BRAINCAKEGas Exchange
Revision notes for Gas Exchange in Edexcel Biology (8BI0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- 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.