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
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
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)