an organism must has a large surface area to volume ratio in order to exchange material easier
in animals erythrocytes have a flat concave shape that allows them to carry more haemoglobin and also increases its surface area to volume ration so that the length and availability of a surface is less for the materials to travel
multi cellular organisms tend to have flat and elongated respiratory surfaces to allow for a higher surface area to volume ratio in order to increase the rate of gas exchange
the ilium in most mammals is flat and elongated and is covered with microvilli to increase surface area and to reduce the cells volume therefore reducing its surface area to volume ratio
hope that helps
