<span>1. What is circulation?
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<span>Circulati3</span>on is the movement of substances such as nutrients and gases within blood vessels and cavities throughout the body.
<span>2. Do all animals have a circulatory system?
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Not all animals have a circulatory system.
Poriferans, cnidarians, platyhelminthes and nematodes (nematodes have pseudocoelom fluid but no vessels) are avascular animals. Echinoderms do not have true circulatory systems either.
<span>3. What is the alternative means of substance transport in animals without a circulatory system? Why is blood important for larger animals?
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In animals that do not contain a circulatory system, the transport of substances occurs by cell to cell diffusion.
Blood is a fundamental means of substance transport for larger animals since, in these animals, tissues are distant from each other and from the environment thus making diffusion impossible.
<span>4. What are the two types of circulatory systems?
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<span>Circulator2</span>y systems can be classified into open ci<span>rculatory systems and clo2</span>sed circulatory systems.
<span>5. What is an open circulatory system?
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An open circulatory system is one in which blood does not circulate only inside blood vessels but also flows into cavities that irrigate tissues. In open circulatory systems, blood pressure is low and generally the blood (called hemolymph) has a low level of cellularity.
Arthropods, molluscs (cephalopods are exception) and protochordates have open circulatory systems.
<span>Circulatory System Review - Image Diversity: open circulatory system</span><span>6. What is a closed circulatory system?
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A closed circulatory system is one in which blood circulates only inside blood vessels. For this reason, the blood pressure is higher in animals with closed circulatory systems. The cellularity of the blood is also higher, with many specific blood cells.
Closed circulatory systems are a feature of annelids, cephalopod molluscs and vertebrates.
<span>Circulatory System Review - Image Diversity: closed circulatory system</span><span>7. What are the advantages of a closed circulatory system over an open circulatory system?
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A closed circulatory system is more efficient. Since blood circulates only inside blood vessels, it has a higher pressure and, as a result, can travel greater distances to the organs where hematosis happens and to peripheral tissues. In addition, the higher circulatory speed increases the animal’s capacity to distribute large supplies of oxygen to tissues that consume it in large amounts, such as muscle tissues, which can then perform faster movements. Animals with an open circulatory system (with the exception of insects, which carry out gas exchange separately from circulation) are generally slower and have a low metabolic rate.
<span>8. What is the difference between octopuses and mussels regarding their circulatory systems? How does that difference have an effect on the mobility of these animals?
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Cephalopod molluscs, such as octopuses and squids, have a closed circulatory system with blood pumped under pressure flowing within vessels. Bivalve molluscs, such as mussels and oysters, have an open circulatory system (also known as a lacunar circulatory system) where blood flows under low pressure, since it falls into cavities in the body and does not only circulate within blood vessels. Molluscs with closed circulatory systems are larger, agile and can actively move; molluscs with open circulatory systems are smaller, slow and some are practically sessile.
<span>9. Why can flying insects such as flies beat their wings at a great speed despite having an open circulatory system?
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In insects, the circulatory system is open but this system does not participate in the gas exchange process or in oxygen supply to tissues. Gases enter and exit through the independent tracheal system, which allows for the direct contact of cells with the ambient air. Therefore, an insect can supply the large oxygen demand of its fast-beating wing muscles even though it has an open circulatory system.
