2.3.3 - Transport (Animals- open/closed)

Question 1

Open circulatory system in animals

Answer 1

• Circulating fluid pumped through open-ended vessels into a cavity that surrounds organs → cells bathed in fluid
• Nutrients and wastes exchanged from fluid via diffusion, then fluid gradually makes its way back into the circulatory system.
• As circulating and interstitial fluid are mixed, it is not possible to determine which is blood and which is interstitial fluid. The substance is hence called haemolymph.
• Heart does not need to be very strong

Pros:
- Lack of an extensive blood vessel network → less energy to maintain
- No need to maintain internal pressure, so organisms can live at greath depths

Cons:
- Slow metabolism due to slow blood flow, unsuited for active animals and endotherms
- Less efficient because RBC concentration in circulating fluid diluted by mixing with interstitial fluid
- Limits the size of organism because haemolymph must be able to directly bathe against all cells
- NO TRANSPORT OF GASES

E.g. arthropods, such as insects and crustaceans, and some molluscs, such as snails.

Question 2

Closed circulatory system

Answer 2

• Blood circulates in closed vessels → interstitial and circulating fluid are distinct
• Blood is pumped through vessels by the heart
• Blood not in direct contact with tissues
• Nutrients, gases, and wastes exchanged. Blood then returns to the heart in a set process
• Heart needs to be strong to pump blood at high pressure

Pros:
- System reaches all parts of the body, so organisms can be larger in size
- Required by endotherms and active animals as nutrient exchange is efficient. Separation of interstitial and circulating fluid allows more oxygen to be carried to cells by blood → faster metabolism

Cons:
- Uses more energy as it is more complex
- Need for the maintenance of internal pressure → organisms cannot survive at great depths

E.g. all vertebrates, and some invertebrate animals such as worms

Question 3

Vertebrate circulatory system: fish

Answer 3

• 1 circuit: 2-chambered heart pumps blood into the systemic circuit.
• Atrium receives deoxygenated blood and pumps it into the ventricle, which pumps the blood out to the gills to be reoxygenated at the gill capillaries, which are arranged countercurrent to water to increase oxygen uptake of blood to 95%
• From the gills, blood flows to the rest of the body and returns to the heart
• Simple and energy efficient

Question 4

Amphibian

Answer 4

• 2 circuits: systemic and pulmocutaneous (oxygenates blood at skin and lungs)
• 3 chambered heart has 2 atria (right deoxygenated, left oxygenated) and 1 ventricle rather than the two-chambered heart of a fish → oxygenated and deoxygenated blood mix, reducing efficiency of oxygenation
• However, mixing of blood allows there to be enough pressure of blood that it can be pumped to the body and to the lungs
• Ventricle pumps blood to the lungs and to the body

Question 5

Vertebrate circulatory system comparisons (link to evolution)

Answer 5

In amphibians, reptiles, birds or mammals have a more evolved circulatory system than fishes. Because fish are evolutionary older/primitive than other vertebrates (others evolved from fishes)

These vertebrates have pulmonary and systemic circulation.

Question 6

Reptile

Answer 6

• 2 circuits: systemic and pulmonary
• 3-chambered heart: right atrium deoxygenated, left atrium oxygenated, ventricle partially divided by a septum → less mixing of oxygenated and deoxygenated blood → more efficient than amphibians or fish

Question 7

Compare the benefits of open and closed circulatory circuits. Use two examples to support your answer (4 marks)

Question 8

Explain how the complexity of circulatory systems is connected to the size and complexity of the animal (bad phrasing sorry, but something about size and endotherm)

Question 9

Compare the circulatory systems in TWO different organisms

Question 10

Valves in the heart

Answer 10

• Tricuspid valve: right side, right atrium into right ventricle
• Pulmonary valve: right ventricle into pulmonary artery
• Bicuspid/mitral valve: left side, left atrium into left ventricle
• Aortic valve: left ventricle into aorta

Question 11

Why endotherms need closed circulatory system

Answer 11

• Closed circulatory system enables vasodilation and vasocontraction (dilation or contraction of blood vessels, stimulated by the nervous system) which helps maintain internal body temeperature
• Vasodilation brings more blood to the body surface so radiation and evaporative heat loss can occur
• Vasocontraction reduces blood flow to surfaces where heat can easily be lost, e.g. hands, to conserve heat for the vital organs and tissues