Transport of substances

Diffusion

The passive movement of particles from high to low concentration—requires no energy.

Osmosis

The diffusion of water across a partially permeable membrane.

Active Transport

The movement of molecules against the concentration gradient (low to high) using ATP (energy).

Examples of Diffusion

Oxygen & carbon dioxide exchange in lungs and leaves.

Examples of Osmosis

Water absorption by plant roots.

Examples of Active Transport

Ion uptake in root hair cells, glucose absorption in the small intestine.

Osmosis Effects on Plant Cells

Causes turgid (swollen), flaccid (soft), or plasmolysed (shriveled) states.

Osmosis Effects on Animal Cells

Causes lysis (bursting in hypotonic solutions) or crenation (shrinking in hypertonic solutions).

Concentration Gradient

The difference in concentration between two regions.

Concentration Gradient Effect on Diffusion

A steeper gradient speeds up diffusion as particles move more rapidly from high to low concentration.

Hypertonic Solution

A solution with more solute—causes water to move out of a cell.

Hypotonic Solution

A solution with less solute—causes water to move into a cell.

Isotonic Solution

A solution with equal solute concentration—no net movement of water.

Facilitated Diffusion

The passive movement of particles through a protein channel in the membrane—no ATP required.

Selectively Permeable Membrane

A membrane that only allows certain molecules to pass through.

Active Transport Location

In membranes where molecules move against the gradient (low to high concentration).

Root Hair Cells Active Transport

To absorb essential minerals from soil, even when the concentration inside is higher.

Small Intestine Active Transport

To absorb glucose into the blood, even when the concentration in the blood is higher.

ATP in Active Transport

Because molecules are moving against the concentration gradient, requiring energy input.

Diffusion Equilibrium

When molecules are evenly spread and there is no net movement.

Temperature Effect on Diffusion

Higher temperature → faster diffusion (particles move more). Lower temperature → slower diffusion.

Surface Area Effect on Diffusion

Larger surface area → faster diffusion (more space for particles to move). Smaller surface area → slower diffusion.

Distance Effect on Diffusion

Shorter distances = faster diffusion, while thicker barriers slow diffusion.

Particle Size Effect on Diffusion

Smaller particles move faster due to lower resistance, while larger molecules diffuse more slowly.

Saturation Effect on Diffusion

When diffusion pathways are crowded, movement slows as fewer free spaces are available.

Molecule Polarity Effect on Diffusion

Molecule polarity affects the ease with which substances can diffuse across membranes.

Non-polar molecules

Diffuse easily, while polar molecules need transport proteins.

Membrane permeability

More permeable membranes allow faster diffusion, while less permeable ones restrict movement.

Transport proteins

Protein channels increase diffusion speed for specific molecules.

Aim of the osmosis required practical

To investigate how different concentrations of salt/sugar solutions affect plant tissue mass.

Type of plant tissue used in the practical

Potato cylinders.

First step of the practical

Measure and record the initial mass of potato pieces.

Duration for potato in solution

Around 30 minutes (or a set time).

Effect of distilled water on potato

The potato gains mass (water enters due to osmosis).

Effect of concentrated sugar/salt solution on potato

The potato loses mass (water leaves due to osmosis).

Reason for drying potato before measuring final mass

To ensure excess surface water does not affect the measurement.

Reason for repeating the experiment

To improve reliability of results.

SA:Vol ratio

The relationship between surface area and volume in an object.

Effect of SA:Vol ratio on diffusion

Smaller objects have a higher SA:Vol ratio, leading to faster diffusion.

Reason for small cells

A higher SA:Vol ratio enhances diffusion efficiency.

How lungs maximize SA:Vol ratio

Alveoli provide a large surface area for gas exchange.

How root hair cells improve diffusion

They have extensions to increase surface area.

How leaves maximize diffusion

They have a large, thin surface for gas exchange.

Need for transport systems in larger organisms

Their SA:Vol ratio is too low for efficient diffusion.

Diffusion in gas exchange in the lungs

Oxygen diffuses from the alveoli into the blood, while carbon dioxide diffuses out for exhalation.

Role of capillaries in diffusion

Their thin walls allow quick diffusion of substances like oxygen and glucose into tissues.

Role of the cell membrane in transport

It is partially permeable, controlling what enters and exits the cell via diffusion, osmosis, and active transport.

Effect of temperature on enzyme-controlled transport processes

High temperature denatures enzymes, slowing down active transport in cells.

Role of carrier proteins in active transport

They bind to molecules and use ATP energy to push them against the concentration gradient.

Need for transport systems in multicellular organisms

Their low SA:Vol ratio means diffusion alone isn't sufficient for supplying nutrients and removing waste.

How ventilation helps diffusion in the lungs

Maintains a steep concentration gradient by constantly bringing in fresh oxygen and removing carbon dioxide.