Roots (ps6) Flashcards
State the primary function of the root - anchorage , water and mineral uptake
Roots are the main anchorage and water absorbing structure types of the plant, and usually develop beneath the surface of the soil. They DO NOT contain chlorophyll and never bear leaves or buds.
The primary function of the roots are to:
1 - Provide anchorage in the soil for the plant
2 - absorb water from the soil
3 - absorb minerals from the soil
Describe the difference between monocotyledon and dicotyledon roots
Dicotyledon- one main root
Monocotyledon - several root
On a Dicotyledon species, when seed germinates the first root to emerge is a RADICLE. If this develops into a persistent and dominant root it is called a tap root.
As the plant grows , secondary roots branch out from the original to form LATERAL ROOTS’
In some dicots species , the radicle doesn’t develop into a persistent tap root, many lateral roots grow and a fibrous root system develops eg: Tagetes patula (French Marigold)
On a monocotyledon species such as grasses, several roots emerge from the seed at the same time to form a FIBROUS’ root system. There is no distinguishable main root and all of the roots are a similar size
A root which develops from a structure other than an existing root (such as stem or leaf) is known as an ADVENTITIOUS ROOT .
Describe TAPROOT
The main primary root of a plant
Describe Adventitious root
Any root which grows from a tissue other than the pericycle of an older root
Describe lateral root
Lateral roots extend horizontally from the primary root (RADICLE) and serve to anchor the plant securely into the soil. This branching of roots also contributes to water uptake, and facilitates the extraction of nutrients required for the growth and development of the plant.
Describe fibrous root system
A fibrous root system is the opposite of a taproot system. It is usually formed by thin, moderately branching roots growing from the stem. A fibrous root system is universal in monocotyledonous plants and ferns. The fibrous root systems look like a mat made out of roots when the tree has reached full maturity.
Describe the structure of the root and state the function of its components
The root growing tip
The growing tip of roots is divided into a number of sections :
THE ROOT CAP
An area of dead cells that forms a protective cap over the apical meristem as the root pushes through the soil
APICAL MERISTEM
An area of rapid cell division and forms the PRIMARY GROWTH PART of the root
ZONE OF ELONGATION
In this region the cells are produced by the apical meristem increase to more than 10 times their original size, pushing the root tip through the soil.
ZONE OF DIFFERENTIATION
The full sized cells mature and become specialised into the different tissue types such as the epidermis or vascular system. There is no cuticle layer on the root epidermis , which allows the water to be absorbed in this region.
The zone of differentiation is characterised by the mass of fine root hairs covering the outside of the root
ROOT HAIRS
The root hairs are tiny elongated outgrowths from the epidermis that develop behind the zone of elongation. The hairs grow out between the soil particles and greatly increase the water absorbing area . Root hairs function for only a few days before they die, but new root hairs are constantly forming at the lower end of the hair region.
EPIDERMIS
The epidermis is made up of a single layer of closely packed cells, which act as a protective cover
CORTEX
The cortex gives structure to the root and consist of loosely packed parenchyma cells.
THE VASCULAR CYLINDER (stele)
This contains the phloem and xylem and is surrounded by the pericycle. The vascular cylinder is sometimes known as the STELE of the root.
Pericycle
The pericycle is the outer layer of cells in the vascular cyclinder. Lateral roots originate in the meristematic tissue of the pericycle
PHLOEM
makes up part of the vascular tissue and is responsible for the transport of sugars
XYLEM
also part of the vascular tissue and transports water and minerals up the plant from root to stem
CAMBIUM A MERISTEM (any tissue of actively dividing cells in a plant) found in the vascular tissue of dicotyledon plants which produces phloem and xylem in the root and stems
Describe Endodermis
This is a single layer of cells, found only in the roots, which encircle the vascular tissue. It is responsible for the regulation of water and mineral movement between the cortex and Xylem.
The cellulose cell walks of root cells are fully permeable to water and dissolved minerals.The amount of water taken up by the plant needs to be regulated , inside the endoderm cell walls is a waterproof band of material called the CASPARIAN STRIP. The strip directs water and minerals into the living cell through the semi permeable cell membrane, which regulates the concentration of minerals reaching the xylem
Describe how the root is adapted to perform other functions
Many plants have evolved specialised roots to carry out different functions for example:
1- food storage Daucus carota (carrot) store food in enlarged tap roots. Other plants that have tuberous roots include Dahlia pinnata (Dahlia)
2- REPRODUCTION
The roots of some plants such as raspberries and sheeps sorrel produce adventitious buds that grow into shoots called suckers
3- WATER STORAGE
Aerial roots of epiphytic plants such as orchids store water. The roots have an outer layer of large hollow cells that hold water
4 - CLIMBING ROOTS
Many climbing plants such as ivy (Hedera helix) have adventitious roots on their stems to cling to other plants and structures
5- SUPPORT
Plants such as maize, and many tropical trees produce ‘prop’ roots to help support their stems and branches
Draw a modification table of root systems , stating
Modification
Function
Name
Modifers: Function: Example
M- SWOLLEN TAP ROOT SYSTEM
F- To store food
E- Daucus carota,
M: ROOT TUBER
F: to store food
E: Dahlia pinnata
M: PROP ROOT
F: supports stems and branches
E: Zea mays
M: BUTTRESS ROOT
F:
E:
M:STILT ROOTS
F: support stems and branches particularly on river beds
E:Ficus benghalensis (check this! Banyan tree?)
M:AIR ROOTS
F: water storage
E: Monstera deliciosa (cheese plant)
M:CLIMBING ROOT
F: to climb to reach optimum light for photosynthesis
E:Hedera helix
PARASITIC ROOT
M: REPRODUCTION
F: produce adventitious roots to grow into shoots called suckers
E;raspberries - find name
