Transcript Chapter 25

Chapter 25
Plant Structure and Function
I. Tissues
A. Dermal Tissue
• Covers the outside of a
plant’s body as
protection
• Forms a “skin” called
the epidermis in
nonwoody plant parts
• A waxy cuticle, which
prevents water loss,
coats the epidermis of
the stems and leaves
• Extensions on the
epidermal cells on
root tips help increase
water absorption
• Forms layers of dead
cells called cork on
woody stems and
roots
B. Ground Tissue
• Makes up most of the inside
of most plants
• Surrounds and supports
vascular tissue
• Specialize in photosynthesis
in leaves, as they are packed
with chloroplasts
• Store water, sugar, and
starch in stems and roots
C. Vascular Tissue
1. Xylem
• Thick-walled cells that conduct water and
mineral nutrients from a plants roots
through its stems to its leaves
• Must lose their cell membrane, nucleus, and
cytoplasm before they can conduct water
- All that is left is the cell wall
a. Tracheid
• Narrow, elongated,
and tapered at each
end
• Water flows through
pits, or thin areas in
between
neighboring cell
walls
b. Vessels
• Wider
• Larger perforations
in their ends that
allow water to move
more quickly
2. Phloem
• Conduct sugars and other nutrients
throughout a plants body through connecting
cells that form sieve tubes
• Cells either lack organelles or have modified
organelles
• Pores in the walls between
neighboring sieve-tube
cells connect the
cytoplasms and allow
substances to pass freely
from cell to cell
• Companion cells lie next to
the sieve-tube cells and
carry out cellular
respiration, protein
synthesis, and other
metabolic function for the
sieve-tube cells
II. Roots
• Absorb water and mineral nutrients
• Store organic nutrients such as sugar and
starch
• Dicots, such as carrots and radishes, have a
large central root from which much smaller
roots branch; a taproot system
• Monocots, such as grasses, have a highly
branched, fibrous root system
• Roots contain a central
core of vascular tissue
that is surrounded by
ground tissue, called the
cortex
• A mass of cells called
the root cap covers and
protects the actively
growing root tip
III. Stems
• House vascular tissue which transports
substances between the roots and the leaves
• Leaves are attached to a stem at points called
nodes
• The space between two nodes is called an
internode
A. Nonwoody Stems
• Also called herbaceous plants
• Xylem and phloem tissue arranged in vascular
bundles which are surrounded by ground
tissue
• Two types of ground tissue
1. Cortex – outside tissue
2. Pith – center of the stem
B. Woody Stems
• Cork covers woody stems and protects them
from physical damage and helps prevent
water loss
• Cork and phloem tissue make up bark
• Heartwood at the center of the stem contains
xylem that no longer conducts water
• Sapwood, (in between heartwood and bark)
contains xylem that can conduct water
IV. Leaves
• Primary
photosynthetic
organs of plants
• Consist of a flat
blade that is
attached to the stem
by a stalk called the
petiole
• A leaf may be divided into two or more leaflets
and is called a compound leaf
- Leaflets reduce the surface area of a leaf
blade
• An undivided blade is called a simple leaf
• Xylem and phloem are found in the veins of a
leaf
• Veins are extensions of vascular bundles that
run from the tips of roots to the edges of
leaves
• The ground tissue in leaves is called mesophyll
• Mesophyll is packed with chloroplasts which
makes the leaves look green
V. Movement of Water
Step 1
• When the pores of a leaf, the stomata, are
open, water vapor diffused out of a leaf
• This loss of water vapor is called
transpiration
• More than 90 percent of the water taken in
by the roots is ultimately lost through
transpiration
Step 2
• The cohesion of water molecules causes water
molecules that are being lost by a plant to pull up
on the water molecules still in the xylem that
extends from the roots to the edges of leaves
Step 3
• Roots take in water from the soil by osmosis
and replaces water displaced by cohesion
through the xylem caused by transpiration
A. Guard Cells and Transpiration
• Stoma are surrounded by a pair of guard cells
• Each guard cell swells in length as they take in
water
• As guard cells take in water, they bend away
from each other, opening the stoma and
allowing transpiration to proceed
• When water leaves the guard cells, they
shorten and close the stoma, stopping
transpiration and further water loss
• Homeostasis in action
VI. Movement of Organic Compounds
• Organic compounds are provided by what
botanists call a source
• Organic compounds are delivered to what
botanists call a sink
• Sugar from a source enters phloem cells by
active transport
Step 2
• When the sugar concentration in the phloem
increases, water enters the cells by osmosis
Step 3
• Water pressure increases inside the cell and
pushes sugar out
Step 4
• Sugar moves to the sink through active
transport