Unit 7 Plants Ch. 23 Roots, Stems, & Leaves

Seed Plant Structure 3 of the principal organs of seed plants are roots, stems, & leaves The root system of a plant absorbs water & dissolved nutrients

Seed Plant Structure A stem has a support system for the plant body, a transport system that carries nutrients, & a defense system that protects the plant against predators & disease Leaves are the plant’s main photosynthetic systems

Plant Tissue Systems Plants consist of 3 main tissue systems: dermal tissue, vascular tissue, & ground tissue

Dermal Tissue The outer covering of a plant, that consists of a single layer of epidermal cells The outer surfaces are often covered with thick waxy layer to protect against water loss & injury

Vascular Tissue Contains several types of specialized cells Xylem consists of tracheids & vessel elements Phloem consists of sieve tube elements & companion cells

Vascular Tissue - Xylem All seed plants have a type of xylem cell called a tracheid, cells that resist water pressure Vessel elements - wide cells that form hollow tubes, which water can move through freely

Vascular Tissue - Phloem Sieve tube elements - main cells in phloem, form tubes through which materials, like sugars & other foods, are carried in a watery stream Companion cells - phloem cells that surround sieve tube elements, help movement of substances in & out of the phloem

Ground Tissue Cells that lie between dermal & vascular tissues Consists mainly of parenchyma - cells that are packed with chloroplasts & are the site of most of a plant’s photosynthesis

Ground Tissue Collenchyma - cells that have strong, flexible cell walls that help support larger plants (makes up “strings” of a stalk of celery) Sclerenchyma - rigid cell walls that make ground tissue tough & strong

Plant Growth & Meristematic Tissue Meristems - clusters of tissue that are responsible for continuing growth throughout a plant’s lifetime Meristematic tissue - undifferentiated cells, they have not yet become specialized for specific functions, such as transport

Plant Growth & Meristematic Tissue Apical meristem - group of undifferentiated cells that divide to produce increased length of stems & roots

Plant Growth & Meristematic Tissue Differentiation - cells develop into mature cells with specialized structures & functions As cells differentiate, they produce each of the tissue systems of the plant: dermal, ground, & vascular tissue

Types of Roots The 2 main types of roots are taproots, found mainly in dicots, & fibrous roots, found mainly in monocots Taproot - primary root Ex.) carrots, dandelions, beets, etc.

Types of Roots Fibrous roots - roots that branch to such an extent that no single root grows larger than the rest Ex.) grass

Root Structure & Growth A mature root has an outsider layer, the epidermis, & a central cylinder of vascular tissue Between these 2 tissues, lies a large area of ground tissue

Root Structure & Growth Root hairs - tiny cellular projections that penetrate the spaces between soil particles & produce a large surface area through which water can enter the plant

Root Structure & Growth Cortex - spongy layer of ground tissue just inside the epidermis Endodermis - another layer of cells that completely encloses the root’s vascular subsystem in a region called the vascular cylinder

Root Structure & Growth Root cap - protects the root as it forces its way through the soil

Root Functions Roots anchor a plant in the ground & absorb water & dissolved nutrients from the soil

Stem Structure & Function Stems have 3 important functions: they produce leaves, branches, & flowers; they hold leaves up to the sunlight; & they transport substances between roots & leaves

Stem Structure & Function Nodes - where leaves are attached Internode - regions between the nodes Buds - contain undeveloped tissue that can produce new stems & leaves

Monocot & Dicot Stems In monocots, vascular bundles are scattered throughout the stem In dicots & most gymnosperms, vascular bundles are arranged in a cylinder

Monocot & Dicot Stems Vascular bundles - contains xylem & phloem tissue Pith - the parenchyma cells inside the ring of vascular tissue

Primary Growth of Stems Primary growth - growth occurring only at the ends of a plant Its produced by cell divisions in the apical meristem, & takes place in all seed plants

Secondary Growth of Stems Secondary growth - method of growth where stems increase in width In conifers & dicots, secondary growth takes place in lateral meristematic tissues called the vascular cambium & cork cambium

Secondary Growth of Stems Vascular cambium - produces vascular tissues & increases the thickness of stems over time Cork cambium - produces the outer covering of stems

Formation of Wood Heartwood - older xylem near the center of the stem that no longer conducts water Sapwood - surrounds heartwood, active in fluid transport

Formation of Bark Bark - includes all of the tissues outside the vascular cambium, includes: phloem, the cork cambium, & cork

Leaf Structure The structure of a leaf is optimized for absorbing light & carrying out photosynthesis

Leaf Structure Blades - flattened section, attached to the stem by a thin stalk - petiole

Leaf Functions A leaf can be considered a system specialized for photosynthesis Subsystems of the leaf include tissues that bring gases, water, & nutrients to the cells that carry out photosynthesis

Leaf Functions Guard cells - specialized cells in the epidermis that control the opening & closing of stomata (air spaces) by responding to changes in water pressure

Leaf Functions Plants keep their stomata open just enough to allow photosynthesis to take place, but not so much that they lose an excessive amount of water

Leaf Functions Transpiration - the loss of water through its leaves