Movement of Substances

Question 1

Diffusion definition?

Answer 1

Diffusion is the random movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient.

Question 2

Factors that affect the rate of diffusion?

Answer 2

• Temperature
• Concentration gradient
• Distance
• Surface area : Volume

Question 3

How does temperature effect the rate of diffusion?

Answer 3

At higher temperatures, molecules have more kinetic energy and so
move faster. Therefore diffusion occurs faster.

Question 4

How does concentration gradient effect the rate of diffusion?

Answer 4

The larger the difference in concentration between two areas, molecules will diffuse from the higher to the lower concentration quicker.

Question 5

How does distance effect the rate of diffusion?

Answer 5

Diffusion takes longer if the molecules have to travel further. Therefore cells are small, smaller volume reduces distance.

Question 6

How does SA:V effect the rate of diffusion?

Answer 6

A larger surface area speeds up the rate of diffusion as there
are more opportunities for the molecules to move.

Question 7

Definition of osmosis?

Answer 7

Osmosis is the net diffusion of free water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane.

Question 8

Isotonic solution definition?

Answer 8

When the solution outside the cell has the same water potential as inside the cell - no net movement.

Question 9

Hypotonic solution definition?

Answer 9

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 10

Hypertonic solution definition?

Answer 10

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 11

What do plant and animal cells look like in a hypotonic solution?

Answer 11

Animal: lysed/burst
Plant: turgid

Question 12

What do plant and animal cells look like in a hypertonic solution?

Answer 12

Animal: shrivelled
Plant: plasmolysed

Question 13

Active transport definition?

Answer 13

Active transport is the movement of molecules from an area of low concentration to an area of high concentration using ATP.

Question 14

Two experiments to investigate osmosis?

Answer 14

• potato chips in different solution
• sugar solution in visking tubing

Question 15

What is the xylem and what is its properties?

Answer 15

• Made up of thick walled dead
  cells that are completely hollow
• Cell wall contains lignin which is waterproof
• The end walls are broken down
  to form a continuous transport system

Question 16

What is the role of the xylem?

Answer 16

Transports water and mineral
ions from the roots to the leaves. Theses minerals include:
- Nitrate ions - needed to make
amino acids and proteins
- Magnesium ions - needed to
make chlorophyll

Question 17

What is the phloem’s role and what is its properties?

Answer 17

• Consists of living cells.
• Tubes are formed by cells
  arranged end to end; cell walls made of cellulose.
• Phloem transports sucrose and
  amino acids from the leaves to the
  growing points or storage areas.

Question 18

How does the root hair cell transport water into a plant?

Answer 18

The water has some solutes dissolved in it but their concentration is much lower than the concentrations of solutes inside the root hair cells. Mineral ions are actively transported into the root hair cells. The soil water has a higher concentration of water molecules and water will enter the cell by osmosis.

Question 19

Adaptations of root hair cells?

Answer 19

They are thin walled (short distance) and have hair like extensions that greatly increase the surface area of the root epidermis.

Question 20

What is transpiration?

Answer 20

Transpiration is the evaporation of water from the surface of a plant

Question 21

What is the role of the transpiration stream?

Answer 21

• To carry mineral ions to the leaves for the synthesis of amino acid and chlorophyll.
• To keep turgor pressure high in leaf cells, holding the leaves up.
• Evaporation cools the leaves.
• Supplies water for photosynthesis

Question 22

What factors effect the rate of transpiration?

Answer 22

• temperature
• humidity
• wind speed
• light intensity

Question 23

How does temperature effect the rate of transpiration?

Answer 23

As temperature increase so does rate of transpiration because the water will evaporate more quickly as the water molecules have more kinetic energy.

Question 24

How does humidity effect the rate of transpiration?

Answer 24

If humidity increases air contains a greater deal of water vapour so there is a smaller concentration gradient, so transpiration slows down.

Question 25

How does wind speed effect the rate of transpiration?

Answer 25

As wind speed increases water vapour will be blown away from the leaf as it diffuses out, this keeps the concentration gradient high. Therefore the rate of diffusion will increase.

Question 26

How does light intensity effect the rate of transpiration?

Answer 26

As light intensity increases the stomata of the leaves will open more, this allows more water to diffuse out therefore rate of transpiration increases.

Question 27

What happens to the stomata in the light?

Answer 27

In the light the guard cells photosynthesise. The concentration of sugars increases, the water potential in the guard cells falls and so water moves into the guard cells by osmosis. They become turgid, this causes the guard cells to become banana shaped, due
to the inflexible inner cell wall, and opens the stomata.

Question 28

What happens to the stomata in the dark?

Answer 28

Photosynthesis stops in the dark. As the sugar concentration falls (due to respiration), water potential increases and water moves out of the guard cells. They become flaccid and the stomata close.

Question 29

How to set up potometer to measure the rate of transpiration?

Answer 29

1. The potometer must be set up under water to prevent any air bubbles from entering the system.
2. Cut the stem of a shoot.
3. Put the shoot stem into the bung, grease the joint with plenty of petroleum jelly
4. Put the bung into the potometer.
   Make sure the tap is closed and it is full of water. Then lift the potometer out of the water.
5. Leave the end of the capillary tube out of the water until an air bubble forms then put the end
   into a beaker of water.
6. You can measure the transpiration rate as distance the bubble travels in five minutes.
7. Take repeats and calculate an average.

Question 30

What is excretion?

Answer 30

The removal of waste/toxic substances from the body.

Question 31

Examples of excretion?

Answer 31

• Respiration
• Ultrafiltration

Question 32

How is urea formed?

Answer 32

1. Amino acids are filtered into the liver in the bloodstream.
2. Excess amino acids cannot be stored and need to be broken down so they can be excreted. They are broken down into carbohydrates and ammonia.
3. Ammonia is very toxic and must be converted into a slightly less toxic chemical called urea
4. Amino acids that are needed and the urea are released back into the
   blood stream.

Question 33

Stage one of ultrafiltration?

Answer 33

The diameter of the efferent arteriole is smaller than the
diameter of the afferent arteriole. This creates a build-up of pressure in the capillaries forming the glomerulus.

Question 34

Stage two ultrafiltration?

Answer 34

The pressure forces small molecules such as urea, glucose,
amino acids and salts out of the
capillaries of the glomerulus and
into the Bowman’s Capsule. This
forms the glomerular filtrate.

Question 35

Stage 3 of ultrafiltration?

Answer 35

Larger molecules like proteins or red blood cells are too big to fit
across the capillary walls and therefore stay in the blood; they are stopped by the basement membrane.

Question 36

What happens in the PCT?

Answer 36

Selective reabsorption:
- glucose and amino acids actively transported into the bloodstream.
- harmful substances actively transported into the filtrate in the PCT.
- water moves out the PCT via osmosis.

Question 37

What happens in the Loop of Henle?

Answer 37

80% of water is reabsorbed in the PCT but the remaining water is reabsorbed in the collecting duct/loop of henle.

Question 38

When is respiration and photosynthesis fastest in plants?

Answer 38

Day: photosynthesis
Night: respiration

Question 39

How is a leaf specialise for gas exchange?

Answer 39

• The leaf is thin for short diffusion distance.
• It also has a large surface area,
  increasing the number of stomata, for quicker diffusion.
• Stomata allow gases to diffuse into / out of the air spaces of the leaf. This provides a short diffusion distance to the mesophyll cells.
• The guard cells can change shape, altering the size of the stomata.
• The stomata close to reduce water loss at night.