CHAPTER 3

MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE

Learning Outcomes

Explain the movement of substances across the plasma membrane through the process of active transport,

Explain the process of passive transport in living organisms using examples,

Explain the process of active transport in living organisms using examples,

Compare and contrast passive transport and active transport.

Explain what hypotonic, hypertonic and isotonic solutions are,

Explain the effects of hypotonic, hypertonic and isotonic solutions on plant cell and animal cell,

Explain plasmolysis, deplasmolysis, haemolysis and crenation.

Active Transport Active transport is the movement f dissolved ions or

molecules across the plasma membrane, against the concentration gradient.

Energy ATP (adenosine triphosphate) is required.

Active transport requires both carrier proteins and energy to transport molecules or ions.

Examples of active transport in living organisms:

a) Ions intake by root hairs of a plant

b) Ions intake by sea weeds and algae

c) Potassium ions intake by red blood cells

d) Ion intake by Hydra sp.

Active Transport

Active Transport

Active Transport

Active Transport

Active Transport

Mechanism of Active Transport The molecule or ion for example, potassium ion,

attaches to the binding site of a specific carrier protein.

ATP attaches to carrier protein and is hydrolysed to produce energy, ADP and P.

The carrier protein changes shape or position and releases the potassium ions into the cell. Phosphate group is released.

The carrier protein reverts back to original position.

Active Transport

Active Transport

The process of passive and active transport in living organisms Gaseous exchange in the alveoli and blood

capillaries (simple diffusion)

Absorption of digested food in the villi (facilitated diffusion)

Absorption of water in root hairs of plants (osmosis)

Ion intake by root hairs of a plant (active transport)

Gaseous exchange in the alveoli and blood capillaries (simple diffusion) The concentration of oxygen is higher in the

alveolus than in the blood capillary around it. Hence oxygen diffuses from alveolus into the blood capillary.

The concentration of carbon dioxide in the blood capillary is higher than the alveolus. Thus, carbon dioxide diffuses out of the blood capillary into the alveolus.

Simple diffusion also occurs during gaseous exchange between body cells and blood capillaries.

Gaseous exchange in the alveoli and blood capillaries (simple diffusion)

Gaseous exchange in the alveoli and blood capillaries (simple diffusion)

Absorption of digested food in the villi (facilitated diffusion)

Digested food such as glucose and amino acids are absorbed in the villi by facilitated diffusion. The concentration of this digested food is higher in the ileum than in the blood capillaries of the villi. Thus, the digested food diffuses across the membrane of the villi with the help of carrier proteins.

Absorption of digested food in the villi (facilitated diffusion)

Absorption of water in root hairs of plants (osmosis) Plants take in most of the water through their root hairs.

Root hairs are long and narrow. This increases the surface area for absorption of water. Root hairs have large vacuoles. The cell sap in the large vacuole creates a diffusion (concentration) gradient so that water moves into the root hair cell easily by osmosis.

Root hairs have thin walls o absorb water and mineral salts.

Normally, the soil has a lower osmotic concentration than the cytoplasm in the root hairs. As a result, water in the soil move into the root hairs of the plant by osmosis.

Ion intake by root hairs of a plant (active transport) In the soil, the mineral salts dissolve in water to form

mineral ions, for examples potassium ions.

The concentration of potassium ions in the root hairs is higher than its concentration in the soil. So, potassium ions are taken into the root hairs by active transport.

Ion intake by root hairs of a plant (active transport)

Ion intake by root hairs of a plant (active transport)

Ion intake by root hairs of a plant (active transport)