PLANT TISSUES

Seed plants have 3 principle organs

1. Roots—absorb water and dissolved nutrients, anchor the plant to ground

2. Stems—is a support system for the plant, nutrient transportation highway, defense from disease and predators

3. Leaves—photosynthesis factories for plants

Plant tissue types

1. Dermal tissue Consists of the single layer of epidermal

cells that line the outside of a plant There is a thick waxy coating on these cell

called the cuticle which prevents water loss In the roots, the root hair are made up of

this tissue type and do most of the plant absorption

2. Vascular Tissue

This tissue forms the transport system that move water and nutrients throughout the plant

Xylem and Phloem are included in this

3. Ground Tissue

These are the cells the lie between dermal and vascular tissue

There are 3 types of Ground tissues 1. Parenchyma 2. Collenchyma 3. Sclerenchyma

Parenchyma

Most plants ground tissue is composed primarily of this tissue

Has thin cell walls and large central vacuoles surrounded by a thing layer of cytoplasm In the leaves they also have chloroplasts

(where photosynthesis occurs)

Collenchyma

Have strong, flexible cell walls that help support larger plants They make of the “strings” on celery stalks

Sclerenchyma

Have extremely thick, rugged cell walls that make ground tissue tough and strong

Plant Growth

Plants grow only at the end of each stem or root, these places are called the apical meristems

Meristems are clusters of cells that can become any type of plant cells (like stem cells in animals), they aren’t differentiated

Roots

There are two types of plant roots

1. Taproot One big primary root

and secondary are all small

2. Fibrous root Roots branch so

much that there is no one single large root

Roots

A mature root has all 3 layers of plant tissues Epidermal, Ground and Vascular

Root hairs do most of the work of absorption

These are small root

projections off of main roots

Stems

Stems have 3 important functions: 1. Producing Leaves, Branches and Flowers 2. Holding leaves up to the sunlight 3. Transporting substances between roots

and leaves

Stem Growth

Primary Growth Is growth that increases the length of a

plant, it is produced by cell divisions in the apical meristem.

Takes place in all seed plants Secondary Growth

Growth which increases the width of stems It takes place in lateral meristematic

tissues called vascular cambium (produces new xylem and phloem) and cork cambium (produces bark)

Formation of Wood

Most of what we call wood is actually layers of Xylem A tree is constantly making new xylem as it

grows outward, and inner xylems no longer function

Heartwood is old xylem that no longer conducts water Sapwood is newer xylem that still conducts water

Tree Rings

Tree rings form due to seasonal growth Typically in the spring nutrients are

abundant and the cells grow rapidly As winter closes in, cell are growing slower

and are much smaller and have a darker appearance

Each tree ring indicates a year

Leaves

Are structures optimized for absorbing light and carrying out photosynthesis

Leave have blades and petioles Blades are the flat sections Petioles are thin stalk that attaches a blade to the stem

Stomata and Guard Cells

Leaves run photosynthesis and thereby require gaseous exchange

Stomata are pore like openings in leaves that allow for Carbon dioxide or Oxygen to enter or exit the leaf

Each stoma is protected by two cells called guard cells that can cover or uncover the stoma when needed

Open Stoma Closed Stoma

Why have Guard cells?

Guard cells keep the stomata open just enough to allow photosynthesis to occur but not so much that they lose an excessive amount of water

On a hot day, the stoma may remain closed Some desert plants open the stomata only at night

Note… If it is a hot day, a plant will have water pulled out of its leaves from the stomata and have to pull up excessive amounts of water from the soil…This is called transpiration (think evaporation but the water is coming from plants)

Transpiration