Transport Across Membranes

Question 1

what does the cell membrane do

Answer 1

controls what molecules enter and leave a cell

Question 2

what does the cell membrane consist of

Answer 2

phospholipids and proteins

Question 3

what is meant by permeability

Answer 3

the ability of a surface to allow molecules to pass through it

this means that it allows molecules to move through it easily, but others move more slowly, and some cannot move across it at all

Question 4

what small molecules can get through the cell membrane

Answer 4

glucose
water
oxygen
carbon dioxide

Question 5

what large molecules can’t pass through a cell membrane

Answer 5

starch and proteins

Question 6

what is meant by a selectively permeable membrane

Answer 6

they allow certain molecules to pass through but not others

Question 7

what is a concentration gradient

Answer 7

a difference in concentration between two solutions is called a concentration gradient

Question 8

what is passive transport and give the 2 examples

Answer 8

• occurs DOWN a concentration gradient and doesn’t require energy
• diffusion and osmosis are the two types

Question 9

what happens to molecules during passive transport on the concentration gradient

Answer 9

molecules move DOWN the concentration gradient from high concentration to low concentration and stop loving when the 2 concentrations are equal

Question 10

what is diffusion

Answer 10

diffusion is the movement of molecules in a liquid or gas DOWN a concentration gradient from higher to lower concentration until the molecules are evenly spread out

Question 11

what do animal cells take in for aerobic respiration

Answer 11

glucose and oxygen

Question 12

what leaves animal cells by diffusion

Answer 12

carbon dioxide and other waste materials

Question 13

what is osmosis

Answer 13

osmosis is the movement of WATER from a higher water concentration to a lower water concentration through a selectively permeable membrane

Question 14

what will a dilute solution have

Answer 14

a high concentration of water , low concentration is solute e.g sugar

Question 15

what will a concentrated solution have

Answer 15

a lower water concentration , higher concentration of solute e.g sugar

Question 16

what will happen to plant cells in pure water

Answer 16

they gain water by osmosis

water molecules move into the vacuole by osmosis and makes the cells go TURGID

Question 17

what will happen to a plant cell placed in a strong salt solution

Answer 17

• they lose water by osmosis

- water molecules leave the vacuole by osmosis and the cells are said to be PLASMOLYSED

Question 18

what will happen to an animal cell with a concentrated salt solution

Answer 18

cell will lose water by osmosis and SHRINK

Question 19

what will happen to an animal cell with an equal concentration solution

Answer 19

no net osmosis, cell stays the same

Question 20

what will happen to an animal cell in pure water

Answer 20

cell takes in water by osmosis , swells up and eventually BURST

Question 21

describe active transport

Answer 21

• some molecules and ions like sodium and potassium, are moved across the membrane by active transport
• this involves the movement of molecules and ions AGAINST a concentration gradient
• active transport requires energy
• membrane proteins are involved in this process