2.1 - CELL THEORY

2.1.1 Outline the cell theory

The 3 main principles of the cell theory:

-          All organisms are composed of one or more cells

-          Cells are the smallest units of life

-          All cells come from pre-existing cells

2.1.2 Discuss the evidence for the cell theory

-          Robert Hooke (1665) described cells whilst observing cork with a microscope he built himself.

-          A few years later Antone van Leeuwenhoek observed the first living cells & referred to them as ‘animalcules’.

-          In 1838, botanist Mathias Schleiden stated that plants are made up of ‘independent, separate beings’ called cells.

-          In 1839, zoologist Theodor Schwann made a similar statement about animals.

-          To date, there has been no organism found without at least one cell.

-          Louis Pasteur in 1860s performed experiments supporting the 3^rd principle. He sterilized chicken broth via boiling; showed that living organisms would not ‘spontaneously’ reappear.

2.1.3 State that unicellular organisms carry out all the functions of life

Unicellular organisms carry out all the functions of life

Functions of Life:

Metabolism: includes all chemical reactions that occur within an organism

Growth: may be limited but always evident

Reproduction: involved hereditary molecules that can be passed on to offspring

Response to the environment: important to the survival of the organism

Homeostasis: refers to maintaining a constant internal environment

Nutrition: all about providing a source of compounds with chemical bonds that can be broken to provide the organism with energy & essential nutrients to maintain life

2.1.4 Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit

Molecules	1 nanometer (nm)
Membranes	10 nm
Viruses	100 nm
Bacteria	1 micormeter ( µm )
Organelles	10  µm
Cells	~100  µm  (depends on type of cell)

Guide:

1 nm = 10^-9 m
1 µm = 10^-6 m
1 mm = 10^-3 m
1 cm = 10^-2 m

2.1.5 Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification

Magnification = Size of Image / Size of Specimen

Simply rearrange this formula to obtain size of image or size of specimen as necessary

2.1.6 Explain the importance of the surface area to volume ratio as a factor limiting cell size

-          Surface area (SA) to volume ratio limits cell size

-          In the cell, rate of heat, waste production & rate of resource consumption are functions that depend on its volume

-          Chemical reactions occur within the cell which is affected by cell size

-          Surface/membrane of cell allows materials to move in & out of the cell

o   Cells with more SA per unit volume are able to move more materials in & out of the cell

-          As width of cell increases, SA increases but at a slower rate

o   Because of this, cells are limited in size in order to retain the ability to carry out the functions of life

-          Large animals don’t have large cell but more cells

-          Larger cells have modified shapes to survive, e.g. long & thin, infoldings/outfoldings

Sphere Formulas: SA = 4*pi*r² Volume = (4/3)*pi*r³

2.1.7 State that multicellular organisms show emergent properties

Multicellular organisms show emergent properties

2.1.8 Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others

-          Cell can go through a differentiation process to produce all the required cell types that are necessary for the survival of the organism

o   Differentiation process is the result of expression of certain genes & not others

-          Each cell becomes a specific type of cell depending on which DNA segment becomes active

-          Some cells can continue to reproduce after differentiation (skin/epithelial cells) whereas others cannot reproduce at all (muscle cells)

2.1.9 State that stem cells retain the capacity to divide and have the ability to differentiate alone different pathways

Stem cells retain the capacity to divide and have the ability to differentiate along different pathways

Pluripotent: can differentiate into any type of cell
Multipotent: can differentiate into many types of cells (but not all)

2.1.10 Outline one therapeutic use of stem cells

Helps treat Leukaemia:

1-      The placenta & umbilical cord of a baby is used as a source of stem cells

The blood from both is drained as it contains many hematopoietic (can divide & differentiate into any type of blood cell) stem cells

2-      Red blood cells are removed from the fluid which is then tested for diseases. It is then stored in liquid nitrogen in a special bank

3-      Cord blood can be used to treat Leukaemia, especially in children. Patient is first given chemotherapy drugs to kill bone marrow cells.

4-      The suitable cord blood is then taken from the bank, thawed & introduced to the patient’s blood system. The hematopoietic stem cells establish themselves in the bone marrow & divide repeatedly to restore healthy bone marrow cells to replace those killed by the chemotherapy drugs