PLANT UNIT - SEEDS

SCOOBY DOO & THE GANG are trying to discover how a seed grows into a plant. They need your help to investigate the mysteries of the seed. Remember: Keep your eyes open for clues!

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When you finish this case, you should be able to:

• Talk about the importance of seeds.
• Tell what is needed for a seed to germinate.
• Describe the differences in seeds and tell how they survive.
• Describe nonflowering plants that produce seed-like structures (mushrooms, ferns).
• Describe a seed's structure and what's needed for seed growth.
• List seeds that are used for food.

While you're solving the mysteries, pay special attention to these key ideas:

• Seeds can remain alive over a long period of time, but they only grow when there are the proper conditions.
• Some seeds have special structures that let them move from one place to another.
• Seeds have different shapes, sizes, colors, and patterns.
• Seeds have special needs that must be met to germinate.
• Seeds have specific parts.

Before you can solve the mysteries, you'll need to learn the facts of the case.

All About Seeds

Seeds come in different sizes, shapes, and colors. Some can be eaten and some can't. 

Some seeds germinate easily while others need certain conditions to be met before they will germinate.

Do you know that within every seed lives a tiny plant or embryo? You can hold in your hand 500 radishes, many thousands of petunias, or an entire meadow if you remember that each seed is a plant!

Seeds travel! They can't just get up and walk to a new location, but structures on the seed may allow it to move to a new location. Some of the moving forces might be wind, water, animals, and gravity. Look at the seeds below and think about how they might travel from place to place.

Seed Structure

The outer covering of a seed is called the seed coat. 

• Seed coats help protect the embryo from injury and also from drying out. Seed coats can be thin and soft as in beans or thick and hard as in locust or coconut seeds. 

Endosperm, a temporary food supply, is packed around the embryo in the form of special leaves called cotyledons or seed leaves. These generally are the first parts visible when the seed germinates.

Plants are classified based upon the number of seed leaves (cotyledons) in the seed. Plants such as grasses can be monocots, containing one cotyledon. Dicots are plants that have two cotyledons.

Germination

Seeds remain dormant or inactive until conditions are right for germination. All seeds need water, oxygen, and proper temperature in order to germinate. Some seeds require proper light also. Some germinate better in full light while others require darkness to germinate.

When a seed is exposed to the proper conditions, water and oxygen are taken in through the seed coat. The embryo's cells start to enlarge. Then the seed coat breaks open and a root or radicle emerges first, followed by the shoot or plumule that contains the leaves and stem.

Many things can cause poor germination. Overwatering causes the plant to not have enough oxygen. Planting seeds too deeply causes them to use all of their stored energy before reaching the soil surface. Dry conditions mean the plant doesn't have enough moisture to start the germination process and keep it going.

Some seed coats are so hard that water and oxygen cannot get through until the coat breaks down. Soaking or scratching the seeds will help break down the seed coat. Morning glories and locust seeds are examples. Other seeds need to be exposed to proper temperatures. Apple seeds will not germinate unless they are held at cold temperatures for a period of time.

Nonflowering Plants

Nonflowering plants like ferns reproduce by "seed-like" structures called spores. Spores are usually found on the undersides of leaves and look like tiny tufts of velvet. Spores are ripe when they easily fall off the leaf. You may want to try to germinate them but it takes a long time for germination and for a plant to develop.

What Is a Seed?

The purpose of all seeds is reproduction.

What Are the Parts of a Seed?

Now that you've discovered some of the differences among seeds, it's time to look at what seeds have in common. Help the GANG discover how the parts of a seed work together to form a new plant!

1. The plant produces its seed.
2. The seed is dropped from a plant, blown by the wind, or carried away by an animal.
3. The seed ends up on good soil.
4. The seed takes up water.
5. One part of the seed, the embryo, begins to get energy from another part of the seed--the endosperm.
6. The embryo begins to grow a small root--called the radicle--downward to find moisture.
7. A shoot--called the plumule--begins to grow upwards in search of light and air.
8. The seed leaves--called the cotyledons--emerge.
   
   
   
   

VOCABULARY TERMS & DEFINITIONS

Germination -The magic process when a seed comes to life.

Seed Coat

The protective outer layer of a seed.

Endosperm Endosperm is a short-term food supply used by the embryo to help its growth. Cotyledon They look like leaves and they are the first plant part you see when a seedling pokes its head out of the ground. Cotyledons help keep the new seedling fed until it can make its own food. Sometimes cotyledons are called seed leaves.

Monocot

A plant that has only one cotyledon. Corn is an example.

Dicot

A plant that has not one but two cotyledons. A bean is an example.

Dormant

A plant that is in a resting or nongrowing state.

Radicle An immature root. Plumule The part of an embryo that turns into the shoot of a plant. Spore These unique structures are only found on plants like ferns, mosses and mushrooms. They look like dust. Spores move around in the wind, and when they land, they germinate and grow into more ferns, mushrooms and mosses.