Quiz: IGCSE Biology Core Concepts — 18 questions

1. Regarding the balanced equation for photosynthesis, which proposition(s) is/are correct?

A. Photosynthesis produces six carbon dioxide molecules and one water molecule.

B. Photosynthesis produces six glucose molecules and six oxygen molecules.

C. Photosynthesis requires one carbon dioxide molecule and six water molecules.

D. Photosynthesis uses six carbon dioxide molecules and six water molecules.

E. Photosynthesis uses six oxygen molecules and six glucose molecules.

Answer: (D)

Explanation

The balanced equation contains six carbon dioxide molecules and six water molecules as reactants. Oxygen and glucose are products, while the stated quantities of glucose and carbon dioxide in the other propositions are incorrect.

2. Concerning factors affecting the rate of photosynthesis, which proposition(s) is/are correct?

A. Increasing light intensity raises the rate until another factor becomes limiting.

B. Photosynthesis reaches its maximum rate before light intensity affects it.

C. Increasing light intensity raises the rate without any limiting factor.

D. Temperature cannot limit photosynthesis when light intensity is high.

E. Carbon dioxide concentration becomes irrelevant when light intensity increases.

Answer: (A)

Explanation

The rate increases with light intensity until carbon dioxide concentration, temperature, or another factor becomes limiting. The other propositions incorrectly remove or reverse the limiting effect of these factors.

3. The permanent vacuole and cell wall of a plant cell are associated with which functions?

A. The permanent vacuole performs protein synthesis, while the cell wall contains chlorophyll.

B. The permanent vacuole provides structural strength, while the cell wall stores cell sap.

C. The permanent vacuole contains cell sap, while the cell wall strengthens plant cells.

D. The permanent vacuole contains cell sap, while the cell wall supports plant cells.

E. The permanent vacuole carries air, while the cell wall absorbs nutrients.

Answer: (C), (D)

Explanation

The permanent vacuole contains cell sap, whereas the cell wall provides strength and support. Protein synthesis and chlorophyll are associated with other structures, and the other proposed functions are not assigned to these structures.

4. Regarding the trachea, which proposition(s) is/are correct?

A. The trachea is strengthened by alveoli that prevent airway collapse.

B. The trachea carries air toward the bronchi and has cartilage rings.

C. The trachea carries food toward the stomach through muscular contractions.

D. The trachea is the main surface where oxygen enters the blood.

E. The trachea contains villi that absorb nutrients from inhaled air.

Answer: (B)

Explanation

The trachea carries air toward the bronchi and is supported by cartilage rings. Gas exchange occurs mainly at the alveoli, while food transport and nutrient absorption belong to the digestive system.

5. Concerning cartilage rings in the airways, which proposition(s) is/are correct?

A. Cartilage rings support air passages during breathing.

B. Cartilage rings provide the main surface for gas exchange.

C. Cartilage rings maintain the openness of the airways.

D. Cartilage rings help prevent the bronchi from collapsing.

E. Cartilage rings help prevent the trachea from collapsing.

Answer: (A), (C), (D), (E)

Explanation

Cartilage rings prevent collapse of the trachea and bronchi, helping keep the airways open during breathing. The main gas-exchange surface is provided by the alveoli, not by cartilage rings.

6. Which structure is the main site of gas exchange in the lungs?

A. Gas exchange mainly occurs across the alveolar surface.

B. The trachea provides the main site of gas exchange.

C. The lungs use alveoli as their principal gas-exchange structures.

D. The alveoli provide the main site of gas exchange.

E. The bronchi provide the main site of nutrient absorption.

Answer: (A), (C), (D)

Explanation

Alveoli are the main site of gas exchange, and their surface allows this exchange to occur. The trachea and bronchi conduct air, while nutrient absorption is not a respiratory function.

7. Concerning the oesophagus, which proposition(s) is/are correct?

A. The oesophagus produces chlorophyll for cellular respiration.

B. The oesophagus carries air from the trachea to the bronchi.

C. The oesophagus absorbs most nutrients from digested food.

D. The oesophagus stores oxygen before it reaches the alveoli.

E. The oesophagus carries food from the mouth to the stomach.

Answer: (E)

Explanation

The oesophagus transports food from the mouth to the stomach. Most nutrient absorption occurs in the small intestine, while the other propositions describe respiratory or plant-cell functions.

8. Which propositions correctly describe the small intestine?

A. The small intestine is the main site of nutrient absorption.

B. The small intestine transports food from the mouth to the stomach.

C. The small intestine receives digested food for nutrient absorption.

D. The small intestine transfers absorbed nutrients into the body.

E. The small intestine has a digestive role linked to nutrient uptake.

Answer: (A), (C), (D), (E)

Explanation

The small intestine is the main site of nutrient absorption and transfers nutrients into the body. Transporting food from the mouth to the stomach is the function of the oesophagus.

9. Regarding peristalsis, which proposition(s) is/are correct?

A. Peristalsis transfers absorbed nutrients directly into body tissues.

B. Peristalsis is a wave of muscular contraction moving food through the gut.

C. Peristalsis moves food through the digestive tract by muscular waves.

D. Peristalsis occurs when alveoli exchange gases with the blood.

E. Peristalsis is the storage of excess carbohydrate as body fat.

Answer: (B), (C)

Explanation

Peristalsis consists of waves of muscular contraction that move food through the gut. Nutrient absorption, fat storage, and alveolar gas exchange are different processes.

10. Why do young animals require increased protein in their diet?

A. Young animals need more protein because it replaces absorbed water.

B. Young animals need more protein to convert oxygen into glucose.

C. Young animals need more protein mainly to produce chlorophyll.

D. Young animals need more protein to form additional alveolar cartilage.

E. Young animals need more protein for growth and new cell production.

Answer: (E)

Explanation

Young animals require more protein for growth and the production of new cells and tissues. The other propositions assign protein a plant, respiratory, or water-balance function not given in the material.

11. Regarding respiration in yeast, which of the following propositions are correct?

A. Aerobic respiration in yeast produces carbon dioxide and ethanol without oxygen.

B. Aerobic respiration in yeast requires oxygen for the process to occur.

C. Anaerobic respiration in yeast produces carbon dioxide and ethanol.

D. Anaerobic respiration in yeast produces oxygen and ethanol.

E. Anaerobic respiration in yeast converts glucose directly into oxygen and water.

Answer: (B), (C)

Explanation

Anaerobic respiration in yeast produces carbon dioxide and ethanol, while aerobic respiration requires oxygen. The other statements assign incorrect products or conditions to yeast respiration.

12. The movement of water across a partially permeable membrane is described by which propositions?

A. Osmosis describes solute movement from a concentrated solution toward a dilute solution.

B. A concentration difference across the membrane drives osmotic water movement.

C. Water moves from a dilute solution toward a concentrated solution during osmosis.

D. A partially permeable membrane allows water movement while restricting some solutes.

E. Osmosis involves the movement of water through a partially permeable membrane.

Answer: (B), (C), (D), (E)

Explanation

Osmosis is water movement through a partially permeable membrane from a dilute solution to a concentrated solution. The final statement incorrectly describes solute movement rather than osmotic water movement.

13. Regarding red blood cells placed in solutions of different concentrations, select the correct propositions:

A. A concentrated salt solution causes a red blood cell to lose water and shrink.

B. A concentrated salt solution causes a red blood cell to gain water and burst.

C. A very dilute solution causes a red blood cell to gain water and potentially burst.

D. A very dilute solution causes a red blood cell to lose water and shrink.

E. A red blood cell maintains its size in both concentrated and dilute solutions.

Answer: (A), (C)

Explanation

A concentrated salt solution draws water out of a red blood cell, causing shrinkage. A very dilute solution causes water entry and may make the cell burst; the remaining statements reverse or deny these effects.

14. Which approach best improves the reliability of an experiment involving organisms?

A. Using one unusually large organism provides a reliable population estimate.

B. Using several organisms without considering their measurements improves reliability.

C. Using several organisms and calculating a mean improves reliability.

D. Using fewer organisms makes biological variation easier to eliminate.

E. Using a single organism and calculating a mean improves reliability.

Answer: (C)

Explanation

Reliability is improved by using several organisms and calculating a mean. A single organism, ignoring measurements, or reducing the sample does not provide the same protection against biological variation.

15. In an investigation measuring snail growth, which statements correctly identify the measured variable?

A. Shell height is the dependent variable in a snail-growth investigation.

B. The independent variable is the measured shell height of each snail.

C. The factor deliberately changed is the dependent variable in the investigation.

D. Shell height represents the controlled variable rather than the dependent variable.

E. Shell height is measured to assess the growth of the snails.

Answer: (A), (E)

Explanation

Shell height is the dependent variable because it is measured to assess snail growth. The deliberately changed factor is the independent variable, so the remaining statements misclassify shell height.

16. When preparing a glucose solution for yeast, which propositions are correct?

A. The glucose solution should be cooled before yeast is added.

B. Yeast should be added while the glucose solution remains boiling.

C. Cooling the solution removes the need to consider enzyme activity.

D. A hot glucose solution may denature enzymes in the yeast.

E. A hot glucose solution may kill yeast cells.

Answer: (A), (D), (E)

Explanation

The glucose solution should be cooled because excessive heat may kill yeast or denature its enzymes. Adding yeast to a boiling solution is inappropriate, and cooling does not remove the relevance of enzyme activity.

17. How does cell size affect the surface-area-to-volume ratio?

A. Larger cells have a larger surface-area-to-volume ratio than smaller cells.

B. Larger cells have a smaller surface-area-to-volume ratio than smaller cells.

C. Smaller cells have a larger surface-area-to-volume ratio than larger cells.

D. Cell size does not affect the surface-area-to-volume ratio.

E. Smaller cells have a smaller surface-area-to-volume ratio than larger cells.

Answer: (B), (C)

Explanation

Smaller cells have a larger surface-area-to-volume ratio, whereas larger cells have a smaller ratio. The other statements reverse this relationship or incorrectly claim that size has no effect.

18. Which propositions correctly describe the calculation of light intensity?

A. Light intensity is calculated using $\text{Intensity} = \text{distance}^2$.

B. Doubling the distance reduces light intensity according to the inverse-square relationship.

C. Light intensity is calculated using $\text{Intensity} = \frac{1}{\text{distance}}$.

D. Light intensity is calculated using $\text{Intensity} = \frac{1}{\text{distance}^2}$.

E. Light intensity increases with the square of the distance from the source.

Answer: (B), (D)

Explanation

Light intensity follows the inverse-square formula $\text{Intensity} = \frac{1}{\text{distance}^2}$. Therefore, increasing distance reduces intensity according to that relationship; the other formulas and the claimed increase are incorrect.