4.1.3.1 Diffusion

Question 1

Diffusion:

Answer 1

• The net movement of particles from an area of high concentration to an area of low concentration down a concentration gradient until equilibrium Is reached
• It Is a passive form of transport

Question 2

What direction does diffusion occur in?

Answer 2

Diffusion occurs in all directions and travels from an area of high concentration to an area of low concentration

Question 3

How may substances move into and out of cells?

Answer 3

Via diffusion

Question 4

What are factors which increase the rate of diffusion?

Answer 4

• The difference in concentrations (steeper concentration gradient)
• The temperature – the higher the temperature the more kinetic E for the particles and the faster they can diffuse
• The surface area of the membrane for particles to diffuse
• Short diffusion pathway – thin membrane for particles to diffuse into

Question 5

What does every living organism need to do?

Answer 5

Exchange materials with its surroundings

Question 6

What does the amount of material which needs to be exchanged depend on?

Answer 6

Its volume

Question 7

Passive:

Answer 7

process where no E is required

Question 8

What are some substances that are transported into cells by diffusion?

Answer 8

Take in substances like glucose and oxygen (gas exchange) for respiration in gas exchange

Question 9

What are some substances that are transported out of cells by diffusion?

Answer 9

• CO2 from gas exchange
• The waste product urea from cells into the blood plasma for excretion in the kidney
• Waste products need to be removed

Question 10

What are some factors which increase the rate of diffusion?

Answer 10

• The difference in concentrations (steeper concentration gradient)
• The temperature – the higher the temperature the more kinetic E for the particles and the faster they can diffuse
• The surface area of the membrane for particles to diffuse
• Short diffusion pathway – thin membrane for particles to diffuse into

Question 11

Why do organisms stop growing after a certain stage?

Answer 11

Organisms stop growing after they reach a certain stage because if their volume increased more required substances may not be able to reach cells in the inside and their surface area wouldn’t be big enough for their volume

Question 12

Why can’t cells grow enormous?

Answer 12

Cells can’t grow enormous because there wouldn’t be enough accessible substances

Question 13

What is the SA:V ratio for unicellular organisms?

Answer 13

• Unicellular organisms have a relatively large SA:V ratio - allows sufficient transport of molecules into and out of the cell to meet the needs of the organism
• When the surface area to volume ration is large, there is a lot of surface area for diffusion and not much volume to travel through
• Therefore, organisms can get all the substances it needs by simple diffusion

Question 14

In multicellular organisms, the surfaces and organ systems are specialised for exchanging materials. What does this allow?

Answer 14

It allows sufficient molecules to be transported into and out of cells for the organisms’ needs

Question 15

What is the effectiveness of an exchange surface (allows better diffusion) is increased by?

Answer 15

• Having a large surface area – increases site of exchange
• A membrane that is thin – provides a short diffusion pathway
• (in animals) having an efficient blood supply
• (in animals for gaseous exchange) being ventilated
• A method of transporting substances to and from the exchange site (e.g. a good blood supply) – maintains a steep concentration gradient

Question 16

Gas exchange in humans:

Answer 16

• Gas exchange happens in the alveoli
• Oxygen enters the lungs and diffuses into the bloodstream via capillaries that cover the alveoli
• There is a higher concentration of oxygen in the alveoli than in the blood, so oxygen moves into the blood
• There is a higher concentration of carbon dioxide in the blood than in the alveoli, so carbon dioxide moves out of the blood

Question 17

Function of villus in the small intestine:

Answer 17

• Absorption of nutrients, such as glucose and amino acids, takes place in small intestine
• These are taken into the bloodstream using diffusion and active transport

Question 18

Adaptations for exchanging materials of villus in small intestine:

Answer 18

• Good blood supply (due to it being surrounded by capillaries) – maintains steep concentration gradient
• Have thin cell wall which is only one cell thick – short diffusion distance
• Covered in finger-like projections called villi and microvilli that increase the surface area of the small intestine – increases site of exchange

Question 19

Function of plant roots:

Answer 19

Efficient uptake water and mineral ions from the soil

Question 20

What substances are exchanged in plant roots?

Answer 20

• Water
• Mineral ions

Question 21

Adaptations for exchanging materials of plant roots:

Answer 21

• Root hair cells have a projection to increase the surface area – increasing site of diffusion
• Constant water flow – maintaining a steep concentration gradient in cells
• Thin cell wall – short diffusion distance
• Roots project deep into the soil - meaning there will be more substances that can diffuse into the root hair cell maintaining a steep concentration gradient

Question 22

Function of plant leaves:

Answer 22

• Exchange the O2 produced in photosynthesis and the CO2 needed for the process
• Exchange takes place on the bottom of the leaf

Question 23

Adaptations for exchanging materials in plant leaves:

Answer 23

• Exchange surfaces covered in small holes called stomata where the gases can diffuse into and out of the leaf – good ventilation maintaining a steep conc gradient
• Leaves have a flattened shape in order to increase the surface area available to make diffusion more effective
• Thin cell walls – short diffusion distance
• Air spaces within the leaf also act to increase the surface area available for this gas exchange to take place

Question 24

Function of gills in fish:

Answer 24

• So that fishes can obtain their O2 from the water so have a specialised exchange surface - gills
• Water passes over the gills, allowing O2 to diffuse into the blood and CO2 to move out as it does

Question 25

Adaptations for exchanging materials in gills in fish:

Answer 25

• Gills are made up of thin plates called gill filaments which increase the surface area of the tissue – increases site of diffusion
• Gills are covered in structures called lamellae which increase the surface area further – increases site of diffusion
• Gills have a very good blood supply – as O2 is constantly moving away from the lungs a steep concentration gradient is maintained (same for CO2 leaving blood)
• Gills have very thin walls which allows for quick diffusion of gasses across this wall into or out of the blood – short diffusion distance

Question 26

Function of lungs:

Answer 26

Gas exchange – oxygenates deoxygenated blood and sends it out across the body

Question 27

How have lungs ensured maximum gas exchange?

Answer 27

Evolved

Question 28

Adaptations for exchanging materials in lungs:

Answer 28

• The alveoli provide a large surface area for gas exchange – increase site of diffusion
• Alveoli wall is very thin – short diffusion distance
• Capillaries surround the alveoli ensuring a good blood supply as O2 is constantly moving away from the lungs a steep concentration gradient is maintained (it is same for leaving CO2 leaving blood)
• Well ventilated – maintains steep concentration gradient
• Alveoli surfaces are moist – gases dissolve to aid efficient diffusion

Question 29

How does the circulatory system contribute to the diffusion of gases?

Answer 29

• Capillaries surrounding the alveoli collect the O2 and then distribute throughout the body so cells can release E through aerobic respiration.
• Capillaries also excrete CO2.
• This helps in the diffusion of gases into and out of the body.

Question 30

Equilibrium:

Answer 30

equal number of particles on each side

Question 31

Net Movement:

Answer 31

the overall movement in one direction

Question 32

Where can the process of exchange only take place?

Answer 32

Across its surface