In this topic of IBDP Biology, we will learn about cells.
Cell theory
- All living things are made of cells.
- Cells are the smallest unit of life.
- Existing cells have come from other cells.
- Stated in this way Cell Theory might be attributed to Schleiden and Schwann (1838).
- Robert Hooke first coined the term 'cell' after observing the structure of cork in 1655.
- The first observation of living cells was by Anton van Leeuwenhoek in 1674.
The evidence of cell theory
Referring to the IBDP Biology specification, The cell theory has amassed tremendous credibility through the use of the microscope in the following:
- Robert Hooke- studied cork and found little tiny compartments that he called cells
- Antonie van Leeuwenhoek- observed the first living cells, called them 'animalcules' meaning little animals
- Schleiden- stated that plants are made of 'independent, separate beings' called cells
- Schwann- made a similar statement to Schleiden about animals
State that unicellular organisms carry out all of the functions of life
- Metabolism; chemical reactions inside the cell, including cell respiration to release energy
- Response; perceiving and responding to changes in the environment
- Homeostasis; keeping conditions inside the organism within tolerable limits
- Growth; an irreversible increase in size
- Reproduction; producing offspring either sexually or asexually
- Nutrition; obtaining food, to provide energy and the materials needed for growth
- Defense; protection against enemies
Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit
nm = nanometer µm = micrometer
- Molecules - 1 nm
- Thickness of membrane - 10 nm
- Viruses - 100 nm
- Bacteria - 1 µm
- Organelles - up to 10 µm
- Most cells - up to 100 µm (three dimensional nature/shape)
Magnification
If you look at the IBDP Biology curriculum, Magnification = measured size of object/ actual size of object
Explain the importance of the surface area to volume ratio as a factor limiting cell size.
- A cell needs a large surface area in order to carry out metabolic functions (as chemical reactions require a surface). As a cell grows, it needs to carry out more and more reactions. Therefore, since a cell has to maintain a certain surface area to volume ratio, its size is limited.
- The rate of exchange of materials (nutrients/waste) and energy (heat) is a function of its surface area.
Thus: As a cell grows in size (volume), the distance increases between the cytoplasm at the center of the cell and the cell membrane. The rate of chemical exchange with the surrounding environment may hence become too low to maintain the cell. It is not able to excrete waste quickly enough or take in important minerals.
Volume of a cell determines requirements while surface area determines supply.
State that multicelluar organisms show emergent properties
- When it comes to IBDP Biology, Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts
That's the end of this topic.