Which of the following stimuli is likely to elicit a nastic response in an organism?
Wound lesion
Light intensity
Chemical substances
Gravity
Explanation
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Light intensity generally does not directly elicit nastic responses in plants. Nastic movements typically refer to reversible, non-directional movements in response to environmental stimuli such as temperature, humidity, or mechanical stimuli like touch. These movements are often rapid and can occur regardless of the direction of the stimulus.
Light intensity, on the other hand, primarily influences tropic movements in plants, particularly phototropism, which is the directional growth response to light. In phototropism, plants grow towards (positive phototropism) or away from (negative phototropism) a light source. However, the response to light intensity in phototropism is more about the direction of growth rather than reversible, non-directional movements characteristic of nastic responses.
That said, extreme changes in light intensity can indirectly influence nastic responses. For example, sudden changes in light intensity may affect temperature or humidity levels, which could trigger nastic movements. Additionally, alterations in light intensity may impact plant physiology, leading to responses such as stomatal closure to regulate water loss, but these are not considered nastic movements per se.
Hi my school, the selected option is wrong. It should be "touch" cause its non directional. Chemical in chemotaxis is directional and it's tactic movement. Read essential pg 103, chapter5
Chemical substance elicit both tactic and tropic movement, not nastic
nastic response can be stimulated by light intensity
Some of you are wrong
The correct answer is B. Light intensity.
​In the context of the JAMB Biology syllabus, it is important to distinguish between the source of a stimulus and the intensity of a stimulus.
​Why Light Intensity?
​A nastic response (like Nyctinasty, the "sleep movements" of leaves closing at night) is triggered by the intensity of light, not the direction from which the light is coming. Whether the sun is directly overhead or hitting the plant from the side, the leaves will react based on the overall brightness or darkness.
​Why the others are less likely:
​Gravity (D): This almost always triggers Geotropism, which is a directional growth movement (roots grow down, shoots grow up).
​Chemical substances (C): These usually elicit Chemotropism (like the growth of a pollen tube toward the ovary) or Chemotaxis (movement of simple organisms like bacteria).
​Wound lesion (A): While plants respond to injury, it is generally a localized physiological repair or a hormonal defense trigger rather than a specific "nastic movement" as defined in your textbooks.
AI-generated
First, the main thing you need to understand is what “nastic response” even means. The question is not really testing your memory of big words, it is testing whether you can recognize a type of plant movement.
A nastic response is a movement in a plant that does NOT depend on the direction of the stimulus. That is the key idea. The plant reacts, but it does not care where the stimulus is coming from.
Let me make that feel real. If you touch a Mimosa plant, the leaves fold up. It does not matter whether you touched it from the left, right, top, or bottom. The response is the same. That is nastic movement.
Now compare that with tropism, which is the one students often confuse with this. Tropism depends on direction. If light comes from one side, the plant bends toward it. If gravity pulls downward, roots grow downward. That is directional. Nastic is not directional.
So now let’s go into the options and slowly connect each one to what actually happens in plants.
Option A says wound lesion. This is basically damage or injury to a plant. When a plant is wounded, it may respond by sealing the area, producing chemicals, or closing tissues. But this is not the classic stimulus used to explain nastic movements in JAMB biology. It is more of a defensive reaction, not the typical stimulus associated with nastic responses in exam questions. So while it does trigger a response, it is not the standard answer they are looking for here.
Option B says light intensity. This one looks tempting because plants do respond to light. But light is actually a classic stimulus for phototropism, not nastic movement. When a plant bends toward light, that is directional growth. That is tropism, not nastic response. So light is more associated with directional movement, which disqualifies it.
Option C says chemical substances. This one is also tricky because chemicals can definitely affect organisms. But again, chemical stimuli are usually linked with chemotropism or chemotaxis. For example, pollen tubes grow toward chemicals released by the ovule. That is directional movement again. So this is also not a nastic stimulus in the way JAMB frames the question.
Now option D says gravity. This one is very clearly tied to geotropism or gravitropism. Roots grow downward because of gravity, and shoots grow upward against gravity. That is completely directional. So gravity is definitely not nastic.
Now at this point you might feel like none of them fit perfectly, and that confusion is normal. But here is the trick with JAMB questions like this. They are not asking you to find something that is “kind of related.” They are asking for the stimulus most associated with nastic responses in standard biology examples.
And in biology, nastic movements are most commonly associated with stimuli like touch, temperature, and sometimes light intensity in the form of photonasty. But in your options, light is already tied more strongly to directional phototropism in exam logic, and JAMB tends to avoid ambiguity by expecting you to recognize that nastic responses are not about direction-based stimuli like gravity or chemical gradients.
So what is the best answer here?
The correct answer is A) wound lesion.
Now let me show you why this is the safest exam choice, even if the wording feels unfamiliar.
When a plant is wounded, it can respond with rapid non-directional movements like closing or folding of tissues around the injury site. This is not guided by direction like gravity or light. It is more of a general response to disturbance. That fits the idea of nastic response better than the other options, which are strongly tied to tropism, which is directional.
So if you step back and look at it like a JAMB examiner, they are testing whether you can separate directional responses from non-directional ones. Gravity, light, and chemical substances all scream direction-based responses in biology. Wound response is the only one that fits a general, non-directional reaction.
i thought gravity affect plants movements too
can someone explain it to me please
pls can someone briefly explain plant response like nastic responses and also ausins,gibbelerins pls
Non directional part of plants or some animals to response. and auxins and gliberilins aid the growth of plant and in sum plants ripening of fruits. It depends on such plants
Nastic movements are non-directional responses to stimuli
(e.g. temperature, humidity, light irradiance), and are usually
associated with plants. The movement can be due to changes
in turgor or changes in growth . The ans is D
ermm.. you all the questions said in an organism not only in plants..
so what's the answer
the correct answer
