Cell Transport

Movement of substances in and out of cells

Substances move in and out of cells by:

1. Passive transport

2. Active transport

Passive Transport

No energy (ATP) is required to move gas or liquid molecules from one place to another!

(Is this an example of a “free lunch” or perpetual motion?… imagine if our cars worked like this….)

Need to understand concepts of : • Diffusion, • Osmosis,• Concentration gradient, • Net movement

Diffusion

• The random movement of molecules from an area of high concentration to an area of low concentration.

• Down the concentration gradient.• Animation

• Animation2 Conc. Grad

Rate (speed) of diffusion depends on:

» fast slow

Size of molecules

Temperature

State of matter

Concentration gradient

Osmosis

• Net movement of water molecules from an area of high water concentration to an area of low water concentration, through a semi-permeable membrane.

• Animation Animation2

• Hypertonic – more solute and less water

• Hypotonic – less solute and more water

• Isotonic – same conc. of solute and water

Think (don’t write)

• Most marine fish die if transferred to freshwater.

• When a drop of blood is mixed with distilled water, the blood cells burst.

• Living plant tissues that had lost water become firm when supplied with water.

Net movement

The overall movement of all molecules of a substance back and forward along the concentration gradient.

e.g. when oxygen or water molecules diffuse into a cell, some molecules move out at the same time. Overall more are moving inwards than outwards so the net movement is………..

Osmoregulation

• The control of water in a cell.

• Plasmolysis – – Water leaves cell and membrane shrinks from

wall. – Cell becomes flaccid.– Full plasmolysis is irreversible.

Animation

• Turgor– Water enters cell causing it to swell– Cell becomes turgid– Cell wall prevents rupture

• Animation

Active Transport

Energy (ATP) is required for:

Endocytosis (phago- and pino-),

Exocytosis,

Ion pumps

• e.g. re-absorption of glucose by kidney, salt uptake by the roots of plants, amino acid uptake by fungi

• The movement of substances from an area of low concentration to an area of high concentration.

• Against the concentration gradient

Conc. Grad

Cytosis1.Endocytosis

• Movement in (enter) to a cell• Phagocytosis – cell eating – forms a food

vacuole. • e.g. Lysosomes fuse to enable digestion.• Pinocytosis – cell drinking – forms a

vesicle• e.g. Amoeba and white blood cells (WBC)

– pseudopodia• Animation

2.Exocytosis

• Movement out (exit)

• Vesicles bud off from golgi apparatus or ER, vacuole fuses with cell membrane and expels contents

• Secretions e.g. digestive enzymes released, glands

• Animation

Ion Pumps

• Proteins in the cell membrane can actively accumulate specific ions on one side of the membrane to control the amount

• Animation

• Animation2