Parts of a Bean Seed

What’s inside a bean? Take a peek into the beginnings of a beanstalk, and see how a bean grows.

What are the parts of a bean seed?

Materials

• Jar
• 8 pinto bean seeds
• Distilled water
• Refrigerator
• Paper towel
• Magnifying glass
• Knife
• 5 small cups
• Paper
• Pencil
• 5 pots
• Soil
• Spray mister

Procedure

1. Put the eight seeds into the jar and pour distilled water onto them. After 24 hours, remove the beans and place them on a paper towel.
2. The beans should be damp and easy to pry open with your fingernail. Remove the outside of the bean. This part is called the seed coat, and it protects the bean inside. Place your fingernail at the rounded edge and spread the halves of each bean open lengthwise.
3. Use a magnifying glass to look inside. What can you see? Sketch the inside of each bean, labeling each half from 1 to 16. Do different bean plants look different inside?

Results

When you look inside a bean, it’s not just empty space in there. A bean is made up of different growing parts, and you’ll be able to see them quite clearly with your magnifying glass.

The cotyledon is the largest part of the inside of the bean. It stores a lot of the food for the growing bean. Like a chick embryo has a yolk and a baby has an umbilical cord, a bean seed has a cotyledon to act as a source of food.

At the top of the cotyledon is the epicotyl. This is the beginning of the bean’s shoot and will eventually form the leaves. Look closely. Can you see what will form the bean’s future leaves? Just under the epicotyl is the hypocotyl. This is the beginning of the bean’s stem. The radicle is under the hypocotyl. This is the beginning of the bean’s roots. A whole baby plant is nestled inside that tiny, growing bean seed.

A bean needs water to grow. At first, it absorbs this through a small hole called the micropyle that is found in the hilum, the scar on the side of the bean that shows where it was attached to its parent plant. When the bean germinates, or begins to grow, the baby bean plant starts to take shape inside the bean seed. It uses the starch that’s in the cotyledon as food.

What would happen if you cut away part of the cotyledon? To extend your experiment, get 5 new bean seeds and soak them overnight. Cut off the lower half of one of the cotyledons of one bean, the lower half of both cotyledons on another bean, ¾ of the cotyledon on another bean, and all of the cotyledon on the last bean, leaving only the embryo. Leave one unaltered bean plant as the control.

Label your pots like this:

• 100%—Do not cut away any part of the cotyledons.
• 75%—Cut away the lower half of one cotyledon.
• 50%—Cut away the lower half of both cotyledons.
• 25%—Cut away all but one-fourth of the cotyledons, leaving the section attached to the embryo.
• 0%—Cut away both cotyledons, leaving only the embryo.

Plant these seeds in soil in five pots and see how each one grows. Mist the beans daily. Remember what the cotyledon gives to a plant. Which one will grow the best?