​Cell Theory-
  • All organisms are composed of one or more cells.
  • Cells are the smallest unit of life.
  • All cells come from pre-existing cells.

Evidence for Cell Theory-
  • Matthias S. - stated different parts of plants are composed of cells.
  • Leeuwenhoek- observed single cellular organisms.
  • Teddy Schwann- stated that animals are also made up of cells.
  • Louis Pasteur- spontaneous generation idea and stated living things come from living things.

Unicellular organisms carry out all the functions of life, metabolism, response, homeostasis, growing, reproduction, and nutrition.
Ex. An amoeba

Compared relative sizes of molecules, cell membrane thickness, viruses, bacteria, orgenells, and cells, in the appropriate SI unit:

Molecules: 1nm
Thickness of Membrane: 10nm
Viruses: 100nm
Bacteria: 1um
Organelles: up to 10um
Most Cells: up to 100um

Drawings should show cells and cell ultrastructure.
A scale bar: |------| = 1 µmMagnification: ×250
To calculate magnification:
Magnification = Measured Size of Diagram ÷ Actual Size of Object

Importance of the surface area to volume ratio as a factor limiting cell size:
Each internal region of the cell has to be served by part of the cell surface. As a cell grows bigger, its internal volume enlarges and the cell membrane expands. Unfortunately, the volume increases more rapidly than does the surface area, and so the relative amount of surface area available to pass materials to a unit volume of the cell steadily decreases. The surface area to the volume ratio gets smaller as the cell gets larger Finally, at some point, there is just enough surface available to service all the interior; if it is to survive, the cell must stop growing. If the cell grows beyond a certain limit, not enough material will be able to cross the membrane fast enough to accommodate the increased cellular volume. When this happens, the cell must divide into smaller cells with favorable surface area/volume ratios, or cease to function. That is why cells are so small.
Surface Area to Volume Ratio

Multicellular organisms show emergent properties, new properties that emerge with each step up in the heirarchy of life, owing to the arrangement and interactions of parts as complexity increases.This
means that the organism can achieve more than the sum of what each cell could achieve individually. This is caused by the fact that cells interact, allowing them to perform tasks together that they not achieve, even in part, if they were alone.

Cells in multicullur organism differentiatie to carry out specialized functions be expressing some of their genes but not others.While every cell contains all the genetic informationto carry out every function, only a small portion of the genetic material is activated. A cell in your toes has the information on how to make the pigment which colours your eyes, but will not use it. So cells differentiate by expression of some of their genes and not others. The genes which are not expressed by the cell, remain present in the nucleus but are packed away so tightly that they cannot be accessed.

Diagram of E.coli, an example of prokaryote:

external image 20080715_6689082fbba7b462122dK8PPOmyCFvM4.jpg

Cell Membrane- Regulates what substances enter and leave the prokaryotic cell.
Cell Wall-Gives rigidity and structure to the cell. It also protects from physical abuse and prevents the cell from bursting in a hypotonic environment.
Pili- Hairlike prokaryotic appendage that is used to adhere to other cells or transfer DNA during conjugation. During conjugation or "bacterial sex", the pili are used to grasp a mate cell and pull them in. Then, a cytoplasmic bridge is formed to transfer DNA.
Flagella- Locomotion appendages that are located at a concentrated point (as shown above) or scattered around the cell. They can propell the cell up to 50 times its body length per second.
Nucleoid- Location of the prokaryotic chromosone. Unlike eukaryotic cells, the nucleoid is not bound by a membrane.
Cytosol- The cytoplasm suspends the contents of the cell. Especially important in prokaryotic cells because they do not have membrane bound organelles.
Ribosomes- Organelle that floats freely in the cytoplasm of a prokaryotic cell. Facilitates the orderly linking of amino acids into polypeptide chains. In other words, they synthesize proteins.

external image msb4100050-f7.jpg

The capsule is the outermost line surrounding the cell, the cell wall is the next one, then the plasma membrane. Flagella are the long stands and pili should be all over the capsule. The nucleoid is the white areas and the dark colored area is where the protein synthesizing ribosomes are.

Here is a labeled diagram of a liver cell, which can be used as an example for animal cells.


Prokaryotic Cells
  • Unicellular
  • Consists of bacteria and bacteria like organisms
  • No membrane bound nucleus
  • Reproduce using binary fission
  • No membrane bound organelles

Eukaryotic Cells

  • Normally has lots of cells surrounding it
  • Consists of all plant and animal cells
  • Contain a nucleus
  • Reproduce using meiosis or mitosis
  • Lots of membrane bound organelles

Plant Cells

  • Contain chloroplasts which are used to give the green color to the plant and contain chlorophyll
  • Contains a cell wall
  • Carry out photosynthesis to get the energy they need

Animal Cells

  • Get the required energy from the nutrients digested in their surroundings
  • Contain more and smaller vacuoles than plant cells
  • Cannot contain as much water as plant cells

One role of an extracellular component, like the plant cell wall is to give the cell its shape.Another role is to protect the cell from foreign substances through the use of a semi-permeable membrane. Only certain substances are allowed to pass through the membrane which will keep the cell safe.

The cell is enclosed by a semi-permeable membrane. The membrane consists of a lipid bi-layer. Other components of the membrane are other lipids (e.g. cholesterol, glycolipids) and proteins.

external image Cell_membrane.png

How Facilitated Diffusion Works:

Passive Transport: