Movement of Substances : Transport Processes

Question 1

what is diffusion?

Answer 1

• the random movement of particles from an area of high concentration to an area of lower concentration

Question 2

why do all particles move randomly?

Answer 2

• all particles move randomly and in different directions all the time due to their kinetic energy

Question 3

what does diffusion describe?

Answer 3

• the overall direction and speed of the movement

Question 4

what is it called when over time, all of the particles will be equally distributed?

Answer 4

equilibrium

Question 5

does equilibrium mean that the particles stop moving?

Answer 5

no!

Question 6

describe the speeds and rates for diffusion and osmosis.

Answer 6

• diffusion and osmosis can happen at different speeds or rates

Question 7

what are the four main factors which affect the rate of diffusion?

Answer 7

• temperature
• concentration gradient
• distance
• surface area : volume

Question 8

how can temperature affect the rate of diffusion?

Answer 8

• at higher temperatures, molecules have more kinetic energy and so move faster
• therefore diffusion occurs faster

Question 9

how does concentration gradient affect the rate of diffusion?

Answer 9

• if there is a very large difference in concentration between two areas, molecules will diffuse from the higher to the lower concentration quickly
• if the concentration gradient (difference) is small, diffusion will happen more slowly

Question 10

how does distance affect the rate of diffusion?

Answer 10

• diffusion takes longer if the molecules have to travel further, molecules don’t travel in a straight line which slows the process
• therefore cells are small as smaller volume reduces distance

Question 11

how does surface area: volume affect the rate of diffusion?

Answer 11

• a larger SA speeds up the rate of diffusion as there are more opportunities for the molecules to move, which is why surfaces such as alveoli in lungs are so large
• SA:V is more significant, as the two oppose each other: an efficient exchange surface has a surface area which is very large compared to the distance the molecules must travel
• SA:V is increased when structures are small

Question 12

what do cells rely on for their function?

Answer 12

• diffusion

Question 13

what is osmosis?

Answer 13

• a special type of diffusion
• it is only ever used to describe the movement of water molecules across a membrane

Question 14

what is the definition of osmosis?

Answer 14

• osmosis is the net diffusion of free water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane

Question 15

draw a diagram to represent and describe free water molecules.

Answer 15

one note page

Question 16

draw a diagram to represent and describe partially permeable molecules.

Answer 16

one note page

Question 17

what is water potential?

Answer 17

• a measure of the concentration of free water molecules in a solution
• pure water has a water potential of 0
• as a solute is added, water potential falls as there will be a lower concentration of free water molecules
• concentrated solutions have a very low water potential.

Question 18

what are constantly moving in and out of cells?

Answer 18

• free water molecules

Question 19

how do animal and plant cells react to being placed in different concentrations and why?

Answer 19

• they react differently
• this is because plant cells are placed in different solutions

Question 20

what is an isotonic solution?

Answer 20

• when the solution outside the cell has the same water potential as inside the cell - no net movement

Question 21

what is a hypotonic solution?

Answer 21

• when the solution outside the cell has a higher water potential then inside the cell - net movement of free water molecules into the cell

Question 22

what is a hypertonic solution?

Answer 22

• when the solution outside the cell has a lower water potential then inside the cell- net movement of free water molecules out of the cell

Question 23

draw a diagram to describe as to how an animal vs a plant cell would react in a hypotonic solution.

Answer 23

one note page

Question 24

draw a diagram to describe as to how an animal vs a plant cell would react in an isotonic solution.

Answer 24

one note page

Question 25

draw a diagram to describe as to how an animal vs a plant cell would react in a hypertonic solution?

Answer 25

one note page

Question 26

what is active transport?

Answer 26

• active transport is used by organisms to transport substances against the concentration gradient
• in order to do this, the organism ends special carrier proteins in the cell membrane
• these use ATP to provide the energy to move the substances across the membrane against the concentration gradient

Question 27

what is absorbed by active transport in the small intestine?

Answer 27

• glucose

Question 28

how do plants use active transport?

Answer 28

• in their root hair cells
  -to absorb mineral ions

Question 29

define active transport.

Answer 29

• active transport is the movement of molecules from an area of low concentration to an area of high concentration using ATP

Question 30

describe an experiment to demonstrate the relationship between surface area: volume ratio and the rate of diffusion.

Answer 30

• agar cubes of different sizes
• the cubes contain alkali and an indicator - they are placed in an acid
• as the acid diffuses into the cube it reacts with the alkali
• this neutralisation turns the indicator colourless
• the smallest (0.5cm length) cube becomes colourless quickest

Question 31

describe an experiment to demonstrate the relationship between the concentration gradient and the rate of diffusion and osmosis.

Answer 31

• potato chips placed in sucrose or salt solutions of different concentrations
• osmosis will occur until the water potential of the tissue and the solution are the same
• which causes a mass change
• if the solution has a higher water concentration, water will move into the potato chip and the mass will increase
• if the solution has a lower water concentration, water will move out of the potato chip and the mass will decrease
• this method can be used to determine the water potential of the potato, if there is no change in mass, the concentration of the solution is the same as the concentration of the cytoplasm.
• by leaving the experiment for a short time , e.g. 20 minutes, you would be able to see that the potato chips in solutions where the concentration has the biggest difference to the cytoplasm will experience the biggest mass changes.

Question 32

describe an experiment to demonstrate the relationship between concentration/temperature and the rate of diffusion.

Answer 32

• one note page
• visking tubing only allows small soluble molecules to pass through (e.g. glucose and water).
• therefore osmosis can occur

Question 33

how else could you study the effects of osmosis?

Answer 33

• use thin sections of onion cells
• one note page
• the cells on the left are turgid - they are soaked in pure water
• the cells on the right are plasmolysed - they have been soaked in a concentrated salt or sugar solution