ESTUDYR
OCR A-LEVEL BIOLOGY - MODULES 1-4 MOST TESTED QUESTIONS AND
ANSWERS GRADED A+ WITH RATIONALES
1. Why do specimens need to be thin when observing them under a light microscope?
A) To make staining easier
B) To reduce air bubbles
C) To allow light to pass through
D) To enhance contrast
Answer: C. To allow light to pass through
Rationale: Thin specimens permit light to pass through them, making cellular structures visible under a
light microscope.
2. Identify and explain the starch test.
A) Add Benedict's solution and heat.
B) Add Biuret solution.
C) Add iodine dissolved in potassium iodide solution.
D) Add ethanol and shake.
Answer: C. Add iodine dissolved in potassium iodide solution.
Rationale: Iodine reacts with starch, turning blue-black if present. A negative test remains orange-
brown.
3. Why is the structure of the plasma membrane referred to as the fluid mosaic model?
A) Because it is solid but flexible.
B) Because it has a uniform surface.
C) Because the phospholipids are fluid, and proteins are scattered like a mosaic.
D) Because it is static in nature.
Answer: C. Because the phospholipids are fluid, and proteins are scattered like a mosaic.
Rationale: The fluid nature arises from moving phospholipids, and embedded proteins give it a mosaic
appearance.
4. Why is cell signaling important?
A) So that cells can communicate with each other.
B) To transport nutrients efficiently.
,ESTUDYR
C) To increase metabolic activity.
D) To maintain homeostasis only.
Answer: A. So that cells can communicate with each other.
Rationale: Cell signaling enables coordination and communication between cells for various
physiological processes.
5. How do cells communicate?
A) By direct physical contact.
B) By releasing heat energy.
C) By producing electrical impulses.
D) By releasing messenger molecules that bind to specific receptors.
Answer: D. By releasing messenger molecules that bind to specific receptors.
Rationale: Cells release signaling molecules that travel and bind to specific receptors on target cells.
6. Why is cell signaling specific?
A) Because all cells have identical receptors.
B) Because different receptors are specific to different signaling molecules.
C) Because it is a random process.
D) Because it only occurs in specialized cells.
Answer: B. Because different receptors are specific to different signaling molecules.
Rationale: Specificity arises from the unique structure of receptors and their selective binding to
molecules.
7. What does cell signaling initiate?
A) Increased metabolism
B) A physiological response
C) Breakdown of ATP
D) Production of energy
Answer: B. A physiological response
Rationale: Signaling triggers changes such as gene expression, enzyme activation, or secretion of
substances.
,ESTUDYR
8. What is the approximate size of eukaryotic cells?
A) 1-10 µm
B) 10-100 µm
C) 100-1000 µm
D) 0.1-1 mm
Answer: B. 10-100 µm
Rationale: Eukaryotic cells range from 10-100 micrometers in size, much larger than prokaryotic cells.
9. State the defining features of eukaryotic cells.
A) No nucleus or organelles.
B) Nucleus and membrane-bound organelles.
C) Cell walls and plasmids.
D) Small ribosomes and circular DNA.
Answer: B. Nucleus and membrane-bound organelles.
Rationale: Eukaryotic cells contain a defined nucleus and organelles, unlike prokaryotic cells.
10. What happens during inspiration?
A) Ribs move down, and diaphragm domes.
B) Diaphragm flattens, and ribs move up and out.
C) Lung pressure increases, forcing air out.
D) The thorax volume decreases.
Answer: B. Diaphragm flattens, and ribs move up and out.
Rationale: These movements increase thoracic volume, reducing pressure and allowing air to enter the
lungs.
11. What is the function of the cytoskeleton?
A) Store nutrients
B) Replicate DNA
C) Produce proteins
D) Maintain cell shape and transport organelles
Answer: D. Maintain cell shape and transport organelles
Rationale: The cytoskeleton provides structure and enables movement of organelles within the cell.
, ESTUDYR
12. What is the function of microfilaments?
A) Form spindle fibers during cell division.
B) Aid in cell movement and contract during division.
C) Provide mechanical strength.
D) Transport proteins.
Answer: B. Aid in cell movement and contract during division.
Rationale: Microfilaments play a role in cell motility and cytokinesis during division.
13. What is the function of microtubules?
A) Form spindle fibers and determine cell shape.
B) Maintain homeostasis.
C) Anchor cells to extracellular structures.
D) Store calcium ions.
Answer: A. Form spindle fibers and determine cell shape.
Rationale: Microtubules help in cell division and act as structural components of the cytoskeleton.
14. What is the function of intermediate fibers?
A) Aid in protein synthesis.
B) Conduct electrical signals.
C) Transport vesicles.
D) Provide mechanical strength.
Answer: D. Provide mechanical strength.
Rationale: Intermediate fibers offer stability and support to cells, maintaining their integrity.
15. How does blood circulation maintain a concentration gradient of oxygen?
A) By creating high blood pressure.
B) By constantly removing oxygen and bringing in carbon dioxide.
C) By thickening blood.
D) By increasing temperature.
Answer: B. By constantly removing oxygen and bringing in carbon dioxide.
Rationale: Continuous blood flow ensures a gradient necessary for gas exchange in tissues.
OCR A-LEVEL BIOLOGY - MODULES 1-4 MOST TESTED QUESTIONS AND
ANSWERS GRADED A+ WITH RATIONALES
1. Why do specimens need to be thin when observing them under a light microscope?
A) To make staining easier
B) To reduce air bubbles
C) To allow light to pass through
D) To enhance contrast
Answer: C. To allow light to pass through
Rationale: Thin specimens permit light to pass through them, making cellular structures visible under a
light microscope.
2. Identify and explain the starch test.
A) Add Benedict's solution and heat.
B) Add Biuret solution.
C) Add iodine dissolved in potassium iodide solution.
D) Add ethanol and shake.
Answer: C. Add iodine dissolved in potassium iodide solution.
Rationale: Iodine reacts with starch, turning blue-black if present. A negative test remains orange-
brown.
3. Why is the structure of the plasma membrane referred to as the fluid mosaic model?
A) Because it is solid but flexible.
B) Because it has a uniform surface.
C) Because the phospholipids are fluid, and proteins are scattered like a mosaic.
D) Because it is static in nature.
Answer: C. Because the phospholipids are fluid, and proteins are scattered like a mosaic.
Rationale: The fluid nature arises from moving phospholipids, and embedded proteins give it a mosaic
appearance.
4. Why is cell signaling important?
A) So that cells can communicate with each other.
B) To transport nutrients efficiently.
,ESTUDYR
C) To increase metabolic activity.
D) To maintain homeostasis only.
Answer: A. So that cells can communicate with each other.
Rationale: Cell signaling enables coordination and communication between cells for various
physiological processes.
5. How do cells communicate?
A) By direct physical contact.
B) By releasing heat energy.
C) By producing electrical impulses.
D) By releasing messenger molecules that bind to specific receptors.
Answer: D. By releasing messenger molecules that bind to specific receptors.
Rationale: Cells release signaling molecules that travel and bind to specific receptors on target cells.
6. Why is cell signaling specific?
A) Because all cells have identical receptors.
B) Because different receptors are specific to different signaling molecules.
C) Because it is a random process.
D) Because it only occurs in specialized cells.
Answer: B. Because different receptors are specific to different signaling molecules.
Rationale: Specificity arises from the unique structure of receptors and their selective binding to
molecules.
7. What does cell signaling initiate?
A) Increased metabolism
B) A physiological response
C) Breakdown of ATP
D) Production of energy
Answer: B. A physiological response
Rationale: Signaling triggers changes such as gene expression, enzyme activation, or secretion of
substances.
,ESTUDYR
8. What is the approximate size of eukaryotic cells?
A) 1-10 µm
B) 10-100 µm
C) 100-1000 µm
D) 0.1-1 mm
Answer: B. 10-100 µm
Rationale: Eukaryotic cells range from 10-100 micrometers in size, much larger than prokaryotic cells.
9. State the defining features of eukaryotic cells.
A) No nucleus or organelles.
B) Nucleus and membrane-bound organelles.
C) Cell walls and plasmids.
D) Small ribosomes and circular DNA.
Answer: B. Nucleus and membrane-bound organelles.
Rationale: Eukaryotic cells contain a defined nucleus and organelles, unlike prokaryotic cells.
10. What happens during inspiration?
A) Ribs move down, and diaphragm domes.
B) Diaphragm flattens, and ribs move up and out.
C) Lung pressure increases, forcing air out.
D) The thorax volume decreases.
Answer: B. Diaphragm flattens, and ribs move up and out.
Rationale: These movements increase thoracic volume, reducing pressure and allowing air to enter the
lungs.
11. What is the function of the cytoskeleton?
A) Store nutrients
B) Replicate DNA
C) Produce proteins
D) Maintain cell shape and transport organelles
Answer: D. Maintain cell shape and transport organelles
Rationale: The cytoskeleton provides structure and enables movement of organelles within the cell.
, ESTUDYR
12. What is the function of microfilaments?
A) Form spindle fibers during cell division.
B) Aid in cell movement and contract during division.
C) Provide mechanical strength.
D) Transport proteins.
Answer: B. Aid in cell movement and contract during division.
Rationale: Microfilaments play a role in cell motility and cytokinesis during division.
13. What is the function of microtubules?
A) Form spindle fibers and determine cell shape.
B) Maintain homeostasis.
C) Anchor cells to extracellular structures.
D) Store calcium ions.
Answer: A. Form spindle fibers and determine cell shape.
Rationale: Microtubules help in cell division and act as structural components of the cytoskeleton.
14. What is the function of intermediate fibers?
A) Aid in protein synthesis.
B) Conduct electrical signals.
C) Transport vesicles.
D) Provide mechanical strength.
Answer: D. Provide mechanical strength.
Rationale: Intermediate fibers offer stability and support to cells, maintaining their integrity.
15. How does blood circulation maintain a concentration gradient of oxygen?
A) By creating high blood pressure.
B) By constantly removing oxygen and bringing in carbon dioxide.
C) By thickening blood.
D) By increasing temperature.
Answer: B. By constantly removing oxygen and bringing in carbon dioxide.
Rationale: Continuous blood flow ensures a gradient necessary for gas exchange in tissues.
