Biology Diffusion and Osmosis Quiz

Diffusion

• Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.
• It stops when particles reach dynamic equilibrium; a state of constant random motion with no net movement.
• Potassium permanganate diffusing in water demonstrates this; particles move from high to low concentration, resulting in a homogenous solution.
• The process responsible for the smell of food reaching the nose is diffusion of food molecules.
• Moths use diffusion to distribute pheromones in the air to attract mates.

Osmosis

• Osmosis is the net movement of water molecules from a solution of higher water potential to a solution of lower water potential across a partially permeable membrane.
• Water potential is the tendency of water to move; dilute solutions have higher water potential than concentrated solutions.
• Water always moves down a water potential gradient.
• An experiment using a thistle funnel with a sucrose solution demonstrates osmosis; the liquid level inside the funnel rises due to water entering.

Types of Solutions

• Solutions with the same water potential are isotonic.
• A hypotonic solution has higher water potential, a hypertonic solution has lower water potential.
• These terms mainly apply to animal, not plant systems.

Osmosis in Living Organisms

• Animal and plant cells are surrounded by partially permeable membranes.
• Osmosis occurs across the cell surface membrane.

Osmosis in Animal Cells

• In a hypotonic solution (high water potential), water enters the cell causing it to swell and potentially burst.
• In an isotonic solution (same water potential), there's no net water movement, cell size remains unchanged.
• In a hypertonic solution (low water potential), water leaves the cell, causing it to shrink (crenation).

Osmosis in Plant Cells

• Plant cells in a hypertonic solution lose water, becoming plasmolysed (cell membrane shrinks from the cell wall).
• This causes flaccidity, and prolonged plasmolysis kills cells. Excess fertilizer can cause this.
• Turgor pressure due to osmosis maintains the shape of plant tissues. Changes in turgor cause movement in some plant parts (e.g., flower opening/closing, mimosa leaves).

Surface Area to Volume Ratio

• Cells exchange materials (oxygen, nutrients in; carbon dioxide, waste out) across their surface membranes.
• The surface area to volume ratio affects the efficiency of this exchange; a large ratio enables faster diffusion.
• As cell size increases, the surface area to volume ratio decreases. Smaller cells have larger ratios and more efficient exchange.
• Actively metabolizing cells are usually small to maintain a high surface area to volume ratio.

Cells for Absorption

• Root hair cells have long projections to increase surface area for water and mineral absorption.
• Red blood cells have a biconcave shape to increase surface area for oxygen uptake.
• Epithelial cells in the small intestine have microvilli to enhance the absorption of digested food.

Active Transport

• Active transport uses energy to move substances against a concentration gradient (from a lower to a higher concentration).

Test your knowledge of diffusion and osmosis with this quiz. Explore key concepts such as concentration gradients, dynamic equilibrium, and water potential. Understand how these processes impact living organisms and their environments.