Transport systems in multicellular animals

Why do organisms need transport systems

1. Distance to inner mass cells too great

2. SA:V ratio too small for sufficient diffusion of materials to/ from cells

3. Too active for diffusion to provide sufficient exchange of materials

4. Remove waste from cells such as CO₂

5. Transport molecules around body

6. Move digested food to cells for respiration and other uses

What is mass transport systems

Substances in a mass of fluid with a means of moving the fluid around body

What are open circulatory systems

Blood empties into body cavities and there is low pressure, and slow flow

Describe open circulatory systems in insects

• Haemolymph fills body cavity (haemocoel), directly bathes tissues, supplying nutrients and removing wastes

• Dorsal tube acts as a heart draws haemolymph in through open-ended pores called ostia back into heart when it relaxes

• Peristaltic contractions pump haemolymph forward to the head, where it empties back into haemocoel.

• Large/ active insect have vessels to help deliver haemolymph efficiently to active tissue such as legs and wings.

What are the advantages of open circulatory systems

• Requires little energy to transport haemolymph

• In insects they have a tracheal system to handle gas exchange

What are the disadvantages of open circulatory systems

• Haemolymph moves at low pressure so slow flow

• Organism cannot control or vary haemolymph being transported to different organs

• Haemolymph does not create a diffusion gradient so less efficient

• Unsuitable for larger animals

Descibe closed circulatory systems

Blood stays in vessels, high pressure so faster transport. Two main types

Single closed system

Double close system

Describe single closed system

Blood stays in vessels, blood passes heart once for every complete circuit of the body. Found in poikilothermic organisms ( body temp fluctuates with its surroundings). Tissue fluid moves out of vessels to bate cells and exchange materials.

An example of animal which uses a single closed system are fish

What are the advantages of single closed systems

• Blood stays inside vessels so can be pumped at high pressures

• Blood vessels can vary their width to control how much blood reaches different tissues

• Faster and more efficient delivery of oxygen and nutrients and quicker removal of waste by diffusion

What are the disadvantages of single closed systems

• In fish blood pressure drops as it passes narrow gill capillaries so slows blood flow

• Blood still flows slow, less suitable for large, active animals

Describe what a double closed circulatory system is

Blood passes through heart twice per complete circuit

Describe double closed circulatory systems in birds and mammals

Uses two circuits:

• Pulmonary circuit- carries blood to lungs for gas exchange

• Systemic circuit- delivers blood to the rest of the body for material exchange with cells

Heart has evolved to pump both circuits simultaneously, so blood passes through heart twice for one complete circuit of the body.

What are the advantages of double closed circulatory systems

• Blood flows quickly

• Systemic circuit ensures a high pressure supply to the body

• System delivers enough oxygen and nutrients to support highly active, warm-blooded organisms

• Oxygenated and deoxygenated blood kept separate so blood from lungs can be re-pressurised to be pumped to rest of body without damaging lungs

• Blood sent to rest of body at high pressure increasing rate of oxygen delivery to tissues, supports metabolic rates

Why do mammals require transport systems but smaller organisms don’t

• Mammals have small SA:V so diffusion alone too slow

• Mammals have a high metabolic rate

• Need to deliver nutrients to specific organs

• Smaller organisms have small diffusion distances due to large SA:V