Transcript Plants – Our Most Important Resource • The food that you eat, oxygen that you breathe and fabric that you wear all.

Plants – Our Most Important
Resource
• The food that you eat, oxygen that you breathe
and fabric that you wear all come from plants.
• It is sometimes difficult to imagine all the
materials that we rely on daily originate from
plants. In fact, plants changed the way of life
some 10, 000 years ago.
• Civilization changed from a nomadic lifestyle to
domestication when people began to grow plants
and raise livestock.
• Farming food staples like corn, wheat, rice and
potatoes and rearing goats, chickens and cows
allowed for the development of settlements and
communities.
• In this section, we will learn about many
different uses of plants and the communities
that depend on plants.
Medicine
• Prior to local drugstores being opened on every
other street corner, people relied on the healing
powers of plants.
• Plants produce over 10 000 different compounds
to protect themselves against predators.
• Chemists are able to extract and use these
chemicals to cure and treat common illnesses and
diseases.
• The following table summarizes a few examples:
Plant
Active Compound
Uses in Medicine
Ephedra
Ephedrine
Decongestant, treat low
blood pressure and asthma
Cinchona
Salix
Quinine
Salicin
Treatment of malaria
Anti-Inflammatory
Digitalis purpurea
Digitoxin, digoxin
Cardiac stimulant, diuretic
Papaver
Morphine, codeine
somniferum
Rauwolfia
Reserpine
serpentina
Nicotiana tabacum
Nicotine
Dioscorea
Catharanthus
roseus
Cough suppressant
High blood pressure and
psychosis
Stimulant
Steroids
Production of cortisone
Vinblastine
Leukemia, Hodgkin's disease
and other cancers
• Poppy seeds contain opium
which has been used since
4 000 B.C.
• In the 1800s, opium was a
common ingredient in cough
syrup.
• Opium has a dark side as
well. It contains morphine
which can then be made into • Heroin affects multiple
heroin.
organ systems including
• Heroin is an extremely
respiratory, nervous
additive illegal drug that once
and reproductive.
metabolized is converted
back to morphine.
Lumber
• In the story of the three little pigs, you may
recall that the pig that built his house out of
bricks was able to withstand the force of the
hungry wolf's gusts of air.
• However, you probably were not informed
that in order to build a brick home, a frame
made out of wood would be necessary.
• Canada exports seven billion dollars worth of
lumber to the United States each year and
over 200 000 Canadians are employed within
this industry.
• The spin-off construction,
transport, and
manufacturing jobs that
result from the lumber
industry are significant to
the Canadian economy.
• Softwood lumber includes
wood that is easy to saw
and comes from coniferous
• These hardwoods can be
trees like pine, cedar and
used in construction,
spruce.
furniture, and flooring as
• Hardwood lumber includes
they are harder and denser
beech, cherry and oak.
than softwood.
Food
• The most important use of plants is food. Up to
90% of our caloric intake comes from wheat,
corn, rice, and potatoes.
• Grains provide an excellent source of complex
carbohydrates.
• Beans, lentils, and peanuts offer a good source of
protein.
• Leafy green vegetables, like cabbage and lettuce,
provide fibre, minerals and vitamins.
• Oils from avocadoes, sunflowers and olives
nourish us with healthy unsaturated fats.
• In addition to food, herbs and spices also originate
from plants.
• Oregano, cinnamon, chili peppers, and other spices
help to flavour and preserve food.
• The two most popular drinks in the world, coffee and
tea, are made from plants.
• Through the process of selective breeding,
cloning, and genetic engineering, many new
plant species have been created.
• The diversity of plants is increasing in the
creation of hybrid plants that contain
desirable qualities.
• These newly formed plants may be able to
sustain harsh environmental conditions such
as droughts or floods and therefore provide a
better yield.
Other Products
• If you think about all the major holidays, some type of
plant is involved.
• From the Christmas tree to the Halloween pumpkin,
plants have an impact on celebrations.
• The colour and aroma of flowers fills a church during
weddings and funerals.
• The cornucopia's presence at Thanksgiving is a symbol of
the importance of harvest time.
• The use of plant crops as an alternative to
gasoline is having a global impact.
• Ethanol is the fuel that is produced from the
combination of gasoline and an organic
compound like sugar cane or corn.
• The use of a renewable resource as a fuel has
many benefits.
• The emissions from biofuels do not release as
much carbon dioxide and therefore reduce the
greenhouse effect.
• However, biofuels are affecting more than oil
companies, with corn and sugar being grown for
fuels, the world's food prices increased by 75% in
2008 (World Bank, 2008).
• Plants provide leisure activities to millions of
people around the world who enjoy planting,
growing, and nurturing their gardens.
• Growing seasons are celebrated all over the
province of Ontario.
• Annual festivals celebrating strawberries,
corn, and tomatoes are a reminder of the
importance of locally grown crops.
Required Reading
• The Boreal Forest – A Global Legacy (on
website)
• Biofuels – The Promise and the Risks (on
website)
• Our Life Medicine Path (on website)
• Answer the questions (on website) on this
article
Plant Structure
• One of the distinguishing characteristics that you
may recall from the diversity unit is that all plants
carry out the process of photosynthesis.
• This process is essential not only for the survival
of a plant, but for the survival of all living things.
• The organelle whose duty it is to carry out this
daunting task is the chloroplast.
• The image on the next slide highlights all the
components of a plant cell.
• You should be able to describe the function of all
the organelles shown below. If not, then please
take the time to review.
Roots
• There are many analogies equating roots with
positive attributes like strength, stability, and
support.
• A person who has strong roots implies that he or
she has a solid foundation that is built upon firm
principles.
• It is no surprise then to learn that those qualities
that are assigned to people are the same qualities
that roots provide to plants.
• In addition to anchoring plants in soil, roots also
absorb and transport water and minerals to the
stems.
• Not all roots are the same.
• Tap roots grow deep into the ground in search of
nutrients. They are generally large and fleshy and
store food which is necessary for perennial plants
(plants that last more than two growing seasons)
which experience periods of dormancy.
• Fibrous roots do not dig deep into the soil; rather
they arrange themselves close to the soil surface
and collect water and nutrients before they sink
deep into the ground.
• Adventitious roots are found in climbing plants
like ivy. These roots develop from other plant
tissue like stems and leaves. Adventitious roots
can help support a plant.
• Roots contain tiny little projections called root hairs.
• The root hairs absorb water and nutrients from the
soil.
• Much like alveoli that increase surface area for gas
exchange, the root hairs amplify the surface area
which increases the rate of absorption.
Stems
• Stems provide the structural and physical support
to leaves and flowers.
• The stems hold the leaves and flowers in a
position that will allow for nutrient gathering and
reproduction.
• Xylem and phloem cells transport materials
within the stem from areas of plenty to areas of
need.
• The xylem and phloem cells are arranged in
vascular bundles.
• Within these bundles, the phloem cells are
always situated closer to the outside of the stem
while the xylem cells are located closer to the
centre of the stem.
• There is a thin layer of
tissue that separates
the xylem from the
phloem in dicot plants.
• Stems also store
nutrients for future use.
• Rhizomes, tubers, and
bulbs are all types of
stems that have been
modified to suit the
needs of a plant.
• Tubers grow underground and develop buds called eyes.
These buds grow into new shoots above the ground.
• Bulbs are small stems that grow underground. They
usually have short and thick leaves.
• Rhizomes grow just below the surface of the ground and
are thick and fleshy. They can survive through the winter
and develop buds in the spring.
• There are two main types of stems.
• Herbaceous stems are soft and green
and woody stems are more complex and are
hard.
• Most trees and plants that can survive
through winter have woody stems. Woody
stems grow thicker over time.
• Each year a new layer forms and the stem of
the tree widens.
• This is the result of new xylem being formed
each spring. The older xylem no longer
transports fluids and fills with oils and other
chemicals to become heartwood.
• The vascular cambium appears as rings when looking
at the cross section of a woody stem.
• The rings can be counted to determine the age of the
tree. The outer part of a woody stem is called the
bark. The bark is composed of phloem cells and cork
tissue. These cells and tissues protect the stem from
water loss.
Leaves
• The primary site of photosynthesis occurs at
the leaves.
• Leaves are positioned on trees to receive and
absorb the sun's rays.
• This is necessary to drive the process of
photosynthesis.
• Leaves have many variations in their shape,
size and structure.
• A compound leaf contains a leaf that is
divided into many smaller leaflets.
• A simple leaf has just one blade.
Compound Leaves
Simple Leaves
• A leaf is made up of many specialized cells and
tissues as illustrated in the image below:
• 1. Cuticle - The cuticle is a waxy, water resistant
covering that protects the leaf from excessive
absorption of light and evaporation of water.
• 2. Upper Epidermis - These cells appear on the top of
the leaf and are transparent and colourless. They allow
light to pass through to mesophyll cell where most of
photosynthesis takes place. The epidermis lack
chloroplasts therefore no photosynthesis takes place.
• 3. Palisade Mesophyll - These cells are arranged close
together and contain chloroplasts. These
photosynthetic cells form the bulk of plant leaf.
• 4. Spongy Mesophyll - These cells also contain
chloroplast, but not as many as the palisade cells. The
spongy mesophyll cells are not as densely packed
together. This allows more surface area for gas
exchange.
• 5. Lower Epidermis - These cells appear on the
bottom of the leaf and are transparent and
colourless. They allow light to pass through to
mesophyll cell where most of photosynthesis
takes place. The epidermis lack chloroplasts
therefore no photosynthesis takes place.
• 6. Stoma - Stomata (pl.) are small openings
located on the underside of the leaf of most
plants. These small openings allow for oxygen,
carbon dioxide, and water vapour to move into
and out of the leaf.
• 7. Guard Cells - Guard cells are specialized
epidermal cells that contain chloroplasts. Guard
cells regulate the opening and closing of the
stoma. When weather conditions are hot and dry,
the guard cells collapse and the stoma closes.
• The process that regulates the opening and
closing of the stoma involves the movement
of ions and water.
• This animation shows how the shape of the
guard cells affects the condition of the stoma.
• Well it would if it worked! Grrrrrr.
• 8. Xylem - Xylem are
specialized structures
that transport water
and minerals from the
roots to the rest of the
plant.
• 9. Phloem - Phloem
cells are specialized
structures that
• 10. Vascular Bundle - The
transport
veins of the leaf contain
carbohydrates
both xylem and phloem
produced in the leaves
cells.
to all parts of the
plant.
Homework
• Roots contain specialized cells and tissues.
• Determine the role of the:
Epidermis, Cortex, Endodermis and
Vascular Cylinder.
• If you use the Internet, be sure to use
academic sites.
Classifying Plants
• You briefly explored the different types of
plants in the diversity unit.
• In this unit, you will take a closer look at the
differences that exist between the species of
plants.
Vascular Tissue
• The transportation of materials within
multicellular organisms is vital for survival.
• Plants require water, minerals, sugars, etc., to
circulate throughout its tissues and cells.
• Some plants lack specialized structures to
carry out this transportation and simply rely
on the process of diffusion.
• Other plants contain specialized structures
that move materials throughout the plant.
• Non vascular plants lack
these specialized
structures.
• They have poorly
developed roots, stems
and leaves.
• They must exist in moist
environments for
reproduction and
transportation to occur.
• These plants cannot grow
very tall and do not
provide much
nourishment for humans.
• Non vascular plants
include mosses,
liverworts and
hornworts.
• Vascular plants contain
specialized structures
called xylem and
phloem.
• These tissues move
materials throughout
the plant.
• The xylem is composed
of dead cells and it
transports water and
mineral from the
ground upwards.
• The phloem is composed
of living tissue and it
transports sugars from the
leaves to the other areas
of the plant.
• Vascular plants can be divided into two
categories:
• gymnosperms and angiosperms.
• Gymnosperms are
plants that produce
cones instead of
flowers.
• They include pine, furs,
spruce, ginkgoes and
cycads.
• Gymnosperms are
• These types of plants
important for the Canadian
thrive in environments
economy as the wood from
that have long cold
these trees is used to for
winters and low
construction, fuel and pulp
nutrients in the soil.
and paper.
• Angiosperms are more
diverse than
gymnosperms and
include flowering
plants.
• All angiosperms
produce food, although
not all the food is
edible.
•
• Included in this group
are grasses, wheat, rice,
corn, fruits, vegetables
and wildflowers.
•
Angiosperms provide
nourishment, fibre for
clothing and medicinal
ingredients.
In addition, the wood from
these plants can also be
used as building materials.
Angiosperms are divided into monocots and dicots.
Monocots and Dicots
• Angiosperms are divided into two subclasses
monocotyledon (monocots) and dicotyledon
(dicots).
• Most angiosperms are monocots and include
grasses, wheat, rice and bananas.
• Dicots include the tomato plant, cacti, maple and
oak trees.
• The name of each subclass is determined by the
structure of its seeds.
• A seed is made up of three parts: seed coat,
embryo and endosperm.
• Monocots have only
one seed leaf
(cotyledon)
whereas dicots
have two seed
leaves.
• Seed leaves provide
nourishment.
• Monocots get their
nourishment from
the endosperm.
• It is believed that
monocots came
from an early dicot
plant.
Homework
• You have learned that angiosperms are divided
into monocots and dicots. The division was made
based upon the structure of their seeds.
Monocots contain one cotyledon and dicots
contain two cotyledons.
• However, there are many more differences
between monocots and dicots.
• Using the following criteria listed below, compare
monocot and dicot plants. Your comparison
should be completed using an organized data
table.
Criteria: Vascular Bundles; Leaf Venation; Roots;
Flowers; Pollen; Secondary Growth.
Plant Reproduction
• Like all other living things, plants also need to
reproduce to produce more plants.
• Plants can reproduce asexually or sexually.
• Botanists and farmers have been able to
interfere in the reproductive process of plants
to produce new plants with desirable
characteristics.
• This has had an impact on diversity and
quality plant food production.
Reproduction in Nonvascular Plants
• Nonvascular plants can reproduce asexually through
the process of vegetative reproduction. This occurs
when part of the plant breaks off and a new identical
plant develops.
• Most nonvascular plants reproduce sexually. The male
gamete is called an antheridium and it produces a
flagellated sperm. The female gamete is called an
archegonium and it produces a single egg.
• A moist area is needed for reproduction to occur.
Water allows the male sperm cells to swim from the
antheridium to the archegonium.
• The fertilized egg cell divides by mitosis and develops
into an embryonic sporophyte within the archegonium.
• Most plants have a life cycle that includes a
diploid generation, sporophyte, and a haploid
generation, gametophyte.
• The gametophyte generation is the dominant
generation in nonvascular plants.
• The sporophyte grows into a long stalk but
remains attached to the archegonium.
• A sporangium forms at the tip of
the long stalk and haploid spores
develop through meiosis.
• The sporangium bursts and the
spores scatter and they
germinate by mitosis forming
mature gametophytes.
Reproduction in Vascular plants
• Gymnosperms produce cones that are either
male cones or female cones.
• Male cones are small and generally found in
clusters.
• The male cones produce and release haploid
pollen cells that resemble yellow dust.
• Female cones are also
small but are very sticky.
• This allows the pollen to
adhere to the cone so that
fertilization can occur.
• When the pollen grain
attaches to the female cone,
it must travel to the female
gametophyte where the
archegonium houses the egg
cell.
• The pollen grain travels to
the opening of the ovule
called the micropyle and
attaches itself to the
nucellus.
• Here it will grow and develop
into a male gametophyte.
• The male gametophyte releases haploid
sperm cells that will eventually fertilize the
female egg cell to produce a diploid zygote.
• The zygote grows and develops into a seed
within the female gametophyte.
• It is protected by a layer of tissue called the
integument that will become the seed coat.
• Soon enough the seeds will be released and
germination will occur.
Reproduction in Angiosperms
Flowering plants usually contain both the female and male
parts. The female area of the plant is called the carpel and
it includes the stigma, style, ovary, and ovules or eggs. The
male part of the flower is called the stamen and it includes
the filament, anther, and pollen or sporangium.
• When a pollen grain reaches the stigma, it
germinates into a pollen tube.
• The germ cell divides by mitosis forming two
sperm cells.
• These sperm cells migrate down the pollen
tube as it grows through the style, micropyle,
and into the ovule chamber.
• The pollen tube enters the ovule through the
micropyle and it breaks open.
• One sperm cell fertilizes an egg cell forming a
diploid zygote.
• The other sperm cell fuses with a polar egg
cell (non-functioning) to form the endosperm.
• This is called double fertilization.
• The endosperm will provide nourishment to
the developing seed.
• After fertilization, each ovule develops into a
seed.
• The ovule covers and protects each seed.
Germination
• When a seed is released, it may not germinate
immediately. Growth may be delayed until
favourable conditions are present. Most seeds
will experience a period of dormancy. This period
may be a couple of days or even a couple of years
before germination starts.
• Germination begins when a hormone called
gibberellin is released into the seed from the
embryo. This hormone activates enzymes that
break down starch into smaller molecules to be
used as a source of energy for the embryo.
• As this occurs, water moves into the seed through
osmosis and the seed coat begins to swell.
• Often small cracks will result from the swelling of the
seed and this allows oxygen to enter the seed.
• With oxygen present, the embryo can undergo
aerobic cellular respiration and produce even more
energy in the form of ATP.
• The tip of the radicle
emerges out of the seed
first and elongates
downwards forming the
roots.
• The hypocotyl emerges
next and it forms a hook
and elongates upwards
and becomes the stem.
• Initially the cotyledons act
• The hypocotyl grabs the like leaves and carry out
cotyledon as it moves
photosynthesis, but as the
upwards towards light.
plant develops, true leaves
form and the cotyledon fall
off.
Artificial Reproduction
• The need to produce more food and
commercially viable plant products has caused
horticulturists and farmers to influence the
natural fertilization process of plants.
• Here are a few modified processes of plant
reproduction.
• Selective breeding has been used by farmers
for many years.
• In this process of sexual reproduction, farmers
choose plants that have desirable qualities
and only allow them to fertilize each other.
• Over time, the desirable qualities will be
present in all the seeds and the unfavourable
characteristics will be eliminated.
• This procedure is similar to what Gregor
Mendel did in order to get his pure bred
plants.
• Wheat, corn, and bananas are a few examples
of plants that have been selectively bred.
• Cutting is a form of asexual reproduction that
is very easy to perform.
• If there is plant that has desirable traits you
can simply cut a piece of the plant that
includes the stem and place it in water or soil.
• Tissue will start to develop from the cut end of
the stem.
• This tissue is called a callus and will eventually
develop into roots.
• This new plant is genetically identical to the
parent plant it came from.
• Grafting is a form of asexual reproduction that
can only be done with plants that have vascular
cambium, the tissue between xylem and phloem
cells in dicot plants.
• A bud (scion) from a plant that has desirable
characteristics is grafted or attached to the root
or stem (stock) of another plant.
• At the site of attachment, the
cambium of the scion fuses with the
cambium of the stock.
• This process allows farmers to grow
genetically identical trees.
• Apples, grapes, plums, and peaches
are all produced by grafting.
• The Macintosh apple was discovered in Ontario in
1811 by John Macintosh. Learn about the history of
the Macintosh apple.
Homework
• There are many good sites that animate the
process of fertilization in gymnosperms. Life
cycle of a Conifer is one that you can try.
• There are many good animations that show
how fertilization occurs in angiosperms. You
should view this Double Fertilization Video.
Informal Quiz Time – Is it True or Is It False?
1. Nonvascular plants require a moist environment for
asexual reproduction.
2. The sporophyte is the dominant generation in the life
cycle of nonvascular plants.
3. Male cones are smaller than female cones and are
arranged in clusters.
4. In gymnosperms, pollen attaches to the egg cell and
fertilization occurs.
5. The female part of an angiosperm includes the
stigma, style, and ovary.
Answers
1. False. A moist environment is needed for
sexual reproduction.
2. False. The gametophyte generation is the
dominant generation in the life cycle.
3. True.
4. False. Pollen attaches to the nucellus and
grows and develops into a gametophyte. The
gametophyte releases sperm cells that
fertilize the egg cell.
5. True.
6. Double fertilization occurs in angiosperms.
7. The endosperm provides nourishment to the
developing embryo.
8. A growth hormone called radicle starts the
germination process.
9. The radicle eventually develops into the root
and the hypocotyl develops into the stem.
10.Grafting is a form of asexual reproduction that
combines the buds of one plant with the stem of
another.
Answers
6. True.
7. True.
8. False. The hormone that starts the
germination process is called gibberellin.
9. True.
10.True.
Plant Growth
• Plants require basic nutrients to sustain
themselves.
• Since plants are autotrophic, they need water,
carbon dioxide, and sunlight to produce the
organic compounds needed for cellular
processes like growth and energy.
• In addition to manufacturing organic
compounds, plants acquire water and
minerals from the soil through their roots.
• The ability of plants to attain water, nutrients,
and sunlight can greatly affect their growth
and ultimately their survival.
• Recall from the last activity that plant growth
begins when a seed begins to germinate.
• From the tiny seed, a main root and stem start to
appear and soon enough an entire plant exists.
• Just like multicellular organisms, plants contain
specialized structures, tissues and cells that
perform specific tasks.
• Growth in plants occurs at the meristematic
tissue where rapid mitosis produces new cells.
This is called primary growth.
• Plants can only grow in areas where meristematic
tissue occurs and these areas are called
meristems.
• Apical meristems are
located at the root tip and
at the ends of shoots.
• Apical meristems located
in the root tip produce
cells that enable the stem
to grow in length.
• The apical meristems that
are located at the end of
shoots give rise to buds
and leaves.
• The vascular cambium
which you looked at
earlier in this unit causes
a plant to grow wider.
This is called secondary
growth.
• The vascular cambium is a
ring of meristematic
tissue that separates the
xylem from the phloem in
dicots.
• Recall that the xylem cells
are located in towards the
centre and the phloem
cells are located near the
exterior.
• There are three requirements for plant growth:
1. Soil Nutrients
2. Sunlight
3. Water
Soil Nutrients
• Soil consists of many
different components that
are required by plants and it
is arranged in several layers.
• Using the diagram on the
right as a guide, the top layer
of soil (O) is called humus
and it is composed of dead
and decaying plant and
animal remains.
• The presence of high
concentration of humus in
the soil will support plant
growth.
• The next layer (A)
is topsoil and this is the layer
that will support plant
growth.
• It is made up of humus, clay,
minerals and sand.
• The next layer (B) is called
subsoil. Many worms,
insects and microorganisms
live in the first three layers.
• In addition, the roots absorb
water and dissolved minerals
• As shown in the
in these layers. The last layer
illustration, the growth of
(C) is bedrock and it does not
the roots stops at the end
support plant growth.
of the subsoil level.
• The minerals that are needed by plants in
small amounts include iron, zinc and copper
and are referred to as micronutrients.
• Macronutrients like nitrogen, phosphorus,
potassium, calcium and magnesium are
required in larger amounts.
• The absence of any of these nutrients may
cause a plant to die.
• Each nutrient is required by plants to carry out
cell functions like cellular respiration or
photosynthesis.
• Sometimes people will help replenish the soil by
adding fertilizers that contain specific nutrients.
• Commercially produced fertilizers usually contain
nitrogen, phosphorus and potassium as
percentages.
• The percent composition of each nutrient allows
people to choose the appropriate fertilizer for the
type of plant or the type of growth they want to
achieve.
• Some people may choose to apply organic fertilizers
like manure on their crops or in their gardens.
• One of the benefits of organic fertilizers is that they
release the nutrients slowly into the soil.
• This prevents accidental chemical burns that may
occur when too much commercial fertilizer is
applied.
Sunlight
• Plants use the energy of the sun to drive the process
of photosynthesis.
• The light from the sun's rays is needed to activate
special enzymes within the chlorophyll of the
chloroplasts.
• There are many factors associated with light and its
effect on plant growth and photosynthesis.
• Light Intensity: The growth of a plant affected by its
location. A plant may be placed in direct sunlight, partial
sunlight or in the shade. Plants that are in the shade
grow the least.
• Light Quality: Chlorophyll, the green pigment common to
all photosynthetic cells, absorbs all wavelengths of visible
light except green, which it reflects to be detected by our
eyes.
•
Duration: Plants that are exposed to longer periods of
light will grow faster. Shorter periods of light provide less
energy to drive the process of photosynthesis. Excessive
amounts of light may cause a plant to lose excessive
amounts of water through transpiration
Water
• Plants require water for growth, temperature
regulation, and for support.
• Remember that water is one of the reactants
needed for photosynthesis. A plant that does not
have sufficient amounts of water will wilt.
• Plants that receive too much water actually
prevent the roots from taking in oxygen. The root
cells require oxygen for cellular respiration and
they get the oxygen from tiny pores in the soil.
• If the soil is drenched with water, the root hairs
are not able to take in oxygen.
Activity
• Why Are my Plants turning Yellow?
Plant Hormones
• You have already learned the effect that the
plant hormone gibberellin has on germination.
• There are two other groups of plant hormones
that control the cell division and growth in
plants: auxins and cytokinins.
• Two additional hormones called abscisic acid
and ethylene also alter rate of cell division and
growth.
Auxins
• You probably have noticed that plants grow
and gravitate towards light.
• You can see that effect if you have ever placed
a plant near a window or walked through a
forest and noticed the shapes of stems and
branches of trees.
• Auxin is a plant hormone that is released from
a plant tip when the cells are exposed to light.
• Auxin is released and it travels to the cells of
the stem that are not exposed to light.
• This causes the cells on
the dark side to elongate
and as a result, the stem
bends towards the light.
• In the root, auxin is
released from the apical
meristems and it causes
the roots to grow
downwards away from
the light.
• If a root cell is exposed to • The cells that are not
exposed to sunlight do not
light, auxin will cause
elongate.
these cells to elongate
downward away from the
cell.
• The height of trees is also
affected by the presence
of auxins.
• Some trees release auxin
from the highest bud
which inhibits the growth
of buds that appear
below.
• Plants that have this
feature usually grow tall • Some trees show apical
dominance through the early
and straight.
development and then lose
• Plants that do not release
the feature as they mature.
auxin from their terminal
• The result is a beautiful shade
bud are usually shorter
tree that is tall and provides a
and bushier.
nice reprieve from the sun.
• In the spring, auxins are
present in the leaves of
deciduous trees, but
the tree stops
producing auxin once
the growing season has
ended.
• Auxin is also commercially
• Without the presence
available and can be applied
of auxin, the leaves can
to promote root growth in
no longer stay attached
cutting, prevent fruits from
to the tree and fall off.
falling off of trees, inhibit
stored potatoes from
sprouting, and to produce
seedless tomatoes and
watermelons.
• Gibberellins are
produced in the apical
meristems and work
with auxins to
encourage the growth
of roots and stems.
• By itself, gibberellin
stimulates the growth
• Commercial gibberellin
of leaves, flowering,
promotes the growth of
and the development of
fruits and vegetables, it
vascular tissue.
delays the ripening of citrus
fruits, and it can speed up
the flowering of
strawberries.
Cytokinins
• This hormone is important in the
development of specialized plant
cells and tissue.
• As well, it also promotes rapid cell
division.
• This hormone is produced in the
roots of plants and is transported
throughout the plant.
• Commercially cytokinins are used
by florists to keep cut flowers
looking fresh.
• Cytokinins prevent plant cells
from aging.
Other Hormones
• Abscisic acid is a hormone that is produced in
green leaves, fruits, and root caps. It prevents the
germination of seeds, inhibits the growth of buds,
and prevents the stomata from taking in carbon
dioxide.
• Ethylene is gas that is naturally produced by
fruits. It stimulates the aging of plant tissue and
increases the ripening of fruit. This gas is a
problem when fruits are picked and are shipped
to other areas. The ethylene gas causes the fruit
to ripen quickly.
Homework
• http://home.howstuffworks.com/how-toplant-an-annuals-garden4.htm
• Look through each of the series of animations
and complete the exercises:
• http://www.sumanasinc.com/webcontent/ani
mations/content/plantgrowth.html
• http://www.kscience.co.uk/animations/auxin.
htm
Movement in Plants
• Just like the circulatory system moves
materials throughout your body, plants also
rely on a system to transport materials.
• Remember that xylem and phloem are
responsible for moving material within a
plant, but without a main pump, how is it that
plants can move materials against gravity to
heights that surpass the tallest human?
• Some of the tallest trees in
the world are located in
south western British
Columbia.
• The giant Sequoia can grow
between 50 - 85 metres high.
• That is the about the length
of a football field.
• Nevertheless, water
molecules travel from the
roots to the tip of the tree
every moment.
Xylem
• Xylem vessels are very long, narrow, and hollow
tubes that do not contain any living material.
They are connected end to end and stretch all the
way from the roots to the leaves. Xylem cells only
transport water and minerals that have been
absorbed by the root hairs.
• Water and dissolved minerals enter the root hairs
by osmosis. Recall that osmosis is the movement
of water from an area of high concentration to an
area of low concentration. The illustration shows
the process of osmosis across a cell membrane.
• For water to enter the
root hairs by osmosis
there must always be a
lower concentration of
water within the root of
the plant.
• The only way that this
can happen is if the
•
water is continuously
being pulled out of the
root or if there is a
higher concentration of
ions with the root.
Each scenario mentioned
lowers the concentration of
water within the root. The
water enters the xylem
through pits in the vessels
called tracheids.
Root Pressure
• Plant roots can build up pressure and the
pressure forces the water to move upwards.
• The increase in pressure can be caused by
active transport of water into the xylem or
active transport of ions to create a
concentration gradient.
Capillary Action
• Capillary action is based on a specific property
of water called adhesion.
• Water has the ability to cling to water
molecules (cohesion) or to cling to other
molecules (adhesion).
• Imagine you have straw and you place it in a
glass of water.
• The water molecules move up the straw
because of the attraction between the water
and the straw.
• However, water
molecules are also
attracted to each other,
so as one water
molecule moves closer
to the straw molecule
(adhesion), a second
water molecule moves
closer to the original
• The xylem cells are made up
water molecule
of tiny thin tubes.
(cohesion).
• The smaller the diameter of
the xylem cells, the higher
the water will climb.
Cohesion Tension
• As was mentioned with capillary action, water
molecules have an affinity to each other and that
is what helps them move up through the xylem.
• Remember the specialized structure in the leaf
that allows carbon dioxide gas to enter the plant?
• The stoma is also the spot where water
molecules can escape.
• Therefore, as the stoma opens to allow carbon
dioxide gas in, water molecules move out. As one
molecule leaves, it pulls other water molecules
up.
• Water leaves a plant in a
process called transpiration.
• Transpiration allows a plant
to control its temperature
through evaporative cooling.
• Excessive water loss through
transpiration causes plants
to wilt and may also lead to
plants dying.
• An increase in transpiration
increases the movement of
water through the xylem.
Transpiration Animation
• http://passel.unl.edu/pages/informationmodu
le.php?idinformationmodule=1092853841
Practice Questions
• How do the following weather conditions
affect the rate of transpiration?
a) Wind
b) Light
c) Temperature
d) Humidity
Answers
a. Wind: Windy conditions increase the rate of
transpiration because the wind reduces the effects of
a special layer on the leaf that slows the rate of
transpiration.
b. Light: The stoma open during the day when sunlight is
available to drive the process of photosynthesis.
Carbon dioxide enters through the stoma for
photosynthesis; however, water can also leave
through this opening if the temperature is hot.
c. Temperature: Warmer air will increase transpiration
and cooler air slows down the process of
transpiration.
d. Humidity: High humidity decreases the amount of
water loss through transpiration. Dry air increases the
rate of transpiration.
Practice Questions
• Explain what is happening in the diagram
below.
Answers
• Water has two important properties: cohesion
and adhesion.
• Cohesion is the attraction of water molecules to
each other and adhesion is the attraction of
water molecules to other molecules. This image
shows the cohesive property of water. The water
droplets stick together and form a droplet on the
leaf because of its higher affinity to water
droplets than to the surface of the leaf.
Homework
• Take another look at the animation on
transpiration:
• http://passel.unl.edu/pages/informationmodu
le.php?idinformationmodule=1092853841
• Click on “transpiration” under where it says
lesson media objects.
• You could also take a look at the associated
readings in the lesson outline on the left!
Phloem
• Phloem transport sugars, hormones and other
organic molecules throughout the plant. This
process is called translocation.
• While xylem transport is generally one direction,
the transport of materials within the phloem can
go in any direction.
• In addition, phloem is composed of living cells.
• How materials move within the phloem is yet to
be determined.
• One of the most supported theories is the
Pressure Flow Hypothesis, also called the Mass
Flow Hypothesis.
• In the leaf, glucose is produced by photosynthesis
and is converted into sucrose for transportation.
• The sucrose is actively transported into the cells
of the phloem.
• This lowers the concentration of water in the
phloem.
• Water from the xylem moves into the phloem by
osmosis and increases the pressure in the phloem
area.
• As the pressure increases, the sucrose will move
to areas of lower pressure.
• Once the sucrose arrives at
the lower pressure areas it is
actively removed from the
phloem and into the
surrounding cells.
• The cells will convert the
sucrose back to glucose or
another organic compound.
• When the sucrose is
removed, the pressure drops
as water also moves out of
the phloem by osmosis.
Tropisms
• A Venus fly trap plant is one
of the few carnivorous plants
that exist.
• Through highly sensitive hairs,
the lobes of the Venus fly trap
can rapidly close upon
stimulation trapping the
unsuspecting insect or spider.
• Once trapped inside, any
movement by the insect
triggers the lobes to close
tighter and digestive enzymes
are secreted by glands inside
the lobes.
• This type of rapid
movement is seen
in very few plants.
• http://www.arkive.org/venus-flytrap/dionaeamuscipula/video-00.html
• However, all plants show movement in
response to an external stimulus like the sun,
gravity or touch.
• This type of motion is called tropism.
• If a plant moves towards the stimulus, then it
is a positive tropism. If the plant moves away
from the stimulus, then it is negative tropism.
• Some parts of a plant may show positive
tropism and other parts of the same plant
may show negative tropism.
Phototropism
• This tropism is a response to
light.
• The tips and stems of plants
demonstrate positive tropism as
they grow towards the light.
• The roots of plants grow away
from the light and are negatively
phototropic.
• You will recall that the hormone
auxin is released to stimulate
growth in stem cells that are not
exposed to sunlight.
Geotropism or Gravitropism
• This type of tropism is affected by gravity.
• Roots will display positive tropism and stems
and shoots will demonstrate negative tropism.
• Charles Darwin was one of the first scientists
to identify the growth responses in both roots
and stems in relation to gravity.
Thigmotropism
• This growth movement is in
response to physical contact
with another object.
• Ivy clinging to the surface of
walls is an example of
positive tropism.
• An example of negative
tropism includes roots
growing away from objects
in the soil.
Hydrotropism
• Growth of roots towards water is an example
of a positive hydrotropism.
• Roots will gravitate towards a supply of water.
Nastic Response
• The movement shown by the Venus fly trap is
an excellent example of nastic movement.
• The nastic movement of plants is not
dependent on the direction of the stimulus.
• Rather the movements are random and are
not permanent.
Homework
• Various tropism videos:
• http://plantsinmotion.bio.indiana.edu/plantm
otion/movements/tropism/tropisms.html
• http://www.nasa.gov/audience/foreducators/
topnav/materials/listbytype/Tropisms_of_Plan
ts.html#.VWt2rtLBxjM
Succession
• How many times have you heard about forest
fires destroying acres upon acres of forests in
British Columbia or Southern California?
• Earthquakes that shake the foundation of
landscapes occur randomly throughout the
Earth.
• It seems that these natural disasters occur
more frequently and each one leaves a lasting
imprint on the landscape and habitants of the
area.
• Perhaps there is an acceptable explanation for
these natural disasters in preserving the
diversity of native plants and organisms?
Review!
• Before you proceed through this activity, you
will need to familiarize yourself with some
terminology.
• Define and explain the following terms in your
notebook:
• ecology, biomes, ecosystem, population,
community, habitat, niche, competition,
biotic, abiotic.
Definitions
• Ecology is the scientific analysis and study of
interactions among organisms and their
environment.
• Biomes are large communities of plants and
animals that occupy a distinct region.
Terrestrial biomes, typically defined by their
climate and dominant vegetation, include
grassland, tundra, desert, tropical rainforest,
and deciduous and coniferous forests.
• An ecosystem is a community of living
organisms in conjunction with the non-living
components of their environment (things like
air, water and mineral soil), interacting as a
system.
• A population is a summation of all the
organisms of the same group or species,
which live in a particular geographical area,
and have the capability of interbreeding.
• A community is a group of a species living in
the same place.
• A habitat is an ecological or environmental
area that is inhabited by a particular species of
animal, plant, or other type of organism.
• A niche is a position or role within a
community.
• Competition in biology and sociology, is a
contest between organisms, animals,
individuals, groups, etc., for territory, a niche,
or a location of resources, for resources and
goods, mates, for prestige, recognition,
awards, or group or social status, for
leadership.
• Biotic components are the living things that
shape an ecosystem. A biotic factor is any
living component that affects another
organism, including animals that consume
the organism in question, and the living food
that the organism consumes.
• In biology and ecology, abiotic components
or abiotic factors, are non-living chemical and
physical parts of the environment that affect
living organisms and the functioning of
ecosystems. Abiotic factors and phenomena
associated with them underpin all biology.
• The landscape
of Ontario did
not always
appear as it
does today.
• Thousands of
years ago,
Ontario was
covered in ice
and not much
vegetation was
able to exist.
• But as the glaciers retreated new
rock was exposed and the
process of primary succession
began.
Primary Succession
• Primary succession begins the process of
establishing a new ecosystem upon newly
formed rocks.
• It may begin on lava rock emitted from a
volcano or on ground that has been turned
upside down by an earthquake or landslide.
• Pioneer plants are the first plants to begin
growing in the new environment.
• Lichens represent the
first plant-like material
to start growing.
• Lichens are a type of
fungus that closely
associate with green
algae and can grow on
rocks, tree bark, and
other places with
minimal soil.
• The rocky materials along
• The lichens produce
with the dead and decaying
acids that slowly
lichens start to accumulate
corrode the rocks.
and soil formation begins.
• The formation of soil
can now support more
plant life.
• Mosses, ferns and even
seed plants begin to
establish themselves in
the new area.
• Wind carries seeds from • The formation of roots
other areas and
also helps to break up the
germination of the new
rocky material.
plants can begin.
• Soil accumulation is the key factor to supporting
the growth and development of larger native
plants.
• When larger plants take over the area and
vegetation reaches equilibrium, a climax
community forms.
• Climax communities consist of large trees that
take longer to grow and are more shade-tolerant.
• Climax communities represent the final stage in
primary succession.
• Canada has several different climax communities
as the environmental conditions will ultimately
determine the type of vegetation that will be
supported.
• Virtual Tour of Canadian climax communities:
Secondary Succession
• Secondary succession follows the disturbance
of a natural ecosystem either by fire, flood or
human activities where the soil remains
intact.
• That is the difference between primary and
secondary succession.
• The rate of secondary succession occurs faster
due to the presence of soil.
• Pioneer organism may also be present in the
soil immediately following the disturbance.
• It is important for you
to recognize that
secondary succession
begins in areas that are
not completely void of
living matter as is the
case with primary
succession.
• Ecological succession is best described as a
process of change in the species and structure
of a community over a period of time.
• The population of one species of plant may
dwindle over time due to the presence of a
natural predator so that eventually the species
no longer exists within that community.
• Unfortunately, the damage caused by forest
fires affects more than one species of plant.
• Forest fires erase decades of growth and
development, but also bring the promise of
new growth.
• In fact, forest fires are a
natural way to maintain
the structure of
ecosystems.
• A prescribed forest fire is
a management tool that
is used to maintain and
restore the natural
ecosystem by eliminating
invasive plant and animal
species and allowing the
native species of plants
and animals to return.
Homework
• Secondary succession animation:
• http://www.wiley.com/college/strahler/04714
80533/animations/ch23_animations/animatio
n1.html
• Fire management:
• http://www.pc.gc.ca/eng/progs/nppn/eco/eco5.aspx