Cell Theory
learning outcomes
1. summarise cell theory.
2. name 2 main types of cell and describe the differences between them.
3. explain the importance of magnification and resolution and microscopy.
4. discuss the main types of microscopes and images they produce.
what is a cell?
Robert Hooke 1665 - coins the term cell
Anthony van Leeuwenhoek - living cells.
Matthew schleiden 1838 - cell theory
Louis Pasteur 1862 -disproves spontaneous generation.
what is cell theory?
cell theory summarises the results of Hooke’s and other findings.
all organisms are composed of cells.
cells are the smallest living things.
cells arise only from pre-existing cells.
all cells today came from the first ever cells.
cell size
is limited.
small due to reliance on diffusion
rate of diffusion as affected by surface area, temperature, concentration gradient and
distance.
surface area to volume ratio
as the cell increases the radius increases
surface area and volume both increase but the volume increases more rapidly than the
surface area.
if diameter 3 then the surface area is 9 and the volume is 27
large size gives an evolutionary advantage, so organisms became multicellular.
collections of cells provide benefits of larger size and circumvent size constraints of single
cell.
functional specialisation allows individual cells to coordinate action.
organisms made of many small cells have an advantage over an Organism composed of
fewer larger cells.
exceptions
cells have strategies at their disposal to solve the problem of surface area to volume ratio.
some cells overcome limitation by being long and thin like neurons e.g., giant squid has
neuron one metre long but thin, so it has less volume.
egg cells are mostly metabolically inactive, so they need fewer nutrients and produce little
waste.
learning outcomes
1. summarise cell theory.
2. name 2 main types of cell and describe the differences between them.
3. explain the importance of magnification and resolution and microscopy.
4. discuss the main types of microscopes and images they produce.
what is a cell?
Robert Hooke 1665 - coins the term cell
Anthony van Leeuwenhoek - living cells.
Matthew schleiden 1838 - cell theory
Louis Pasteur 1862 -disproves spontaneous generation.
what is cell theory?
cell theory summarises the results of Hooke’s and other findings.
all organisms are composed of cells.
cells are the smallest living things.
cells arise only from pre-existing cells.
all cells today came from the first ever cells.
cell size
is limited.
small due to reliance on diffusion
rate of diffusion as affected by surface area, temperature, concentration gradient and
distance.
surface area to volume ratio
as the cell increases the radius increases
surface area and volume both increase but the volume increases more rapidly than the
surface area.
if diameter 3 then the surface area is 9 and the volume is 27
large size gives an evolutionary advantage, so organisms became multicellular.
collections of cells provide benefits of larger size and circumvent size constraints of single
cell.
functional specialisation allows individual cells to coordinate action.
organisms made of many small cells have an advantage over an Organism composed of
fewer larger cells.
exceptions
cells have strategies at their disposal to solve the problem of surface area to volume ratio.
some cells overcome limitation by being long and thin like neurons e.g., giant squid has
neuron one metre long but thin, so it has less volume.
egg cells are mostly metabolically inactive, so they need fewer nutrients and produce little
waste.
