The radioactive isotope that can be used to track the uptake of fertilizer from root level to leaves is:
P-32
Tracking Fertilizer Uptake with Radioactive Isotopes
Understanding how plants absorb and transport nutrients like fertilizers is crucial for agriculture. Scientists use special techniques, including radioactive isotopes, to follow the movement of these substances within the plant body.
Using Isotopes as Tracers
Radioactive isotopes are atoms of an element with an unstable nucleus, which decays over time, emitting radiation. When a plant takes up a compound containing a radioactive isotope, researchers can detect the radiation to track where the compound goes inside the plant. This method is called radioactive tracing.
Why P-32 is Used for Fertilizer Tracking
Phosphorus is a vital nutrient for plant growth and is a major component of many fertilizers. The radioactive isotope of phosphorus, \text{P-32} (or ^{32}\text{P}), is widely used as a tracer for studying phosphorus uptake and movement in plants because:
- It is radioactive and emits beta particles, which are relatively easy to detect using standard radiation detectors like Geiger counters or by techniques like autoradiography.
- It behaves chemically just like stable phosphorus, meaning the plant's metabolic processes handle it in the same way as the non-radioactive form.
- It has a suitable half-life (about 14.3 days). This half-life is long enough to conduct experiments that track nutrient movement from roots to leaves over several hours or days, but short enough that the radioactivity declines relatively quickly after the experiment, reducing long-term environmental impact.
When a fertilizer containing \text{P-32} is applied to the soil, the plant absorbs it through the roots. The \text{P-32} is then transported within the plant's vascular system (specifically the xylem) to various parts, including the stem and leaves. By measuring the radioactivity in different plant tissues over time, scientists can determine the rate and pattern of phosphorus uptake and translocation.
Analyzing the Options
Let's look at why the other options are less suitable for tracking general fertilizer uptake from roots to leaves:
- P-32 (^{32}\text{P}): As discussed, this isotope of phosphorus is the standard tracer for phosphorus uptake and movement in plants due to its appropriate half-life and chemical behavior.
- P-30 (^{30}\text{P}): This is also a radioactive isotope of phosphorus, but it has a very short half-life of approximately 2.5 minutes. This half-life is too short for tracking movement from roots to leaves, which can take hours or even days.
- N-13 (^{13}\text{N}): This is a radioactive isotope of nitrogen and is used to study nitrogen uptake and transport. However, the question refers to tracking "fertilizer" uptake generally, which often implies major nutrients like phosphorus or potassium, or components of mixed fertilizers. While nitrogen is a key nutrient, N-13 has a short half-life (about 10 minutes), making it primarily useful for rapid, short-term studies of nitrogen metabolism near the point of uptake. It's also typically produced by cyclotrons, making it less accessible than P-32.
- N-16 (^{16}\text{N}): This is another radioactive isotope of nitrogen with an extremely short half-life of about 7.13 seconds. This half-life is far too short for any practical tracing experiment involving transport from roots to leaves.
Considering the properties and typical applications of these isotopes in plant science, \text{P-32} is the most appropriate choice for tracking the uptake and translocation of fertilizer components (specifically phosphorus) from the root level to the leaves.
Revision Table: Properties of Isotopes for Plant Tracking
| Isotope | Element | Approximate Half-life | Relevance for Root-to-Leaf Tracking |
|---|---|---|---|
| \text{P-32} (^{32}\text{P}) | Phosphorus | 14.3 days | Highly suitable. Sufficiently long half-life for transport studies. Behaves like stable P. |
| \text{P-30} (^{30}\text{P}) | Phosphorus | 2.5 minutes | Unsuitable. Half-life too short for typical transport studies from roots to leaves. |
| \text{N-13} (^{13}\text{N}) | Nitrogen | 10 minutes | Limited suitability. Used for N uptake, but half-life is relatively short for long-distance transport over many hours. Question implies general fertilizer, not just N. |
| \text{N-16} (^{16}\text{N}) | Nitrogen | 7.13 seconds | Completely unsuitable. Half-life is extremely short. |
Additional Information: Radioactive Tracers in Plant Science
Radioactive tracers are powerful tools in plant research. They allow scientists to non-invasively study the dynamics of nutrient uptake, transport, metabolism, and accumulation within living plants. Beyond \text{P-32} and nitrogen isotopes, other isotopes are used for different purposes:
- \text{Carbon-14} (^{14}\text{C}): Used to study photosynthesis, the movement of sugars (photoassimilates) through the phloem, and plant metabolism. It has a very long half-life (approx. 5,730 years).
- \text{Potassium-42} (^{42}\text{K}): Used to study potassium uptake and transport, which is another essential plant nutrient. It has a half-life of about 12.36 hours.
- \text{Iron-59} (^{59}\text{Fe}): Used to investigate iron uptake, translocation, and storage in plants. Its half-life is about 44.5 days.
The choice of tracer depends entirely on the specific element being studied and the timescale of the process being investigated. Safety precautions are always necessary when working with radioactive materials.
Important Questions from Radioactivity
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