1. The Fluid Mosaic Model Cell Transport
The Cell Membrane
The Fluid Mosaic Model
Cell Transport

2. The Fluid Mosaic Model
The membrane of the cell is the boundary that keeps the cell separate from its environment.
Its function is to control the movement of materials in and out of the cell.

3. The Fluid Mosaic Model
The cell membrane has to be flexible to allow for cell movement but strong enough that it doesn’t break.
The Fluid Mosaic Model explains how cell membranes can meet both requirements.

4. The Fluid Mosaic Model
The cell membrane is made of lipids and proteins. These combine to form a flexible layer made of many molecules (Fluid Mosaic Model).

5. The Fluid Mosaic Model
The main part of the cell membrane is the phospholipid bilayer (bottom left).
Phospholipids have a hydrophilic head (top left) that is attracted to water in the environment and in the cytoplasm. (Color these red.)
They also have a hydrophobic tail (bottom middle) that is repelled by water.
(Color these orange.)

6. The Fluid Mosaic Model
This double layer of lipids forms the main part of the membrane.
It also forms a layer that is impermeable to polar molecules such as water, glucose, and ions. That is a problem.

7. The Fluid Mosaic Model
Membrane proteins help cells communicate with each other and transport materials (water, glucose, and ions) across the membrane.
These proteins are embedded within the lipid bilayer.

8. The Fluid Mosaic Model
Fibrous proteins (top right) cross the bilayer and receive information from the outside environment (Color these blue)
Pore proteins (bottom right) cross the bilayer and make openings for water and other molecules to pass through. (Color these purple)

9. The Fluid Mosaic Model
All of these proteins help make the cell membrane semipermeable (some materials can pass through but other materials cannot.)

10. Cell Transport and Homeostasis
The cell functions in a way similar to a larger organism: it uses energy and must maintain homeostasis.
The cell membrane is responsible for helping the cell maintain internal homeostasis by controlling what moves in and out of the cell.

11. Cell Transport and Homeostasis
The way that cells move materials include:
Passive Transport (not requiring energy from the cell)
And
- Active Transport (requires energy from the cell)

12. Check the Cell

13. Concentration
Because cells use up materials and create waste, the concentration of these materials changes all of the time.
“Concentration” means the amount of solute in the solvent.

14. Concentration
It is easier for a cell to move solutes “down” a concentration gradient; from high concentration to lower concentration.

15. Concentration
Sometimes the cell needs to move solutes “against” the concentration gradient; from low concentration to high concentration.
This requires the cell to work very hard.

16. Passive Transport
When cells move solutes down the concentration gradient, it requires no energy from the cell and is known as Passive Transport.

17. Passive Transport
Diffusion is the movement of any substance from a high concentration to a low concentration.
This relies on random molecule movement; eventually the concentration will be equal – even though the molecules don’t stop moving.

18. Passive Transport
Osmosis is the diffusion of water molecules through a semi-permeable membrane.

19. Passive Transport
Isotonic solutions have equal concentrations of water on both sides of the membrane.
Water moves back and forth equally.
Cells in isotonic do not change size.

20. Passive Transport
Hypertonic solutions have low amounts of water and high amounts of solute. (like salt water)
Cells in hypertonic solutions lose water and shrink.

21. Passive Transport
Hypotonic solutions have high amounts of water and low amounts of solute.
Cells in hypotonic solutions gain water and swell in size.

22. Diffusion in Animal Cells
Animals cells use glucose and oxygen to perform cellular respiration; releasing water and CO2.
The exchange of oxygen and carbon dioxide is crucial to the survival of animal cells.

23. Diffusion in Animal Cells
The lungs are one site of gas exchange; blood cells low in oxygen and high in carbon dioxide are pumped to the lungs.
Oxygen diffuses across the membrane into the blood cells while carbon dioxide diffuses out of the blood and into the lungs.

24. Passive Transport
Cells that are exposed to fresh water (hypotonic) require the extra protection of a cell wall to keep them from bursting.
When plant cells are full of water, they are called turgid.

25. Passive Transport
Facilitated diffusion happens when protein pores act like open gates to let in molecules such as glucose.
The protein pores only let in glucose molecules and do not require energy from the cell, but they “help” or facilitate diffusion.

26. Active Transport
Some materials are too big to diffuse across a membrane and require energy from the cell in order to move them.
Materials moved in this manner moved by Active Transport.

27. Active Transport
Channel proteins act like pumps to move molecules against the concentration gradient.
Moving against the gradient requires energy; so the molecules moved this way are important to the cell.

28. Active Transport
Materials that are too big for the protein pumps can be moved into the cell by endocytosis (endo = inside; cyto = cell)
Solids are moved by phagocytosis.
(phago = eat)
Liquids are moved by pinocytosis.
(pino = drink)

29. Active Transport
Exocytosis (exo = out of; cyto – cell) is a similar process but in reverse. The cell uses this process to move large items out of the cell.

30. Cell Size and Material Transport
Cells are small for a reason.
They have to be able to move materials through the entire cell very quickly or they will die.

31. Cell Size and Transport
A large cell has a small surface area to volume ration; which means that it takes a long time to move substances through the membrane.

32. Cell Size and Transport
Small cells have a large surface area to volume ratio; which means that it takes a short time to move materials through the membrane.

33. Cell Size and Transport
The need to move materials quickly keeps cells small.
When they become too large, they divide and increase their surface area to volume ratio.