1.3 Transport in Cells

Question 1

What is diffusion?

Answer 1

The net movement of particles from an area of higher concentration to an area of lower concentration.

Question 2

What three main factors affect the rate of diffusion?

Answer 2

• Concentration gradient - larger gradient, faster diffusion.
• Temperature - higher temperature, faster diffusion.
• Surface area - larger surface area, faster diffusion.

Question 3

Give examples of substances transported by diffusion in the lungs and kidney. (2)

Answer 3

• Lungs: oxygen diffuses into the blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient.
• Kidney: urea diffuses from cells into blood plasma so it can be excreted in urine.

Question 4

How is surface area to volume ratio calculated? (3)

Answer 4

1. Calculate the surface area.
   Surface Area = Number of Faces x (Face Length x Face Width)
2. Calculate the volume.
   Volume = Length x Width x Depth
3. Substitute into ratio.
   Ratio = Surface Area:Volume
   (divide SA by V to see how many times larger the SA is to the V)

Question 5

What four factors increase the effectiveness of a gas exchange surface?

Answer 5

• Large surface area
• Thin membrane (short diffusion path)
• Efficient blood supply (animals)
• Ventilation (animals)

Question 6

How is the surface area to volume ratio of an organism affected by its size?

Answer 6

As the size of the organism increases, the surface area to volume ratio decreases.

Question 7

What is osmosis?

Answer 7

The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.

Question 8

What is meant when a solution is isotonic to a cell?

Answer 8

The concentrations of the external and internal (inside cell) solutions are the same.

Question 9

What is meant when a solution is hypertonic to a cell?

Answer 9

The concentration of the external solution is higher than that of the internal solution (inside cell).

Question 10

What is meant when a solution is hypotonic to a cell?

Answer 10

The concentration of the external solution is lower than that of internal solution (inside cell).

Question 11

What may happen when an animal cell is placed in a very hypotonic solution?

Answer 11

Water moves into the cell, causing it to burst.

Question 12

What may happen when an animal cell is placed in a very hypertonic solution?

Answer 12

Water moves out of the cell, causing it to shrivel up.

Question 13

How do plant leaves and stems remain rigid?

Answer 13

Turgor pressure - water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall.

Question 14

What may happen when a plant cell is placed in a very hypertonic solution? (2)

Answer 14

• Water moves out of the cell by osmosis and the vacuole and cytoplasm decrease in size.
• The cell membrane may pull away from the cell wall, causing the cell to become plasmolysed.

Question 15

What does it mean when a plant tissue gains mass after being placed in water? (2)

Answer 15

• Water must have moved into the plant tissue from the solution surrounding it by osmosis.
• The solution surrounding the tissue is more dilute than the plant tissue (which is more concentrated).

Question 16

What does it mean when a plant tissue loses mass after being placed in water? (2)

Answer 16

• Water must have moved out of the plant tissue into the solution surrounding it by osmosis.
• The solution surrounding the tissue is more concentrated than the plant tissue (which is more dilute).

Question 17

What does it mean when there is no overall change in the mass of a plant tissue after being placed in water? (2)

Answer 17

There has been no net movement of water as the concentration in both the plant tissue and the solution must be equal.

Question 18

What is active transport?

Answer 18

The movement of molecules from a more dilute solution to a more concentrated solution against a concentration gradient, using energy from respiration.

Question 19

How are plant root hair cells adapted to use active transport?

Answer 19

Root hair cells use active transport to take up mineral ions (e.g. magnesium and nitrates), which are needed for healthy growth, from a more dilute solution in soils.

Question 20

What do plans need magnesium and nitrate ions for?

Answer 20

• Magnesium: to make chlorophyll
• Nitrate ions: to make amino acids for protein synthesis (and growth).

Question 21

How is active transport used to absorb the products of digestion? (2)

Answer 21

1. Active transport is used to transport glucose from a lower concentration in the gut to a higher concentration in the blood.
2. Glucose is then transported to the tissues where it can be used in respiration.

Question 22

How does active transport enable cells to absorb ions from very dilute solutions?

Answer 22

It uses energy to transport the surrounding ions, from a low concentration (outside) to a high (inside) through respiration.

Question 23

Why does active transport require energy?

Answer 23

To move substances against the concentration gradient.

Question 24

How are the small intestine adapted for the exchange of substances? (4)

Answer 24

• Villi and microvilli increase surface area for more absorption of food molecules
• Villi and microvilli have very thin walls to provide a short diffusion distance.
• Microvilli have many mitochondria to provide energy for active transport.
• Villi have good blood supply to maintain a high concentration gradient.

Question 25

How are roots in plants adapted for the exchange of substances? (3)

Answer 25

• Root hair cells increase surface area for faster rate of diffusion, osmosis and active transport.
• Highly branched root network increases the surface area.
• They use osmosis to transport water into the cell, and active transport to transport mineral ions into the cell, using energy.

Question 26

How are the lungs adapted for the exchange of substances? (4)

Answer 26

• Small size and large numbers of alveoli provide a large surface area for gas exchange.
• Good blood supply (many capillaries) to maintain a concentration gradient of oxygen and carbon dioxide.
• Alveoli wall is very thin to provide a short diffusion distance.
• Lungs are ventilated to bring fresh oxygen to maintain a concentration gradient.

Question 27

How are the gills of fish adapted for the exchange of substances? (2)

Answer 27

• Gills and gill filaments increase surface area.
• Counter current flow of blood in capillary network to water maintains a concentration gradient.

Question 28

How are leaves in plants adapted for the exchange of substances. (4)

Answer 28

• Flat and wide to provide a large surface area
• Thin to provide a short diffusion pathway
• Air spaces between cells that increase the rate of diffusion
• Stomata that can open and close to increase or decrease gas exchange

Question 29

What surface area to volume ratio do single-celled organisms have? What does this allow? (2)

Answer 29

• High
• Transport by diffusion, osmosis or active transport alone to be sufficient for the organism to meet its needs.

Question 30

What surface area to volume ratio do multicellular organisms have? What does this mean?

Answer 30

• Low
• Larger organisms need exchange surfaces and transport systems to ensure their cells obtain the materials they need.