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Sensing Energy

In some animals, the organ used to detect light is the eye. Although most large animals (humans, fish, birds, reptiles) have similar eyes, not all eyes are the same. Some eyes are very complex, while others are simple in their function. With our human eyes, we can see a variety of colors, shades, and sharp details of shapes, by collecting the light reflected off of objects.

Life as seen through the eyes of an insect would look very different. Insect eyes come in two varieties–simple and complex. Simple insect eyes, called ocelli, detect little detail but can tell different shades of light and dark. Compound eyes are more complex. These organs function similarly to many human eyes bundled together and working as one.

Interesting note: Some organisms have eyes that swivel on short stalks which help them to see in all directions without turning their heads. Ever tried to swat a fly? They have compound eyes that help them see behind them. They see behind them but can't detect shapes very well. So the next time you sneak up on a fly, pretend to be doing something else.

  Plants can also detect light. In fact, if they couldn’t, we could not exist. Special organs in plants, called chloroplasts, collect light energy and use it to convert carbon dioxide and water into sugar for us. Chloroplasts are found in leaves because leaves are exposed to more sunlight than other parts of the plants.
Even though we can feel many types of vibrations with our hands, feet, or other body parts, we understand sounds by using our ears. Human ears, and the ears of other large animals, are generally made of an air chamber covered by a thin piece of skin-like material (your eardrum).
Insect ears, like human ears collect and transform sound vibrations. But, insect ears are called tympanic organs. Any idea why they have this name? It is because the membrane vibrates like a drum.
Fish have what is called a lateral line system to help detect sound vibrations in water. This helps them detect when predators and other objects are near. The lateral line looks like dashed or dotted lines on the sides and around the head of fish, reptiles and amphibian.

This system also helps these animals sense movement of water past their bodies, and the temperature of the water.


Have you ever burned your hand on the stove? How does your brain actually know that your hand is getting warm? We, like other animals, have certain nerve endings that are sensitive to heat. These are often called thermoreceptors.

For some animals, such as some amphibians, fish, and reptiles, these receptors are part of the lateral line system. Insects also have thermoreceptors located on all sorts of different body parts.

Many animals have a variety of sense organs that allow them to detect different forces of energy. For example, some animals can actually sense changes in electrical fields. Fish are the most common electrical detectors. Some, such as certain sharks, can detect the presence of an external electrical field (such as metal in trash dumped in the ocean by humans). Others create their own electrical field and sense external electrical fields by detecting changes in their own. Your dog can sense different pitches of sound that you cannot hear.


  • Large beaker
  • 500 ml of room temperature water
  • One goldfish
  • Watch, clock, or stopwatch
  • Cold water
  • Eye dropper
Safety concerns: icon Be sure to keep all glassware, animal, and chemical safety rules. As with all science lab activities, the most important safety rule is to follow all teacher directions.


  1. Put the 500 ml. room temperature water into the large beaker.
  2. Carefully place the fish into water.
  3. Count the number of gill movements per minute.
  4. Use the eye dropper to add ten drops of cold water.
    • Count the number of gill movements per minute.
    • Continue this process until you have collected data for 15 minutes.
  5. Graph the number of gill movements as a line graph compared to the time.


  1. How many gill movements did you observe with water at room temperature?
  2. How did the gill movements relate to the fish sensing a change in temperature?
  3. How many gill movements did you observe during the last minute of your observations?

Review Science safetey rules here.

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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