Topic 2 - Cells

All living things are made of cells

Cells are the smallest unit of life

Cells come only from other cells

Evidence for cell theory

Cells taken from organisms survive for a time; smaller parts of organisms do not.

Experiment to show that spontaneous generation of life is impossible – sterilised soup in an open container decays whereas a sterilised soup in a sealed container does not decay.

Size of a Molecule

1 nm

size of cell membrane thickness

10 nm

virus

100 nm

Bacteria

1 um

Size of an organelle

less than 10 um

Size of a cell

more than 100 um

Calculation of magnification

Magnification = length on the image

                             Length of the Specimen

Importance of the surface area to volume ratio as a factor limiting size

As the size of a structure increases the surface area to volume ratio decreases (rate of exchange decreases)

The rate of exchange of substances depends on the organism’s surface area that is in contact with the surroundings

Exchange depends on the volume of the organism Surface area : Volume

As organisms get bigger their volume and surface area both get bigger, but not by the same amount

In large organisms, the rate of exchange with their surroundings occurs more slowly

Large organisms have had to create a respiratory system as their volume:surface area ratio became such that they could no longer supply adequate oxygen by diffusion for respiration.

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

-          Multi-cellular organisms are large and have to specialise parts of their structure to complete the various functions that are characteristic of life

-          Differentiation: cells within a multi cellular organism specialise their function

-          Specialised cells have switched on particular genes (expressed) that correlate to these specialist functions

-          Specific gene expressions produce particular shapes, functions and adaptations within a cell

Outline one therapeutic use of stem cells

Leukemia

1.       Blood is drained out of umbilical cord and placenta. This contains many haematopoietic stem cells. These cells can divide and differentiate into any type of blood cell.

2.       Red blood cells are removed from the cord blood and the remaining fluid is then tested to find its tissue type, checked for disease-causing organisms and stored in liquid nitrogen.

3.       Cord blood can be used to treat patients who have developed certain forms of leukaemia. This is a cancer where the bone marrow divides uncontrollably, producing far too many white blood cells.

4.       The patient is given chemotherapy drugs that kill bone marrow cells, including the cells causing leukaemia

5.       The cord blood is taken from the bank, thawed and introduced into the patient’s blood system.

6.       The hematopoietic stem cells establish themselves in the patient’s bone marrow, where they divide repeatedly to build up a population of bone marrow cells to replace those killed by the chemotherapy drugs.