Movement of substances across the

plasma membrane

Chapter 3

• Many biochemical reactions take place in a cell.

• The cells require many substances to carry out these biochemical reaction.

• Waste products that are formed during biochemical reactions within the cells must be eliminated because they are poisonous.

• There is movement of substances across the plasma membrane so that the cell can

Obtain nutrients and gases

Excrete metabolic wastes

Maintain a suitable pH and ionic concentration with the

cell for enzyme activity

Red Blood Cell Near Some Body cell

Moving in Moving out

Carbon dioxide

Oxygen

Photosyntesising Plant Cell

Moving in Moving out

Carbon dioxide

Oxygen

Water

Glucose

Plant Cell With No Chloroplast

Carbon dioxide

Oxygen

Glucose

Water

Moving in Moving out

Liver cellCarbon dioxide

Oxygen

Glucose

Water

Amino acids

Urea

Moving in Moving out

The structure of the plasma membraneThe plasma membrane has 3 components

1. Double layer of phospholipids molecules.

2. Pore

3. Carrier Proteins

A phospholipid molecule

Hydrophilic head

Hydrophobic tails

Phospholipid bilayer

Outside of cell

Inside of cellP

hosp

holip

id la

yer

• The phospholipids bilayer, proteins and other parts are not rigid or static, but form a dynamic and flexible structure.

• The protein molecules float about in the phospholipid bilayer to form a mosaic pattern that is always changing like fluid.

• Singer and Nicolson call it ‘fluid-mosaic model’

The plasma membrane is generally described as semi-permeable or selectively permeable because it only lets certain substances through.

Fat soluble molecules and small molecules such as oxygen are able to pass through unaided.

Water soluble substances such as glucose and amino acids and ions need to aided by carrier protein.

Water molecules can move across plasma membrane.

Which of these substances can pass through phospholipids layer or carrier protein?

Na+ Sodium ion

K+ Potassium ion

Carrier Protein

Channel Protein

Movement Of Substances Across The Plasma Membrane

Passive transport Active transport

Simple diffusion

Facilitated diffusion

Osmosis

The differences between PT and AT

Does not require energy

Substances move with concentration

gradient

Will continue until an equilibrium is

reached

Require energy from cell respiration

Substances move against concentration

gradient

Process leads to accumulation or elimination of the

substance from the cell

Passive Transport Active Transport