|
Cell Theory
All organisms contain one or more cells which are
capable of carrying on the life activities needed by the
organism. This idea is often referred to as
the cell theory.
|
Parts of the Cell
Theory |
- The cell is the unit of structure in all living
things.
- The cell is the unit of function in all living
things.
- All cells come from preexisting cells.
|
A few exceptions to this theory exist. Viruses
lack typical cellular structure. There also is some
question as to how the the first cell arose. In
general, the cell theory holds true for most living things,
however.
Cell Organelles
Cells have particular structures that perform specific jobs.
These cell structures are called organelles and perform
the actual work of the cell. These
organelles are formed from many different molecules.
Some functions carried out by organelles include the transport
of materials, energy capture and release, protein building,
waste disposal, and information storage. Single
celled organisms also have organelles similar to those in more
advanced organisms to complete their life
processes. Many enzymes are needed for the
chemical reactions involved in cellular life processes to
occur.
|
A Typical Animal
Cell |
 |
|
Some Cell
Organelles |
|
Cell Organelle |
Function |
| nucleus |
control center of the cell
contains DNA which directs the synthesis of proteins by
the cell |
| mitochondrion |
carries on the process of cell respiration
converting glucose to ATP energy the cell can use |
| endoplasmic reticulum |
transport channels within the cell |
| ribosome |
found on the endoplasmic reticulum and free
within the cell
responsible for the synthesis of proteins for the cell |
| cell membrane |
selectively regulates the materials moving
to and from the cell |
| food vacuole |
stores and digests food |
| contractile vacuole |
pumps out wastes and excess water from the
cell |
| chloroplast |
found in plant cells and algae
carries on the process of photosynthesis |
| cell wall |
surrounds and supports plant cells |
Cell Membrane
The
cell membrane or plasma membrane performs
a number of important functions for the cell. These functions
include the separation of the cell from its outside
environment, controlling which molecules enter and leave the
cell, and recognition of chemical signals. The cell
membrane consists of two layers of phospholipids with proteins
embedded within these layers. The surface of the
cell contains molecules which recognize other molecules which
may attach to or enter the cell.
|
Cell Membrane
Structure |
 |
Membrane Processes
The processes of
diffusion and active transport are important in the movement
of materials in and out of cells.
|
Diffusion |
| Diffusion
or passive transport is the movement of materials
from a region of higher to a region of lower substance
concentration. The diagram at the right shows
the movement of molecules from higher concentration on
side A to a lower concentration on side B. |
 |
|
Active Transport |
| In active transport, molecules move from a
region of lower concentration to a region of higher
concentration. As this process does not
naturally occur, the cell has to use energy in the form of
ATP to make active transport occur. |
 |
Cell Chemistry
Many
organic and inorganic substances dissolved in cells allow
necessary chemical reactions to take place in order to
maintain life. Large organic food molecules such as proteins
and starches must initially be broken down through the life
process of digestion in order to enter cells.
|
Organic Molecules
and Digestive End Products |
|
Organic Molecule |
Digestive End Product(s) |
|
carbohydrates |
simple sugars (glucose) |
| proteins |
amino acids |
| lipids (fats) |
fatty acids and glycerol |
|
