ESSENTIAL CONTENT BREAK-DOWN
- Cell theory
- Unicellular and multicellular organisms and the idea that an ORGANISM, whether unicellular or multicellular, carries out all the functions of life
- Surface area : volume ratio and its impact on the functioning of cells
- Emergent properties
- Cell differentiation:
- specialisation of cells
- gene expression
- ‘raw, mother’ cells, known as stem cells, differentiate into specialised cells
- The wider aspects of stem cell biology especially in medicine
- The use of microscopes and making scale drawings
The important concepts, ideas and implications follow. Otherwise much of the content – plant v animal v prokaryotic cells, microscope use, scale, cells-tissues-organs-etc, is covered in the READING (at the end of this page) or should already be reasonably well known and understood.
Cell theory has moved on from the three essential tenets that we all know:
- Cells are the smallest units of an organism capable of surviving independently
- All living organisms are comprised of one or more cells
- New cells are derived from existing cells
In addition, we now add:
- Metabolic processes take place in cells
- Cells possess the genetic material of an organism which is passed from parent to daughter cells
The origins of cell theory is an interesting insight into the way science makes advances (NoS):
(Biology Second Edition, C.J. Clegg)
Cell theory timelines:
Cell theory powerpoint (not very brilliant, so give it a miss if you don’t have time!): cell-theory-ppt
There are exceptions to the cell theory – justifiable arguments as to why the theory might not apply to all and every organism. (Nature of Science NoS)
FUNCTIONS OF LIFE
What you might simply have known as The Characteristics of Living Things. The idea is that ALL living things, however simple (ie unicellular or multicellular) must carry out all the functions of life, otherwise they are not living.
Note that the IB syllabus looks at this Topic through two unicellular organisms – the animal, Paramecium and photosynthesising green plant, Chlorella.
SIZE IN BIOLOGY
Forget centimetres and focus on metres! Then it all becomes easy.
- 1000 metres = 1 kilometre (km)
- 1/1000 metre (10-3m) = 1 millimetre (mm)
- 1/1000 mm (10-6m) = 1 micrometre (µm)
- 1/1000 µm (10-9m) = 1 nanometre (nm)
- Physicists go smaller than this to Ångström (Å) units, one of which is 1/10 of 1 nanometre (10-10m)
This is such an important concept and applies not just at the biological, cellular level but also upwards through ecological levels.
STEM CELL BIOLOGY
STEM CELLS are undifferentiated biological cells that can differentiate into specialized cells and can divide (through mitosis) to produce more stem cells. They are found in multicellular organisms. (Thankyou Wikipedia!)
Plants contain various areas known as meristems from which cells can develop, differentiated and specialise – apical meristems and cambium tissue are the best known. Multicellular animals, such as humans, of course have embryonic stem cells and various sites and organs around the body where other stem cells are found, such as bone marrow, blood and blood vessels, liver and skin.
This is so very much the medical biology of today. A lot of hope is being pinned on the idea that raw, ‘mother’ cells, which are unspecialised but contain the genetic blueprint for whatever type of cell and cell function, can be developed into differentiated and specialised cells, tissues and ultimately organs. It is a medical science in its infancy and with a great deal of hype but, so far anyway, not a lot of genuine results. Watvch this space!
The syllabus contains references to stem cells, not just in ‘Understandings’, but also in ‘Utilization’, ‘Applications and Skills’ and ‘Aims’. Take note of this importance given to the topic!
SURFACE AREA : VOLUME RATIOS – Why cells cannot be huge
IB likes this concept! The idea that as volume increases as a cubic (x³) function, surface area increases only as a square (x²) function. This limits the size of cells – they cannot get so big (their volume cannot increase too much) because their outer surface no longer would be sufficient for the movement to and fro of all the nutrients and chemicals which the cell requires. Also distances would become unmanageable inside the cytoplasm of the cell – in a huge cell, many parts of the cell would be so far from the surface membrane that diffusion and movement of substances in the cytoplasm would be impossibly slow or not happen at all.
If you want to carry out a really neat investigation into this phenomenon, all you need are some scissors, cardboard, glue, sand and a weighing balance.
(These pages are from Biology Second Edition, C.J. Clegg, Hodder Education 2014)