Chapter 5 ~ Plasma Membrane

Question 1

What is the role of cell membranes?

Answer 1

It provides a partially permeable membrane
Cell communication/cell signalling
Site of chemical reaction

Question 2

What is a cell membrane formed of?
Describe the formation of answer to q1?

Answer 2

It is formed of a phospholipid bilayer
It contains hydrophilic phosphate heads on the outside which attract water and hydrophobic fatty acid tails on the inside which repel water

Question 3

Describe the fluid mosaic model

Answer 3

The phospholipids are free to move within the layers and proteins are embedded within the bilayer which vary in size and shape.
it describes the free movement of phospholipids and proteins and the random arrangement of proteins.
it is fluid as the phospholipids are constantly moving around and mosaic as they are scattered throughout the phospholipid like tiles in a mosaic.

Question 4

What are the two types of proteins?

Answer 4

Intrinsic and extrinsic

Question 5

Describe extrinsic proteins include 2 examples.

Answer 5

Extrinsic proteins are present on one side of the bile layer. They contain hydrophilic groups on the outer surface which interact with polar heads of phospholipids/intrinsic proteins. They provide mechanical support.
Glycolipids and glycoproteins are examples which are used in cell recognition/cell signalling

they usually function as enzymes and catalyse chemical reactions occurring inside the cell.

Question 6

Describe intrinsic proteins

Answer 6

Present in both layers.
There are carrier proteins which have tubes filled with water which enables water soluble ions to diffuse
There are proteins which bind with other ions and large molecules and change shape to transport them

they act as channel or carrier proteins to transport water soluble molecules.

Question 7

Describe the function of cholesterol

Answer 7

It is to regulate fluidity

Question 8

What factors affect membrane structure?

Answer 8

Temperature and solvent

Question 9

Describe how high temperature affects membrane structure

Answer 9

High temperature increases the kinetic energy of the phospholipid which causes them to move more. This increases fluidity and increases permeability which causes the structure to begin to break. This makes it easier for particles to cross.

Question 10

Describe how solvent affect membrane permeability

Answer 10

Organic solvent, for example, alcohol (ethanol) dissolve within the phospholipid bile layer which causes fluidity to increase, which makes it more permeable

Question 11

What is simple diffusion?

Answer 11

When particles move from the area of high concentration to an area of low concentration down the concentration gradient
they pass directly through the phospholipid bilayer.

Question 12

what does the rate of diffusion depend on

Answer 12

1. Concentration Gradient -
   steeper gradient, faster rate
2. Thickness of exchange surface -
   thicker, longer diffusion distance
3. Surface area-
   larger surface area, more diffusion distance

Question 13

What is facilitated diffusion?

Answer 13

This is diffusion across a membrane through protein channels and carrier proteins

Question 14

what molecules cannot pass using simple diffusion and have to use facilitated diffusion

Answer 14

large polar molecules
ions

Question 15

how do channel and carrier proteins work

Answer 15

channel proteins are gated and open and close to allow molecules to diffuse through
carrier proteins change shape to allow molecules to pass through

Question 16

What is active transport?

Answer 16

This is the movement of molecules/ions into and out of cells from a lower concentration to a higher concentration against the concentration gradient. This uses energy in the form of ATP and carrier proteins..
It is a selective process as only certain molecules combine into the receptor site

Question 17

Explain the process of active transport

Answer 17

1.active transport by protein
2.it is hydrolyse into ADP and PI
3. this causes protein to change, shape and open inwards inside of the membrane
4. This causes molecules to be released on other side of the membrane.
5. PI molecules release, which results in protein reverting into original shape

Question 18

What type of transport is endocytosis
How many types of endocytosis is there?

Answer 18

Endocytosis is a type of bulk transport into the cell.
2 types of endocytosis-
There is phagocytosis, which occurs with solids and pinocytosis, which occurs with liquids

Question 19

Explain the process of endocytosis
Why does it require energy

Answer 19

1. Cell surface membrane bends inwards
2. This forms a vesicle
   3.vesicle pinches off and moves within the cytoplasm to transfer material
   It requires energy to engulf and change shape

Question 20

What is exocytosis?

Answer 20

Movement out of cell

Question 21

Describe the process of exocytosis
Why does this process require energy?

Answer 21

1. Vesicle moves towards cell surface membrane.
2. Vesicle fuses with the membrane.
3. Contents are released outside of cell.
   Requires energy to move vesicle along cytoskeleton

Question 22

What is osmosis?

Answer 22

It is water particles, moving from higher water potential to a lower water potential

Question 23

What is water potential?

Answer 23

It is the pressure exerted by water molecules as they collide with a membrane or container it is measured in pascals

Question 24

What is a water potential of water?

Answer 24

0 Kpa

Question 25

What is isotonic solution?

Answer 25

Water potential is the same in solution and the cell

Question 26

What is hypotonic solution?

Answer 26

Water potential in the solution is more positive than cell

Question 27

What is hypertonic solution?

Answer 27

Water potential in the solution is more negative than cell

Question 28

what are the components of the plasma membrane

Answer 28

1. phospholipids
2. glycoproteins
3. glycolipids
4. cholestrol
5. intrinsic and extrinsic proteins

Question 29

glycoproteins

Answer 29

these are proteins with a sugar molecule attached. they act as recognition sites and antigens.

Question 30

glycolipids

Answer 30

phospholipids with a sugar molecule attached, they also act as recognition sites and antigens (similar to glycoproteins). they increase membrane stability by forming HYDROGEN bonds with water molecules.

Question 31

cholesterol

Answer 31

regulates and maintains stability and fluidity of plasma membrane.