2.5 biological membranes

Question 1

What are the 5 purposes of cell membranes?

Answer 1

Form a barrier between the contents of a cell and it’s environment.
Also regulates transport of material in and out of cell
May contain enzymes involved in metabolic pathways
Has antigens
May be the site of chemical reactions

Question 2

What is the plasma membrane composed of?

Answer 2

A phospholipid bilayer with a hydrophilic phosphate head and hydrophobic fatty acid tails causing them to form a bilayer when in water.

Question 3

What is the fluid mosaic

Answer 3

1972 Proposed that the phospholipid bilayer had proteins floating in it and that lipid molecules can change places with each other and some of the proteins may move giving it fluidity allowing it to interact with its environment e.g. phagocytic cells.

Question 4

What spans the cell membrane.

Answer 4

proteins
carrier proteins
cholesterol
glycocalyx
carbohydrates

Question 5

What is the purpose of proteins spanning the membrane?

Answer 5

Some proteins have pores and act as channels for polar ions
Carrier proteins
Proteins that act as enzymes, antigens, receptor site.

Question 6

What is the purpose of cholesterol in the membrane?

Answer 6

regulates fluidity and resists the effects of temperature change.

Question 7

What are the glycocalyx spanning the membrane?

Answer 7

Formed from the carbohydrate chains to either proteins or lipids

Question 8

What is the purpose of carbohydrate in the membrane

Answer 8

Hydrophilic molecules and they attract water with dissolved solutes

Question 9

Define simple diffusion.

Answer 9

If there is a high concentration of molecules will bump into each other randomly and spread out further.
Small molecules can diffuse through the membrane or fat soluble molecules can dissolve through the membrane
However, polar molecules such as water diffuse through channels called aquaporins.

Question 10

What can affect simple diffusion?

Answer 10

Temperature
concentration gradient
diffusion distance
surface area
size of molecule

Question 11

Define facilitated diffusion.

Answer 11

Movement of molecules down a concentration gradient via protein channels or carrier proteins and doesn’t require ATP

Question 12

Define osmosis

Answer 12

Net diffusion from an area of high water potential to an area of low water potential

Question 13

Define water potential.

Answer 13

measure of tendency of water molecules to diffuse from one region to another

Question 14

What is the highest water potential?

Answer 14

Pure water (0kPa) and when solutes are added the water potential is lowered

Question 15

Define cytolysis

Answer 15

animal cell swells and burst due too much water

Question 16

Define turgid.

Answer 16

The cell will swell and the membrane pushes against the cell wall and the strong cellulose cell wall prevents bursting

Question 17

Define crenation

Answer 17

animal cell shrinks due to water loss and appears wrinkled

Question 18

Define plasmolysis/flaccid

Answer 18

Plant cell membrane pulls away from cell wall as water leaves

Question 19

How does a drop in temperature affect the membrane

Answer 19

Unsaturated fatty acids as they become compressed the kinks in their tails push adjacent phospholipid molecules away, maintaining fluidity

Cholesterol also prevents phospholipid molecules from packing together too closely

saturated fatty acids become compressed

Question 20

What happens to the membrane when temperature increases?

Answer 20

Phospholipids acquire more kinetic energy and move more increasing fluidity
Embedded proteins may also drift
Increased fluidity affects the infolding of the plasma membrane during phagocytosis
It can cause some proteins to denature creating gaps and if both the membrane embedded and cytoskeleton threads begin to denature then the plasma membrane will begin to fall apart.

Question 21

What happens to the membrane when in solvents?

Answer 21

Organic solvents such as acetone will damage the membrane ad the dissolve lipids

Question 22

Define active transport

Answer 22

The movement of substances against a concentration gradient using ATP and carrier proteins
For example, mineral ions to root hair cells and potassium ions to guard cells

Question 23

Describe the process of active transport

Answer 23

Carrier proteins act similarly to enzymes and bind reversibly with certain solute molecules and they also have a site that binds and allows hydrolysis of ATP

Question 24

What are the 3 types of bulk transport?

Answer 24

Endocytosis
pinocytosis
exocytosis

Question 25

Define endocytosis

Answer 25

A segment of the plasma membrane surrounds and encloses the particle and brings it into the cell enclosed in a vesicle e.g phagocytosis

Question 26

define pinocytosis

Answer 26

Intake of liquid.
ATP is needed to produce energy to form the vesicle and move them using cytoskeleton threads and motor proteins

Question 27

Define exocytosis

Answer 27

A membrane bound vesicle containing the substance to be secreted is moved towards the cell surface membrane. The cell surface membrane and vesicle fuse together and the fused site opens releasing the contents of the secretory vesicle

Question 28

How is ATP turned into energy.

Answer 28

ATP is hydrolysed into ADP+Pi