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2 Structure and Functions in Living Organisms

This topic area is the structural core of the course. It connects cells, molecules and movement across membranes to whole-organism systems such as transport, gas exchange, excretion and coordination.

Core Role

  • Build from cell structure and organisation to whole-organism systems.
  • Link biological molecules and enzymes directly to transport, nutrition and respiration.
  • Carry practical patterns that recur across food tests, enzymes, osmosis, photosynthesis and respiration investigations.

Topic Pages

  • 2a Level of Organisation: Biology moves from the smallest working parts of cells to whole systems. This hierarchy matters because each level depends on the successful co-operation of the level below it. 1 learning objective.
  • 2b Cell Structure: Cell structure links what cells contain to what they can do. In this course the key comparisons are between plant and animal cells, and between unspecialised cells, specialised cells and stem cells. 3 learning objectives.
  • 2c Biological Molecules: Biological molecules supply energy, build structures and allow reactions to happen at useful rates. The main focus here is the relationship between basic chemical building blocks, food tests and enzyme function. 3 learning objectives.
  • 2d Movement of Substances into and out of Cells: Exchange across membranes is one of the big unifying ideas in biology. The key comparisons are between passive movement down gradients and active movement that uses energy. 3 learning objectives.
  • 2e Nutrition: Nutrition in this course brings plant food production and human feeding into one topic. The link between them is that both depend on molecules being made, broken down and transported where they are needed. 4 learning objectives.
  • 2f Respiration: Respiration is how cells release usable energy from food. The main distinctions here are between aerobic and anaerobic pathways and between energy release in living tissue and what you can measure in practical work. 2 learning objectives.
  • 2g Gas Exchange: Gas exchange links diffusion to whole-organism survival. Plants need carbon dioxide and oxygen moving in opposite directions at different times, while humans need a ventilated surface that keeps diffusion rapid. 3 learning objectives.
  • 2h Transport: Transport systems solve the problem that large multicellular organisms cannot rely on diffusion alone. In this topic the course compares plant transport in xylem and phloem with animal transport in blood and the circulation. 4 learning objectives.
  • 2i Excretion: Excretion is about removing waste products of metabolism and keeping water and ion balance under control. In this course that means linking plant waste gases with the much more detailed kidney story in humans. 3 learning objectives.
  • 2j Co-ordination and Response: Co-ordination links stimulus detection to effective response. The topic includes both plant responses and the faster nervous or hormonal control systems used in humans to maintain stable internal conditions. 4 learning objectives.