TOPIC 1: CELL BIOLOGY
1.1 Introduction to Cells
Cells are the bases for all living things, according to the cell theory:
o All living things are composed of cells
Multicellular organisms have specialised cells to carry out various functions
o The cell is the smallest unit of life
Cell components cannot survive alone
o Cells only arise from pre-existing cells
Cells multiply by division (mitosis or meiosis)
Pasteur’s experiment was used to prove it
Although the cell theory, fits most organisms there are some exceptions:
o Striated Muscle: Much larger than most cells and are multinucleated (challenges idea
cell has one nucleus)
o Giant Algae: Can grow up to 100mm and therefore expected to consist of many small
cells. However, they are unicellular with a single nucleus (challenges idea cell is small &
simple)
o Aseptate Fungi: Consist of hyphae (thread-like structures) which consist of long
undivided, multinucleated sections (challenges idea cell is a single unit)
Unicellular organisms can carry out all the functions of life (Mr. H Gren)
Function Paramecium Chlamydomonas
Metabolism Both: Produce enzymes which catalyse reactions in the cytoplasm
Response Reacts to stimuli (e.g. changes direction when Has an eyespot that is able to detect the
it touches a solid object) brightest light and swim towards it
Homeostasis Both: Keep internal conditions within limits e.g. expels excess water
Growth Increases in size and mass by accumulating Increases in size and mass due to
organic matter & minerals from its food photosynthesis and absorption of minerals
Reproduction Both: Asexually (mitosis) as well as sexual reproduction (meiosis & gametes)
Excretion Expels waste products e.g. CO2 diffuses out of Expels waste products e.g. oxygen diffuses out
the cell of the cell
Nutrition Feeds on smaller organisms by ingesting and Produces own food through photosynthesis
digesting via endocytosis using chloroplasts
One of the major factors limiting cells size is surface area: volume ratio
o A cell that is too large may not be able to take in essential materials or excrete waste
quickly enough
o Cells want a large surface area to volume
ratio (however this may cause for faster
heat loss)
o As a result, large organisms are
multicellular
This also allows for cell
differentiation (specialisation of cells)
1
, Multicellular organisms have emergent properties that arise from the interaction of their cellular
components
o Even though one cell can function on its own, many cells can form tissues and organs
which are able to perform a wider range of functions
o The whole is greater than the sum of its parts
Differentiation involves the expression of some genes (given by chemical instructions) and not
others in a cell’s genome
o An organisms entire set of genes is its genome, and during differentiation only the genes
required for the cells function are turned on
These activated genes encode for proteins which affect the structure and
function of the cells
o Once development has begun, the cell cannot change and is said to be ‘committed’
o Specialized tissues develop by cell differentiation in multicellular organisms
Stem Cells are cells that have the capacity to divide and differentiate along different pathways
o Human embryos consist entirely of stem cells
o Small numbers of stem cells are found in the adult body in most tissues, including bone
marrow, skin and liver
o There are four main types of stem cells present at various stages of development:
Totipotent: can differentiate into any type of cell (zygote)
Pluripotent: can differentiate into many types of cell (embryonic stem cells)
Multi-potent: can differentiate into closely related cell types (bone marrow)
Unipotent: Can regenerate, but only into their associated cell type (liver cell)
Stem cells are ideal for therapeutic use, for example in treating Stargardt’s Disease
o Stargardt’s Macular Dystrophy is a genetic disease that develops in children causing
retinal cells to malfunction and a progressive deterioration in vision
o A trial was conducted where retinal cells, derived from embryonic stem cells were
injected into the patient’s eyes
o There was an improvement in the patient’s vision and no harmful side-effects
Stem cells could also be used to treat Leukaemia, a type of cancer where abnormally large
numbers of white blood cells are produced in the bone marrow
o First stem cells are extracted from the bone marrow and are frozen and stored
o High doses of chemotherapy drugs are given to the patient to kill the cancer cells, with
the bone marrow losing its ability to produce blood cells
o Stem cells are returned to the body and begin to multiply and produce new cells
There are many arguments regarding stem cell use and their source, with the main point in
favour of it being the health and quality of life of patients suffering from incurable diseases may
be greatly improved
o Stem cells taken from specially created embryos are the most controversial, with people
arguing that an embryo is a human life even at the earliest stage and if it dies the
procedure is immoral.
o Counter arguments include, early stage embryos are just balls of cells and do not feel
pain or suffer. Large numbers are also produced by IVF and are never implanted, so they
should be used for stem cell research, if given consent
o Taking cells from adult tissue/umbilical cord can only give rise to limited cell types
A light microscope can be used investigate the structure of cells and tissues
2
1.1 Introduction to Cells
Cells are the bases for all living things, according to the cell theory:
o All living things are composed of cells
Multicellular organisms have specialised cells to carry out various functions
o The cell is the smallest unit of life
Cell components cannot survive alone
o Cells only arise from pre-existing cells
Cells multiply by division (mitosis or meiosis)
Pasteur’s experiment was used to prove it
Although the cell theory, fits most organisms there are some exceptions:
o Striated Muscle: Much larger than most cells and are multinucleated (challenges idea
cell has one nucleus)
o Giant Algae: Can grow up to 100mm and therefore expected to consist of many small
cells. However, they are unicellular with a single nucleus (challenges idea cell is small &
simple)
o Aseptate Fungi: Consist of hyphae (thread-like structures) which consist of long
undivided, multinucleated sections (challenges idea cell is a single unit)
Unicellular organisms can carry out all the functions of life (Mr. H Gren)
Function Paramecium Chlamydomonas
Metabolism Both: Produce enzymes which catalyse reactions in the cytoplasm
Response Reacts to stimuli (e.g. changes direction when Has an eyespot that is able to detect the
it touches a solid object) brightest light and swim towards it
Homeostasis Both: Keep internal conditions within limits e.g. expels excess water
Growth Increases in size and mass by accumulating Increases in size and mass due to
organic matter & minerals from its food photosynthesis and absorption of minerals
Reproduction Both: Asexually (mitosis) as well as sexual reproduction (meiosis & gametes)
Excretion Expels waste products e.g. CO2 diffuses out of Expels waste products e.g. oxygen diffuses out
the cell of the cell
Nutrition Feeds on smaller organisms by ingesting and Produces own food through photosynthesis
digesting via endocytosis using chloroplasts
One of the major factors limiting cells size is surface area: volume ratio
o A cell that is too large may not be able to take in essential materials or excrete waste
quickly enough
o Cells want a large surface area to volume
ratio (however this may cause for faster
heat loss)
o As a result, large organisms are
multicellular
This also allows for cell
differentiation (specialisation of cells)
1
, Multicellular organisms have emergent properties that arise from the interaction of their cellular
components
o Even though one cell can function on its own, many cells can form tissues and organs
which are able to perform a wider range of functions
o The whole is greater than the sum of its parts
Differentiation involves the expression of some genes (given by chemical instructions) and not
others in a cell’s genome
o An organisms entire set of genes is its genome, and during differentiation only the genes
required for the cells function are turned on
These activated genes encode for proteins which affect the structure and
function of the cells
o Once development has begun, the cell cannot change and is said to be ‘committed’
o Specialized tissues develop by cell differentiation in multicellular organisms
Stem Cells are cells that have the capacity to divide and differentiate along different pathways
o Human embryos consist entirely of stem cells
o Small numbers of stem cells are found in the adult body in most tissues, including bone
marrow, skin and liver
o There are four main types of stem cells present at various stages of development:
Totipotent: can differentiate into any type of cell (zygote)
Pluripotent: can differentiate into many types of cell (embryonic stem cells)
Multi-potent: can differentiate into closely related cell types (bone marrow)
Unipotent: Can regenerate, but only into their associated cell type (liver cell)
Stem cells are ideal for therapeutic use, for example in treating Stargardt’s Disease
o Stargardt’s Macular Dystrophy is a genetic disease that develops in children causing
retinal cells to malfunction and a progressive deterioration in vision
o A trial was conducted where retinal cells, derived from embryonic stem cells were
injected into the patient’s eyes
o There was an improvement in the patient’s vision and no harmful side-effects
Stem cells could also be used to treat Leukaemia, a type of cancer where abnormally large
numbers of white blood cells are produced in the bone marrow
o First stem cells are extracted from the bone marrow and are frozen and stored
o High doses of chemotherapy drugs are given to the patient to kill the cancer cells, with
the bone marrow losing its ability to produce blood cells
o Stem cells are returned to the body and begin to multiply and produce new cells
There are many arguments regarding stem cell use and their source, with the main point in
favour of it being the health and quality of life of patients suffering from incurable diseases may
be greatly improved
o Stem cells taken from specially created embryos are the most controversial, with people
arguing that an embryo is a human life even at the earliest stage and if it dies the
procedure is immoral.
o Counter arguments include, early stage embryos are just balls of cells and do not feel
pain or suffer. Large numbers are also produced by IVF and are never implanted, so they
should be used for stem cell research, if given consent
o Taking cells from adult tissue/umbilical cord can only give rise to limited cell types
A light microscope can be used investigate the structure of cells and tissues
2
