Download 2.1 Cell Theory

2.1 Cell Theory
*NS = Not Included in Syllabus
Outline
 Theory acts as a bridge between living and non-living
 Cells are the smallest functional units of life
 All living organisms consist of cells (smallest organisms are unicellular)
 All cells come from pre-existing cells by division (cannot create life from non-living)
 Exceptions: skeletal muscles and fungal hyphae (not divided but multinucleated)
History
 Microscope – invented in 17th century
 Robert Hooke
 1662/1665 (???)
 Used compound microscope to observe the structure of cork and other plant
tissues
 First to use the term “cells”
 Anthony van Leeuwenhoek (NS)
 1680
 No formal science training, made microscopes for fun
 x240 magnification achieved
 Observed blood cells, sperms, protozoa with cilia, bacteria, and more
 Robert Brown (NS)
 1831
 Observed and named the cell nucleus
 Observed random movements of tiny particles (pollen grains) when suspended
in water (Brownian movement)
 Matthias Schleiden (1838) and Theodor Schwann (1839)
 Established cells as the natural unit of form and function in living things
 “Cells are organisms, and entire animals and plants are aggregates of these
organisms arranged to definite laws.”
 Rudolf Virchow
 1856
 Established the idea that cells arise only by division of existing cells
 Louis Pasteur (NS)
 1862
 Disproved spontaneous generation theory
 Bacteria and broth experiment
 Microbes in air contaminate exposed matter, causing growth of bacteria
Evidence
 Living things are made of cells
 Observations using microscopes on the structure of unicellular and
multicellular organisms (tissues, organs)
 Cells are the smallest unit of life
 Discovery of viruses as particles that are crystalline (non-cellular) when
outside a host cell and cannot reproduce without a host

Biochemical investigations of organelles showed ability to function outside a
cell under lab-controlled conditions, but only for a limited time
 Cells come from pre-existing cells
 Pasteur’s observations from the bacteria and broth experiment
 Discovery that life cycles of many microorganisms include a resistant spore
phase (inactive) and become active only in favourable growing conditions
 Observations on the behaviour or cells at division (mitosis and meiosis) and
during reproduction
 Cells contain a blueprint for growth, development, and behaviour
 Observations on the behaviour of chromosomes and discovery of the nature
and role of genes/DNA in control of cells and heredity
 Experimental evidence of the effects on cells of genetic engineering
 Cells are the site of the chemical reactions of life
 Discovery of enzymes (cell aerobic respiration and fermentation)
 Discovery of biochemical events (formations of proteins from amino acids)
 Discovery of cell ultrastructure (organelles and functions)
Functions of Life
 Metabolism – chemical reactions inside the cell
 Response – reacting to stimuli
 Homeostasis – maintenance/control of environment/conditions inside the cell
 Growth – increasing in size
 Reproduction – producing offspring
 Nutrition – obtaining food
Relative Sizes
 Molecules (1 nm)
 Thickness of membranes (10 nm)
 Viruses (100 nm)
 Bacteria (1 µm)
 Organelles (up to 10 µm)
 Most cells (up to 100 µm)
 Cells are 3D!
Surface Area to Volume Ratio
 Surface area doubles, volume triples
 Rate of heat/waste production and resource consumption is a function of volume
 Rate of exchange of materials and heat energy is a function of surface area
 Ratio should be high to allow easy movement of materials into and out of the cell
 If ratio is low, diffusion and osmosis can’t occur
Multi-Cellular Organisms
 Def n: a single mass of cells fused together
 Different from colonies in that colonies co-operate but do not fuse together
 Differentiation
 When a cell becomes specialized for a specific function
 Occurs when genes in stem cell are turned off
 When a gene is being used, it is called an “expressed” gene.
 Emergent Properties

Arise from the interaction of component parts; the whole is greater than the
sum of its parts
Stem Cells
 Def n: cells that have the capacity to self-renew by cell division and to differentiate
 Embryonic Stem Cells
 Easier to obtain than adult stem cells
 Almost unlimited growth potential
 Less chance of genetic damage
 Greater differentiation capacity
 Adult Stem Cells
 No embryo needs to be destroyed
 Cells are fully compatible with tissues of the adult; no rejection problems
 Lower chance of developing malignant tumours
 Can be used to replace neurons and other cells lost in the nervous system due to
accidents, strokes, or degenerative conditions such as Parkinson’s and MS
 Largely experimental treatments
 Could be used to grow organs, etc in the future
 Cord blood cells collected from the placenta and umbilical cord of a baby is used as a
source of stem cells which is used to treat certain types of leukemia. Chemotherapy
kills all bone marrow cells which eliminates the leukemia. Cord blood is then
transfused into the patient where the haematopoietic stem cells establish themselves in
the patient’s bone marrow and divide to replace the bone marrow cells killed by the
chemotherapy drugs.