Biological membranes

Question 1

roles of membranes

Answer 1

• partially permeable barriers between the cell and its environment, between organelles and the cytoplasm within organelles.
• site of chemical reaction
• site of cell signalling
• compartalisation: provides specific conditions for certain reactions to occur

Question 2

fluid mosaic model

Answer 2

proposed that the fabric of the membrane consisted of a phospholipid bilayer with proteins floating in it making up a mosaic pattern. The lipid molecules can change places with each other, and some of the proteins may move, giving fluidity

Question 3

role of components in the membrane

Answer 3

phospholipid bilayer- allows the membrane to be partially permeable
cholesterol- restricts the lateral (sideways) movement of other molecules in the membrane regulating the fluidity.
peripheral proteins - provides mechanical support, or are connected to proteins or lipids to make glycoproteins and glycolipids which function is cell recognition, as receptors.
integral proteins- protein carriers or channel proteins involved in the transport of molecule across the membrane.

Question 4

how do drugs and hormones move into a cell

Answer 4

they bind to the membrane-bound receptors

Question 5

why is it important that the membrane fluidity is controlled?

Answer 5

so that at high temperatures the membrane is less fluid therefore preventing water and dissolved ions leaking out of the cell.

Question 6

How does an increase in temperature affect the cell membrane structure?

Answer 6

as temperature increases, the phospholipids gain kinetic energy meaning thy will move more. This causes gaps to appear between the phospholipids so the membrane will become more permeable. at high temperatures the proteins in the membrane will denature,

Question 7

How does a decrease in temperature effect the cell membrane permeability?

Answer 7

when water freezes it expands and forms ice crystals which pierce and break the cell membrane

Question 8

how does ethanol and detergents affect the cell membrane permeability?

Answer 8

they both dissolve the phospholipid bilayer making the membrane more permeable

Question 9

passive transport

Answer 9

substances that can be exchanged across cell membranes without requiring metabolic energy from cells(no ATP)

Question 10

diffusion

Answer 10

the net movement of molecules from an area of higher concentration to an area of lower concentration

Question 11

facilitated diffusion

Answer 11

the net movement of molecules from an area of higher concentration to an area of lower concentration across a partially permeable membrane via protein channels or carriers

Question 12

what happens at an equilibrium?

Answer 12

the particles are still moving freely and randomly but there is no net movement

Question 13

factors that affect the rate of diffusion

Answer 13

temperature- as temperature increases, molecules have more kinetic energy so rate of diffusion increase visa versa.
diffusion distance- the thicker the membrane the slower the rate of diffusion
surface area-more diffusion takes place across larger surface areas
concentration gradient- the steeper the concentration gradient the faster diffusion

Question 14

osmosis

Answer 14

the movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

Question 15

water potential of water

Answer 15

0Kpa

Question 16

effects of osmosis on animal cells

Answer 16

when water diffuses into the cell it cannot withstand the hydrostatic pressure so swells and burst this is known as cytolysis.
when water diffuses out of the cell the cell shrinks (crenated)

Question 17

effects of osmosis on plant cells

Answer 17

when water diffuses into the cell the hydrostatic pressure increases and the cell becomes turgid due to its strong cellulose walls.
when water diffused out of the cell it becomes plasmolysed as the cytoplasm shrinks.

Question 18

active transport

Answer 18

the movement of substances against their concentration gradient from low to high concentration of the substance, using ATP and protein carriers.

Question 19

endocytosis

Answer 19

how large particles and molecules are transported into the cell(bulk transport).

Question 20

types of endocytosis

Answer 20

phagocytosis- solid molecules

pinocytosis-fluid molecules

Question 21

exocytosis

Answer 21

-Cytoskeleton contracts; to move the vesicle to the plasma membrane;
- The membrane of the vesicle and plasma membrane fuse;
releasing the contents.

Question 22

explain how cell surface membrane contribute the process of cell signalling

Answer 22

• they release signal molecules by exocytosis
• glycoproteins and glycolipids act as receptors that are specific
• the signal molecule attaches to the glycoprotein/lipid causing a change in shape
• cell surface membrane allow entry of some signal molecules,.

Question 23

how do vesicles move from one organelle to another

Answer 23

they move along microtubules which are extended

Question 24

What is cell signalling

Answer 24

-Communication between cells;
-Cells working together;
To trigger a response;

Question 25

Why do phospholipids arrange themselves in a bilayer at the cell surface?

Answer 25

-The hydrophilic heads orientate themselves towards water and the hydrophobic tails orientate themselves away from water;

-There is water outside of the cell (extracellular fluid)
and inside the cell (cytoplasm/intracellul ar fluid);

Question 26

Role of glucolipid and glycoprotein

Answer 26

• Cell recognition/identification;
  -Cell signalling;
• Act as antigens:

Question 27

Carrier protein

Answer 27

• transport large and polar substances

Question 28

Channel proteins

Answer 28

• transports polar substances

Question 29

What do we controll in the beetroot experiment

Answer 29

• Mass/length of the beetro¢t;
• Same species of beetroot;
• Same volume of water;
• ensure you dry beetroot sample once cut to remove any excess pigment caused by damaging the membrane in the cutting process

Question 30

Control variables of the osmosis experiment

Answer 30

-same length of potato
-same potato
- same volume of solution
-same length of time

Question 31

Why is it important to use percentage change in the osmosis experiment

Answer 31

• it takes into consideration the starting masses

Question 32

Why would the mass of potato increases when put in pure water

Answer 32

-There is a higher water potential in the solution/water;
-Therefore water moves into the potato, from the solution; by osmosis; down the water potential gradient;
so the mass of the potato increases:

Question 33

Why would the mass of potato decrease in a sugar solution

Answer 33

-There is a higher water potential inside the potato;
-Therefore water moves out of the potato, into the solution; by osmosis; down the water potential gradient; so the mass of the potato decreases