Which is heavier, one hundred pounds of feathers, or one hundred pounds of bricks?

Cell Boundaries

Macromolecules in cells!

• All the cell parts are made up of these macromolecules

• We will start with just looking at cell boundaries

What organelle allows molecules to pass from outside the cell to inside

the cell?Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

The Cell Membrane

• All cells are bound by a cell membrane.

The Cell membrane consists of:• Lipid bilayer [Phospholipid bilayer]• Proteins• Carbohydrates• Cholesterol

Cell Walls

• lay outside the cell membrane. They are rigid and made of carbohydrates

• Present in:– Plant cells– Fungi– Bacterial cells

• Cell membrane is semi-permeable - it allows certain things across but restricts other things

• The structure of the cell membrane fits its function– Flexible barrier– Semi-permeable– Sends and receives chemical messages from

other cells

Membrane Structure

To Recap…

• Phospholipids are water resistant and flexible

• Carbohydrates are like ID tags for the cell

• Proteins are for stability and act like passageways for substances to enter and leave the cell.

Diffusion• Diffusion: The movement of a molecule, or

atom from an area of high concentration to an area of low concentration until equilibrium is reached

– Equilibrium means equal concentrations on both sides of the membrane

– This naturally occurs and normally no energy is required

Diffusion video

Glucose Molecules will move from an area of high concentration to the area of low concentration.

Osmosis: the movement of water across a semi permeable

membrane

1. Isotonic solution

• The same concentration of solute on both sides of the membrane

• Water will continue to move into and out of the cell at an EVEN RATE

Water moves in AND out!

Hypotonic Solutionoutside solution has a

lower concentration of solute than inside the cell

(Higher concentration of water outside the cell)

Result: Water will move into the

cell

These red blood cells are in a hypotonic solution and have gained water

Hypertonic Solutionoutside solution has a higher

concentration of solute than inside the cell

(Lower concentration of water outside the cell)

Results:

Water moves out of the cell

These Red blood cells are in a hypertonic solution and have lost water

Click on Image to watch video

Click on image to watch video

Click on image to watch video

Facilitated Diffusion

I. Movement of a molecule across a membrane when protein channels are required.

II. Sometimes molecules are too large to pass or they are charged and can’t pass through the membrane without help

1. When a protein channel helps a molecule this is called Facilitated diffusion

2. Protein channels are specific for one kind of molecule

Active Transport

• Movement of molecules from low concentration to high concentration. (This is the opposite of diffusion)

1) Molecular transport1. Used for small ions such as calcium,

potassium and sodium

2. Must pump ions across the membrane (This requires ENERGY!!)

3. Involves changes in protein shape

Active Transport: TypesActive Transport: Types

2) Endocytosis– For transport of larger

molecules into the cell– Occurs with pockets of

the cell membrane that fold into the cells creating a vacuole that is released into the cytoplasm

– A vacuole is a bubble-shaped part of the cell used for storage

Active Transport: TypesActive Transport: Types

2 types of Endocytosis

aa) Phagocytosis) Phagocytosis: “cell eating”- : “cell eating”- cells take up particles and form a food cells take up particles and form a food vacuolevacuole

Pinocytosis: “Cell drinking”- cells take up liquid from the surrounding environment.

Exocytosis

• Release of materials from the cell