Plant Roots and Their Functions Quiz

Plant Organs: Roots

• Roots make up one-third to half of a plant's total dry weight.
• Roots are vital for several functions including absorption, anchorage, storage, and nitrogen fixation.
• Roots need an extensive contact area with soil particles to absorb water and dissolved nutrients.
• Roots need oxygen for respiration.

Absorption

• Roots absorb water and dissolved nutrients.
• Plants need significant amounts of water; for example, spring wheat in southern Alberta requires 420-480 mm of water annually.
• Roots absorb simple minerals (e.g., N, P, K, S) and organic substances from decaying matter (vitamins, hormones).

Anchorage

• Roots provide stability and support to plants.
• Anchorage allows effective photosynthesis.
• Environmental factors like wind and rain necessitate anchoring.
• Poorly developed roots lead to lodging in susceptible plants.
• Adventitious roots, those from stem tissue not roots, provide additional support.
• Corn has a unique anchoring system called "prop roots."

Storage

• Biennial, perennial, and winter annual plants rely on root storage for survival through winter and subsequent growth.
• The plant stores food in its roots at the end of the growing season.
• Stored food provides energy for shoot growth in the spring.
• Alfalfa requires sufficient root storage, so late harvest can hinder winter survival.
• Other root crops for storage include carrots, beets, turnips, and radishes (though not potatoes).
• Biennial root crops, such as beets, carrots, and radishes, are harvested during their first year of growth to utilize stored food rather than for seed production.

Root Crops

• Common harvested biennial root crops include sugar beets, carrots, and radishes.

Sugar Beet

• An important root crop grown in southeastern Alberta for its sugar content.
• Harvested in the fall of the year they are planted.
• Tops are used as animal feed, and the root is washed, shredded, and processed into sugar.
• Sugar produced from sugar beets is similar to sugarcane sugar.

Nitrogen Fixation

• Nitrogen fixation occurs in legumes (plants that have their seeds in true pods).
• Legume roots form relationships with rhizobium bacteria.
• Examples of legumes include peas, soybeans, lentils, chickpea, and alfalfa.
• Frankia is a nitrogen-fixing genus of bacteria found in actinorhizal plants—various trees and shrubs in Canada.

Rhizobium (Nitrogen Fixation)

• Rhizobium bacteria live within the roots of legume plants.
• Rhizobium form colonies in root nodules.
• Rhizobium helps plants use nitrogen obtained from the air.
• Nitrogen is necessary for plant growth.
• Farmers often use inoculation with Rhizobium to enhance soil nitrogen for successful legume crop growth.
• Rhizobium viability is temperature-dependent.

Inoculation

• When planting peas, lentils, and alfalfa, seeds are inoculated with Rhizobium bacteria for better nitrogen use.
• Rhizobium, usually mixed with peat, is applied to the seeds.
• Special care is required during Rhizobium handling to maintain its viability.

Monocot and Dicot Roots

• Monocot roots differ from dicot roots developmentally.
• Dicot roots often have a main tap root, with secondary roots originating from it.
• In contrast, monocot roots primarily comprise a fibrous system of branching roots.

Root Development

• The radicle, the embryonic root, emerges first from the seed allowing germination to absorb nutrients and water.
• Smaller seminal roots develop simultaneously (i.e., side roots).

Tap Roots/Dicot Plants

• Dicots have a major, primary root from which numerous secondary roots arise.
• Examples include alfalfa.

Fibrous Roots/Monocot Plants

• Monocot roots develop from a crown (just below the soil surface), quickly producing fibrous (branched) roots.
• Examples include onions.

Crown

• The crown is the area of plant stem or roots just below the soil surface.

Root Hairs

• Root hairs expand the surface area for improved absorption and efficient water uptake.
• Water and nutrients are absorbed through root outer layers and transported to the xylem.
• Root hairs are fragile and easily damaged, so precautions during transplanting are necessary.

Water Uptake

• Root hairs absorb water via osmosis.
• Water moves through outer root layers transporting to xylem in the centre.
• Xylem transports water to the shoot and the plant.