Date: 21/August/2014
http://t1.gstatic.com/images?q=tbn:ANd9GcTvuz9maav
OI4KZeaQePn2OtWFUGtLGSNsPGXycMG020_eAiuS6
• 1665- Robert Hooke observes the first cells.
He coined the word ‘cell.’
Why do you think he called them cells?
Monk Cell Remains in Sanchi, Madhya Pradesh, India
• He examined very thin slices of cork and saw a multitude of tiny pores that
looked like the walled compartments a monk would live in
1700’s-Anton van Leeuwenhoek made a light
microscope with higher quality lenses to observe
smaller organisms (animalcules)
First to see organisms living in a drop of water
1864: Spontaneous generation of life
persisted for almost two centuries,
until Louis Pasteur disproved it.
smithlifescience.com
http://t2.gstatic.com/images?q=tbn:ANd9GcQCN3ZBOquHYFfzX8C
a5oc4xwBxspq4Y75fje06GCTBj3ZmjuUY
History of the Cell
1665- Robert Hooke observes the first cells. He came
up with the word “cell” & said all living things are
made of cells
1700’s- Anton van Leeuwenhoek made a light
microscope with quality lenses to observe smaller
organisms (animalcules) living in a drop of water
1855- Jewish Robert Remak discovers cell division
1864: Spontaneous generation of life persisted for
almost two centuries, until Louis Pasteur disproved it.
Whereas cells taken from an organism often survive
for a time, smaller parts of an organism do not.
• According to the cell theory, living
organisms are composed of cells.
The Cell Theory
• All living things are
composed of cells
• Cells are the basic
unit of structure and
function in living
things
• All cells come from
pre-existing cells
Stated in this way Cell Theory
might be attributed to Schleiden
and Schwann (1800’s)
Acetabularia sp.
Giant algae
Up to 100 mm in lenght
Questioning the cell theory using atypical
examples, including striated muscle, giant
algae and aseptate fungal hyphae.
All organisms exist in either a unicellular (one cell) or
multicellular (many cells) form.
All organisms carry out the functions of life:
– Metabolism: Chemical reactions
– Growth: Size increase
– Reproduction: Producing offspring
– Responses: Reaction to changes in the environment
– Homeostasis: Control of internal conditions
– Nutrition: Synthesis or absorption of food
• Organisms consisting of only one cell carry
out all functions of life in that cell.
Why do cells not grow to larger sizes?
Because of the surface-area to Volume Ratio! (relación
superficie/area)
As the organism gets bigger, their volume and surface
area both get bigger, but not by the same amount. The
volume increases as the cube but the area of the
surface only increases by the square.
The rate of exchange of substances depends on the
organism's surface area that is in contact with the
surroundings.
Surface area to volume ratio is important
in the limitation of cell size.
Multicellular organisms show Emergent properties
Emergence is the occurrence of unexpected characteristics or
properties in a complex system, which emerge from the
interaction of the “parts” of the system.
Emergent properties are seen at every level of increasing
complexity, from the atom to the molecule, to the cell to the
organism, to the biosphere.
Tungsten
Metal cup
Glass container.
When studied individually
they do not allow the
prediction of the
properties of the light
bulb.
• Multicellular organisms have properties that emerge from the
interaction of their cellular components.
Multicellular organisms are large and have to specialize parts of their
structure to complete functions characteristic of life.
This differentiation process is the
result of the expression of specific
genes.
Specialised cells express particular
genes that relate to these specialist
functions, producing particular
shapes, functions and adaptations
within a cell.
• Specialized tissues can develop by cell differentiation
in multicellular organisms.
• Some cells have a diminished ability to reproduce once they
become specialized, e.g.: Nerve and muscle cells.
• Other cells retain the ability to rapidly reproduce throughout
their life, e.g.: epithelial cells (skin)
A stem cell:
• Retains the capacity to divide and has the ability to differentiate
along different pathways.
• Is able to divide but has not yet expressed genes to specialize to a
particular function.
• Can be obtained from a variety of different places including the
blastocyte (adult bone marrow, embrionic tissue,
The capacity of stem cells to divide and differentiate
along different pathways is necessary in embryonic
development and also makes stem cells suitable for
therapeutic uses.
Good link that includes an
explanation:
http://www.teachersdomai
n.org/asset/biot09_int_ste
mcells/
infocelulasmadre.blogspot.com
Investigation of functions of life in Paramecium
and one photosynthetic unicellular organism
(Chlorella or Scenedesmus).