C2- Adaptations for transport in plants

Question 1

Describe the distribution of vascular tissue in the roots and why it is as it is.

Answer 1

• the xylem is central and star shaped
• the phloem is between groups of xylem cells
• the arrangement resists vertical stretches and anchors the plant in the soil

Question 2

Describe the distribution of vascular tissue in stems and why it is as it is.

Answer 2

• vascular bundles are in a ring at the periphery
• phloem are towards the outside
• xylem are towards the centre
• this gives flexible support and resists bending

Question 3

Describe the structure of a plant root from the outside, in.

Answer 3

• root hair
• epidermis
• cortex
• endodermis
• pericycle
• phloem
• xylem

Question 4

Describe the structure of a plant stem from the outside, in.

Answer 4

• epidermis
• collenchyma
• cortex
• vascular bundle
• medulla

The vascular bundle is composed of the following…

• fibres
• phloem
• xylem

Question 5

Describe the distribution of vascular tissue in the leaves of plants and why it is as it is.

Answer 5

• the vascular tissue is in the midrib
• it is also in a network of veins
• this gives flexible strength and resistance to tearing

Question 6

Describe the structure of a leaf.

Answer 6

• adaxial surface- facing the central axis of the plant
• abaxial surface– facing away from the central axis of the plant
• vascular bundles in leaf vein- located in the thinner part of the leaf
• collenchyma surrounds the compact parenchyma that is around the vascular bundle in the midrib
• the vascular bundle in the midrib is composed of xylem and phloem

Question 7

What are the two main cell types in xylem?

Answer 7

tracheids and vessels

Question 8

What plants do tracheids occur in?

Answer 8

• ferns
• conifers
• angiosperms (flowering plants)

Question 9

What is the structure of tracheids?

Answer 9

They’re spindle-shaped so water takes a twisting rather than straight path up a plant.

Question 10

Why can moses not grow as tall as other plants?

Answer 10

They have non-conducting tissue and so are poor at transporting water.

Question 11

What plants do vessels occur in?

Answer 11

angiosperms (flowering plants)

Question 12

Describe the features of vessels.

Answer 12

• occur only in angiosperms
• lignin builds up in their cell walls, the contents dies leaving empty space called lumen
• the tissue develops and the end walls of the cells break down so that a long hollow tube forms that water can move through
• lignin is laid down in a characteristic spiral pattern

Question 13

How would you identify the xylem from a sample?

Answer 13

The xylem stains red so can be identified under a microscope once stained.

Question 14

What are the functions of the xylem?

Answer 14

• to transport water and dissolved minerals

- providing mechanical strength and support

Question 15

What increases the surface area of the roots, their uptake of water and why?

Answer 15

The root hair cells which have a thin cell wall.

Question 16

How does water move from the soil to the root hair cell?

Answer 16

By osmosis down the water potential gradient. This is due to the vacuole of the root hair cell containing a concentrated solution of solutes and having a lower more negative water potential.

Question 17

Name the three pathways water can take through the root cortex to get to the xylem.

Answer 17

• apoplast pathways
• symplast pathway
• vacuolar pathway

Question 18

Describe the apoplast pathway.

Answer 18

• water moves in the cell walls

- cellulose fibres in the cell walls are separated by spaces through which water moves

Question 19

Describe the symplast pathway.

Answer 19

• water moves through cytoplasm and plasmodesmata
• plasmodesmata are strands of cytoplasm through pits in the cell wall joining adjacent cells so the symplast pathway is a continual path across the root cortex

Question 20

Describe the vacuolar pathway.

Answer 20

Water moves from vacuole to vacuole.

Question 21

What pathway across the root cortex is fastest?

Answer 21

The apoplast pathway.

Question 22

Why can water not enter the xylem from the apoplast pathway and how is it moved out of this pathway in order to enter the xylem?

Answer 22

• lignin makes the xylem walls waterproof
• water can only pass into the xylem from the symplast or vacuolar pathways so much leave the apoplast
• the vascular tissue is surrounded by the pericycle which is surrounded by a single layer of cells called the endodermis
• the cell walls are impregnated with a waxy material called suberin
• suberin forms a band called the casparian strip
• this drives water into the cytoplasm

Question 23

How does water move from the root endodermis into he xylem and why is this possible?

Answer 23

By osmosis due to the water potential of the xylem being more negative than that of the endodermal cells. This is achieved by…

• the water potential of the endodermal cells is raised by water being driven into the Caspian strip
• the water potential of the xylem decreasing by the active transport of mineral salts from the endodermis and pericycle into the xylem