transport systems in multicellular animals Flashcards
Reasons for multicellular organisms needing a transport system.
1- Multicellular organisms are complex and very active. They have a lot of cells requiring oxygen and glucose and also have a lot of waste product to get rid of.
2- The larger the organism, the smaller the SA:volume ratio, so the distance for diffusion to the cells in the centre is too big and that’s is a smaller surface area to do it.
3- Many molecules e.g hormones/enzymes are produced in one part of the body, but need to travel to another- must somehow be transported.
4- Food is digested in the digestive system, but the products of this are needed all over the body.
5- All cells produce water products, which need transporting to the excretory organs.
What are the features that most circulatory systems have in common?
-Liquid transport medium, circulates around system (blood).
-Usually have vessels to carry the blood.
- Usually have a pumping mechanism to move the fluid around the system (heart).
What happens during a single circulatory system?
- Blood passes through the heart once during each circuit of the body.
How many sets capillaries does the blood pass through in single circulatory systems and what happens in each?
- Blood passes through 2 sets of capillaries before it returns to the heart.
- In the first, it exchanges oxygen and carbon dioxide.
- In the second, substances are exchanged between the blood and cells.
What is a disadvantage of a single circulatory system?
- Blood has to pass through 2 sets of narrow capillaries before returning the heart.
Pressure is lost along the way, so the flow-rate slows down, less efficient.
How can fishes have a single closed circulation system and still be active?
- They have a countercurrent gaseous exchange mechanism in their gills that allows them to take a lot of oxygen from the water. This reduces metabolic demands.
What happens during a double circulatory system
- Blood passes through the heart twice during each circuit of the body.
- Left side deals with oxygenated blood and right side deals with deoxygenated blood.
- Blood is pumped from the right side of heart to the lungs to pick up oxygen, and unload CO2 and then returns to heart.
- Blood flows through the heart and is pumped out to travel all around the body before returning to heart again.
Advantage of double circulatory system.
- When blood travels through the capillaries of the lung, it’s pressure and flow rates are reduced.
- In the double system- this blood then flows back to the heart and is re-pressurised before flowing around the body to the cells. This increases the flow rate again, which is more efficient for delivery of oxygen to cells.
What happens during open circulatory system?
- Very few vessels to contain transport medium.
- It is pumped straight from the heart into the body cavity of the animal.
What is an open body cavity called and what happens in it?
- Open body cavity is called the haemocoel.
- In haemocoel transport medium is under low pressure. It comes into direct contact with tissues and cells.
- This is where exchange takes place between transport medium and the cells.
- Transport medium returns to the heart through an open-ended vessel.
What is a disadvantage of an open system?
The blood flow rate to all cells and tissues is the same - the amount of blood reaching a particular tissue cannot be varied to meet demand.
What happens during a closed system?
- The blood is enclosed in blood vessels and does not come into contact directly with the cells of the body.
- Substances leave and enter the blood by diffusion through walls of the blood vessels.
How can blood flowing to a particular tissue be adjusted in a closed system?
- adjusted by widening or narrowing blood vessels.
Examples of each circulatory system.
open = insects
closed single = fish
closed double = mammals and birds
closed = starfish and phyla
