Transport in Animals Flashcards
The Need for a Transport System
For O2 and nutrients to grow & survive, to remove waste products (CO2 and urea) so these don’t build up and become toxic. Also transport of hormones and heat.
• Single-celled animals don’t need a circulatory system as their cells are surrounded by/very close to the environment they live in, diffusion will supply all the O2 and nutrients the cell needs.
• Multicellular animals will have more than 2 layers of cells, the diffusion pathway becomes too long, so diffusion will be too slow to supply the requirements to cells.
Factors that influence the need for a transport system:
Size
Surface area to volume ratio
Level of metabolic activity
Size
Cells inside large organisms are further from its surface – diffusion pathway is increased. The rate of diffusion is reduced and too slow to supply the cells. Also, the outer layer of cells use up the supplies so less reach the cells deep inside the body.
Surface area to volume ratio:
Multicellular organisms have a small SA:V ratio – the tissue in their body doesn’t have sufficient area of the body surface through which exchange can occur, diffusion is not sufficient to supply the cells with O2/nutrients for aerobic respiration, therefore a transport system is needed.
Level of metabolic activity:
Animals need energy from food for movement, the energy is released from aerobic respiration, which requires O2. The cells of active animals (multicellular) need good supplies of nutrients (glucose) and O2, animals that keep themselves warm (mammals) need even more energy.
Features of an effective transport system:
• Fluid/medium to carry O2, nutrient and wastes around the body – blood.
• Pump to create pressure to push the fluid around – heart.
• Exchange surfaces to enable substances to enter the fluid and leave again when needed – capillaries.
Efficiency – tubes/vessels to carry blood by mass flow, and 2 circuits, one to pick up O2 and another to deliver it to tissues.
