1. Cells

1.1     Cell theory

1.1.1   State one contribution made by each of the following:

Robert Hooke, Anton van Leeuwenhoek, Matthias Schleiden, Theodor Schwann and Rudolph Virchow.

1590                Jansen invents the compound microscope (two lenses)

1665                Robert Hooke examines cork with an improved compound microscope; coins the term 'cell'.

1650-1700       Anton van Leeuwenhoek, using a simple lens (x2OO) observes unicellular organisms and nuclei. Describes bacteria as ‘animalcules'.

1838                Schleiden concludes that all plants are made of cells or their derivatives, a theory he called phytogenesis.

1839                Schwann working with Schleiden proposed the cell theory, which suggested that all animals and plants were made of cells. and that within an organism these cells are identical.

1840                Purkinje coined the term protoplasm for the living contents of cells.

1855                Virchow studied pathogenic organisms and showed that 'omnis cellula e cellula’ - all cells arise from pre-existing cells (by cell division). This  way will make clear the fact that advances in  technology and manipulative techniques had to be developed, before any theory could be developed.

1.1.2   Describe three advantages of using light microscopes.

1.1.3   Describe two advantages of using electron microscopes.

In comparing electron and light microscopes, the terms 'resolution' and 'magnification' need to be explained.

Details of differences between the types of electron microscopes or the principles of how they work is not required.

1.1.4   Define organelle.

1.1.5  Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units.

Appreciation of relative size is required, such as:

molecules (I nm), thickness of membranes (10 nm), viruses (100 nm), bacteria (1 μ), organelles (up to 10 μm),  cells (up to 100 μm).

The three dimensional nature/shape of cells should be understood.

1.1.6   Explain the importance of the surface area to volume ratio as a factor limiting cell size.

The rate of metabolism of a cell is a function of its mass/volume; whereas the rate of exchange of materials and energy (heat) is a function of its surface area.

Study simple mathematical models involving cubes and the changes in the ratio that occur as the sides increase by one unit could be compared.

1.2       Prokaryotic cell structure

1.2.1    Draw a generalised prokaryotic cell as seen in electronmicrographs.

Study pictures of bacteria as seen under transmission EM and scanning EM to see the structure.

Classification of prokaryotes and the Gram stain are not required. Diagram should show the structures specified in 1.2.2.

1.2.2    State one function for each of the following:            ribosomes, mesosome, slime capsule, cell wall, flagellum, cell surface membrane, plasmid and naked nucleic acid

1.3     Eukaryotic cell structure

1.3.1   Discuss the possible origin of eukaryotic cells, referring to the theory of endosymbiosis.

1.3.2   Draw a diagram to show the ultrastructure of a generalised animal cell as seen in electron micrographs.

1.3.3   State one function of each of these organelles:     ribosome, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion, nucleus and chloroplast.

13.4     State two similarities between prokaryotic and eukaryotic cells.

13.5     State two differences between the eukaryotic nucleus and prokaryotic nuclear material.

1.3.6   Describe three differences between plant and animal cells.  

                                                      Plant Cell                                                                    Animal Cell

1.4 - Membranes

1.4.1    Draw a diagram showing the fluid mosaic model of a cell membrane. Include;

Watch this video of the cell membrane

Use the term "Cell surface membrane" rather than plasma membrane. Mention the outside of the cell membrane (outer face and the links with the protruding proteins.

1.4.2    Explain how the hydrophobic and hydrophilic properties of phospholipids help maintain the structure of cell membranes.

1.4.3    Define diffusion  

1.4.4    State that Osmosis is the passive movement of water molecules, across a partially permeable membrane from a region of lower solute concentration to a region of higher solute concentration.  

Discuss principles of permeability, non-permeability and partial permeability with reference to water and solutes.

1.4.5    Describe passive transport across membranes in terms of diffusion including osmosis

Osmosis could be refered to as a special sort of diffusion

1.4.6    Describe active transport across membranes including the roles of protein carriers, ATP and a concentration gradient ("against a concentration gradient")  

Mention carrier-assisted transport and the role of the transport proteins in the membrane which results in high selectivity.  Also 'favourable' concentration gradients for facilitated (diffusion) transport.  Students could predict conditions needed for active transport.  Offer examples of cases of "against -a-concentration" gradient (eg., some algae pumping iodine inwards to reach a 2 x 10⁶ higher concentration inside).  Membrane pumps should be mentioned avoiding biochemical details.

1.4.7    Compare endocytosis(phagocytosis and pinocytosis) and exocytosis

Phagocytosis could be likened to the cell 'eating' and pinocytosis to the cell 'drinking'.  Vesicle-mediated transport to be discussed with endocytosis and it's types (phago and pinocytosis)

1. 5 - Cell division - Mitosis

1.5.1    State that all cells arise from division of other cells

1.5.2    Describe the cell cycle as an alternation between interphase and mitosis  

1.5.3    State that interphase is an active period in the life of a cell, where many biochemical reactions, DNA transcription and DNA replication occur.  

In this core section the names of the phases are not required.  Students should know that in most cells interphase is a longer period than mitosis.

1.5.4    Outline how replicated DNA molecules (chromosomes) are moved to opposite ends of the cell by microtubules.  

The terms centriole, centrosome, centromere and chromatid are not expected.  A simple series of diagrams could be used.

1.5.5    State that the products of mitosis are 2 genetically identical nuclei  

It is important to concentrate on the student understanding the general principles of the process; the relationship between the DNA molecules and the changes observed in the chromosomes and the final product of the process - two genetically identical nuclei. 

Mitotic division of a Diploid somatic cell (2n)

1.5.6    State that tumours(cancers) are  result of uncontrolled cell division and that these can occur in any organ.