Chapter 21 Plant Structure and Function Section 1

Chapter 21 Plant Structure and Function

Section 1 Plant cells and Tissue • Parenchyma – Loosely packed – Cube-shaped or elongated – Large central vacuole – Flexible cell walls – Involved in metabolic functions

2 • Collenchyma – Thicker than parenchyma – Support for cells that are still lengthening • Schlerenchyma • Thick, even, rigid cell walls • Support and strengthen where growth has ended.

Tissue Systems • 1. Dermal system – Forms the outside covering of the plant – Outer layer is made up of parenchyma cells – Outer epidermal wall is the Cuticle –waxy layer.

• 2. Ground tissue system – Contains all three types of plant cells – Covered by the dermal tissue – Storage, metabolism, support – Parenchyma most common cell found in the ground tissue.

• 3. Vascular tissue system – Transports, and supports – Contains xylem and phloem – In angiosperms ( flowering plants) xylem has tracheid's made up of schlerenchyma cells. Called vessel elements – water moves through tracheid pits which are located in the cell wall

– Vessel elements have large holes in the top or bottom walls or no end walls at all – Stacked to form long tubes called vessels – Most seedless and gymnosperms contain only tracheid's. – In angiosperms the parenchyma conducting cells are called sieve tube member – Stacked to form long sieve tubes, compounds move through end walls called sieve plates – Sieve tubes have a companion cell next to them, they help to transport materials.

Plant growth • Meristems- cells continuously divide. Two types: –Apical meristem • Where plants grow in length • Located at the tips of stems and roots

• 2. Lateral meristem – Gymnosperms (woody) and most Dicots stems and roots grow in diameter. – Two types of lateral meristem • 1. Vascular cambium – Between the xylem and phloem – Produces more vascular tissue 2. Cork Cambium - outside of the phloem - produces cork - cork replaces epidermis in woody stems and roots

Section 2 Roots • A primary root, first root if it becomes large it is called a taproot ex. Carrot • Fibrous root system – Numerous small branching roots – Many monocots ex. Grasses • Adventitious roots • Grow from uncommon places like stems and leaves ex. Prop root, aerial root

Root structure • Root cap- covers the apical meristem – Produces a lubricating oil to move the root through the soil. • Root hairs • Extensions of epidermal cells • Increases surface area • Increases the plants ability to absorb water

• Root grows in length by cell division – Elongation and maturation occurs in the apical meristem in the root tip – Dermal tissue matures to form the epidermis – Ground tissue matures into the Cortex, and endodermis – Vascular tissue matures innermost core of the root. • Outermost layer is called the pericycle • Pericycle forms the lateral roots

Secondary growth roots • Dicot and Gymnosperm has secondary growth – Cells from pericycle and vascular cambium form between the primary xylem and phloem. – Produces secondary xylem inside and phloem to the outside.

• Root functions – Absorbing water and minerals • Macronutrients- N, K, P, Ca, S • Micronutrients- Mg in smaller amounts – Storage of water, and carbohydrates • Converted to starch and stored in parenchyma cells • Stores water for dry periods

Section 3 Stems • Woody • Non-woody • Modified stems – Stolon ex. Strawberry – Tuber ex. Potato – Succulent ex. cactus

• Growth in length at the apical meristems • Growth in circumference is at the lateral meristems • Leaf attaches to the stem at a node • The space between nodes is the internode. • Each node has a bud which can form a new shoot • Bud is enclosed by specialized leaves called bud scales • Stems apical meristem is protected by bud scales when they aren’t growing

Primary Growth • Apical meristem gives rise to dermal, ground, and vascular tissue • The dermal is the epidermis • Gymnosperms and dicots the ground tissue forms the cortex and pith • Pith is in the center for storage • Monocots ground tissue doesn’t separate into pith and cortex it is mixed up.

Secondary growth • Secondary xylem (wood) • Older xylem stops transporting of water and turns dark. • Heartwood- in the center and is darker in color. • Sapwood- lighter in color, nearer to the outside • Bark- phloem produced outside of the stem • Springwood- formed in wide rings if water is plentiful

• Summer wood- water is limited, smaller cells are produced • Annual rings- the change between summerwood and springwood.

Stem Function • Transport of nutrients, water, storage, and support • Phloem transports, carbohydrates, and plant hormones • Translocation- the movement of carbohydrates. They are moved from storage which is called the source to the use site called sink

• pressure-flow hypothesis- active transport of the sieve tubes • Xylem – transports water • Transpiration when water evaporates through the stoma • Cohesion-tension theory – Water is pulled up the stem by cohesion of water molecules to each other – Adhesion of water molecules to the xylem walls

Section 4 Leaves • Example of leaf type – Tendril- found in vines, wrap around objects – Tubular- traps food in carnivorous plants – Spines- protection, reduce water transpiration – Blade- broad flat portion – Petiole- stalk like that attaches the leaf to the stem

• Simple – only one blade • Compound- blades divided into leaflets • Double compound- when the leaflet divides

Leaves Tissue • Dermal tissue – Epidermis – Cuticle – Stomata – Epidermal hairs

• Ground Tissue – Photosynthesis occurs in the mesophyll – Mesophyll have two layers • Palisade- below the upper epidermis, it is the site for most photosynthesis • Spongy- irregularly shaped cells, large air spaces.

• Vascular tissue – Large bundles- in the veins – Veins are embedded in the mesophyll – Venation- arrangement of veins in a leaf. Monocots- have parallel venation Dicots- net venation

Leaf Function • Primary site for photosynthesis • Modifications for capturing light – Dry environments, they conserve water by the closing of stomata Guard Cells- located on both sides of the stomata, regulate gas and water exchange K ions pumped into the guard cells cause them to bow and open forming a pore. Darkness, K ions are pumped out closing the stomata