Figure 2.2: A bird fluffs his feathers to stay warm (keep from losing energy) and to maintain
homeostasis. ( 6 )
Mammals and birds arehomeotherms–meaning they maintain the same temperature most
of the time. A lizard or an earthworm is aheterotherm, meaning its temperature can
change.
Humans and other mammals may deliberately do things to stay warm or to cool off, like
lie down under a shady tree. But most mammals maintain a steady temperature primarily
through unconscious processes. A portion of your unconscious brain regulates your body
temperature. If you get too warm, you start to sweat and the blood vessels in your skin
open up to let the blood flow to the surface of your body. If you are too cold, you start to
shiver and the blood supply to your skin, hands and feet may be reduced.
Therearemanyformsofhomeostasisbesidestemperatureregulation. Forexample, whenyou
have a big lunch, your body produces the hormone insulin, which helps maintain the right
amount of sugar in your blood. Meanwhile, your kidneys are hard at work maintaining the
right amount of water and salts in your blood. Both of these processes happen unconsciously
and are part of homeostasis.
Living Things Grow and Reproduce
All living things reproduce. Organisms that do not reproduce go extinct, every time. As a
result, there are no species that do not reproduce.
Reproduction, the process of creating a new organism, is different for different organisms.
Many organisms reproduce sexually, where an egg and sperm go together to form a new