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Plant Growth
Objectives
1. Identify the parts of the plant that are responsible for growth
2. Explain the mechanisms of plant growth
3. Discuss the external and internal factors that affect plant
growth
Homework: Using your notes from Friday’s lesson and
Today’s lesson, create a poster showing the life cycle
of an angiosperm.
Plant Growth and Development
• Growth: Process of increasing in size
• Differentiation: Cells become specialized
to perform a particular function.
Primary Growth
Plants continue to grow in height for their entire lives.
• Increase in height comes
from apical meristems.
– Regions of actively dividing
cells found at the tips of
plants
– Buds, stems, roots
• Growth from apical
meristems is called primary
growth.
• Always increases the
height, not the width, of a
plant.
Secondary Growth
• Arises from the
lateral meristems
(cambium).
– Areas of actively
dividing tissue in
stems and roots.
• Increases the width
of a plant.
Primary Growth
• Increases length of root or shoot.
• Cells divide by mitosis, increasing number of
cells.
• Cells growth longer and then differentiate into
different cell types.
– Ie: parenchyma, epidermal, vascular
• Shoot: Produces tissues that form stem,
leaves and flower.
• Increase in plant height
• Differentiation is determined by cell’s
location.
– Ie: outer cells become epidermal cells
Root: Produces cells of root
cap and other root cells.
Zone of cell division
Cells divide to create
more cells.
Zone of elongation
Cells stop dividing and
increase in length.
Zone of differentiation
Cells differentiate and
tissues of root take on
specialized functions.
Secondary Growth
• Arises from lateral
meristems.
• Forms secondary
tissue.
• Causes an increase in
diameter or width of
plant.
• Cambium produces
secondary xylem and
phloem.
• Every year
vascular cambium
produces new
secondary xylem
and phloem.
• Produces growth
rings.
Check Point
1. Where are the apical meristems?
2. What results from their activity?
3. What is the difference between primary
and secondary growth?
4. How would plants that exhibit secondary
growth differ in size and structure from
plants that exhibit only primary growth?
Homework..
Homework: Use you notes and text book to create a
poster showing the life cycle of an angiosperm.
You must include diagrams showing: (Don’t copy the text
book – You should include more detail…)
– Reproductive parts
– Pollination
– Fertilization
– Germination
– A cycle starts and ends in the same place (p 398)
• How would you fit what you learned today about plant
growth into this cycle?
Plant Growth – Part II
External and Internal Factors
Affecting Plant Growth
Control of Plant Growth…
• What do plants require to grow?
• Some of the external factors affecting
plant growth are…
• Light – Energy Source
• Food
• Water
• Temperature
• Soil pH
Light Requirements…
• Light is required for photosynthesis.
• Quantity is limited by environmental
factors
– Latitude and competition from other plants
• Quality is influenced by . . .
– Shade from other plants
– Cloud cover
– Time of day
– Seasons
Nutrient Requirements
• Create a table to
– summarize the function of water, nitrogen,
potassium, calcium and magnesium and
phosphorus in plant growth
– summarize some symptoms that plants may
exhibit when they are deficient or lacking
these nutrients.
• What role do you think water plays in
helping plants absorb these nutrients?
Deficiency Symptoms
Nitrogen Deficiency
Magnesium Deficiency
Phosphorous
Deficiency
Internal Factors Affecting
Plant Growth…
• Plant growth is influence by hormones just
like our growth is influence by hormones…
Tropisms…
• A directional change in growth
or movement in response to a
stimulus…
• Controlled by plant growth
regulators.
– Chemicals produced by plant
cells that regulate growth and
differentiation
• Phototropism: A change in
direction of growth in response
to light.
Gravitropism: A change in growth pattern in
response to gravity.
Thigmotropism: A directional change in
growth pattern in response to touch.
Heliotrope: A plant that turns,
throughout the day, so it is
facing the sun.
This is an example of what type of tropism?
Growth Regulators..
• They can stimulate or inhibit growth.
• There are five main hormone groups:
1. Auxins
2. Gibberellins
3. Cytokinins
4. Ethylene
5. Abscisic Acid
Find out what they do…(Student Activity)
Auxins
• Apical stem is main site of synthesis
• Primary role: promote cell elongation
• Also…
• Can inhibit cell division in some tissues.
• Stimulates cell division in vascular cambium.
• Helps regulate gravitropism.
• How auxin and
phototropism causes
the plant to grow in the
direction of the sun.
• The auxin collects on the
dark side of the shoot;
therefore, more growth
will occur on this side of
the plant. The shoot will
gradually lean towards the
sun.
Gibberellins…
• Promotes cell division and elongation in
plant shoots.
• Plays a role in flowering and fruit
formation.
• Can be used commercially to stimulate
seed germination.
Cytokinins…
• Promotes cell division and leaf mesophyll
growth.
• Found in meristems, young leaves and
growing seeds (actively dividing).
• Slow cell aging by inhibiting protein break
down and stimulating protein synthesis.
Ethylene…
• A gas produced at various stages of
development
• Causes changes that protect plant against
environmental stress
• Ie stimulates plants to lose leaves in drought
(prevent water loss)
• Regulates the growth of plant roots and shoots
around obstacles
• Stimulates fruit ripening, root and shoot
growth, cell differentiation, flower opening,
leaf and fruit drop…
Abscisic Acid (ABA)…
• Primary role: Inhibit growth
• Levels increase in response to seasonal
changes
– Maintains dormancy in leaf buds and seeds
– Dormant plants are less vulnerable to damage
• Controlling the closing of stomata in dry
conditions.
– Dry leaves wilt inducing the production of ABA
which diffuses into guard cells inducing them to
close
Plenary…
1. Name the five growth regulators that are
found in plants.
2. Which growth regulators promotes cell
elongation? Cell elongation?
3. What problem would a plant have if it
were deficient gibberellins? Why?
4. What is phototropism and how does it
affect plant growth? What role does auxin
play in this?
Homework…
Finish your assignment outline for tomorrow.
You will be marked out of 4 for
completeness, organisation, collection of
information, citing of sources.
Page 542 in your text
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