SECTION 4-1, THE HISTORY OF CELL BIOLOGY
Both Living and Nonliving Things are composed of molecules made from
chemical elements such as carbon, hydrogen, oxygen, and nitrogen. The
organization of these molecules into Cells is one feature that distinguishes
Living Things from all other matter. The CELL is the smallest unit of matter
that CAN Carry on ALL the PROCESSES OF LIFE.
OBJECTIVES:
1.
2.
3.
4.
Name the scientists who first observed living and nonliving cells.
Summarize the research that led to the development of the cell theory
State the three principles of the cell theory.
Explain why the cell is considered to be the basic unit of life.
THE DISCOVERY OF CELLS
1. All living things are made up of one or more cells -from the tiniest bacterium
to the largest whale. A cell is the smallest unit that can carry on all of the
processes of life.
2. Before the seventeenth century, no one knew that Cells existed.
3. Most Cells are too small to be seen with the unaided eye.
4. Cells were not discovered until after the invention of the microscope in the
early seventeenth century.
5. One of the First Microscopes was made by the Dutch drapery store owner
Anton von
Leeuwenhoek. With his hand-held microscope, Leuwenhoek became the FIRST
person to OBSERVE and DESCRIBE MICROSCOPIC ORGANISMS and LIVING
CELLS. (Figure 4-2)
6. In 1665, the English Scientist Robert Hooke used a microscope to examine a
thin slice of cork and described it as consisting of "a great many little boxes". It
was after his observation that Hook called what he saw "Cells". They looked like
"little boxes" and reminded him of the small rooms in which monks lived, so he
called the "Cells". (Figure 4-1)
7. In 1838, German Botanist Matthias Schleiden studied a variety of PLANTS
and concluded that all PLANTS "ARE COMPOSED OF CELLS".
8. The next year, German Zoologist Theodor Schwann reported that ANIMALS
are also made of CELLS and proposed a cellular basis for all life.
9. In 1855, German Physician Rudolf Virchow induced that "THE ANIMAL
ARISES ONLY FROM AN ANIMAL AND THE PLANT ONLY FROM A PLANT" OR
“THAT CELLS ONLY COME FROM OTHER CELLS".
10. His statement contradicted the idea that life could arise from Nonliving
Matter. "Theory of Spontaneous Generation" The process by which life begins
when ethers enter nonliving things.
11. The COMBINE Work of Schleiden, Schwann, and Virchow make up what is
now known as the modern CELL THEORY. (Table 4-1)
12. The Cell Theory consist of THREE Principles:
A. All living organisms are composed of one or more cells.
B. Cells are the basic units of structure and function in an organism.
C. Cells come only from reproduction of existing cells.
SECTION 4-2, INTRODUCTION TO CELLS
Cells come in a variety of shapes and sizes that suit their diverse functions.
There are least 200 types of cells, ranging from flat cells to round cells to
rectangular cells.
OBJECTIVES:
1. Explain the relationship between cell shape and function.
2. Identify the factor that limits cell size.
3. Describe the three basic parts of a cell.
4. Compare prokaryotic cells and eukaryotic cells.
5. Analyze the relationship among cells, tissues, organs, organ systems, and
organism.
CELL DIVERSITY
1. Not all cells are alike. Even cells within the same organism show Enormous
Diversity in Size, Shape, and Internal Organization. Your Body contains at
least 200 Different Cell Types.
CELL SHAPE (figure 4-4)
1. Cells come in a variety of Shapes.
2. Notice the neurons on the wall, the basic cell of our Nervous System. This
diversity of form reflects a diversity of function.
3. Most Cells have a Specific Shape.
4. THE SHAPE OF A CELL DEPENDS ON its FUNCTION.
5. Cells of the Nervous System that carry information from your toes to your
brain are long and threadlike.
6. Blood Cells are shaped like round disk that can squeeze through tiny blood
vessels.
CELL SIZE
1. A few types of cells are large enough to be seen by the unaided eye. The
Female Egg is the largest cell in the body, and can be seen without the aid of a
microscope.
2. Most cells are visible only with a microscope.
3. MOST CELLS ARE SMALL FOR TWO REASONS:
A. Cells are limited in size by the RATIO between their Outer Surface Area
and Their Volume. A SMALL CELL HAS MORE SURFACE AREA THAN A
LARGE CELL FOR A GIVEN VOLUME OF CYTOPLASM. This is important
because the nutrients, oxygen, and other materials a cell requires must enter
through it surface. As a cell grows larger at some point its surface area
becomes too small to allow these materials to enter the cell quickly enough to
meet the cell's need. (Figure 4-5)
B. THE CELL'S NUCLEUS (THE BRAIN) CAN ONLY CONTROL A CERTAIN
AMOUNT OF LIVING, ACTIVE CYTOPLASM.
BASIC PARTS OF A CELL
1. Cells contain a variety of Internal Structures called ORGANELLES.
2. An organelle is a Cell Component that PERFORMS SPECIFIC FUNCTIONS
FOR THE CELL.
3. Just as the organs of a multicellular organism carry out the organism's life
functions, the Organelles of a cell maintain the Life of the Cell.
4. There are many different cells; however, there are certain features common
to all, or most Cells. All cells have an outer boundary, an interior substance,
and a control region.
PLASMA MEMBRANE - (THE OUTER BOUNDARY)
1. The entire cell is surrounded by A THIN MEMBRANE, called the PLASMA
OR CELL MEMBRANE.
This is the cell's outer boundary that covers a cell's surface and acts as a
barrier between the inside and the outside of a cell.
2. Inside the Cell are a Variety of Organelles, most of which are surrounded by
their own Membrane.
CYTOPLASM (SIET-oh-PLAZ-uhm) (THE INTERIOR SUBSTANCE)
1. EVERYTHING BETWEEN THE PLASMA MEMBRANE AND THE NUCLEUS IS
THE
CELL'S CYTOPLASM. This includes the Fluid, the Cytoskeleton, and all the
organelles Except the Nucleus.
2. CYTOPLASM consists of TWO MAIN COMPONENTS: CYTOSOL and
ORGANELLES.
3. CYTOSOL is a jellylike mixture that consists MOSTLY OF WATER, along
with PROTEINS,
CARBOHYDRATES, SALTS, MINERALS and ORGANIC MOLECULES. About 20
percent of the cytosol is made up of protein.
4. Suspended in the Cytosol are tiny ORGANELLES (ORGANS).
5. ORGANELLES ARE STRUCTURES THAT WORK LIKE MINIATURE
ORGANS,
THEY CARRY OUT SPECIFIC FUNCTIONS IN THE CELL.
6. The ORGANELLES PLUS THE CYTOSOL makes up the CYTOPLASM.
7. In Eukaryotic Cells, most Organelles are surrounded by a MEMBRANE.
8. Prokaryotic Cells have NO MEMBRANE-BOUND Organelles.
CONTROL CENTER - THE NUCLEUS (DNA)
1. A Large Organelle near the Center of the Cell is the NUCLEUS. IT
CONTAINS THE CELL'S GENETIC INFORMATION AND CONTROLS THE
ACTIVITIES OF THE CELL.
2. The PRESENCE OR ABSENCE of a NUCLEUS is important for Classifying
Cells.
A. ORGANISMS WHO’S CELL CONTAIN A NUCLEUS AND OTHER
MEMBRANE-BOUND ORGANELLES ARE CALLED EUKARYOTES. (Figure 4-6)
B. ORGANISMS WHOSE CELLS NEVER CONTAIN (OR LACK) A NUCLEUS
AND OTHER MEMBRANE-BOUND ORGANELLES ARE CALLED
PROKARYOTES. (Figure 4-7)
3. UNICELLULAR ORGANISMS such as bacteria and their relatives are
Prokaryotes.
4. All other organisms are Eukaryotes; plants, fish, mammals, insects and
humans.
5. The difference between Prokaryotes and Eukaryotes is such an important
distinction that Prokaryotes are placed in Two Domains Separate from
Eukaryotes - Domains Bacteria and Archaea.
COLONIES
1. A Colonial Organism is a collection of Genetically Identical Cells that live
together in a closely connected Group.
Colonial organisms are not truly multicellular because few cell activities are
coordinated.
2. Many of the Cells of the Colony carry out Specific Functions that Benefit the
Whole Colony.
3. Colonial Organisms appear to straddle the border between a collection of
Unicellular Organisms and a True Multicellular Organism. They Lack Tissues
and Organs, but do exhibit the principle of Cell Specialization.
TRUE MULTICELLULAR
1. In most Multicellular Organisms, we find the following organization: (figure
4-9)
Cellular Level: The smallest unit of life capable of carrying out all the
functions of living things.
Tissue Level: A group of cells that performs a specific function in an
organism form the TISSUE.
Organ Level: Several different types of tissue that function together for a
specific purpose form an ORGAN.
Organ System Level: Several organs working together to perform a
function make up an ORGAN SYSTEM. The different organ systems in a
multicellular organism interact to carry out the processes of life
2. Plants also have Tissue and Organs, although they are arranged somewhat
differently from those of Animals.
A. Dermal Tissue System forms the outer layer of a plant.
B. Ground Tissue System makes up the bulk of roots and stems
C. Vascular Tissue transports water and food throughout the plant.
D. The FOUR Plant Organs are ROOTS, STEMS, LEAVES AND FLOWERS.
SECTION 4-3 CELL ORGANELLES AND FEATURES
Eukaryotic cells have many membrane systems. These membranes divide cells
into compartments that function together to keep cells alive.
OBJECTIVES:
1.
2.
3.
4.
5.
Describe the structure and function of a cell's plasma membrane.
Summarize the role of the nucleus.
List the major organelles found in the cytosol and Describe their roles.
Identify characteristics of mitochondria.
Describe the structure and function of the cytoskeleton.
THE PLASMA OR CELL MEMBRANE
1. A Cell cannot survive if it is totally isolated from its environment. The
Plasma Membrane is a complex barrier separating the cell from it's external
environment.
2. This "Selectively Permeable" Membrane regulates what passes into and out
of the cell.
3. All cells, from all organisms, are surrounded by a Plasma Membrane.
4. The Cell Membrane is a thin layer of Lipid and Protein that separates the
cell's content from the world around it.
5. The Cell Membrane Functions like a GATE, Controlling what ENTERS and
LEAVES the Cell.
6. The Cell Membrane CONTROLS the ease with which substances pass into
and out of the cell-some substances easily cross the membrane, while others
cannot cross at all. For this reason, the Cell Membrane is said to be
SELECTIVELY PERMEABLE.
7. Cell Membranes are made mostly of PHOSPHOLIPID MOLECULES. (Figure
4-10) Phosphate + Lipid.
8. Lipid is a simple form of FAT.
9. Phospholipids are a kind of Lipid that consists of TWO FATTY ACIDS
(TAILS), and PHOSPHATE GROUP (HEADS).
10. A Phospholipid Molecule has a POLAR "Head" and Two NONPOLAR
"Tails".
11. POLAR - The two ends of the Phospholipid Molecule have different
properties in Water.
12. The Phosphate Head is HYDROPHILIC meaning "WATER
LOVING". Because of its hydrophilic nature, the head of a Phospholipid will
orient itself so that it is as close as possible to water molecules.
13. The Lipid Tails are HYDROPHOBIC meaning "WATER-FEARING", the
Hydrophobic tails will tend to orient themselves away from water.
14. When dropped in WATER, PHOSPHOLIPIDS line up on the surface with
their Phosphate Heads Sticking into the Water and Lipid Tails pointing up from
the surface.
15. Cells are bathed in aqueous, or watery, environment. Since the inside of a
cell is also an aqueous environment, both sides of the Cell Membrane are
surrounded by Water Molecules. These Water Molecules cause the
Phospholipids of the Cell Membrane to form TWO LAYERS.
16. Cell Membranes CONSIST of TWO Phospholipid LAYERS Called a LIPID
BILAYER.
17. Heads face the watery fluids inside and outside the cell.
18. Lipid Tails are sandwich inside the Bilayer.
19. The Cell Membrane is constantly being formed and broken down in living
cells.
MEMBRANE PROTEINS (Figure 4-11)
1. A Variety of PROTEIN MOLECULES are EMBEDDED in the Lipid Bilayer.
2. Some Proteins are attached to the surface of the cell membrane, these are
called PERIPHERAL PROTEINS, and are located on both the Internal and
External Surface.
3. The Proteins that are embedded in the Lipid Bilayer are called INTEGRAL
PROTEINS.
4. Some Integral Proteins extend across the entire Cell Membrane and are
exposed to both the inside of the cell and the exterior environment. Others
extend only to the inside or only to the exterior surface.
5. There are many kinds of Proteins in membranes; they HELP to MOVE
Material INTO and OUT of the Cell.
6. Some Integral Proteins form Channels or Pores through which certain
substances can pass.
7. Other Proteins bind to a substance on one side of the Membrane and carry it
to the other side of the Membrane.
8. Integral Proteins exposed to the Cell's External environment often have
Carbohydrates attached to them serve as identification badges that allow cells
to recognize each other and may act as Site where viruses or chemical
messengers such as hormones can attach.
FLUID MOSAIC MODEL OF CELL MEMBRANES
1. Membranes are FLUID and have the consistency of vegetable oil.
2. The Lipids and Proteins of the Cell Membrane are always in motion.
3. Phospholipids are able to drift across the membrane, changing places with
their neighbor.
4. Proteins in and on the membrane Form PATTERNS, or MOSAICS. (Figure
4-11)
5. Because the Membrane is FLUID with a MOSAIC of Proteins, scientists call
the modern view of Membrane Structure THE FLUID MOSAIC MODEL.
6. The Pattern, or "Mosaic" of Lipids and Proteins in the Cell Membrane is
Constantly Changing.
THE NUCLEUS (plural, Nuclei) (figure 4-12)
1. The Nucleus is often the most Prominent Structure within a Eukaryotic Cell.
2. It maintains its shape with the help of a Protein skeleton known as the
NUCLEAR MATRIX.
3. The Nucleus is the CONTROL CENTER (BRAIN) of the Cell.
4. Most Cells have a Single Nucleus some cells have more than one.
5. The nucleus is surrounded by a Double Layer Membrane called the
NUCLEAR ENVELOPE.
6. The Nuclear Envelope is covered with many small pores through which
PROTEINS and CHEMICAL MESSAGES from the Nucleus can pass. Golf Ball
like dimples (pores).
7. The Nucleus contains DNA, the HEREDITARY MATERIAL OF CELLS.
8. The DNA is in the form of a long Strand called CHROMATIN.
9. During Cell Division, Chromatin strands COIL and CONDENSES into thick
structures called CHROMOSOMES.
10. The Chromosomes in the nucleus contain coded "BLUEPRINTS" that
control all cellular activity.
11. Most Nuclei contain at least ONE NUCLEOLUS (plural, Nucleoli) (Figure 412).
12. The NUCLEOLUS MAKES (synthesizes) RIBOSOMES, WHICH IN TURN,
BUILD PROTEINS.
13. When a Cell prepares to Reproduce, the NUCLEOLUS DISAPPEARS.
OTHER ORGANELLES
MITOCHONDRIA (MET-oh-KAHN-dree-uh)
1. Mitochondria are found scattered throughout the Cytosol, and are relatively
Large Organelles.
2. Mitochondria are the sites of Chemical Reactions that transfer Energy from
Organic Compounds to ATP. Energy contain in food is released. Converted to
ATP. ATP is the molecule that most Cells use as their main Energy Currency.
3. THE "POWERHOUSE" OF THE CELL.
4. Mitochondria are Usually more numerous in Cells that have a High Energy
Requirement - Your muscle cells contain a large number of mitochondria.
5. Mitochondria is surrounded by TWO Membranes. (Figure 4-13)
A. The smooth outer membrane serves as a boundary between the
mitochondria and the cytosol.
B. The inner membrane has many long folds, known as CRISTAE (KRIStee). The Cristae greatly increases the surface area of the inner membrane,
providing more space for the Chemical Reactions to occur.
6. Mitochondria have their own DNA, and new mitochondria arise only when
existing ones Grow and divide.
7. ATP Production is called CELLULAR RESPIRATION.
RIBOSOMES (RIE-buh-SOHMZ) (figure 4-14)
1. Unlike most other organelles, Ribosomes Are Not Surrounded by a
membrane.
2. Ribosomes are the site of PROTEIN SYNTHESIS (Production or
Construction) in a cell.
3. They are Most Numerous Organelles in almost all cells.
4. Some are free in the Cytoplasm; others line the membranes of ROUGH
ENDOPLASMIC RETICULUM.
ENDOPLASMIC RETICULUM (ER) (EN-doh-PLAZ-mik ri-TIK-yuh-luhm)
1. The ER is a system of membranous tubules and sacs.
2. The ER functions Primarily as an Intracellular Highway, a path along which
molecules move from one part of the cell to another.
3. The amount of ER inside a cell fluctuates, depending on the Cell's Activity.
4. Poisons, waste, and other toxic chemicals are made harmless.
5. ER is an extensive network of membranes that connect the Nuclear Envelope
to the Cell Membrane.
6. Transports materials through the cell.
7. Can be ROUGH OR SMOOTH. (Figure 4-15)
A. ROUGH ER is studded with RIBOSOMES and processes PROTEINS to be
exported from the cell.
B. SMOOTH ER IS NOT Covered with RIBOSOMES and processes LIPIDS
and CARBOHYDRATES. The Smooth ER is involved in the synthesis of steroids
in gland cells, the regulation of calcium levels in muscle cells, and the
breakdown of toxic substances by liver cells.
GOLGI APPARATUS (GOHL-jee) (Figure 4-16)
1. The Golgi Apparatus is the Processing, Packaging and Secreting Organelle of
the Cell.
2. The Golgi Apparatus is a system of membranes. Made of Flattened SAC like
Structures called CISTERNAE.
3. It works Closely with the ER, the Golgi Apparatus modifies proteins for
export by the cell.
4. Golgi apparatus is also the site of producing vesicles called Lysosomes.
(Figure 4-16)
VESICLES - membrane sacs
1. Cells contain several types of vesicles, which perform various roles.
2. Vesicles are small, spherically shaped sacs that are surrounded by a single
membrane and that are classified by their contents.
3. Vesicles often migrate to and merge with the plasma membrane to release
their contents outside of the cell.
LYSOSOMES (LIE-suh-SOHMZ)
1. Lysosomes are small spherical organelles that enclose hydrolytic (digestive)
enzymes within a single membrane.
Lysosomes are vesicles that bud (break off) from the Golgi apparatus and that
contain digestive enzymes. (Look at figure 4-16)
2. Lysosomes are the Site of Food Digestion in the Cell. They can break down
large molecules such as proteins, nucleic acids, carbohydrates, and
phospholipids.
3. In the liver, they break down glycogen to release glucose into the blood
stream.
4. Some white blood cells use lysosomes to break down bacteria.
5. Within a cell, lysosomes digest worn-out organelles in a process called
Autophagy.
6. Lysosomes are also responsible for breaking down cells when it is time for
the cells to die - Apoptosis.
7. The digestion of damaged or extra cells by the enzymes of their own
lysosomes is called Autolysis.
8. Lysosomes play a very important in maintaining an organism's health by
destroying cells no longer functioning properly.
9. Lysosomes are common in the Cells of Animals, Fungi, and Protists, But
they are Rare in Plant Cells.
PEROXISOMES
1. Peroxisomes are similar to lysosomes but contain different enzymes and are
not produced by the Golgi apparatus.
2. Peroxisomes are abundant in liver and kidney cells, where they neutralize
free radicals (oxygen ions that can damage cells) and detoxify alcohol and other
drugs.
3. They are named for the Hydrogen Peroxide, H2O2, they produce when
braking down alcohol and killing bacteria.
4. Peroxisomes also break down fatty acids, which the mitochondria can then
use as an energy source.
OTHER VESICLES
1. Other vesicles can be found in different types of cells:
A. Glyoxysomes - can be found in the seeds of plants to break down stored
fats to provide energy for the developing plant embryo.
B. Endosomes - vesicles formed from cells engulfing material by
surrounding it with its plasma membrane.
C. Food Vacuoles - are vesicles that store nutrients for the cell.
D. Contractile vacuoles - are vesicles that can contract and remove excess
water from inside a cell.
CYTOSKELETON
1. Just as your body depends on your skeleton to maintain its shape and size,
so a Cell needs structures to maintain its shape and size.
2. In Animal Cells, an internal framework called CYTOSKELETON maintains
the Shape of the Cell.
3. THE CYTOSKELETON MAINTAINS THE THREE-DIMENSIONAL STRUCTURE
OF THE CELL, PARTICIPATES IN THE MOVEMENT OF ORGANELLES WITHIN
THE CYTOSOL, AND HELPS THE CELL MOVE.
4. The Cytoskeleton is a network of long protein strands located in the Cytosol
that are NOT surrounded by a membrane.
3. The CYTOSKELETON consists of Three Types: MICROTUBULES
MICROFILAMENTS AND INTERMEDIATE FILAMENTS.
MICROTUBULES (figure 4-18)
1. Microtubules are HALLOW TUBES like plumbing pipes. They are the Largest
Strands of the Cytoskeleton.
2. Microtubules are made of a PROTEIN called TUBULIN.
3. Microtubules have THREE FUNCTIONS:
A. To maintain the shape of the cell and hold organelles in place.
B. To serve as tracks for organelles and molecules to move along within the
cell.
C. When the Cell is about to divide, two short cylinders of Microtubules at
right angles known as Centrioles can be found situated in the cytoplasm near
the nuclear envelope. Centrioles organize the microtubules of the cytoskeleton
during Cell Division in animal cells, plant cells lack centrioles. (Figure 4-20)
MICROFILAMENTS
1. MICROFILAMENTS are NOT HALLOW and have a structure that resembles
ROPE made of
TWO TWISTED CHAINS OF PROTEIN called ACTIN.
2. MICROFILAMENTS can CONTRACT, causing movement.
3. Muscle Cells have many microfilaments.
INTERMEDIATE FILAMENTS
1. Intermediate filaments are rods that anchor the nucleus and some other
organelles to their place in the cell.
2. They maintain the internal shape of the nucleus.
3. Hair-follicle (hair-root) cells produce large quantities of intermediate filament
proteins. These proteins make up most of the hair shaft - your hair!
CILIA AND FLAGELLA
1. Cilia and Flagella are Hairlike Organelles that extend from the surface of the
cell, where they assist in movement.
2. Microtubules are sometimes bundled into structures called CILIA AND
FLAGELLA.
3. CILIA ARE SHORT HAIRLIKE PROJECTIONS.
4. FLAGELLA ARE LONG WHIPLIKE PROJECTIONS.
5. The Cilia and Flagella of all Eukaryotes consist of ONE PAIR OF
MICROTUBULES SURROUNDED BY NINE MORE PAIRS.
6. CILIA ARE OFTEN NUMEROUS.
7. FLAGELLA ARE OFTEN SINGULAR.
8. Unicellular organisms such as Paramecium and Euglena use Cilia and
Flagella to move through water.
9. Sperm use flagella to swim to the egg.
10. In Humans, beating Cilia line parts of the respiratory system, moving dust
particles and bacteria away from the lungs.
SECTION 4-4, UNIQUE FEATURES OF PLANT CELLS
Plant Cells have Three Kinds of Structures that are NOT found in animal’s cells
- CELL WALLS, VACUOLES, AND PLASTIDS that are extremely important to
Plant Function.
OBJECTIVES:
1. List three structures that are present in plant cells, but are not in animal
cells.
2. Compare the plasma membrane, the primary cell wall, and the secondary
cell wall.
3. Explain the role of plastids in the life of a plant.
4. Identify features that distinguish prokaryotes, eukaryotes, plant cells, and
animal cells.
PLANT CELLS (figure 4-21)
1. Most of the Organelles and other parts of the cell are common in ALL
Eukaryotic Cells. Cell from different organisms have even greater difference in
structure. (Figure 4-21)
2. Plant Cells have Three Additional Structures Not found in animal’s cells
- CELL WALLS, VACUOLES, AND PLASTIDS that are extremely important
to Plant Function.
3. In addition to their unique structures, Plant Cells have: MITOCHONDRIA,
RIBOSOMES, AND the other organelles.
4. To understand why plant cells have different structures NOT found in
animal cells, consider how a plant's lifestyle differs from and animals.
5. Plants make their own carbon-containing molecules (food) directly from
carbon dioxide in the environment.
6. Plant cells take carbon dioxide gas from the air, and in a process called
Photosynthesis, they convert carbon dioxide, water and energy from the sun
into sugars - Autotrophs.
CELL WALL
1. One of the most important differences between Plant and Animal CELLS is
the Presence of a CELL WALL IN PLANT CELLS.
2. Fungi such as Mushrooms and Yeast also have Cell Walls. Cell Walls of
Fungi are made of CHITIN.
3. A Cell Wall DOES NOT REPLACE the Cell Membrane; Cells with WALLS also
have a CELL MEMBRANE. Plant Cells are covered by a Rigid Cell Wall that lies
Outside the Cell Membrane.
4. The Rigidity of Cell Walls Helps SUPPORT and PROTECT the Plant.
5. Cell Walls of Plants contain POLYSACCHARIDE (long chains) CELLULOSE a
complex carbohydrate.
6. CELL WALLS ARE OF TWO TYPES: (Figure 4-15)
A. PRIMARY CELL WALL - While a Plant cell is being formed, a primary cell
wall develops just outside the cell membrane. As the cell expands in length,
cellulose and other molecules are added, enlarging the cell wall. When the cell
reaches full size, a Secondary Cell Wall MAY Form.
B. SECONDARY CELL WALL - The secondary cell walls forms Between the
Primary Cell Wall and the Cell Membrane. The Secondary Cell Wall is Tough
and Woody, in fact the Secondary Cell Wall is what we call WOOD. One a
Secondary Cell Wall forms, a plant cell can Grow NO Further. The Cells are
Dead.
CENTRAL VACUOLES
1. The SECOND prominent structure in Plant Cells is the large
CENTRALVACUOLE.
2. The VACUOLE is a large membrane-bound sac that takes up a large
amount of space in most Plant Cells.
3. The VACUOLE serves as a STORAGE AREA, and may contain stored
PROTEINS, IONS, WASTE, OR, OTHER CELL PRODUCTS.
4. VACUOLES of some plants contain Poison that discourages animals from
eating the plant's leaves.
5. Cells of Animals and other organisms also MAY contain VACUOLES, but
they are much smaller and are usually involved in FOOD DIGESTION.
PLASTIDS
1. A THIRD distinguishing feature of PLANT CELLS is the presence of
STRUCTURES CALLED PLASTIDS THAT MAKE OR STORE FOOD. Plastids
are organelles like mitochondria that are surrounded by a double membrane
and contain their own DNA.
2. A common kind of PLASTID is the CHLOROPLAST, (figure 4-23) an
organelle that converts SUNLIGHT, CARBON DIOXIDE, AND WATER INTO
SUGARS. This process is called PHOTOSYNTHESIS.
3. Each Chloroplast encloses a system of Flattened, Membranous Sacs called
THYLAKOIDS. It is in the Thylakoids that Photosynthesis occurs.
4. Chloroplasts are GREEN because they contain CHLOROPHYLL, a
PIGMENT that ABSORBS ENERGY IN SUNLIGHT. THEY ARE FOUND ONLY
IN ALGAE, SUCH AS SEAWEED, AND IN GREEN PLANTS.
5. Other Plastids called Chromoplasts store reddish-orange pigments that
color fruits, vegetables, flowers, and autumn
leaves.
COMPARING CELLS (figure 4-24)
1. All cells share common features, such as a plasma membrane, cytoplasm,
ribosomes, and genetic material (DNA).
2. But there is a high level of diversity among cells, there are significant
differences between prokaryotes and eukaryotes. In addition plant cells have
features that are not found in animal cells, although both plant and animal
cells are eukaryotic cells.
PROKARYOTES VERSUS EUKARYOTES
1. Prokaryotes differ from eukaryotes in that prokaryotes Lack a Nucleus and
Lack Membrane-Bound Organelles.
2. In place of a nucleus, prokaryotes have a region called a Nucleoid in which
their genetic material is concentrated.
3. Prokaryotes lack an internal membrane system.
EUKARYOTIC PLANT CELLS VERSUS EUKARYOTIC ANIMAL CELLS
1. Three unique features distinguish plant cells from animal cells:
(1) Plant cells have cell walls.
(2) Plant cells contain a large central vacuole.
3) Plant cells contain a variety of Plastids which are not found in animal
cells.