why do large,multicellular organisms need a circulatory system if all of their individual cells are small?
928880
More importantly, large multicellular organisms have "specialized" cells. This means that if you took the average cell from the body it would simply die since most cells have outsourced various things to cells that can do it more efficiently. Blood for transporting oxygen, muscle cells for movement, etc.
827641
Locusts do not have separate, closed circulatory systems comparable to mammals. They have an open system, basically the entire internal portion of their exoskeleton is filled with a fluid (hemolymph) that transports immune cells, nutrients, amino acids, waste products, hormones, etc. There is an organ loosely corresponding to the heart that keeps the fluid moving but there are no veins or arteries or lymph glands or lymph vessels.
93541
wouldn't teh functions of the systems be the same for every organisms.  for example the respiratory system is for breathing in both cows and humans and probably for the toad as well.  the circulatory system is for circulating blood in every organsim.  the excretory system extrects toxins and metabolic wastes and the nervous system allows for cordiation of muscles and autonomic behaviors as well as cognitive thinking.  \n\nhowever the real functions of all these organs is SURVIVAL.  SURVIVAL is the driving force of life and you are kidding yourself if you think otherwise.
765260
Each cell must have the ability to get oxygen, nutrients, get rid of waste products like CO2. This is accomplished by the fluid in the tissues and the fluid around each cell. When blood goes through a capillary fluid can leak to the tissues, this is where it comes from. Now through the process of osmosis some of this fluid must go back into the circulatory system, but not all of it does. The fluids left over makes up the lymphatic fluid and is carried in lymphatic vessels.
391628
Yes, they have hearts, to circulate their body fluids, and some may even be said to have 2 (or more?) hearts. So insects are good-hearted little animals. However, their circulation isn't as efficient as in larger animals which have a completely-closed system of arteries and veins (insects lack this).
128882
I agree.  They pretty much all need water, but they can take up many different substances.  In some circles, it is believed that for every substance in the world, there is a microorganism that can break it down.  Things like nitrogen, different carbon sources and a polethora of other things are commonly taken up by bacteria.
451346
I'd say circulatory system, because nutrients that are decomposed in the small intestine go into the blood stream to be transported to wherever part of the body the nutrients are required.
272227
Very big cells usually can't survive because the ratio of their surface area to their volume is too small, and they can't get enough nutrients in and waste out. So maybe a faster method of exchanging substances with its environment? Sorry if I'm not much help.
344872
Organ is a the correct answer but still if your wondering how it works look back in any basic biology text book where it talks about Levels of Organization.As anyliving thing unicellular to multicellular organism is based on level of organization.\nFor example, ORGANELLE-----CELLS--\n-TISSUE--ORGANs----ORGAN SYSTEM\nAs you already know Tissues are made up of cells rigth so what makes an organ is a group of tissues and in order to have organ system you need different organs a simple example is digestive system where you G.I.tract,stomach,intesitne,pancrea,liver,gall bladder all playing some important role in the functioning of the body.
769238
Ok, in general, specialised cells in the human body perform a single function in relation to the needs of the organism to which they belong. They respond to signals from within the organism like, hormones in the blood stream and signals from nerves.\nA unicellular organism cannot specialise to the degree of a multicellular, all the functions and needs of the organism must be made by the one cell. For example, water balance in a multicellular organism like a human uses specialised cells in the kidney, which respond to hormones like the AntiDiuretic Hormone (ADH) whereas a unicellular organism like the freshwater paramecium have a contractile vacuole (a organelle) to get rid of excess water.\n\nsorry i took so long
34900
The protist needs to maintain homeostasis, the balance in the body, in order to live. Diffusion and Osmosis acheive this by allowing nutrientrs to come in and wastes to leave.
1068530
Wow, I don't know if they'd let me type 1000 pages on the subject to cover your question even close to adequately, but I'll give the Reader's Digest version a go...\n\nThe circulatory system is a liquid highway your body uses to transport oxygen and nutrients everywhere they need to go and waste products away from those tissues to be disposed.  The heart is a just a positive displacement pump that keeps your blood flowing through the arteries and veins.  Lungs serve as an interface between the circulatory system and the outside world, a place where oxygen can be drawn into the body through the thin membranes of the alveoli to be absorbed by red blood cells and bound by the hemoglobin molecules within, to be carried to every point in the body.  The lungs are also the place where carbon dioxide, also bound by hemoglobin and brought to lungs for disposal, can pass back out and be exhaled.  Much of this system is automatic and completely involuntary, and some of it isn't even controlled by the brain, at least not directly -- you can hold your breath, for instance, but you do have to consciously think about not breathing.  Your brain does have some say in how fast everything works, sending a message to your heart and lungs during times of stress or exertion to say, "Hey!  We're working kind of hard here; maybe we need more oxygen to the muscles!  Work a little faster, please!" and you start to breathe hard and your heart starts to beat faster.
451866
It depends whether you are talking about organisms that are single cells, or cells that exist in eukaryotic tissues.\n\nThe problem with finding the smallest cells is that they will undoubtedly turn out to be the smallest bacteria... these organisms are likely to exist only in places that are very difficult to reach, because extremely small size is in fact an adaptation to a (typically harsh) environment: reduction in size maximises surface area in proportion to volume.  When life gets very tough, having a maximal surface area is important, because in general, important life processes occur through cell walls and surface membranes.\n\nSome hyperthermophilic archaea (archae-bacteria that colonise hot volcanic and deep subterranean environments) are rod-shaped organisms 0.17 microns in diameter (genus Thermofilium), disk-shaped organisms 0.2-0.3 microns in diameter, 0.08-0.1 thick (genera Thermodiscus & Pyrodictium).\n\nCells in the human body are typically 5-20 microns thick.  I think Bacteria_Boy could be right about the nerve cell.\n\nIndividuals of the genus Acetabularia, a protist (single-celled) marine green alga, are composed of clearly differentiated parts (eg: foot, stalk, head), but grow up to about 5 cm in height.  These are the largest single-celled organisms that I know of.
713031
Red cells that group together normally tend to do so in rouleaux; those that stay as individuals will have greater opportunities to absorb oxygen.  If they pass through capillaries individually will be more efficient as transporters of oxygen.
530041
Organisms resembling the mitochondria in cells today. That is the simple reason why all living things have them and why they (mitochondria) have their own nucleic acids.
1072914
smallest to largest in a multicellular organism.\ncell-tissue-organ-organ system-organism
72921
Many small organisms rely on ciliary or flagellar motion to move. These mechanisms only work efficiently at low dimensions, i.e. when the density and viscosity of the medium are more important than inertia (which is given by greater body mass).\nThere are also ameboidal movements, caused by relative displacement of citoskeletal elements. These movements are more common in single-celled organisms, but also in some of our own cells (some of the white blood cells, for example)