KEGS Biology Blog

Wednesday 23rd January Section 2
January 23, 2013, 3:50 pm
Filed under: Uncategorized

Why we need a transport system, open and closed, single and double circulatory systems


7 Comments so far
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Closed Circulatory System-

In a closed circulatory system, the blood is enclosed inside having blood vessels. Closed system is found in annelids, cephalopods, vertebrates.


Fish have a closed circulatory system. The heart pumps blood into arteries. These branch out into millions of capillaries. Substances like oxygen and glucose diffuse from the blood in the capillaries into the body cells, but the blood stays inside the blood vessels as it circulates. Veins take the blood back to the heart.

Comment by roobennithi

In terms of levels of activity, large animals such as humans need transport systems so that the necessary nutrients and oxygen can be supplied to all the cells in the body, especially when the animal is active. This is because the energy required for this activity is obtained via respiration, and to do this we
require oxygen and therefore a transport system.

Comment by elliswhyte

An open circulatory system essentially means that blood is not confined to the blood vessels, as it is in mammals. The blood therefore flows through the entire body, bathing the tissies and cells in this blood fluid. Open circulatory systems (evolved in crustaceans, insects, mollusks and other invertebrates) diffuse blood back to the circulatory system between cells. All insects have this type of circulatory system.
In insects, a muscular pumping organ is used to circulate the blood. This tube lies under the upper surface of the insect, and blood enters the heart through pores called ostia. Blood is then pumped from the heart and towards the head by peristalsis.
In other animals, circulation is helped by the movement of the body muscles, and insects such as locusts have open ended tubes attached to the heart in order to direct blood flow towards the wings and legs.
Good revision site :

Comment by georgiawinfield

The double circulatory system.

This type of circulatory system is most commonly found as part of a mammals anatomy. It has two separate circuits for blood, and blood passes through the mammalian heart twice. The two types of circulation are the pulmonary circulation, which carries blood to lungs to become oxygenated and is powered by the right side of the heart, and systematic circulation, which carries oxygen and nutrients around the body to the tissues, which is powered by the left side of the heart.

The systematic circulation can carry blood at higher pressure than the pulmonary circulation, as the pulmonary circulation contains some very fine capillaries, such as those surrounding the alveoli in the lungs, which have walls only one cell thick. These very fine capillaries would be damaged by high blood pressure.

What are the advantages of a double circulatory system for mammals?

Unlike the single circulatory system, the heart also increases the pressure of the blood after it has been oxygenated in the lungs, which allows blood to reach the body tissues quickly. This ensures the body tissues have a rapid supply of oxygen and nutrients for respiration. Mammals are more active than animals such as fish which have a single circulatory system, and they also maintain a constant body temperature, which means they respire more, and need a better supply of oxygen for respiration.

Comment by eilishsmyth

Single Circulatory Systems-
Fish have a single circulatory system, which means the blood is pumped around the body of the fish along a single circuit, as opposed to the two separate circuits present in a double circulatory system. The blood is pumped from the heart to the gills of the fish, where oxygen is obtained via diffusion of o2 molecules from the water into the gills. The disadvantage to the single circulatory system is that oxygenated blood can mix with deoxygenated blood, making the system less efficient at providing oxygen to organs and muscles throughout the body of the fish than the double circulatory system present in mammals.
This is a simple breakdown of the direction the blood flows:
Heart – Gills – Body – Back to heart

Comment by benpessell

If an animal has several layers of cells or more this means that the diffusion pathway is relatively large and any nutrients that are diffusing to the cells in the middle of the organism will be used up by the cells nearer the surface. Therefore the cells in the middle will be deprived of the necessary nutrients, and therefore they will not be able to function properly. An effective transport system will be able to reduce the diffusion pathway so the nutrients diffuse directly into the cells rather than through 3, 4 or more.

Comment by harrymoseley

Single-celled organisms can get all the substances they need by diffusion across their outer membrane. For multicellular organisms it is harder to supply all their cells with everything via diffusion as some cells are deep within the body. Multicellular organisms such as mammals have a low surface area to volume ratio and have high levels of activity. This means that a large number of cells are respiring very quickly, so they need a constant, rapid supply of glucose and oxygen. To make sure every cell has a good enough supply, a transport system is needed. In mammals, this is the circulatory system, which uses blood to carry oxygen and glucose around the body. It also carries hormones, antibodies and waste such as carbon dioxide.

Comment by charlieshah

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