Exchange between Organisms (Mass Transport) - The Circulatory System Flashcards
What do you need for transport over large distances?
Diffusion is fast enough for transport over short distances. The efficient supply of materials over larger distances requires a mass transport system.
Why do large organisms have a transport system?
All organisms exchange materials between themselves and their environment. In small organisms this exchange takes place over the surface of the body.
However, with increasing size, the sa:v ratio decreases to a point where the needs of the organism cannot be met by the body surface alone.
As organisms have evolved into larger and more complex structures, the tissues and organs of which they are made have become more specialised and dependent upon one another. This makes a transport system all the more essential.
What are exchange surfaces?
Specialist exchange surfaces are required to absorb nutrients and respiratory gases, and remove excretory products. These exchange surfaces are located in specific regions of the organism.
A transport system is required to take materials from cells to exchange surfaces and from exchange surfaces to cells. Materials have to be transported between different parts of the organism. They also need to be transported between different parts of the organism.
What factors determine whether or not there is a specialised transport medium, and whether or not it is circulated by a pump?
- the surface area to volume ratio
- how active the organism is
The lower the surface area to volume ratio, and the more active the organism, the greater is the need for a specialised transport system with a pump.
What features do the transport systems of many organisms have in common?
- A suitable medium in which to carry materials. This is normally a liquid based on water because water readily dissolves substances and can be moved around easily, but can be a gas such as air breathed in and out of the lungs.
- A form of mass transport in which the transport medium is moved around in bulk over large distances - more rapid than diffusion.
- A closed system of tubular vessels that contains the transport medium and forms a branching network to distribute it to all parts of the organism.
- A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system and another.
- A mechanism to maintain the mass flow movement in one direction.
- A means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism.
- A mechanism for the mass flow of water or gases, e.g. intercostal muscles and diaphragm during breathing in mammals.
How do you achieve a pressure difference between one part of the system and another?
- Animals use muscular contraction either of the body muscles or of a specialised pumping organ.
- Plants rely on natural, passive processes such as the evaporation of water.
What is the circulatory system in mammals?
Mammals have a closed, double circulatory system in which blood is confined to vessels and passes twice through the heart for each complete circuit of the body.
The heart at the centre has two pumps. One pumps blood to the lungs to be oxygenated whilst the other is larger and stronger and pumps the oxygenated blood around the body to supply vital organs and tissues.
Why do we have a double circulatory system?
Because when blood is passed through the lungs, its pressure is reduced. If it were to pass immediately to the rest of the body, its low pressure would make circulation very slow. Blood is therefore returned to the heart to boost its pressure before being circulated to the rest of the tissues.
As a result, substances are delivered to the rest of the body quickly, which is necessary as mammals have a high body temperature and hence a high rate of metabolism.
What are the three types of vessels that make up the circulatory system of a mammal?
- arteries
- veins
- capillaries
What is the final stage of transport exchange?
Although a transport system is used to move substances longer distances, the final part of the journey to cells is by diffusion. The final exchange from blood vessels into cells is rapid because it takes place over a large surface area, across short distances and there is a steep diffusion gradient.
Why don’t unicellular organisms need a transport system?
In single-celled organisms, the substances needed enter directly from the environment. The waste products leave the cell in the same way.
What type of circulatory system do insects have?
- Insects have an open circulatory system.
- Insect blood (hemolymph) flows freely through the body cavity and makes direct contact with organs and tissues.
- The insect circulation system does not carry oxygen, so the blood does not contain red blood cells.
- Hemolymph is usually green or yellow.
- A single blood vessel runs along the dorsal (back or top) side of the insect.
- Few little heart pumps push the hemolymph through this vessel (in one direction) to the haemocoel (body cavity).
- The hemolymph is then re-absorbed by the dorsal vessel.
What type of circulatory system do earthworms have?
- Earthworms have a closed circulatory system.
- The blood contains an oxygen-carrying pigment.
- There is a heart and 5 pseudo-hearts to pump the blood around.
What are the major blood vessels in earthworms?
- Ventral blood vessel: distributes the blood to various parts of the body.
- Branches of the ventral blood vessel: Takes the blood to all the structures within each segment.
- Dorsal blood vessel: collects the blood from the body.
What is single circulation (e.g. fish)?
- Blood passes through the heart once per complete circuit.
- Blood pressure reduced as blood passes through the gill capillaries.
- Slows down the flow to the rest of the body.
- Limits the rate of delivery of oxygen and nutrients to cells and removal of waste.
- Efficient for the level of activity of fish but not mammals.
- Fish do not maintain their body temperature so need to respire relatively less compared to humans.
