Answer: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.
Land and aquatic energy pyramids
Trophic Level Desert Biome Grassland Biome Pond Biome Ocean Biome
Producer (Photosynthetic) Cactus Grass Algae Phytoplankton
Primary Consumer (Herbivore) Butterfly Grasshopper Insect Larva Zooplankton
Secondary Consumer (Carnivore) Lizard Mouse Minnow Fish
Tertiary Consumer (Carnivore) Snake Snake Frog Seal
Quaternary Consumer (Carnivore) Roadrunner Hawk Raccoon Shark
Food Web: At each trophic level, there may be many more species than indicated in the table above. Food webs can be very complex. Food availability may vary seasonally or by time of day. An organism like a mouse might play two roles, eating insects on occasion (making it a secondary consumer), but also dining directly on plants (making it a primary consumer). A food web of who eats who in the southwest American desert biome might look something like this:
Explanation:
Which simple machine can be described as a rope that is threaded through a wheel or disk?
The correct answer is B - Pulley
A pulley is a simple machine that is used to lift loads. It consists of a wheel on which a rope is placed and the rope is pulled by the person towards himself to lift the load that is tied on the other side of the rope. There are three main types of pulleys: fixed, movable, and compound.
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