1.1 Transport

Question 1

What is diffusion?

Answer 1

Diffusion is the spreading out of particles, resulting in a net movement of particles from an area of high concentration to an area of low concentration

Question 2

Where do substances diffuse in and out of cells?

Answer 2

Substances diffuse into and out of cells across the cell membranes

Question 3

Give 3 examples of substances that are transported in and out of cells by diffusion

Answer 3

• Oxygen and Carbon Dioxide during gas exchange
• Urea when waste products move out of cells and into the blood

Question 4

List the three factors that affect the rate of diffusion

Answer 4

• Temperature
• Concentration Gradient
• Surface area of cell membrane

Question 5

How does the concentration gradient difference affect the rate of diffusion?

Answer 5

The bigger the difference in concentration, the faster the rate of diffusion

Question 6

How does temperature affect the rate of diffusion?

Answer 6

A high temperature means particles have more kinetic energy, so they can spread and diffuse faster

Question 7

How does the surface area of a cell membrane affect the rate of diffusion?

Answer 7

The large surface area of cell membrane means there is more membrane for particles to diffuse through

Question 8

How are single celled organisms adapted for diffusion?

Answer 8

They have a large surface area to volume ratio

Question 9

What happens to the surface area to volume ratio as organisms get larger?

Answer 9

As organisms get larger, the surface area to volume ratio decreases

Question 10

Which four factors increase the effectiveness of an exchange surface?

How are exchange surfaces adapted?

Answer 10

• Having a large surface area, which means that there is more cell membrane for particles to diffuse through
• Having a thin membrane, to provide a short diffusion path
• Having an efficient blood supply, to maintain the high concentration gradient (in animals)
• Being ventilated (to maintain a high concentration gradient) (in animals, for gaseous exchange)

Question 11

How is the small intestine adapted for diffusion?

Answer 11

• The small intestine has projections of villi and epithelial cells, which increases the surface area
• Each villus has a good blood supply, so a good concentration gradient is maintained
• The cell wall of the villi is thin, so shorter diffusion pathway

Question 12

How are the lungs adapted for gas exchange?

Answer 12

Millions of alveoli that collectively provide a large surface area
Each alveoli has a one cell thick wall, so there is a shorter diffusion pathway
Each alveolus is surrounded by capillaries which have a good blood supply to maintain a good concentration gradient

Question 13

What are the gills of fish covered in?

Answer 13

Gills are covered in a very large number of fine filaments, which is where gas passes in and out

Question 14

How are the gills adapted for gas exchange?

Answer 14

• The large number of gill filaments give the gills a large surface area
• The filaments have a thin membrane which provides a shorter diffusion pathway
• The filaments have an efficient blood supply to take the deoxygenated blood away and ensure that the concentration gradient is always high

Question 15

How are the roots and leaves of plants adapted for gas exchange?

Answer 15

• Plants have root hair cells that increase the surface area of the roots for the absorption of mineral ions and water
• Leaves have an internal surface area of the diffusion of gases
• Leaves are thin to reduce the diffusion distance to cells

Question 16

What is osmosis?

Answer 16

Osmosis is the diffusion of water particles from an area of high concentration to an area of low concentration through a partially permeable membrane

Question 17

What is a partially permeable membrane?

Answer 17

A partially permeable membrane is a membrane that allows water molecules through, but not larger molecules

Question 18

What do the terms dilute solution and concentrated solution mean?

Answer 18

• A dilute solution contains lots of water molecules (high concentrattio of water)
• A concentrated solution has a higher concentration of solutes and lower concentration of water

Question 19

Label the dilute sugar solution and the concentrated sugar solution

Answer 19

The dilute sugar solution is the one on the left as it has more concentration of water
The concentrated sugar solution is the one on the right as it has less concentration of water

Question 20

What happens here, when there is a partially permeable membrane separating a dilute and concentrated sugar solution?

Answer 20

The water molecules will diffuse to the right

Question 21

What happens here, when there is a partially permeable membrane separating a dilute and concentrated sugar solution?

Answer 21

The water molecules will diffuse to the right

Question 22

What happens here, when there is a partially permeable membrane separating a dilute and concentrated sugar solution?

Answer 22

The water molecules will diffuse to the right as Osmosis is the diffusion of WATER molecules

Question 23

What is active transport?

Answer 23

Active transport is the movement of particles, from an area of low concentration to an area of high concentration, against a concentration gradient and it requires energy

Question 24

What does active transport require? From where does it get it from?

Answer 24

Active transport requires energy from respiration

Question 25

Why does active transport require energy from respiration?

Answer 25

• Because it is an active process, not passive like diffusion. It needs energy to transport substances across a concentration gradient…
• …because the carrier proteins needs energy to carry molecules across the cell membrane and then return to its original position

Question 26

Give 2 examples of where active transport occurs

Answer 26

• Small Intestine, which is part of the guts
• Root hair cells in plants

Question 27

Explain the importance of active transport in plants

Answer 27

• The concentration of ions in the soil is lower than the concentration in the root hair cell
• The plants require these ions for healthy growth

Question 28

Explain the importance of active transport in the gut

Answer 28

• Active transport is used to transport glucose out of the gut (small intestine - from digestion of food molcules), where there is a low concentration of glucose, and into the bloodstream, where there is a high concentration of glucose
• The glucose (energy) is needed by cells for respiration so it is important to get as much as possible out of the gut