Roots

Roots

Roots

• Originally deemed the part of the plant that grew underground, but with the evolution of aerial roots (ones that grow above ground) and aerating roots (ones that grow upward especially above water), the definition has changed.

Roots

• The better definition of a root is the part of the plant body that bears no leaves and therefore has no nodes (places where branches come up).

Root Functions

• The major functions of roots are:

1) Anchor the plant

2) Absorb water and inorganic nutrients

Root Functions

• Roots also can act as storage organs for the plant

• They also enter into a symbiotic relationship with fungi and/or bacteria in the soil in order to obtain nutrients easier.

Root Morphology

• The tip of each root has a conical covering of tissue known as the root cap.

• Underneath the root cap lies the apical meristem, which is the root region undergoing mitosis in order to grow and push the root through the soil.

Root Morphology• The outer surface of the

root is known as the epidermis.

• The epidermis produces outgrowths known as root hairs that increase the surface area for absorption.

• Root hairs typically only live a few days before they are replaced by new ones.

Root Morphology• Under the epidermis lies the

cortex whose primary role is starch storage.

• The innermost layer of the cortex is the endodermis (containing Casparian Strips) which acts as a barrier to nutrients, preventing them from passively entering the vascular tissue.

• This allows the plant to accumulate lots of minerals in its roots.

Root Morphology

• Inside the endodermis lies the vascular tissue.

• This is where water and nutrients start their journey up the plant.

• It is also an area of sugar movement or storage depending on the environmental conditions.

Dicot Roots

Monocot Roots

Root Growth

• Roots will grow in the direction of the correct oxygen, moisture and nutrient levels for plant growth.

• Primary growth is elongation whereas secondary growth is an increase in diameter.

Root Systems

• There are two main types of root systems:

1) Taproot system where there is a large primary root with lots of smaller, secondary roots emerging from it. It is found mostly in dicots where starch storage is key.

Root Systems

• 2) Fibrous System where there is no primary root and all roots are similar in size. They jut out in all directions. Found commonly in monocots. The main function is anchorage.

Monocot and Dicot Roots

Roots (below ground)

• The first structure to appear when a seed germinates and is called the radicle in the embryo.

• The function of the root system is to absorb water and nutrients from the soil for the growing plant, as well as providing a stable anchor.

• Water is absorbed by a process called OSMOSIS (Note: Root cells are usually hypertonic to soil, so water will enter the cells passively by osmosis.)

• The walls of root cells are very thin and have a large surface area.• The depth of the root depends on the moisture content of the soil.

General Structure

• Each root has a meristemic area near its tip to allow for growth.

•  At the tip of each root is a cluster of cells forming the root cap; these cells produce a mucus-like substance which lubricates the movement of the root through the soil.

• Root hairs increase surface area of the epidermis increasing absorption of nutrients and water.

Some definitions:• Xylem – a series of pipes running through the

roots, stems and leaves carrying water through plant

• Phloem – carries food and dissolved materials through plant

• Vascular Cylinder – central portion of a root that contains the xylem and phloem

Monocot Roots

• fibrous roots (many branched roots of equal size)• Examples: grasses, grains, corn

Cross Section- separate strands of xylem and phloem alternate

around a pith-like region

Monocot root

epidermis

cortex

xylem

phloem

pith/parenchyma

endodermis

Vascular Cylinder

Note the xylem and phloem in these differently stained monocot roots.

Dicot Roots

• tap roots (1 large main root and smaller lateral roots)• Examples: carrots, beets, beans, dandelions, most trees

Cross Section- xylem is irregular and a solid strand- phloem is arranged in separate strands

Dicot root

epidermis

cortex

phloem

xylem

NO pith/parenchyma

endodermis

Vascular Cylinder

Note the xylem and phloem in these differently stained dicot roots.

More Definitions:Epidermis  provides protection and regulates

water movement epidermal cells can elongate and form root

hairs which increase the surface area for water absorption

Cortex the innermost layer of cortex cells is called the endodermis

the endodermal cells are coated with a waxy layer called the casparian strip (this prevents water from moving in the spaces between the endodermal cells)

Lab Activity• Look at monocot and dicot root slides

using the microscope.• Describe how to tell the difference

between monocot and dicot roots.

Home Fun:• Read 558-563• Describe:

a) cortexb) endodermisc) Casparian stripd) vascular cylinder e) pith/parenchyma

• Do P. 563#4