Chapter 23 Roots, Stems,& Leaves

Specialized Tissues

• Seed plants are organized into different tissues and organs

Three principal organs are:1. Roots2. 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 branches2. transport system that carries nutrients3. defense system against predators and disease

Leaves

• Functions:1. primary photosynthetic organ of the plant2. contains subsystems that prevent

water loss3. Gas exchange (CO2 and O2)

Plant Tissue Systems

Three main tissue systems:1. Dermal tissue – outer layer much like skin2. Vascular tissue – bloodstream for transport of water and nutrients3. 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 plantEx: 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 elements2. 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 RootsTwo main types of roots:1. Taproots – primary root grows long and thick, while others are small

Ex: carrots, beets, radishes, oak trees

*Mainly Dicots2. 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