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Specialized and Organized
Chapter 9
Section 1
To Old for Bill Nye?
• Why do we say that Plants and Cars don’t
mix?
– Can we make them mix?
– How could they be beneficial to each other?
• Plants and Cars don’t mix?
The Functions of Leaves
• Leaves are responsible for:
– Gas exchange
– Release of water
– Protection of leaf cells
– Photosynthesis
– Transport of nutrients and water
• In single-celled organisms, one cell
performs all the functions of life.
• In a multi-cellular organisms, groups
of similar cells (called tissues) are
specialized to perform specific tasks.
What are some specialized cells
to the human body?
Multiple Levels of Cell Organization
CELLS
TISSUES
ORGANS
SYSTEMS
• The most basic level of organization in organisms
• A group of similar cells clustered together
• Multiple tissues can be arranged in a combination to
form organs
• Organs and tissues perform a shared, complex function
Specialized Cells
Plants
Animals
•
•
•
•
• Nerve cells
• Skin cells
• Blood cells (Red &
White)
• Muscle cells
• Etc.
Epidermal cells
Palisade tissue cells
Spongy tissue cells
Stomata & Guard
cells
• Vascular tissue cells
Photosynthesis
• The process by which plants use light
energy to produce food in the form of
carbohydrates.
6CO2
6H2O
6O2
C6H12O6
LIGHT ENERGY
• Photosynthesis occurs in the Chloroplasts
of Plant cells
• Uses energy to make food for the plant
Cellular Respiration
• The process by which cells obtain energy by
breaking down glucose in the presence of
oxygen.
Energy
C6H12O6
6O2
6CO2
6H2O
• Cellular Respiration occurs in the Mitochondria of
Plant & Animal cells
-Produces Energy
Cells Within Leaves
1. Epidermal Cells – make up the Epidermis
-
Flat, single cell layer covering the upper and lower surfaces of
the leaf
Main function is to protect the leaf
No chloroplast = no photosynthesis
Transparent so sunlight can pass through to photosynthetic
cells
Cuticle: a waxy covering that prevents evaporation
2. Palisade Tissue Cells
- long, narrow (columnar) cells that are tightly
packed lying just below the surface
- One of the main type of photosynthetic cells
- Main function is photosynthesis, so they are
packed full of chloroplasts
3. Spongy Tissue Cells
- Cells are round and loosely packed found just
below palisade layer
- Air spaces between cells (intercellular
spaces) that perform gas exchange
- They also contain chloroplasts in order to
perform photosynthesis
4. Stomata and Guard Cells
- Stomata are tiny openings on the underside
of leaves that allow gases to diffuse in and out
- Stomata are surrounded by 2 guard cells
which regulate when the stomata is open or
closed
5. Vascular Tissue Cells
- Cells transport fluid throughout the plant using
a system of tubes or veins which are arranged
together in bundles
- Xylem carries water and nutrients from the
roots to the leaves
- Phloem carries sugars (made through
Photosynthesis) from the leaves to other parts of
the plant
Cross Section of a Leaf
For Tomorrow:
• Complete pg. 8-9.
• Text page 324: #1-7
9.2 Gas Exchange in Plants
P.325-330
Discussion:
Can sleeping in a room full of plants can be
dangerous? A common myth states that, at night,
plants compete with people for oxygen!
What do you think?
A moment in science
Ralph Hockens (Flickr)
REMEMBER:
• During cellular respiration in animal and plant cells O2
Is used up and CO2 and H2O is produced.
• During photosynthesis, plants consume CO2 and H2O
and produce O2.
Leaves
• Gases diffuse into stomata of plant leaves and
move through air spaces between the spongy
and palisade tissue cells.
• CO2 diffuses and dissolves into the cells of the
leaf where chloroplasts use the CO2 for
photosynthesis.
• O2 produced in photosynthesis diffuses out of
the leaf cells and leaves through the stomata.
The Role of Stomata
• Found on the underside of leaves
• Stomata allow gases to diffuse in and out of the plant
– CO2, O2 and Water vapor move in and out of intercellular
spaces – Passive Transport
The Movement of Gases
Air diffuses into the plant through
Stomata and circulates in intercellular
spaces
CO2 diffuses into the cell where it is used
for photosynthesis
O2 diffuses out of the cell, into the
intercellular spaces, and than out
through the Stomata
Lenticels
• Some gas exchange occurs in the roots and
stems as well.
• In woody plants, layers of dead cork cells, bark
and wax prevents direct gas exchange.
• Small, lens-shaped openings called lenticels
perforate the bark and allow for gas exchange
in the roots and stem.
• Investigation 9-A Carbon Dioxide
Consumption by Cabomba p.326
Gas Exchange Is Tied to Water Loss
• Transpiration is the evaporation of water from
leaves of plants. This can be as much as 99%
of the water absorbed by the roots.
FYI
• A single corn plant can lose up to 200 L of
water through transpiration in one growing
season.
• Transpiration can cool a leaf 10-15 C by
evaporative cooling.
• Transpiration and gas exchange are controlled by the
shape of guard cells which open stomata to allow
CO2 in and O2 and H2O out.
• OPENED STOMATA
– occurs when high water pressure, called turgor pressure
– Causes water to move into the guard cells by osmosis.
– The guard cells swell and the stomata open, allowing
transpiration.
– Occurs most during the day.
• CLOSED STOMATA
• occurs when the amount of water in the guard
cells decreases
• The guard cells shrink and the stomata close.
• Occurs most during the night, except in desert
plants where stomata only open at night due to
dry conditions.
The mechanism of stomatal opening and closing
Daytime – Open
Nightime - Closed
Guard Cells
Water moves in and out of Guard cells through Osmosis
• H2O moves in  Guard Cells
swell  High H2O pressure
(turgor pressure) causes a
change in shape  Open
Stomata
• H2O moves out  decrease in
turgor pressure  Guard cells
deflate  Stomata close
WILTED PLANTS – result from reduced turgor
pressure as a result of water loss.
• If transpiration rate is larger than Xylem
delivery; loss of turgor
CAM plants
•CAM plants mechanism is usually used by desert plants to reduce
the amount of water loss during the day.
• Since their stomata are closed during
the day, CO2 cannot enter the leaves
so photosynthesis cannot occur.
• Photosynthesis cannot occur at
night, when the guard cells could be
open, because light is needed by the
chloroplasts.
What do we do?
CAM plants
Solution!
• During the night, when the stomata are open it takes in the
CO2 and stores it in organic acids.
• During the day, CO2 is released from the acids to make the
sugar needed in photosynthesis
Assignment:
• Do “Check Your Understanding” p.330 #1,2,
and 4
Lab Activity: “
• Do p.322 and 330 Finding Out Activity “Open
and Shut”, “Turn over a new leaf” and
“suffocating leaves”
Water Transport in Plants
Chapter 9
Section 3
Vascular Plants
• Vascular System:
– A system of vessels to transport Water, Minerals,
and Sugars
– A series of interconnected tubes throughout the
plant (like our Circulatory system – veins and
arteries)
Xylem & Phloem
• Specialized tissues that make up the Vascular
System in plants
– Found in the Roots, Stems, and Leaves
Xylem
• Transports Water and dissolved Minerals from
the roots  leaves
– As Xylem cells mature, they die and become
hollow (only the Cell Wall is left)
• These dead cells are called tracheid's or vessel
elements
Xylem
• Tracheids have a pit (a
hole) on their end wall
between cells. They are the
only conducting elements in
gymnosperms (conifers)
and ferns.
• Vessel elements are found
in angiosperms (flowering
plants) have perforation
plates and are more
efficient.
• Cells link end-to-end
forming Xylem Vessels –
tubes (highways for Water)
Xylem Vessels
Phloem
• Transports Sugars (produced by
photosynthesis) from the leaves to various
locations throughout the plant
• Living cylinder shaped cells called sieve tubes
are linked end-to-end connecting at a sieve
plate form Phloem Vessels
Phloem tissue
• Their cell wall is porous therefore sugary sap
flows down through these pores.
• Sieve tubes have no nuclei.
• Companion cells (nucleated) control the sieve
tubes
•
•
•
•
Water Uptake in Roots
At the core of the roots are the xylem and
phloem.
Epidermal tissue covers the root.
At the tip of the root the epidermal layer is
permeable to water.
Most of the water enters here, by osmosis.
• Root hairs increase surface area of
the roots.
• Each root hair is an outgrowth of a
single epidermal cell.
• Minerals enter the Root cell either by
Facilitated Diffusion or Active Transport
• Minerals meet Water and a solution called
Xylem Sap
Water is pulled up through the plant by three forces:
1. Root Pressure: Active transport brings minerals
into the root tissues creating an osmotic
gradient. Water follows by osmosis.
Water is pulled up through the plant by three forces:
1. Root Pressure
2. Transpiration: Evaporation from the leaves
creates vacuum pressure that draws up the
water column.
Water is pulled up through the plant by three forces:
1. Root Pressure
2. Transpiration
3. Capillary Action (cohesion): Cohesion of water
molecules (due to H-bonding) creates a
continuous column of water in the xylem.
Water movement in plants
Sugar Transport in the Phloem
• Sugars are
produced in the
leaves by
palisade cells and
spongy tissue
cells during
photosynthesis.
• Sugars, minerals
and nutrients are
pumped into the
leaf phloem by
active transport.
Sugar Transport in the Phloem
• Water follows by
osmosis and the fluid
pressure forces the
phloem sap through
the pores in the sieve
plates.
• The osmotic gradient
is maintained
because nutrients are
continuously being
used up by the plants
tissues.
• Do Investigation 9-C “The Flow in Phloem”
P.339 and answer Analyze #1-4
• Do Check your understanding
P.340 # 1,3, 4, 5, 7
• Pkg pg. 23
9.4 Plant Control
Systems
• Tropisms are plant responses in which the
plant grows towards or away from a stimulus.
Phototropism
• the growth of a plant toward a light source.
• Plant cells respond to light by growing at different
rates.
• When cells on one side of a stem grow more
elongated than cells on the other side, the stem
curves.
Darwin’s Experiment
• Charles Darwin concluded that the tip of the seedling
detects light, transmits that information to the stem,
and the rate of growth of stem cells is affected.
Darwin suspected a chemical signal triggered the
growth.
The Experiment
• Decades later, Peter Boysen-Jensen tested the
presence of a chemical signal, finding that the
chemical could pass through gelatin but not mica.
(See Fig. 9.19, p.344)
The hormone:
• In 1926, Frit Went confirmed that a chemical he named “auxin”
(meaning to grow”) was produced in the plant tip.
• Auxin is actively transported through the cells towards the
shaded side of the stem causing cells there to grow longer than
cells on the lighted side, resulting in bending towards the light.
• Went’s experiment: Agar containing auxin caused cell
elongation in stems on which ever side it was placed (light not
being a factor)
Video
Gravitropism
The growth of a plant in response to the force of
gravity
•Negative gravitropism – stem grows towards
sunlight and against the force of gravity
•Positive gravitropism – roots grow into the soil &
towards the force of gravity
Gravitropism
Occurs as soon as seeds germinate and the
response is consistent regardless of how the seed is
oriented when it is planted.
Auxin is responsible for the plant growth response
to gravity.
• In the stem – when a plant is placed on its side, more
auxin collects in the cells on the stems lower side.
These cells then grow longer resulting in the stem
curving upward.
• In the root – increased auxin concentration
inhibits root growth. When a root is placed
sideways, auxin collects along the lower side
and cell growth is inhibited here. Cells on the
upper side continue to grow longer, resulting
in the root growing downward.
• Another theory of positive gravitropism is that
dense starch grains in the root tip cells may
settle at the low point in cells signaling the
direction of gravity and influencing the
direction of growth.
• Video: Phototropism and Gravitropism
Nastic Response:
• a plant’s response to touch.
• Stimulus of touch sends electrical signal to certain leaf
cells resulting in a drop in turgor pressure, causing the
leaf to collapse.
• Video: Venus fly trap - The Private Life of Plants David Attenborough
• Video: Nastic Response - Mimosa Pudica
Thigmotropism: Rapid growth of certain plant cells in
response to touch. Seen in plants that use tendrils
• Eg. Tendrils of a pea plant that come in contact with
a chain-link fence wrap around it, gaining support as
it grows.
gravitropism
leaves
day
roots
phototropism
touch
turgor pressure at base of
night
stems
elongate
day and night
do not elongate
Assignment:
• BLM 9-6 Discovering Tropisms
• 9.4 Review: p.348 #1-7
• Chapter 9 Review p.350 #1-8, 10, 11