transport system in plants

Question 1

what is the function of the phloem?

Answer 1

the phloem conducts manufactured food from the green parts of the plant, especially the leaves, to all parts of the plant via translocation.

Question 2

what is the function of the xylem?

Answer 2

1. conducts water and dissolved mineral salts from the roots to all parts of the plant
2. provides mechanical support for the plant

Question 3

why did the cell shrink when it was places in a sucrose solution?

Answer 3

the cell sap in the plant cell had a higher water potential than the sucrose solution. Thus, there is a net movement of water molecules from the cell to the sucrose solution through the partially permeable cell surface membrane, down a water potential gradient by osmosis. Therefore, the plant cell becomes plasmolysed and flaccid.

Question 4

What are some structural adaptations of root hair cells?

Answer 4

1. The long and narrow extension increases the root hair cell’s surface area to volume ratio, allowing for faster absorption of mineral salts and water in the soil.
2. The numerous mitochondria in the root hair cell can carry out aerobic respiration, where oxygen is used to oxidise food molecules to release a large amount of energy. This enables the absorption of mineral salts against the concentration gradient from the soil by active transport.
3. the cell sap in the root hair cell is more concentrated than the soil solution due to the presence of sugars, amino acids, and mineral salt. This causes the root hair cell to have a lower water potential than the soil solution. Hence, water enters the root hair cell through osmosis down a water potential gradient.

Question 5

How do mineral salts enter the root hair cell from the soil?

Answer 5

The concentration of mineral salts in the soil is lower than that of the RHC. Thus, energy is required to move the mineral salts from the soil to the cell across the partially permeable cell surface membrane, against the concentration gradient by active transport.

Question 6

What is the definition of transpiration?

Answer 6

The loss of water vapour from a plant, mainly through the stomata of the leaves.

Question 7

How does transpiration pull work?

Answer 7

As water vapour is lost through the stomata of the leaves, it creates a suction force, known as transpiration pull, pulling the water up the xylem vessels.

Question 8

what are some adaptations of the xylem?

Answer 8

1. it is a long and hollow tube that extends from the roots to the leaves with no cross-wall. This provides minimal obstruction for water flow through the lumen.
2. the cellulose cell wall is thickened by lignin, which strengthens the vessel and prevents the tube from collapsing.

Question 9

Why do plants need water?

Answer 9

• Water is essential for
  photosynthesis.
• Water is the solvent in which chemical reactions take place.
• Water is needed for the transport of mineral salts up the xylem vessel OR
• Water is needed for the transport of food substances from the leaves to
  other parts of the plant through the phloem.
• Water helps keep plant cells turgid and plant upright

Question 10

What effect does the removal of the xylem vessel have on the leaf?

Answer 10

The removal of the xylem vessel prevents water from reaching the leaf. When the rate of transpiration exceeds the rate of which water reaches the leaf, the leaf’s plant cells lose their turgor pressure and become flaccid via plasmolysis. This causes the leaf to wilt.