1. Cell in its environment
Coulter 2017

2. Cell membrane
cell membrane- controls what substances come into and out of the cell.
all cells have cell membranes.
In plant cells the cell membrane is just inside the cell wall
In animal cells the cell membrane forms the outside boundary that separates the cell from its environment
Like a window screen, lets air pass in and out but keeps insects out.

3. Cell membrane cont.
The plasma membrane (Figure below) is made of a double layer of special lipids, known as phospholipids.
The phospholipid is a lipid molecule with a hydrophilic ("water-loving") head and two hydrophobic ("water-hating") tails.
Because of the hydrophilic and hydrophobic nature of the phospholipid, the molecule must be arranged in a specific pattern as only certain parts of the molecule can physically be in contact with water.
Remember that there is water outside the cell, and the cytoplasm inside the cell is mostly water as well.
So the phospholipids are arranged in a double layer (a bilayer) to keep the cell separate from its environment.
Lipids do not mix with water (recall that oil is a lipid), so the phospholipid bilayer of the cell membrane acts as a barrier, keeping water out of the cell, and keeping the cytoplasm inside the cell.
The cell membrane allows the cell to stay structurally intact in its water-based environment.

4. Cell membrane function
The function of the plasma membrane is to control what goes in and out of the cell.
Some molecules can go through the cell membrane to enter and leave the cell, but some cannot.
The cell is therefore not completely permeable. "Permeable" means that anything can cross a barrier.
An open door is completely permeable to anything that wants to enter or exit through the door.
The plasma membrane is semipermeable, meaning that some things can enter the cell, and some things cannot.

5. Plasma membrane http://www.youtube.com/watch?v=moPJkCbKjBs
What makes up the "head" region of a phospholipid? Is it hydrophobic or hyrdrophilic?
What makes up the "tail" region of a phospholipid? Is it hydrophobic or hyrdrophilic?
What happens when you drop a phospholipid in water?
How are phospholipids arranged in a plasma membrane?
What is a glycoprotein? What is one of the uses of glycoproteins?
What is "Brownian movement"? How is this movement related to the cell membrane?

6. Diffusion
The cell membrane is selectively permeable, which means that some substances can pass through the membrane while others cannot.
Diffusion- is the process by which molecules move from an area of higher concentration to an area of lower concentration.
Concentration- is the amount of a substance in a given volume.

7. What causes diffusion?
Molecules are always moving. As they move they bump into each other.
The more molecules in an area the more they will collide.
Collisions cause molecules to move away from each other.
The molecules will continue to spread out until they are eventually evenly spread out throughout the area.

8. Diffusion of oxygen
There is higher concentration of oxygen molecules in water than inside the cell.
The cell membrane is permeable to oxygen molecules.
Oxygen molecules diffuse from the higher concentration to lower concentration

9. Osmosis!!
Osmosis- is the diffusion of water molecules through a selectively permeable membrane
Because cells cannot function properly without adequate water, many cellular processes depend on osmosis.

10. Osmosis and diffusion
In osmosis water molecules move by diffusion from an area where they are highly concentrated through the cell membrane to an area where they are less concentrated.

11. Effects of osmosis on plants
Plant cells are enclosed by a rigid cell wall.
When the plant cell is placed in a hypotonic solution , it takes up water by osmosis and starts to swell, but the cell wall prevents it from bursting.
The plant cell is said to have become "turgid" i.e. swollen and hard.
The pressure inside the cell rises until this internal pressure is equal to the pressure outside.
This liquid or hydrostatic pressure called the turgor pressure prevents further net intake of water .
Turgidity is very important to plants as it helps in the maintenance of rigidity and stability of plant tissue and as each cell exerts a turgor pressure on its neighbor adding up to plant tissue tension which allows the green parts of the plant to "stand up" into the sunlight.

12. Effects of osmosis in animals
Animal cells do not have cell walls. In hypotonic solutions, animal cells swell up and explode as they cannot become turgid because there is no cell wall to prevent the cell from bursting.
When the cell is in danger of bursting, organelles called contractile vacuoles will pump water out of the cell to prevent this.
In hypertonic solutions, water diffuses out of the cell due to osmosis and the cell shrinks.
Thus, the animal cell has always to be surrounded by an isotonic solution.
In the human body, the kidneys provide the necessary regulatory mechanism for the blood plasma and the concentration of water and salt removed from the blood by the kidneys is controlled by a part of the brain called the hypothalamus.

13. Effects of osmosis
HYPERTONIC SOLUTION: CELL IS A GIVERS TO THE SURROUNDING AREA!
HYPOTONIC SOLUTION: CELL IS A TAKERS FROM THE SURROUNDING AREA!
ISOTONIC SOLUTION: BOTH CELLS AND SURROUNDING ARE AT EQUILIBRIUM

14. Passive Transport
Is the movement of substances through a cell membrane without using the cell’s energy.
Passive transport depends on the amount of a substance on each side of a membrane.
Movement of particles from a high concentration to a low concentration.
Example: Riding a bike down hill! No energy needed.

15. Facilitated diffusion
When molecules pass through a cell membrane using special proteins called transport proteins.
Does not require a cell to use energy.
Two types of transfer proteins
Carrier proteins: carry large molecules such as sugar
Channel proteins: form pores through the membrane. (sodium ions and potassium ions pass)
Example: Riding a bike down hill with training wheels! No energy needed.

16. Active transport
Active transport describes what happens when a cell uses energy to transport something.
Active transport usually happens across the cell membrane. There are thousands of proteins embedded in the cell's lipid bilayer.
Those proteins do much of the work in active transport.
They are positioned to cross the membrane so one part is on the inside of the cell and one part is on the outside.
Only when they cross the bilayer are they able to move molecules and ions in and out of the cell.
The membrane proteins are very specific.
One protein that moves glucose will not move calcium (Ca) ions.
There are hundreds of types of these membrane proteins in the many cells of your body.
Example: Riding a bike uphill with training wheels! Needs a energy.

17. Active transport
Many times, proteins have to work against a concentration gradient. That term means they are pumping something (usually ions) from areas of lower to higher concentration.

18. Cell transport Endocytosis Exocytosis Objects enter the cell.
Objects exit the cell

19. Cell transport Phagocytosis Pinocytosis Endocytosis of large objects.
Endocytosis of small objects.

20. Review What is the plasma membrane? Describe a phospholipid.
What are the components of the cytosol?
What is meant by the description of the plasma membrane as “semipermeable”?
What is the difference between the cytosol and the cytoplasm?
Describe passive transport.
What is the difference between facilitated transports and active transport?
Describe active transport.
What is osmosis? Is it different then diffusion?