Plant Transport

Question 1

What is the primary function of root hairs in plants?

Answer 1

Provide a large surface area for water absorption

Root hairs are freely permeable and enhance the plant’s ability to absorb water from the soil.

Question 2

What is the apoplast route in water absorption?

Answer 2

Water travels through the cell walls or spaces between cells, drawn by the transpiration stream

This route allows water to move without crossing cell membranes.

Question 3

How does water cross the plasma membrane in plants?

Answer 3

By osmosis

Osmosis is the movement of water across a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration.

Question 4

What is the symplast route for water movement?

Answer 4

Water moves through the cytoplasm of cells via plasmodesmata

Plasmodesmata are microscopic channels that allow for transport and communication between plant cells.

Question 5

What is the vacuolar pathway?

Answer 5

Water travels through the cell vacuoles

This pathway is another route for water movement within plant cells, utilizing the large central vacuoles.

Question 6

What surrounds the pericycle and contains vascular tissue in a dicotyledon root?

Answer 6

The endodermis

The endodermis regulates the flow of water and nutrients into the vascular tissue.

Question 7

What is the function of the Casparian band in the endodermis?

Answer 7

Blocks the apoplast route and forces water to cross the plasma membrane

The Casparian band is made of water-proof suberin, which ensures selective uptake of nutrients.

Question 8

What is root pressure?

Answer 8

Positive hydrostatic pressure inside the xylem that forces water upwards

Root pressure is generated when water potential in the xylem is lowered, causing water to be drawn through the endodermis.

Question 9

What types of plants are classified based on their water supply structure?

Answer 9

Hydrophytes, mesophytes, xerophytes

This classification is based on the plant’s adaptations to different water availability conditions.

Question 10

What is a characteristic of hydrophytes?

Answer 10

Roots submerged in water with floating leaves

Hydrophytes have little need for support or transport tissues due to their aquatic environment. They also have little or no cuticle and stomata only on the upper surface of the leaves. Large air spaces.

Question 11

What adaptations do xerophytes have for water conservation?

Answer 11

Modified structures to prevent excessive water loss

Examples include thick cuticles, sunken stomata, and specialized leaf shapes.

Question 12

What is the main function of phloem in plants?

Answer 12

Transport products of photosynthesis in soluble form (sucrose)

Phloem consists of sieve tubes and companion cells that facilitate the movement of nutrients.

Question 13

What is the mass flow hypothesis?

Answer 13

Suggests a passive flow of sucrose from source to sink

This hypothesis explains the movement of nutrients but does not account for all observations in plant transport.

Question 14

What is the role of stomatal pores in transpiration?

Answer 14

Alter water loss through transpiration

The opening and closing of stomata regulate gas exchange and water loss in plants.

Question 15

How does transpiration affect water movement in plants?

Answer 15

Creates tension that pulls water up through the xylem

The loss of water from leaves generates a negative pressure that helps transport water from roots to leaves.

Question 16

What are the two routes for nutrient uptake at the endodermis?

Answer 16

Apoplast and symplast routes

Nutrients can enter the plant through passive diffusion or active transport mechanisms.

Question 17

What is the composition of xylem tissue?

Answer 17

Dead, lignified tracheids and vessels, supporting fibers, and living parenchyma

Xylem is primarily responsible for water transport and structural support in plants.

Question 18

What are characteristics of mesophytes?

Answer 18

Plants of temperate regions and flourish in habitats with adequate water supply.

They need to survive unfavourable times by shedding their leaves, surviving underground or as dormant seeds.

Question 19

How and where are the products of transports of photosynthesis transported?

Answer 19

They’re transported in soluble form (Surcose) to all parts of the plant in the phloem.

Question 20

What demonstrated translocation being a rapid process?

Answer 20

The technique of radioactive tracing combined with using aphid mouthparts

Question 21

How wwas it showed that Sucros is transported bi-directionally to sinks?

Answer 21

Radioisotope labelling using CO2 combined with autoradiography.

Question 22

How are the columns of water in the xylem held up?

Answer 22

By cohesive force between H2O molecules.

And Adhesive forces between the H2O molecules and the hydrophilic lining of the xylem vessels.

Question 23

What is Transpiration?

Answer 23

The loss of water from the leaves which gives rise to the transpiration stream.

Continued removal of H2O molecules from the top of the xylem vessels results in a tension casuing a pull in the xylem column.

Question 24

What are 3 external factors which affect the rate of transpiration?

Answer 24

Temperature
Humdidity
Air Movement

Question 25

How is the water potential lowered to generate Root Pressure in the Xylem? (5 points)

Answer 25

N usually enters the plant as nitrate ions which diffuse along the conc. gradient into the apoplast stream but enter symplast by active transport and then flow via plasodesmata in cytoplasmic stream. ## Footnote At the endodermis, ions must be actively taken up to by-pass the Casparian band which allows the plant to selectively take up the ions at this point.