Exploring Light and Plant Pigments with littleBits and FastPlants


Exploring Light

Based on original research in Michael Wilkinson’s 4th Grade Science Classroom at Fieldston Lower School ECFS (http://www.ecfs.org,http://mwmathsci.blogspot.com)

Introduction

Authentic scientific exploration often relies on engineering apparatus to support obtaining the data that authenticates or contradicts a hypothesis. With littleBits, students can easily design and build prototypes of lab apparatus that would otherwise be inaccessible. The following project is an illustration of how littleBits can be used to support authentic scientific inquiry.

OBJECTIVE

Students will engineer a littleBits lab apparatus to control the color(s) of light the seedlings are exposed to and test their effect on the expression of chlorophyll in plant seedlings.

GUIDING QUESTION

How can we prove that the color of light will affect the amount of chlorophyll produced by seedlings?

EXPERIMENTAL TRIALS

A minimum of 5 trials need to be conducted. Depending upon student familiarity with: seed germination, the concepts of light and color, and the process of experimental design, class time can be expanded or abbreviated to suit your instructional plan.

1 class period for prelab and engineering brainstorm

1 class period for building prototypes and begin trials

1 class period (after 5 days of growth) for observation

1 class period for discussions and conclusions

APPLICABLE NGSS (Next Generation Science Standards)

K-PS2; 3-PS2-1-2; 5-PS2-1

K-LS1; 1-LS1; 3-LS1-1; 5-LS1-1

2-PS1-3

2-LS2-1

4-PS3-2,4

K-2-ETS1; 3-5-ETS1; MS-ETS1; HS-ETS1

For more details on how to construct the prototype and apparatus, see the corresponding project page: http://littlebits.cc/projects/exploring-light-and-plant-pigments-with-littlebits-and-fastplants

Duration: 4 Class Periods; 5 Trials

GRADE LEVEL
Elementary (ages 8-10)
Middle School (ages 11-13)

DIFFICULTY
Advanced

SUBJECT
Science

MODULES & ACCESSORIES USED (27)
branch (5)
usb power (5)
led (3)
rgb led (6)
bright led (3)
wire (5)

LESSON GUIDE

STEP 1 : 1st Period: Prelab

Based on the the knowledge that we perceive objects as a particular color because those wavelengths are reflected back to our eyes, my students hypothesized that green light was not used by the plants because they appeared green. The chloroplasts in the leaves must be using other colors of light for photosynthesis.

Hypothesis: Chlorophyll is not expressed under green light or in the dark.

Brainstorm: What procedures and apparatus are needed to test hypotheses?

Design Challenge: How can littleBits be combined with other materials to build an apparatus to prove that the color of light will affect the expression of chlorophyll in the leaves.

STEP 2 : 1st Period Outcomes

Exploring Light1

Students will have drafted their procedures and plans. They will build prototypes during the next session.

After brainstorming procedural ideas, the students determined that the experiment would need the following trials:
-no light

-white light

-red light

-green light

-blue light

STEP 3 : 2nd Period: Build Prototypes and Begin Trials

Exploring Light2

Working in small groups, students built and tested prototypes to achieve each of the lighting conditions above. Prototypes were shared and groups converged on the following circuits:

For white light: usb power + wire +branch + 3x bright LED

For red light: usb power + wire +branch + 3x RGB LED

For green light: usb power + wire +branch + 3x standard LED

For blue/violet light: usb power + wire +branch + 3x RGB LED

These circuits were mounted inside the top of an opaque box large enough to cover a small container of petri dish germination chambers. The same box was used for the dark trial with no LEDs. Brassica rapa seeds (FastPlants) were germinated in each of the 5 lighting condition and grown for 5 days.

See the complete project instructions on how to build and set up the experimental materials here: http://littlebits.cc/projects/exploring-light-and-plant-pigments-with-littlebits-and-fastplants.

STEP 4 : 3rd Period: Observations

Exploring Light3

After 5 -7 days, remove each germination chamber and observe the seedlings. Note specifically the color of the cotyledons. Compare the color of cotyledons between the different lighting conditions.

STEP 5 : *Optional Extension Step*

Exploring Light4

Perform chromatography analysis of the cotyledons.

Materials per lab group:

-test tube rack

-5 test tubes

-rubbing alcohol (about 5 ml per tube)

-5 chromatography paper strips 1 cm wide and 3 cm longer than test tube

-chopstick

Prepare chromatography strips, one for each lighting condition. Label each at one end with the lighting condition and lab group. At opposite end, draw a line across the width of the strip about 1 cm from end. Only use regular graphite pencil for labeling.

Remove seedlings from germination chambers, one petri dish at a time. Gently blot the seedlings dry with a paper towel.

Using the wide end of the chopstick, press the pigments from the cotyledons onto the filter paper just above the pencil line.

Place chromatography strip in test tube so that the end of the paper just touches the alcohol. Fold the remainder of the strip over the lip of the test tube to maintain position. Allow the alcohol to work for 1 – 2 hours until the pigments have spread up the strip and separated.

Remove strips from test tube and allow them to air dry completely. If they are not to be read immediately, store the strips in a dark place as the pigments will quickly fade in the light.

Compare which pigments, as well as how much of each, are present in each lighting condition. The five pigments that may be observed are: Chlorophyll A (dark blue-green), Chlorophyll B (light yellow-green), Xanthophyll (yellow-orange), Carotene (orange-brown) and Anthocyanin (red).

Expected Results (For discussion):

Dark: only xanthophyll and carotene

White: chlorophyll A and B, xanthophyll, and carotene

Red: chlorophyll A and B, xanthophyll, and carotene

Green: chlorophyll B (possibly), xanthophyll, and carotene

Blue/Violet: chlorophyll A and B, xanthophyll, and carotene

It is not likely that anthocyanins will be observed as they are primarily produced by plants under stress.

STEP 6 : 4th Period: Discussion and Conclusions

Exploring Light5

By the end of the experiment, students will be able to articulate that:
…the red and blue ends of the light spectrum are most critical for photosynthesis.

…the green wavelengths of light are primarily reflected by the leaves and are not used for photosynthesis.

…chlorophyll A is only produced in the presence of red or blue light.

…photosynthesis cannot occur in the dark.

…photosynthesis is limited in green light.