transport in plants

What are water and organic substances transported by in the plant?

The xylem and the phloem

What are the xylem and phloem collectively described as?

The vascular bundle

What is the organisation of the xylem like in the roots?

The xylem is found at the center of the root, often resembling a star shape with between 3 and 6 spokes/points.

What is the organisation of phloem in the roots?

It is found in between each of the points of the star shape.

What does the organisation of the vascular bundle look like in roots?

Where is the xylem found in the stem of the plant?

Found on the inner edge of each bundle, closest to the center of the stem

Where is the phloem found in the stem of the plant?

Found in the outer edge of each bundle, closest to the surface of the stem.

What is found in between the xylem and phloem in the stem?

A layer of cambium.

What is cambium?

Is a meristematic tissue, containing actively dividing pluripotent cells.

In the leaf how is the vascular bundle organised?

Runs down the center of the leaf as a vein and contains both xylem and phloem tissues.

Where is xylem found in the leaf?

xylem is towards the top of the leaf in each bundle.

Where is phloem found in the leaf?

Phloem is found towards the bottom of the leaf.

What two key cells does the phloem tissue contain?

1. sieve tube elements

2. companion cells

What are sieve tube elements?

• living cells

• contain no nucleus

• contain few organelles

What are companion cells?

• provide ATP required for active transport of organic substances

What are xylem cells?

dead and hollow cells

How do xylem cells create a continuous hollow column?

They do not contain any organelles or end walls, as a result they stack on top of each other to make a continuous hollow column, ideal for transporting water and mineral ions,

What is the name of the chemical that the xylem wall is strengthened with?

Lignin

How does water get transported into the plant?

Water is absorbed into the plants through the root hair cells by osmosis

How are root hair cells adapted to maximise osmosis?

They have thin walls and a large surface area

How is water transported to the xylem?

Once he water has moved into the root hair cell by osmosis, it then travels to the xylem by either the symplast pathway or apoplast pathway.

What is the symplast pathway?

• Through the cytoplasm of the cell

• the water moves from cell to cell, towards the xylem, by osmosis through the cytoplasm and through gaps in each cell wall called plasmodesmata

Why is the water able to move by osmosis when being transported to the xylem?

Each successive cells cytoplasm has a lower water potential.

What is the Apoplast pathway?

• It is through the cell walls

• water can enter the cell wall and move due to the cohesive force of water.

• The water molecules stick together, forming a continuous stream of water which move toward the xylem.

• This pathway transports the water faster, as there is little resistance to the water in the cell wall.

What type of plants exchange gases through the stomata?

Dicotyledonous plants

What are stomata?

Stomata are tiny pores mainly on leaves. These pores can open or close, determined by the guard cells surrounding them.

What does the mechanism of stomata help to do?

Helps to prevent excessive water loss by evaporation.

What are Xerophytes?

They are plants with adaptations to reduce water loss and are thus found in locations with minimal water e.g the dessert

Where are Marram grass found? and why is there limited water?

They are found on sand dunes, near the ocean. However limited water due to the sand being so porous.

What are some adaptations of Xerophytes?

• Curled leaves to trap moisture to increase local humidity.

• hairs to trap moisture to increase local humidity

• sunken stomata too trap moisture to increase local humidity

• Thicker cuticle to reduce evaporation

• Longer root network to reach more water

What are hydrophytes?

Plats which live in or on water, so require adaptations to survive in an excess of water.

What is an example of a hydrophyte?

lilies, which grow on the surface of water

What are some adaptations that hydrophytes have to ensure that no additional water is retained in the plant and efficient water loss?

• short roots

• very thin to no waxy cuticles

• stomata being permanently open and on the top surface of the leaf.

What adaptations do hydrophytes have to ensure enough light is still absorbed for photosynthesis?

• Leaves being large

• leaves being wide

• being on the surface of the water

What is transpiration?

The loss of water vapour from the stomata by evaporation.

How many conditions is the rate of transpiration effected by?

Four

How can transpiration be measured?

Using a potometer

What are the 4 factors which affect transpiration?

• Light intensity

• Temperature

• Humidity

• Wind

What affect does light intensity have on transpiration?

• Positive correlation

• More light causes more stomata to open = larger surface area for evaporation

What affect does temperature have on transpiration?

• Positive correlation

• More heat means more kinetic energy, faster moving molecules and thus, more evaporation.

What affect does humidity have on transpiration?

• Negative correlation

• More water vapor in the air will make the water potential more positive outside of the leaf, therefore reduces the water potential gradient

What affect does the wind have on transpiration?

• positive correlation

• More wind will blow away humid air containing water vapour, thus maintaining the water potential gradient.

How is it possible that water moves up a plant from the roots against gravity?

• cohesion-tension theory

• cohesion

• adhesion

• root pressure

Where is there more of a negative water potential?

The top of the plant

Where is there more of a positive water potential?

The bottom of the plant

How is cohesion created?

• Water is dipolar(slight negative oxygen and slight positive hydrogens)

• This enables hydrogen bonds to form between the hydrogen and oxygen of different water molecules

What is cohesion?

When the hydrogen bond holds together water molecules- they stick together.

How does water travel up the xylem due to cohesion?

Travels up the xylem as a continuous water column

What is adhesion?

When water sticks to other molecules. Water adheres to the xylem walls

What is the relationship between how narrow the xylem is and the impact of capillarity?

The narrower the xylem the bigger the impact of capillarity

What do water molecules adhere to?

The lignin in xylem walls

What is root pressure?

As water moves into the roots by osmosis it increases the volume of liquid inside the root and therefore the pressure inside the root increases.

What does this increase in the roots do to water?

Forces water above it upwards (positive pressure)

What is the cohesion-tension theory?

cohesion + adhesion + root pressure = cohesion-tension theory

What is step 1 for the process of water moving up the xylem?

1. water evaporates out of the stomata on leaves. This loss in water volume creates a lower pressure

What is step 2 in the process of movement of water up the xylem?

2. When this water is lost by transpiration more water is pulled up the xylem to replace it (moves due to negative pressure)

What is step 3 in the process of movement of water up the xylem?

3. Due to the hydrogen bonds between water molecules, they are cohesive (stuck together). This creates a column of water within the xylem

What is step 4 of the process of movement of water up the xylem?

4. Water molecules also adhere (stick) to the walls of the xylem. This helps to pull the water column upwards.

What is step 5 in the process of movement of water up the xylem?

5. As this column of water is pulled up the xylem it creates tension, pulling the xylem in to become narrower.

What do all cells need in order to respire?

sugar

What is the function of the leaves?

Transports organic substances to all cells in a plant via the PHLOEM.

What is the equation to get glucose and oxygen?

co2 + water = glucose + oxygen

What is Translocation?

The transport of organic substances in a plant.

What does translocation require?

It requires energy- active (co-transport)

Where does translocation take place?

source —> sink

What is the source of production?

The leaves

What is the sink?

The site where organic substances such as sucrose and amino acids are used up in respiring tissues.

What lowers the water potential of the source cell?

Sucrose.

Why does the sink cell- respiring cell, have a more positive water potential?

Because the respiring cell is using up sucrose

How does water leave the sink cell?

Water leaves the sink cell by osmosis.

What is step 1 of sucrose transporting from the source to the sieve tube element? (translocation 1)

1. Active transport of hydrogen ions occurs from the companion cell into the photosynthesising cells of the source.

What is step 2 of sucrose transporting from the source to the sieve tube element? (translocation 1)

2. A concentration gradient is created and therefore the hydrogen ions move down their concentration gradient via carrier proteins back into the companion cells.

What is step 3 of sucrose transporting from the source to the sieve tube element? (translocation 1)

3. co-transport of sucrose with the hydrogen ions occurs via protein co-transporters to transport the sucrose into the companion cells. Sucrose then diffuses through plasmodesmata into the sieve tube elements

What is step 1 for the movement of sucrose within the phloem sieve tube element ?( translocation 2)

The increase of sucrose in the sieve tube element lowers the water potential.

What is step 2 for the movement of sucrose within the phloem sieve tube element? ( translocation 2)

Water enters the sieve tube elements from the surrounding xylem vessels via osmosis

What is step 3 for the movement of sucrose within the phloem sieve tube element? ( translocation 2)

The increase is water volume in the sieve tube element increase the hydrostatic pressure causing the liquid to be forced towards the sink.

What is step 1 for transport of sucrose to the sink- respiring cells? (translocation 3)

Sucrose is used in respiration at the sink, or stored as insoluble starch.

What is step 2 for transport of sucrose to the sink-respiring cells ? (translocation 3)

More sucrose is actively transported into the sink cell, which causes the water potential to decrease.

What is step 3 for transport of sucrose into the sink cell-respiring cells? (translocation 3)

This results in osmosis of water from the sieve tube element into the sink cell ( some water also returns to the xylem)

What is step 4 for transport of sucrose into the sink-respiring cells? (translocation 3)

The removal of water decreases the volume in the sieve tube element and therefore the hydrostatic pressure decreases

What is step 5 for transport of sucrose into the sink-respiring cells? (translocation 3)

Movement of soluble organic substances is due to the difference in hydrostatic pressure between the source and sink end of the sieve tube element.