Roots Stems and Leaves Chapter 23 Biology Miller

Roots, Stems and Leaves Chapter 23 Biology – Miller • Levine

Specialized Tissue in Plants n n n The three organs of a plant are the roots, stems and leaves The three tissue systems of a plant are dermal tissue, vascular tissue, and ground tissue A special type of tissue called meristematic tissue is the only plant tissue that can produce new cells by mitosis n Found in the tips of shoots and roots

Dermal Tissue n n n The outer covering of a plant Consists of a single layer of epidermal cells Cuticle – a waxy layer that often covers the epidermis n n Provides protection against water loss & injury May include specialized structures such as root hairs and guard cells

Vascular Tissue n n n Transports water and nutrients throughout the plant Xylem – transports water; composed of dead cells Phloem – transports nutrients; composed of living cells called sieve tube elements

Ground Tissue n n Lies between the dermal and vascular tissues Parenchyma – has thin cell walls and large central vacuoles Collenchyma – has strong, flexible cell walls and is found in larger plants Sclerenchyma – has extremely thick, rigid cells walls

Roots n Types of roots: n n Taproot - A thick primary root that grows long and is found mainly in dicots Fibrous roots – branch extensively and are found mainly in monocots

Root Structure & Growth n n Root hairs – tiny projections from the epidermis that increases the surface area for absorption of water Cortex – layer of ground tissue Endodermis – layer of tissue that encloses the vascular tissue Root cap – protects the root as it forces its way through the soil

Root Structure & Function

Root Function Anchor a plant in the ground n Absorb water and dissolved nutrients from the soil n

Stem Function & Types n Three important functions: n n Produce leaves, branches and flowers Hold leaves up in the sunlight Transport substances between roots and leaves Two types: n n Monocot – has vascular bundles that contain the xylem & phloem scattered randomly Dicot – have vascular bundles organized in a ringlike pattern

Monocots and Dicots

Stem Structures n n n Nodes – where leaves are attached Internodes – regions between the nodes Buds – contain undeveloped tissue that can produce new stems and leaves

Leaf Structure n n n Blade – thin, flattened section Petiole – thin stalk that attaches the leaf to the stem Veins – contain the xylem and phloem

Leaf Structure n n Palisade mesophyll – tightly packed cells that absorb light Spongy mesophyll – loosely packed cells with air spaces Stomata – pore-like openings for taking in CO 2 and releasing O 2 Guard cells – cells that open and close the stomata

Leaf Structure

Leaf Functions n n n Photosynthesis – takes place in the mesophyll cells of the leaf Transpiration – the loss of water from a plant through its leaves (helps to pull water up from the roots) Gas exchange – taking in carbon dioxide and releasing oxygen