Xylem and Phloem

Question 1

What is a vascular bundle?

Answer 1

• Vascular bundles transport water and solutes throughout a plant.
• Formed by xylem and phloem vessels

Question 2

What is the difference between monocots and dicots in the vascular bundle?

Answer 2

Dicots have a ring of vascular bundles close to the epidermis.
Monocots have vascular bundles distributed throughout the stem.

Question 3

What are the factors affecting transpiration?

Answer 3

• humidity
• temperature
• wind

Question 4

What is the xylem?

Answer 4

Transports water in a one-way stream from the roots to the leaves.
It comprises dead cells.
It is also in the centre of the plant’s vascular bundle.

Question 5

What is the phloem?

Answer 5

Transports sugars produced in photosynthesis bidirectionally.
It is composed of sieve cells surrounded by companion cells which produce ATP and assist in transporting sugars to sinks for storage.
The phloem is on the outside of the plant’s vascular bundle.

Question 6

Describe the process of transpiration

Answer 6

1. Water is absorbed from the soil into the roots. There is a higher solute concentration in the root cells than in the soil, so water moves into the roots by osmosis.
2. Water moves through the root cells until it reaches the xylem.
   Water is transported through the xylem to the leaves.
3. Water evaporates from the leaves through the stomata. This evaporation is called transpiration.
4. Water is pulled upwards to replace the water lost through the stomata. This is called the transpiration stream.

Question 7

What is transpiration?

Answer 7

Transpiration is the movement of water from the roots to the leaves.

Question 8

What are the two qualities of water that allow it to stick together and be pulled up the xylem against gravity?

Answer 8

Water is:
Cohesive - water molecules are attracted to each other due to hydrogen bonds
Adhesive - water molecules can adhere to the walls of the xylem due to the polarity of the water molecules and xylem walls

Question 9

What are the male parts of a flower?

Answer 9

STAMEN: anther + filament

Question 10

What are the female parts of a flower?

Answer 10

CARPEL/PISTIL: stigma + style + ovule

Question 11

Explain the translocation of sugars in the phloem of plants.

Answer 11

· Sugars are produced in leaves/ source cells through photosynthesis.
· Sugars are moved to companion cells by active transport
· Sugars are moved to the phloem by facilitated diffusion
· Water moves from the xylem to phloem by osmosis
· This generates a high pressure at source/ this generates a pressure gradient
· Movements of sugars from high pressure region to low pressure region (from source to sink)
· Sugars are moved into the companion cell by facilitated diffusion
· Sugars are moved from the companion cells to the sink cells via active transport
· Water moves back into the xylem via osmosis