How is heat like a river?
They both flow “downhill.” You will
never see a river flow up a mountain. A
river only goes one way, down. Heat
also goes one way. Heat only flows
from something that is hotter to
something that is colder.
Most light comes from things
that give off heat. Natural
light comes from the Sun, other
stars, and certain animals that
glow in the dark.
Light from the Sun makes
Earth warm enough for life.
Light from the Sun makes green
plants grow. Plants are food for
animals. Plants also give off
oxygen that you breathe in the
air. Dead plants provide fuel
that we use for energy.
Plants need sunlight
Houseplants lean toward the Sun, and
if they do not get enough light they
wither and die. Plants use sunlight to
make their food. This process is called
Human needs sunlight
Solar energy shines down on us every day.
Humans need the light coming from the sun to
be able to see and the heat that it gives off
as well as the vitamin D to develop strong
bones. You play in sunshine. You see in
daylight. The Sun keeps you warm.
Animals need sunlight
Cold-blooded animals, such as snakes,
lizards, frogs, salamanders, and insects,
cannot produce their own heat and rely on
the Sun to warm their bodies.
Hot, dry summers are rough on plants,
especially on non-native plants and those weak
from improper care. Since many of our
landscape plants aren't naturally adapted to
heat, they need special attention and care.
Exposure to the intense sunlight of bright,
cloudless, summer days can be too much for
sensitive plants. Reflected light from walls
and other surfaces can also add to the
problem. Stunted plant growth and a yellow-
white "burn" on the upper surface of older
leaves are familiar symptoms of too much
The long sunny days
produce dry weather or
drought. When the
lands are too dry and
plants can hardly live,
the animals are
affected too. Animals
depend on plants for
food. When there are
few plants, animals will
have less to eat. They
become sick or they