Module 2 - Biological Membranes

Question 1

Give 4 ways molecules can move across membranes?

Answer 1

• diffusion/facilitated diffusion
• osmosis
• active transport
• bulk transport

Question 2

what is selective permeability?

Answer 2

It means certain molecules can move across it relatively easily whilst others may need a little help or may not be able to move it across all.

Question 3

what is the method by which molecules crosses a membrane depends on?

Answer 3

• its size
• whether it is charged or polar
• whether it needs to move down or against a concentration gradient

Question 4

what is diffusion?

Answer 4

The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient until equilibrium is reached.

Question 5

Is diffusion an active or passive method of transport?

Answer 5

passive

Question 6

what does it mean by diffusion being an passive method of transport?

Answer 6

• It will continue until there is a concentration equilibrium between the two areas.

Question 7

what does equilibrium mean?

Answer 7

There is a balance or no difference in concentrations

Question 8

give two ways molecules can diffuse through the plasma membrane?

Answer 8

• directly through the phospholipid bilayer
• through the channel or carrier proteins by facilitated diffusion

Question 9

what is the hydrophobic core?

Answer 9

• the hydrophobic interior of the membrane.
• it repels substances with a positive or negative charge (ions), so they cannot easily pass through

Question 10

what type of molecules can diffuse through the hydrophobic core?

Answer 10

• small, non-polar molecules can diffuse easily between the phospholipids and across the hydrophobic core as they are lipid soluble.
• large, non-polar molecules , e.g. steroid hormones (they are lipid soluble)
• small polar molecules (water and ethanol) even though they are hydrophillic as they are small

Question 11

what type of molecules cannot diffuse through the hydrophobic core?

Answer 11

• large polar or charged molecules (ions, glucose, amino acids) are repelled by the hydrophobic core

Question 12

Examples of factors that affect the rate of diffusion?

Answer 12

• distance
• temperature
• characteristics of substances
• increasing difference of concentration

Question 13

how does distance affect the rate of diffusion?

Answer 13

the greater the distance that needs to be travelled, the slower the diffusion rate

Question 14

how does temperature affect the rate of diffusion?

Answer 14

the higher the temperature rate, the more movement of the molecules, the faster the diffusion rate

Question 15

how does characteristics of substance affect the rate of diffusion?

Answer 15

a substance with a greater mass has a lower diffusion rate

Question 16

how does increasing the different in concentration affect the rate of diffusion?

Answer 16

the greater the difference in concentration, the quicker the rate of diffusion

Question 17

what is facilitated diffusion?

Answer 17

The movement of large polar or charged molecules through the plasma membrane via the channel or carrier proteins

Question 18

how facilitated diffusion happen through channel proteins?

Answer 18

• the membranes contain channel proteins through which polar molecules can pass
• membranes with protein channels are selectively permeable as most protein channels are specific t one molecule or ion.
• the more channel proteins the higher the diffusion

Question 19

how facilitated diffusion happen through carrier proteins?

Answer 19

• facilitated diffusion can involve carrier proteins which change the shape when a specific molecules binds.
• in facilitated diffusion, the movement of molecules id down a concentration gradient and does not require external energy

Question 20

what is the name of the transport protein?

Answer 20

glucose transporter

Question 21

What the glucose transporter have a specific binding site to?

Answer 21

glucose

Question 22

How does the glucose transporter bind to the glucose?

Answer 22

• The binding of glucose on the extracellular side changes the conformation of the glucose transporter
• this changes in shape exposes the binding site to the cytosol
• the glucose moves into body cells

Question 23

What does facilitated diffusion and other processes depend on?

Answer 23

the membrane transport proteins which are regulated by controlling the number of transport proteins present in the membrane.
-e.g. glucose uptake is regulated by the hormone insulin.

Question 24

What are ion channels?

Answer 24

• they are very specific and only allow certain ions through the membrane
• some are always open and some are closed

Question 25

what are gated ion channels?

Answer 25

They can open or close in response to different types of stimuli, such as electrical or chemical signals.

Question 26

why are sodium ions important in the control of cell functions

Answer 26

• they allow the formation of a concentration gradient between the extracellular fluid and the cytosol.
• the concentration gradient can then be used to drive another cellular process.

Question 27

What are some roles of the cell surface membrane?

Answer 27

• provides some structural support for the cell
• acts as partially permeable barriers between the cell and the environment