1. Which of the following only contains organisms
that are secondary consumers in this food web?

Have you ever wondered why we can't seem to feed the world's hungry? It's a complex issue, but it might surprise you to learn that it's not because there isn't enough food; current agricultural capacity, based on current technology, exists to feed as many as 10 billion people. The Earth's population is "only" about 7 billion. The big question really is: If we want to feed everyone, what would everyone need to eat? To answer that question, download this excel spreadsheet and try plugging in some numbers.

Example: One acre of a grain crop could be used to feed cattle, and then the cattle could be used to feed people. If 50% of the energy is lost to the cattle, you could feed twice as many people if you fed them the grain directly. Another way of looking at it is that it would only take a half acre of land to feed the people grain, but a whole acre if you feed the grain to the cattle and the cattle to the people. A common practice to grow cattle faster is to feed them ground up animal protein. This means that when we eat the meat from the cow, we're at the tertiary level or higher. The loss of energy between trophic levels may also be even higher. Recent studies suggest that only ~10% of energy is converted to biomass from one trophic level to the next!

The Food Chain: The answer has to do with trophic levels. As you probably know, the organisms at the base of the food chain are photosynthetic; plants on land and phytoplankton (algae) in the oceans. These organisms are called the producers, and they get their energy directly from sunlight and inorganic nutrients. The organisms that eat the producers are the primary consumers. They tend to be small in size and there are many of them. The primary consumers are herbivores (vegetarians). The organisms that eat the primary consumers are meat eaters (carnivores) and are called the secondary consumers. The secondary consumers tend to be larger and fewer in number. This continues on, all the way up to the top of the food chain. About 50% of the energy (possibly as much as 90%) in food is lost at each trophic level when an organism is eaten, so it is less efficient to be a higher order consumer than a primary consumer. Therefore, the energy transfer from one trophic level to the next, up the food chain, is like a pyramid; wider at the base and narrower at the top. Because of this inefficiency, there is only enough food for a few top level consumers, but there is lots of food for herbivores lower down on the food chain. There are fewer consumers than producers.

Explanation:

halogen, any of the six nonmetallic elements that constitute group 17 (group viia) of the periodic table. the halogen elements are fluorine (f), chlorine (cl), bromine (br), iodine (i), astatine (at), and tennessine (ts).