Chapter 23 Roots, Stems, & Leaves

Specialized Tissues Seed plants are organized into different tissues and organs Three principal organs are: 1. Roots 2. Stems 3. Leaves Each work together to at a slow efficient pace to ensure the plant’s survival

Roots Functions: 1. absorb water and dissolved nutrients 2. anchor plants to ground; prevent erosion 3. Protect plant from harmful bacteria and fungi 4. transport water and nutrients to rest of the plant

Stem Functions: 1. support system that maintains or hold leaves and branches 2. transport system that carries nutrients 3. defense system against predators and disease

Leaves Functions: 1. primary photosynthetic organ of the plant 2. contains subsystems that prevent water loss 3. Gas exchange (CO2 and O2)

Plant Tissue Systems Three main tissue systems: 1. Dermal tissue – outer layer much like skin 2. Vascular tissue – bloodstream for transport of water and nutrients 3. Ground tissue – layers of plant in between dermal and vascular tissue

Dermal Tissue Epidermal cells make up the outer layer of plant Cuticle - outer waxy covering of the epidermal cells that protects the plant from water loss and injury Dermal tissue appears in different ways throughout structure of the plant Ex: root hairs that increase water absorption - guard cells on the leaf that regulate gas exchange and water loss

Vascular Tissue Forms that transport system that moves water and nutrients throughout the plant - much like circulatory system in humans Two tissues of vascular system: 1. Xylem – water conducting tissue - composed of tracheids & vessel elements 2. Phloem – food conducting tissue - composed of sieve tubes & companion cells

Ground Tissue Found between dermal and vascular tissue - Parenchyma – cells with thin cell walls and large vacuoles that help with storage in leaf - Collenchyma – strong flexible cell walls that help with support in stem - Sclerenchyma – thick, rigid cell walls for support in stem

Growth and Meristematic Tissue Meristematic tissue is only plant tissue that produces new cells by mitosis - tissue is undifferentiated or does not have a function yet - forms cluster of cells that will contribute to growth of roots and stem - Apical meristem – found at the end or tip and will increase length of stem and roots when the cells divide

Types of Roots Two main types of roots: 1. Taproots – primary root grows long and thick, while others are small Ex: carrots, beets, radishes, oak trees *Mainly Dicots 2. Fibrous roots – branch out so that each root is about the same size - prevents topsoil from washing away Ex: grasses *Mainly Monocots

Monocots vs. Dicots

Root Uptake and Nutrients Part of the roots function is to absorb water and nutrients- plants expend energy to do this - nutrient uptake help facilitate other processes that will aid in growth, reproduction and flowering - Nitrogen, phosphorus, potassium, magnesium, and calcium are essential nutrients - sulfur, iron, zinc, chlorine, boron, copper, manganese, and molybdenum are trace elements

Stem Stems can be any shape or size Stems can grow entirely underground or high into the air Nodes – distinct regions where leaves attach to the stem Buds – undeveloped tissue that can produce new stems and leaves

Vascular Bundles Vascular bundles carry out the transport of materials from the roots to the leaves - includes xylem and phloem tissue - Monocots have bundles scattered throughout the stem - Dicots have bundles arranged in a ring

Growth of Stems Primary growth occurs with cell divisions of the apical meristem As most plants grow they must also increase in thickness to support more branches and leaves Secondary growth occurs by expansion of 2 kinds of tissue in the lateral meristem - vascular cambium – thickens by producing new layers of xylem and phloem - cork cambium – tissues that form outer protective covering

Formation of Wood Wood is simply older layers of xylem When xylem at the center of the stem has stopped conducting water it is known as heartwood (dark wood) Sapwood surrounds heartwood, and is active in fluid transport (lighter wood) Alteration of dark and light wood produces tree rings which are used to estimate age of tree

Bark Bark is formed from vascular cambium, phloem, cork cambium, and cork Each layer expands to accommodate the other Outermost cork contains cells with thick cell walls and usually contains fats, oils, and waxes (waterproofing) Dead cells of cork (bark) crack and flake off in patches or strips

Wood and Bark

Leaves Considered the most important manufacturers of food that directly or indirectly affect all organisms Blades are the flattened sections of the leaf that collect sunlight Petiole connects the blade to the stem No matter the shape, same structures in all leaves

Leaf Structure In order to carry out photosynthesis the leaf depends on specialized ground tissue called mesophyll Palisade mesophyll contains the chloroplasts to absorb sunlight Spongy mesophyll connects to exterior through the stomata (pores)

Leaf Functions Guard cells regulate the opening and closing of stomas in response to water pressure - Water pressure high guard cells pull away from each other opening the stomata to relieve pressure - Water pressure low guard cells move together to conserve - acts same in both cases of water conservation and gas exchange Transpiration - loss of water through the leaves

Transport Xylem is the main tissue of water transport that spans from roots to leaves Active transport draws water into the roots Capillary action is the tendency of water rise in thin tubes - xylem network changes to thinner transport tubes as it reaches leaf