7
Cell Organization and Functions

Jump To: Levels of Organization |Kinds of Cells |Movement across the Cell Membrane|
Active Transport | Passive Transport |Endocytosis and Exocytosis Movement

The Cell:
The smallest organized unit of a living organism.
Protoplasm:
All the living material found in a cell capable of carrying on all the life processes.
So how large is a cell?
size of cell in comparison to other things.
The Levels of Cell Organization:
Single Cell - smallest structural unit of an organism that is capable of independent function.

Example - White Blood Cell
Tissue A group of cells that all do the same work

Example - Muscle
Organ A group of tissue that works together for perform a function

Examples - Heart, Kidney, Lung
Organ System A group of organs that do a certian job.

Examples - Circulatory System, Digestion System, Lymphatic System (immune System)

Important Point:
Cells in an organism may differ in appearance and function,
but they all work together to keep the organism alive

The Two Major Kinds of Cells

Prokaryotic Cell
Cells that do not have a cell membrane around their Nucleus. Example - Bacteria

Prokaryotes are molecules surrounded by a membrane and cell wall. Prokaryotic cells lack characteristic eukaryotic subcellular membrane enclosed "organelles", but may contain membrane systems inside a cell wall.
Bacterial cell
Eukaryotic Cell
Cells that have a membrane around their nucleus. Example - Plant and Animal Cells
Eukaryotic Cells usually are 10 Times Larger than Prokaryote Cells.

    The basic eukaryotic cell contains the following:

            1. Plasma membrane
            2. Cytoplasm (the semifluid inside the membrane)
            3. Has a cytoskeleton - the microfilaments and microtubules that suspend organelles, this gives it shape, and allow for motion.
            4. Has membrane enclosed subcellular organelles.
Animal cell Jump to Top of Page
GETTING AROUND - Movement across the Cell Membrane
Materials move into and out of the cell by either using the process of passive transport or active transport.

http://www.usd.edu/~bgoodman/Membrane.htm
  1. The cell membrane is made up of three parts
        • phospholipids
        • proteins
        • carbohydrates
  2. The cell membrane acts like a fence with gates through which only certain things can enter.
        • This regulates the molecules by making sure that only the molecules that the cell needs can enter through the phospholipid bilayer into the cells.
          • This system helps to gets rid of the harmful products that cannot be used and allow the healthy products into the cell that it needs to use.
        • This gate keeping activity by the cell membrane is called selective permeability.
  3. The cell membrane acts as a fence that isolates the inside of the cell from its external enviroment.
  4. The cell membrane is really thin. Approximately 11,000 membranes stacked on each other equals the thickness of one piece of paper.
TYPES OF MOVEMENT ACROSS THE CELL MEMBRANE
Passive Transport
  1. Passive transport is the movement of molecules across the cell membrane and does not require energy.
  2. It is dependent on the permeability of the cell membrane.
  3. There are three main kinds of passive transport - Diffusion, Osmosis and Facilitated Diffusion.
Diffusion The movement of molecules from a region of higher concentration to a region of lower concentration.
Facilitated diffusion

This process does not require ATP but does require cell membrane proteins which are called carrier proteins to carry the molecules across the cell membrane from an area of higher concentration to an area of lower concentration.

Osmosis The movement of water across a semi permeable membrane.

Osmosis is the movement of water (red dots) through a semipermeable membrane to a higher concentration of solutes (blue dots).

How Do Hypotonic, Hypertonic, and Isotonic Solutions
Affect the Water Movement of a Cell?
Cell membranes are permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.
Hypertonic
Solution
A Hypertonic solution contain a high concentration of solute in relation to the solution within the cell (e.g. the cell's cytoplasm).

When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel up.

Hypotonic
Solution
A hypotonic solution contain A solution with a lower salt concentration than in normal cells

When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic
Solution
A solution that has the same salt concentration as the normal cells of the body and the blood.

When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.
Active Transport
  1. Active Transport requires the cell to use energy, usually in the form of ATP.
  2. Active Transport creates a charge gradient in the cell membrane. For example in the mitochondrion, hydrogen ion pumps pump hydrogen ions into the intermembrane space of the organelle as part of making ATP. 
Active Transport keeps unwanted ions or other molecules out of the cell that are able to diffuse through the cell membrane. 
Active transport uses energy to send substances against the direction they would travel by simple diffusion: that is from a region of low concentration to a region of high concentration.
Moving other Materials and Substances into and out of the cell
ENDOCYTOSIS and EXOCYTOSIS
ENDOCYTOSIS
Endocytosis (Endo (within) cytosis (cell) ) is a process in which a substance (e.g. proteins) gains entry into a cell without passing through the cell membrane.
EXOCYTOSIS

Endocytosis (Exo (exit) cytosis (cell) ) is a process in which a substance is exited from the cell without passing through the cell membrane.

Examples of thigs that migh be exited include secretion of proteins like enzymes, hormones and antibodies.

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