뒤로Study Guide: Pigments, Light Absorption, and Photosynthesis Experiments
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Q1. What colors are least absorbed and most absorbed by this pigment, according to the graph? What color would you perceive the solution to be?
Background
Topic: Light Absorption by Pigments
This question tests your understanding of how pigments absorb light at different wavelengths and how this relates to the color you perceive. It is a fundamental concept in photosynthesis and plant biology.
Key Terms:
Absorption Spectrum: A graph showing how much light a pigment absorbs at each wavelength.
Wavelength: The distance between two peaks of a wave, measured in nanometers (nm) for visible light.
Visible Light: The range of wavelengths humans can see, roughly 400–700 nm.
Step-by-Step Guidance
Examine the graph to identify which wavelengths (colors) are absorbed the least and the most by the pigment.
Recall that the color you perceive is the color of light that is not absorbed (i.e., transmitted or reflected).
Match the wavelength ranges to their corresponding colors (e.g., 400–500 nm is blue, 500–600 nm is green, 600–700 nm is red).
Determine which color is least absorbed (lowest point on the graph) and which is most absorbed (highest point).
Use this information to hypothesize what color the solution would appear to your eyes.
Try solving on your own before revealing the answer!
Final Answer:
The color least absorbed by the pigment is green (around 500–600 nm), and the color most absorbed is blue and red (around 400–500 nm and 600–700 nm). The solution would appear green because that is the color of light that is transmitted or reflected, not absorbed.
This is why many plant leaves appear green—they absorb blue and red light for photosynthesis and reflect green light.
Q2. Why did the pigment closest to the top of the chromatography strip travel faster than the ones closer to the bottom?
Background
Topic: Chromatography and Pigment Separation
This question tests your understanding of chromatography, a technique used to separate mixtures of pigments based on their solubility and affinity for the solvent and paper.
Key Terms:
Chromatography: A method for separating and analyzing mixtures of chemicals.
Solubility: The ability of a substance to dissolve in a solvent.
Affinity: The tendency of a pigment to stick to the paper versus move with the solvent.
Step-by-Step Guidance
Recall that pigments are separated based on their solubility in the solvent and their affinity for the paper.
The pigment that travels the farthest (closest to the top) is more soluble in the solvent and has less affinity for the paper.
Pigments that stay closer to the bottom are less soluble in the solvent and have greater affinity for the paper.
Think about the chemical properties (e.g., polarity) that might cause a pigment to move faster or slower.
Try solving on your own before revealing the answer!
Final Answer:
The pigment closest to the top traveled faster because it was more soluble in the solvent and had less affinity for the paper. This allowed it to move with the solvent front, while less soluble pigments stayed closer to the bottom.
Chromatography separates pigments based on their solubility and interaction with the paper.
Q3. Hypothesize the results you would expect to see in each of the following situations, and explain why:
Background
Topic: Photosynthesis, Starch Test, and Experimental Design
This question tests your understanding of how light exposure affects photosynthesis and starch production in plants, as well as how the iodine test reveals the presence of starch.
Key Terms:
Photosynthesis: The process by which plants convert light energy into chemical energy (glucose).
Starch: A storage form of glucose in plants, produced during photosynthesis.
Iodine Test: A chemical test for starch; iodine turns blue-black in the presence of starch.
Step-by-Step Guidance
For each scenario, consider how much light the plant receives and how this affects photosynthesis and starch production.
Recall that boiling the leaf in ethanol removes chlorophyll, and placing it in water rehydrates it. The iodine test then reveals starch.
Scenario A: Plant receives light 24 hours a day. Predict whether starch will be present in the leaf.
Scenario B: Plant receives light for 6 hours, then darkness for 18 hours. Predict whether starch will be present after 10 hours of darkness.
Scenario C: Plant receives no light for a week. Predict whether starch will be present in the leaf.
Explain your reasoning for each scenario based on the relationship between light, photosynthesis, and starch production.
Try solving on your own before revealing the answer!
Final Answer:
A) The leaf will test positive for starch (blue-black color) because continuous light allows for constant photosynthesis and starch production.
B) The leaf will likely test negative for starch (no blue-black color) because after 10 hours of darkness, the plant has used up its starch reserves for respiration, and no new starch is produced without light.
C) The leaf will test negative for starch (no blue-black color) because no photosynthesis occurs in complete darkness, so no starch is produced.
The iodine test reveals the presence or absence of starch, which depends on whether the plant has been photosynthesizing.
