Movement In and Out of Cells

O Level Biology Questions and Answers

Subject: Biology

Level: O Level

This resource provides a complete set of O Level Biology Questions and Answers focused on movement in and out of cells. You will explore diffusion, osmosis, and active transport through exam‑style questions, detailed explanations, and practical exam tips. Perfect for mastering these essential concepts.

Topic Overview

Substances move across cell membranes by three main processes. Diffusion is the net movement of particles from an area of higher concentration to lower concentration. Osmosis is the diffusion of water across a partially permeable membrane. Active transport uses energy to move particles against a concentration gradient. These processes are vital for nutrient uptake, gas exchange, and waste removal in organisms.

Exam Questions and Answers

Question 1

Question:
Define diffusion and give one example in living organisms.

Answer:
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Example: oxygen diffusing from alveoli into the blood.

Explanation:
Diffusion continues until particles are evenly distributed. In the lungs, oxygen concentration is higher in alveoli than in capillaries, so oxygen moves into the blood. This process requires no energy.

Exam Tip:
Use the phrase “net movement” in your definition. Always give a specific example from gas exchange or nutrient absorption.

Question 2

Question:
What is osmosis? How does it differ from diffusion?

Answer:
Osmosis is the net movement of water molecules from a dilute solution (high water concentration) to a concentrated solution (low water concentration) across a partially permeable membrane. Unlike diffusion, osmosis is limited to water and requires a membrane.

Explanation:
Diffusion can involve any substance, but osmosis specifically involves water moving across a partially permeable membrane. Both are passive processes that do not require energy.

Exam Tip:
Always mention “partially permeable membrane” in your osmosis definition. Avoid confusing it with simple diffusion.

Question 3

Question:
Explain why a red blood cell placed in distilled water bursts, while a plant cell does not.

Answer:
Water enters both cells by osmosis. Red blood cells have no cell wall, so they swell and burst (lysis). Plant cells have a rigid cellulose cell wall that expands only slightly; they become turgid but do not burst.

Explanation:
Distilled water has a very high water concentration. The cell cytoplasm has lower water concentration, so water moves in. Animal cells cannot withstand the pressure, while plant cell walls provide structural support.

Exam Tip:
Use the terms “turgid” for plant cells and “lysis” for animal cells. A diagram helps illustrate the effect of osmosis.

Question 4

Question:
Describe how active transport differs from diffusion and osmosis.

Answer:
Active transport moves particles against a concentration gradient (from low to high concentration) and requires energy (ATP). Diffusion and osmosis are passive and move particles down a concentration gradient without energy.

Explanation:
Active transport allows cells to absorb essential substances even when their concentration inside is already high, such as the uptake of mineral ions by root hair cells.

Exam Tip:
Memorise the phrase “against the concentration gradient” and “requires energy” for active transport. Give an example (e.g., root hair cells taking up nitrates).

Question 5

Question:
A potato strip placed in concentrated sugar solution becomes flaccid. Explain why.

Answer:
The concentrated sugar solution has a lower water concentration than the potato cells. Water moves out of the potato cells by osmosis, causing them to lose turgor pressure and become flaccid (limp).

Explanation:
Water moves from the potato cells (higher water concentration) into the surrounding solution (lower water concentration) across the cell membranes. This results in shrinkage of the cytoplasm and loss of rigidity.

Exam Tip:
Relate flaccidity to loss of water. In such experiments, measure the change in mass or length to confirm water loss.

Question 6

Question:
List three factors that increase the rate of diffusion.

Answer:
1. Increased temperature. 2. Steeper concentration gradient. 3. Larger surface area to volume ratio.

Explanation:
Higher temperature gives particles more kinetic energy, increasing movement. A steeper gradient means a bigger difference in concentration, speeding net movement. A larger surface area allows more particles to cross the membrane at once.

Exam Tip:
Always mention how each factor affects particle movement. In exam questions, relate them to adaptations like alveoli or villi.

Question 7

Question:
Explain how root hair cells are adapted for the absorption of water and mineral ions.

Answer:
Root hair cells have long, thin extensions that increase surface area for water absorption by osmosis. They also have carrier proteins and use active transport to absorb mineral ions from the soil, even when the concentration inside the cell is higher.

Explanation:
The large surface area speeds up water uptake. Mineral ions are often in low concentration in soil water, so active transport (requiring energy from respiration) is needed to move them into the cell.

Exam Tip:
Link structure to function: “large surface area” for diffusion/osmosis; “mitochondria” for active transport energy.

Question 8

Question:
Describe an experiment to demonstrate osmosis using a potato and sugar solutions.

Answer:
Prepare three potato cylinders of equal size and mass. Place one in distilled water, one in dilute sugar solution, and one in concentrated sugar solution. After one hour, re‑weigh them. The cylinder in distilled water gains mass (water entered), the one in concentrated solution loses mass (water left), and the dilute solution shows little change.

Explanation:
The change in mass shows the direction of water movement by osmosis. The distilled water has a higher water concentration than the potato cells, so water enters. The concentrated solution has a lower water concentration, so water leaves.

Exam Tip:
Use control variables (same size potato, same time, same temperature) and repeat for reliability. Record percentage change in mass.

Key Concepts Summary

Diffusion: net movement from high to low concentration, no energy, any substance.
Osmosis: diffusion of water across a partially permeable membrane.
Active transport: movement against a concentration gradient, requires energy.
Factors affecting rate: temperature, concentration gradient, surface area, distance.
Plant cells become turgid in dilute solutions, flaccid or plasmolysed in concentrated solutions.

Frequently Asked Questions

What is the difference between osmosis and diffusion?

Osmosis is a specific type of diffusion that involves only water molecules moving across a partially permeable membrane. Diffusion can involve any substance and does not require a membrane.

How does temperature affect the rate of diffusion?

Increasing temperature increases the kinetic energy of particles, making them move faster. This increases the rate of diffusion because particles collide and spread more quickly.

Why do animals not have cell walls?

Animal cells rely on flexible membranes and a cytoskeleton for shape. Cell walls would restrict movement and the ability to change shape, which is important for functions like muscle contraction and phagocytosis.

Conclusion

Mastering O Level Biology Questions and Answers on movement in and out of cells gives you a solid foundation in cell biology. By understanding diffusion, osmosis, and active transport, you can explain many physiological processes. Practice these questions, review the concepts, and use the exam tips to approach your tests with confidence.

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