Biology Standard Level Chapter 2- Cells

• All organisms are composed of one or more cells. 

• Cells are the smallest unit of life. 

• All cells come from pre-existing cells.

• All organisms are composed of one or more cells- This theory has gained tremendous creditability through the use of the microscope. 

• Cells are the smallest units of life- We have not been able to find any living living entity that is not made of at least one cell.

• All cells come from pre-existing cells- Some very famous scientists, such as Louis Pasteur in the 1860´, have performed experiments to support this principles. After sterilizing chicken broth by boiling. Pasteur showed that living organisms would not spontanously reappear. Only after exposure to pre-existing cells was life able to re-establish itself in the sterilized chicken broth.

Unicellular organisms carry out all the functions of life.

• Metabolism- includes all the chemical reactions that occur within a living organism.
• Growth- May be limited but always evident in one way or another.
• Reproduction- involves hereditary molecules that can be passed down to offspring.
• Response- To the environment is imperative to the survival of the organism.
• Homeostasis- refers to maintaining a constant internal environment.
• Nutrotion- is all about providing a source of compounds with many chemical bonds which can be broken to provide the organism with the energy and the nutritients neccessary to maintain life.

Cells - 100 micrometers

Organelles - 10 micrometers

Bacteria - 1 micrometer

Viruses- 100 nanometers

Membrane thickness- 10 nanometers

Molecules- 1 nanometer

Magnification = Size of image / size of specmien

A cell needs a large surface area in order to carry out metabolic functions (as chemical reactions require a surface). As a cell grows, it needs to carry out more and more reactions. Therefore, since a cell has to maintain a certain surface area to volume ratio, its size is limited.

Emergent properties arise from the interaction of component parts; the whole is greater than the sum of its parts.

During the early development stages of multicellular organisms, cells undergo differentiation, becoming specialized in structure and function. These cells are then organized into tissues and organs. Cells of multicellular eukaryotes express only a small fraction of their genes, allowing them to perform highly specialized functions. Cells, such as those of muscle or nervous tissue, express only a tiny fraction of their genes.

Stem cells retains the capacity to devides and have ability to differentiate along different pathways.

Some of the most promessing research recently has been directed towards growing large numbers of embryonic stem cells in culture so that they could be used to replace differentiated cells lost to injury or disease. This involves theraoeutic cloning. Parkinson´s disease and Alzheimer´s disease are caused by by loss of brain cells, and it is hoped that implanted stem cells could replace many of these lost brain cells thus relieving this disease sympthomes.

Prokaryotic cells divide by a very simple process called binary fission. During this process, the DNA is copied, the two daughter chromosomes becomes atteched to different regions on the plamsa membrane, and the cell divides into two genitically identical daughter cells.

Prokaryotic Cells                                                      Eukaryotic Cells

DNA in a ring form without proteins.         DNA with proteins as chromosomes.    

DNA free in the cytoplasm.                       DNA enclosed with a nuclar envelope.

No Mitrochondria.                                     Mitrochondria present.                        

70S ribosomes.                                        80S rimosomes.                                   

No internal compartmentalization to         Internal compartmentalization to form     

form organelles.                                      many types of organelles.                    

Size less than 10 micrometers.               Size more than 10 micrometers.                 

Plant Cells 

• Chloroplasts are present in the cytoplasm.
• Store carbohydrates as starch.
• Possess large centrally located vacuoles.                                                                                                                   

Animal Cells 

• There are no chloroplasts.
• Stores carbohydrates as glycogen.
• Vacuoles are usually not present or very small.

• The cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity. 

• Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhension and movement.

Hydrophilic molecules are attracted to water. Hydrophobic molecules are not attracted to water, but are attracted to each other. The phosphate head is hydrophilic and the two hydrocarbon tails are hydrophobic. In water, phospholipids form double layers with the hydrophilic heads in contact with water on both sides and the hydrophobic tails away from the centre. The attraction between the heads and the surrounding water makes membranes very stable.

• hormone binding sites

• enzymes
• electron carriers
• Channels for passive transport
• Pumps for active transport
• cell to cell recognition
• receptors for neurotransmitters

Diffusion- is the passive movement of particles from a region of high concentration to a region of low concentration.

Osmosis- is the passive movement of water molecules, across a partially permable membrane, from a region of lower solute concentration to a region of higher solute concentration.

Simple diffusion- substances other than water move between phospholipid molecules or through proteins which possess channels.

Facliltated diffusion- Non-channel protein carriers change shape to allow movement of substances other than water.

The soduim potassium pump on page 35-37

• Protein produced by the ribosomes of the rough ER enters the lumen of the ER.
• Protein exits the ER and enters the cis side of face of the golgi apparatus; a vesicle involved.
• As the proteins moves  through the golgi apparatus, it is modified and exits on the trans pace inside the vesicle.
• The vesicle with the modified protein inside moves to and fuses with the plasma membrane- this results in the secretion of the contents from the cell.

Endocytosis- allows macromolecules to enter the cell.

Exocytosis- allows macromolecules to leave the cell.

Tumors (cancers) are the result of uncontrolled cell division and can occur in any organ or tissue.

Interphase in an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.

Growth, embryonic development, tissue repair and asexual reproduction involve mitosis.