Transcript File - Achal Science

Unit 3
Cycling of Matter in Living Systems
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1.0 The Cell
Enduring Understanding:
Our current understanding of the cell is due in part to developments
in imaging technology
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A Window on a New World
Development of the Cell Theory
Development in Imaging Technology and Staining Techniques
Cell Research at the Molecular Level
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1.1 A Window on a New World
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Our understanding of life processes is the result of developments
that date back to the time of Aristotle
Although early Greeks chose to propose answers to questions,
but never test them, Aristotle followed a pathway of accurate
observation and record making
He classified more than 500 animal species based on his
scientific methods
It wasn’t until the development of the microscope that we were
able to understand and see the building blocks of life
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Early Microscopes
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Hans and Zacharias Jensen, Dutch lens makers, invented the first
compound microscope in 1595
They used a two lens system, with an eye lens and an objective
lens
It had a magnifying power of about 20x
By 1665, Robert Hooke was using a microscope with a three lens
system with light illumination
Although he studied lots of items under the microscope, he is
most famous for his observations of cork
When he observed cork under the microscope, he saw empty
chambers that he called “cells”, which later became the name for
the building blocks of life
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At about the same time, a Dutch business man, Antoine van
Leeuwenhoek, was observing single celled organisms under a
single lens microscope
He was the first to observe cells living as free, independent
systems, and named them “animalcules”
His microscope, although small, was able to view organisms at
250x their original size
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Improvements in Technology
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Early microscopes were often blurry and had a halo of light
around the object being viewed
During the 18th century, scientists had discovered a way to
correct the lens and develop views that were clear, with better
detail than the predecessors
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1.2 Development of the Cell Theory
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Many scientists helped develop our current understanding of cells
Many had to discredit theories that were long held by people of
their time
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Spontaneous Generation
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Spontaneous generation proposes that life could emerge
spontaneously from non-living matter
Widely accepted by Greeks and Romans through the 19th century
Ex. Mice developed from underwear and husks of wheat
Ex. Maggots appear spontaneously from meat
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Contributions of Louis Pasteur
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Louis Pasteur disproved the theory of spontaneous generation
using the scientific method
Was one of the first scientists to develop the concept of
controlled, manipulated and responding variables
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Scientists Who Contributed to the
Development of Cell Theory
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It wasn’t until the 1830’s that the importance of the cell was
identified
Robert Brown was the first to identify the importance of the
nucleus
M.J. Schleiden was the first to identify plant cells, and also
proposed that the nucleus was responsible for the development
of the rest of the cell
Theodor Schwann believed that there must be similarities
between animal and plant cells, and observed similar structures
in animal cells, as Schleiden has seen in plant cells
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The Cell Theory
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Together they proposed that all living things were made of cells
and that the cell was the basic structure of all living organisms
Rudolf Virchow extended this statement to propose that all
existing cells came from pre-existing cells
The Cell Theory States:
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All living things are made up of one or more cells
All life functions take place in cells, thus the cell is the smallest unit
of life
All cells are produced from pre-existing cells through a process of
cell division
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1.3 Development in Imaging
Technology and Staining Techniques
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Light microscope depends
on a series of curved
lenses to magnify objects
with a light source
But they are limited; can
only magnify 1000-2000x
Compound microscopes
are also limiting because
of their contrast and
resolution
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Contrast
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Contrast refers to the differences between the organism being
viewed and the surrounding of the object being viewed
Most cells are colourless when light passes directly through them
under the microscope
Manipulating the light source can alter the contrast between
structures in the cell
Scientists also experimented with various stains and colouring
agents to improve contrast between the cells and their
background
Ex. Methylene Blue or Iodine
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Resolution
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It’s not enough to simply magnify an object
Resolution is an important factor in determining how much can
be seen under a microscope
Resolution or resolving power refers to the microscope’s ability
to distinguish between two structures that are very close
together
It is how much detail can be seen under the microscope
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Contrast Enhancing Techniques and
Fluorescence
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Staining is not the only method for developing clear images
Darkfield, phase contrast and differential interference contrast
(DIC) illumination are other techniques to help clarify images
under the microscope
These techniques all alter the light passing through the specimen
Fluorescence microscopy helps scientists study different parts
within the cells by attaching fluorescent substances to molecules
within the cell
When viewed under UV light, the molecules fluoresce and
individual parts are able to be studied
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Confocal Technology
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The use of laser beams and computers have made it possible to
view living, transparent cells in 3-dimension using the compound
light microscope
In the confocal microscope, a laser concentrates light into a
specimen
The reflection is passed through a tiny opening called the
confocal pinhole and reaches an electron detector
Only the light returning from an exact plane of focus can pass
through the pinhole to the detector, because out of focus, the
light is blocked by the pinhole
Thus, every image formed is of a very thin section through the
specimen
This image is stored on a computer to be combined with other
images to form a three dimensional image of the object
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Electron Microscopy
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In the first half of the 20th century, as scientists struggled to
improve the light microscope, the electron microscope was
developed by James Hillier and Albert Prebus
An electron microscope uses a beam of electrons, instead of light
waves, producing images with finer detail
The image is formed by the absorption or scattering of the
electron beam because electron –dense materials do not let
electrons pass through
These microscopes are focused by adjusting the electromagnets,
rather than a glass lens
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Transmission Electron Microscopes
(TEM)
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Depend on a beam of electrons passed through a very thin
section of fixed and stained tissue embedded in plastic
The electrons that pass through fall onto a fluorescent
screen/photographic film and black and white photographs are
produced
Magnifies up to 1 500 000x and has a much higher resolution
than compound microscopes
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Scanning Electron Microscope (SEM)
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The SEM was developed in the 1940’s
This microscope gives views of the surface features of specimens
The specimens are fixed and covered with an electron dense
material, like gold which reflects the beam of electrons
The scientist will scan the surface of the specimen, the electrons
which are reflected back form a 3-dimensional image of the
specimen
Magnifies up to 300 000x
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1.4 Cell Research at the Molecular
Level
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As a result of new technology and technological development,
research on cells has made incredible breakthroughs in medicine
and industry
The Scanning Tunnelling Microscope (STM) and the Atomic Force
Microscope (AFM) allow scientists to produce images of
molecules
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Gene Mapping
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Refers to understanding gene placement within the genome of
an organism
Scientists have begun to map the genome of many plant and
animal species
Helps scientists to understand how genes may work together,
and may one day allow scientists to cure genetic-based disease
Gene mapping may also help insert foreign genes into organisms
to help benefit the species
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Cell Communication
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Cells are considered open systems, ones which can exchange
matter and energy with their environments
To function efficiently, cells need to communicate with
neighbouring cells and interpret their environment
For cell-to-cell communication, messenger molecules, known as
receptors, travel through the organism and attach at target sites
on different cells
The binding of these molecules cause change in shape and
trigger a chain reaction to carry the message within the cell
Scientists have found a way to attach fluorescent molecules to
the messengers, and thus study cellular process, function and
infections of cells
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Three Dimensional Structure of
Molecules
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Molecules inside the cell or on its surface act as switches to
control cell activity
The structure of the molecule determines the effect that it has
on the functioning of the cell
X-ray crystallography uses x-ray and computer technology to
allow scientists to study the structure of messenger molecules
Also allows scientists to study normal and defective protein
structures within cells
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GFP Technology and Genetics
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Green Fluorescent Protein (GFP) technology has allowed
scientists to tag molecules and study their function at a cellular
level
It allows scientists to compare normal proteins with abnormal
proteins in cell tissues, and may lead to treatment of
degenerative diseases, such as Huntington's, Alzheimer’s and
Parkinson’s
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2.0 The Function of Cell Structures
and Organelles
Enduring Understanding:
Living systems are dependent upon the functioning of cell
structures and organelles
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The Cell as an Efficient, Open System
The Role of the Cell Membrane in Transport
Applications of Cellular Transport in Industry and Medicine
Is Bigger Better?
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2.1 The Cell as an Efficient, Open
System
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Cells carry on all life processes including:
• Intake of Nutrients
• Movement
• Growth
• Response to Stimuli
• Exchange of Gases
• Waste Removal
• Reproduction
Cells work constantly to maintain a balance, while being efficient
and conserving energy
Organelles are sub-structures within cells to help meet life
processes
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The Chemical Composition of Cell
Structures
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Organelles of the cell
include:
• The cell membrane
• The nucleus
• The cytoplasm
• Cell Wall
• Chloroplasts
• Vacuoles
• Endoplasmic Reticulum
• Ribosomes
• Lysosomes
• Golgi Complex
• Mitochondrion
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Cell Membrane
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A protective barrier
Semi-permeable
Useful for cell-to-cell
interaction and
communication
Interacts with molecules,
such as hormones
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Nucleus
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Contains the DNA
Directs cell activity
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Cytoplasm
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Gel – like substance within the cell membrane
Contains nutrients for cell in order to carry on life processes
Organelles are suspended in cytoplasm
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Cell Wall
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Provides structure and
support
Found in plant cells,
and some protists and
fungi
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Chloroplasts
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Found in plants cells and some
protists
Contain chlorophyll
Site for photosynthesis
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Vacuoles
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Large structures that
store nutrients,
secretion and fats
In plants, stores water
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Endoplasmic Reticulum
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Transports materials
through a series of tubes
Rough ER has ribosomes
attached, associated with
protein production
Smooth ER, ribosomes are
absent, associated with fat
and oil production
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Ribosomes
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Where amino acids are
made into proteins during
protein synthesis
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Lysosomes
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Membrane bound sacs in
which digestion occurs
Defend against invaders
Destruct damaged cell
organelles
Digest tissues during
development
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Gogli Complex
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Receives proteins from the
ER, packages and helps
transport them around the
cell
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Mitochondrion
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Convert large sugars
into usable forms of
energy for the cell
during the process of
cellular respiration
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What Are Organelles Made Of?
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Cell organelles are made of four basic components:
Lipids, like fats and oils
Carbohydrates, such as sugars
Proteins, like muscle fiber
Nucleic Acids, such as DNA
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Water is another major component of cell systems
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Similarities Between Plant and Animal
Cells
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Both have a cell membrane, and a cytoskeleton – a network of
fibers made of proteins and lipids
Both have DNA made of sugars,nitrogen base and phosphate
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Differences Between Plant and
Animal Cells
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Animal cells have centrioles, which are involved in reproduction
Animal cells are generally smaller and smoother
Plant cells have a cell wall made of cellulose
Plant cells contain the chemical chlorophyll which makes
photosynthesis possible
Plant cells have a large central vacuole
Plant cells are generally larger and more boxy
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The Structure of the Cell Membrane
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The cell membrane is composed of two major components:
Phosopholipids
Glycoproteins
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Phospholipids
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The phospholipids are organized into a lipid bi-layer, which is
essentially a double layer of lipids with a phosphate group
attached
Each phospholipid has a hydrophilic head made of phosphate
and a hydrophobic tail made of lipid
A layer of phospholipid heads faces the inside of the cell, tails
pointed inward, and a second layer of heads face the
environment tails facing inward
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Glycoproteins
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The glycoproteins are suspended in the phospholipid bi-layer
and serve as transport mechanisms for the cell
They also help anchor the cytoskeleton
Proteins may have sugar groups attached, and act as hormone
and other chemical receptors
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The Function of the Cell Membrane
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Major Functions of the Cell Membrane:
Helps the cell maintain equilibrium
Allows materials to pass in and out of the cell
Protects the cell from foreign invaders
Holds the cell together
Binds to neighbouring cells
Communicates with neighbouring cells using chemical
transmitters
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2.2 The Role of the Cell Membrane in
Transport
The cell membrane is very important at transporting materials
inside and outside of the cell
• Two basic process that are controlled by the cell membrane:
(1) Passive Transport
(2) Active Transport
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Cell membranes are selectively permeable in the type of
substances that are permitted to pass through the cell
membrane
This means that some substances are able to be transported,
while other substances are not
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The Particle Model of Matter
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All matter is made of molecules; particles in different substances
may vary in size and composition
Particles are constantly moving; particles in gases have more
energy than in solids
The particles of matter are attracted to one another or are
bonded together
Particles have spaces between them; spaces being smaller in
solids than in gases
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Passive Transport
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Passive Transport is a form of cell transport that does not use
additional energy to transfer substances across the cell
membrane
The only energy required is kinetic molecular energy, or energy
contained naturally in each atom
Three forms of passive transport include:
• Diffusion
• Facilitated Diffusion
• Osmosis
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Diffusion
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Diffusion is the natural movement of particles from a region of
high concentration to a region of low concentration
A concentration gradient is all that is required; an uneven
distribution of concentrations
Molecules are small enough, and soluble in lipids, that they can
slip easily through the phospholipid bi-layer of the cell
The charge of the particle, or how soluble the molecule is in
lipids will also determine whether of not it will use this form of
transport
Gases diffuse more quickly than liquids, which diffuse more
quickly than solids
Ex. Oxygen, carbon dioxide, nitrogen, salts, potassium ions
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Factors that Affect the Rate of
Diffusion
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Temperature: The warmer the temperature, the faster the
movement of the molecules, thus the faster they diffuse
Surface Area: If there is more cell membrane exposed, there
is more area for the transport of molecules, thus diffusion will
occur faster
Pressure: If the cell is in an environment that is of higher
pressure, the molecules will diffuse faster
Concentration Gradient: If there is a steeper concentration
gradient, then the molecules will diffuse quickly to reach
equilibrium
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Facilitated Diffusion
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Facilitated diffusion is very similar to diffusion except the use
of a transport channel is needed, usually a channel protein or
carrier protein
A channel protein creates a large opening or pore in the cell
membrane
A carrier protein will change shape once the molecule is attached
to it and force the substance across the membrane
This type of transport is for molecules that are too large to pass
through the phospholipids, and thus need a transport channel to
assist in their transport
Molecules are still moving from high to low concentration, and no
energy is required
Ex. glucose
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Osmosis
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The diffusion of water across the cell membrane is called
osmosis
The direction of water movement is dependent upon the
environment the cell is placed in
The membrane cannot be permeable to the solute dissolved in
the water; the concentration of solute is going to determine the
direction of diffusion
Three Environments:
• Hypertonic
• Hypotonic
• Isotonic
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Hypertonic Environments
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A hypertonic solution is one in which there is a higher
concentration of solutes in the environment than that found in
the cell
Because this solution has less water molecules per unit volume
outside the cell, water tends to flow out of the cell to reach
water equilibrium
This cause the cell to shrink
In plant cells, this is called deplasmolysis
In animal cells, this is called crenation
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Hypotonic Environments
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A hypotonic solution is one in which there is a lower
concentration of solutes in the environment than that found in
the cell
Because the solution has more water molecules per unit volume
outside of the cell, water tends to flow into the cell to reach
water equilibrium
This causes the cell to swell
In plant cells, this is called plasmolysis
In animal cells, this is called cytolysis
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Isotonic Environments
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An isotonic solution is one in which an equal number of solutes
in the environment than that found in the cell
Because the solutions are equal in terms of the number of water
molecules found per unit volume, no concentration gradient has
been set up
Thus, there is no net movement of water inside and outside of
the cell
The cell maintains size as equilibrium has been reached
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Active Transport
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Active transport is different from passive transport because it
requires the use of additional energy to transport molecules
across the cell membrane
The energy is usually in the form of ATP
ATP is made by the cell during the process of cellular respiration
Different Examples of Active Transport:
• Use of a Pump
• Endocytosis
• Exocytosis
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Pumps
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A protein carrier, called a pump, will transport molecules across
the membrane in the presence of ATP, usually against the
concentration gradient of the substance (from low to high)
Ex. Sodium is required to be outside the cell for the nerve cell to
operate properly. Sodium is small enough that it naturally
diffuses into the cell. The pump finds sodium ions that have
diffused in, and puts the out of the cell. This is moving sodium
from area of low concentration (inside) to an area of high
concentration (outside)
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Endocytosis and Exocytosis
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In some cases, molecules that may need to be taken in
(endocytosis) or secreted (exocytosis) are too large to use
diffusion or a transport pump
Endocytosis and exocytosis use membrane bound sacs called
vesicles
The purpose of the sac is to surround the large particle and
contain it
When the cell engulfs the substance into a sac, and then brings
it into the cell, this is known as endocytosis
When a cell releases the substances from the sac into the
environment, this is known as exocytosis
The vesicles are usually temporary structures and dissipate after
their purpose has been served
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Endocytosis
Exocytosis
2.3 Applications of Cellular Transport
in Industry and Medicine
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Industry has used transport in cells as knowledge that they can
apply to developing technology, known as membrane
technology, to aid in the following areas:
• Disease
• Drug Therapy
• Hormone Transport
• Peritoneal Dialysis
• Reverse Osmosis
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Recognition Proteins
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Most of the technology that has been developed takes into
consideration special proteins
Recognition proteins are proteins that are embedded in cellular
membrane, exposed to the cells environment, that allow cells to
recognize one another
Ex. An egg and sperm
Receptor proteins are proteins which are embedded in the
cellular membrane to which messenger molecules, such as
hormones can bind for cell–to–cell communication
Ex. Bacteria and the immune system
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Membranes, Proteins and Disease
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Researchers have been searching for treatments for constantly
changing viruses such as HIV
New discoveries focus on recognition or receptor proteins in
human cell membranes that appear to be the attachment sites
for the virus
Scientists are trying to find a lock ad key combination that would
prevent the HIV virus from getting into the cell
This process would work theoretically by blocking the receptor so
that cell would not recognize the virus
Cancer treatment has also targeted this concept
Scientists are trying to only target and destroy defective cells,
rather than using treatments that target and destroy healthy
cells as well
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Synthetic Membrane Technology
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Drug therapies also use a structure manufactured to act like a
cell membrane
Liposomes can be manufactured and inserted into infected body
tissue
Manufactured liposomes can hold medication need to treat
infected body cells
Once they are inserted, they are free to circulate the boy and
attach to infected cells, as in the treatment of HIV and cancers
The advantage of using liposomes is that they stay in the body
for longer periods of time, and they can concentrate on the area
of infection, rather than treating the entire body for the disease
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Transport of Protein Hormones
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Insulin is a small protein produced in the pancreas and necessary
for glucose absorption into cells.
Once released using exocytosis from the pancreas, insulin will
bind to cells and activate cellular processes for the absorption of
sugar
People who are not able to produce their own insulin, as in the
case of diabetics, injected insulin allows their body to function
normally
Scientists are developing pills that will simulate insulin activity to
stimulate cells in the absence of insulin for alternatives to
traditional drug treatments of diabetes
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Peritoneal Dialysis
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People who had kidney failure prior to recent technologies
usually died because their body could not rid their blood of toxic
substances
Dialysis is a process that helps complete the job of the kidneys in
the absence of two normally functioning kidneys
Humans have a membrane called the peritoneum, that lines the
abdominal cavity
During dialysis, waste substances pass from the blood through
the peritoneum cells into the dialysate fluid
The dialysate fluid is pumped into the abdomen via a small tube
and consists of a mixture of water, glucose and other substances
the body needs
Because the fluid contains no toxins or waste, toxins and waste
diffuse to the fluid for removal
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Reverse Osmosis
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Desalination is the process of removing salt from seawater in
order to make is suitable for drinking
Today’s technologies contain filters that operate on the concepts
of reverse osmosis, in which water is pumped though
progressively smaller filters to become salt free
The progressively smaller semi-permeable membranes allow
water to be forced through the filter, but filter out other
molecules and micro-organisms of progressively smaller and
smaller size
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2.4 Is Bigger Better?
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Cells are all microscopic in size
Why are cells so small?
As efficient, open systems, cells must be able to carry out all of
the life functions
Transport in and out of the cell is critical to these life functions; it
determines how the life processes function
Transport must be kept at maximum efficiency to maintain life
functions
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The Ratio of Surface Area to Volume
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As a cell becomes larger, its volume increases
More molecules will need to be transported across the cell
membrane to take part in the cell’s functions
The distance any molecule will travel, will increase as well
If the cell is going to maintain the ability to transport substances,
the surface area must increase to match the increased need for
molecules
As cells increase in size, the surface area to volume ratio
increases, which means the cell cannot transport as many
molecules because of the low surface area
If the cell remains small, it has a large surface area to volume
ratio, and thus remains efficient at transporting molecules
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Calculating Surface Area to Volume
Ratio
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R = SA/V
Rectangles:
• SA = 2lw + 2lh + 2wh
• V = lwh
Cubes:
• SA = 6s2
• V = s3
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The Size and Shape of Organisms
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No matter what the size of the organism, the surface area
exposed to the environment is critical
Remember the surface area exposed the environment
determines the opportunities for transport of materials
Cells, and often tissues, need to maximize the amount of surface
area exposed to the surroundings
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Maximizing Potential
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Examples on how organisms achieve this:
• Structures that have many folds in the membrane (i.e. small
intestine)
• Structures that are long and flat (i.e. leaves)
• Structures that branch off to create many smaller, attached
structures (i.e. root hairs, micro-villi, alveoli in the lungs)
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3.0 Plants
Enduring Understanding:
Plants are multi-cellular organisms with specialized structures
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Cells, Tissues, and Systems
The Leaf and Photosynthesis
The Leaf Tissue and Gas Exchange
Transport in Plants
Control Systems
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3.1 Cells, Tissues, and Systems
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Cells  Tissues  Systems in multi-cellular organisms
Advantages of multicellularity:
1) Division of Labour:
• Cells are specialized to perform one function, rather
than all functions as in single-celled organisms
• Specialized cells, tissues and organs
• When specialized, they can perform the function more
effectively
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Cells, Tissues, Systems (cont)
2) Size:
• Multi-cellular organisms are not limited by size, as they just
add more cells to become bigger
• Single-celled organisms are restricted by the surface area to
volume ratio
• Multi-cellular organisms have developed transport systems
within their bodies to maximize transport throughout the
organism
3) Interdependence of Cells:
• The life of multi-cellular organisms does not depend on one
cell; if one cell dies, it does not kill the entire organism
• Single-celled organisms rely on one cell, if it dies, they die.
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Plant Structure
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Plants are multicellular, and have
developed specialized cells, tissues and
systems
Although every cell contains the same
genetic information, individual cells perform
particular jobs within the organism
Groups of cells working together to perform
the same function are known as tissues
(i.e. xylem tissue)
Tissues that work towards a particular
function are known as organs (i.e.
vascular system)
Organs which work together to perform a
particular function are known as organ
systems (i.e. shoot system)
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Specialization in Plant Tissues
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Different types of tissues exist in plants:
• Dermal or Epidermis tissue
• Ground Tissue
• Vascular Tissue; Phloem and Xylem
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Dermal Tissue
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The Dermal tissue is the outer layer of cells that cover all nonwoody plants
One layer thick
Responsible for the exchange of matter and gases into and out
of the plant
The dermal tissue of shoot systems is responsible for the gas
exchange of carbon dioxide and oxygen, and for protecting the
plant from disease
The cells of the leaves and stems secrete a waxy substance,
known as the cuticle, that resists attack from microorganisms
and helps reduce water loss from the plants
The dermal tissue of the root system is responsible for the
uptake of water and minerals from the soil
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Ground Tissue
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The ground tissue is the layer of tissue found below the dermal
layer
Makes up the majority of the plant
Responsible for providing strength and support to the plant, food
and water storage in the roots, is the location of photosynthesis
in the leaves
The cells in this layer are loosely-packed together to allow spaces
between them where gases can diffuse quickly
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Vascular Tissue
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The vascular tissue is found throughout the roots, shoots and
leaves
It is responsible for the transport of materials throughout the
plant
Two types of tissues:
• Xylem
• Phloem
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The Xylem
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The xylem tissue is responsible for moving water and minerals
from the roots to the stems to the leaves where the
substances can be used in photosynthesis
Very thick walled tubes of varying diameters
Once made of living cells, the xylem is residual cell walls that
have been fused together after the cells died, to form long
straw-like structures
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The Phloem
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The phloem tissue is responsible for transporting sucrose and
other dissolved sugars from the leaves to other parts of the plant
The phloem is formed from individual long sieve tube cells
Sieve tubes form continuous ducts, made from living cells
The sugar that is transported by the phloem can then be used in
cellular processes, such as protein making
Is the sugar is not used, it is stored as cellulose (used for
structure and support) or as starch in the roots (carrots, sweet
potatoes), stems (ginger, potatoes) or leaves (green onion,
rhubarb)
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Specialization in Plant Cells
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Cells become specialized for particular functions and produce
products necessary only for that function
Examples:
• Dermal cells produce the cuticle to protect cells form water
loss
• Guard cells control pore size in the leaves to control gas and
water exchange with the environment
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3.2 The Leaf and Photosynthesis
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The leaf is a collection of tissues whose main purpose is to
produce energy for the plant through photosynthesis
Each type of tissue has a specialized purpose
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The Chloroplast:
A Unique Plant Organelle
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Only plant cells contain chloroplasts
Chloroplasts contain a pigment called chlorophyll, and are the
location of the process of photosynthesis
During photosynthesis:
• Plants transport water and carbon dioxide to the leaf tissue
• CO2 and H2O diffuse into the plant cells and are transported
to the chloroplasts
• As chlorophyll is exposed to sunlight, the cell converts CO2
and H2O into glucose and oxygen
• The plant stores the glucose for later use, or converts glucose
into a more usable form of energy, ATP, during cellular
respiration
CO2 + H2O + light energy  C6H12O6 + O2
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Gas Production in Plants
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Photosynthesis is not the only process that produces gas;
Cellular Respiration also produces gas in plants, as well as animal
cells
Cellular Respiration takes glucose, with oxygen, and converts it
into a form of energy the plant can more readily use, Adenosine
Tri-Phosphate (ATP)
After glucose is produced, it can be stored in the form of starch,
or transported to the mitochondrion
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•
During Cellular Respiration:
• Plant and animal cells transport glucose and oxygen to the
cytoplasm
• Cellular respiration begins with glucose and oxygen being
converted to CO2 and H2O
• The products are moved to the mitochondria, where the
process of cell respiration is completed, and ATP is released
C6H12O6 + O2  CO2 + H2O + ATP
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3.3 The Leaf Tissue and Gas Exchange
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Air can diffuse into the plant cells, but it would take a very long
time for the plant to get all of the air it needs if it relied solely on
diffusion, especially with the cuticle covering the outer portion of
the leaf
The plant has specialized structures to help maximize gas
exchange
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Dermal Tissue
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The epidermis is very thin and clear on both the top and the
underside of the leaf
Dermal tissue contains specialized cells called guard cells,
whose role is to control gas and water exchange between the
plant and the environment
Guard cells form tiny pores, called stomata, in the leaf
Guard cells will open to allow exchange of gas and water through
diffusion or transpiration
Most stomata are located on the underside of the leaf and can
change in numbers in response to environmental changes
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Ground Tissue
Between the upper epidermis and lower epidermis of the leaf are
specialized ground tissues called mesophyll
• There are two basic types of mesophyll:
(1) Pallisade Tissue Cells
(2) Spongy Mesophyll Tissue
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Pallisade Tissue Cells
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Found just below the upper epidermis
Long, rigid and rectangular cells, tightly packed together
Arranged such that the majority of cells have exposure to the
sun
Responsible for photosynthesis
Contain many chloroplasts in these cells
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Spongy Mesophyll Tissue
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Located between the pallisade tissue cells and the lower
epidermis
Irregularly shaped, less rigid, loosely packed together
Responsible for gas exchange by diffusion throughout the leaf
Move oxygen toward the stomata for expulsion, and carbon
dioxide towards the pallisade cells for photosynthesis
The space between the cells maximizes their main function of
gas exchange
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Vascular Tissue
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Located throughout leaves, stem and
roots
Long, hollow structures, specialized in
transporting substances throughout the
plant
Xylem and Phloem tissues are bunched
together in a vascular bundle
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Xylem transport H2O from roots to the leaves
Phloem transport glucose from the leaves to
the rest of the plant
Provides water to the leaf needed for
transpiration and photosynthesis
Removes glucose produced by
photosynthesis
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Gas Exchange in Plants
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All gas exchange occurs through diffusion
The stomata allow for more efficient gas exchange, and more
rapid diffusion of carbon dioxide in and oxygen out
Diffusion is also maximized by the air spaces within the leaf
tissue
The leaf is not the only site for gas exchange
Lenticels, found along stems and mature roots, form pores
which are pathways for gas exchange
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3.4 Transport in Plants
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Many factors are involved in transport in plants
Transport is dependent on the cellular transport processes, such
as osmosis and diffusion, and specialized structures
Transport is dependent on how these structures and processes
work together
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Cohesion and Adhesion
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Water must be transported throughout the plant against the
force of gravity
Water has specific properties that facilitate this transport
Water molecules are attracted to one another because of their
polar nature, known as cohesion
Water is also attracted to other polar substances, known as
adhesion
The processe of transport is dependent on adhesion and
cohesion
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Root Pressure
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Root pressure is created in the xylem
Dissolved minerals are present in the cells of the roots as a result
of active transport, thus creating a higher salt concentration
inside the cells
Through osmosis, water is drawn into the cells, creating positive
pressure
This positive pressure forces water up the xylem, as water
travels from an area of high pressure to an area of low pressure
This only moves water a few meters
Plants that are larger require another process to move water,
transpiration
Transpiration occurs at the stomata and lenticels
As water is lost in the stem and leaves, water is pulled up the
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stem
From Root to Leaf: Water Transport
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Dissolved minerals enter the roots through active transport
(requires the plant to expend energy)
Water will naturally diffuse into the roots as a result of osmosis
This results in root pressure
Root pressure and transpirational pull will force the water up the
stem to the leaves
Once the water is at the leaf, the water will evaporate, or be
used in the process of photosynthesis
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The Effect of Tonicity on Plants
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Tonicity refers to the concentration of solute particles in any
solution
Tonicity affects the arrangement of cells in plant tissues and
osmosis
If the cells are in a hypertonic environment, they will lose water
and undergo plasmolysis, where the cell membrane pulls away
from the cell wall as the cell shrinks
If the plant cells are placed in fresh water (hypotonic
environment), the cells will undergo deplasmolysis in which the
water will diffuse into the cells, causing them to become turgid
(increased turgor pressure)
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From Source to Sink: Sugar
Transport
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Once plants have undergone photosynthesis, they need a way to
transport the products of photosynthesis to the rest of the plant
to provide the cells energy
At the leaf, the phloem use active transport and carrier proteins
to absorb glucose
Water then moves into the phloem through osmosis
This increases the pressure in the phloem, and forces water out
of the leaves to the rest of the plant, known as pressure flow
theory
The sugars can then be used for life processes, such as gaining
cell nutrients, reproducing cells, or growing
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3.5 Control Systems
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Living organisms respond to stimuli in the environment
Phototropism and gravitropism are two examples of how plants
respond to stimuli
Photo =
Trop/o =
Gravi =
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Phototropism
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The growth movement is a response of the plant to the stimulus
of light and is called phototropism
There are two types of phototropism:
Positive Phototropism: Exhibited by stems, in which the
stems grow towards light
Negative Phototropism: Exhibited by roots, in which the
roots grow away from light
Stems need to maximize the amount of light exposure to
maximize the process of photosynthesis in the leaves
Roots, growing away from light, are more likely to find soil,
where the minerals and nutrients are located
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The Role of Scientists in Developing
Theories about Control Mechanisms
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Charles Darwin and his son Francis, asked in 1880, What part of
the plant detects and responds to the phototropic stimulus?
Peter Boysen-Jensen, who asked in 1913, What was the signal
that initiates the phototropic response?
F.W. Went, who asked in 1926, What is the specific substance
responsible for initiating the phototropic response?
These scientists focused on different shoot systems in the oat
seed and other seedlings
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Seedling Development and Early
Experiments
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The outer sheath of an oat seedling covers the developing leaves
The shoot grows as a lengthening of the cells on this outer
sheath
Once the shoot reaches 4 – 6 cm, the sheath stops growing ,
and the enclosed stem and leaves continue growing through
If light comes only from one direction, the seedling’s sheath will
bend towards the light
Seedlings with tips covered do not respond to light, thus the tip
is responsible for the detection of light stimulus
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The area of elongation, (on the side of the stem away from
the direction of the light), must communicate with the tip, and
elongate the cells on the far side to force the plant to bend
Auxin is a hormone that is manufactured in one part of the
seedling and transported to another part of the seedling to allow
for communication in the seedling
Auxin is responsible for elongation
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Gravitropism
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Plants also respond to the pull of the Earth, or gravity, known as
gravitropism
There are two types of gravitropism:
Positive Gravitropism: Exhibited by roots, in which roots grow
with the force of gravity
Negative Gravitropism: Exhibited by stems, in which stems
grow against the force of gravity
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Mechanisms of Gravitropism
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Scientists believe that roots rely on starch particles in specialized
cells
The starch particles settle at the lowest point in the root system
due to gravity
This movement is detected by plants, and the roots grow as a
response
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Other Control Mechanisms
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Phototropism and Geotropism are important control systems in
plants that help guarantee survival in the plant
Response to touch, temperature and water, daylight length
Ex. Plants flower and seed in response to daylight periods longer
than 12 hours, typical of longer summer days
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