The Transpiration Stream Flashcards

1
Q

What is adhesion?

A

The attraction between water molecules and the walls of the xylem vessels.

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2
Q

What is cohesion?

A

The attraction between water molecules caused by hydrogen bonds.

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3
Q

What is the transpiration stream?

A

The movement of water from the soil, through the plant, to the air surrounding the leaves.

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4
Q

What are root hair cells and what do they do?

A

Root hair cells are cells with a long extension that increases the surface area of the root.

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5
Q

Where are root hair cells found? (be specific)

A

On the epidermis of the roots of a plant

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6
Q

What do root hair cells do?

A

They absorb mineral ions and water from the soil.

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7
Q

How does water move in a root?

A

Down the concentration gradient across the root cortex to the endodermis of the vascular bundle.

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8
Q

What prevents water from travelling along the apoplast pathway all the way to the endodermis of the roots?

A

The casparian strip.

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9
Q

If the casparian strip blocks the apoplast pathway what pathway must the water then take?

A

Symplast

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10
Q

What is the movement of water in the root driven by?

A

An active process that occurs at the endodermis.

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11
Q

What is the endodermis?

A

The endodermis is a layer of cells surrounding the medulla and xylem. It is also known as a starch sheath as it contains starch.

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12
Q

What does the casparian strip do?

A

Blocks the apoplast pathway between the cortex and the medulla.

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13
Q

What does the casparian strip ensure?

A

That water and dissolved mineral ions have to pass into the cell cytoplasm through the membrane.

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14
Q

Mineral ions are actively pumped by what and where?

A

Transporter proteins in the plasma membrane.

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15
Q

Where are the mineral ions pumped to and from?

A

Pumped into the medulla from the cortex.

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16
Q

Why is the water potential of the medulla and xylem more negative?

A

So that water moves from the cortex cells to the medulla and xylem.

17
Q

Why can’t the water move back into the root?

A

The apoplast pathway blocks it from doing so.

18
Q

What is mass flow?

A

The movement of water and minerals in the same direction (up the stem).

19
Q

How far up a stem can root pressure push water?

A

A few metres

20
Q

How is root pressure formed?

A

By moving minerals into the medulla and xylem by active transport water moves into the root by osmosis. The pressure of the root builds up and forces water into the xylem pushing water up the xylem.

21
Q

Describe the transpiration pull.

A

As molecules of water evaporate whole chains of molecules are pulled up due to the cohesion between water molecules.

22
Q

How is tension created in the plant stem and what is it called?

A

The pull from above creates tension in columns of water. It is called the cohesion tension theory.

23
Q

What does the cohesion tension theory rely on?

A

An unbroken column of water.

24
Q

How does capillary action also assist the movement of water?

A

Water molecules also attract water molecules to the side of the xylem vessel. This is called adhesion.

25
Q

How are the xylem vessels adapted to assist the forces of attraction between the water molecules?

A

They are very narrow so these forces of attraction can pull the water up the sides of the vessel.

26
Q

how does water leave the leaf?

A

Water evaporates the cells lining the cavity immediately above the guard cell.

27
Q

What is the cavity immediately above the guard cells called?

A

The sub-stomatal air space.

28
Q

What happens to the water potential when water evaporates from the leaf?

A

It lowers.

29
Q

What are the two ways that water can enter the leaf?

A

By osmosis down the concentration gradient to level out the water potential, or via the apoplast pathway.