2.1 Cells, tissues and organs
Multicellular organisms contain many different types of cells, which are specialised to carry
out particular functions. A large number of specialised cells together make up tissues and
various tissues together make up an organ.
Specialised animal cells
There are numerous specialised cells in animals which perform particular functions.
Some examples of specialised animal cells and their functions are described below.
Muscle cells
These are long,
thin cells which contract to cause movement. The cells
contain a large number of mitochondria to produce the
large amount of energy required for this contraction.
Sperm cells
A sperm cells particular function is to fertilise an egg cell. It has a specialised tail to allow it
to swim towards an egg and the head of the sperm cell contains enzymes to digest the
exterior of the egg, which allows the sperm to enter the egg and fuse with it.
Tail
Head contains
nucleus and enzymes
Nerve cells
These cells form connections with other nerve cells to
create a huge network which is used to transmit impulses
throughout the body; this allows us to co-ordinate
movement and thoughts. They have long projections which
allow them to make connections with other cells; these
connections can be made with cells some distance away.
Projection to connect
with other cells
Blood cells
Red blood cells are small and have a ‘bi-concave’ shape to
increase their surface area and to allow them to squeeze
through tiny blood capillaries. Their function is to transport
oxygen around the body; to achieve this, they contain a
pigment called haemoglobin which binds with oxygen and they
lack a nucleus to maximise the amount of pigment they can
carry.
White blood cells fight infection in the body. They have an irregular shape to squeeze
through blood vessels and their shape allows them to surround a microbe; they also contain
enzymes which digest the microbe into harmless waste substances.
Specialised plant cells
Phloem cells
These cells are involved in the transport of sugar in plants;
they have perforated end walls which allow sugars to be
transported to the next phloem cell. They also possess
companion cells with a large nucleus to control the phloem
cells.
Root hair cells
These cells are responsible for absorbing water (for
photosynthesis) from soil around the roots. Each cell has
a large surface area to maximise the volume of water it
can absorb.
Palisade mesophyll cells (leaf cells)
These are found in the upper layer of a leaf and have the main function
of carrying out photosynthesis; they contain a very large number of
chloroplasts to maximise photosynthesis.
Tissues
Tissues are groups of specialised cells which will carry out a particular function.
Examples of animal tissues include:
 Muscle
 Blood
 Nerves
Examples of plant tissues include:
 Vascular tissue (i.e. transport tissues such as xylem and phloem)
 Palisade tissue (layer of palisade cells within the leaf)
 Root tissue
Organs
Organs are made up of several types of tissue grouped
together, for example, the small intestine is made up of
muscle tissue, connective tissue, epithelial lining tissue
and also nerve tissue to control its action. Organs can
carry out specific function due to the large variety of
specialised cells within them.
Other examples of animal organs include:
 Heart (pumps blood around the body)
 Lungs (site of gas exchange)
 Eyes
Examples of plant organs include:
 Leaves
 Reproductive organs (e.g. anther)
Examples of the link between cells, tissues and organs are shown below:
Muscle cells
Cell
Nerve cells
Cell
Muscle tissue
Heart
Tissue
Organ
Nerve tissue
Brain
Tissue
Organ
2.2 - Stem cells and meristems
Part a: Stem cells
Stem cells are unspecialised cells which are found in all
multicellular organisms. Stem cells have the potential to become
many different types of cells and so are described as the site of
production of specialised cells. As with other body cells, stem
cells undergo mitosis and therefore increase the number of cells
in an organism; specialised cells produced by division of stem cells
can be used for growth or repair.
The diagram shows a few of the
possible cell types which can be
produced by stem cells.
Potential uses of stem cells
Stem cells are currently being used after
cancer treatment to restore destroyed stem
cells; bone marrow (which contains stem cells)
is transplanted into a patient and the cells it
contains will begin to produce blood cells.
There is a vast range of possible uses of stem
cells in medical science which may improve
health. The diagram outlines some of these
potential stem cell uses:
Due to the unspecialised nature of stem cells, they could potentially be used to cure or
repair damage caused by a wide range of conditions.
Stem cell technology could be used to:

repair damaged heart tissue after a heart attack

grow new skin cells to repair skin damage after burns

grow complete organs (removing the need for waiting lists for transplants)
Stem cell technology is a promising but ethically controversial procedure due to the source
of some stem cells; stem cells can be derived from adult tissues (and other sources) or they
can be sourced from embryos. The use of embryonic stem cells has been criticised by many
groups due to the ethics of creating, using and destroying potential embryos.
Part b: Meristems
Within plants, only particular areas can undergo mitosis and therefore contribute to growth,
these areas are called meristems. Meristems produce non-specialised cells in plants and
these non-specialised cells can potentially become any type of plant cell (e.g. leaf mesophyll
cells, phloem cells etc).
meristem
Root hair
young leaves
meristem
Root cap
Shoot tip
Root tip
Areas which undergo growth, such as root tips and shoot tips, will contain meristems.