Tropic Responses in Seedlings Allow Plants to Grow Toward Light and Gravity
- Unlike animals, plants lack a nervous system to control their growth and responses to the environment.
- However, they have coordination mechanisms that regulate their development, allowing them to sense and respond to external stimuli such as light and gravity.
- These responses are known as tropic responses and are controlled by plant hormones, primarily auxins.
- Imagine planting a seed in a pot and placing it on a windowsill. After a few days, you notice the shoot bending toward the light.
- This is phototropism, a type of tropic response where plants grow in response to environmental stimuli.
Key Tropic Responses in Seedlings
- Tropism refers to the directional growth response of a plant to an environmental stimulus.
- Several types of tropic responses can be observed in seedlings:
1. Phototropism
- This type of tropism is growth in response to light.
- Seedlings often grow toward the light, a process driven by auxins that accumulate on the side of the plant furthest from the light source, causing the cells there to elongate more than those on the light-facing side.
2. Gravitropism (Geotropism)
- This type of tropism is growth in response to gravity.
- Roots typically exhibit positive gravitropism (growing downward), while shoots show negative gravitropism (growing upward).
- Remember that gravity pulls us down.
- Hence, positive gravitropism means the plant grows downwards (since it's doing what it's supposed to do).
- Negative gravitropism on the other hand, means the plant grows upwards (since it's not doing what it's supposed to do)
3. Thigmotropism
- This type of tropism is growth in response to touch.
- This response is often observed in climbing plants or vines, which wrap around supports as they grow.
Types of Observations: Qualitative vs. Quantitative
Understanding the distinction between qualitative and quantitative observations is crucial in scientific investigations.
Qualitative observations
- Qualitative observations refer to descriptive data that involve the senses (e.g., observing the direction of growth or the pattern of bending in response to light).
- Example of Qualitative Data:
- The seedling bends toward the light.
- The roots grow downward.
Quantitative observations
- Quantitative observations involve measurable data, such as measuring the angle of curvature of seedlings or recording the rate of growth over time.
- Example of Quantitative Data:
- The seedling bent at a 30° angle towards the light after 24 hours.
- The roots grew 4 cm downward in the first 3 days.
