IB Biology 2.1 Cell Theory
|Cell Theory|| - all organelles are made up of one or more cells|
- all cells come from existing cells
- cells are the smallest units of life
|Evidence for cell theory|| - use of a microscope |
- no living entity has been discovered that is not made up of at least one cell
- anything smaller than a cell can not live on its own
- Scientific experiments such as :
* Louis Pasteur in the 1860's (Chicken broth experiment)
|Unicellular organisms|| - Organisms with only one cell |
- carry out functions of life within that one cell
|Multicellular organisms|| - Organisms with more than one cell |
- Have developed separate systems to carry out these processes
|Basic functions of life (6)|| Metabolism |
Phrase to help you remember:
Molly Gets Really Really Hungry @ Noon
|Why are cells small|| A cell that becomes to large may not be able to take in essential materials or excrete waste substances quickly enough.|
Cells that generate heat my not be able to lose it quickly enough if they grow very large.
|Size: Plant/ Animal Cells||10-100 um|
|Size: Organelles||up to 10 μm|
|Size : Bacteria Cells||1-10 μm|
|Size: Virus Cells||100 nm|
|Size: Membrane thickness||10 nm|
|Size: Molecules||1 nm|
|Formula for Magnification||M = size of image/size of specimen|
|Define : Emergent Properties||Multicellular Organisms show emergent properties |
Eg. cells form tissues, tissues form organs, organs form organ systems and organ systems form multicellular organisms. Eg. The lungs - many cells work as a unit to allow the lungs to perform their function.
The idea is that the whole is greater than the composition of its parts.
|Explain : Cell reproduction and differentiation|| - start out with a single cell|
- reproduce rapidly
- resulting cells go through differentiation : to produce the different cell types that are necessary for the well being of the organism.
- differentiation : result of the expression of certain genes but not others .
|Role of DNA in differentiation||- DNA allows for the production of all different cells in the organism|
Every cell in a multicellular organisms contains all the genes of that organism. However, the genes that are activated vary from cell to cell. Each cell becomes a specific type of cell depending on which segment of DNA becomes active.
Eg. the gene that produces keratin will be active in hair and nail cells. Keratin is the protein which makes up hair and nails. Genes encode for proteins and the proteins affect the cell's structure and function so that the cell can specialize.
|Advantages of Differentiation||It is an advantage for multicellular organisms as cells can differentiate to be more efficient unlike unicellular organisms who have to carry out all of the functions within that one cell.|
|Stem cells|| cells within an organism that retain their ability to divide and differentiate into various cell types. |
eg. Cells in the meristem of plants
Stem cells can not be distinguished by appearance. They an only be isolated on the basis of behaviour.
|Therapeutic uses of stem cells||Replacement of lost differentiated cells due to injury and disease|
- Bone marrow stem cells for cancer : produce red blood cells, white blood cells and platelets in the body. These stem cells can be used in bone marrow transplants to treat people who have certain types of cancer.
-Parkinson's and Alzheimer's disease : caused by loss of brain cells. It is hoped that implanted cells could replace these.