1

7-3: Cell Boundaries

2

CELL WALL

• Strong supporting layer around the

membrane

• May be present in plants, protists, fungi,

and many prokaryotes

• Main function: to provide support and

protection for the cell

3

4

CELL WALL

5

CELL MEMBRANE

• Regulates what enters and leaves the cell;

provides protection and support

• Made up of two phospholipid layers called

a lipid bilayer

• Referred to as a “fluid mosaic model”

• http://www.dnatube.com/video/360/Fluid-

Mosaic-Model

Cell membrane TEM 436,740X

6

7

8

Cell Membrane Proteins

• Recognition Proteins: cell-to-cell

recognition

• Receptor Proteins: recognize and respond

to different extracellular molecules,

generating specific responses within cell

• Transport (Channel & Carrier) Proteins:

allow specific molecules and ions to pass

through the membrane

9

10

DIFFUSION THROUGH CELL

BOUNDARIES

• Process by which molecules move from areas of

higher concentration to areas of lower

concentration (examples: oxygen, carbon

dioxide, water)

• Continues until equilibrium is reached; particles

will still continue to move

• No energy is required by the cell

11

12

13

OSMOSIS

• Diffusion of water through a selectively

permeable membrane

• Some water molecules can pass through

cell membrane but most need channel

proteins

• Selectively permeable membrane - some

substances can pass and some cannot

14

15

Effects of Osmosis on the cell

1.Isotonic: concentration is the same on

both sides of the cell. (Normal Cell)

2.Hypertonic: The solution, in which the cell

is in, has higher solute concentration than

the cell. (Skinny Cell)

3.Hypotonic: The solution, in which the cell

is in, has lower solute concentration than

the cell. (Swollen Cell)

16

Image source: mywellnesswarehouse.com

17

FACILITATED DIFFUSION

• Process that helps large molecules that can’t

pass through the membrane by osmosis

(example: glucose, amino acids)

• Protein molecules act as channels for large

molecules to pass from one side of the

membrane to the other side

• No energy is required by the cell

18

19

20

ACTIVE TRANSPORT

• Process which does require energy to

transport materials across the cell

membrane

• Movement of molecules against the

concentration differences

• Types of active transport consist of:

– Endocytosis

– Exocytosis

21

• Occurs by infoldings, or pockets, of the

cell membrane

• Phagocytosis= “cell eating” cytoplasm

surrounds a particle and package it within

a food vacuole

• Pinocytosis= “cell drinking” tiny pockets

form along the cell membrane, fill with

liquid and then pinch off to form vacuoles

within the cell

Endocytosis

22

23

24

Exocytosis

25

• removal of contents from the cell.

Ex: Contractile vacuoles

26