02 the plasma membrane

A View of the Cell

The Plasma Membrane

A View of the Cell

Cells maintain homeostasis Depends on the movement of materials in and

out of the cell Nutrients, waste and ions

Two factors govern the movement of materials in and out of the cell Diffusion The plasma membrane

Diffusion

Diffusion is caused by the random motion of atoms and molecules Types of motion: vibrational, rotational and

translational

The diffusion of water through a membrane is called osmosis

Diffusion in a Cell

The direction a molecule travels depends on… The concentration gradient The function the molecule plays in cell

metabolism

3 situations exist between cells and their environment based on concentration Hypotonic Hypertonic Isotonic

Diffusion in a Cell

Diffusion in a Cell

The Plasma Membrane

The plasma membrane separates the cell from its environment and controls what passes through it

The fluid mosaic model The plasma membrane has a dynamic – ever changing

– structural composition A phospholipid bilayer Cholesterol Proteins

Phospholipids

The Role of Cholesterol

Cholesterol helps to maintain the proper fluidity of the membrane in cases of extreme temperature change

Cholesterol Rigidity Fluidity

Cholesterol Rigidity Fluidity

The Role of Proteins

Transport proteins Move needed substances or waste material

through the membrane

Methods of Cellular Transport

Passive Transport

Requires no cell energy

Diffusion

Osmosis

Active Transport

Requires the cell to expend energy

Used to get necessary metabolic chemicals

Particles move against the concentration gradient or are too large to pass through transport proteins

Passive Transport – Facilitated Diffusion

Channel proteins (a type of transport protein) create a passage or channel through which molecules can pass

Active Transport

Carrier proteins (a type of transport protein) bind with a molecule and uses energy to move it against the concentration gradient

Active Transport

When a molecule is too large to pass through the membrane…

…cells can absorb them by engulfing them Endocytosis Ex/ White blood cells, feeding

…cells can excrete or secrete them Exocytosis Ex/removal of waste, release of cellular product

(neurotransmitters, hormones, enzymes)

Endocytosis

To absorb a large molecule (or organism!) a cell can…

…completely engulf it Phagocytosis https://www.youtube.com/watch?v=aWItglvTiLc

Endocytosis

To absorb a large molecule a cell can…

…make a small pocket (called a vesicle) out of the membrane to store it Pinocytosis

Exocytosis

When a cell directs the contents of a vesicle out of the membrane into the extracellular space Waste = excretion Products = secretion