cell membranes

Question 1

All cells are surrounded by__________. In eukaryotic cells many organelles are surrounded by_________ too.

Answer 1

membranes

Question 2

properties and functions of cell surface membranes

Answer 2

-sometimes called a plasma membrane
-acts as a barrier between cell and it’s environment.
-controls what substances enter and leave the cell
-partially permeable
-substances move across the membrane via : diffusion,osmosis ,active transport

Question 3

how do substances move across the cell surface membrane?

Answer 3

diffusion, active transport, osmosis.

Question 4

Functions of membranes within the cell

Answer 4

-divide the cell into different compartments
-act as a barrier between organelles and the cytoplasm/separate organelles from the cytoplasm.
-partially permeable: controls what substances enter and leave the cells.

Question 5

The basic structure of all cell membranes, including cell-surface
membranes and the membranes around the cell organelles of
eukaryotes, is _________.

Answer 5

The basic structure of all cell membranes, including cell-surface
membranes and the membranes around the cell organelles of
eukaryotes, is the same.

Question 6

The basic structure of all membranes is the same. They contain……

Answer 6

lipids (mainly phosolipids)
proteins
carbohydrates (attached to proteins or lipids)

Question 7

what is the role of phospholipids in cell membranes?

Answer 7

they make up the bilayer of the cell membrane.
They have a hydrophillic heads (attract water) and hydrophobic tails (repel water).
forms a double layer with the head facing outwards towards the water.
The hydrophobic tails are in the centre so soluble substances can’t easily pass through.

Question 8

The ______ ________ model was suggested to describe the arrangement of molecules in the membrane.

Answer 8

fluid mosaic

Question 9

What is the arrangement of molecules in the fluid mosaic model?

Answer 9

-Phospholipids create a continuous bilayer
-‘fluid’ because lipids and some proteins are constantly moving
-cholesterol molecule are present within the layer
-proteins are scattered through the bilayer, like tiles in a ‘mosaic’ (channel and carrier proteins)
-receptor proteins on cell surface membranes allow cell to detect chemicals released from other cells- a signal to respond to
-some proteins can move sideways through the bilayer- others in a fixed posistion.
-some proteins and some lipids have poly saccharide chains attached ( carbohydrates) forming glycoproteins and glycolipids.

Question 10

cholesterol gives the membrane __________.

Answer 10

stability

Question 11

cholesterol is a type of _________.

Answer 11

lipid

Question 12

How does cholesterol give membranes stability?

Answer 12

1) cholesterol is a type of lipid
2)present in all membranes ( except bacteria)
3)Fit between phospholipid molecules-binding to the hydrophobic tails causing them to pack closer together
4)this restricts movement of the phospholipids, making the membrane less fluid and more rigid
5)Helps maintain shape of animal cells - particularly improtant for cells not supported by other cells I.e red blood cells that float free.
-have hydrophobic regions so create barrier for some substances moving through mebrane

Question 13

Cell membranes are affected by ______________. It effects how much the phospholipids in a bilayer can _________ it impacts the membrane structure and _________.

Answer 13

Cell membranes are affected by temperature. It effects how much the phospholipids in a bilayer can move it impacts the membrane stucture and permeability.

Question 14

How is permeability of membranes effected by temperatures below 0 degrees Celsius?

Answer 14

-phospholipids don’t have much energy so can’t move
-the phospholipids packed tightly together so membrane is rigid.
-channel proteins and carrier proteins denature increasing permeability
-ice crystals may form piercing the membrane so highly permeable.

Question 15

How is permeability of membranes effected by temperatures 0-45 degrees Celsius?

Answer 15

-phosopholipids have enough energy to move
-they aren’t packed tightly together
-membrane is particularly permeable
-as the temperature increases they move more as they have more energy incrase cell permeability

Question 16

How is permeability of membranes effected by temperatures above 45 degrees Celsius?

Answer 16

-phospholipid bilayer begins to melt (break down)
-increasing membrane permeability
-water inside cell expands increasing the pressure inside the membrane
-channel/carrier proteins in membrane denature so can’t control what enters and leaves cell
-increase in permeability

Question 17

diffusion

Answer 17

the net movement of molecules or ions from a region of their high concentration to a region of their low concertraion

Question 18

In diffusion the ions/molecules move __________ the concentration gradient.

Answer 18

In diffusion the ions/molecules move down the concentration gradient.

Question 19

molecules will diffuse ______ ways , but net movement is to an area of _____ concentration.

Answer 19

molecules will diffuse both ways , but net movement is to an area of low concentration.

Question 20

Diffusion is a ______ process (it requires no energy)

Answer 20

Diffusion is a passive process it requires no energy

Question 21

what are the three factors rate of diffusion depends on?

Answer 21

concentration gradient-Higher it is the faster the rate of diffusion . As diffusion takes place the difference in concentration both sides of the membrane decreases until it reaches equilibrium. This means the rate of diffusion slows over time.
Thickness of the exchange surface- Thinner surface= faster diffusion (particles have to travel less distance)
Surface area-larger surface area = faster diffusion

Question 22

Facilitated diffusion

Answer 22

-large molecules (e.g glucose and amino acids and charged particles (e.g ions and polar molecules) diffuse slowly.
-the rate if diffusion of these molecule can be sped up by specific proteins (carrier and channel proteins) -this is facilitated diffusion

Question 23

facilitated diffusion moves particles____ the concentration gradient

Answer 23

facilitated diffusion moves particles down the concentration gradient.

Question 24

Facilitated diffusion is a _________ process

Answer 24

facilitated diffusion ids a passive process

Question 25

Carrier proteins

Answer 25

-move large molecules across the membrane (down the concentration gradient)
-different carrier proteins facilitate the diffusion of different molecules.
1) large molecules attach to the carrier protein in the membrane
2)The protein changes shape
3)This releases the molecule on the opposite side of the membrane

Question 26

Channel proteins

Answer 26

-Channel proteins form pores in the membrane for charged particles to diffuse through.
-Different channel proteins facilitate the diffusion on different charged particles

Question 27

Factors that effect the rate of facilitated diffusion:

Answer 27

-concentration gradient
-Number of carrier/channel proteins.