2.1 Osmosis And Plant Transport

Question 1

What is osmosis

Answer 1

Osmosis is the movement of water molecules from a dilute solution to a more concentrated solution, through a selectively permeable membrane

Question 2

What is a dilute solution ?

Answer 2

A dilute solution contains less solute molecules

Question 3

What is a concentrated solution?

Answer 3

A concentrated contains more solute molecules

Question 4

What is a selectively permeable membrane?

Answer 4

A selectively permeable membrane is a membrane which allows some molecules through but not others

Question 5

What molecules cannot move across a selectively permeable membrane?

Answer 5

Larger molecules cannot move across a selectively permeable membrane

Question 6

How do water molecules move across the selectively permeable membrane

Answer 6

Water molecules move across the membrane from a dilute solution to a concentrated solution.

Question 7

Why does water move across the membrane?

Answer 7

Water moves to balance the solute concentration on both sides of the membrane

Question 8

When a solution is dilute what does this mean in terms of water

Answer 8

There is more water in a dilute solution

Question 9

When a solution is concentrated what does this mean in terms in terms of water

Answer 9

There is less water and more solute molecules

Question 10

When does osmosis stop ?

Answer 10

Osmosis continues until the solute is at the same concentration on both sides of the membrane or until further water movement becomes limited by the cell wall (plant cells only)

Question 11

What happens when water enters a plant cell ?

Answer 11

• Water flows into the cell from a more dilute solution outside the cell, to a more concentrated solution inside the cell sap
• Vacuole fills with water and increases in size
• Pushing the cytoplasm backwards against the cell wall
• Cell membrane pushed against the cell wall
• Cell wall stretches slightly and cell becomes turgid

Question 12

What does the force of the cell membrane pushing against the stiff cell wall do ?

Answer 12

It increases the pressure in the cell making it firm or turgid.

Question 13

What does the turgor pressure do ?

Answer 13

• The turgor pressure stops too much water from entering the cell so that it cannot burst.
• It gives the plant cells support and keeps non-woody plants upright.

Question 14

What happens if there is a shortage of water in the plant cell and what is this described as?

Answer 14

• Plant cells cannot remain turgid and wilting occurs.
• Cells that are not turgid are described as being flaccid or plasmolysed

Question 15

What happens if a plat cell loses too much water by osmosis?

Answer 15

A condition called plasmolysis occurs and the cell is unlikely to survive

Question 16

What happens in a plasmolysed plant cell ?

Answer 16

• The water flows from the more dilute solution inside the cell sap to the more concentrated solution outside the cell
• Vacuole loses water and decreases in size
• Cytoplasm shrinks
• The cell membrane pulls away from the cell wall
• cell wall becomes soft/flaccid
• Cell becomes plasmolysed

Question 17

Cell membranes let through small molecules like ?

Answer 17

Oxygen and water

Question 18

The movement of molecules from a high to low concentration is ?

Answer 18

Diffusion

Question 19

What is diffusion?

Answer 19

The movement of molecules from a high to low concentration

Question 20

What 4 things do plants use water for ?

Answer 20

1. Supply water to leaves for Photosynthesis
2. To transport minerals and dissolved nutrients round the plant in specialised vascular tissue called xylem (water) and phloem (food)
3. To provide support to the cells by filling them with water due to osmosis and making them turgid
4. For transpiration

Question 21

Where can water only enter through in a plant ?

Answer 21

Water can only enter a plant through the root hair cell which have a large surface area to allow greater uptake of water

Question 22

How does water move through the plant ?

Answer 22

Water moves through the plant and is pulled from the roots up the stem to the leaves the process of evaporation

Question 23

What is the equation to remember the processes of water up take of a plant

Answer 23

Water uptake by a plant (root hair cells) = water used for photosynthesis (leaves, mostly palisade ) + water used for support/turgor (stem) + water lost in transpiration (goes out through stomata in the leaves)

Question 24

What are plants that live in areas where water is limited called ?

Answer 24

Xerophytes

Question 25

What are 3 adaptations found in a xerophytic plant ?

Answer 25

• reduced leaf size
• thick waxy cuticle
• extensive root system

Question 26

What do some plants that face difficulty finding water because it is not easily available have ?

Answer 26

• They may have extensive root systems to help them find water underground
• others try to reduce water loss by transpiration e.g. by closing the stomata on the underside of the leaf to slow the rate of evaporation

Question 27

What is transpiration?

Answer 27

Transpirtation is the process of evaporation of water from the mesophyll cells followed by diffusion through the stomata

Question 28

Describe the water movement through a plant ?

Answer 28

• Water molecules surround the soil particles
• Water enters the root hair cell by osmosis as well as mineral salts
• water molecules are pulled up xylem ( dead vessels with no cell contents transport water and mineral salts up the stem)
• water evaporates from the spongy mesophyll cells into air spaces
• water is lost through the stomata by evaporation

Question 29

What is the bubble potometer used for ?

Answer 29

The bubble potometer is designed to measure water uptake of a leafy shoot

Question 30

What five factors influence transpiration?

Answer 30

• Light
• Temperature
• Wind speed
• Humidity
• Surface area of leaves

Question 31

How does the bubble potometer work ?

Answer 31

• As water evaporates from the leaves of the cut shoot, the shoot sucks up water through the potometer
• The distance the air bubble moves in a period of time can be used to calculate the rate of water uptake

Question 32

What precautions must be taken when setting up the bubble potometer?

Answer 32

• Apparatus must be assembled underwater to prevent the development of air bubbles in the water column entering the plant
• All joints must be sealed with petroleum jelly to prevent air leaks which may hinder water uptake by the plant

Question 33

Why is a bubble potometer a more accurate measurement of water uptake than transpiration?

Answer 33

The bubble potometer cannot measure transpiration accurately as not all of the water uptake is transpired. Some is used by the plant for cell support (turgor) as well as photosynthesis making the bubble potometer a more accurate measurement of water uptake than for measurement of transpiration

Question 34

What is a more accurate measurement of the rate of transpiration?

Answer 34

Weight potometer

Question 35

What precautions need to be taken when using the weight potometer to measure a more accurate the rate of transpiration in a plant ?

Answer 35

• A layer of oil is needed to ensure any loss of mass will be from the leaves (transpiration) and not due to evaporation of water from the flask.
• A rubber stopper will also prevent evaporation of water from the flask
• using a top pan balance as it can measure to 2 decimal places and so provides greater accuracy

Question 36

How do you use the washing line method to investigate the factors affecting the rate of water loss from plant leaves?

Answer 36

1. Remove a number of leaves from a plant
2. Smear petroleum jelly over the cut stalks to make them waterproof
3. Leaf 1 will be untouched
   Leaf 2 has vaseline smeared on the top surface
   Leaf 3 has vaseline smeared on the bottom surface
   Leaf 4 has vaseline smeared on both surfaces
4. Measure the mass of each leaf
5. Using paper clips hang the leaves at intervals on a line of string held up by 2 retort stands
6. After a period of time, find the new mass of each leaf
7. Calculate the average loss of mass at each temperature

Question 37

How do you use the weight potometer to investigate the factors affecting the rate of water loss ( transpiration) by a plant shoot ?

Answer 37

1. Set up a weight potometer
2. Measure the mass of the container