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Roots—Chapter 5 vocabulary Adventitious root Fibrous root system Lateral root Mycorrhiza Prop root Radicle Root apical meristem Root cap Root hair Tap root Zone of elongation Pericycle Endodermis Root nodule Function of Roots Three main functions ◦ Anchor the plant in the ground ◦ Absorb water and minerals ◦ Produce hormones Root System types Taproot system-a single prominent root that is bigger than the rest ◦ Examples: radish, carrot Fibrous root system- mass of roots that are very similarly sized ◦ Examples: onions, Palm trees, grasses Monocots have only fibrous roots because they are not capable of secondary growth. Therefore, they only grow primarily, or upward (downward) once. Dicots are capable of secondary growth, or growing outward, so a large primary root could grow very large. May have both types of roots Fibrous v. Tap Roots Root systems will generally exist as a function of the environment and the organism. ◦ Plants that grow where rain is plentiful will often grow roots closer to the surface. ◦ Plants that grow where rain is seasonal will often grow deep roots top access under ground water. Taproots Develops from a radicle, or embryonic seed root Lateral Roots: Roots that branch off of the primary root. Fibrous Root system Roots do not grow from a radicle. Radicle disappears shortly after germination Adventitious Roots Roots that do not arise on preexisting roots and not part of the radicles Tubers A tuber is a thickened underground stem, and the stem tissue serves as the primary storage tissue. Meristems (where new shoots grow) occur on the tuber and are commonly called "eyes" on a potato. Rhizome A rhizome is a modified stem, and the stem tissue itself is the primary storage tissue. The rhizome, however, is unique in that it grows horizontally through soil Prop Roots Roots that are partly exposed in the air Used to help support the plant Aerial Roots Roots that are entirely exposed above the ground. Special cells on the outside of the root, called velamen, prevent the roots from drying out Mycorrhizae Roots of 80% of all seed plants have a symbiotic relationship with soil fungi, both benefit. Plant gains phosphorus and other minerals that it normally can’t absorb efficiently Fungi gets sugars from photosynthesis in return Root Nodules Some plants have the ability to grow nitrogen fixing bacteria in their roots. (The original farmers?) Roots swell to accommodate bacteria Even though 78% of the atmosphere is nitrogen, plants can’t use it. The bacteria can take it out of the atmosphere a fix it into usable forms like ammonia Parasitic plants Some plants can actually be parasites on other types of plants Haustoria- Roots of parasitic plants are modified to penetrate other plants and absorb nutrients. ---------------------------------------------- Dodder—parasitic on wheat Mistletoe—parasitic on trees…hmmm Root hairs Root hairs are extensions of the epidermis ◦ Greatly increases surface area. Aids in anchoring the plant Aids in absorbing water and nutrients