Roots, Stems & Leaves
Chapter 23
Overview of the Cell
Nucleus
• The nucleus contains
nearly all of the cell’s
DNA, which includes all
the instructions for
making proteins and other
important molecules. Also
contains a structure called
the nucleolus, where
ribosomes are produced.
Cell Membrane
• The cell membrane (or plasma membrane)
regulates what enters and leaves the cell, and
provides protection and support. Many
substances can pass through the cell
membrane, through active or passive
transport.
Cell Wall
• The cell wall (found in plants, algae, and fungi,
but not in animals) lies outside the cell
membrane. The main function of the cell wall
is to provide support and protection for the
cell. Plant cell walls are made mostly of
cellulose. Most cell walls are porous enough
to allow transport of some materials in and
out of the cell.
Cell Wall
Cytoplasm
• The portion of the cell outside the nucleus is
the cytoplasm or plasma. The cytoplasm
includes all of the specialized structures that
carry out specific tasks within the cell. These
structures are known as organelles.
• The main organelles are:
Ribosomes
• Ribosomes are small particles of RNA and
protein where the coded messages from DNA
are used to produce proteins.
Endoplasmic Reticulum (ER)
• The ER is an internal membrane system where
lipid components of the cell membrane are
assembled.
• Some ER is covered in ribosomes, and the
proteins produced by those ribosomes are moved
into the ER to be modified. This type of ER is
known as rough ER because of its appearance.
• Other portions of the ER do not have ribosomes,
and is known as smooth ER. This smooth ER often
contains specialized enzymes to perform specific
tasks.
Rough & Smooth ER
Golgi Apparatus
• The Golgi apparatus functions to modify, sort,
and package proteins and other materials
from the ER, for storage in the cell or export
from the cell.
Lysosomes
• These are small organelles filled with
enzymes, they are designed to digest or
breakdown lipids, carbohydrates, and proteins
into small molecules that can be reused by the
cell.
• Lysosomes perform the vital function of
cleaning up “junk” in the cell, including
breaking down old organelles and other items
that would clutter up the cell.
Vacuoles
• These are saclike structures that store
materials such as water, salts, proteins, and
carbohydrates.
• Plant cells often contain a central vacuole
filled with liquid. This central vacuole helps to
maintain the structure of the plant through
turgor pressure.
Central Vacuole
Mitochondria
• These are organelles that
convert stored chemical
energy from food into
compounds that can be
use immediately by the
cell for energy.
• Mitochondria are known
as the “powerhouse” of
the cell.
Chloroplasts
• Chloroplasts – these are organelles that
capture the energy from sunlight and convert
it into chemical energy through
photosynthesis.
Label Your Diagram
Label Your Diagram
Colour-Code your Diagrams
• Pick a colour for each type of organelle or
structure, use it to underline the term in your
notes and on the diagram
– Then colour in that structure in that colour
• If the structure is found in both types of cells,
then use the same colour for both!
• This diagram will go into your logbook
• I’ll play a couple of summary videos while you
colour 
Crash Course - Cells
• Eukaryotic cells (animal cells)
https://www.youtube.com/watch?v=cj8dDTH
GJBY (11:34)
• Plant cells
• https://www.youtube.com/watch?v=9UvlqAV
CoqY (10:30)
Seed Plant Structures
• Roots – Roots absorb water and dissolved
nutrients and transport them to the rest of the
plant. Roots also anchor the plant in the soil and
hold plants upright against wind and rain.
• Stems – Stems include a support system, a
transport system, and a defense system.
• Leaves – Leaves are the main site of
photosynthesis – the broad surfaces allow for
effective light absorption, but also make water
loss an issue, so leaves also need to contain
systems to reduce water loss.
Plant Tissue Systems
• Plants contain 3 main
tissue systems –
Dermal tissue, vascular
tissue, and ground
tissue.
Dermal Tissue
• Dermal tissue is like the skin of a plant, it consists
of a single layer of cells called epidermal cells.
These cells are often covered in a waxy coating
(the cuticle) to protect against damage and
prevent water loss.
Dermal Tissue
• Dermal cells sometimes have tiny projections
called trichomes, which protect the leaf (this
is also why leaves sometimes look fuzzy).
• On the bottom of leaves, the dermal tissue
includes guard cells to regulate water loss and
gas exchange through the stomata.
• In roots the dermal cells include root hairs
which increase the surface area for water
absorption.
Vascular Tissue
• Vascular tissue makes up a transport system
to move water and nutrients throughout the
plant.
• The main subsystems are the xylem (waterconducting tissue) and phloem (foodconducting system).
• Both these systems are made up of systems of
hollow, specialized cells that can carry fluids
through the plant body.
Xylem
• Xylem is made up mostly of cells called
tracheids; long narrow cells with cells walls
that are impermeable to water. There are
openings in the cell walls to connect
neighbouring cells together.
• These cells mature and die, and their
cytoplasm disintegrates, leaving a series of
hollow cells that are interconnected.
Vessel Elements
• Angiosperms have an additional type of xylem
cell, called a vessel element.
• They also mature and die, leaving hollow cells
behind, but they are much wider than
tracheids, and the cell walls at their ends are
lost when the cell dies, creating a continuous
tube, through which water can flow easily.
Phloem
• Phloem is made up mostly of cells called sieve
tube elements. These cells are placed end to end,
like vessel elements, to form sieve tubes.
• The end walls have many small holes in them. As
sieve tube elements mature, they lose their
nuclei and most other organelles. Any remaining
organelles stick to the side walls.
• The cell is then mostly cytoplasm, and sugars and
other substances can be easily transported from
one cell to another through the holes in the end
walls.
Phloem – Companion Cells
• Phloem also contains
companion cells, which
surround sieve tube
elements. These cells keep
their nuclei and other
organelles, and they
support the phloem cells
and help to move
substances into and out of
the phloem.
Ground Tissue
• All the cells between the dermal tissue and
the vascular tissues are known as ground
tissue. In most plants, the main cells in the
ground tissue are parenchyma cells.
Parenchyma Cells
• These cells have thin cell
walls, large central
vacuoles and a thin
layer of cytoplasm. In
leaves these cells are
packed with
chloroplasts, and are
the site where most
photosynthesis takes
place.
Ground Tissue
• There are 2 other types of cells found in
ground tissue, both with thicker cell walls.
• Collenchyma cells have strong, flexible cell
walls that help to support larger plants.
• Sclerenchyma cells have extremely thick and
rigid cell walls to make the ground tissue
tough and strong.
Plant Growth & Meristematic Tissue
• Plants produce new cells at the tips of their
roots and stems for as long as they live. These
new cells are produced at meristems –
clusters of tissue that produce new cells
through mitosis. A meristem that is found at
the tip of each growing root or stem is called
an apical meristem.
Meristems
• The new cells produced
by the meristems are
initially undifferentiated
(not yet specialized). As
they mature, they take
on specialized structures
and functions to become
part of particular tissuetypes. This process is
called differentiation.
Floral Meristems
• In angiosperms, certain shoot apical
meristems can have particular genes turned
on, and they change into floral meristems. A
floral meristem produces both the modified
leaves that become the petals, and the
reproductive tissues of the flower.
Celery Demonstration
• I’ll set it up, fill in your predictions
• We’ll fill in the “before” masses
• We’ll check it again next week to see what has
happened.
Roots
• When a new seed germinates, it produces its
first root to absorb water and nutrients from
the soil, then other roots branch out from the
first to increase the surface area. The total
surface area of the roots can be much larger
than that of the stems and leaves.
Types of Roots
• There are two main types of roots
• Taproots – found mostly in dicots
– The primary root grows long and thick, any
secondary roots remain small
– Some tap roots of trees can grow long enough to
reach water in aquifers
– Examples: carrots, dandelions, beets, radishes
Types of Roots
• Fibrous roots – found mostly in monocots
– No single root grows larger than the others, there
is extensive branching
– These roots help to prevent topsoil from washing
away in heavy rain
– Examples: grasses, coconut palm
Types of Roots
Root Structure
• Roots contain cells form all three tissue layers:
dermal, vascular, and ground tissue.
Dermal System
• The epidermal system of the root has two
functions, protection & absorption
– Covered in cellular projections called root hairs
• Penetrate the spaces between soil particles and
increase the surface area for water absorption
• There’s also an endodermal layer between the
ground tissue and the vascular tissue
– Completely surrounds the vascular cylinder
Ground Tissue
• A spongy layer of ground tissue called the
cortex is sandwiched between the epidermis
and endodermis
Vascular Tissue
• The vascular cylinder of xylem and phloem
allows water, nutrients, and sugars to be
transported into and out of the roots.
Root Growth
• The root grows as the root apical meristem
produces new cells near the root tip. Most of
the increase in root length is produced at this
meristem, as new undifferentiated cells
elongate and then differentiate into their
specialized cell types.
Root Growth
• These new cells are fragile and would be
damaged when pushing through the soil, so
they must be protected by a tough root cap.
The root cap also produces a slippery
secretion to help the root move through the
soil more easily. Cells on the root cap are
continuously scraped away and must be
replaced regularly.
Amazing Plant Roots
• https://www.youtube.com/watch?v=_jVyhSe5
pvk (3 min)
Root Functions
• Water does not just “soak” into the root from
the soil - the plant has to spend energy to
absorb water.
Soil
• Soil is a complex mix of sand, silt, clay, air, and
bits of decayed matter from plants and
animals. Depending on the location and
depth, soil will have a different mix of these
ingredients. Sandy soils are low in nutrients,
while silty or clay soils with more organic
matter are higher in nutrients.
Essential Nutrients
• In addition to water and carbon dioxide,
plants require a variety of essential inorganic
nutrients such as phosphorus, nitrogen,
potassium, magnesium and calcium. See
below for the role of each nutrient. These
nutrients are found in varying amounts in the
soil, and are drawn up through the roots.
Trace Elements
• Lastly, plants also require trace elements in
very small quantities for proper plant growth
(although large amounts of these trace
elements can be poisonous to the plant).
Trace elements include sulfur, iron, zinc,
molybdenum, boron, copper, manganese, and
chlorine.
Essential Plant Nutrients
Nutrient
Role in Plants
Result of Deficiency
Nitrogen
Proper leaf growth and colour; synthesis of Stunted plant growth,
amino acids, proteins, nucleic acids (for
pale yellow leaves
DNA and RNA), and chlorophyll
Phosphorus
Synthesis of DNA; development of roots,
stems, flowers, and seeds
Potassium
Synthesis of proteins and carbohydrates;
Weak stems and stunted
development of roots, stems, and flowers; roots; edges of leaves turn
resistance to cold and disease
brown
Magnesium
Synthesis of chlorophyll
Calcium
Cell growth and division; cell wall
structure; cellular transport; enzyme
action
Poor flowering, stunted
growth
Thin stems; mottled, pale
leaves
Stunted growth; curled
leaves
Homework
• Start your Glossary
– Find all of the BOLD TERMS in your textbook for
Chapters 22-24
• Those are your glossary terms!
• You need to define these in your own words for your
logbook (Due Jan 9th)
Unit Test Thursday Dec 18th
On all of Chap 22 &23
(Chap 24 will be after the break)
Active Transport of Minerals
• The cell membranes of epidermis cells in the
roots contain active transport proteins. These
proteins use ATP (the quick-energy source
produced by the mitochondria) to pump
mineral ions from the soil into the plant.
Water Movement
• Moving these ions into the plant produces a
difference in concentration inside and outside of
the root.
• Osmosis is the movement of water to equalize
the concentrations on each side of a membrane.
Therefore water “follows” the mineral ions into
the root via osmosis.
• Notice that the root does not actually “pump” in
water – it pumps in ions, and water simply
follows via osmosis to try to equalize the
concentrations.
Osmosis Video
• https://www.youtube.com/watch?v=eQsAzXr
0UCU (4:30)
Into the Vascular Cylinder
• Once the minerals and water have moved into
the cortex, then they pass the inner boundary
of the cortex and into the endodermis.
• The endodermis completely surrounds the
vascular tissue of the root, creating a cylinder.
• The endodermis is ringed by a water-proof
strip called the Casparian strip – this prevents
the backflow of water from the vascular
cylinder back into the root cortex.
Osmosis
• Water moves into the vascular cylinder by
osmosis. Water and minerals cannot pass
back through the Casparian strip, so they
become trapped in the vascular cylinder once
they pass through the endodermis. This
produces a one-way movement of these
materials into the vascular cylinder of plant
roots.
Root Pressure
• This one-way movement of water and
minerals into the vascular cylinder is
necessary because it produces the pressure
needed to move water up and into the rest of
the plant.
• As minerals are pumped into the vascular
cylinder, more and more water follows,
creating a strong pressure.
Root Pressure
• Since the Casparian strip prevents the water
from flowing back, this pressure can only go
upward into the xylem, and through the
xylem to the rest of the plant.
• This is known as root pressure, and it is the
starting point for the movement of water
through the vascular system of the plant. We
will learn about the other processes when we
cover stems and leaves.
Stems
• Stems have three key functions – to produce
leaves, branches, and flowers; to hold up the
leaves to access sunlight; and transporting
substances between the roots and the leaves.
Stems
• Stems are made up of all 3 types of tissue. They
are surrounded by a layer of epidermal cells,
which have thick cell walls and a waxy protective
coating.
• The xylem and phloem form continuous vascular
tubes to link the leaves with the roots and all
parts of the plant.
• Stems can also function as storage systems in
some plants, and some also participate in
photosynthesis.
• Leaves are attached to
the stem at locations
called nodes, and the
regions between these
nodes are called
internode regions.
Buds form at these
nodes – buds are made
of undeveloped tissue
that can produce new
stems and leaves.
Dicot & Monocot Stems
• A stem cut in cross-section shows the three
tissue layers clearly, but they look quite
different in monocots and dicots.
Monocot Stems
• Distinct epidermis on the outside
• Ground tissue is fairly uniform, made up of
mostly parenchyma cells
• There is a series of vascular bundles, each
made up of xylem & phloem
– Scattered throughout the ground tissue
– Phloem faces the epidermis (outside of the stem)
– Xylem faces the centre of the stem
Dicot Stems
• Distinct epidermis on the outside
• Vascular bundles (made up of xylem and
phloem) are arranged in an orderly ring
• Ground tissue is in two sections
– Pith – parenchyma cells inside the ring of vascular
bundles
– Cortex – parenchyma cells outside the ring –
between the vascular tissue and epidermis
Primary Growth
• The growth of a plant at the ends of its stems
and roots by the apical meristems is called
primary growth.
• This produces an increase in length, but not
any increase in width.
• Each year a new length of stem is added
through this primary growth, which can be
seen easily on a tree branch.
Secondary Growth
• Plant stems cannot simply increase in length
forever – they must also increase in thickness.
• This increase in mass also means they need
more vascular tissue to transport water and
nutrients. This type of growth is called
secondary growth.
• How can plants grow wider, when only
meristem tissue can produce new cells?
Monocots & Dicots
• Some monocots (including palm trees) can
grow thick stems from a meristem that grows
wider as the plant grows. However most
monocots don’t grow to be very tall or large.
• Dicots can grow to be extremely tall, and they
must grow wider to support the extra weight.
Lateral Meristems
• In conifers and dicots, secondary growth
occurs in lateral meristem tissues called the
vascular cambium and the cork cambium.
– Vascular cambium produces new vascular tissues
– Cork cambium produces the outer coating of
stems
– A separate type of cambium allow roots to grow
thicker and create new branching roots
Cambium
Vascular Cambium
• In a young dicot stem produced by primary
growth, the vascular bundles are found in a
ring.
• A vascular cambium appears as a thin layer
between the xylem and phloem of each
vascular bundle.
• This meristematic tissue can divide to produce
new cells to add to the vascular bundles. As a
result, the stem becomes thicker and thicker.
Homework
• Read Section 23-3 (pg 589-594)
– Questions 1-4 pg 594
• Start your Glossary
– Find all of the BOLD TERMS in your textbook for
Chapters 22-24
• Those are your glossary terms!
• You need to define these in your own words for your
logbook (Due Jan 9th)
Unit Test Thursday Dec 18th
On all of Chap 22 &23
(Chap 24 will be after the break)
Formation of Wood
• Most of what we call wood is actually layers of
xylem. These cells build up year after year as
the stem grows thicker. The older xylem near
the centre stops conducting water, and
becomes heartwood. Heartwood becomes
darker over time because of accumulated
impurities.
Heartwood & Sapwood
• Heartwood is surrounded
by sapwood. This
sapwood is still active in
transporting water and
sap, so it is usually lighter
in colour.
Seasonal Growth
• In the temperate zone, tree growth is seasonal.
• During the spring when growth begins, the
vascular cambium grows quickly, producing large,
lightly-coloured xylem cells with fairly thin cell
walls.
– This produces a light coloured wood called “early
wood”.
• Later in the growing season the rate of growth
slows, and cells become smaller and have thicker
cell walls.
– This produces a thin layer of darker wood known as
“late wood”.
Early Wood and Late Wood
Tree Rings
• This alternation of light and dark wood in each
year’s growth produces what we usually call tree
rings.
• By counting these tree rings you can estimate the
age of a tree.
• These rings can also tell us about the weather
conditions during that year – wide rings indicate
years with favourable growing conditions,
whereas thin rings indicate years with poor
growing conditions.
Tree Rings
Formation of Bark
• The bark on most trees is made up of all of the
tissues outside the vascular cambium –
including phloem, cork cambium, and cork.
Process of Forming Bark
• As a tree lays down new xylem, it expands in
width, which forces the phloem outward
• If the phloem does not grow as well, this could
lead to splitting of the epidermis
• The cork cambium (another layer of
meristematic tissue) surrounds the cortex and
produces a thick layer of protective cork
Cork
• Cork is make up of cells with thick cell walls
• These cork cells usually contain fats, oils, or
waxes
– These substances are waterproof and help
prevent the loss of water from the stem
• Outer cork cells are usually dead, and as the
stem grows in size this cork often cracks and
flakes off in patches or strips
Layers of Wood & Bark
Modified stems
• Many plants have modified stems that have
been adapted to store food and to remain
dormant while waiting for favourable
conditions.
• Some examples include tubers, bulbs,
rhizomes and corms.
Tubers
• A tuber is a section of underground stem that
stores food for the plant. Potatoes and yams
are common examples.
Bulb
• A bulb is made of a central stem surrounded
by thick, short leaves. The leaves wrap around
to protect the stem and also store food. Bulbs
can remain dormant for a long time, and then
grow into a new plant when conditions are
right.
• Common examples include tulips, onions and
garlic.
Bulb
Rhizomes
• Rhizomes are horizontal underground stems,
from which new plants can grow after long
periods of dormancy.
• Ginger and turmeric are rhizomes, and plants such
as bamboo, asparagus and lily of the valley use
rhizomes to spread asexually.
Corms
• Corms look like bulbs, but instead of being a
combination of stem and leaves, a corm is a
thickened stem that stores food.
• Taro, crocuses and gladiolus plants produce
corms.
Svalbard Seed Vault
• https://www.youtube.com/watch?v=Mm8hsU
XJ8Jk&list=PL4LEUrNDNoyRQqVGWYpMS_lbg2HLQjcm&index=9 (3 min)
Celery Demonstration
• General Observations
– How have the 4 stalks changed since last week?
– Can you tell which one has pulled up the most water?
• Masses
– The sub will use the scale to weigh the 4 stalks
• Careful not to wipe off the vaseline!
– Record these “after” values in your chart
• Finish up the results/analysis/discussion sections
for homework – this will go into your logbook.
Review for Unit Test on Thursday
• Start Chapter Reviews from Textbook:
– Chapter 22: 574-575
– Chapter 23: 604-605
• Mrs. Mishra will give you the topics list and
more information tomorrow.
• You can work on these while we watch this
summary episode of the Magic School Bus
– https://www.youtube.com/watch?v=W8nfkS40u
Wc (25 min)