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Topic 2 of 8 · Form 5

Membranes, the cell cycle and nucleic acids

Fluid mosaic model (phospholipids, cholesterol, glycolipids, glycoproteins, channel and carrier proteins); cell signalling; diffusion, facilitated diffusion, osmosis (water potential), active transport, endocytosis and exocytosis; surface area to volume ratio.

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Cell membranes and transport

Fluid mosaic model (phospholipids, cholesterol, glycolipids, glycoproteins, channel and carrier proteins); cell signalling; diffusion, facilitated diffusion, osmosis (water potential), active transport, endocytosis and exocytosis; surface area to volume ratio.

Worked example: A cube of agar has sides of 2 cm. Find its surface area to volume ratio.

SA = 6 × 4 = 24 cm²; V = 8 cm³ → 3 : 1

The mitotic cell cycle

Interphase (G1, S, G2), mitosis (prophase, metaphase, anaphase, telophase), cytokinesis; chromosomes, chromatids, centromeres, telomeres; stem cells; cancer from uncontrolled division.

Nucleic acids and protein synthesis

Structure of DNA and RNA; semi-conservative replication; transcription (RNA polymerase, mRNA); translation (ribosomes, tRNA, codons and anticodons); the genetic code; gene mutations (substitution, insertion, deletion) and their effects.

Exam tip: Explain how the structure of DNA (complementary base pairing) allows accurate replication.

Check yourself

  1. What happens during the S phase of interphase?
  2. Why does a deletion mutation usually have a greater effect than a substitution?
  3. What is the role of tRNA?
Show answers
  1. DNA replication.
  2. It causes a frameshift, changing all following codons.
  3. To carry specific amino acids to the ribosome and match anticodons to mRNA codons.
Next topicTransport in plants and mammals; gas exchange

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