Plant Anatomy

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Information about Plant Anatomy

Published on January 3, 2008

Author: Breezy


Chapter Twelve:  Chapter Twelve Plant Anatomy Classification of Parts:  Classification of Parts Woody Trunks and branches are generally “woody” Generally strong (because of thick cell walls). Some cells within the woody plant parts remain unspecialized – allowing whatever type of future tissue needed by the plant to form. Long-lived – sometimes for centuries. Classification of Parts, cont.:  Classification of Parts, cont. Herbaceous Short-lived (usually a year or less) Lack thick cell walls – rely on turgor pressure for structural support. Leaves, flowers, nonwoody roots and stems. If it contains chlorophyll, it usually remains green until it dies. A “Woody” vs.. “Herbaceous” Plant:  A “Woody” vs.. “Herbaceous” Plant If a plant contains any woody parts, it is classified as a woody plant. If a plant has no woody parts, it is considered a herbaceous plant. Plant Organs:  Plant Organs Vegetative organs Leaves Roots Stems Reproductive organs Flowers Fruits Seeds Plant Organs, cont.:  Plant Organs, cont. Edible vegetative organs are considered “vegetables” Edible reproductive organs are either “fruits” or “seeds” All plant organs are made up of three basic types of tissues. Meristematic Vascular Structural Meristematic Tissues:  Meristematic Tissues Only the cells in these tissues are usually capable of mitosis. Cells in these tissues can usually develop into any tissue found in a particular plant. Are found in the growing areas of the plant. Vascular Tissues:  Vascular Tissues Complex tissues Composed of many different types of cells. Transports water and dissolved materials throughout the plant. The skeletons of some of the cells of these tissues form the long conducting tubes for this transportation. Movement can often be up or down the plant as needed. Structural Tissues:  Structural Tissues Structural tissues: Produce food Store food Cover, support, and protect the plant The Leaf:  The Leaf Functions:  Functions Absorbing energy from the sun Without efficient energy absorption, photosynthesis could not take place. Photosynthesis Food production to support the plant Sometimes… Attract insects Protect plant Anchor plant Structures:  Structures Blade The large flattened part of the leaf. Petiole The stalk that connects the blade to the stem. Stipules The thin membrane that covers a leaf when it first emerges. Leaf Venation (Veins):  Leaf Venation (Veins) Leaf veins normally form in one of two patterns. Parallel Netted Parallel Venation:  Parallel Venation Parallel venation occurs when the leaf vein begins at the petiole (stalk) and moves toward the margin of the leaf in a relatively parallel fashion. Netted Venation:  Netted Venation Large veins branch to form smaller veins throughout the leaf. Simple Leaf vs. Compound Leaf Structure:  Simple Leaf vs. Compound Leaf Structure 1 blade per petiole – simple Multiple blades per petiole – compound The individual blades of a compound leaf are called leaflets Pinnately Compound vs. Palmately Compound:  Pinnately Compound vs. Palmately Compound Pinnately – the leaflets are arranged down the midrib. Palmately – the leaflets all originate at the same point. The Outside of the Leaf:  The Outside of the Leaf The outer covering of the leaf is called the epidermis One cell thick No chlorophyll May secrete a waxy protective coating called a cuticle May have epidermal hairs Give the leaf a velvety appearance, may produce scents, chemicals, toxins, needle-like protection. Leaf Epidermis, cont.:  Leaf Epidermis, cont. The stomata are little openings (usually in the underside of the leaf) that allow gas exchange to take place. Each stomata contains two “guard cells”. When the plant has plenty of water, these guard cells are turgid and the stomata is open. When the leaf begins to wilt, it is because turgor pressure has dropped – the guard cells relax, and the stomata cells close – preventing any further lose of water. The Inside of the Leaf:  The Inside of the Leaf The interior of the leaf is called the mesophyll. The palisade mesophyll is the primary location for photosynthesis. Cells are columnar to maximize the number of cells near the surface. Chloroplasts rotate around the central vacuole by what is known as cytoplasmic streaming. This insures that all the chloroplasts have turns at the top of the cell where sunlight is the strongest. Spongy Mesophyll:  Spongy Mesophyll Located under the palisade mesophyll Loosely packed cells with lots of air space around them Where gas exchange takes place. Contains fewer chloroplasts Why the undersides of many leafs are not as dark as the tops. Roots:  Roots Functions:  Functions To anchor the plant. Absorption of water and minerals necessary for plant growth and transportation of theses substances where needed. Place for food storage by the plant. Root Systems:  Root Systems If the plant’s original root (when sprouting from the seed) continues to grow and remains the primary root, the plant has a taproot system. The taproot is considered the primary root and the small branching roots that come from the primary root are called secondary roots. If the plant has only secondary roots, then it is called a fibrous root system. Root Growth:  Root Growth The tip of a root is covered with dead cells that protect the underlying tissues as the roots push through the soil. This is called the root cap. Just under the cap is the meristematic region, where undifferentiated cells perform rapid mitosis. Behind the meristematic region is the elongation region. This is where cells grow and develop into specific root tissues. When fully developed, the cells are said to be in the maturation region. The Primary Root Tissues:  The Primary Root Tissues The outermost layer is the epidermis. One cell thick. Protects the root and absorbs materials. Produces root hairs, which penetrate the soil to increase water absorption. The next layer is the cortex. Primary location for storage. Inside the cortex is the endoderm. Cells are tightly packed so that substances most go through the cells to enter the vascular system of the plant – not around them. Primary Root Tissues, cont.:  Primary Root Tissues, cont. The vascular cylinder is the central area of root. Where the xylem and phloem vessels are located. Stems:  Stems Functions:  Functions Manufacture, support, and display leaves. Conduct materials between the leaves and the roots. Branching Pattern:  Branching Pattern Excurrent: One main stem with the secondary branches radiating from it (such as a pine tree). Deliquescent: A branching pattern that makes it difficult to distinguish the main stem in older plants (such as a maple). Columnar: A crown of leaves on top of an unbranched stem (such as a palm tree). Stem Buds:  Stem Buds The buds at the growth end of a stem are called apical buds. The buds along the sides of a stem are called lateral buds. Lateral buds will typically only develop if the apical buds are damaged. The place where leaves are produced on a stem are called nodes. Stem Structure:  Stem Structure Once again, the exterior layer of a stem is called its epidermis. The interior is mostly xylem, which comprises most of what we refer to as wood. The most interior area of the xylem is called the pith. This is where materials are transported and stored. Spoke like rays extend from the pith toward the epidermis of the stem. They are called pith rays and conduct materials to and from the outer layers to the pith. Stem Structure, cont.:  Stem Structure, cont. The horizontal channels that move water are known as vascular rays. Springwood and summerwood produce the annual rings in trees. Springwood is the lighter wood. Summerwood is the darker wood (the wood produced in summer is usually denser and therefore darker) Scientist study past climate conditions by the width of these bands. Bark:  Bark Bark is the remains of phloem tissue. Phloem tissues called cork cambium are thin cells that die and produce a protective wall that is resistant to water, insects, disease, ect. This forms what is known as the inner bark. As the stem grows and expands, cork cambium cannot stretch to accommodate the growth, so it splits. This forms the rough textured outer bark. Lenticels:  Lenticels Lenticels are tiny openings in the stems that allow oxygen into the interior tissues for respiration. Herbaceous Plants:  Herbaceous Plants Unlike a “woody” plant, herbaceous plants do not produce cork cambium, and therefore do not produce bark – but retain their epidermal layer for the life of the stem. Limits overall growth potential. More susceptible to damage or disease.

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