3A

Exchange substances with the environment:

1) Cells take in O2 for respiration + nutrients

2) Excrete waste products like CO2 and are

3) Most organisms need to stay at the same temp, so heat is exchanged. How easy the exchange depends on the SA: vol ratio

Smaller animals have higher SA: vol ratio

Multicellular organisms need exchange organs and mass transport systems:

An organism needs to supply energy to every cell with substances and remove waste product from every cell to avoid damage                                          

1) in single-celled organisms, substances can diffuse directly into/out of cell across cell surface membrane. The diffusion rate is quick as substances have to travel small distances

2)in multicellular animals, diffusion across the outer membrane is too slow as some cells deep within the body - big distance from outside environment                                            

Larger animals have low SA; vol ratio, difficult to change enough substances to supply a large vol through a small outer surface                                                                                             Multicellular organisms need specialised exchange organs and an efficient system to carry substances to and from individual cells - mass transport

In mammals, mass transport refers to the circulatory system, which uses blood to carry O2 and glucose around the body. Its also carries hormones, antibodies + waste. Mass transport in plants involves the transport of water and solutes in the xylem and phloem (using water potential). 

Body size and shape affect heat exchange:

Size - the rate of heat loss from an organism depends on it SA. If an organism has. a large vol its SA is small. This makes it harder for it to lose heat from its body. If an organism is small is SA is large, so heat is lost more easily. This means smaller organisms need a relatively high metabolic rate, in order to generate enough heat to stay warm. 

Shape - Animals with a small compact shape have a small SA relative to their vol - minimizing heat loss. Animals with less compact shape have larger SA relative to vol - increases heat loss. The shape of an animal depends on the temp of the environment. 

Behavioural and physiological adaptations to aid exchange:

Animals with high SA: vol ratio loses more water as evaporates from the surface. Some small desert animals have kidney structure adaptation so that they produce less urine to compensate. 

to support high metabolic rates, small animals in cold region need to eat large amounts of high energy foods e.g seeds and nuts

Smaller mammals may have thick layers of fur/hibernate

Larger…