Basic Needs of Living Things

Lesson 12 -- Alien Minds

     Social beings have many concerns, including concerns about providing for their basic needs. The more difficult these needs are to meet, the more time is devoted to thinking about them.

    How much time do your aliens spend on thinking about getting nourishment? Read this page and see how your aliens fit into these patterns.


     All living things need energy, i.e., fuel. What governs how much food an organism needs?

Activity Level

     Living cells need energy to carry out life processes, such as using energy, repairing themselves and discarding waste products. If an animal is living at a low temperature it is metabolizing slowly, and does not need much energy for survival. Some ocean animals and reptiles stay alive without needing much energy. If food is abundant animals do not need to expend much energy in capturing it.

    Growth and reproduction both require energy in excess of what an organism needs to merely survive. Both are dependent on periods of good food availability. Many animals on earth have adapted their growth patterns and reproductive cycles to take advantage of seasonal variation in food supplies.

     Earth does not have any animals that float in water and use chlorophyll to feed themselves. Is it possible that such animals might exist?  Perhaps. However, consider how few plants move, even slowly, in response to stimuli. Could plants could provide enough surplus energy to support structures that could think, even slowly? Could thought be useful if one had no power to act?

Environmental Stresses

     Stresses in the environment force animals to use more energy. Dealing with temperature variations is necessary for land animals: seasonal variations are especially challenging. Maintaining body temperature requires energy, especially for warm blooded animals. They need to eat more or burn stored fat to stay alive in cold weather.


    It takes energy to capture food, and energy to escape from predators. Prey animals need to be alert all the time, as they do not know when predators will strike. Territorial animals also need to be on guard against possible trespassers on their territory. Watchfulness takes energy.


     Animals that live a long time (see Reproductive Strategies) and successfully raise young do not need to reproduce as frequently as animals which are continuously being killed by predators. On earth, rabbits and frogs, for example, are eaten by many other animals. They need to invest a lot of their energy in the physical process of reproduction if their species are to survive.

     Successful reproduction also requires a set of behaviors to ensure that the parents meet at the right time and that the young arrive at a time and place favorable to their survival. This may require the parents to defend territory or compete for mates, both of which require energy. The parents may feed the young, which also requires increased energy supplies. The young may also need special protection. Reproductive patterns can lead to social structures as a species increases in intelligence.


    A liquid, probably water, is needed to help chemical reactions take place in living cells. Dehydration kills quickly. Organisms must have access to liquids, and intelligent beings ensure the availability of their supply.

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1999. © Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at