Welcome my Thursday readers. Today it’s all about the outside and how seeds become plants and flowers !
- learn how to sort and classify seeds by external characteristics.
- discover what’s inside a seed, to predict how seeds will change after sprouting, and to observe the sprouting (germination) process.
Seeds grow into new plants. Each seed has a seed coat and an embryo containing tiny leaves, a stem, and roots. The seed coat protects the embryo while a temporary food supply nourishes it, either as an endosperm packed around the young plant or stored in special leaves called cotyledons. Most seeds are either moncots, having one cotyledon, or dicots, with two. Seeds remain inactive until conditions are right for them to begin to grow, or germinate.
All seeds require oxygen, water, and the proper temperature range in order to germinate. Oxygen and moisture, initially taken in through the seed coat and later by the root, help the seed get energy from its food supply. Different types of seeds have specific temperature requirements and preferences for germination. Many seeds also require proper light conditions to germinate: some require light, while others are inhibited from germinating by light.
Seeds have their own source of nutrients (in the cotyledons or endosperm) to sustain them through early life, so they do not require additional nutrients. The proteins, fats, and carbohydrates stored for the benefit of the young plant are what make seed such a rich and vital food source for humans and other animals.
When a seed is exposed to proper conditions for germination, water is taken in through the seed coat. The embryo’s cells begin to enlarge and the seed coat breaks open. The root emerges first, followed by the shoot, which contains the stem and leaves.
Exploration:
- Give each pair of students two lima bean seeds (from step 3 above), ½ cup of water, and a hand lens. Have them place their seeds in water for twenty-four hours and examine them regularly. Be sure to start some extra seeds, in case some don’t germinate. Ask: What do you predict will happen to the seeds while they are soaking?
- After twenty-four hours, ask: How did your seeds change while they soaked in water? Did this match your prediction? What do you think was happening inside the seed? Have students in each pair help one another carefully peel the outer coat from one of the seeds. Then guide them or help them to pull the coatless seed in half with a fingernail.
- On the same drawing students made in step 3 above, ask students to draw a picture of the inside of one of the split seeds. Ask: How does what you see inside the seed compare to your original prediction? Does any part of the inside of the seed look like a familiar plant part? Which? Do you think the seed is alive? Why or why not?
- Have students place their seeds (both the whole bean seed and the seed that was split in half) in a plastic bag with a moist paper towel for a week. Ask: What do you predict will happen to the seeds during the week?
- Continue observing the seeds daily for a week. Students should record changes by making new drawings next to their originals. Consider having students make a growth chart to record changes during germination, by folding a long strip of paper like an accordion and clipping it with a paper clip. Draw on one section at a time as the seed grows. When complete, unfold to view the sequence.
- At the end of the week, discuss findings. Ask: How did different parts of the seeds change during the week? What happened first? Next? Did everyone’s seeds change at the same speed? In the same order?