IB Biology 2016 syllabus

1. 1. CELL THEORY
1.1 – According to the cell
theory, living things are
composed of cells
1.5 – cells can only be
formed by division of pre-
existing cells

2. CELL THEORY
o The development of cell theory has taken hundreds of years
o Much of its development parallels with advances in technology –
including staining techniques and the development of both light and
electron microscopes
o The three main principles of cell theory are:
1. All organisms are composed of one or more cells
2. Cells are the smallest units of life
3. All cells come from pre-existing cells

3. CELL THEORY
o Prior to cell theory – Spontaneous generation
was largely accepted
oRobert Hooke – made important improvements
to the microscope and was the first to describe
cells in 1665
o Maggots in meat example – Francesco Redi
1668
o Antoine van Leeuwenhoek (lens maker) also
observed living cells in 1680s
o As microscope technology further improved,
scientists became less sceptical of these ‘artificial
images’ and these observations were accepted as
Brief history of the
microscope: the tube that
changed the world

4. CELL THEORY
o 1839 - Matthias Schleiden (studied plants) and Theodore Schwann
(studied animals) formulated the first two main points of cell theory
o The last point of cell theory was developed by Rudolf Virchow 1855
o Walther Fleming 1879 confirmed Virchow’s observations and named
the process ‘mitosis’
o The experiment conducted by Louis Pasteur provided the scientific
evidence in support of this third point
o The wacky history of cell theory

5. COMPARISON
Historical Modern Day
1839 – Schwann/Schleiden
1. The cell is the unit of structure
of all living things
2. The cell exists as a distinct
entity and as a building block in
the construction of organisms
1855 – Virchow
3. Where a cell exists there must
have been a pre-existing cell
1. All living things are made of
cells
2. The cell is the basic structural
and functional units of
organisms
3. All cells come from pre-existing
cells

6. CELL THEORY AND LOUIS PASTEUR
o Louis Pasteur performed the famous swan-necked flask experiment
to prove the third main point of cell theory – this experiment
ultimately disproved the long standing idea of ‘spontaneous
generation’
o Louis Pasteurs experiment (brief)
o Louis Pasteurs experiment (explained)

7. THE EM AND DEVELOPMENTS IN
CELL THEORY
o The development of the Electron Microscope (EM) has allowed
scientists to study parts of cells that are too small to be seen with a
light microscope
o EM’s are now linked to computers which allows the study of sub-
cellular structures in enormous detail, providing evidence of their
functioning. Used in areas such as genetics and ecology.
o This technology has improved our understanding of the cell and as a
result there are modern day additions to cell theory [HL]:
4. Cells contain hereditary information which is passed on during cell
division
5. All cells have the same basic chemical composition
6. All energy flow (resulting from chemical reactions) of life occurs
within cells

8. TEM & SEM

9. EXCEPTIONS TO CELL THEORY
o Scientists use the term theory to represent a well substantiated
natural phenomenon
o A theory comes from extensive observation, experimentation and
logical inferences.
o Cell theory is a good example of this – it has been modified since its
first proposal (with revision of existing points and addition of new
ones)
o As biology has advanced and technology improved we have
examined many different types of cells. Some cells are different to
the ‘normal cells’ that we see in most organisms. These are as
follows…

10. EXCEPTIONS TO CELL THEORY
o Striated muscle:
o This is the type of tissue that we use to move our
body
o The building blocks of this tissue are muscle fibres
which are similar to cells.
o They are surrounded by a membrane and are formed
by pre-existing cells
o However, they are much larger than most animal cells
and instead of having one nucleus they have many
(sometimes hundreds)

11. EXCEPTIONS TO CELL THEORY
o Aseptate fungal hyphae:
o Fungi consist of narrow thread-like structures called hyphae.
Hyphae are usually white in colour and have a fluffy
appearance
o They have a cell membrane and outside that a cell wall
o In some types of fungi the hyphae are divided up into small
cell-like sections by cross walls called septa
o However, in aspetate fungi there are no septa – each hyphae is
an uninterrupted tube like structure with many nuclei spread
along it

12. EXCEPTIONS TO CELL THEORY
o Giant algae:
o Algae are organisms that feed themselves by
photosynthesis and store their genes inside nuclei, but
they are simpler in organisation and structure than
plants
o Many algae consist of one microscopic cell. There are
vast numbers of these in the oceans and they form the
basis of marine food chains
o However there are algae that grow to a much larger
size, yet are still single cells – known as giant algae.

13. EXCEPTIONS TO CELL THEORY
o Concerns as to how the following can be explained by cell theory
have also arisen:
o Viruses?
o If all cells come from pre-existing cells – how can you explain the ‘first cell’
without spontaneous generation?

14. MODELLING PASTEUR’S
EXPERIMENT
AIM 6 [1.5] – Pasteur’s
experiment can be
repeated using modern
apparatus