Plant Transport

Question 1

What is the structure of the Xylem?

Answer 1

• They are hollow cylindrical tubes that pull up water from the roots
• Xylem is made of dead cells (only the cell wall remains)
• Walls strengthened with cellulose and waterproofed with lignin

Question 2

What is the structure of the Phloem?

Answer 2

• Elongated tubular cells with walls between them
• Phloem cells are living
• Sieve structures between each companion cell

Question 3

What is the purpose of the Xylem?

Answer 3

To transport water and mineral ions upwards through the plant to the leaves

Question 4

What is the purpose of the Phloem?

Answer 4

To transport Sugars (as well as hormones, amino acids and lipids) up and down the plant

Question 5

In which form is sugar in when transported in the phloem?

Answer 5

Sucrose

Question 6

Compare the Xylem and the Phloem

Answer 6

Xylem
- Made of dead cell tissue
- Transports mineral ions and water
- Hollow tube made of dead cell walls strengthened with lignin for waterproofing
- Transports up

Phloem
- Made of living companion cells
- Transports sugars, hormones and amino acids
- Has sieves between cells
- Transports up/down

Question 7

In what ways is the Root Hair Cell adapted to its purpose?

Answer 7

• Finger-like protrusion to maximise surface area
• Large vacuole to mantain lower water potential in the inside of the cell than outside and to store mineral ions, sugars and water

Question 8

What adaptations do plants have to surivive in dry conditions?

Answer 8

• Waxy cuticle and stomata to reduce loss of water ions
• Shallower roots to collect more water at the surface of the earth where it is more humid

Question 8

Why do plants need water?

Answer 8

• Cooling (done via transpiration)
• Photosynthesis
• Support system (makes cells turgid to prevent the plant from wilting)
• Movement of minerals

Question 9

Describe the process of the movement of water from the soil to the xylem

Answer 9

• The soil has a higher water potential than the root hair cell
• The water moves down the water potential gradient through the semi.permeable cell membrane
• The water then moves into the cells of cortex where the water potentials get evemn lower
• Eventually, the water gets to the Xylem which has the lowest water potential

Question 10

Describe the process of the movement of mineral ions from the soil to the xylem

Answer 10

• The soil a lower concentration of ions than the root hair cell
• The ions are carried by the carrier protein against the concentration gradient, which requires energy
• The root passes the ions to the next cells of cortex by active transport as well
• This is repeated until the ions reach the xylem

Question 11

Describe the movement of water in a plant

Answer 11

• Water evaporates from the internal leaf cells through the stomata
• Water passes from the xylem vessels to leaf cells due to osmosis
• This pulls the water in that vessel upwards by a very small amount.
• Water enters xylem from root tissue to replace water which has moved upwards.
• Water enters root hai cells by osmosis to replace water which has entered the xylem

Question 12

Describe transpiration pull

Answer 12

• As water moves out of the spongy mesophyll and diffies out tof the leaf through the stomata, it causes a change – Water potential gradient changes and water moves from the xylem into the spongy mesophyll
• Cohesion between water molecules causes them to follow and move upward

Question 13

What is Cohesion?

Answer 13

The intermolecular forces between water molecules that cause them to stick together and follow eachother as water moves upward in the xylem

Question 14

What is Adhesion?

Answer 14

The intermolecular forces between the water and the celluslose in the cell wall of the xylem that causes attraction between them when transpiration pull is weak. This prevents water from moving back down.

This force is overcome when transpiration pull is strong enough.

Question 15

dfrd

Describe transpiration

Answer 15

• Water passes from xylem to mesophyll cells by osmosis down the water potential gradient.
• Water evaporates (liquid to gas) from the surfaces of mesophyll cells to the air spaces in the leaf down water concentration gradient
• Water vapour diffuses down water concentration gradient from the air spaces in the leaf to the outside air through the stomata

Question 16

What are the 4 factors that affect the rate of Transpiration?

Answer 16

• Temperature
• Humidity
• Light Intensity
• Wind

Question 17

Def. Translocation

Answer 17

The movement of sucrose and amino acids in the phloem from regions of production (e.g. leaf) to regions of storage, aka ‘source’, to regions of utilisation in respiration and growth, aka ‘sink’

Question 18

What is a Source in Translocation?

Answer 18

Regions of the plant where materials such as sucrose is made

Question 19

What is a Sink in Translocation?

Answer 19

Regions of the plant where materials such as sucrose is stored or used

Question 20

Describe the process of translocation

Answer 20

1. Photosynthesis produces glucose in the leaves (the source), which is converted into sucrose and then actively transported into the phloem tube
2. Water travels into the phloem tube by osmosis down a water potential gradient, generating pressure which forces the sucrose away from the source (mass flow)
3. Sucrose enters growing or storage tissues (the sink) by active transport
4. Water flows back into the xylem by osmosis down a water potential gradient

Question 21

Explain how parts of a plant can serve as sources and sinks at different parts of their lives?

Answer 21

The leaf, which is normally a source, which sends sucrose down to the root hair cells for storage as starch, which is a sink. However, during winter or spring, the roles are reversed as the root hair cells send back sucrose they were storing for the growth of new plant parts.