Why do most food chains consist of no more than three of four levels?
824130
Because they expect you to eat your food within 20 minutes and then get out.  If people just continue to come and go very quickly, there should always be empty tables even if there are a limited amount of floors.  Why build extra floors that won't get much use?
8776
If you mean trophic level, not tropic level, many time intestine lengths get relatively shorter as you move up trophic levels. So a lion has a much shorter relative intestinal tract length than a water buffalo would.
143810
they don't add up because of complex carbohydrates (Polysaccharides), on some labels you might notice "Other Carbohydrates" and that usually is complex carbohydrates.
77575
because math is weird.and 3 is one less than 4.
353801
The answer is (D) the hawk.\n\nThe concept you are asking about is called biological magnification.  As energy flows through the food chain, there is significantly less energy available to each trophic level.  To accommodate, the organisms must eat a higher biomass from the trophic level below it.  Therefore, each level of the food chain accumulates higher amounts of DDT in their system.  Because the hawk is the third-order consumer in the example provided, it will have the highest concentration of DDT.\n\n<edited for spelling>
808843
the mink...  it is likely due to the fact that they have short, active lifespans... they need a constant, high energy diet but can not eat too much in one sitting..  during evolution, it's likely that there was little to no energy invested in development of the digestive tract because of its short lifespan...\n\nalso, being a carnivore, they have no need for a cecum and long digestive tract (like rabbits, sheep, and deer) which is useful in extracting the low amounts of energy from plant material...
337410
None of these answers are correct for all food chains.  "D" would seem to be the best answer, but it is not always true.  It always depends on the ecosystem.  In most cases, producers will outnumber the consumers.  But not always.  For example, in a forest ecosystem a single large producer (oak tree or whatever) may support thousands of caterpillar and hundreds of  consumers like spiders and birds. If you have to pick one, pick D. Just know that it is not always true.
517414
There is a finite amount of energy in the ecosystem, regulated by the amount of sunlight plants can convert to usable forms of energy.  As you go up the food chain, a bit of this energy is lost at each level, meaning that at or above a certain trophic level, the energy input is insufficient to support an organism.  It's pouring water from bucket to bucket... You're going to spill some each time, and eventually, none will be left to pass on.
690764
food chain and bird food
1026025
I'm not certain anyone but a biologist can answer this one correctly, but I'll take a stab: the organisms in any ecosystem are related to each other in a hierarchy, like a food chain. Other relationships are helping, symbiotic or parasitical relationships in which one organism's function allows another to live. An ecosystem thrives when all its organisms are in balance.
1139356
The nature of a system is to function, its components are but smaller systems.
19341
The Food Group Pyramid is a way that most food groups are broken down. Normally there are 7 different groups with those that you should eat the least of at the top and those you should eat the most of at the bottom.\n\nthe 7 groups (in order from bottom to top)\nBread (6-11 servings)\nVegetables (3-5 servings), Fruits (2-4 servings)\nDairy (2-3), Meats/Dry Beans/Nuts (2-3 Servings)\nFats/Oils/Sweets (Rarely)\n\nan image can be found at http://www.fda.gov/diabetes/pyramid.gif\n\nMany diets such as Atkins, conflict with the pyramid as well as research showing that Monounsaturated fats and Polyunsaturated fats are in fact good for your body by lowering LDL (High LDL levels often cause blood clots)  and raising HDL (HDL clears cholesterol from the body)\n\ni hope this helps more than it confuses
1135493
Biology has become such a vast research enterprise that it is not generally regarded as a single discipline, but as a number of clustered sub-disciplines. This article considers four broad groupings. The first group consists of those disciplines that study the basic structures of living systems: cells, genes etc.; the second group considers the operation of these structures at the level of tissues, organs, and bodies; the third group considers organisms and their histories; the final constellation of disciplines focuses on their interactions. It is important to note, however, that these boundaries, groupings, and descriptions are a simplified characterization of biological research. In reality, the boundaries between disciplines are fluid, and most disciplines frequently borrow techniques from each other. For example, evolutionary biology leans heavily on techniques from molecular biology to determine DNA sequences, which assist in understanding the genetic variation of a population; and physiology borrows extensively from cell biology in describing the function of organ systems.
659354
Dead plants and animals cannot be said to occupy a level in the food chain as being dead they are not able to eat and therefore occupy the lowest space on the trophic level  as food for fungus, microbes, insects, animals and other plant life.\n\nStrange question.
1038146
Diversity of environment, also called biodiversity, relates to the number of different species of flora and fauna in the environment. Biodiversity is important not because more species looks pretty, but because more biodiversity is healthier for the ecosystem, specifically the food chain. Consider a simple food chain that includes grass, rabbits, and coyotes. If all the rabbits die from disease, the coyotes are hopeless. But if there were more biodiversity, coyotes may also rely on raccoons for food. Forests have good biodiversity, especially the tropical rain forests around the world.
917889
Actually, the statement is not true. Most creatures in the world don't have four legs. Insects, with 6 legs, are far more abundant than all four legged creatures. \n\nHowever, the main groups of vertebrates - amphibians, reptiles, mammals and birds all evolved from a common tetrapod (meaning four-legged) ancestor. This is the reason they all have four legs, even if they have subsequently lost them (such as snakes, whales, etc). \n\nFish are also vertebrates. However, they are an evolutionarily older group, and the tetrapod ancestor of the other vertebrates is believed to have evolved from sarcopterygii, which evolved from lobe finned fishes.
166068
Most of the energy in every process that uses it is lost (transforms to heat). The best processes in nature use about 33% of the energy, and release the other 67% as heat.\nWhen an organism eats another organism, it only eats the energy that the "lower" organism transformed to material (biomass) - and here the energy is lost (all the energy an organism transforms to movement/breath, all the organimsm that die and their energy goes to a lower link in the chain, and the biomass an organism loses in excrement).