unit b: plant anatomy · what are the functions of a plant’s roots? a plant’s health is...
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Vocabulary Apical meristem Epidermis Fibrous root system Primary root Root cap Root hairs Secondary roots Taproot system
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What Are the Functions of a Plant’s Roots?
A plant’s health is directly related to its roots Weak and diseased roots
decrease a plant’s health Roots need to continuously
grow in order to stay healthy This is why plants become
pot-bound: the roots start growing out of the pot because it is too small
A pot bound plant in need of transplanting
Courtesy of Delmar Publishing 3
Functions of a Root System 1. Absorb water and
minerals from the environment
2. Anchor the plant in the ground
3. Store food that has been made in the leaves by photosynthesis Can be used later by the
plant to grow and survive Taraxacum officinale – the common dandelion
Courtesy of Wm. C. Brown Publishers 4
What Are the Parts of a Root?
When a seed germinates, the first structure to appear is the root, or radicle A. It becomes the
primary root Usually the most
important root in some plants
B. Other roots branch out from the primary root; called secondary roots
Cotyledon Radicle = Primary root; notice all the root hairs
Courtesy of McGraw Hill 5
C. The apical meristem, found at the root tip, is where new cells develop It is covered by the root
cap – protects it from damage as it passes through coarse soil particles
Epidermis
Vascular cylinder (xylem & phloem)
Cortex (food storage)
Root Cap
Apical meristem
Courtesy of Dorling Kindersley, Inc. 6
D. The surface of the root is protected by skin cells called the epidermis
Where water and minerals enter the root by osmosis & diffusion
Can grow long, hair like projections called root hairs
They greatly increase the surface area of the root to allow more water intake
Epidermis
Courtesy of Delmar Publishing 7
Regions of Cell Development
Notice that cell division occurs at the tip of the root
Older cells are found farther away from the root tip
Root Cap
Region of Cell Division
Region of Elongation
Region of Maturation
Apical meristem Courtesy of McGraw
Hill Publishers 8
What Are the Two Types of Root Systems? Plant root systems are organized in two
basic ways; It has to do with primary and secondary roots A. A root system comprising one main
primary root and many secondary roots branching off the primary root is called a taproot system Their roots reach far into the ground; they
can be several feet long
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Tap Root Systems Advantages Penetrate deeper into the soil
Obtain water from lower levels
Anchor the plant
Disadvantages Difficult to remove/harvest plants
Do not stabilize the soil well 11
B. A system which has no
dominant primary root but is made of many primary and secondary roots of similar size is called a fibrous root system Ex. Grasses, Magnolia,
Rhododendron, Euonymus
The roots are smaller, shorter and more compact; They usually never grow below the first 6-12 inches of soil
These roots form a large network underground
Fibrous root system of grass
Courtesy of McGraw Hill Publishing 12
Fibrous root system Advantages
Shallower, thus respond more quickly to fertilization/irrigation
Stabilize the soil better
Disadvantages
Less drought resistant
Tend to get exposed during cultivation 13
What Does a Healthy Root System Look Like? A healthy root system is white or nearly white
in color and smells fresh, or earthy
If roots are black, brown, or dark orange and smell rotten or sour, the root system is having some problems
Watering a plant properly is one of the most important ways to keep the root system healthy
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If the plants are grown in pots, be sure that there are drainage holes in the bottom to allow excess water to drain Soak the pot until the growing medium is
saturated and water drips out of the drainage holes This encourages the roots to grow through
the entire pot Allow the pot to dry out slightly between
watering Watering too frequently is a common cause
of root death Medium that is kept wet has limited air
exchange; the root tissues die for lack of air 16
Recognize the economical importance of roots. Roots impact society in many different ways
The term root crops refers to any edible underground plant structure, but many root crops are actually stems, such as potato tubers
Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from roots include and licorice. sassafras, angelica, sarsaparilla
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Sugar beet is an important source of sugar. The fish poison and insecticide rotenone is obtained from roots of Lonchocarpus spp.
Important medicines from roots are ginseng, aconite, ipecac, gentian and reserpine
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Several legumes that have nitrogen-fixing root nodules are used as green manure crops, which provide nitrogen fertilizer for other crops when plowed under.
Specialized bald cypress roots, termed knees, are sold as souvenirs, lamp bases and carved into folk art. Some people have used the flexible roots of white spruce for basketry.
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Summary What are the three functions of a root?
What is another name for a primary root?
In the tip of the root, what kinds of cells are the only ones that divide?
What is the epidermis and what is its function?
Where do root hairs grow from?
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Summary Why does a plant have to have numerous root
hairs instead of just two or three?
Pretend you are a water molecule and you need to get into the center of the root. What are all the layers you must go through before reaching the center?
Describe the functions of the xylem and phloem.
Where is food stored in the root?
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