1. Chapter 7.3 - Transport of Substances across the Cell Membrane
Cell Boundaries
Cell Wall
Cell Membrane
Diffusion & Osmosis
Diffusion
Osmosis
Transport of Substances
Passive Transport
Active Transport

2. Cell Walls & Cell Membranes
Cell Boundaries
Cell Walls &
Cell Membranes

3. Cell Walls
Plants, Algae, Fungi, and many prokaryotes have cell walls – Animal cells do not!
The cell wall is located outside of the cell membrane and surrounds the cell.
The cell wall provides strength, support, shape, and protection to the cell.

4. Cell Wall Composition
The cell wall is porous, which means it easily allows for the transport of water, oxygen, carbon dioxide, and other substances.
The cell wall is composed of polysaccharide carbohydrate fibers called “Cellulose”.
Wood and paper are made up of these cellulose fibers.

5. Continuing Research – We are not done!!!

6. Cell Membranes Definitions Cell membrane = plasma membrane
= cytoplasmic membrane
Protoplasm = everything within the cell
Cytoplasm = everything within the cell except the nucleus
Cytosol = everything within the cell except the nucleus and the organelles

7. Cell Membrane Composition
The cell membrane is composed of:
Phospholipids
Proteins
Carbohydrates
Cholesterol

8. Cell Membrane Functions
Provide protection and support
Separate the cell from its surroundings
Communicate with other cells
Recognize foreign material
Maintains HOMEOSTASIS = Maintenance of an organism’s internal environment

9. The Cell Membrane Floats
The cell membrane is flexible and dynamic.
The cell is suspended in fluid surroundings with a fluid interior.
The cell membrane is composed of a Lipid Bilayer which is a “waterproof” membrane separating the contents of the cell from its surroundings
The cell membrane is selectively permeable, allowing some substances to cross, but not others.

10. Cell Membrane – Lipid Bilayer
Contains two opposing chains of PHOSPHOLIPIDS.
Each phospholipid is composed of a phosphate group with two fatty acid tails
The phosphate head is HYDROPHILIC = water loving
The fatty acid tails are HYDROPHOBIC = water fearing
The phospholipids are arranged with the hydrophilic heads facing the fluid in and out of the cell, with the hydrophobic tails to the inside.
This arrangement creates a “waterproof” barrier which is difficult to cross.

11. Cell Membrane – Lipid Cholesterol
CHOLESTEROL is a non-polar lipid which helps maintain the fluidity of the cell membrane by keeping the fatty acid tails from sticking together.

12. Cell Membrane - Proteins
Glycoproteins (Marker Proteins) – identifies cell
Receptor Proteins – senses environment
Aquaporins – water transport
Channel/Carrier Proteins – passive transport
Protein Pumps – active transport

13. Cell Membrane - Carbohydrates
Cell membrane CARBOHYDRATES are polysaccharides which act as markers for cell recognition. These molecules help white blood cells recognize and attack harmful bacteria.
Carbohydrates

14. Osmosis & Diffusion

15. Diffusion
Molecules move constantly in a random motion = Brownian Motion
The molecules bump into each other causing them to move from an area of high concentration to an area of lower concentration = DIFFUSION down a CONCENTRATION GRADIENT
No extra energy is needed because the molecules are already in motion (like busy bees).
Diffusion will continue until EQUILIBRIUM is reached and particles are spread throughout the container.

16. Diffusion Across a Semipermeable Membrane
Permeable = Allows liquids or gases to pass through
=> Porous => Penetrable
Semipermeable = Allows only certain liquids or gases to pass through
The semipermeable membrane above is permeable to small substances,
but not large substances.

17. Osmosis
Hypotonic
Solution
Hypertonic
Solution
WATER moves across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration until equilibrium is reached.
OSMOSIS only applies when solute movement is restricted by a semipermeable membrane.
Semipermeable
Membrane

18. How Osmosis Affects our Cells
HYPERTONIC solution = water outside of cell has a HIGH solute concentration (salty) which pulls water out of the cell.
ISOTONIC solution = solute concentration is the SAME inside the cell as outside of the cell. Water moves back and forth freely.
HYPOTONIC solution = water outside the cell has a LOW solute concentration (pure water), water moves into the cell.

19. Transport of Substances Across a Semipermeable Membrane
Passive Transport
Simple Diffusion
Facilitated Diffusion
Channel Proteins
Carrier Proteins
Active Transport
Protein Pumps
Vesicles
Endocytosis
Exocytosis

20. Passive Transport Across a Cell Membrane – SIMPLE DIFFUSION
SMALL – small enough to squeeze through the membrane
NON-POLAR – no positive or negative end to the molecule
Oxygen
Carbon Dioxide
Hormones
NO ENERGY REQUIRED!

21. Passive Transport Across a Cell Membrane – Facilitated Diffusion
LARGE – too large to squeeze through the membrane
POLAR – molecule has a positive end and a negative end
The cell membrane
allows SPECIFIC molecules
to DIFFUSE across the membrane using
tunnels (CHANNEL PROTEINS)
or gates (CARRIER PROTEINS).
Water (Aquaporins)
Ions (Na+)
Carbohydrates
Amino acids
NO ENERGY REQUIRED!

22. Active Transport Across the Cell Membrane - Pumps
(like the Na+K+ Pump)
use
CARRIER PROTEINS & ENERGY
to transport molecules
AGAINST
the
CONCENTRATION GRADIENT.
ENERGY is REQUIRED!

23. Active Transport Across the Cell Membrane - Vesicles
Endocytosis = the process of taking material into the cell
a. Phagocytosis = intake of matter
b. Pinocytosis = intake of liquids
Exocytosis = the process of
removing material from the cell

24. Phagocytosis