Living Creatures: Exploring their Characteristics · Lesson 3 of 8
How Seeds Germinate
“Use a four-pot investigation to discover what a bean seed needs to begin growing.”
• Describe germination and identify the seed coat and embryo. • Predict and compare outcomes for dry, flooded, moist-dark and moist-lit pots. • Explain why bean seeds need a suitable amount of water and access to air. • Distinguish light needed for germination from light needed for later seedling growth. • Recognise that light and darkness requirements can differ among kinds of seeds.
A quiet seed with the potential to grow
A bean seed on a shelf may not move or increase in size, yet under suitable conditions it can develop into a new plant. When the seed produces a sprout, we say it has germinated. The tiny embryo inside is the part that develops, and a seed coat surrounds it. What must the seed receive to start? A fair investigation is more useful than guessing from one successful pot.
The beginning of a seed’s development into a sprout under suitable conditions.
The outer covering of a seed, which becomes softer when the seed takes in water.
Compare four pots, not four stories
Put four bean seeds into each of four similar pots of garden soil. Keep A dry in sunlight; give B excess water so water stands above its soil, also in sunlight; keep C moderately moist in darkness; and keep D moderately moist in sunlight. Write a prediction for each, then observe for 7–10 days within the approximately 15-day setup. Record what happens as well as a possible reason. More than one seed per pot helps you see whether an outcome is repeated.
| Pot | Water | Air around seed | Light | Expected bean germination |
|---|---|---|---|---|
| A | None added | Present in soil spaces | Sunlight | Unlikely without water |
| B | Excess, standing above soil | Limited when spaces fill with water | Sunlight | Unlikely with too little accessible air |
| C | Soil kept moist | Present in soil spaces | Dark | Can germinate |
| D | Soil kept moist | Present in soil spaces | Sunlight | Can germinate |
Compare A with D to examine the need for water, B with D to examine the effect of excess water, and C with D to examine sunlight. We should describe what actually germinates before explaining it. If A remains unsprouted while C and D sprout, lack of water is a strong explanation. If B fares poorly although it has water, more water is clearly not always better.
Problem
Bean seeds in moderately moist pots C and D both sprout, although C is in darkness and D in sunlight. What can we infer?
- 1.Both sets of seeds had water and access to air in the spaces around the soil.
- 2.The important difference was access to sunlight during the start of germination.
- 3.For these bean seeds, sunlight is not essential to begin germination. This does not show that a growing seedling can remain healthy without light indefinitely.
Why water and air matter
Water softens the seed coat and enables processes needed for the embryo to grow. Without enough water, that development cannot begin. Bean seeds also need air for respiration. Soil has spaces between its particles that provide air and later allow roots to grow through it. When excess water remains above the soil, it can fill those spaces and limit the air available to seeds.
Problem
A student reasons that pot B should sprout best because it has the most water. How would you test that explanation?
- 1.Compare B with D: both are in sunlight, but B is flooded while D is moderately moist.
- 2.If D sprouts and B does not, ask what flooding changes besides water quantity. It reduces the air spaces available around the seeds.
- 3.Conclude that a suitable amount of water and access to air matter; “more water” is not automatically better.
Light for the seed and light for the seedling
For beans in this investigation, a moist seed can germinate even in a dark place. After germination, a seedling needs sunlight for further healthy growth. Do not mix up the start of sprouting with the longer period of growth. Most seeds do not require light to start germinating, but the chapter gives useful exceptions: Coleus and Petunia need light, while Calendula and Zinnia need darkness and are covered with enough soil.
Knowing that water starts germination also suggests a practical reason to keep stored grains and pulses dry: unwanted moisture may allow seeds to sprout or spoil in storage. A different investigation could vary temperature while keeping the seed kind, water, air and observation period comparable; that experimental-design question returns in the final practice lesson.
The four-pot result establishes what happened with bean seeds under those conditions. Other seeds can have different light or darkness requirements.
Quiz
When is a seed said to have germinated?
Which pair most directly tests whether bean seeds need sunlight to begin germination?
Why can permanently flooded soil prevent bean seeds from germinating?
What does water do for a seed in the chapter’s explanation?
Which statement follows from the bean-pot comparison?
Which named seeds are examples of seeds needing light to germinate?
Practice Problems
- Draw a four-pot comparison table with columns for water, air and sunlight. Predict and then explain the outcome of each pot.
- Why is pot D a useful comparison with A, B and C? Explain what differs in each comparison.
- Describe the seed coat and embryo and explain how water helps the start of growth.
- A child puts ten bean seeds in a water-filled closed jar. Explain why abundant water alone does not ensure sprouting.
- Explain why a bean seed may germinate in darkness although the resulting seedling will later need sunlight.
- Use your knowledge of germination to explain why grains and pulses are usually stored dry.
Key Takeaways
• Germination begins when a seed sprouts; an embryo develops within a seed coat. • Bean seeds require a suitable amount of water and access to air. • Flooding can reduce the air available in soil spaces. • Bean seeds can begin germinating without sunlight, but the seedling later needs light. • Light requirements can differ among seed kinds, so avoid a universal rule from one experiment.