2.3 Roots

Question 1

Name the different root types (6)

Answer 1

Primary tap root

Lateral roots

Fibrous roots

Adventitious roots

Aerial roots

Monocot roots

Question 2

Primary tap root - function

Answer 2

Main root in dicots - derives from the radicle of the seed.

“Digs” down vertically, produces laterals.

Thickens to become woody in perennials

Question 3

Roots - what happens when a dicot seed germinates?

Answer 3

Radicle (embryonic root) grows downwards

Radicle thickens, forming primary tap root

Thinner, secondary roots form from the tap root (lateral roots if horizontal)

Microscopic root hairs form on the larger root surfaces

Results in complex root ball filling the space below the plant

Question 4

Lateral root - function and origin

Answer 4

Origin: Branch off the primary taproot

Increase water uptake; provide anchorage; form root ball

Question 5

Fibrous roots - function and origin

Answer 5

Roots typical of monocots - no primary taproot

Radicle dies back leaving a dense network of similar sized, fine, fibrous roots, closer to the soil surface

Question 6

Adventitious roots - function and origin

Answer 6

Origin: stem or other non-root structures.

Functions: climbing and spreading.

(Also develop from cuttings)

Question 7

Aerial roots - function and origin

Answer 7

“Special” adventitious roots

Can act as props, or are green and photosynthetic

Origin: stem

Question 8

Growing root tip - name the parts (10)

Answer 8

Root cap

Mucilage

Root apical meristem

Epidermis

Cortex

Endodermis

Casparian strip

Pericycle

Stele

Primary phloem

Primary xylem

Question 9

What is the root cap?

Answer 9

Part of the epidermis (layer of dead cells) which covers the root tip

Protects the apical meristem as the root grows through the soil

Produces mucilage to aid passage through soil

Site of the root’s gravity-sensing mechanism

Question 10

What is the mucilage?

Answer 10

A jelly substance that allows root tip to slip easily through soil, and protects against fungal infections

Question 11

What is the root apical meristem?

Answer 11

Site of active cell production and division in root tip

Site of cell division which leads to lengthwise growth, down through the earth

Behind this lies the “zone of elongation” - cells don’t divide, but elongate rapidly;

and then the “zone of differentiation” - cells differentiate and develop into their final, specialised forms.

Question 12

What is the epidermis?

Answer 12

Outer layer of “skin” of main body of root

Question 13

What is the cortex?

Answer 13

Lies just inside the epidermis

Thick layer of structural tissue

Question 14

What is the endodermis?

Answer 14

Lies just inside cortex - inner layer of “skin”

Controls/regulates uptake of water and minerals in and out of vascular system

Includes the casparian strip (prevents back-flow of water and minerals - waterproof!)

Question 15

What is the pericycle?

Answer 15

Lies just inside the endodermis

Gives rise to lateral roots

Makes up the outer layer of the stele.

Question 16

What is the stele?

Answer 16

Includes the vascular transport tissues (xylem & phloem) and other packing cells

DICOTS ONLY: Stele includes vascular cambium

Question 17

What is the primary phloem?

Answer 17

Tubes that transport the sugary products of photosynthesis between the leaves and other parts of the plant (up and down!)

Arranged in a ring around the central xylem (root!)

Question 18

What is the primary xylem?

Answer 18

Tubes of dead cells that transport water and dissolved minerals drawn UP from roots

Question 19

Functions of roots (6)

Answer 19

Water and mineral uptake for plant (large surface area to draw up as much as possible)

Anchorage - in trees and shrubs the root ball should be same size as plant above ground)

Climbing - adventitious roots

Reproduction - roots sometimes spread away and send up new shoots (suckers are identical clones!)

Storage - swollen tap roots (root veg); tissues rich in starch, sugars, carbs; plants survives through harsh conditions.

Breathing - waterlogged environments have very little oxygen in soil, so plant roots raise projections above surface of water - to absorb oxygen. Called breathing roots or pneumatophores.

Question 20

Differences between tap root and lateral root

Answer 20

Tap root is a single, main, central root,

whereas lateral roots are secondary roots that branch from the tap root.

Question 21

What is the zone of differentiation?

Answer 21

Lies behind the zone of elongation.

Cells differentiate and develop into their final, specialised forms.

Question 22

What is the zone of elongation?

Answer 22

Lies behind the root apical meristem.

Cells don’t divide but elongate rapidly.

Question 23

Describe root hairs:

Answer 23

Single, elongated epidermal cells

Increase the surface area for uptake of water and minerals

Positioned close to the root tip (near zone of diff.)

Question 24

What is the Casparian strip?

Answer 24

Waterproof layer of cells that lie within the endodermis that prevent the backflow of water and nutrients back into the soil.

Question 25

Where does sugar transport take place?

Answer 25

In the phloem

Question 26

Where does the selection of minerals take place?

Answer 26

At the root hairs

Question 27

Where does the production of lateral roots take place?

Answer 27

At the pericycle

Epidermis and endodermis also produced here

Question 28

Three root adaptations

Answer 28

Swollen tap roots for large amounts of starch storage (perennation) - make good root vegetables!

Adventitious roots - allow plant to climb to reach light for photosynthesis (Ivy)

Prop roots - for support in wet ground or windy conditions