Roots, Stems, & Leaves

Roots 2 Main Types: Tap Roots Fibrous roots long & thick primary root with small secondary roots Found in dicots like oaks, carrots, beets, dandelions Fibrous roots Branching with no single larger root Mainly found in monocots Extensive root systems help prevent topsoil erosion

Root Structure & Function Structures: Epidermis - both protects and absorbs Root hairs - penetrate soil & provide larger surface area for absorption Cortex - Ground tissue between epidermis & vascular cylinder Endodermis - layer that surrounds vascular cylinder

Function Roots anchor the plant in the ground and absorb water & dissolved minerals from soil

Leaves Characteristics: Main organs of photosynthesis Blade – thin, flattened sections for collecting sunlight Petiole – stalk which attaches blade to stem

Guard cells One of the paired epidermal cells that control the opening and closing of a stoma in plant tissue.

Stems Functions: Produce leaves, branches, & flowers Hold leaves up to sunlight Transport substances between roots & leaves

Stem Structure Stems are composed of dermal, vascular, & ground tissue Nodes - where leaves are attached Internode - regions in between nodes Buds - undeveloped tissue that can produce new stems & leaves; found where leaves attach to nodes

Specialized Stems Stems that store food and can remain dormant for a time Tuber – usually grows underground, stores food (potato) Bulb – central stem surrounded by short, thick leaves (onion) Corm – similar to bulb but stem is thickened to store food (gladiolus flower) Rhizome – horizontal underground stem that can form new shoots (ginger)

Plant Adaptations & Plant Tropisms

Plant Adaptations Dormancy – period during which growth & activity decrease or stop

Plant Adaptations Aquatic plants must tolerate mud nearly devoid of oxygen Tissues with air-filled spaces for O2 to diffuse Seeds often ­ float and grow quickly

Plant Adaptations Xerophytes - desert plants Root systems spread out for long distances Leaves may be reduced to spines; photosynthesis occurs in stems, which also store water

Plant Adaptations Carnivorous plants – live in bogs with little nitrogen Use specialized leaves to trap & digest insects to meet nutritional needs Pitcher plants - drown insects in specialized leaves Sundews - trap insects with sticky secretions Venus’ flytrap - has leaves that snap shut

Plant Adaptations Parasites & Epiphytes – extract water & nutrients from a host plant Parasites harm the host Epiphytes grow on bodies of other plants but gather their own water & produce their own food Ex: Spanish moss, bromeliads, many orchids

Plant Adaptations Chemical defenses – manufacture poisons, insect hormones, etc. that effect animals/insects

Plant Tropisms Plant Tropisms - responses of plants to external stimuli Gravitropism – stems grow up & roots grow down Phototropism – plants grow toward light Thigmotropism – response to touch – vines & climbing plants wrap around support structures

Plant Hormones 1. Auxins – cause of phototropism Stimulate cell elongation Higher concentration on shaded side of the plant causing stem to elongate and bend -- Cause of gravitropism higher concentration on lower part of root stem inhibit cell growth, causing root to grow downward. Help move root through the soil and around objects in the soil

Plant Hormones 2. Cytokinins – produced in growing roots and in developing fruits and seeds. Cause dormant seeds to sprout Cells grow thicker 3. Gibberellins – growth promoting Increase size of stems and fruits 4. Ethylene – stimulates fruit to ripen