(a)
Introduction: The specialisation of cells
- differentiation
Undifferentiated cells are called stem cells
and develop into all the different types of cells an organism needs to
grow and develop.
A stem cell nucleus contains ALL the instructions
to switch genes 'on and off' so it has the ability to change into any
specialised cell needed by an organism.
Depending on the instructions a stem cell
receives, it can divide by
mitosis producing new cells which
can then differentiate into various types of cells for specific functions.
Multicellular organisms (eukaryotic) contain a variety of cells, with
different structures, which are adapted - specialised, to perform a
variety of functions.
Differentiation is the process by which a
cell develops into a form to do its specialised role.
Cells which have a particular structure adapted for a particular
function are called specialised cells.
After this the cells from mitosis start to
become specialised and the process of cell differentiation begins
in earnest to ensure growth and development.
In a multicellular organisms, many different types
of cell adopt different roles to ensure the organism functions correctly
in its life sustaining behaviours.
In cell differentiation, cells become
specialised by switching genes off and on to form tissues with
particular functions.
In the process of differentiation the stem cells
develop different sub-cellular structures to turn into the different
types of cells - specialisation.
The specialised cells can now carry out their
important specific functions - essential for the efficient and
healthy viability of any organism.
The cell's size, shape and internal structures
(e.g. organelles) must be all adapted for its function in the
organism.
Most differentiation occurs as an organism
develops - stem cells are found in early human embryos.
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and sub-index
(b)
Examples of specialised animal
cells adapted to their functions
On the right is a diagram of the basic structure
of an animal stem cell which has the features characteristic to most
cells e.g. membrane, nucleus of DNA/RNA for instructions, mitochondria
for respiration, cytoplasm, vacuoles, ribosomes for making proteins etc.
In most animal cells, this ability to
differentiate is lost at early stage of development once the cells have
become specialised. But, most plant cells retain the ability to
differentiate throughout the life of the plant.
The cells that differentiate in mature animals are
mainly used for replacing damaged/dead cells e.g. skin or blood cells.
Skin cells live for 14 to 21 days and blood
cells have a lifetime of 80 to 120 days.
Reminder: Other cells, stem cells, are
undifferentiated.
For more on stem cells see later section on
stem cells
and their potential uses on this page.
Note that stem cells are undifferentiated and have not changed
into a specialised cells in the developing embryo.
See also
Introduction to the organisation of cells =>
tissues => organs => organ systems (e.g. in humans)
Note that you can often work out how
the structure of the cell relates to its function in the organism.
e.g. consider its shape, size and
surface area AND the subcellular structure it contains e.g. organelles
like ribosomes and mitochondria, and also food stores like fat cells.
Gamete cells -
the function of egg cells and sperm cells in sexual reproduction -
adaptations described in detail
Egg cells and sperm cells are the specialised cells of sexual
reproduction.
In sexual reproduction the nucleus of an egg cell fuses with the
nucleus of a sperm cell to produce a fertilised egg.
The fertilised egg develops into an embryo.
Both the sperm cell and an egg cell are referred to as being
haploid, because their nuclei only contain half the number of
chromosomes that you find in a normal body cell.
This ensures that when the egg and sperm nuclei combine at
fertilisation the created cell will have the right number of
chromosomes (now referred to as a diploid cell see diagram
below).
With reference to the human reproduction
diagram above:
The zygote is a diploid cell resulting from
the fusion of two haploid gametes (sperm + egg cells) to give a
fertilized ovum.
For the first 5 days the cells from the
fertilised egg divide by mitosis producing identical cells.
The egg cell - its
structure and its adapted functions
Simple diagram of egg cell
The principal function of the female egg cell is to convey the female
DNA and to provide nutrients for the developing embryo in the early
stages of the organism's development.
The egg cell has a haploid
nucleus (half set of chromosomes) and the cytoplasm contains the
nutrients to feed the growing embryo - its nourishment.
Immediately after
fertilisation the egg cell's membrane changes structure to stop
another sperm getting into the egg cell and this ensures the right
amount of DNA is present in the fertilised cell.
See also
CELL
DIVISION - cell cycle - mitosis and meiosis in sexual reproduction
The sperm cell - its
structure and its adapted functions
Simplified diagram of sperm cell
The sperm cell, like the egg cell has a haploid nucleus (half of
the full set of required chromosomes).
It is about 55
µm long and about 3
µm wide.
The principal function of a male sperm cell is
to convey the male's DNA and combine with the female's DNA in the egg
cell, to fertilise the egg in the female reproductive system - to
produce the zygote.
The
sperm cell has a long tail and streamlined head to enable it to swim
efficiently to the egg.
A sperm
cell contains lots of mitochondria arranged in a spiral in
the middle section.
Mitochondria are sites of respiration
- releasing energy to provide the energy for it to
swim to the egg cell, as well as the rest of the cell chemistry.
At the front of the head of a sperm cell is an
acrosome where enzymes are stored.
These enzymes are needed so that
the sperm cell can digest its way through the membrane of the egg
cell to fertilise it.
See also
CELL
DIVISION - cell cycle - mitosis and meiosis in sexual reproduction
Ciliated Epithelial Cells
- these line the surface of organs
Simple diagram of epithelial cells
Organ surfaces are lined with epithelial cells.
Some types of
epithelial cells are adapted with hairs called cilia on the top
of the cell's surface.
The function of these ciliated epithelium cells
is to move substances in one particular direction along the surface of
the tissue.
The hair-like structure of the cilia beat
in tandem to move the
material along.
A good example is the lining of your air passage, the
surface of which is covered in lots of epithelial cells.
The 'beating'
cilia move mucous and any particles from air trapped on the surface up
the throat and away from your delicate lungs.
This allows the mucous to
be swallowed or blow out through your nose.
Ciliated epithelial cells contain lots of
mitochondria to power the cells chemistry including the
energy needed to move cilia to move 'stuff' along! - for most
cells this is not an extra energy requirement - but note energy
requirements of muscle cells in the next section.
See also
Introduction to the organisation of cells =>
tissues => organs => organ systems (e.g. in humans)
Muscle cells
Muscle cells form soft tissue found in most animals,
they are relatively long and must be able to contract quickly.
Muscle cells have a striped
appearance.
They contain protein filaments of actin and myosin that
can slide past one
another.
This adaptation produces a contraction that changes both the
length and the shape of the cell.
The contraction can be reversed and
allows muscle tissue cells to function in such a way as to produce force
and motion.
Muscle cells contain lots of mitochondria to supply the
larger amounts of energy from respiration needed to work the muscles.
There are actually three types of
muscle cells, all adapted for different movement effects:
(i) heart muscle cells -
found in the walls of the heart and under involuntary control
- automatically work,
cardiac muscle tend to be
more chunky (than the diagram above!),
(ii) skeletal muscle cells
- in muscle tissue and are the most striated in appearance,
muscle tissue is under
voluntary control, and the fibres join up (in development)
to give strength and co-ordinated movement
(iii) smooth muscle cells
- these are 'spindle-shaped' (like the diagram above) and found in
'hollow' organs e.g. stomach, intestine, bladder,
these are also under
involuntary control - automatically work.
See also
Introduction to the organisation of cells =>
tissues => organs => organ systems (e.g. in humans)
Nerve cells
Neurones are nerve cells that
have adapted to carry information as tiny
electrical signals from one part of the body to anther e.g. between the
brain and muscles.
On the right is a simplified diagram
of a nerve cell.
These sensory neurone cells are
elongated and adapted to cover the relatively 'long' distances over
which they have to carry the nerve signals
from receptors to the spinal cord and brain.
Nerve cells have branched connections
at their ends to form a network of connections with other cells throughout the body.
For much more on the structure
of nerve cells and how the nervous system works see
...
An introduction
to the nervous system including the reflex arc
gcse biology revision notes
Blood Cells
Red blood cells
Red blood cells are adapted to carry
oxygen via the haemoglobin molecules inside them.
Their shape is biconcave to give a
larger surface area to absorb oxygen molecules more efficiently to
combine with haemoglobin and transport them around the body where they
needed e.g. in mitochondria.
Without this adapted
cell transportation of oxygen you could not have efficient energy
releasing respiration in mitochondria.
White blood cells
White blood cells are part of the immune
system.
White blood cell change shape to
engulf a microbe thereby ingest disease-causing bacteria and destroy them.
White cells can produce antibodies to
destroy pathogens.
For much more detail see
The human circulatory system - heart, lungs, blood,
blood vessels
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(c) Specialised plant cells
Root hair cells
- are adapted to absorb water and minerals from soil and then through
the root system to transport these minerals around the plant. Root hair
cells are long and cover the surface of plant roots to create a large
surface area to absorb water and minerals.
Xylem cells - are not
living cells, but rod-like cells that form hollow tubes that can move
water and dissolved minerals from the roots around the plant.
Phloem cells - phloem
vessels (columns of living cells) move dissolved sugars, produced during
photosynthesis, and other soluble food molecules from the leaves to
growing tissues (e.g. the tips of roots and shoots) and storage tissues
(e.g. in the roots).
Palisade leaf cells -
their structure is
adapted to support the sites of photosynthesis. Their tall and thin shape allows
lots of light to be
absorbed and have a large surface area for absorbing carbon dioxide.
Palisade cells contain lots of chloroplasts, subcellular structures that contain
the chlorophyll needed for
photosynthesis and the shape
allows lots of them to be packed together on the top side of a leaf for
maximum exposure to light - essential for photosynthesis. See
diagram below.
Guard leaf cells -
can open and close the pores (stomata) in leaves and allow oxygen and carbon dioxide to
pass in and out. See diagram above.
For details see
Transport and gas exchange in plants,
transpiration, absorption of nutrients, leaf and root structure
and
Photosynthesis,
importance
explained, limiting factors affecting rate, leaf adaptations
gcse biology revision
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(d) Animal
stem cells
- an introduction
Stem cells are unspecialised
(undifferentiated) cells
that can produce many different types of cells - a process of cell
differentiation.
Most types of animal
cells only differentiate at an early stage whereas many plant cells retain the
ability to differentiate throughout life.
In mature animals, cell division
is mainly restricted to replacement of damaged or dead cells.
Most differentiation occurs as an organism
develops - embryonic stem cells are found in early human embryos.
Initially, from the fertilised egg, the cells in an embryo are
all the same and referred to as embryonic stem cells and
divide by mitosis (reminder diagram below of the context of discussing
stem cells in detail here).
Stem cells are undifferentiated and have
not changed
into a specialised cells in the developing embryo.
Stem cells are found in the early human embryo
as it develops in the womb.
Since they are unspecialised, they are able
to divide and ultimately produce any type of specialised cell (like those
described so far on this page), but stem cells lose this ability as
the animal matures.
It seems remarkable that all the different
types of cell found in the human body all come from a few cells in
the early embryo!
AND, this emphasises how important stem
cells are for growth and development.
In human embryos the cells are unspecialised as
far as the eight cell stage after three cell divisions by
mitosis.
The process of stem cells becoming specialised is
called cell differentiation.
Every type of cell in your body is derived
from these stem cells.
Cell differentiation enables the embryo to grow
and develop tissues - groups of specialised cells working
together to perform a particular function e.g. skin, muscle, organs etc.
Adults also have stem cells in their
bone marrow (spongy tissue in bones) but these can only be converted into a few specific type of cells
- so only quite limited specialisation is possible.
The stem cells in the bone marrow
are important in replacing dead or damaged cells e.g. producing new skin or red blood
cells, but they are not as versatile as embryonic stem cells
- they cannot produce any type of cell.
All body cells contain the same
genes, this differs from specialised cells in which most genes are
not active.
This means specialised cells only
produce the specific proteins they need.
Stem cells can switch any gene
'on' or 'off' during their development.
Genes which are switched on
('active') facilitate the production of proteins that will determine
the type of specialised cell a stem cell becomes.
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(e) The potential uses of stem cells,
particularly in medicine
Cells from early human embryos and
adult bone marrow, called stem cells, can be made to differentiate into many
different types of cells, e.g .nerve cells - so have the potential to be converted into any type of cell
found in the human body.
However, whereas early embryonic
stem cells can differentiate into any type of specialised cell,
adults only have stem cells in a few places like bone marrow and
these can only turn into a few types of cell e.g. blood cells.
Since human stem cells have the
ability to develop into any kind of human cell, they have great potential
for use in
treating certain medical conditions.
Reminder: As the embryo develops,
the stem cells divide, producing more stem cells, but also differentiated
cells - the process of differentiation in which cells for a specific
specialised function are produced e.g. cells for skin, organ tissue, blood
cells etc.
Transplanting stem cells or
transplants of specialised cells grown from stem cells can potentially
help with certain medical conditions
It is possible to extract stem
cells from early human embryos and adult bone marrow and reproduce
(growing) them under different particular
conditions so that they differentiate into particular types of specialised
cells.
After growing the embryonic
stem cells you can then stimulate them to differentiate
into specialised cells for use in further research or medical
applications - treatments.
In the laboratory you can
produce clones of stem cells - genetically engineered
identical cells.
Doctors are already using stem
cells to cure some diseases e.g. sickle cell anaemia can
sometimes be cured with a bone marrow transplant containing
adult stem cells that produce new red blood cells.
In the UK there is a shortage
of blood donations to give sick patients blood transfusions, so
it is hoped that sufficient artificial blood can be created
using stem cells.
Another possible source of
stem cells is blood left in the umbilical cord and placenta
after a baby is born. Cord blood is easy to collect and store.
It also avoids the ethical issues involved with using stem cells
from embryos.
These embryonic stem cells can be
used to treat various medical conditions such as
replacing diseased damaged tissue or tissue damage from injury e.g.
initiate new nerve cell connections
for people paralysed by spinal injury e.g. treatment with stem cells may
be able to help conditions such as paralysis and it is hoped to be able to grow
nerve cells for people disabled by a spinal injury.
transplant new cardiac/heart
muscle cells to replace tissue
of people suffering from heart disease,
insulin-producing cells for
diabetics,
treating conditions in which
certain body cells degenerate, especially with ageing e.g.
Alzheimer's disease, diabetes and multiple sclerosis.
treating leukaemia -
replacing rapidly produced abnormal white cells with normal
healthy cells (more on this below),
cancer or following
treatments for cancer like chemotherapy or radiation e.g.
patients suffering from leukaemia,
blind patients have had there
sight restored with stem cell treatment by treating the part of
the eye responsible for central vision.
Quite simply, there is huge
potential from stem cell research and application to alleviate many medical
conditions, which up to now, have been very difficult to treat - hence the
huge scientific interest in the potential for new cures - but such
strategies are not without risks and hot debates on the ethical
issues involved.
It is hoped that in the future
large scale storage banks of stem cells can be created so as to be
readily available for clinicians to treat many medical conditions.
Treating leukaemia (leukemia)
Leukaemia is a type of cancer found in
your blood and bone marrow and is caused by the rapid production of
abnormal white blood cells.
These abnormal white blood cells are
not able to fight infection and impair the ability of the bone marrow to
produce red blood cells and platelets.
Adults have stem cells in their
bone marrow but these can only be converted into a few specific type of cells
- so only quite limited specialisation is possible.
The stem cells in the bone marrow
are important in replacing dead cells e.g. producing new red blood
cells.
Leukaemia is a cancer of the
blood or bone marrow.
Leukaemia can be successfully
treated using stem cell technology.
You may have heard the phrase 'bone marrow transplant' - this involves
treating a patient with a supply of healthy stem cells to differentiate into
specific healthy cells to replace damaged or faulty cells e.g. in
this case, blood cells.
A stem cell or bone marrow
transplant is a gene therapy procedure that involves replacing damaged bone
marrow with healthy bone marrow stem cells.
It isn't a transplant of an
actual organ like a lung or heart, but the blood system can be
considered as a tissue system.
A stem cell transplant involves destroying any unhealthy blood
cells and replacing them with stem cells removed from the blood
or bone marrow.
The
bone marrow contains the stem cells that become specialised to
form any type of blood cell, so the transplanted bone marrow
produces the healthy blood cells.
A
stem cell transplant can involve taking healthy stem cells from
the blood or bone marrow of one person – ideally a close family
member with the same or similar tissue type and transferring
them to another person.
Stem cells in bone marrow
produce three important types of blood cells : red blood cells – which carry
oxygen around the body, white blood cells – which help fight infection and
platelets – which help stop bleeding.
Bone marrow transplants are not
only used to treat sufferers of
leukaemia, but also patients with non-Hodgkin's lymphoma and sickle cell anaemia.
A stem cell transplant has 5
main stages. These are:
-
Tests and examinations –
to assess your general level of health
-
Harvesting – the process
of obtaining the stem cells to be used in the transplant,
either from you or a donor
-
Conditioning – treatment
with chemotherapy and/or radiotherapy to prepare your body
for the transplant
-
Transplanting the stem
cells
-
Recovery
Stem cell transplants also enable
chemotherapy patients, whose bone marrow has been destroyed by
the anti-cancer chemicals, to produce red blood cells again.
It is hoped one day to culture
stem cells in huge quantities and produce stem cell lines
from patients with rare and complex diseases that can potentially
transform treatments in a health service.
At the moment the number of stem
cell therapies is quite limited, but it is hoped to be able to
stimulate stem cells to differentiate into a much wider range of
tissues - the process is called transdifferentiation.
Therapeutic cloning
One of the latest developments is
called therapeutic cloning.
Therapeutic cloning involves
producing stem cells with the same genes as the patient.
Because they are genetically have
the same genes, they shouldn't be rejected by the patient's immune
system.
An embryo can be modified to have the
same genetic information as the patient.
This means these stem cells
have the same genes and less likely to be rejected by the patient's
body.
Therapeutic cloning involves
nuclear transfer.
1. The nucleus is
removed from a human egg cell.
2. The nucleus of a
body cell from the patient is transferred to the egg cell from
which the nucleus was removed.
3. The modified egg
cell is stimulated to divide and cause an embryo to grow.
4. After 4-5 days the
stem cells are removed from the embryo and cultured to produce
enough to treat the patient.
(The embryo is discarded)
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and sub-index
(f) Some risks and concerns
in using stem cells and future research
Unwanted diseases
Transplanted stem cells divide very quickly
and if the speed of cell division cannot be controlled inside a
patient a tumor (tumour) may develop.
Cultured stem cells can show
similarities with cancer cells.
After many cell divisions you
can get mutations changing the genetic character of the cell -
so how might affect the cell's behaviour? Will it increase the
chance of rejection by the patient's immune system? Might it
cause cancerous growths?
Inside the stem cells, viruses can co-exist
with their host. If, unknowingly, donor stem cells are infected with
a virus, this virus can be passed on to the patient under treatment
worsening their condition - a case of unwanted disease
transmission!
Transplant rejection -
perhaps the single biggest problem in applying stem cell treatments.
The stem cells from a storage
bank come from different people and often will not perfectly
match a the patients cells and so the patient's immune system
will respond in a negative way.
In other words, if the transplanted cells/tissues/organs aren't grown using the
patient's own stem cells, the patient's body might recognise the donor
cells as 'foreign' and trigger the usual immune response to attack
and remove invasive cells.
The clinicians will do their
best to match the donated stem cells with the patient's body
cells.
Quite often, the transplant
patient has to take drugs to suppress the body's natural immune
response and avoid rejection of the donated cells, but this makes the patient more susceptible to other
diseases.
The problem of rejection can
be minimised by using the patient's own stem cells from
somewhere else in the body - the idea being the body's immune
system will recognise them as non-foreign and not offer a
response.
Stem cell research and its
applications are very controversial
This is despite the obvious great medical benefit to individual patients of using
stem cell therapy and therapeutic cloning.
Stem cell research is necessary
to find out more how to use this new area of medicine and how to
develop and extend the range of effective medical treatments,
BUT, public education about
stem cell research and applications is essential because of the
moral and ethical implications of this new biotechnology.
The use of embryonic stem
cells, obtained from a living human embryo, is especially
controversial.
Moral question: Is it
morally right or wrong to use embryonic stem cells for research
or treatments?
Is it right to create an
embryo for research or medical treatments that you will
ultimately destroy after extracting stem cells?
Ethical question-issues:
We need, as a society, to ethically discuss reasons
whether the use of embryonic stem cells is right or wrong.
'Pros and cons': We have
to weigh up the potential medical benefits from successful
stem cell treatments versus the moral and ethical objection
of such procedures.
Do the medical benefits
outweigh moral and ethical objections.
Also, should patients be
given false hope by giving/requesting an unproven stem cell
based medical treatment?
The ethical issue of using
embryos for medical purposes is abhorrent to some people who would argue
that human embryos shouldn't be used to provide stem cells
because the embryo is destroyed in the process - removing one
that had the potential for human life.
People, perhaps of a
particular religious belief, argue that life begins at
conception and the embryo has rights like any other human being.
So, where does a human life really begin? Your choice?
This is the argument of
'potential life' versus help for seriously ill 'living people' i.e. each
embryo has the potential to develop into a human being, but equally
potently, using embryonic stem cells might save a life.
In other words
the rights of suffering patients overrides the rights of the embryo
- would you deny blind people to the right to see again?
It is possible to use unwanted
embryos from fertility clinics (IVF) because there is no other source of universal
stem cells and these unwanted embryos would be destroyed.
(IVF: Fertility treatments
involving in-vitro fertilisation)
The unwanted
embryos often come from fertility clinics and would be destroyed if
not used for research purposes - but this argument would not satisfy
campaigners want to completely ban the use of human embryos.
Many campaigners believe
scientific research should be directed towards finding and
developing other sources of stem cells and avoid the use of human
embryos.
Stem cell research is allowed
in some countries like the UK, but there are very strict rules
and guidelines as to how it can be carried out.
UK law does now allow embryos
to be created for scientific research.
Stem cell
research is completely banned in some countries.
However, there are stocks of
stem cells that scientists can use to continue their research
without involving the use of more embryos - this is allowed in
the UK but not in the USA.
As already mentioned, another
possible source of stem cells is blood left in the umbilical
cord and placenta after a baby is born.
Cord blood is easy to
collect and store and avoids the ethical issues involved
with using stem cells from embryos.
Scientists have managed to
remove human skin cells and reprogrammed them to become like
embryonic cells.
This gets around some of
the ethical issues discussed above about the use of stem
cell transplants from embryonic tissue.
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(g) Plant stem cells - the production of
identical plants from meristems
In plants, the only cells that divide
by mitosis are found in plant tissues called
meristems.
Meristem tissue is found in the tips
of roots and shoots - the parts of plants that are growing.
Meristems make undifferentiated
(unspecialised) cells
that can divide and form any type of cell the plant needs.
These unspecialised cells are
effectively acts as 'embryonic' stem cells.
However, unlike human stem cells,
they can differentiate to form any type of cell for the lifetime of the
plant.
These unspecialised cells can form
the specialised tissue cells of the xylem and phloem.
Plant stem cells can be used to make
clones - so identical genetic copies of a plant can be grown quickly
and cheaply.
This means plant growers can grow
crops of identical plants that have been genetically engineered
to have more desirable features for farmers e.g. increased
size of wheat grain, more disease resistant - but GM crops are also a
controversial topic too!
Cloning has an important application
in preserving rare species of plants - to grow more of those in
danger of becoming extinct.
See
Hormone control of plant growth and uses of plant hormones
gcse biology revision notes
and
section on plants
in
Cloning -
tissue culture of plants gcse
biology revision notes
Pre-reading:
Introduction to plant and animal cell structure and
function gcse biology revision notes
These notes about
cell specialisation and specialised cell function are developed in detail on
other pages.
and for
the bigger picture
Introduction to the organisation of cells => tissues => organs => organ
systems (e.g. humans)
Some typical learning objectives for
this page on stem cells, cell differentiation & specialisation
Be able to
describe how specialised cells are adapted to their function, including:
(a) sperm cells – acrosome, haploid nucleus, mitochondria and
tail
(b) egg cells – nutrients in the cytoplasm, haploid nucleus and
changes in the cell membrane after fertilisation
(c) ciliated epithelial cells
General CELL BIOLOGY and GENETICS revision notes index
Introduction to plant and animal cell structure and
function - comparison of subcellular structures gcse biology revision notes
Stem cells and medical uses, and introduction to cell
differentiation and specialisation gcse biology revision notes
Cell division - cell cycle - mitosis, meiosis, sexual/asexual reproduction,
binary fission gcse
biology revision
Microscopy - the development and use of microscopes in biology
- optical and electron gcse biology revision notes
Diffusion - including demonstration, factors &
Fick's Law, osmosis investigation and active transport gcse biology
Examples of surfaces for the exchange of substances in
animal organisms gcse biology revision notes
Respiration - aerobic/anaerobic in plants, fungi & animals,
substrates/products, experimental investigations
Enzymes - structure, functions, optimum conditions,
investigation experiments, digestion gcse
biology revision
See also
Enzymes and Biotechnology
(gcse chemistry notes)
Culturing microorganisms like bacteria - testing
antibiotics and antiseptics gcse
biology revision notes
DNA and RNA structure and Protein Synthesis gcse
biology revision notes
An introduction to genetic
variation and the formation and consequence of mutations
gcse biology revision notes
Introduction to the inheritance of characteristics and
genetic diagrams (including Punnett squares) including technical terms, Mendel's work and inherited
genetic disorder, genetic testing gcse biology revision notes
The human GENOME project - gene expression, chromosomes, alleles, genotype, phenotype, variations,
uses of genetic testing including 'pros and cons' gcse biology revision notes
Inherited characteristics and human sexual
reproduction, genetic fingerprinting and its uses gcse biology
Genetic
engineering: uses - making insulin, medical applications, GM crops & food
security gcse biology
More complicated genetics: Sex-linked genetic
disorders, inheritance of blood groups gcse biology revision
See also section on
Cloning -
tissue culture of plants and animals gcse biology revision notes pages
