Biology 30
Module 1
Cells and Biochemical Actions: Foundations of Life
Lesson 1
The Cell
Copyright: Ministry of Education, Saskatchewan
May be reproduced for educational purposes
Biology 30
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Lesson 1
Biology 30
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Lesson 1
Lesson 1
The Cell
Directions for completing the lesson:
Text References for Suggested Reading:

BSCS Biology
Chapter 5, Pages 99-107
Section 5.1 - 5.5; Appendix 2 P. 670
OR
Nelson: Biology
Chapter 1, pages 20-39

Study the instructional portion of the lesson

Review the vocabulary list

Do Assignment 1
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Lesson 1
Vocabulary
cell theory
mitochondria
cell wall
nuclear membrane
centrifuging
nuclear pore
centrioles
nucleolus
chromatin
nucleoplasm
cytoplasm
nucleus
cytoplasmic streaming
organelles
cytosol
phase-contrast microscope
dark-field microscope
phospholipid molecule
differentially permeable
plastid
endoplasmic reticulum
prokaryotes/prokaryotic
eukaryotes/eukaryotic
protoplasm
fluid mosaic model
ribosomes
golgi complex
semi-permeable
lysosomes
selectively permeable
microtoming
vacuole
microtubules
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Lesson 1
The Cell
Introduction
From the moment we are
born, our various senses
are assaulted with a
multitude of different
kinds of stimuli or
sensations. We become
accustomed to many of
them and, at any
particular time, we are
consciously aware of or
pay attention to only a
small fraction of them.
The types of responses
we make or the kinds of
reactions which we may
have are often the result
of learning processes
which are continually
taking place. Learning
builds up the knowledge
which we have about our
Photo by Andreas Praefcke - GNU
environments. Some of
that knowledge is put to practical everyday use, while a large amount is probably
stored in our minds as part of many general understandings about that which is
taking place around us.
We live in an age of science characterized by rapid gains in knowledge. Expansion in
general and scientific information has been coming at ever increasing rates with
advances leading to more advances. Present estimates seem to indicate that our
scientific knowledge is doubling every five to ten years. This is in sharp contrast to
the rather slow developments or accumulations which had been occurring up to the
early 1900's. Many of the technological advances (particularly in the computer fields)
are often outdated before even becoming fully available to the public. Rapid advances
have also occurred in such varied fields as travel, communications, satellites, food
preparations and medical accomplishments.
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The accumulation of new knowledge and the development of more advanced scientific
techniques and instruments have opened up areas of interest which had not
previously been studied or thought of before. However, many kinds of studies have
also been receiving attention for hundreds of years. Attention in these areas have
been maintained as new scientific developments enabled us to probe for information
and answers previously unavailable to us. Despite the continued uncovering of new
information, many "old" questions remain unanswered and newly uncovered
information has often led to new questions. One such broad area of interest which
had intrigued our ancestors and continues to do the same to us revolves around the
characteristics of life and all those actions involved in sustaining life.
Studies of life and body functions eventually lead to cellular studies, or
cytology.
Cells are the smallest units of
organisms. Any actions
necessary for maintaining the
life of an entire organism
must occur in cells first. This
first lesson will examine some
of the kinds of cell studies
which have taken place and
the information which has
been uncovered about cell
structures up to this time.
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Lesson 1
After completing this lesson you should be able to:
•
identify some individuals who made contributions in the
early beginnings of cell studies.
•
have an understanding of the different kinds of
microscopes and their general role in cytology.
•
mention some other developments or techniques which
have helped in cell studies.
•
summarize the major points of the Cell Theory.
•
recall some of the major cell structures or organelles and
their apparent values to cells.
•
state some major differences between plant and animal
cells.
•
explain the various relationships within an organism and
the cellular arrangements which make up an efficient,
functioning organism.
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Lesson 1
Early Cell Studies
Can you imagine not knowing that cells exist? Looking at your hand, you would have
thought that it was just a solid mass. A person with 20/20 vision has a resolving
power down to 0.1 mm, that is if two lines were less than 0.1 mm apart they would
appear as a single line, or a dot with that diameter may just barely be visible to some
people. The human egg is approximately this size, but most of a human body's 50 to
70 trillion cells are much smaller than this. Even the longest nerve cell, which may
extend a little over one meter (from the lower back and into the foot), has a diameter
too small to be seen without the aid of a microscope. It is worthwhile to take a step
back in time to see how the study of cells began with the discovery of magnifying
lenses and how this leads into the development of the microscope.
Microscopy
The credit for developing the first magnifiers appears to belong to two Dutch brothers
by the name of Janssen. Their development of magnifying lenses came in the 1500's.
Whether he had some knowledge of the work of the Janssen brothers or not, Antony
van Leeuwenhoek eventually came to be regarded as being mainly responsible for
opening up the field of microscopy. He was from Holland. In the late 1600's and early
1700's, he produced many hundreds of single lenses or simple microscopes to study
many different things. Somewhat of a jealous person in that Leeuwenhoek never
permitted anyone to freely handle his microscopes or know of his exact techniques in
producing lenses, he nevertheless kept careful records of the discoveries and
observations of things that he examined. These he passed along to a scientific
organization, the Royal Society of England. Leeuwenhoek was probably the first
individual to observe single-celled microorganisms such as yeasts, bacteria, blood
and sperm cells, and some of the common protozoans found in water. A considerable
length of time (about 150 years) went by before microorganisms began to be observed
by anyone else.
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Just prior to Leeuwenhoek's discoveries, English scientist Robert Hooke issued a
publication (in 1665) recording his observations and descriptions of cells. Hooke used
a compound microscope, which made use of two sets of separate lenses.
Hooke Microscope
Hooke was actually the first to observe groups of cells. These initial observations were
really of dead cork cells with just their outer walls remaining.
Observations of living cells
from other organisms began
to be made by Hooke as well
as other individuals.
However, at the time, none of
these really established the
relationship or the
importance of cells to an
entire organism.
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Lesson 1
The initial discoveries and observations of microorganisms and
cells were made possible by the use of light microscopes.
Leeuwenhoek's single lens magnifiers—comparable to a simple
hand-held magnifier of today—and the double-lens or
compound microscopes make use of light which passes
through or is reflected off an object being observed.
Handheld devices can
enlarge up to 20 times actual size
The Compound Light Microscope
Leeuwenhoek's fine work is shown by his ability to produce one simple microscope
which magnified approximately 270 times. Monocular compound light microscopes
found in school laboratories today vary in magnification from 100 to 400 times and
upward. The double magnification systems of some of the better compound light
microscopes can approach 2000 times but not much more, as wavelengths of light
are such that details cannot be resolved much beyond this (much as our eyes cannot
resolve details smaller than 0.1 mm) and the image will blur. Additional
magnification will not improve the ability to see detail clearly, because of the physical
characteristics of light.
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The development of electron microscopes
after the 1930's increased the ability to
magnify dramatically. Instead of using light,
electrons are beamed through an object and
onto a photographic plate – since electrons
are invisible to the eye. The differences in the
numbers of electrons passing through or
being absorbed by various parts of the object
are responsible for creating the image.
Between the object and the photographic
plate are magnetic fields which act in the
same manner as lenses to light by spreading
or condensing electrons, to achieve high
magnifications. Electron microscope
magnifications are usually hundreds of
thousands times and can even be over a
million times.
Photo by tz1_1zt
Aids used to study cells
1.
Microscopes can magnify and resolve images for the most part, but differences
between certain observed parts are so slight that they cannot be clearly
distinguished from each other. Different types of microscopes have been
developed for this purpose:

Dark-field microscopes bend only those light rays passing through a slide
or an object, which makes the image appear bright against a dark
background. This shows up cell structures that are invisible with a light
microscope.

Phase-contrast microscopes bend the light rays passing through an object
in such a way as to make nearby parts stand out from each other. This type
of microscope makes it possible to study very small structures and events
occurring in living cells.

Electron microscopes show cell structures at very large magnifications.
Two types used are:
o transmission electron microscopes for enlarging cell organelles
o the scanning electron microscope for more detailed observations.
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Lesson 1
2.
Special fixatives for killing cells and many different kinds of stains which are
absorbed differently have also been developed for distinguishing between cell
parts. Hundreds of stains and staining techniques are presently being used.
3.
Microtoming, or the slicing of objects into very thin sections, provides
transparent slices for examination with an electron microscope.
4.
The grinding up and centrifuging of objects to separate different substances
has undergone continual refinements to aid in cellular studies.
The Cell Theory
For many years after cells were first observed, their importance or significance to
organisms' bodies was not realized. They were simply regarded as "being there". In
1809, French naturalist Jean Lamarck made a significant interpretation and
generalization when he noted that every living body seemed to consist of masses of
cells, each containing moving fluids. It was not until 1839 that two German
biologists, Schleiden and Schwann, independently stated their ideas which formed an
important beginning to the Cell Theory. Their generalization was:
 All organisms are made up of cells, whether unicellular (single cell) or
multicellular (many cells). That is, cells are the basic structural units making
up all bodies.
The second and third important generalizations making up the Cell Theory came from
the later works of German pathologist Rudolf Virchow. The statements he added
were:
 All processes common to living organisms occur in the individual cells
meaning that individual cells carry out basic functions necessary to maintain the
life of an entire organism (such as respiration, excretion, ingestion and others).

All new cells arise from existing cells.
More recently scientists have added a fourth statement to the Cell Theory. It states:
 Cells contain hereditary material, which ensures the passing of specific
characteristics from parent to daughter cells.
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The statements making up the Cell Theory can be applied as characteristics of living
organisms. One or two possible exceptions exist:
 Viruses are unique in a number of ways. They do not show any criteria for life.
They appear to show life only when inside a living host. Rather than carrying out
their own life-sustaining functions such as respiration and growth, they re-direct
those of their hosts' to satisfy their own requirements to produce more viral
matter.
 Some protozoans, algae and fungi are also difficult to fit into the Cell Theory.
These organisms may contain structures unusual to most other cells. In addition,
it is difficult to determine whether some of their masses are single-celled or
multi-celled.
Cell Structure and Function
Developments in microscopy, staining and other techniques related to cellular
examinations, enabled scientists to begin identifying individual cell parts.
Experiments and various kinds of testing helped to determine what the function of
some of these parts were. The functions of some distinct structures are still not fully
known. The nature or form of these structures and some of their behaviors have led
to scientists stating what they think they do in a cell, but without any definite
certainties.
There is no "normal" or "typical" cell which can be used as a common representative
for all organisms. Differences exist in cell sizes, shapes, colors and in the kinds of
structures found within each. These differences exist not only between different kinds
of organisms but also within individual organisms. If one was to combine all the
possible features of all cells into one, it may be possible to produce a general or
"master" cell which could be used as a study model. It should be emphasized again
that such a cell would not really exist under natural conditions.
The term protoplasm was applied (by Hugo von Mohl in the 1800's) to all the living
material within cells. Most cells have a rounded body or nucleus within them so that
the living matter could be further distinguished by labelling all protoplasm within the
nucleus as nucleoplasm and the remainder outside the nucleus as cytoplasm.
(Again, remember that there are exceptions to the general form as with human red
blood cells which have no nuclei at maturity and some muscle cells have several.)
Within the protoplasm, particularly in the cytoplasm, are small, distinct bodies called
organelles. Collectively, these carry out various functions related to sustaining life
such as energy release or storage, growth and repair, secretion and other actions.
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There are two major types of cells.
1. Cells that have a distinct, membrane-enclosed nucleus that contains the cell's
DNA are called eukaryotes or are eukaryotic. In addition to having nuclei, some
of these cells have photosynthetic membranes enclosed in distinct bodies or
organelles (called chloroplasts). There are other membrane-enclosed organelles so
that, in general, the cytoplasm of a eukaryote shows a fair degree of specialization.
2. Prokaryotes are noted by the lack of distinct nuclear bodies. The absence of
nuclei does not mean an absence of nuclear material. The nuclear matter is
scattered throughout the cytoplasm. Any photosynthetic membranes present are
also freely floating within the cytoplasm. The absence of membrane-enclosed
organelles and general lack of specialization is a common feature of prokaryotes.
A Prokaryotic Cell
A Eukaryotic Cell
(example of a bacteria cell)
(example of an animal cell)
Chloroplast
Nucleoid
(circular DNA)
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Cell Wall
Nucleolis
Cell Membrane
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Nucleus
Lesson 1
With some noticeable differences in form and the presence or absence of some
structures, the following graphics illustrate "typical" plant and animal cells.
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Lesson 1
Cell Wall
The cell wall is found in plants and in some monerans and fungi. Rather thick, its
largely cellulose nature forms a rigid but porous framework which appears to provide
both support and protection for plant cells. Its rigidity generally results in plant cells
showing greater regularity or uniformity in their shapes, as compared to animal cells.
Cell (or plasma) Membrane
Surrounding both plant and animal cells is a thin, flexible and living plasma
membrane. In plant cells it is often pressing against the inside of the cell wall.


The membrane is fluid and thus, flexible.
It consists of two phospholipid layers called a bilayer.
o the outer part or ‘head’ of the phosopholipid molecule is attractive to water
o the inner chain or ‘tail’ is not.
This characteristic enables the membrane to maintain a moist exterior while
offering some barrier to movements of molecules through it.
These phospholipid molecules move and float across the membrane. Different protein
molecules are embedded in and extend right through both layers of the membrane
forming a pattern or mosaic as shown in the diagram below. These protein molecules
drift across the membrane as well.
This model of the cell membrane structure is referred to as the fluid mosaic model.
The Fluid Mosaic Model of the Cell Membrane
Membranes not only surround or enclose entire cells, but also form the outer
boundaries of various organelles within the cytoplasm. The actual kinds of
phospholipids or proteins making up membranes or the ways in which these
molecules are actually arranged have effects on what roles membranes have. Most of
the membranes protectively enclose not only the contents of entire cells or those of
distinct organelles but also seem to control the movements of substances through them.
phosphate
head
phospholipid
layers
(bi-layer)
lipid tail
protein molecules
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The selective nature of such membranes to various substances means that they are
semi-permeable or differentially permeable. Another term, selectively permeable
can also be used. The balancing of the concentrations of substances on either side of
the membranes can be crucial to the proper functioning of cells or their organelles.
(Some of the movements through cell membranes will receive further attention in the
next lesson.) In addition to regulating movements, some membranes may form
partnerships with particular hormones during the synthesis of larger molecules.
Cytoplasm
The cytoplasm contains all the living cell material that extends from the cell
membrane to the nuclear membrane. The cytoplasm contains
 Cytosol
 Organelles
 Cytosol
The cytosol is the gelatinlike portion of the cytoplasm that bathes the organelles.
The cytosol contains a high percentage of water. The rest is made up of amino
acids, lipids, carbohydrates, enzymes, salts, minerals and other elements. All of
these are necessary for the various metabolic processes that are required to keep
the cell alive. These processes are kept separate or are prevented from interfering
with each other by being contained in smaller structures scattered throughout
cytosol called organelles.
 Organelles
nuclear membrane
1. Nucleus
nucleolus
 Most cells contain rounded structures which are
commonly in the center in many animals or off to
one side, as in many plants.
 These nuclei appear to be the "control centers" for
many cell activities and are of particular
importance for cell reproduction and growth.
 Each nucleus is surrounded by a membrane
much like the plasma membrane described earlier,
except that the nuclear membrane is two-layered or
double. Pores in the membrane probably allow certain
substances, which could include "messengers", to travel
chromatin
between the cytoplasm and nucleoplasm.

Nuclear pore
nucleoplasm
Varying numbers of dense bodies called nucleoli may be present. In plants
or animals where they do appear, the actual number is specific for a species
although not all may be visible at any one particular time. (Nucleoli
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Lesson 1


commonly disappear just before cell division occurs.)
A nucleolus appears to consist largely of proteins and nucleic acids (RNA or
ribonucleic acid) which direct or take part in protein synthesis carried on
within a particular cell. In other words, a particular kind of human cell will
keep reproducing its own kind of protein or, when the cell reproduces, new
human cells of the same type will be formed.
All eukaryotic cells (those with distinct nuclei) have thread-like structures of
protein and nucleic acids (mainly DNA or deoxyribonucleic acids) scattered
through the nucleoplasm. This is chromatin and shortly before cells divide,
it shortens and thickens into more distinct and visible chromosomes.
These are responsible for the transmission of traits or characteristics to new
cells or offspring.
2. Endoplasmic Reticulum
smooth endoplasmic reticulum
rough endoplasmic reticulum

Electron microscopes have
nucleus
revealed networks of
channels which
extend
throughout
the
cytoplasm.
These appear
to be formed by
a series of
infolding
membranes
extending from the
nuclear membrane to
ribosomes
the outer plasma
membrane. There is still some
uncertainty as to their actual formation. One theory suggests that the
membranous infoldings arise from the nuclear membrane and extend
outwards to the plasma membrane – perhaps even contributing to its
formation as a cell grows. The entire system of infoldings and channels is
known as the endoplasmic reticulum. In some cells they are quite
numerous, while in others they appear to be absent.

The membranes may have many small bodies called ribosomes attached to
them while in other areas they may be relatively free of them and smooth.
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The varied nature of the endoplasmic reticulum makes it appear to be
responsible for a number of actions:
 biochemical activities such as the production and storage of lipids;
 where ribosomes are common, it seems to be an area of protein formation;
 where there are few ribosomes, enzymes and other substances are thought
to be produced;
 throughout, the network of channels may allow the movements of
substances between the outer membrane and the nucleus.
Therefore, the network appears to function as an area where manufacturing
occurs as well as transportation and possible storage of substances.
3. Ribosomes

Tiny spheres, or ribosomes, are found scattered throughout cells as well as
being attached to the endoplasmic reticulum. In the latter instance, rough
endoplasmic reticulum indicates that there are many attached ribosomes
while smooth endoplasmic reticulum means there are few or no attached
ribosomes.

These small spherical organelles contain enzymes and ribonucleic acid
(RNA) which are involved in the process of putting amino acids together to
form proteins. The proteins may then move through the endoplasmic
reticulum to other parts of the cell or out of the cell and into other parts of
the body.
4. Golgi Complexes


The Golgi material is
a series of
membranes which
has some
resemblance to the
endoplasmic
reticulum. (There is
some speculation that
Golgi Complexes may even
be formed by splitting off from
the endoplasmic reticulum.) They
appear somewhat like flattened discs
or balloons pressed together with small sacs around the edges.
Golgi
complexes
Golgi complexes together with the endoplasmic reticulum packages proteins
and exports them to other locations in the cell. Golgi complexes are
especially common in some secretory cells.
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Lesson 1
5.
Mitochondria



Mitochondria are oval-shaped organelles
which are believed to be the
"powerhouses" of cells.
Each is surrounded by a double
membrane with the inner membrane
forming folds called cristae.
Enzymes on these cristae act on carbon
compounds, during the process of
respiration, to release energy for
numerous cell activities. Mitochondria
are especially numerous in active cells,
such as those of the (heart) muscles.
6. Lysosomes

Approximately the same size and shape as mitochondria, these round
"containers" tend to be more numerous in animal cells. Some plant cells
may not even have any.

Lysosomes function as storage vessels for powerful digestive enzymes in
cells. Foreign particles, such as bacteria, worn-out cell parts and food
particles fuse to, and then are enclosed by, the membrane of a lysosome. Its
digestive enzymes then break down the particles and release energy.

Lysosomes are believed to be formed by small sacs pinching off from the
Golgi Complexes. These round bodies are sometimes called "suicide sacs". If
a cell dies or is injured in any way causing the containing membranes of
lysosomes to release their enzymes, those enzymes will begin breaking down
the cell itself.

In some instances, lysosomes seem to be "programmed" to release their
enzymes at certain times. Not frequent, this sometimes happens as in the
life cycle of frogs where the tail degenerates. Enzymes break down the tail
cells and the cell remains are resorbed as a tadpole changes into a frog. In
other instances, release of the enzymes may also occur in order to break
down organelles or even cells themselves as they wear out. This allows for
cell replacements.
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Lesson 1
7. Centrosomes (Centrioles)
centriole
lysosome
Most animal cells and only a few
plant cells show
centrosomes or
rounded bodies near
the nuclei. Some
references do not even
use the term
"centrosome", which
they regard as more
dense cytoplasm
surrounding a pair of
centrioles.
cytoskeleton
The centrioles exist as a pair of rod-like
organelles which are at right angles to each other. One centriole resembles a
circular bundle of nine rods or microtubules, each consisting of three smaller
rods or microtubules.


Centrioles appear to be involved in cell division. Before a cell divides, a pair of
centrioles will duplicate and separate so that two pairs are formed. The two
pairs of centrioles then move to opposite sides of the cell. Threadlike spindle
fibers develop between the two pairs of centrioles. Chromosomes attach to
these, become separated and are pulled to opposite ends of the cell just before
it divides.
There is still some uncertainty about the role of centrioles, since they appear to
be absent in higher plants and yet spindle fibers are still formed. There is also
some speculation that centrioles may somehow be involved in the development
of cilia or flagella on some cells, which are structures associated with
movement.
8. Cytoskeleton – is composed of microtubules and microfilaments


While the structures making up centrioles appear to be solid rods rather than
tubes, there are other hollow tubes or filaments found throughout the
cytoplasm of many cells. Made of protein, the scattered nature of these tubules
throughout the cytoplasm may form an almost skeleton-like structure
internally.
This framework may give shape and some organization to cells. In addition, the
tubules could be associated with some internal movements or transport.
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Lesson 1
9. Vacuoles
vacuole
Vacuoles, which are fluid-filled spaces,
occur in both plant and animal
cells. In plants they are often
quite prominent, taking up
a large part of the middle of
a cell and pushing the
cytoplasm and the other
organelles to the outer edges.
These vacuoles serve as
reservoirs for a variety of
substances: pigments, salts, food
particles and wastes. Plant vacuoles
tend to be permanent, remaining
throughout cells' lives. Some vacuoles found
in certain animal cells, such as the contractile vacuoles which regulate water balance
in some protozoans, are also permanent. However, other animal vacuoles which may
contain food or act as storage areas, are not usually as prominent as those in plants
and are often only temporary. The above image illustrates a vacuole in an animal cell,
which is much smaller than those found in plant cells.
10. Plastids



These organelles are only present in the
cytoplasm of plant cells and some protists
with some plant-like characteristics. Some
have internal structures which are quite
complex of which a chloroplastid is an
example. Chloroplastids or chloroplasts
contain the green pigment chlorophyll,
which is necessary in converting or
capturing the energy of sunlight into
carbohydrate form. Orange (carotene) and
yellow (xanthophyll) pigments are other
By Thomas Dreps
pigments commonly found in
chloroplasts. (The changing of leaf color in autumn is essentially the result
of the breakdown of green chlorophyll which had previously covered up the
yellows and oranges. Red pigments also appear in reactions where sugar
had been previously produced.)
Chromoplasts are plastids containing not only orange and yellow pigments,
but reds and blues. These frequently show up in the epidermal cells of
flowers and fruits.
Leucoplasts are plastids designed for storing substances such as starches.
When energy is required the (insoluble) starches are changed to (soluble)
sugars, which can then be transported by plant fluids to wherever they are
required. Potato tubers are particularly plentiful in leucoplasts.
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Lesson 1
Emphasizing some Plant and Animal Cell Differences
In the descriptions given of cell parts and organelles, references were made to certain
parts being present or absent, or of a different form in one group of organisms as
compared to the other. Many plant cell organelles are nearly identical to those in
animal cells. Following, is a summary of probably the four distinct differences
between the cells of advanced plants and animals.
1.
Plants have fairly thick (in proportion to total cell sizes) outer cell walls. The
thickness and nature of the cellulose fibers making up a cell wall result in
plant cells commonly having rigid and specific shapes. Animals do not have cell
walls. Animal cell contents are enclosed only by thin, flexible cell membranes.
2.
Plant cells are usually dominated by large, permanent and centrally located
vacuoles. Animals have small scattered vacuoles which may appear and
disappear as food and waste conditions change.
3.
Plastids, and especially chloroplasts, are common features of plant cells. They
are not found in higher animal cells.
4.
Centrioles are found in animals cells but not in plant cells.
Plant and animal cells contain many of the same membrane enclosed organelles
(eukaryotic cells) and structures. Some of these organelles in common are: the
nucleus, mitochondria, endoplasmic reticulum, golgi apparatus, lysosomes, the
cytoskeleton and cytosol.
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Lesson 1
Cell Division-Cell Continuity
Cells and the organelles they may contain within them cannot continue to grow or to
live indefinitely. As will be seen in the next lesson, increasing size makes it more and
more difficult for an individual cell to satisfy its nutrient requirements or to remove
all wastes. At the same time, internal matter and organelles must be replaced or
repaired to maintain efficient functioning. Cell division or reproduction occurs either
on a regular or an irregular basis to meet these needs.
In order for cell reproduction to be meaningful or successful, at least two actions
must take place.
1. The genetic material, which determines the nature of a cell and how it
functions, must be duplicated (or replicated).
2. The cytoplasmic contents must then be equally distributed among the "new" or
daughter cells if they are to function successfully. The processes associated
with the reproduction, growths and functionings of cells follow a general
pattern which makes up what is known as the "cell cycle". This will be looked
at more closely in the next lesson.
Organization of Living Material
In watching young children, or even adults, examining objects which may be new and
interesting to them, they will commonly be seen to take things apart to examine
pieces individually. The same may be done with living matter – although once the
smallest parts are reached and examined, they are not likely to be living anymore!
With the aid of certain techniques, dissecting instruments and microscopes, one
should be able to divide the matter of a living organism down to the smallest unit,
which is the cell. Cells could possibly be broken down further into organelles,
compounds and elements but individually, these are either non-living or would not be
able to sustain life on their own for very long.
Some organisms are
 unicellular, existing as single cells which can function independently of other
cells. Some of these were examined in Biology 20 during the taxonomic studies.
 In certain instances cells are colonial, where they live in groups (as some yeasts,
bacteria, algae and other organisms do) but are still really independent.
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Lesson 1
 Multicellular organisms show higher degrees of organization and divisions of
labor in the living matter. While the simplest units are still cells, these become
specialized and grouped in particular ways to carry out certain functions. Thus,
more advanced animals may have bone cells, nerve cells and muscle cells among
others. These cells are dependent on the others to work together to function.
Similar cells, which together perform the same type of job, are called tissues. Ex:
nerve and muscle tissue, or in plants, palisade cells.
Different tissues grouped together to perform one function become an organ. Ex:
heart, kidney, liver or stomach. In plants, xylem and phloem are organs.
Organs are then grouped into specialized systems. Ex. Digestive, circulatory and
respiratory systems. In plants, examples are vascular bundles and leaves.
Finally, when all organ systems are functioning together, there is a complete
organism. Ex. A human or a plant.
Beyond the organism level, one can find other organizations or relationships of living
matter on ever-broader levels. These may be reviewed as:
Population -
This includes a number of organisms of one kind or one species in
a particular place. (Eg. Elk in the Moose Mountain area.)
Community -
Organisms of different species in a certain area make up that
area's community. (Eg. Frogs, muskrats, cattails, etc. in a marsh.)
Ecosystem -
Relationships involving living and non-living factors in a particular
environment make up an ecosystem.
Biosphere -
Finally, biosphere refers to all the living organisms around this
planet.
Biology 30
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Lesson 1
Summary
The basic building and functioning unit of a living organism is a cell. With a few
exceptions, the cells of most organisms show three recognizable parts or divisions:
1. Cell wall and/or cell membrane.
2. Cytoplasm.
3. Nucleus (or nucleoplasm).
As a summary and study aid, the following table lists some of the parts and
organelles, as well as their functions.
Structure
Function
Cell wall
Support and protection.
Cell membrane
Regulates movements of substances in and out of a
cell.
Nucleus
Directs the synthesis or reproduction of proteins.
Cytoplasm
Contains the organelles and the numerous
substances taking part in, or which are the result
of, various life-sustaining actions.
Endoplasmic reticulum
Manufacturing and storage area as well as a
transporting system.
Ribosome
Arranges amino acids into proteins.
Golgi complex
Secreting, "packaging" and storing various
substances, as well as transport.
Mitochondrion
Releases energy for cell use. The "powerhouse".
Lysosome
Encloses powerful digestive enzymes.
Centrosome
Contains centrioles, which take part in animal cell
division.
Vacuole
Storage or holding area for water, food, salts and
wastes.
Plastid
Captures and stores energy or stores pigments or
food substances.
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Lesson 1
The discovery and accumulation of cell knowledge is not only interesting in itself but,
as will be seen in the remainder of the course, it can be used to help explain the
many processes occurring in living things. Much of this knowledge can be applied to
practical uses in such diverse fields as: plant and animal reproduction and growth;
plant and animal diseases and possible treatments; and, the general area of genetics.
Probably of particular interest to ourselves is information of the type related to
hereditary diseases and other kinds of illnesses, organ transplants and a topic which
has been intriguing generations before us: how and why aging (of cells and
organisms) occurs and how it may be slowed (or even stopped).
Biology 30
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Lesson 1