Roots Lecture – Biology Department, De La Salle University

Question-and-answer flashcards covering root structure, function, tissue organization, water transport pathways, root modifications, symbioses, and economic importance.

What are the four main functions of roots?

Anchorage, absorption, conduction, and storage of food.

Why are most roots non-green in color?

They lack chlorophyll, so no green pigment is present.

Which shoot structures are absent in roots?

Nodes, internodes, leaves, and buds.

Toward which stimuli do roots grow positively and negatively?

Positively toward gravity (geotropism) and water (hydrotropism); negatively away from light (phototropism).

Describe a taproot system.

One prominent main root grows deep with smaller lateral branches; provides strong anchorage and is typical of dicot plants.

Which group of plants usually possesses a taproot system?

Dicots (eudicots).

Describe a fibrous root system.

Many adventitious roots of similar size arise from stem base, form a shallow horizontal mat, and give limited anchorage; typical of monocots.

Which group of plants usually has a fibrous root system?

Monocots.

Which root system offers the strongest anchorage?

Taproot system because it penetrates deeply into soil.

What is the primary function of the root cap?

Protects the delicate root apical meristem and helps orient the root downward.

What root-cap cells perceive gravity and what happens if the cap is removed?

Statocytes perceive gravity; without the cap, roots grow randomly.

Why does the root cap secrete mucilage?

To lubricate the root’s passage through soil and aid communication with soil microbes.

What are root hairs?

Short-lived, unicellular epidermal extensions near the young root tip that greatly increase absorptive surface area.

Which three basic tissue systems are present in a primary eudicot root?

Dermal (epidermis), ground (cortex and sometimes pith), and vascular tissues (xylem and phloem).

Of what cells is the root cortex composed and what is usually stored there?

Parenchyma cells that commonly store starch.

Define the endodermis of a root.

The innermost cortex layer that regulates entry of water and solutes into the vascular cylinder.

What is the Casparian strip and its purpose?

A waterproof band around endodermal cell walls forcing water and minerals to pass through, rather than between, living cells before reaching the xylem.

What is the pericycle and what does it produce?

A cell layer just inside the endodermis that gives rise to lateral (branch) roots.

Give the pathway of water from soil to xylem in a primary eudicot root.

Root hair → epidermis → cortex (via apoplast or symplast) → endodermis → pericycle → xylem.

Define the symplast.

A transport continuum of interconnected cytoplasm of living cells linked by plasmodesmata.

Define the apoplast.

The continuum of cell-wall spaces and intercellular spaces outside plasma membranes through which water can move freely.

How does water travel in the symplastic pathway?

Through cytoplasm from cell to cell via plasmodesmata.

How does water travel in the apoplastic pathway?

Along interconnected cell walls and extracellular spaces without crossing membranes until blocked by the Casparian strip.

Why must apoplastic water eventually cross a membrane at the endodermis?

Because the Casparian strip is impermeable, forcing selective uptake through endodermal plasma membranes.

What is found in the center of most monocot roots but not in eudicot roots?

A pith of parenchyma cells.

Do monocot roots undergo secondary growth?

No; they lack a vascular cambium.

What is a prop root and its function?

An adventitious root from the stem that props and supports the plant, common in maize and mangroves.

What is a contractile root and its function?

A specialized root on bulbs or corms that shortens and pulls the plant to an optimal soil depth.

What is a pneumatophore and its role?

A specialized aerial root of swamp trees (e.g., mangroves) that rises above water to facilitate gas exchange for submerged roots.

Describe buttress roots and their purpose.

Large, flared roots at the base of some tropical trees that provide stability and increase shallow root spread.

Which roots can perform photosynthesis in certain orchids?

Aerial photosynthetic roots that contain chlorophyll and absorb light.

What are suckers in root biology?

Above-ground shoots that arise from adventitious buds on roots, enabling asexual reproduction.

Define mycorrhiza and state a plant benefit.

A mutualistic association between a fungus and a plant root; it increases mineral (especially phosphorus) uptake and pathogen protection for the plant.

What benefit does the fungus receive in a mycorrhizal relationship?

Organic nutrients such as sugars and amino acids from the plant.

Differentiate ectomycorrhizae from endomycorrhizae.

Ectomycorrhizae form a sheath around roots with hyphae between cortical cells; endomycorrhizae penetrate root cortical cells.

What is a root nodule and its biological role?

A swelling on legume roots housing nitrogen-fixing Rhizobium bacteria that convert atmospheric N₂ into usable forms for the plant.

Give three examples of taproot crops important to humans.

Carrots, beets (including sugar beets), and parsnips (others include turnips or radishes).

Which storage roots arise from a fibrous system?

Sweet potatoes and cassava (manioc).

What additional function do storage roots serve for humans?

They provide edible root crops and flavorings (e.g., sassafras roots for traditional root beer).

What happens to root growth direction when the root cap is removed?

The root loses gravity perception and grows randomly.

Besides anchorage, what important ecological role do buttress roots play in rainforests?

They allow trees to spread extensive shallow roots to capture surface nutrients in thin tropical soils.