1. Cells as the basic units of life

1.1 The microscope in cell studies

An understanding of the principles of microscopy shows why light and electron microscopes have been essential in improving our knowledge of cells.

1. make temporary preparations of cellular material suitable for viewing with a light microscope

2. draw cells from microscope slides and photomicrographs

3. calculate magnifications of images and actual sizes of specimens from drawings, photomicrographs and electron micrographs (scanning and transmission)

4. use an eyepiece graticule and stage micrometer scale to make measurements and use the appropriate units, millimetre (mm), micrometre (µm) and nanometre (nm)

5. define resolution and magnification and explain the differences between these terms, with reference to light microscopy and electron microscopy

1.2 Cells as the basic units of living organisms

The cell is the basic unit of all living organisms. The interrelationships between these cell structures show how cells function to transfer energy, produce biological molecules including proteins and exchange substances with their surroundings. Prokaryotic cells and eukaryotic cells share some features, but the differences between them illustrate the divide between these two cell types.

1. recognise organelles and other cell structures found in eukaryotic cells and outline their structures and functions, limited to: • cell surface membrane

• nucleus, nuclear envelope and nucleolus

• rough endoplasmic reticulum

• smooth endoplasmic reticulum

• Golgi body (Golgi apparatus or Golgi complex)

• mitochondria (including the presence of small circular DNA)

• ribosomes (80S in the cytoplasm and 70S in chloroplasts and mitochondria)

• lysosomes

• centrioles and microtubules

• cilia

• microvilli

• chloroplasts (including the presence of small circular DNA)

• cell wall

• plasmodesmata

• large permanent vacuole and tonoplast of plant cells

2. describe and interpret photomicrographs, electron micrographs and drawings of typical plant and animal cells

3. compare the structure of typical plant and animal cells

4. state that cells use ATP from respiration for energy-requiring processes

5. outline key structural features of a prokaryotic cell as found in a typical bacterium, including: • unicellular • generally 1–5 µm diameter • peptidoglycan cell walls • circular DNA • 70S ribosomes • absence of organelles surrounded by double membranes

6. compare the structure of a prokaryotic cell as found in a typical bacterium with the structures of typical eukaryotic cells in plants and animals

7. state that all viruses are non-cellular structures with a nucleic acid core (either DNA or RNA) and a capsid made of protein, and that some viruses have an outer envelope made of phospholipids