Plant Vascular Systems & Root Transport

Question 1

Why do plants require transport systems?

Answer 1

To ensure all cells of the plant receive sufficient nutrition.

Plants have a relatively small SA:V ratio but a high metabolic rate making a transport system necessary. Plants with specialised transport systems are known as vascular plants.

Question 2

Why is simple diffusion not viable in plants?

Answer 2

• large transport distance - substances cannot diffuse from exchange site to rest of the organism
• small SA:V - diffusion cannot be relied upon
• high metabolic rate - greater demand for oxygen and more waste is produced

Question 3

How are plants adapted to increase SA:V?

Answer 3

• plants have a branching body shape
• flat and thin leaves
• roots have root hairs

Question 4

What is a cotyledon?

Answer 4

Organs that act as food stores for the developing embryo

Question 5

What are dicotyledonous plants?

Answer 5

Plants which make seeds that contain two cotyledons

Question 6

What are the differences between monocots and dicots?

Answer 6

• 1 cotyledon vs 2
• fibrous roots vs tap roots
• scattered vascular systems vs ringed
• parallel leaf veins vs net-like leaf veins
• x3 flowers vs 4 / 5 flowers

Question 7

What the two different types of dicots?

Answer 7

• herbaceous dicots (non-woody stems)
• woody dicots

Question 8

What is a vascular bundle?

Answer 8

Xylem and phloem are the transport vessels and are arranged in vascular bundles.

Question 9

What is the cambium?

Answer 9

A layer of meristem cells between the xylem and phloem which is involved in the production of new xylem and phloem tissue.

Question 10

Where is the vascular bundle found in the roots?

Answer 10

It is found in the centre - the core is the xylem, edges of the core is phloem.

This helps the root withstand pulling strains as the plant transports water upwards and grows.

Question 11

Where is the vascular bundle found in the stem?

Answer 11

Bundles are located around the outside - xylem is on the inside (closer to the stem) to help support the plant. Phloem found on outside (closer to epidermis).

Question 12

Where is the vascular bundle found in the leaves?

Answer 12

They form the midrib and veins - they spread from the centre of the leaf in a parallel line. Xylem tissue is found on the upper side (closesr to upper epidermis). Phloem is on the lower side (closer to lower epidermis).

Question 13

What is the structure of xylem?

Answer 13

• dead tissue - no cytoplasm and nuclei
• hollow tubes
• cell wall spiralised lignin
• pits in walls (non-lignified areas where water moves in and out of vessels
• no end walls

Question 14

What is the function of the xylem?

Answer 14

Transports water and dissolved minerals upwards from root hair cells to leaves - called the transpiration stream.

Question 15

What is the function of the lignified cell walls?

Answer 15

Adds strength to withstand the hydrostatic pressure so the vessels do not collapse, impermeable to water.

Question 16

What is the function of xylem having no end plates?

Answer 16

Allows mass flow of water and solutes as cohesive and adhesive forces are not impeded.

Question 17

Why does the xylem vessel being dead help it’s function?

Answer 17

There is no protoplasm to impede the flow of water.

Question 18

Why does the xylem vessel’s small diameter help it’s function?

Answer 18

It helps prevent the water column from breaking and assists with capillary action.

Question 19

How is the phloem tissue structured?

Answer 19

• living tissue
• composed of elongated cells called phloem sieve tubes
• contain sieve plates (pores in the end walls) which transport assimilates
• sieve tubes have an associated companion cell (with a nucleus, organelles, enzymes)

Question 20

What is the function of the phloem vessels?

Answer 20

Transports assimilates (sucrose, amino acids) upwards and downwards - known as bidirectional transport

This is known as translation

Question 21

Why is water needed in plants?

Answer 21

• raw material for photosynthesis
• mineral ions / sugars transported in aqueous solution
• cooling effect (by transpiration)
• turgor pressure (hydrostatic skeleton)

Question 22

What are the adaptations of root hair cells?

Answer 22

• very thin surface layer - diffusion and osmosis can happen quickly
• microscopic size - penetrate between soil particles easily
• large SA:V
• concentration of solutes in the cytoplasm maintains water potential gradient between soil water and cell

Question 23

What are the three pathways taken by water to reach the xylem?

Answer 23

• symplast
• apoplast
• vacuolar

Question 24

What is the symplast pathway?

Answer 24

Water moves through the continuous cytoplasm of living plant cells by osmosis through the plasmodesmata.

Each cell further away from the roots has a lower water potential, meaning water is drawn through the plant.

Question 25

What is the plasmodesmata?

Answer 25

A fine strand of cytoplasm linking adjacent cells.

Question 26

What is the apoplast pathway?

Answer 26

The movement of water through the cell wall and intracellular spaces - cohesive and tension forces acting on the cell walls pull the water up the plant.

The apoplast pathway provides the fastest movement of water.

Question 27

How does water move in the apoplast pathway?

Answer 27

Water moves by diffusion, as it is not crossing a partially permeable membrane.

Question 28

What is the vacuolar pathway?

Answer 28

The same as the symplast pathway, except water moves through the cell’s vacuoles as well as the cytoplasm (through the tonoplast).

It is the slowest route for water transport.

Question 29

What is the casparian strip?

Answer 29

The casparian strip is an impermeable layer of suberin - a waxy material.

Question 30

What is the endodermis?

Answer 30

A continuous cylinder of endodermal cells which surround the central vascular tissue.

Question 31

What happens when water reaches the endodermis from the roots?

Answer 31

It’s path is blocked by the casparian strip - waterproof and impermeable due to the layer of suberin.

The water in the apoplast pathway is forced to move through the cell surface membrane, through the symplast pathway.

Question 32

Why is the casparian strip useful to plants?

Answer 32

The selectively permeable membrane of the cells can control what enters the xylem - meaning toxic solutes can be removed, and only necessary water molecules / mineral ions can enter.

The casparian strip also contributes to increasing root pressure.