Cell Theory
• Until microscopes became powerful enough to view individual cells, no-one knew for certain what living
organisms were made from
• A scientist called Robert Hooke came up with the term "cells" in the 1660's after examining the
structure of cork
• Matthias Schleiden and Theodor Schwann were two scientists who studied animal and plant cells
o In 1837, they came up with the idea that all living organisms are made of cells
o This idea is known as ‘cell theory’
o The cell theory is a unifying concept in biology (meaning it is universally accepted)
• The cell theory includes three main ideas:
o All living organisms are made up of one or more cells
o Cells are the basic functional unit (i.e. the basic unit of structure and organisation) in living
organisms
o New cells are produced from pre-existing cells
• Although cells vary in size and shape they all:
o Are surrounded by a membrane
o Contain genetic material
o Have chemical reactions occurring within the cell that are catalysed by enzymes
Cell Theory: Atypical Examples
NOS: Looking for trends and discrepancies; although most organisms conform to cell theory, there are
exceptions
• Scientists studying cells (e.g. Robert Hooke, Schwann & Schleiden and Pasteur)
discovered trends when making observations of organisms
• The organisms they examined, using microscopes, all appeared to be made of smaller compartments
(which we now refer to as cells). They discovered that even the smallest organisms, such as Amoeba,
were made from at least one cell
• However, advancements in technology (particularly around what can be detailed and seen under a
microscope) have enabled scientists to examine many more organisms and discrepancies have been
discovered which raise questions about whether cell theory applies to all organisms
Atypical examples
• Striated muscle fibres, aseptate fungal hyphae and giant alga are three examples of cells/tissue with
structures that question the integrity of the cell theory
Striated muscle fibres
• Striated muscle fibres (fused muscle cells) are:
o Longer than typical cells (up to 300 mm in length in comparison to a cardiac muscle cell which
has a length of 100 - 150 µm)
, o Have multiple nuclei surrounded by a single membrane (sarcolemma)
• These features question the cell theory because striated muscle cells are formed from multiple cells
which have fused together (which is how they have many nuclei rather than one) that work together as a
single unit, challenging the concept that cells work independently of each other even in a multicellular
organism
Aseptate fungal hyphae
• Fungi have many long, narrow branches called hyphae
• Hyphae have cell membranes, cell walls and some have septa
• Aseptate fungal hyphae do not have septa, thus these cells are multinucleated with continuous
cytoplasm
• This questions the cell theory because the cells have no end walls making them appear as one cell
Giant Alga (e.g. Acetabularia)
• Acetabularia can grow to heights of 100 mm, and yet consist of only one cell with a single nucleus
• Acetabularia have a relatively complex structure. They are divided into three parts: rhizoid, stalk and
cap
• The features above question the cell theory because the trend for most unicellular organisms is to be
small in size and simple in structure
Three atypical examples of the cell theory
, Stem Cells: Therapeutic Use
• Currently, there are very few therapeutic uses of stem cells, although scientists around the world are
actively involved in researching potential therapies
• The research is being carried out on embryonic (totipotent and pluripotent) and adult (multipotent)
stems cells
Use of embryonic stem cells
• Due to their ability to differentiate into multiple cell types, stem cells have huge potential in the
therapeutic treatment of disease
• For many countries, such as the USA and some countries within the EU, the use of embryonic stem
cells is banned, even for research
• In other countries, such as the UK, the use of embryonic stem cells is allowed for research but is
very tightly regulated
• Embryonic stem cells can be one of two potencies:
o Totipotent if taken in the first 3-4 days after fertilisation
o Pluripotent if taken on day 5
• The embryos used for research are often the waste (fertilised) embryos from in vitro fertilisation
treatment
o This means these embryos have the potential to develop into human beings
o This is why many people have ethical objections to using them in research or medicine
Stargardt's disease
• Stargardt's disease is the most common inherited form of juvenile macular degeneration and mainly
affects children and adolescents
• The macula is located in the central region of the retina and damage to this area limits our central vision
and colour perception
• The disease is commonly caused by a mutation of the ABCA4 gene resulting in a protein in the retina
malfunctioning, eventually leaving the person legally blind
• One treatment that was researched was the injection of retina cells derived from embryonic stem
cells into patients eyes. This treatment had success and no harmful side effects were experienced,
however trials are still ongoing
Use of multipotent adult stem cells
• As tissues, organs and organ systems develop, cells become more and more specialised
• Having differentiated and specialised to fulfil particular roles, most adult cells gradually lose the ability
to divide until, eventually, they are no longer able to divide
• However, small numbers of stem cells (known as adult stem cells) remain to produce new cells for the
essential processes of growth, cell replacement and tissue repair
• Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able
to produce a limited range of cell types – they are multipotent
, o For example, the stem cells found in bone marrow (hematopoietic stem cells) are multipotent
adult stem cells – they can only differentiate into blood cells (red blood cells, monocytes,
neutrophils and lymphocytes)
o In adults, multipotent stem cells can be found throughout the body (eg. in the bone marrow,
skin, gut, heart and brain)
• Research is being carried out on stem cell therapy, which is the introduction of adult stem cells into
damaged tissue to treat diseases (eg. leukemia) and injuries (eg. skin burns)
Leukaemia
• Leukaemia is the generalised term referring to a group of cancers that develop in the bone marrow
• It is caused by mutations in genes resulting in the over-production of abnormal white blood
cells (leukocytes)
• To destroy these mutated cells in the bone marrow patients undergo chemotherapy
• However, as the chemicals injected into the patient's body during chemotherapy destroy all bone
marrow cells, hematopoietic stem cells (HSCs), the adult stem cells found in bone marrow, are
removed using a large needle before treatment
• These HSCs are stored frozen and after chemotherapy, they are returned via a transfusion. Once in the
body, the HSCs re-establish themselves in the bone marrow where they begin producing blood cells.
• Until microscopes became powerful enough to view individual cells, no-one knew for certain what living
organisms were made from
• A scientist called Robert Hooke came up with the term "cells" in the 1660's after examining the
structure of cork
• Matthias Schleiden and Theodor Schwann were two scientists who studied animal and plant cells
o In 1837, they came up with the idea that all living organisms are made of cells
o This idea is known as ‘cell theory’
o The cell theory is a unifying concept in biology (meaning it is universally accepted)
• The cell theory includes three main ideas:
o All living organisms are made up of one or more cells
o Cells are the basic functional unit (i.e. the basic unit of structure and organisation) in living
organisms
o New cells are produced from pre-existing cells
• Although cells vary in size and shape they all:
o Are surrounded by a membrane
o Contain genetic material
o Have chemical reactions occurring within the cell that are catalysed by enzymes
Cell Theory: Atypical Examples
NOS: Looking for trends and discrepancies; although most organisms conform to cell theory, there are
exceptions
• Scientists studying cells (e.g. Robert Hooke, Schwann & Schleiden and Pasteur)
discovered trends when making observations of organisms
• The organisms they examined, using microscopes, all appeared to be made of smaller compartments
(which we now refer to as cells). They discovered that even the smallest organisms, such as Amoeba,
were made from at least one cell
• However, advancements in technology (particularly around what can be detailed and seen under a
microscope) have enabled scientists to examine many more organisms and discrepancies have been
discovered which raise questions about whether cell theory applies to all organisms
Atypical examples
• Striated muscle fibres, aseptate fungal hyphae and giant alga are three examples of cells/tissue with
structures that question the integrity of the cell theory
Striated muscle fibres
• Striated muscle fibres (fused muscle cells) are:
o Longer than typical cells (up to 300 mm in length in comparison to a cardiac muscle cell which
has a length of 100 - 150 µm)
, o Have multiple nuclei surrounded by a single membrane (sarcolemma)
• These features question the cell theory because striated muscle cells are formed from multiple cells
which have fused together (which is how they have many nuclei rather than one) that work together as a
single unit, challenging the concept that cells work independently of each other even in a multicellular
organism
Aseptate fungal hyphae
• Fungi have many long, narrow branches called hyphae
• Hyphae have cell membranes, cell walls and some have septa
• Aseptate fungal hyphae do not have septa, thus these cells are multinucleated with continuous
cytoplasm
• This questions the cell theory because the cells have no end walls making them appear as one cell
Giant Alga (e.g. Acetabularia)
• Acetabularia can grow to heights of 100 mm, and yet consist of only one cell with a single nucleus
• Acetabularia have a relatively complex structure. They are divided into three parts: rhizoid, stalk and
cap
• The features above question the cell theory because the trend for most unicellular organisms is to be
small in size and simple in structure
Three atypical examples of the cell theory
, Stem Cells: Therapeutic Use
• Currently, there are very few therapeutic uses of stem cells, although scientists around the world are
actively involved in researching potential therapies
• The research is being carried out on embryonic (totipotent and pluripotent) and adult (multipotent)
stems cells
Use of embryonic stem cells
• Due to their ability to differentiate into multiple cell types, stem cells have huge potential in the
therapeutic treatment of disease
• For many countries, such as the USA and some countries within the EU, the use of embryonic stem
cells is banned, even for research
• In other countries, such as the UK, the use of embryonic stem cells is allowed for research but is
very tightly regulated
• Embryonic stem cells can be one of two potencies:
o Totipotent if taken in the first 3-4 days after fertilisation
o Pluripotent if taken on day 5
• The embryos used for research are often the waste (fertilised) embryos from in vitro fertilisation
treatment
o This means these embryos have the potential to develop into human beings
o This is why many people have ethical objections to using them in research or medicine
Stargardt's disease
• Stargardt's disease is the most common inherited form of juvenile macular degeneration and mainly
affects children and adolescents
• The macula is located in the central region of the retina and damage to this area limits our central vision
and colour perception
• The disease is commonly caused by a mutation of the ABCA4 gene resulting in a protein in the retina
malfunctioning, eventually leaving the person legally blind
• One treatment that was researched was the injection of retina cells derived from embryonic stem
cells into patients eyes. This treatment had success and no harmful side effects were experienced,
however trials are still ongoing
Use of multipotent adult stem cells
• As tissues, organs and organ systems develop, cells become more and more specialised
• Having differentiated and specialised to fulfil particular roles, most adult cells gradually lose the ability
to divide until, eventually, they are no longer able to divide
• However, small numbers of stem cells (known as adult stem cells) remain to produce new cells for the
essential processes of growth, cell replacement and tissue repair
• Although these adult stem cells can divide (by mitosis) an unlimited number of times, they are only able
to produce a limited range of cell types – they are multipotent
, o For example, the stem cells found in bone marrow (hematopoietic stem cells) are multipotent
adult stem cells – they can only differentiate into blood cells (red blood cells, monocytes,
neutrophils and lymphocytes)
o In adults, multipotent stem cells can be found throughout the body (eg. in the bone marrow,
skin, gut, heart and brain)
• Research is being carried out on stem cell therapy, which is the introduction of adult stem cells into
damaged tissue to treat diseases (eg. leukemia) and injuries (eg. skin burns)
Leukaemia
• Leukaemia is the generalised term referring to a group of cancers that develop in the bone marrow
• It is caused by mutations in genes resulting in the over-production of abnormal white blood
cells (leukocytes)
• To destroy these mutated cells in the bone marrow patients undergo chemotherapy
• However, as the chemicals injected into the patient's body during chemotherapy destroy all bone
marrow cells, hematopoietic stem cells (HSCs), the adult stem cells found in bone marrow, are
removed using a large needle before treatment
• These HSCs are stored frozen and after chemotherapy, they are returned via a transfusion. Once in the
body, the HSCs re-establish themselves in the bone marrow where they begin producing blood cells.
