Download document Holes: Can You Dig It? The Incredible, Edible Onion

The MIDAS Project: Supported by the Science Education Partnership Award Program of the
National Center for Research Resources, National Institutes of Health (Grant No. R25 RR018634)
Onions!
• Since the beginning of
civilization, onions have
been an important part of
our diet.
• Onions add flavor to
recipes and have been
used as medicine
throughout history.
What is an Onion?
• What exactly are you
eating when you bite into
an onion?
• The onion is a bulb
vegetable.
• Plants do not have
mouths, but they need
food.
• How do plants get food?
Photosynthesis
• Onions make their own food
using photosynthesis.
• The word photosynthesis
means “putting together with
light.”
• During photosynthesis,
radiant energy from sunlight
is converted to chemical
energy stored in the sugar
glucose.
• Glucose is formed from CO2
and H20.
Chloroplasts
• Photosynthesis takes
place in chloroplasts.
• Chloroplasts are found
throughout plant cells.
• Chlorophyll is a green
pigment found in
chloroplasts.
• Chlorophyll captures
energy from sunlight.
Making Sugar
• H2O is absorbed in the roots.
• CO2 enters the plant through the
underside of the leaf.
• Plants use light energy from the
sun to combine CO2 with H2O.
• The products of photosynthesis
are glucose and oxygen.
• Glucose is a type of sugar used
by the plant for food.
• Oxygen is a product of
photosynthesis that is released
into the air.
Photosynthesis
Equation
6CO2 + 6H2O + Sunlight --> C6H12O6 + 6O2
Onion Leaves
• Onions have upright green
leaves that form from the bulb
below ground.
• The main function of the leaves
is photosynthesis.
• The leaves are the site of
photosynthesis and energy
storage during cool weather.
• In warm weather, energy from
the leaves travels down in a
tissue called phloem. The extra
food is stored in the bulb.
The Bulb
• Onion bulbs are commonly
yellow, white, or red.
• The onion bulb is a tightly
packed globe of food
containing oil that is the
source of the onion’s flavor.
• Thin papery layers form an
outer protective covering
for the bulb.
Onion Roots
• Onions have roots to
anchor it into the soil.
• The roots absorb water
and minerals.
• Water absorbed in the
roots is carried up to the
rest of the plant in a
tissue called xylem.
Onion Cell DNA
• DNA stands for Deoxyribonucleic
Acid.
• The cells of all living things
contain DNA in the nucleus.
• DNA is the molecule that controls
the functions of the cell.
• Copies of DNA are passed on to
offspring when organisms
reproduce.
• Onion bulb color is an example of
a characteristic passed on in DNA.
Onion Cell Division
• Plant cells have cell walls.
• Plants cells divide by a process known as mitosis.
• Observe the following stages of onion root tip mitosis:
Interphase, prophase, metaphase, anaphase, and
telophase.
Weird Onion Fact
• There are more than
700 species of onions
on our planet!
Eat More Onions!
• Onions play an important
role in book Holes. As in
Holes, onion are important
part of our diet.
• The National Cancer
Institute has reported that
onions contain
antioxidants that help
block cancer and may also
lower cholesterol.