Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Life Science to answer the following questions. Show all work where necessary.
Plants depend on photosynthesis to produce sugars made of carbon, hydrogen, and oxygen. These sugars act not only as energy sources, but also as carbon skeletons for constructing more complex molecules such as amino acids, nucleotides, and proteins. For amino acids to form, plants must combine the carbon-based backbones from glucose with key additional elements - including nitrogen (N), sulfur (S), and phosphorus (P). Nitrogen is especially critical because it forms the amino group
When nitrogen levels in the soil are sufficient, plants readily absorb nitrate and ammonium. Inside plant cells, enzymes attach nitrogen to carbon skeletons derived from glucose, creating essential amino acids such as glutamate, serine, and cysteine. Some amino acids also incorporate sulfur, while phosphorus contributes to the regulation of metabolic pathways that allow amino acids to be assembled into proteins. These proteins make up enzymes, structural fibers, chlorophyll-binding complexes, and many other cellular components.
However, when a plant experiences nitrogen deficiency, this biochemical assembly line stalls. The plant continues to produce sugars through photosynthesis - sometimes at even higher levels because growth slows and sugar transport is reduced - but it cannot convert these sugars into amino acids. Without nitrogen, sulfur, or phosphorus, the plant cannot complete amino acid structures, preventing protein synthesis. As a result, sugar levels rise while protein levels fall.
A major visible symptom is chlorosis, or yellowing of leaves. Chlorophyll itself contains nitrogen, so low nitrogen levels reduce chlorophyll production, limiting the plant’s ability to capture light. Nitrogen-deficient plants also exhibit stunted growth, thin stems, and reduced biomass because proteins are required for producing new cells and maintaining metabolic reactions.
Diagram 1.
Source: https://www.visionlearning.com/en/library/Chemistry/
Diagram 2.
Source: https://ccrma.stanford.edu/~woojecho/220a/fp.html
Table 1.
Nitrogen Level (ppm) | Leaf Sugar (% dry mass) | Leaf Protein (% dry mass) |
|---|---|---|
0 | 18.2 | 4.1 |
25 | 15.1 | 6.2 |
50 | 11.6 | 9.5 |
100 | 8.4 | 14.8 |
150 | 7.9 | 15.6 |
Graph of Information - Figure 1.
Table 2.
Nitrogen Level (ppm) | Chlorophyll Content (mg/g) | Plant Biomass (g) |
|---|---|---|
0 | 0.8 | 0.9 |
25 | 1.2 | 1.8 |
50 | 1.9 | 2.9 |
100 | 2.8 | 4.7 |
150 | 3 | 5 |
Graph of Information - Figure 2.
Using Table 1 and Figure 1, describe how leaf sugar and leaf protein levels change as nitrogen levels increase from 0 ppm to 150 ppm.
According to Table 1, at which nitrogen level are leaf protein levels the highest?
Using the reading and Figure 2, explain how nitrogen availability influences interactions among cells, tissues, and the whole plant in supporting growth and metabolism.
Using Table 2 and Figure 2, describe the relationship between nitrogen level and changes in both chlorophyll content and plant biomass.
Based on the reading, which statement BEST explains why nitrogen-deficient plants become chlorotic (yellow)?
Explain how nitrogen availability affects the ability of plants to combine sugars with nitrogen, sulfur, and phosphorus to form amino acids and plant proteins.
In your response, include a clear claim, evidence, and reasoning.