Cell membrane

Question 1

What is the fluid mosaic model

Answer 1

• Singer and nicholson proposed model for the structure of the cell membrane
• fluid- because the phospholipid molecules molecules withon a layer can more relative to each other
• mosaic - becuase the proteins within the phosopholipid layer are of different sizes and shapes and from diffrerent patterns

Question 2

What is the permeabiliy of the cell membranes like

Answer 2

• selectivley permeable
• allow certain molecules through

Question 3

How does temperature increase permeability

Answer 3

• increase above 40 degrees increase vibrations of the phospholipids moving them further apart

Question 4

How does organuc solvents increase permeability

Answer 4

• dissolve phospholipids

Question 5

How do lipid soluble susbtances travel across cell membrane

Answer 5

• vitamin a
• small molecules O2 and CO2
• dissolve and more directly thorugh the phospholipid bilayer

Question 6

How do water soluble susbtances travel across cell membrane

Answer 6

• glucose, ions, all polar molecules
• cannot pass through the hydrophobic fatty acid tails
• must use intrinsic proteins to pass through

Question 7

What are channel proteins

Answer 7

• pores lined with polar hydrophilic groups allow charged ions through

Question 8

What are the carrier proteins

Answer 8

• allow larger polar molecules through such as water soluble sugars and amino acids
• binding the molecules changes the shape and the protein moving the substance into or out of the cell
• the polarity of proteins determines if the sit on the membrane (extrinsic) or through it (intrinsic)

Question 9

What is the phosophlipid bilayer

Answer 9

• the hydrophilic phosphate heads of the phospholipids from the outer and inner surface of the cell membrane
• the hydrophobic fatty acid tails of the phospholipids point towards each other in the centre of the bilayer

Question 10

What are extrinsic proteins

Answer 10

• found on either outer surface of the bilayers

Question 11

What is cholesterol

Answer 11

• found between the phospholipids making it more rigid and stable

Question 12

What are sugar side chains

Answer 12

• sugar attatched form the glycocalyx layer of the membrane which has a role in cell to cell recognition or hormone receptor sites

Question 13

What is osmosis

Answer 13

• the diffusion of water from a region of high to low water potential across a selectivley permeable membrane

Question 14

What is water potential

Answer 14

• tendency of water molecules to move
• solute potential is the osmotic strength of the solution as shown to the left the water potential of pure water is 0 becomes more negative as concentration of solution increases

Question 15

what are turgid cells

Answer 15

• firm cells
• hypotonic cells (less concentrated solution
• cells take up water via osmosis
• pressure potential of the cell increases as the cytoplasm pushes on the cell wall

Question 16

What is incipient plasmolusis

Answer 16

• a cell in this state ha lost enough water for the cell membrane to start being draw away from the cell wall
• lowers presure potential to 0

Question 17

What are plasmolysed

Answer 17

• cells in hypertonic (more concentrated solutions) become flaccid (floppy)

Question 18

Why is it importznt animal cells are in an isotonic solution

Answer 18

• same concentration of dissolved solutes inside and outside of cell
• lack a cell wall
• cells can burty in hypotonic
• shrink in hypertonic solutions due to osmosis

Question 19

What is tonicity

Answer 19

refers to concentration of solute

Question 20

What does hypertonic mean

Answer 20

• means higher concentration of solute and therefore lower water potential

Question 21

What is a hypotonic solution

Answer 21

• means lower concentration of solute therfore higher water potential

Question 22

What is an isotonic solution

Answer 22

• means the same concnetration of solute and the same water potential so no net movement of water between two solutions

Question 23

What is simple diffusion

Answer 23

• diffusion is the movement of moleciles from a region of high concentration onto a region of low concentration down a concentration gradient
• passive process
• requires no ATP
• simple diffusion occurs through phospholipid billayer

Question 24

How is the diffusion rate increased by

Answer 24

• higher concentration gradient
• thinner membrane shorter diffusion distance
• larger surface area
• smaller molecules
• non polar of lipid soluble
• increased temperature
• graph shows a directly proportional rate of uptake across concentration differencce across membranes

Question 25

Describe facilitated diffusion

Answer 25

• process of diffusion for polar molecules of ios cannot pass directly through phopholipid bilayers
• protein channels of carrier are used
• same rules as diffusion
• substances enter through protein channels
• passive process respiratory inhibitor has no effect
• graph shows rate of uptake increases slowly than plateus

Question 26

What is co transport

Answer 26

• type of facilitated diffusion two different substances use the same carrier protein at the same time
• glucose and 2 sodium ions attatch to a carrier protien on outside of membrane
• changing the shape of the protein flip them on the inside of the membrane then diffuse seperatley through the cell

Question 27

What is active transport

Answer 27

• the moves molecles against a concentration gradient from where lower concentration to a higher concentration
• process requires energy in form of ATP from respiration
• ATP activates carrier proteins to more molecule across the cell membrane
• as this relies on ATP addition of respiratory inhibitor lack of oxygen will prevent tranport as there will be no ATP available

Question 28

What is phagocytosis

Answer 28

• solid enters the cell

Question 29

What is pinocytosis

Answer 29

liquid enters the cell

Question 30

What is endocytosis

Answer 30

• phagocytosis
• pinocytosis
• plasma membrane fold inwards
• plama mebrane engulds the material
• vesicle formed from plasma membrane enters the cell
• ATP is require to moe the vesicles so active process

Question 31

What is exocytosis

Answer 31

• veicle formed from golgi moves towards plasm membrane
• vesicle fuses with plasma membrane
• vesicle contents empty out of cell
• ATP is require to move the vesicles so active process