Transpiration And Movement Of Water Throuhg The Roots

Question 1

Where do root hair cells grow from

Answer 1

The epidermis of the root

Question 2

How does water move into root hair cells

Answer 2

By osmosis

Question 3

Adaptations of roots hair cells for rapid osmosis (1)

Answer 3

Densely packed root hair cells massively increase the SA:VOL ratio of the root.

The surface of the root hair consists only of the cell wall and the cell membrane, making the surface extremely thin increasing the rate of osmosis.

Question 4

what is a feature of the soil

Answer 4

The water in the soil contains dissolved mineral ions e.g magnesium which plants use to make chlorophyll (however the concentration of these are lower in the soil than the root hair)

Question 5

Adaptations of roots hair cells for rapid osmosis (2)

Answer 5

Root hair cells use active transport to move these mineral ions into the cell

The root hair cells also contain other dissolved compounds like sugars and because the water potential inside the root hair cell is lower than in the soil, water moves into it down a water potential gradient.

Question 6

What is the movement of water from the soil into the xylem

Answer 6

It moves from the root hair cells through the cortex to the xylem

Question 7

What is the simplest pathway

Answer 7

Water moves form the cytoplasm of one cell to the cytoplasm of an adjacent cell. The water moves through the plasmosdesmata linking the cells

Question 8

What is the simplest pathway driven by (1)

Answer 8

The water potential gradient between the root hair cells and the xylem, where water continuously moves into the root hair cells by osmosis from the soil. Making the water potential of the root hair cells greater than the cortex cell.

Question 9

What is the simplest pathway driven by (2)

Answer 9

In the xylem the water potential is relatively low, so water moves by osmosis across the cortex down the water potential gradient.

Question 10

What is a feature of the symplast pathway

Answer 10

The pathway is relatively slow as the pathway for water in the cytoplasm is obstructed by organelles.

Question 11

What is the apoplast pathway

Answer 11

Water moves within the cell walls and the spaces between the cells.

Question 12

What allows water to move within the cell walls

Answer 12

The cellulose cell walls have a relatively open structure allowing for water to move easily between the cellulose fibres.

Question 13

What is a feature of water and how does affect the apoplast pathway

Answer 13

Water molecules are attracted to each other (cohesion), as they can form hydrogen bonds to each other. This means that as water moves into the xylem and is carried away, more water moves along the apoplast pathway.

Question 14

What is a comparison between the apoplast pathway and symplast pathway

Answer 14

The apoplast pathway offers much less resistance to water flow than the symplast pathway.

Question 15

Before water can pass into the xylem what must it pass through

Answer 15

A layer of cells called the endodermis.

Question 16

What is a feature of the cells in the endodermis

Answer 16

They have an unusual feature and a band of water proof material called Suberin runs around the cell walls. Called the Casparian strip.

Question 17

What does the Casparian strip do

Answer 17

Water can no longer move through the apoplast pathway, instead the water passes through the cell membrane and into the cytoplasm becoming part of the symplast pathway.

Question 18

By passing all the water through the cytoplasm what does it allow

Answer 18

It allows the cell membrane to control which substances can enter the xylem as it is selectively permeable.

Question 19

What happens to that weather once inside the vascular bundle

Answer 19

It then returns to the apoplast pathway to enter the xylem int self and move up the plant.

Question 20

What do cells in the endodermis do

Answer 20

They use active transport to pump mineral ions into the xylem, lowering the water potential of the xylem triggering water to move into the xylem vessels by osmosis. This is called root pressure.

Question 21

Because root pressure is an active process what can stop it

Answer 21

It requires respiration, so if we inhibit respiration then root pressure stops. It will also stop if we prevent aerobic respiration by excluding oxygen.

Question 22

What is Gluttation

Answer 22

The xylem sap is forced out of special pores in the ends of leaves in some condition

Question 23

Where is the main site of photosynthesis in the leaf

Answer 23

In the palisade mesophyll

Question 24

How does water pass into the leaf

Answer 24

Through the xylem vessels in the vascular bundle

Question 25

What is the surface of the leaf covered in and what is its purpose

Answer 25

A waterproof layer called the waxy cuticle and its job is to reduce water loss from the surface of the leaf by evaporation.

Question 26

What is CO2 required for and how does it enter the lead

Answer 26

It is also required for photosynthesis And it diffuses into the leaf from the external air

Question 27

What is produced by photosynthesis and how does it move out of the leaf

Answer 27

Oxygen is produced which diffuses out of the leaf

Question 28

What is present on the lower surface of a leaf

Answer 28

Thousands of tiny pores called stomata When the plants photosynthesises the stomata open allowing CO2 into the lead and O2 to diffuse out.

Question 29

What are the surface of the mesophyll cells in the leaf covered with and what does it do

Answer 29

A thin layer of water and the water evaporates from the surface of the cells. As a result the internal leaf spaces contain high concentrations of water vapour.

Question 30

Where is the concentration gradient in the lead

Answer 30

The level of water vapour in the external air is relatively low, so when the stomata are open, the water vapour diffuses out of the leaf to the external air.

Question 31

What is transpiration

Answer 31

The evaporation followed by the diffusion of water out of the leaf.

Question 32

What occurs because of the continuous evaporation from their surface

Answer 32

The water potential of the cells decreases Causing the water to move by osmosis from adjacent cells (by the symplast and apoplast pathway) This lowers the water potential of these cells and water moves into them. At some point it reaches the xylem and water passes out of the xylem to adjacent cells.

Question 33

What is tension

Answer 33

When transpiration is taking place water is continually moving out of the xylem vessels and this is called tension.

Question 34

What is the transpiration stream

Answer 34

The movement of water from the roots, up the xylem and out of the leaf is called the transpiration stream.

Question 35

What is adhesion

Answer 35

Water molecules can form hydrogen bonds to molecules in the xylem vessels walls - adhesion.

Question 36

Because of cohesion and adhesion what occurs in plants

Answer 36

Because of cohesion and adhesion water can move up very thing tubes against the force of gravity - called capillary action.

Question 37

What happened when water is removed from the top of xylem vessels due to transpiration and what is this referred to

Answer 37

More water moves up the xylem vessels by capillary action to take its place. And is referred to as transpiration pull.

Question 38

What does the combined effect of transpiration pull and cohesion and adhesion do. And what is this process called.

Answer 38

The water is drawn into the roots, it then moves up the stem and passes out of the leaves. The whole process is the cohesion-tension theory.

Question 39

What is the evidence that supports the cohesion-tension theory

Answer 39

1) If a plant stem is cut then air is sucked into the xylem —> indicating that xylem vessels are under tension 2) However, the air prevents cohesion between molecules, so water movement stops 3) If you measure the diameter of a tree trunk it reduces in diameter, when transpiration is at its maximum supporting the idea that transpiration pull is generated by a negative pressure or tension in the xylem.

Question 40

What is one stomata

Answer 40

It is referred to as a stoma

Question 41

What is each stoma surrounded by

Answer 41

2 guard cells of which the shape determines whether it is closed or open.

Question 42

What are the adaptations

Answer 42

The cellulose cell wall on the inner side of the guard cell is thicker than the rest of the cell. Some of the cellulose microfibrils are arranged in ring shapes.

Question 43

What occurs during photosynthesis

Answer 43

During photosynthesis plants absorb light energy to produce sugar. And in order for this to take place, CO2 must diffuse into the leaf through the stomata.

Question 44

What happens in the light conditions to the guard cells (1)

Answer 44

Light conditions trigger solutes such as potassium ions to be transferred into the guard cells. —> Lowering the water potential of the interior of the guard cell.

Question 45

What happens in the light conditions to the guard cells (2)

Answer 45

Water moves into the guard cells by osmosis causing the guard cells to swell (turgid). And as water enters the guard cells, the rings of cellulose prevent the guard cells from expanding width wise and instead expand lengthwise.

Question 46

What happens in the light conditions to the guard cells (3)

Answer 46

The thickened cell walls prevent the guard cells from expanding evenly forcing them to develop a curved shape. —> the curved shape allows stoma to open between the guard cells.

Question 47

What happens when the stomach are open, so what happens at night time

Answer 47

When stoma are open water vapour can diffuse out of the leaf and this loss of water can cause the plant to dry out. So at night time when plants don’t carry out photosynthesis they close to reduce water loss.

Question 48

In droughts what can occur

Answer 48

In certain conditions the level of water in the soil can foil. So the roots and hormonal signals to the leaves, triggering guard cells to loose turgidity causing the stomata to close. —> reducing water loss from the plant

Question 49

What happens when the stomata closes

Answer 49

Closing stomata prevents the plant carrying out photosynthesis

Question 50

Draw the graph for light intensity and the rate of transpiration

Answer 50

For transpiration to take place the stomata must be open. As light intensity increases so does the rate of transpiration As increasing light intensity increases the number of open stomata, allowing more water vapour to diffuse out the leaf.

Question 51

What is required for transpiration to take place

Answer 51

the stomata must be open To allow CO2 to diffuse into the leaf and take part in photosynthesis.

Question 52

How does light intensity affect rate of transpiration

Answer 52

As light intensity increases so does the rate of transpiration As increasing light intensity increases the number of open stomata, allowing more water vapour to diffuse out the leaf. However, at high light intensity the rate of transpiration no longer increases as all of the stomata are open.

Question 53

How does water vapour move out of the leaf

Answer 53

Water vapour diffuses out of the leaf down a concentration gradient. As the concentration of water outside the leaf is lower than inside.

Question 54

What relatively

Answer 54

Is the concentration of water vapour in the air as a percentage of the maximum possible

Question 55

What occurs if relative humidity increases

Answer 55

There is a smaller concentration gradient between the inside of the leaf and the outside. —> so increasing the relative humidity outside the leaf reduces the rate of transpiration

Question 56

How is the rate of transpiration affected by temperature

Answer 56

It is increased by temperature, as the water molecules have more kinetic energy. This means there is a greater rate of evaporation of water during the internal spaces of the leaf. At higher temperatures the relative humidity too of the external air decreases. Due to these two effects, the concentration gradient of water vapour between the inside of the leaf and the external air increases at higher temperatures, increasing the rate of transpiration.

Question 57

What happens when water vapour moves out of the stomata and how does this affect the rate of transpiration

Answer 57

When water vapour moves out of the stomata during transpiration, the water vapour can build up around the external surface of the leaf reducing the concentration gradient for water vapour, between the inside of the leaf and outside.

Question 58

What does air movement do

Answer 58

It removes the water vapour as it diffuses out of the leaf, increasing the concentration gradient of water vapour.

Question 59

What can the rate of transpiration also be affected by

Answer 59

Level of water in the soil