2.3 Roots Flashcards
Name the different root types (6)
Primary tap root
Lateral roots
Fibrous roots
Adventitious roots
Aerial roots
Monocot roots
Primary tap root - function
Main root in dicots - derives from the radicle of the seed.
“Digs” down vertically, produces laterals.
Thickens to become woody in perennials
Roots - what happens when a dicot seed germinates?
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
Lateral root - function and origin
Origin: Branch off the primary taproot
Increase water uptake; provide anchorage; form root ball
Fibrous roots - function and origin
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
Adventitious roots - function and origin
Origin: stem or other non-root structures.
Functions: climbing and spreading.
(Also develop from cuttings)
Aerial roots - function and origin
“Special” adventitious roots
Can act as props, or are green and photosynthetic
Origin: stem
Growing root tip - name the parts (10)
Root cap
Mucilage
Root apical meristem
Epidermis
Cortex
Endodermis
Casparian strip
Pericycle
Stele
Primary phloem
Primary xylem
What is the root cap?
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
What is the mucilage?
A jelly substance that allows root tip to slip easily through soil, and protects against fungal infections
What is the root apical meristem?
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.
What is the epidermis?
Outer layer of “skin” of main body of root
What is the cortex?
Lies just inside the epidermis
Thick layer of structural tissue
What is the endodermis?
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!)
What is the pericycle?
Lies just inside the endodermis
Gives rise to lateral roots
Makes up the outer layer of the stele.
What is the stele?
Includes the vascular transport tissues (xylem & phloem) and other packing cells
DICOTS ONLY: Stele includes vascular cambium
What is the primary phloem?
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!)
What is the primary xylem?
Tubes of dead cells that transport water and dissolved minerals drawn UP from roots
Functions of roots (6)
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.
Differences between tap root and lateral root
Tap root is a single, main, central root,
whereas lateral roots are secondary roots that branch from the tap root.
What is the zone of differentiation?
Lies behind the zone of elongation.
Cells differentiate and develop into their final, specialised forms.
What is the zone of elongation?
Lies behind the root apical meristem.
Cells don’t divide but elongate rapidly.
Describe root hairs:
Single, elongated epidermal cells
Increase the surface area for uptake of water and minerals
Positioned close to the root tip (near zone of diff.)
What is the Casparian strip?
Waterproof layer of cells that lie within the endodermis that prevent the backflow of water and nutrients back into the soil.
Where does sugar transport take place?
In the phloem
Where does the selection of minerals take place?
At the root hairs
Where does the production of lateral roots take place?
At the pericycle
Epidermis and endodermis also produced here
Three root adaptations
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
