Plant Structure (Leaves, Stems, Roots) Honors Biology

Plant Body Shoot system = leaves + stem Root system Meristem = cells that divide for life of plant, can give rise to all plant structures 3 BASIC Organs Roots Stems Leaves

2 BASIC Systems BOTH SYSTEMS DEPEND ON THE OTHER Root System (roots) receive sugars and other nutrients from photosynthetic parts Shoot System (leaves and stems) depends on water & minerals absorbed from the soil by roots.

Tissue Types in Vascular Plants Dermal Tissue Covers/ protects plant Makes cuticle on stems/ leaves Allows for better H2O absorption (root hairs) Make guard cells Vascular Tissue (xylem & phloem) Transport and support Throughout the plant Called “veins” in leaves Called the “stele” in stem or root Ground Tissue Between dermal and vascular tissues Storage Photosynthesis (makes sugars) Support Dermal tissue Vascular Ground

Stoma = opening in the leaf for gas exchange, water evaporation Plant Body-LEAF Leaf = blade + petiole Functions Exposes surface to sunlight Major site of photosynthesis Conserves water Provides for gas exchange Transpiration-water movement throughout the plant; evaporation of water from plant leaves Blade Petiole Stoma = opening in the leaf for gas exchange, water evaporation

Leaf Structure-Dermal layers Cuticle-The thin waxy covering on the outer surface of the leaf has a thin waxy covering This layer's primary function is to prevent water loss within the leaf. (Plants that live entirely within water do not have a cuticle). Directly underneath the cuticle is a layer of cells called the epidermis (upper and lower)

Leaf Tissues Mesophyll Veins Ground tissue between upper and lower epidermis Two types: Palisade parenchyma (mesophyll) cells Lots of chloroplasts in these cells Most photosynthesis occurs here Spongy parenchyma (mesophyll) cells Lots of air spaces where O2 and CO2 circulate Near stomata (Think: sponges have lots of air spaces) Veins Xylem and phloem are continuous from roots through stem to leaves

Vascular Tissue (Veins) Transports materials in roots, stems, & leaves. Xylem (dead cells-water conducting) Carry water & minerals up from roots Tube-shaped dead cells Their walls are used as water pipes Phloem (living cells-food conducting) Carry nutrients (food) throughout plant SUGARS (sucrose), amino acids…. Tube-shaped living cells

Stomata and Guard Cells The underside portion of a leaf has stomata and is the site of transpiration (water loss) and gas exchange. During the day, the stomata of most plants are open, allowing the CO2, necessary for photosynthesis. When the plant is full of water, the two guard cells plump up, opening the stoma. When the stomata are open, water evaporates from the leaves. When the plant is losing water from transpiration faster than it is gaining water at its roots, the guard cells deflate and close the stomata. With stomata closed, the plant may run low on CO2 for photosynthesis. However, when the stomata is closed, the plant may run low on CO2. The stomata closes at night. Factors such as temperature, humidity, hormonal response, and amount of CO2 in the leaves signal the guard cells to open or close.

Stomata help regulate the rate of transpiration Guard cells 2 cells on either side of stomata (surrounds stomata) regulate water loss What conditions will promote closing of guard cells? Hot, dry, windy conditions

Stoma Opening/Closing http://academic.kellogg.edu/herbrandsonc/bio111/animations/0021.swf

Plant Body- ROOTS Root Functions Anchors plant in soil Takes up water and minerals from soil

& gymnosperms

Modified Roots Some plants have modified roots Adventitious roots arise aboveground  spread over large areas Storage roots hold “food”  called root tubers

Phloem transports sugar Plant Body-STEM Stem: series of nodes and internodes Functions Support for the plant body Holds leaves up to light Transports nutrients throughout plant Xylem conducts water and minerals Phloem transports sugar

Division of Meristem Cells Causes Plant Growth Apical Meristem tips of root and shoot increase in height Lateral Meristem cylinders within plant body increase in width

Types of Meristems (like embryonic stem cells) Apical meristems are located at the tips of roots and in the buds of shoots elongate shoots and roots, a process called primary growth Lateral meristems add thickness ONLY to woody plants, a process called secondary growth

MONOCOT PLANTS vs. DICOT PLANTS Monocots: grasses, lilies, orchids, corn, palms, onions Dicots (aka-Eudicots): broadleaf trees, shrubs, most flowers, and vegetables. Cotyledon=seed leaf