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Chapter 3:Cells

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• In 1665, An English Scientist Robert Hooke used a 3 lens microscope to examine thin slices of cork.

• Hooke noticed the cork was made of many tiny compartments.

• These compartments reminded Hooke of the small rooms at his monastery.

• These rooms were called cells - so he termed these small openings cells.

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•Soon after, a man named Anton Van Leeuwenhoek, came up with a very powerful single-lens microscope. •Leeuwenhoek became one of the first people to describe living cells when he observed microscopic organisms swimming in pond water. •Microscopes got better and better over the next century which led to more scientist studying cells.

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•German scientist Matthias Schleiden- studied plant tissue and concluded that plants are made of cells.

•German scientist Theodor Schwann- studied animal tissue and concluded that animals are mad of cells.

•German scientist Rudolph Virchow- concluded that all cells come from pre-existing cells.

•All of these findings led to one unified concept called the Cell Theory

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THE CELL THEORY STATES:1. All organisms are made of cells.2. Cells are the basic unit of life.3. Cells come form pre-existing cells.

•The variety of cell types is enormous. Cells come in many different shapes, sizes, and functions.

•While there are many differences, all cells share some basic common characteristic:• All cells have a cell membrane and cytoplasm.• Cell membrane= outer boundary• Cytoplasm= jellylike substance inside membrane

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There are 2 general types of cells:1. Prokaryotic Cells2. Eukaryotic Cells

Prokaryotic Cells-•Do not contain a nucleus or other membrane bound organelles.•The cell’s DNA floats in the cytoplasm.•Most prokaryotes are microscopic single-celled organisms.

Bacteria are an example of prokaryotic cells.

E. coli

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•Eukaryotic Cells:• Have a nucleus and other membrane bound

organelles.• The nucleus is the largest of the organelles and is

the control center of the cell.• It contains the genetic information for the

cell.• Eukaryotes may be multicellular or single-celled

organisms.

Plant and animals are eukaryotic organisms

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•Eukaryotic Cells:• Eukaryotic cells are highly organized.

They contain many membrane bound organelles that help the cell carry out day to day functions.

• Most organelles are held in place by a cytoskeleton, which is a network of proteins that maintains the cell shape and strength.

• The Cytoplasm also plays a key role in cell structure.

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Cell Organelles:

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The Nucleus:

• Stores most all of the cells genetic information.

• It is known as the control center of the cell.

• The nucleus must:– Protect DNA – Make DNA available for

duplication

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The Nucleus:• Molecules must be able to enter and leave the

nucleus, so the nuclear membrane has pores in it to allow certain molecules in and out.

• Inside the nucleus you will find:– Nucleolus-this is a region where tiny organelles

responsible for making proteins are produced. – These specialized protein making organelles are

called ribosomes.

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Endoplasmic Reticulum:• This organelle usually takes up a lot of the

space of the cytoplasm.• The “E.R.” is an interconnected network of

thin folded membrane. • They makeup of the E.R. is similar to that of

the cell membrane.• The E.R. itself is usually larger than the cell

itself, but it has so many folds that it fits easily.

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Endoplasmic Reticulum:• The E.R.’s major function is the

production of proteins and lipids.

• There are two types of E.R.– Rough E.R.- has ribosomes

attached to surface– Smooth E.R.- has no ribosomes

attached to surface• Both rough and smooth E.R.

perform the same functions; however, rough E.R. does have more of a protein synthesis function.

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Ribosomes:• Small vesicles that are responsible for making

proteins.• Ribosomes take amino acids and chain them

together to make many different proteins.• Ribosomes themselves are made of proteins and

RNA.• Ribosomes are made at the nucleolus and are then

sent to the cytoplasm.• They are either free-floating or attached to the

endoplasmic reticulum.

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Golgi Apparatus:• This is an organelle

that is made up of a stack of closely layered membranes.

• The Golgi’s function is to process, sort, and deliver proteins.

• The membranes contain enzymes that further modify protein.

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Vesicles:• There are many different types of vesicles.

These are structures that take materials from the rest of the cytoplasm and transport them from place to place within the cell.

• Vesicles are short-lived organelles and are replaced by the cell on a consistent basis.

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Mitochondria:• Are known as the power house of the

cell.• These are two-membrane structures.– The inner membrane has many folds that

increase its surface area.• This increased surface area allows for more

area to create energy

• Mitochondria has its own DNA and ribosomes which would suggest they were once independent living organisms.

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Vacuoles:

• These are fluid-filled sacks used for storage of materials needed by the cell.

• These materials may include water, food molecules, ions, and enzymes.

• Vacuoles are different in plant and animal cells!

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Vacuoles:• In animal cells there are many vacuoles that

are smaller in size.• All do the storage function!

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Vacuoles:• In plant cells, there is usually only one vacuole

that is centrally located and takes up most of the space of the cell.

• It still performs the storage function, but it also has a structure function!

• When the vacuole is full, it exerts pressure against the cell membrane and gives the plant structure.

• When the vacuole loses water during a drought, plants wilt.

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Plant Cell Vacuoles

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Lysosomes:• These are membrane bound organelles that

contain enzymes.• They are known as the “clean-up crews” of the

cell.• Lysosomes break down damaged or worn out

cell parts.• They also protect the cell from invading bacteria

and viruses.

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Lysosomes:• Lysosomes are numerous in animal cells, but

are questioned in plant cells.• Most scientists believe that plant cells do not

contain Lysosomes, but others believe they do.

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Centrosome and Centrioles:• The centrosome is an area that

contains centrioles. • Centrioles only occur in animal

cells!• These cylinder shaped organelles

are made of microtubule filaments.• Centrioles organize the filaments in

the cytoskeleton before the cell divides.

• Centrioles are not found in plants, so scientists believe they are not essential to cell division.

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Cell Wall:• ONLY FOUND IN PLANT CELLS AND SOME

ALGAE AND FUNGI.• The cell wall is a rigid layer that gives

protection, support, and shape to the cell.• The cell wall is outside the cell membrane.

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Chloroplasts:• Are organelles that carry out

photosynthesis for plants and some algae.

• Photosynthesis creates energy for the cell by taking sunlight and turning it into chemical energy.

• Like mitochondria, chloroplasts have their own DNA and ribosomes. – Both chloroplasts and mitochondria

are found in plant cells and both are used to create energy.

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Cell Membrane:• Cell membranes are composed of 2

phospholipid layers. • It forms the boundary between the cell and

the outside environment .• The cell membrane is made of the phosphorus

and lipids.• The phosphate part is polar!

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Cell Membrane:• The lipid interior of the cell membrane is non-

polar. – So, the outside layers of a membrane are polar and

the inside are non-polar.– This system allows certain things to enter and leave

the cell.• The cell membrane is made up of many different

other structures. – Lipids, carbohydrates, and proteins also make up the

membrane.

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Cell Membrane:• Because the membrane is made up of so many

different things it is said to be a “Fluid Mosaic Model”.– This means the membrane is not rigid, but rather

flexible. Also mosaic means made of many different things.

• It is also said the membrane is “selectively permeable” – What does that mean?

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Cell Membrane:• Cell membranes are called “selectively

permeable” because they only allow certain materials in and out of the cell.

• The cell must be able to maintain homeostasis (or a constant internal body environment).– In order to do this, the cell must control what

enters and leaves the cell.• How do molecules enter and exit the cell?

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Cell Membrane:• To get in and out of the cell molecules can do

one of two things:– Pass through pores– Use helpful proteins within the cell membrane.

• Size and polarity are the 2 main factors that determine what enters and leaves the cell.

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Osmosis and Diffusion:

• Cells are constantly importing and exporting substances in and out of the cell.

• Some of these functions require energy while others do not

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Osmosis and Diffusion:

• Passive Transport-– Is the movement of molecules across a membrane

with NO ENERGY required from the cell– These processes are:• Diffusion• Osmosis• Facilitated Diffusion

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Osmosis and Diffusion:

• Active Transport-– REQUIRES ENERGY expenditure from the cell.– These processes are:• Endocytosis• Exocytosis

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Passive Transport:• Passive transport requires no energy because

material are moving down a concentration gradient, from an area of high concentration to an area of low concentration (like going down a hill).

High Concentration

Low Concentration

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Passive Transport:

• Diffusion-– Movement of materials from an area of high

concentration to an area of low concentration down a concentration gradient.

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Passive Transport:

• Osmosis-– Movement of water from an area of high

concentration to an area of low concentration. – Osmosis and diffusion move in opposite directions– If the concentration of “other” materials is high,

than the water concentration is low and vice versa.• This creates 3 types of solutions

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Passive Transport:

• Isotonic Solution- concentrations are equal on both sides of a cell membrane. Water will move, but at an equal rate into and out of the cell – The cell remains the same

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Passive Transport:

• Hypertonic Solution- water concentration is higher in the cell…..water will move out of a cell.– The cell shrinks

• Hypotonic Solution- water concentration is higher outside the cell…..water will move into the cell– The cell will burst

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Passive Transport:

• Facilitated Diffusion- – Some molecules can

pass with no energy needed, but need a little direction.

– In facilitated diffusion, transport proteins “direct” certain substances across the cell membrane.

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Active Transport:• Sometimes the cell needs materials it already

has a lot of. So in order to get more of what it needs, it must “spend” energy to move materials against the gradient (up the hill).

• This is called active transport. Active transport uses energy and transports proteins to get materials in the cell

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Active Transport:• There are 2 general types of active transport:– Endocytosis-• Taking materials into the cell by manipulating the cell

membrane. • Particles enter without actually ever crossing the cell

membrane.

– Exocytosis-• The exact opposite of endocytosis.• Particles exit the cell without actually ever crossing the

cell membrane.

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Endocytosis

Exocytosis