9. 2 Cell walls of flowering plants 287 Algal and protist cell walls 301 9. 3 9. 4 Fungal cells walls 304 Overview 305 9. 5 10 Animal hormones and local mediators 309 10. 1 Introduction 309 10. 2 Structure and classification of animal hormones and local mediators 309 10. 3 Structures of receptors in the cell membrane for hormones and local mediators 311 10. 4 Cyclic AMP as a second messenger 313 10. 5 Signalling by cyclic GMP: atrial naturetic peptides and nitric oxide 321 10. 6 Inositol trisphosphate and diacylglycerol as second messengers 322 10. 7 Receptors signalling through tyrosine phosphorylation 328 10. 8 Steroid hormones penetrate the cell membrane 330 10. 9 Overview 335 11 Plant hormones 339 11. 1 Introduction 339 11. 2 Biosynthesis and general effects of major plant hormones 342 11. 3 Mechanisms of plant hormone action 346 11. 4 Second messengers 351 11. 5 Other plant growth regulators 352 11. 6 Interactive effects of plant hormones 357 11. 7 Overview 358 12 Nerves, neurotransmitters and their receptors 361 12. 1 Introduction 361 12. 2 Resting potential 363 12. 3 Action potential 364 12. 4 Synaptic transmission, neurotransmitters and receptors 370 12. 5 The generation of action potentials by sensory stimuli 380 12. 6 Overview 388 13 Muscle contraction 391 13. 1 Introduction 391 The cell biology of skeletal muscle 392 13. 2 13. 3 Other muscle types 396 13. 4 Structural proteins of muscle 398 Energetics of muscle contraction 410 13.