The Structure and Function of
Plants
Section 1:
Levels of Organization in Plants
Levels of Organization in Plants
• What is a plant?
– Multicellular: A plant must
consist of more than one cell.
– Eukaryotic: Plant cells must
contain a nucleus.
– Photosynthesis: many plant
cells have chloroplast, an
organelle that converts
sunlight into carbohydrates.
– Cell Walls: all plant cell
have cell walls made of
cellulose for support.
Levels of Organization in Plants
• Structure and Function: Plants have several structures that
have evolved to make certain functions possible.
• "Structure determines function“
Examples:
Structure: A cell is long, cylindrical and
hollow.
Function: Transports substances
throughout the plant.
Structure: A cell is packed full of
chloroplasts.
Function: Gathers sunlight for
photosynthesis
Levels of Organization in Plants
All multicellular organism have the
same levels of organization:
1. Cells: the basic unit of structure and
function in living things.
2. Tissue: A group of similar cells
working together to perform a
function.
3. Organ: A group of tissues working
together to perform a function.
Plant Organs: Roots, Stems, Leaves
Structure of Function of Plant Tissues
Each of the 3 organs of the plant (roots, stems and
leaves) is made up of three main types of tissue.
1. Dermal Tissue: “skin” of a plant
– the protective outer covering of a plant.
– Epidermis: the outermost single layer of cells
Structure of Function of Plant
Tissues
2. Ground Tissue: Produce and stores
sugars, and provides physical support
for the plant.
Made up of four different types of cells
a) Parenchyma
– Structure: Large cells,
thin cell walls, large
vacuoles.
– Function: Storage
(Stores sugar, starch,
and water)
b) Chlorenchyma
–
–
Stucture: parenchyma
cells packed with
chloroplasts.
Function: carryout
photosynthesis
Structure of Function of Plant Tissues
c) Collenchyma
–
–
–
Structure: Have thick,
but flexible cell walls.
Function: Provides
support
Ex: Prevents plants from
breaking in wind.
d) Sclerenchyma
–
–
–
Structure: Have extremely
thick cell walls, cells are
dead at maturity.
Function: Provide support
Forms seed coats and
plants fibers
Structure of Function of Plant Tissues
3. Vascular Tissue: “bloodstream” of a plant circulating
water and nutrients
There is two types of vascular tissue: xylem and phloem
a) Xylem – Conducts water from
roots to the leaves.
b) Phloem – Transports sugar and
nutrients from the leaves to the
rest of the plant.
Cells are shaped like long hollow
tubes that run continuously from
the roots to the leafs.
Structure of Function of Plant Tissues
How does vascular tissue transport
water in the plant against the force
of gravity?
• Three possible answers:
1. Root pressure – pressure created from
the water moving into the root.
Does not exert enough force to lift
water up into trees
Structure of Function of Plant Tissues
2. Capillary Action – waters ability to climb up thin
tubes.
• The thinner the tube the higher the water climbs.
• Xylem cells are just really thin tubes.
• Even the thinnest tubes can only cause water to
climb a few cm.
3. Transpiration – the loss of water through leaves
• Pulls the water through the plant.
• The strongest force in water transport.
Structure of Function of Plant Tissues
How can water be pulled upward?
• Water molecules are polar – they have a positive and a
negative end.
• Hydrogen bonds from between the positive and negative
charges.
• Two properties of
water
1. Cohesion – attraction
between molecules of the
same substance
2. Adhesion - attraction
between molecules of
different substances.
Structure of Function of Plant Tissues
• How can water be pulled upward?
– The water molecules are all
connected like a chain (cohesion)
– The water molecules also connect
to the sides of the xylem cells
(adhesion)
– Water gets evaporated from the
surface of the leave
(Transpiration)
– The chain of water is pulled
upward to replace the lost water.
Structure of Function of Plant Tissues
Meristem Tissue: regions where
cells are rapidly dividing to
allow for plant growth.
– Cells are unspecialized: they all
initially look alike
– Differentiation: Unspecialized
cells mature into one of the 3 types
of tissue: dermal, vascular or
ground.
Structure of Function of Plant Tissues
Meristem tissue causes 2 types of
plant growth.
a) Primary Growth: Adds
length to the plant
– Apical mersitem: the tip
of each stem or root where
cells are dividing.
What would happen if the stem apical meristem was
damaged?
Structure of Function of Plant Tissues
b) Secondary Growth: increases the thickness of the plant.
– Secondary growth takes place at the vascular cambium.
– Vascular cambium is a single ring of meristem cells.
– Cells produced inside the vascular cambium become
xylem and cells outside become phloem.
Root Structure and Function
1. Root Functions: anchors the plant, absorbs
nutrients and holds plant upright.
Two types:
a) Taproot – primary root grows long and
thick while secondary roots remain
small.
b) Fibrous Roots –highly branched so that
no root grows larger than the rest.
Which root system represents a monocot and
which represents a dicot?
Root Structure and
Function
Dermal Tissue in the Roots
• The roots covered with dermal
tissue called root hairs.
– Roots hairs are
microscopic extension
of the outer cells
– They increase surface
area of the root to
absord bnutrients and
water from the soil.
Root Structure and Function
•
Root hairs have proteins
that pump nutrients from
the soil into the root.
–
Diffusion: molecules
“want” to move to an area
of high concentration (the
root) to low concentration
(the soil).
–
Active transport: using ATP to pump molecules from
low concentration (the soil). to high concentration (the
root) .
What is ATP?
–
Root Structure and Function
• After nutrients are pumped into the root,
water follows by osmosis.
– Osmosis is the movement of water molecules
through a membrane from high concentration to
low concentration.
– Does not require energy.
Root Structure and Function
Gound Tissue in Roots
• Water and nutrients that
enter the root hairs are
stored in a layer of
ground tissue.
• What type of ground tissue
would you expect to find
in a root?
Root Structure and Function
Vascular Tissue in the Roots
• Vascular tissue is always
located in the center of the
roots.
– Xylem transports water up to
the stem.
– Phloem transport nutrients to
wherever they are needed in
the plants.
• Xylem and Phloem are
arranged differently in
monocots and dicots.
Monocot
Dicot
Root Structure and Function
Meristem Tissue in the Roots
• Apical Meristem – adds new cells
to the end of the root.
• Root Cap – protects the apical
meristem at it pushes through the
soil.
• What would happen if the apical
meristem was damaged.
Stem Structure and Function
Stem Functions
a) Produces leaves, branches, and flowers
b) They hold leaves upright to the sunlight
c) They transport substances between throughout the
plant.
What is the primary function of these stems?
Stem Structure and
Function
Dermal Tissue in the Stems
• Woody stems are covered with
bark.
• Bark – all the tissue outside the
vascular cambium
– Phloem: cells that transport
sugars, produced outside the
vascular cambium.
– Cork: outer layer of dead,
water-proof cells.
What is the function of the cork
cells?
Stem Structure and Function
Vascular Tissue in Stems
• Vascular tissue in the stems runs
from the roots to the leaves
carrying water and nutrients.
• In herbaceous stems vascular
tissue is arranged differently in
monocot and dicot plants.
Dicot
Monocot
Stem Structure and Function
Vascular tissue in woody stems
• Xylem cells produced
towards the center of the stem
form wood
– Heartwood: older,
inactive xylem cells;
darker in color
•
– Sapwood: newer, active
xylem cells, lighter in
color
Phloem cells are produced
towards the outer edge of
the stem and fall off as new
cells are produced.
Stem Structure and Function
Ground Tissue in Stems
• All types 4 types of ground tissues can be found in
the stem depending on the function of the stem.
Meristem Tissue in Stems
• Buds: underdeveloped meristem tissue that
produces new stems or flowers.
• Most buds are protected by scales.
• Example: Brussel sprouts are enlarged buds
Leaf Structure and Function
3. Leaf Functions: carryout photosynthesis
a) Designed to absorb sunlight
b) Carryout gas exchange (absorb CO2 and release O2)
What is the function of these leaves?
Leaf Structure and Function
Dermal Tissue in the Leaf
• Cuticle: the waxy layer on the top surface of the leaf that
prevent water loss.
• Stomata: small pores on the underside of the leaf that
allows CO2 in and O2 out.
• Guard Cells: surround the stomata and control their
opening and closing.
Leaf Structure and Function
• Water can also leave with through the
stomata.
• Transpiration: the loss of water
through leaves.
• The Problem
– If stomata are open plant loses water
but can photosynthesize
– If stomata are closed the plant save
water but cannot photosynthesize
• Solution: Plants keep the stomata open
just long enough to allow
photosynthesis but not so long that they
lose too much water.
Leaf Structure and Function
Vascular Tissue in the Leaf
• Xylem and phloem are bundled in veins.
– Monocot leave have parallel viens
– Dicot leaves have branching viens
Ground Tissue in the Leaf
• Mesophyll is a layer of chlorenchyma cells.
• What is the function of chlorenchyma cells?
• Dicots have two layers of mesophyll: palisade
and spongy.
• Monocots only have spongy.
Leaf Structure and Function
Cuticle
Epidermis
Palisade
Mesophyll
Vein – Xylem
and Phloem
Spongy
Mesophyll
Stomata