lab 11 - photosynthesis

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Questions and Answers

What is the primary role of pigments in plants?

To absorb light energy for photosynthesis (correct)

To store starches for energy

To reflect sunlight and prevent overheating

To provide structural integrity to cells

Which type of pigments is masked by chlorophyll in leaves until fall?

Anthocyanins

Carotenoids (correct)

Xanthophylls

Chlorophyll b

What color reflects green light in plants?

Blue

Red

Yellow

Green (correct)

Which accessory pigments are known for their yellow and orange colors?

Carotenoids Signup and view all the answers

In the Coleus plant, what pigment is primarily responsible for the dark red and violet colors?

Anthocyanins Signup and view all the answers

What is the function of I2KI in the starch test during the experiment?

To indicate the presence of starch Signup and view all the answers

Which of the following areas of the Coleus leaf will contain no pigments?

White and light yellow areas Signup and view all the answers

How do carotenoids contribute to photosynthesis despite being accessory pigments?

By absorbing light levels that chlorophyll does not Signup and view all the answers

What is the purpose of placing pigment bands into the beaker with acetone?

To dissolve the pigments for spectrophotometric analysis Signup and view all the answers

At what range of wavelengths do Chlorophyll pigments show peak absorption?

400-500, 600-700 nm Signup and view all the answers

Which cuvette contains the pigment sample during the spectrophotometric analysis?

Cuvette P Signup and view all the answers

Which of the following pigments is expected to have a peak absorption in the 400-500 nm range?

Xanthophyll Signup and view all the answers

What is the first step to ensure accurate readings in spectrophotometric analysis?

Blanking with a pure solvent Signup and view all the answers

In which light condition did the leaf show the highest presence of starch?

Red Filter Signup and view all the answers

What happens to excess glucose produced during photosynthesis in plants?

It is converted into starch for storage. Signup and view all the answers

Which filter condition resulted in no starch presence according to the starch test?

Black Paper Signup and view all the answers

Which statement accurately describes paper chromatography?

It uses a stationary phase and a mobile phase to separate components. Signup and view all the answers

Which color wavelengths were absorbed by the green leaf when using a blue filter?

Blue and Red Signup and view all the answers

Where in a leaf should starch be present to support the hypothesis?

In areas that contain chlorophyll Signup and view all the answers

What is the role of non-polar molecules in paper chromatography?

They dissolve in the solvent and move further up the paper. Signup and view all the answers

Which of the following best describes the transmission of green light through leaves under a green filter?

The green light is transmitted. Signup and view all the answers

What are the products of the photosynthesis equation?

Glucose and oxygen Signup and view all the answers

Which stage of photosynthesis involves capturing energy from sunlight?

Light-dependent reactions Signup and view all the answers

What role do pigments play in photosynthesis?

They absorb sunlight for energy capture. Signup and view all the answers

In the process of photosynthesis, what is produced during the use of ATP and NADPH?

Glucose from carbon dioxide Signup and view all the answers

What is the primary safety precaution when handling ethanol in the lab?

Do not inhale vapors Signup and view all the answers

How does polarity play a role in the chromatography process during this lab?

It separates pigments based on their solubility in a solvent. Signup and view all the answers

What is the reason for using gloves and forceps when handling flammable materials in the lab?

To prevent skin contact and burns Signup and view all the answers

What type of light do human eyes perceive from the electromagnetic spectrum?

Visible light Signup and view all the answers

What is the primary reason most plants appear green?

Green light is the only wavelength reflected and transmitted. Signup and view all the answers

Which filter would best allow for the presence of starch in leaves?

Blue filter, because it transmits blue light. Signup and view all the answers

What can be concluded about leaves under black construction paper?

They will not produce starch due to lack of light. Signup and view all the answers

How does a blue filter affect the pigments in a leaf?

It absorbs primarily blue light, reflecting other colors. Signup and view all the answers

What should be done to test the predictions made about leaf color and starch production?

Use iodine solution on the leaves after removing filters. Signup and view all the answers

What is the expected outcome for leaves with red filter paper?

Will produce some starch due to reflected blue light. Signup and view all the answers

What type of pigments are primarily involved in the deep purple color of some leaves?

Anthocyanins and chlorophylls. Signup and view all the answers

What is the role of chlorophyll in photosynthesis?

Absorbs sunlight to convert it into energy. Signup and view all the answers

What can be used to estimate the polarity of a pigment?

Counting oxygen groups Signup and view all the answers

Which pigment is considered the most polar?

Chlorophyll b Signup and view all the answers

In a paper chromatography experiment, what happens when the solvent moves up the paper?

The pigments are separated based on polarity Signup and view all the answers

Which of the following pigments would move the slowest in paper chromatography?

Chlorophyll b Signup and view all the answers

Which pigment would be expected to dissolve in a non-polar solvent first?

Beta Carotene Signup and view all the answers

What is the order of pigments from most to least polar in the chromatography experiment?

Chlorophyll b, Xanthophyll, Chlorophyll a, Beta Carotene Signup and view all the answers

What is the role of the pencil line in the chromatography procedure?

To provide a starting point for solvent movement Signup and view all the answers

How should the chromatography paper be prepared before placing it in the solvent?

Rolled into a cylinder and secured Signup and view all the answers

Study Notes

Lab 1: Photosynthesis

The lab investigates photosynthetic activity, pigment role, and polarity.
Students will separate pigments using paper chromatography.
A starch test evaluates photosynthetic activity.
An absorption spectrum is generated for photosynthetic pigments.

Lab Safety

Work with flammable and toxic substances.
Always wear gloves and use forceps for handling flammable materials (leaves, chromatography paper).
Beakers with ethanol should never be directly on a heat plate, but should be nested in a larger beaker with water.
Do not inhale solvents used for certain lab exercises, close the jar as quickly as possible to minimize inhalation.
Report any spills to the instructor immediately and do not attempt to clean yourself.
Dispose of all chemical waste in designated glass waste containers, not the sink.

Photosynthesis

Plants absorb sunlight to generate glucose, starch, and other organic molecules.
The equation for photosynthesis is 6H₂O + 6CO₂ → 6O₂ + C₆H₁₂O₆ + H₂O
Photosynthesis occurs in three stages: capturing energy from sunlight, producing ATP and NADPH, using ATP and NADPH to make carbohydrates.

Electromagnetic Spectrum

Light is comprised of packets of energy called photons.
Sunlight contains photons with varying energy levels, represented by the electromagnetic spectrum.
Human eyes perceive photons of intermediate energy levels, which are visible light.

Pigments

Pigments absorb light energy.
Chlorophyll a and b are main plant pigments.
Chlorophyll absorbs blue and red light, reflecting green light.
Pigments used in photosynthesis are located within thylakoid membranes of chloroplasts.
Accessory pigments include carotenoids (yellow, orange, and red) and xanthophylls (yellow and brown). Also anthocyanins (dark red and violet) are found in the vacuole.

Coleus Leaves

Coleus leaves contain multiple pigments.
Green areas contain chlorophyll.
Pink areas contain anthocyanins.
Dark purple areas contain both chlorophyll and anthocyanin pigments.
White and light yellow areas contain no pigments.

Experiment: Pigments in Photosynthesis

The experiment determines the pigments used in photosynthesis.
Students detach multicolored leaves, map color regions, use ethanol and boiling water to extract pigments.
I₂KI is used to test for starch presence in different leaf regions.
Students identify regions with high, medium, and low starch content.

Predictions and Results: Starch Test

The table summarizes predictions and results of the starch test for different leaf colors.
For example, green areas are predicted to have starch.

6.1: Wavelengths of Light

Only specific wavelengths of light reach the leaf.
The color seen is from the wavelengths not absorbed but reflected or transmitted.
Plants primarily appear green because they reflect green wavelengths of light.
The hypothesis predicts different photosynthetic products under different light conditions.

6.1 Predictions

Leaves under green filters have no starch.
Leaves under blue filters have some starch.
Leaves under red filters have some starch.
Leaves under no light (black) have no starch.

Demo Procedure

Students remove leaves with filters from a geranium plant
Draw/photograph the leaf, noting filter locations
Place leaves in ethanol, w/ boiling water
Add iodine solution and observe results.

Demo Procedure and Predictions

Record predictions on light wavelengths that will be absorbed or transmitted.
Observe and record starch amounts in different leaf areas.

Iodine Test for Starch

Results support the hypothesis that photosynthesis occurs only where chloroplasts are present.
Glucose from photosynthesis is stored as starch in plants
Starch is present in chlorophyll-containing areas
No starch in areas containing only anthocyanins (or lack of pigments).

Demo Results

Images demonstrating the results of the experiment.

Paper Chromatography (LM 6.3)

Used to separate components in mixtures.
Involves a stationary (polar) phase (paper) and a mobile (less polar) phase (solvent).
Solvent moves up the paper, carrying different components.
Components move differently based on their interaction with the paper and solvent.

Polarity

Polar molecules bind to the paper (stationary phase), and less polar molecules dissolve in the solvent (mobile phase).
More polar components move slower.
Non-polar components move faster.

Estimating Polarity

Pigments and their relative polarities are identified.
Hypotheses about pigment behavior in paper chromatography can be made based on these relative polarities.

Experiment: Absorption Spectrum of Leaf Pigments (LM 6.4)

Cut pigment bands from chromatography paper to separate them by their polarity.
Place bands into a beaker with 20 ml of acetone and swirl to extract the pigments.
Label two cuvettes, “P” for pigments and “B” for blank (acetone).
Fill the cuvettes with the prepared samples and run the spectrophotometer.
Record %T for each wavelength from 400 nm to 720 nm, 20nm intervals, and convert to absorbance.

Predictions and Results: Absorption Spectrum

Absorption spectrum show the absorption pattern based on wavelength.
Hypothesize and predict absorption peaks for different pigments.

Results: Absorption Spectrum

Graph of absorption spectrum for different pigments.

To Do List

List of remaining lab exercises.

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Description

This lab quiz focuses on the investigation of photosynthetic activity, the role of pigments, and related safety procedures. Students will learn about paper chromatography, starch testing, and the absorption spectrum of pigments involved in photosynthesis. Be mindful of safety practices when handling chemicals and materials during the experiment.