Photosynthesis Rate: Less light energy means less energy is available to drive the photosynthetic reaction. [cite: 335]
  • Oxygen Production: The bubbles are composed of oxygen gas, which is a product of photosynthesis. [cite_start]Therefore, a lower rate of photosynthesis results in less oxygen being released, leading to fewer bubbles. [cite: 335]
More IGCSE Biology (0610) Practice Questions Paper 3 ...........
Scroll to Top