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?

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 CO 2 and H 2 0. Photosynthesis

Photosynthesis takes place in chloroplasts. Chloroplasts are found throughout plant cells. Chlorophyll is a green pigment found in chloroplasts. Chlorophyll captures energy from sunlight. Chloroplasts

Making Sugar H 2 O is absorbed in the roots. CO 2 enters the plant through the underside of the leaf. Plants use light energy from the sun to combine CO 2 with H 2 O. 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 6CO 2 + 6H 2 O + Sunlight --> C 6 H 12 O 6 + 6O 2

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.