Transcript Chapter 9

Chapter 9
From cell to Organism : Plants
 Overview:
 Organization
of the plant cell
 Exchange of gases
 Water transport
 Plant Control Systems
9.1 – Specialized and Organized
 In single celled organisms, one cell must be
able to perform all the functions of like.
 In multi-cellular organisms, many cells work
together to meet the needs of the organism.
Group of specialized cells perform specific
tasks.
Cell Specialization in Leaves
 Leaves contain several types of specialized
cells that help with photosynthesis
 Chemical process where carbon dioxide and
water form glucose and oxygen
 6H2O + 6CO2 ----------> C6H12O6+ 6O2
Epidermal Cells
 Protective layer covers the plant’s leaf
 Forms the epidermis
 Covers the upper and lower surfaces of the
leaf
 A waxy substance (cuticle) coats the cells to
prevent evaporation of water from the leaf
 Do not have chloroplasts
Palisade Tissue Cells
 One of the main types of photosynthetic cells
 Long and narrow like columns and are
packed closely together
 Shape and organization make photosynthesis
within the cells efficient
 Upper surface of the leave and contain
chloroplasts
Spongy Tissues Cells
 Contain chloroplasts and carry out
photosynthesis
 Layered below the palisade tissue cells
 Round and loosely packed and have many air
spaces between them
 Structure helps the cells to exchange gases
and water with the environment
Stomata and Guard Cells
 Stomata - Small opening in the epidermal
later to allow gases in and out of the leaf
 Guard cells – are near the stomata to control
the size of it.

Can change shape to open or close the
stomata
Vascular Tissue Cells
 Two times of tissues are called xylem and
phloem
 Xylem – carries water and minerals from the
roots to the leaves
 Phloem – carries sugars produced by the
leaves to various parts of the plant.
 The tissues are arranged together in
vascular bundles
Cell, Tissue, Organ, System
 Multi-cellular organisms can have:
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A larger size
A variety of specialized cells
An ability to thrive in a broader range of
environment
 In Multi-cellular organisms, groups of
specialized cells are organized so that they
can perform their functions efficiently
 Cells are the most basic level of organization,
while systems are the most complex.
 Cells- most basic unit of organization in
organisms
 Tissues – cells that are similar to each other are
often clustered together
 Organs - can be formed by combining multiple
tissues
 Systems- organs can function together at an
even higher level of organization

Organs and tissues throughout the body perform
a shared complex function
 Page 324

Questions  1 & 7
9.2 Gas Exchange
 The stomata in the outer tissues of the plant’s
leaves allow gases to diffuse in and out of the
leaf
 Inside the leaf, there are spaces between
some of the cells that allow gases to move in
and out freely
Something in the Air
 During photosynthesis, plants consume
carbon dioxide and water to produce oxygen.
Leaves and Lenticels
 The most important gas-exchange organ in
the plant is the leaf.
 Air diffuses through the stomata and into the
leaf.
 It circulates in the spaces between the
spongy and palisade tissue cells.
 Carbon dioxide diffuses down its
concentration gradient.
 Oxygen produced during photosynthesis
passes out of the cells and into the air
spaces.
 Then oxygen will go to the stomata and out of
the plant.
 In the roots and stem, some gas exchange
occurs.
 In woody plants, the layer of dead cork and
waxy substances prevent this.
 In these plants, lens-shaped opening called
lenticels perforate the bark of these plants.
Gas exchange is tied to water loss.
 Palisade and spongy tissue cells are coated
with a thin layer of water
 As the air diffuses out of the stomata, some
water is lost.
 The evaportation of water from leaves is
called transpiration.
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This can lead to 99% of water absorbed by the
root.
 To keep the plant from drying, the guard cells
can change their shape to cause the stomata to
open or close.
 The size of the stomata controls the amount o
gas exchange and transpiration.
 High rates of photosynthesis are possible when
the stomata are open.
 When the stomata is closed, gas exchange and
water exchange are reduced.
 Water moves in and out of the cell through
Osmosis.
 As water moves into the guard cells, the
water pressure inside the cells increases and
causes the cells to swell.
 The high water pressure is called turgor
pressure.
 Turgor Pressure pushes the elastic cell
membrane against the rigid cell wall.
 The swollen guard cells change shape,
opening the stoma.
 This will cause transpiration to make the plant
cell balanced.
 In most plants, the stomata is open during the
day and closed at night.
 Plants though who adapt to extremely dry
condition have their stomata only open at
night.
 In the desert, plants store carbon dioxide to
perform photosynthesis during the day.
 Plants can still dry out though
 The plant’s leaves droop and wither, and the
stem softens and bends.
 Like the guard cells, other cells throughout the
plant have reduced turgor pressure as a result of
water loss.
 If they are supplied with more water, the limp
cells have their turgor pressure restored, which
renews their shape and rigidity.
 Questions 1- 5
 Due Friday November 4th 2010
9.3 Water Transport in Plants
 Some trees are more than 100M from
root to tip.
 We are going to investigate the
transport of water and nutrients in the
plant vascular system.
 You will identify the cells, tissues and
organs that make up this system.
Xylem Vessels and Phloem Vessels
 Like our circulatory system that carries blood,
plants vascular system is made up of
interconnected tubes.
 Xylem and phloem are specialized tissues that
make up this system of transport.
 They are found in the roots and stems of the
plant as well at the leaves
 Xylem tissue transports water and dissolved
minerals from the soil to the leaves.
 In mature plants, most xylem cells are dead, as
they form hollow tubes consisting of only the
cell walls.
 The cells are linked end to end, forming long
continuous tubes called xylem vessels.
 These extend from near the tips of the roots
up into the rest of the plant
 Some sugars produced during photosynthesis
are transported throughout the plant by cells of
phloem tissues.
 The phloem is composed of cylindrical cells
joined end to end to form phloem vessels.
 Phloem cells are living and their cell walls are
porous allowing them to exchange materials.
 Sugary sap flows down the phloem vessels by
passing through these pores.
 The Long hollow cells within xylem vessels
are called Tracheids or Vessel elements.
 Some types of plants have both but some only
have tracheids
 Both begin as living cells until the plant is
mature then the cells die off
 Fluids pass from one tracheid or vessel
element to the next within the xylem to move
water.
 Phloem cells consist of sieve tubes and
companion cells arranged end to end.
 These cells connect in long tubes, separated by
sieve plates, to make the phloem vessels.
Water Uptake in Roots
 Water and minerals enter a plant from the
roots.
 At the core of the root there are the xylem and
phloem encircled by several other layers of
cells
 Epidermal tissues which is where the water
enters the plant by osmosis.
 The surface area for
absorbing water and
dissolving minerals from
the soil is increased by
hundreds of root hairs.
 Each hair is an out growth
of a single epidermal cell.
 Minerals do not readily diffuse across
the cell membranes
 Roots cells use facilitated diffusion or
active transport if against the
concentration gradient
 Solution of water and minerals that
accumulates in the root xylem is called
xylem sap
 Xylem vessels carry the sap upward
from the roots through the stem then
into the leaves
Properties of Water
 The shape of water molecules and the
weak electrical forces between them,
cause water molecules to be attracted
to each other.
 Cohesion, the tendency of water
molecules to stick to other water
molecules, transmits the upward pull
from the tip of the leaves to the tip of
the root.
 Another property of water is adhesion
 The
tendency of water molecules to
stick or adhere to certain surfaces
 Just as water will attract to one
another, they will attract to molecules
of other substances such as the
cellulose wall of a xylem vessel.
Root Pressure Pushes
 In the roots, one force that pushes fluid
upward is turgor pressure inside the
root xylem.
 This is called root pressure
 The root cells bring minerals into the
xylem through active transport.
 This increases the tendency of water to
diffuse into the root xylem by osmosis.
 The pressure from this, will force fluid
up the xylem.
 Adhesion of the xylem sap to the
xylem vessel walls help the fluid climb
upward.
Transpiration Pulls
 Because the pressure changes at you get
higher on a 100m plant, some other factor has
to help bring the water to the top of the tree.
 Transpiration from the leaves generates this
pulling force or tension.
 When water is evaporated, it causes the solutes
to be more concentrated.
 Osmosis must occur in order to restore
balance.
Sugar Transport in Phloem
 After water and minerals enter the
leave, the plant can carry out
photosynthesis.
 The sugars are produced by the
palisade tissue cells and spongy
tissue cells provide energy for the
entire plant.
 As the sugar concentration increases,
water follows the sugar by osmosis.
 The cells swell with the increase in
turgor pressure
 The sugar, nutrient, and water mixture
called phloem sap, flows down the
concentration gradient.
 The phloem vessels transport the sugars and
other substances throughout the plant.
 Sugar, minerals and other nutrients are
pumped into the leaf phloem by active
transport
9.4 Plant Control Systems
 Stimuli – an environmental factor that an
organism is responding to.
 Phototropism – the growth of a plant toward a
light source
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This maximizes the amount of light absorbed
by the plant’s leaves
Plants do this by having there cells grow at
different rates
This will cause one side of the plant to be
elongated more than the other side.
Auxins: Plant Growth Chemicals