Biology- Transport in Animals

Transport systems    

  

ü Very small animals do not need a spate transport system, because all their cells are surrounded by the environment in which they live.

ü A larger organism has a complex anatomy so will have more than two layers of cells.

ü There are three main factors that influence the need for a transport system:

1)   Size

2)   Surface area to volume ratio

3)   Level of metabolic activity

1.   Size:

Cells inside a large organism are further from its surface- so diffusion pathway has increase.

The diffusion rate decreased, diffusion is too slow to supply all the needed nutrients.

2.   Surface areas to volume ratio:

Larger animals have a smaller surface area to volume ratio.

This means that each gram of tissue has a smaller area of body surface for exchange.

3.   Level of metabolic activity:
If an animal is very active, its cells need good supplies of nutrients and oxygen to supple the energy for movement.

ü An effective transport system includes:

1)   A fluid or medium carry nutrients, oxygen and wastes around the body

2)   A pump to create pressure that will push the blood around the body

3)   Exchange surfaces that enable substances to enter the blood and leave it again where they are needed. (capillaries)

ü Single circulatory system is when the blood flows around the body and through the hear once. Such as in a fish:

ü Heart to Gills to Body to heart

ü Double circulatory system has two separate circuits. One of which carried the blood to the lungs to pick up oxygen and the other carries the oxygen and nutrients around the body. The first circulation is known as pulmonary circulation and the second one is called a systemic circulation. Blood will flow through the heart twice.

ü In the single circulatory system of the fish:

1.   The blood pressure drops after the blood has passed through the capillaries of the gills

2.   As the blood flows through the body the pressure decreases so will not flow as quickly

3.   The rate at which oxygen and nutrients are delivered to respiring tissues, and CO2 and urea are removed, is limited.

4.   Fish are not as metabolically active as mammals, as they do not maintain their body temperature. Therefore, they need less energy. Their single circulatory system delivers sufficient oxygen and nutrients for their needs.

ü In the double circulatory system:

1.   The blood pressure must not be too high in the pulmonary circulation, otherwise it may damage the delicate capillaries in the lungs.

2.   The heart can increase the pressure of the blood after it has passed through the lungs, so the blood is under higher pressure as it flows to the body and flows more quickly.

3.   The systemic circulation can carry blood at a higher pressure than the pulmonary circulation.

ü Mammals are active animals and maintain their body temperature. Supplying the energy for activity and the heat needed to keep the body warm requires energy from food.