BIOLOGY – CHAPTER FIVE - BIOLOGYCHAPTERFIVE...

BIOLOGY – CHAPTER FIVE
• Cells first observed in 1600 by Robert Hooke (cork)
• 1820’s: nucleus first observed by Robert Brown
• Theodore Shawann later proposed that that all animals and plant cells
have a nucleus and that cells that make up multicellular organisms retain
independence.
• Rudolf Virchow discovers that all cells come from pre-existing cells.
• Basic cellular theory:
o All organisms are composed of one or more cells
o The cell is the smallest unit that has the properties of life
o Cells only arise from the growth and division of pre-existing cells
• Single cells can vary in size, from 5 micrometers (smallest bacteria) to 30
micrometers (the largest cells of multicellular organisms)
• Light microscopes are used to view larger cells, while electron
microscopes are used to view smaller cells and cellular functions.
• Cells are small because, as the diameter of the cell increases, the volume
of the cell increases much faster than the surface area of the cell. The
volume of a cell determines how much chemical activity can occur in the
cell. The surface area of the cell determines the amount of substances
that can enter and exit the cell. A cell with a large volume could not
maintain the required levels of waste and nutrient exchange for cell life.
• Some cells increase their surface area by flattening themselves or by
folding their cell membranes upon themselves (eg, intestinal cells).
• Genes – segments of DNA that code for specific individual proteins.
• Cytoplasm contains cystol, a solution containing ions and organic
molecules.
• Organelles – small, organized structures important for cellular function.
• Plasma membrane – bilayer of lipids with embedded protein molecules.
• Select water-soluble substances can penetrate the cell membrane through
the use of transport proteins channels. (eg, ions and molecules)
• Most of the cells functions occur in the cytoplasm
• The cytoplasm also conducts stimulatory signals from outside of the cell
into the cells interior and then carries out chemical reactions that respond
to these signals and converts chemical and light energy into forms that
can be used by the cell.