Roots - Structure & Function

Question 1

What are the 3 main functions of the root?

Answer 1

Anchorage
Water uptake
Mineral uptake

Question 2

Adapted root example for storage

Answer 2

Storage/perennation Daucus carota

Question 3

Adapted root example for vegetative reproduction?

Answer 3

Dahlia ‘Bishop of Landaff’ rooted tuber.

Question 4

Adapted root example for climbing?

Answer 4

Hedera helix ‘Glacier’ Advantitious roots grow from the stem and adhere to a vertical surface enabling plant to cling to the support and climb.

Question 5

Adapted root example for support?

Answer 5

Prop roots on Zea Mays help to anchor the plants. Adventitious roots grow from the node at the base and spread to help anchor plant. A bit like guy ropes on a circular marquee!

Question 6

What two types of root system are there?

Answer 6

Tap roots with laterals

and Fibrous roots

Question 7

What are the four different types of roots?

Answer 7

Tap roots
Lateral roots
Fibrous roots
Adventitious roots

Question 8

Where does the tap root develop from?

Answer 8

The radicle

Question 9

What type of roots does a typical dicotyledons have?

Answer 9

Tap root and lateral roots.

Question 10

What type of roots does a typical monocotyledons have?

Answer 10

Fibrous roots

Question 11

Describe a tap root?

Answer 11

A primary root that develops from the radicle and becomes the dominant. Extends vertically down through the soil to access water where the soil does not dry out. Plants with a deep tap root don’t transfer well. Eg. Lathyrus odoratus . Some tap roots store food eg. Daucus carota. Only found in dicots!

Question 12

What are lateral roots?

Answer 12

Extend horizontally from the tap root. Secondary roots grow sideways from the plant. Help to anchor the plant securely in the soil. Branching also increases surface area for water absorption. Only in dicots.

Question 13

What are fibrous roots?

Answer 13

These grow from the base of the stem. Not developed from the radicle from another part of the plant. Therefore technically a type of adventitious root. No main central root, as the embryonic root dies back when plant is still young. Roots grow downwards and outwards to form a mass of fine roots all same thickness. Explore top soil much more effectively than tap roots, however much shallower rooting. More susceptible to drought. Only on MONOCOTS
Eg. Lolium perenne
Poa annua
Narcissus tete a tete

Question 14

What are adventitious roots?

Answer 14

These grow from unexpected areas eg. the stem or other plant organ. in monocots the primary roots are short lived, and replaced by adventitious roots. (fibrous roots).
Roots which grow from stolons of Fragaria x ananassa
Prop roots on Zea Mays
Side roots on aerial stems of Hedera Helix glacier
New roots that form on stem cuttings.

Question 15

What is the endodermis?

Answer 15

The inner most layer of cortex. Closely packed cells. The control point for water and selective mineral uptake.

Question 16

What is the casparian strip?

Answer 16

A waxy band around the endodermal cell wall which forces water and dissolved minerals to pass across the cell membrane and into the endodermal cell rather than between the cells and through the cell wall.

Question 17

What is a root hair?

Answer 17

A root hair is one epidermal cell with a protrusion.
It is not a lateral root.
Is is a single specialised epidermal cell.

Question 18

What are the 12 features of a root?

Answer 18

1. Root cap
2. Apical Meristem
3. Zone of elongation
4. Zone of differentiation
5. Root hairs
6. Epidermis
7. Cortex
8. Endodermis
9. Pericycle
10. Phloem
11. Xylem
12. Vascular cambium. (not present in monocots)

Question 19

What is the function of the root cap?

Answer 19

Thimble like cup over the root tip. High turn over of cells, as under a lot of pressure to push through the soil but cells constantly replaced.
Protects the growing root tip.
Secretes mucilage to lubricate the root tip and protect it.

Question 20

Describe the apical meristem and it’s function?

Answer 20

Dome shaped area of meristematic cells with prominent nuclei, constantly dividing.
Function is to produce new cells.

Question 21

Describe the Zone of elongation and it’s function?

Answer 21

Cells elongate by filling their vacuoles with water. Most elongation of the root takes place here. Cells are undifferentiated. (not specialised).
It’s function is to push the root cap and meristem through the soil. When elongation ends, differentiation begins.

Question 22

Describe the zone of differentiation and it’s function?

Answer 22

Root hairs are formed here.
Specialised tissues develop - xylem, phloem, cortex, endodermis.
Cells here do not elongate. They differentiate.
Root hairs form for water absorption..
Lateral roots grow from the pericycle.
Xylem cells thicken and die.

Question 23

Describe a root hair and it’s function?

Answer 23

Root hairs are a single epidermal cell with hair like projections. Water and Mineral absorption by increasing the surface area.

Question 24

Describe the epidermis and it’s function?

Answer 24

1 cell thick layer dermal cells. Lacks cuticles in roots. Covers all root except cap.
Protects underlying tissue.
Absorbs water and dissolved minerals.

Question 25

Describe the cortex and it’s function?

Answer 25

Contains storage parenchyma. Packing tissue.

Food storage. Protects internal tissue.

Question 26

Describe the endodermis and it’s function?

Answer 26

Innermost layer of the cortex.
Cell walls impregnated with casparian strip made of lignin like a rubber band around a rectangular box. The Casparian Strip is water resistant.
Forces water and minerals to pass through the cell cytoplasm and not the cell wall.
Regulates movement of nutrients and water into the Xylem.

Question 27

What is the Pericycle and it’s function?

Answer 27

Thin meristematic layer of thin walled parenchyma cells. Produces lateral roots.

Question 28

Describe Phloem and it’s function?

Answer 28

Transport tissue - Sieve tubes and companion cells.
Function is the movement of water, products of photosynthesis, minerals, hormones etc around the plant in both directions.

Question 29

Describe Xylem and it’s function?

Answer 29

Xylem vessels and tracheids.
Movement upwards of water and mineral nutrients from root to aerial parts of plant.
Also gives structural support to root due to lignin.

Question 30

Describe the Cambium Vascular and it’s function?

Answer 30

Meristematic cells. Produce xylem and phloem. Secondary thickening. (not present in monocotyledons.)

Question 31

What are the differences between Monocotyledon and Dicotyledon roots?

Answer 31

Dicot has a tap root with lateral roots.
Monocot has fibrous roots - no main root. Also adventitious.
Vascular cambium present between xylem & phloem in a Dicot.
Vascular cambium not present in a Monocot.
Secondary thickening present in DIcot but NOT in Monocot.
Xylem arranged in 4-5 simple lobes in a Dicot root. Multi lobed/polyarch in a monocot.
Pith is present in a Monocot but NOT in a dicot.

Question 32

What is osmosis?

Answer 32

Movement of water from an area of high concentration to an area of low concentration across a semi permeable membrane. In an attempt to make both solutions equal in concentration.
A specific type of diffusion that only ever involves the movement of water.
It does not require energy.

Question 33

What are the two routes that water can take from soil water to the vascular system (xylem) or the root?

Answer 33

Apoplastic route - through cell walls diffusion.

Symplastic route - through the cytoplasm = osmosis.

Question 34

What is diffusion?

Answer 34

Movement of a gas or liquid from an area of high concentration to an area of low concentration.

Question 35

How does water diffuse in the plant root?

Answer 35

In the root, water will diffuse through the cell walls of the root hairs and across the cell walls of the cortex as long as their is favourable concentration gradient.

Question 36

What two ways can water move through the route?

Answer 36

Apoplastic route (diffusion)
Symplastic route (osmosis)

Question 37

What is the path of water from the roots to the Xylem?

Answer 37

Water moves by diffusion through the cell walls and between the cell walls until it reaches the Casparian strip which is waterproof.
Then it has to pass through the plasma membrane and cytoplasm of the cells - the Symplastic route. This is a way of controlling the uptake of water and nutrients. After the endodermis, water can continue once again to move through the cell walls of the pericycle and into the xylem vessels and tracheids.

Question 38

Facts about Roots?

Answer 38

Root type affects the type and timing of watering.
Fibrous roots are useful for preventing soil erosion. Eg. grass lolium perenne.
Storage roots allow plants to over winter. Eg. Dahlia Bishop of Landaff
Adventitous roots allow some plants to climb. Eg. Hedera helix
Storage of carbohydrates in roots make them useful as a food source. Eg Daucus carota.

Question 39

Name the part of the embryo from which the root develops in a dicot?

Answer 39

Radicle

Question 40

State one role of a root hair?

Answer 40

Provide a large surface area for the uptake of water and minerals.

Question 41

State one role of the endodermis?

Answer 41

Controls the uptake of water and nutrients as it has a waxy layer called the Casparian strip which forces the water to go through the cell cytoplasm rather than through the cell walls.

Question 42

Describe the pericycle?

Answer 42

A layer between the Endodermis and the xylem tissue. It becomes meristematic and produces lateral roots. It is also the outer layer of the stele.

Question 43

Describe the zone of differentiation?

Answer 43

The layer which sits above the Zone of Elongation. This is where cells differentiate to become specialised into their final form to perform specific functions.

Question 44

Describe the root hair?

Answer 44

This is an elongated epidermal cell which creates a large surface area for water and mineral absorption.

Question 45

Describe the root cap?

Answer 45

This is a protective cap at the tip of the root as it pushes through the soil. It also secretes a lubricant which assists penetration.