BRAINCAKEGas Exchange
Revision notes for Gas Exchange in Edexcel Biology B (8BI0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Gas Exchange in Small OrganismsAll organisms need to take in oxygen for aerobic respiration and get rid of carbon dioxide.
- Surface Area to Volume RatioThe surface area to volume ratio (SA:V) compares how much surface an object has with how much volume it contains.
- Gas Exchange in Large OrganismsLarge multicellular organisms cannot rely on diffusion across their body surface for gas exchange, for three main reasons: • They have a low surface…
- Factors Affecting the Rate of DiffusionThe rate at which a gas diffuses across an exchange surface depends on three main factors.
- Effective Gas Exchange SystemsAn effective gas exchange system maximises the rate of diffusion described by Fick's law.
- The Human Gas Exchange SystemThe human gas exchange system is inside the chest cavity (thorax).
- Gas Exchange in the AlveoliGas exchange in the lungs takes place across the walls of the alveoli.
- Adaptations of the Human Gas Exchange SystemLarge Surface Area, Short Diffusion Distance, Steep Concentration Gradient These are the three key adaptations that make the human lungs so…
- BreathingBreathing (ventilation) is the movement of air into and out of the lungs.
- InhalationInhalation (inspiration) is an active process: it needs muscle contraction, and therefore energy from ATP.
- ExhalationExhalation (expiration) at rest is mainly a passive process: it happens when the muscles used for inhalation relax, so little extra energy is needed.
- Protecting the LungsEvery breath brings dust, pollen, bacteria and viruses into the airways.
- Gas Exchange in InsectsInsects are small, so they have a large surface area to volume ratio.
- The Tracheal SystemThe tracheal system is a network of air-filled tubes that carries oxygen from the spiracles directly to every respiring cell of an insect. •…
- Very Active InsectsAt rest, diffusion through the tracheal system supplies an insect with enough oxygen.
- Gas Exchange in FishFish face a harder gas exchange problem than land animals, because water is a poor source of oxygen: • water holds far less dissolved oxygen than…
- Fish GillsThe gills of a bony fish are a highly folded exchange surface with a structure built for fast diffusion. • On each side of the head there are…
- Ventilating the GillsTo keep a steep concentration gradient at the gills, a bony fish must keep a continuous, one-way flow of water over them, even when it is not…
- The Countercurrent Exchange SystemIn the gill lamellae, blood flows in the opposite direction to the water flowing over them.
- Gas Exchange in PlantsPlants, like animals, respire all the time, so their cells need a constant supply of oxygen and must remove carbon dioxide.
- StomataStomata (singular: stoma) are small pores in the epidermis of leaves and young stems through which gases diffuse in and out.
- Opening and Closing the StomataGuard cells open and close the stomata by changing their turgidity.
- LenticelsWoody stems and roots are covered by bark, whose outer layer is made of cork.
On the specification
- 4.1 Surface area to volume ratio
- 4.3 Gas exchange