Transport Systems In Multicellular Animals Flashcards
Why do bigger organisms need transport systems
As organisms get bigger, the distances between the cells and the outside of the body get greater. Diffusion would transport substances into and out of the inner core of the body, but it would be so slow that the organism would not survive.
5 reasons why specialised transport systems are needed
-The metabolic demand of most multicellular animals are high, so diffusion over the long distances is not enough to supply the quantities needed.
-The SA:V ratio gets smaller as multicellular organisms get bigger so no only do the diffusion distances get bigger but the amount of surface area available to absorb or remove substances becomes relatively smaller.
-molecules such as hormones or enzymes may be made in one place but needed in another.
-Food will be digested in one organ system, but needs to be transported to every cell for use in respiration and other aspects of cell metabolism.
-waste products of metabolism need to be removed from the cells and transported to excretory organs.
Three features of a transport system
-They have a liquid transport medium that circulates around the system (blood)
-They have vessels that carry the transport medium.
-They have a pumping mechanism to move the fluid around the system.
What’s a mass transport system
When substances are transported in a mass of fluid with a mechanism for moving the fluid around the body it is known as a mass transport system. Large, multicellular animals usually have either an open circulatory system or a closed circulatory system.
What’s an open circulatory system
-Few vessels to contain the transport medium. Pumped straight from the heart into the body cavity of the animal. Open body cavity is called the haemocoel. In the haemocoel the transport medium is under low pressure.
-It comes into direct contact with the tissues and the cells. Where exchange takes place between the transport medium and the cells. The transport medium returns to the heart through an open-ended vessel.
Where are open-ended circulatory systems found
-invertebrate animals, including most insects and some molluscs.
-Insect blood is called haemolymph- doesn’t carry oxygen or carbon dioxide. It transports food and nitrogenous waste products and the cells involved in defence against disease.
What are closed circulatory systems
In a closed circulatory system, the blood is enclosed in blood vessels and doesn’t come directly into contact with the cells of the body. Heart pumps blood around the body under pressure and relatively quickly, and the blood returns directly to the heart. Substances leave and enter the blood by diffusion through the walls of the blood vessels.
-amount of blood flowing to a particular tissue can be adjusted by widening or narrowing blood vessels.
What’s a single closed circulatory system
Fish- blood flows through heart then whole body
-blood passes through two sets of capillaries, in first it exchanges oxygen and carbon dioxide, in the second, substances exchanged between blood and cells.
-Blood pressure gets low, returns to heart slowly-limitation.
-however fish are efficient- can be active-countercurrent gas exchange system in gills.
What’s a double closed circulatory system
-Humans- efficient system
-Blood pumped to lungs
-Back to heart then throughout body.
-Only passes through one capillary network- relatively high pressure and fast flow of blood maintained.
What are the three components of blood vessels
-Elastic fibres- composed of elastin and can stretch and recoil, providing vessel walls with flexibility .
-Smooth muscle- contracts or relaxes, which changes the size of lumen.
-collagen-provides structural support to maintain shape and volume of the vessel.
What is the lining of an artery called
The endothelium-is smooth to reduce friction so blood flows easily over it.
What’s the arterioles composed of
They have more smooth muscle and less elastin in their walls than arteries, as they have little pulse surge, but can constrict or dilate to control the flow of blood into individual organs.
What is vasoconstriction
When the smooth muscle in the arteriole contracts it constricts the vessel and prevents blood flowing into a capillary bed.
What are capillaries
Microscopic blood vessels that link the arterioles with the venules. RBC travel through in single file. The gaps between endothelial cells which make up capillaries are large- substances pass out. The exception is the capillaries in the nervous system.
What are the three adaptations of the capillary
-provide a very large surface area for the diffusion of substances into and out of the blood
-The total cross-sectional area of the capillaries is always greater than the arteriole supplying them so the rate of blood flow falls.
-Walls are a single endothelial cell thick, giving a thin layer for diffusion.
