BRUNEI → Pre-University → GCE A Level


1. Cell structure
All organisms are composed of cells. Knowledge of their structure and function underpins much of biology. The fundamental differences between eukaryotic and prokaryotic cells are explored and provide useful biological background for the section on Infectious disease. Viruses are introduced as non-cellular structures, which gives candidates the opportunity to consider whether cells are a fundamental property of life.

The use of light microscopes is a fundamental skill that is developed in this section and applied throughout several other sections of the syllabus. Throughout the course, photomicrographs and electron micrographs from transmission and scanning electron microscopes should be studied.

Candidates will be expected to use the knowledge gained in this section to solve problems in familiar and unfamiliar contexts.

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.

a) compare the structure of typical animal and plant cells by making temporary preparations of living material and using photomicrographs

b) calculate the linear magnifications of drawings, photomicrographs and electron micrographs

c) use an eyepiece graticule and stage micrometer scale to measure cells and be familiar with units (millimetre, micrometre, nanometre) used in cell studies

d) explain and distinguish between resolution and magnification, with reference to light microscopy and electron microscopy

e) calculate actual sizes of specimens from drawings, photomicrographs and electron micrographs

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.

a) describe and interpret electron micrographs and drawings of typical animal and plant cells as seen with the electron microscope

b) recognise the following eukaryotic cell structures and outline their functions:

• cell surface membrane

• nucleus, nuclear envelope and nucleolus

• rough endoplasmic reticulum

• smooth endoplasmic reticulum

• Golgi body (Golgi apparatus or Golgi complex)

• mitochondria (including small circular DNA)

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

• lysosomes

• centrioles and microtubules

• chloroplasts (including small circular DNA)

• cell wall

• plasmodesmata

• large permanent vacuole and tonoplast of plant cells

c) state that ATP is produced in mitochondria and chloroplasts and outline the role of ATP in cells

d) outline key structural features of typical prokaryotic cells as seen in a typical bacterium (including: unicellular, 1–5μm diameter, peptidoglycan cell walls, lack of membrane-bound organelles, naked circular DNA, 70S ribosomes)

e) compare and contrast the structure of typical prokaryotic cells with typical eukaryotic cells (reference to mesosomes should not be included)

f) outline the key features of viruses as non-cellular structures (limited to protein coat and DNA/RNA)
  • Notes
Completion rules
  • All units must be completed