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Chapters 8 and 9

Cell Structure and Homeostasis and the Plasma Membrane

Cell Theory

Today's Cell Theory

  1. All organisms are made of cell(s).
  2. The cell is the basic unit of organization and function in a living thing.
  3. Cells come from other cells.
  4. There is no "general" cell. No cell can do everything and live everywhere.

Review Questions

  1. How could one test the cell theory?
  2. Assuming that viruses are alive, what could happen to the cell theory?

Microscopes (X-Ref: Biologist's tools in Earlier Notes)

Anton van Leeuwenhoek (c. 1600) made the first simple microscope. Later, scientists made compound microscopes with more lenses in them.

A microscope is an instrument that magnifies and resolves further detail.

RESOLUTION POWER is the ability to show detail of the object. This depends on the wavelength of the magnification medium.

Light Microscope

The light microscope can go up to 1500x. The practical maximum is set at about 1200x. This is the only microscope that can view live specimens.

Parts of the Light Microscope

Electron Microscopes

Review Questions

Can microscopes effectively determine the molecular structure of a organism?

If a medium existed to view subatomic particles, how would the specimen have to be handled?

Cell Types


This type of cell allows junk to freely float about. These are mainly bacteria. This form is ancient and is about 3.8 billion years old. This is characterized by simple structure, no nuclear membrance, few organelles, and small size (5 or five microns or 5 thousandths of a millimeter).


This type of cell has discrete parts that are membranized. These components are called ORGANELLES. The biggest of these is the brains of the cell, the NUCLEUS. This cell is more modern. The largest of these is an ostrich egg. These have more organelles and a nuclear membrane. The "eu" means true.

Essential Part

Cell Membrane

This regulates what goes in and out of the cell.

Nuclear Region

This is the region with the DNA and is the control center of the cell.

Metabolic Structures

These things are also known as organelles, little organs. They rebuild parts of the cell and make energy.

Review Questions

Why do you think that prokaryotes have a nuclear region?

What is a disadvantage of the Eukaryote structure?

Eukaryotic Cell Structure

Plasma Membrane (Cell membrane)

This is flexible and allows nutrients and waste to pass through. Some other cells supplement this with a CELL WALL. Only plant cells normally have a cell wall. A cell wall is usually made up of CELLULOSE in plants and in fungi and other animals, CHITIN.

Nuclear Envelope

This contains DNA in strands called CHROMATIN. The NUCLEOLUS, in the nucleus, produces RIBOSOMES. Ribosomes are not bounded by a membrane. This is the membrane for the NUCLEUS.


Ribosomes synthesize proteins. Ribosomes are not bounded by a membrane.


This transports and stores stuff for the cell. This contains the ER.


This is a long series of folded things called the ENDOPLASMIC RETICULUM or ER for short. The ER serves as a container for chemical reactions and the synthesis of lipids. To do this, the ER is, in some parts, bordered with ribosomes. This ER is called rough ER while the non-ribosomified ER is called smooth ER.

Golgi Apparatus

This is much like the ER, but it just stores proteins that come from the ER. This puts the final packaging on the proteins and ships them to their destination.


This is a sac that stores stuff, both food and waste. A plant has a single large water vacuole with smaller food and waste vacuoles.


These are the killer organelles that hunt and destroy the weak and sick. They are like vacuoles, but they contain digestive stuff. An amoeba uses these to digest its prey.


This releases energy by digesting food molecules. It is internally folded to increase surface reaction area.


These transform light into chemical energy like sugar and starch. They use a molecule called CHLOROPHYLL. They are catagorized as PLASTIDS. Some plastids contain food and others color. These are only in plants and protistas.


This provides structure and shape to the cell and organelles. It is composed of MICROTUBULES and MICROFILAMENTS. Microtubules are hollow protein cylinders while microfilaments are solid protein fibers.

Cilia and Flagella

Cilia are tiny hairs that cover the cell and beat like waves to move. Flagella whip around to move. Cells usually have only one or two flagella.

Review Questions

Organization of Cells


The organism has one cell to do everything.


These cells cooperate and split up work to do things. Each group of worker cells is called a TISSUE. There are additional cell to help the cells communicate by passing certain molecules between them. An ORGAN is two or more tissues that work together. A group of organs that work together form an ORGAN SYSTEM.

Review Questions

Plasma Membrane


The cell must keep certain stuff in certain concentrations. The cell a.k.a. plasma membrane must allow nutrients in and wastes out. Allowing certain things through and certain things out is called SELECTIVE PERMEABILITY.


The membrane is two sheets of lipids with proteins in it.

The lipids are PHOSPHOLIPIDS. They have a triglycerol and two fatty acids and a phosphate group which is water soluble. This makes the phosphates point out with the fatty acids in between the two layers. These layers are free to move. The FLUID MOSAIC MODEL means that the fluidic membrane has stuff stuck in it. Nuclei, vacuoles, mitochondria, and chloroplasts all have this type of membrane. Only the proteins change to let in different substances.

Fatty Acids

The unsaturated fatty acid bends at a double bond. It also hardens at a lower temperature. Some cells add cholesterol to make the membrane rigid.


Some proteins go all the way through the bilayer and others only part way. Some proteins are markers for immune systems while others allow certain particles past the membrane. The ones that go through the whole thing are transport proteins while the others are identification points.

Review Questions

Why do the lipids stay together?

What is the name for the plasma membrane's structural metaphor?


The net movement of particles from an area of higher concentration to and area of lower concentration.

This happens by the random motion of the particles. The random motion eventually evenly mixes the stuff.

The result of diffusion reaches a DYNAMIC EQUILIBRIUM which means that the movement is in balences. For example, a cell will maintain dynamic equilibrium by taking in as much as it puts out. The amount remains the same.

A CONCENTRATION GRADIENT is required for diffusion so that the substance must move from one place of high concentration to the area of low concentration until the concentrations are equal and make a dynamic equilibrium.

Brownian Motion

Discovered in 1827 by Robert Brown, this type of motion was frist observed in random pollen and pigment particle motion.

Selective Membranes

These membranes allow certain molecules to pass through and others to stay out. The bilipid layer keeps out polar molecules by the internal fatty acids. Only water, carbon, oxygen and carbon dioxide can directly diffuse through the plasma membrane.


The diffusion of water is called osmosis. Specifically, the diffusion of water across a selectively permeable membrane. (X-Ref Text Page 226)

The water diffuses just like other fluid based substances.

An ISOTONIC SOLUTION means that the concentration of dissolved substances is equal to the concentration of junk in the cells. No osmosis occurs. (0.1% saline)

HYPOTONIC SOLUTIONS are characterized by a lack of dissolved substances outside, read outside, the cell. The cells, unless they have CONTRACTILE VACUOLES, present in protistas, blow up, yes blow up. This is the coolest part of biology. In the part of blowing up, the cell increases internal pressure. This is called TURGOR PRESSURE. This mainly refers to plants which, because of their cell wall, do not blow up but become hard.

On the other hand, included specifically because it is very confusing, a HYPERTONIC SOLUTION has tons of dissolved junk outside the cell versus inside. The cells lose water and shrivel up. The lose in turgor pressure is called PLASMOLYSIS.

Review Questions

Diffusion can occur in a _______. (Matter state)

Diffusion is only possible in a _______. In other words the thing being diffused must be in what matter state or be able to transform into this mixture state.

Cellular Transport

There are two types. Active requires energy. Passive requires no energy.

Passive Transport

Passive Transport is when the cell expends no energy to move something in or out.

TRANSPORT PROTIENS allow substances to move through the plasma membrane

When transport protiens are used, this is called FACILITATED DIFFUSION.

Active Transport

Active transport requires energy to move the particles back and forth. This is accomplished by reshaping the protein to capture the cell and bring it in and release it. Larger particles are taken in using a process of ENDOCYTOSIS. This is where the cell membrane encapsulates the protien, forming a vacuole. The opposite of this is EXOCYTOSIS.

For example, the sodium potassium pump sends out Na and takes in K. This is a nervous system active transport.

PHAGOCYTOSIS is when the cell gobbles and engulfs something. This a type of endocytosis.

Review Questions

A typical carnivorous protista eats by ____.

Diffusion or passive transport without transport proteins can occur with ____.