3.2.2- Circulatory Systems

Question 1

What is the need for a circulatory system?

Answer 1

The cells of all living organisms need a constant supply of reactants for metabolism, e.g. oxygen and glucose
- These materials are gained from the environment via exchange surfaces

Question 2

How do single-celled organisms gain reactants for metabolism?

Answer 2

Single celled organisms can gain oxygen and glucose directly across their surface membranes and the molecules can diffuse to all parts of the cell quickly due to short diffusion distances

Question 3

How do larger organisms gain reactants for metabolism?

Answer 3

Their exchange surfaces are connected to a mass transport system

Question 4

What are circulatory systems?

Answer 4

systems that transport fluids containing oxygen, nutrients and waste

Question 5

Describe a single circulatory sytstem.

Answer 5

In a single circulatory system, the blood passes through the heart once during one complete circuit of the body

Question 6

Describe a double circulatory system.

Answer 6

In a double circulatory system, the blood passes through the heart twice during one complete circuit of the body

Question 7

Describe the single circulatory system in fish

Answer 7

• Deoxygenated blood is pumped to the gills from the heart
• The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood
• The oxygenated blood flows from the gills to the rest of the body
• It travels through the capillaries in organs, delivering oxygen and nutrients
• The blood returns to the heart
• The heart only has one atrium and one ventricle

Question 8

Describe the double circulatory system in mammals

Answer 8

• In mammals the blood passes throught the heart twice during a single circuit of the body
• As a result the mammalian heart has a left side and right side with a wall (septum) dividing the two
• The left side contains oxygenated blood and the right side contains deoxygenated blood
  Blood in the right side of the heart leaves and travels to the lungs
• The blood returns to the left side of the heart before being pumped around the rest of the body
• Once the blood has passed through all the other organs and tissues it returns to the right side of the heart

Question 9

What are the advantages of double circulation?

Answer 9

• When blood enters a capillary network the pressure and speed drops significantly
• In a single circulatory system, the blood has to pass through two capillary networks before returning to the heart
• In a double circulatory system, the blood only passes through one capillary network before returning to the heart
• As a result, the double circulation maintains higher blood pressure and average speed of flow
• This increased pressure and speed helps to maintain a steeper concentration gradient which allows for the efficient exchange of nutrients and waste with the surrounding tissues

Question 10

What is a closed circulatory system?

Answer 10

• In a closed circulatory system, blood is pumped around the body and is always contained within a network of blood vessels
• All vertebrates and many invertebrates have closed circulatory systems

Question 11

What is an open circulatory system?

Answer 11

• In an open circulatory system, blood is not contained within blood vessels but is pumped directly into body cavities
• Organisms such as arthropods and molluscs have open circulatory systems.

Question 12

What type of circulation system do humans have?

Answer 12

Humans have a closed double circulatory system: in one complete circuit of the body blood passes through the heart (the pump) twice

Question 13

What is the pulmonary circulatory system?

Answer 13

The right side of the heart pumps deoxygenated blood to the lungs for gas exchange

Question 14

What is the systemic circulatory system?

Answer 14

Blood then returns to the left side of the heart, so that oxygenated blood can be pumped efficiently (at high pressure) around the body

Question 15

Describe the circulatory system in an insect.

Answer 15

• Insects have one main blood vessel - the dorsal vessel
• The tubular heart in the abdomen pumps haemolymph (this is what blood in insects is called) into the dorsal vessel
• The dorsal vessel delivers the haemolymph into the haemocoel (body cavity)
• Haemolymph surrounds the organs and eventually reenters the heart via one-way valves called ostia
• Unlike the blood in a mammals circulatory system, the haemolymph is not specifically directed towards any organs in an insect
• Insects are able to survive with this less efficient circulatory system because oxygen is delivered directly to their tissues via tracheae (a system of tubes) that connect directly to the outside