7.5A: Photosynthesis
Matter and Energy
,
!
Thanks Leaves
Lexile 850L
1
Have you ever taken the time to thank a leaf? It
may seem silly to thank leaves, but they are
essential for our existence. In fact, we could not
survive without the energy produced by leaves
through the chemical process called
photosynthesis. Life as we know it relies on radiant
energy captured from the sun. The process of
photosynthesis converts this energy to forms that
are vital for human survival. This is where the
energy in our
food comes from. Certain kinds of household energy that we use are also
the result of photosynthesis. There are other benefits to radiant energy
conversion. Photosynthesis helps maintain levels of oxygen in the
atmosphere which is necessary for our survival. All of this occurs in leaves!
2
During the process of photosynthesis, the chlorophyll in leaves captures
energy from the sun. Photosynthesis converts this radiant energy to
chemical energy. Chemical energy is the form used by all living organisms.
Using radiant energy, photosynthesis converts water and carbon dioxide into
a form of sugar called glucose. Plants use glucose to live and grow. Extra
glucose is stored in the plant as a carbohydrate called starch. When animals
eat plants, they take in the energy from the stored carbohydrates in the
plant. Therefore, all energy that animals get from food originally comes from
the process
1 7.5A: Photosynthesis
Matter and Energy
of photosynthesis. This is true even for animals that are carnivores, or meateaters. The energy is passed along to them through the food chain. Without
photosynthesis, there would be no food. Animals, including humans, would
not survive.
3
4
5
Some types of common household energy come directly from
photosynthesis. Have you ever sat around a blazing camp fire or gathered
around the warm hearth in your home on a wintry evening? If so, you have
felt heat energy from photosynthesis. Dry wood and other fibrous plant
material are made of a carbohydrate called cellulose. Burning converts the
radiant energy stored in wood into heat. Another form of energy that comes
from photosynthesis is ethanol. Ethanol is made by fermenting sugars and
starches. Ethanol is used in automobile fuel in Brazil and the United States.
During the process of photosynthesis, carbon dioxide is removed from the
atmosphere. Oxygen is released as a by-product. Humans, and all other
aerobic organisms, can only survive in environments with oxygen. Through
respiration, we take in oxygen and release carbon dioxide into the
atmosphere. Humans need the oxygen produced by plants for our survival.
We also make carbon dioxide that plants need for photosynthesis.
For humans, it is essential that photosynthesis converts energy from the sun
into chemical energy. Our lives rely on the results of photosynthesis. That’s
why the next time you see a leafy green tree, or a garden full of leafy plants,
you might want to say, “Thanks!”
2 7.5A: Photosynthesis
Matter and Energy
1
2
In paragraph 1 of this passage,
which clues help you figure out the
meaning of the word vital?
3
In paragraph 3 of this passage,
which clues help you figure out the
meaning of the word hearth?
A
“captured from the sun”
A
“common household energy”
B
“energy produced”
B
“energy from photosynthesis”
C
“chemical process called
photosynthesis”
C
“burning”
D
“essential for our existence”
D
“you have felt”
4
Which is the best summary of the
selection?
A
B
Leaves are something to be
thankful for because they
produce carbohydrates.
Leaves conduct photosynthesis,
which converts energy from the
sun into chemical energy which
is useful and important to
humans.
C
Photosynthesis is a vital part of
the food chain.
D
Radiant energy is the most
important part of
photosynthesis. It is energy
from the sun, which leaves are
thankful for.
3 What is the main point of paragraph
2?
A
how photosynthesis impacts
human’s food supply.
B
how carbohydrates cause
weight gain in humans.
C
how humans and other animals
use radiant energy from the
sun.
D
how carnivorous animals hunt
and get energy from their prey.
7.5A: Photosynthesis
Matter and Energy
5
How is ethanol is made?
A
fermenting sugars and starches.
B
composting grass cuttings and
dinner table scraps.
C
boiling water and corn oil.
D
carbon dioxide being released into
the atmosphere.
4