Cell Membranes & movement

Question 1

the cell surface membrane

Answer 1

a plasma membrane which surrounds cells and forms the boundary between the cell cytoplasm and the environment

Question 2

what are the functions of the cell-surface membrane?

Answer 2

forms a barrier between two environments
allows different conditions to be established and maintained
controls the movement of substances between environments - partially permeable

Question 3

What is a phospholipid?

Answer 3

made of a hydrophilic phosphate head and a hydrophobic hydrocarbon tails forming a bilayer

Question 4

what is the function of a bilayer?

Answer 4

allows lipid-soluble substances to enter and leave the cell,
prevents water-soluble substances entering and leaving the cell,
makes the membrane flexible and self-sealing which provides structure

Question 5

What do enzymes do embedded in the cell-surface membrane?

Answer 5

Speed up reactions in the cell and meditate a response

Question 6

Plasma membrane

Answer 6

all membranes around and within cells cells have the same basic structure

Question 7

What do extrinsic proteins embedded in the phospholipid do?

Answer 7

Serve as receptor molecules eg: for hormones

Question 8

What do intrinsic proteins do?

Answer 8

Some act as carriers to transport water soluble material across the membrane

Question 9

What is the overall function of proteins?

Answer 9

Provide structural support
Act as channels - allow active transport
From cell membrane receptors

Question 10

What is the role of cholesterol in the cell-surface membrane?

Answer 10

Add strength
Maintain fluidity and integrity
Prevents loss of water as hydrophobic
Pulls the fatty acids tails close together preventing lateral movement and therefore increasing stability

Question 11

What is the role of glycolipids in the cell-surface membrane?

Answer 11

Act as recognition sites
Maintains stability of the membrane
Helps cells attach to one another & form tissues

Question 12

What is the role of glycoproteins in the cell-surface membrane?

Answer 12

Act as recognition sites - receptors

Aids the formation of tissues

Question 13

What does the carb chain do?

Answer 13

Combines with lipids to form larger molecules

Question 14

What does the hydrophilic channel do?

Answer 14

Allows facilitated diffusion to occur - highly selective

Question 15

What is the pore for?

Answer 15

Get, store and distribute resources

Capture, absorb and filter liquids

Question 16

Why are some molecules not able to diffuse across the cell-surface membrane?

Answer 16

As they are not soluble in lipids so can’t pass through the phospholipid bilayer, they are also too large to pass through the channels or have the same charge (or are polar so are repelled by the non-polar hydrophobic tails) as the charge on the protein channel so are repelled

Question 17

Why is the cell-surface membrane referred to as a fluid mosaic model?

Answer 17

Fluid because the phospholipid molecules can move relative to one another and mosaic because the proteins in the bilayer vary in shape, size and pattern

Question 18

what is the ease at which the proteins move dependent on?

Answer 18

The number of phospholipids with unsaturated fatty acids

Question 19

What are protein carriers?

Answer 19

Proteins responsible for moving substances across the plasma membrane

Question 20

Define simple diffusion?

Answer 20

The passive net movement of molecules from an area of high concentration to an area of lower concentration.

Question 21

What are the factors that increase the rate of diffusion?

Answer 21

Larger surface area
Thinner absorbing surface
Increased temperature
Steep concentration gradient

Question 22

Define facilitated diffusion?

Answer 22

The passive net movement of molecules from an area of high concentration to an area of lower concentration with the aid of a protein carrier

Question 23

What is a protein channel?

Answer 23

Water filled membrane bound hydrophilic channel across the width of the membrane allowing specific water-soluble ions to pass through

Question 24

What is a carrier protein?

Answer 24

A large molecule binds to the protein causing a change in shape of the protein so the molecule is able to be released into the membrane on the opposite side, the protein then reverts back to its original shape

Question 25

What is osmosis?

Answer 25

The passive net movement of molecules from a area of high water potential to an area of lower water potential through a semi-permeable cell membrane

Question 26

The lower the water potential (lots of solute in a solvent)…

Answer 26

…the more negative its value

Question 27

What is active transport?

Answer 27

The active movement of molecules from an area of low concentration to an area of high concentration with the aid of a protein carrier and ATP

Question 28

What are the factors that affect active transport?

Answer 28

The speed of the carrier
The number of carriers
Rate of respiration - how much ATP

Question 29

What are the adaptations of the small intestine for absorption of products of digestion?

Answer 29

Villi on the lining of the lumen
Each epithelial cell has microvilli
Rich blood supply - maintains a high concetration gradient
Epithelial cells = one cell thick
Mitochondria present in the epithelial cells - constant supply of ATP

Question 30

What is co-transport?

Answer 30

The process by which two molecules bind together and move through the protein carrier due to the concentration of one molecule is used to move the other against its own concentration gradient