As terrestrial organisms scale up in size, simple diffusion across their outer body surface becomes insufficient to meet metabolic demands. In insects, a specialized internal gas exchange system has evolved to overcome this challenge of size by delivering oxygen directly to active tissues.
Which of the following shows the correct sequence of structures that oxygen passes through as it diffuses from the atmosphere to the site of cellular respiration?
tracheae→spiracles→tracheoles→respiring cells\text{tracheae} \rightarrow \text{spiracles} \rightarrow \text{tracheoles} \rightarrow \text{respiring cells}tracheae→spiracles→tracheoles→respiring cells
spiracles→tracheae→tracheoles→respiring cells\text{spiracles} \rightarrow \text{tracheae} \rightarrow \text{tracheoles} \rightarrow \text{respiring cells}spiracles→tracheae→tracheoles→respiring cells
spiracles→tracheoles→tracheae→respiring cells\text{spiracles} \rightarrow \text{tracheoles} \rightarrow \text{tracheae} \rightarrow \text{respiring cells}spiracles→tracheoles→tracheae→respiring cells
spiracles→tracheae→bronchioles→respiring cells\text{spiracles} \rightarrow \text{tracheae} \rightarrow \text{bronchioles} \rightarrow \text{respiring cells}spiracles→tracheae→bronchioles→respiring cells
17 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.