Cell Membranes

Question 0

Outline the roles of membranes within cells

Answer 0

Cell signalling
Separate cell cytoplasm from outside environment
Regulate transportation of substances 
Cell recognition 
Separating cell contents from cytoplasm

Question 1

Why do we not refer to membranes as “semi permeable”?

Answer 1

Because that suggests that 50% of everything can pass through when actually, it’s partial because only certain types of substances can mow trough

Question 2

What are membranes made out of?

Answer 2

A bilayer of phospholipid molecules

Question 3

What is the fluid mosaic model?

Answer 3

It refers to the model of cell membrane structure.

Lipids give fluidity and proteins create a mosaic structure

Question 4

What are the main features of a membrane?

Answer 4

A bilayer of phospholipid molecules forming the basic structure

Various protein molecules floating in the phospholipid bilayer, some completely free, some bound to other components

Some extrinsic proteins partially embedded in the bilayer on the inside or outside, other intrinsic proteins completely spanning the bilayer

Question 5

What is a glycolipid?

Answer 5

When phospholipid molecules have a carbohydrate part attached

Question 6

What is a glycoprotein?

Answer 6

When protein molecules have a carbohydrate part attached they are called glycoproteins

Question 7

What is the role of cholesterol?

Answer 7

Gives membranes mechanical stability in some eukaryotic cells.

It’s fits between fatty acid rails, so that water molecules can’t pass through so easily.

Question 8

What is the role of carrier proteins?

Answer 8

actively move substances across the membrane e.g magnesium ions are pumped into root hair cells

Question 9

What is the role of channel proteins?

Answer 9

Allow substances eg water molecules and ions are too large and too hydrophilic to pass directly though so they enter and leave through the channels

Question 10

What is the role of receptor sites?

Answer 10

Allow some hormones to bond with them so that a cell response can be carried out eg glycoproteins and glycolipids are involved in cell signalling in immune response

Question 11

What is the role of enzymes and coenzymes?

Answer 11

Some stages of respiration take place in membranes of mitochondria. Enzymes and coenzymes may be bound to these membranes.

Question 12

What is the effect of temperature on membrane?

Answer 12

Higher than 45 degrees: there’s more kinetic energy which causes the phospholipids to vibrate which manes increased movement. It’s makes the membrane leaky which allows substances to leave and enter the cell

0 -45 degrees: the membrane is partially permeable and the phospholipids can move around

Question 13

What is cell signalling?

Answer 13

Cell signalling means the processes that lead to communication and coordination between cells eg in can lead to cell identification as recognition

Question 14

How does cell signalling work?

Answer 14

One cell releases a messenger molecule eg hormone

The molecule travels to another cell eg by the blood

The messenger molecule has a complementary shape to a receptor site and so it binds

Question 15

What is diffusion?

Answer 15

Diffusion is the movement of molecules from a region of high concentration to a region of lower concentration of that molecule down a concentration gradient

Question 16

What is equilibrium?

Answer 16

When molecules are distributed evenly.

Living organisms try and not reach equilibrium because it would stop gaseous exchange

Question 17

What are the factors that affect rate of diffusion?

Answer 17

Temperature
Concentration gradient 
Stirring/moving
Surface area
Distance/thickness
Size of molecule

Question 18

What is facilitated diffusion?

Answer 18

The passive movement of molecules across membranes down their concentration gradient using transport proteins such as channel and carrier proteins

Question 19

What kind of substances to carrier proteins allow?

Answer 19

Charged molecules and ions

Question 20

What kind of substances to channel proteins allow?

Answer 20

Ions and and too hydrophilic molecules

Question 21

What is active transport?

Answer 21

It refers to the movement of molecules or ions across a membrane which uses ATP to go from low concentration to high concentration

Question 22

Roles of carrier pumps:

Answer 22

Carry specific molecule one way across the membrane

The use ATP energy to carry molecules across the membrane

They carry molecules in the opposite direction to the concentration gradient

They can carry molecules at a much faster rate than by diffusion

Question 23

What is endocytosis and exocytosis?

Answer 23

Endocytosis refers to the bulk transport of materials pumped in to the cell

Exocytosis involves moving materials out of the cell

Question 24

What is osmosis?

Answer 24

It refers to only the movement of water molecules by diffusion and across a partially permeable membrane

Question 25

What is water potential?

Answer 25

A measure of the tendency of water molecules to diffuse from one place to another

Question 26

What happens when animal and plant cells are place in a concentrated water area?

Answer 26

There is a water potential gradient

Water molecules will enter the cell through the plasma membrane because the concentration of water is lower in the cells.

Animal cell will eventually burst because it becomes too full

Plant cells will become turgid because the vacuole and cytoplasm will fill up as push the membrane against the cell wall

Question 27

What happens when an animal an plant cell is put in a solution of high concentration of solute?

Answer 27

There is a water potential gradient.

The concentration of water outside the cell is higher than inside

Water will move out of the cell.

Animal cells will become crenated because the membrane will shrink and so will the contents.

The plant cells become plasmolysed because the cell membrane pulls away from the cell wall because the vacuole shrinks