Transport Across Cell Membranes

Question 1

Name the 4 Key features of a plasma membrane

Answer 1

Phospholipid bilayer
Cholesterol
Proteins
Partially permeable

Question 2

What are the features of the phospholipid bilayer?

Answer 2

-Two layers of phospholipids
-Head is hydrophilic so attracts water
-Tail is hydrophobic so repels water

Question 3

How does cholesterol function in the plasma membrane?

Answer 3

-restricts lateral movement of molecules in the membrane
-Makes membrane less fluid at high temps which prevents water/ions leaking out

Question 4

What are the proteins in the plasma membrane and what do they do?

Answer 4

•peripheral proteins- can be connected to lipids and proteins
•Channel protein- Fills with water to transport water soluble molecules via diffusion
•Carrier proteins- Larger molecules bind to them which causes change in shape and molecules move in

Question 5

What is the definition of simple diffusion?

Answer 5

The net movement of molecules from an area of higher concentration to an are of lower concentration until equilibrium is reached

Question 6

What is the definition of osmosis?

Answer 6

The movement of water from an area of higher water potential to lower water potential across a partially permeable membrane

Question 7

What are Isotonic, Hypertonic and hypotonic solutions?

Answer 7

•Isotonic- water potential of the solution is equal to the cell
Hypertonic- water potential of the solution is more negative than cell, cell becomes limp
Hypotonic- water potential of solution is more positive than cell, cell can burst

Question 8

What type of response is phagocytosis?

Answer 8

Non-specific

Question 9

Describe the process of phagocytosis

Answer 9

1. Phagocyte attracted to pathogen by debris/chemicals
2. Receptors on phagocyte attach to chemicals on pathogen
3. Phagocyte engulfs pathogen and phagosome develops around it
4. lysosomes fuse with phagosome and release their lysozymes into it which hydrolyse pathogen
5. Pathogen is destroyed and soluble products are absorbed and used

Question 10

Where are all lymphocytes made?

Answer 10

In bone marrow

Question 11

What are antigen presenting cells (APCs)? Give examples

Answer 11

An APC is any cell that presents a non-self antigen on its surface eg.
- Infected body cells
- A phagocyte which has destroyed a pathogen
- Transplanted cells
- Cancer cells

Question 12

What do cytotoxic t-cells do?

Answer 12

• Destroy abnormal/infected cells
• Release preform which makes pore in cell membrane
• Kills cell

Question 13

What happened during cell mediated response?

Answer 13

1. APC presents antigens on cell surface
2. Helper T-cells receptors attach to antigens on APC
3. Once attached activates helper t-cells to divide by mitosis
4. Cloned helper t-cells turn to different cells eg. Memory, cytotoxic and stimulate phagocytes

Question 14

What is the humoral response?

Answer 14

The response involving b cells and antibodies

Question 15

How does b cell activation work?

Answer 15

1. Antigens in blood collide with complementary antibody on a B cell which takes in antibody and presents it
2. B cell collided with helper T cell, triggers b cell clinal expansion
3. B cell undergoes mitosis into many cells; either plasma or b memory
   - plasma cells make antibodies
   - B memory divide rapidly into plasma when re infected

Question 16

What do antibodies do?

Answer 16

• Bind to antigens to form antigen-antibody complex
• Cause agglutination which makes it easier for phagocytes to destroy pathogens