![]() ![]() Rich blood supply to maintain a steep concentration gradientįor example, in the lungs there are structures called alveoli which are adapted for gas exchange. Thin walls to provide a short diffusion pathway In contrast, smaller organisms such as worms do not have a gas exchange system as there is a much shorter diffusion pathway to obtain the substances they need.Įxchange surfaces have the following features which increase the speed of diffusion: If we relied on diffusion to obtain these substances, the cells in the middle of our bodies would not receive much glucose and oxygen because of the large distance for diffusion. ![]() This is why larger mammals, such as humans, have lungs and a blood transport system to deliver all of the oxygen and glucose needed for cellular respiration. If we apply this idea to organisms, animals like worms and mice will have a large surface area to volume ratio whereas humans and elephants have a much smaller surface area to volume ratio.Īs the ratio between surface area and volume decreases, it becomes more important for the organism to have a specialised gas exchange system to deliver the substances needed for respiration and remove the waste products. As you inflate the balloon the ratio between the surface area and the volume decreases as the amount of air (volume) increases. A deflated balloon consists of mostly rubber (surface area) and not much air (volume). You can think about this by imagining a balloon. Smaller objects will always have a bigger surface area to volume ratio. This is important because they will rely on diffusion to obtain the oxygen and glucose it needs to take in for respiration and for the removal of waste products out of the cell. Single-celled organisms such as bacteria, have a rod-like shape which gives them a large surface area to volume ratio. Surface area – the larger the surface area, the more space there is for diffusion to take place Temperature – the higher the temperature, the more kinetic energy molecules have so they diffuse faster The size of the concentration gradient – the larger the difference in concentration, the faster the rate of diffusion There are several factors which increase the speed of diffusion: Another waste product called urea, which is a component of urine, diffuses out of cells and into the bloodstream where is it transported to the kidney for excretion. ![]() ![]() Carbon dioxide, the waste product of respiration, will diffuse out of cells into the bloodstream to be transported to the lungs. For example, oxygen moves from the bloodstream into our cells by diffusion where it is used for respiration. Some substances can move into and out of cells by diffusion through the cell surface membrane. Diffusion is the movement of molecules (either particles within a solution or gas particles) from an area of high concentration to an area of lower concentration i.e. ![]()
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