Grade Level/Subject
Unit
Enduring
Understanding
SOL Objectives
Title
Lesson Objective
Inquiry Level
Materials Needed
How is it Level 3?
7th grade/Life Science
Energy (Photosynthesis)
Almost all life on earth is ultimately maintained by transformation of
energy from the sun and the existence of water. Each part of a
system is only fully understandable in relation to the rest of the
system.
LS.1 The student will demonstrate an understanding of scientific
reasoning, logic, and the nature of science by planning and
conducting investigations in which
a) data are organized into tables showing repeated trials and
means;
c) triple beam and electronic balances, thermometers,
metric rulers, graduated cylinders, and probeware are
used to gather data;
e) sources of experimental error are identified;
f) dependent variables, independent variables, and
constants are identified;
g) variables are controlled to test hypotheses, and trials are
repeated;
h) data are organized, communicated through graphical
representation, interpreted, and used to make predictions;
i) patterns are identified in data and are interpreted and
evaluated
LS.5 The student will investigate and understand the basic physical
and chemical processes of photosynthesis and its importance to
plant and animal life. Key concepts include
a) energy transfer between sunlight and chlorophyll;
b) transformation of water and carbon dioxide into sugar and oxygen
Which gas is used up in photosynthesis?
Design an experiment to determine which material is best at
absorbing heat from the sun
3
Materials listed on front page of lab
Teacher provides the research question and the materials. The
methodology is developed largely by the students, although the lab
packet does provide some guidance.
Life Science Inquiry Lab: PHOTOSYNTHESIS
What Conditions Are Needed For Plants to Carry Out Photosynthesis?
NOTES FOR THE INSTRUCTOR
Students, working in pairs or groups of four, will be provided a variety of materials that they can choose to use
in their experimental design. The objective is to show evidence of photosynthesis by observing either a
reduction in carbon dioxide or the production of oxygen bubbles from the submerged leaves. Students should
set up samples with contrasting variables. Three contrasting pairs should become evident; namely, light vs. dark
conditions, carbon dioxide-infused water vs. carbon dioxide-depleted water, and acidic vs. neutral/slightly basic
pH. (A fourth variable, temperature, may be included if the classroom has the refrigerator capacity; but that
variable is not considered in this discussion.) Each pair of students should design only one experiment. Class
data can be shared in the post-lab activity.
Materials:
4 – Empty water bottles (8 fl.oz.) w/ screw caps
(Approx. per 4 – Yew branch cuttings or Elodea sprigs, 7-10 cm
4 students) 500 mL – Tap water (unheated)
500 mL – Low CO2 tap water (heated & cooled)
10 mL – White vinegar (acid)
2 pcs. – Aluminum foil (15 cm x 15 cm)
2 pcs. – Medium-sized (8 in.) soda straws
50 mL – Bromthymol blue std. solution (0.04%)
Refrigerator (optional)
(44 mL FOSS vials w/ snap caps)*
(5-7 cm)
(80 mL)
(80 mL)
(2 mL)
(10 x 10 cm)
(2 pcs.)
(8 mL)
PRE-LAB ACTIVITY SCHEDULE:
DAY 1:
Since students will not be testing indirectly for the disappearance of a reactant (CO2) of
photosynthesis, and directly for a product (O2) they should first be familiar with the process through a study of
the chemical equation, which is provided for reference at the beginning of the lab activity handout.
DAY 2: Teacher- or student-centered demonstrations of the following reactions/techniques:
1) (Oxygen) bubble production on submerged leaves in sunlight. This is easily achieved by blowing
exhaled air through a soda straw into the water for 30-45 seconds before placing the container in the
sunlight or under artificial bright light. A second sample should be prepared with water that has been
heated above 70 C (a microwave oven works well here) and then allowed to cool. After adding the
plant cutting both containers should be tightly covered to limit exposure to the air and left in a sunny
or well-lit space for inspection the following day. The heated water will have lower than normal
carbon dioxide levels. The 12-dram (about 45 mL) capped vials provided in the FOSS kits work well
here.
2) Bromthymol blue (about 1 mL standard 0.04% solution per 20 mL water) color change from blue to
yellow when the solution is turned acidic with (1 mL per 20 mL water) distilled vinegar.
3) Bromthymol blue color change from blue to yellowish-green after blowing exhaled air into the
solution through a soda straw. (To avoid bubbling over and spillage, pinch the straw tightly as air is
blown through. This produces a very steady and controlled bubbling, with the color change usually
occurring after 30-45 seconds.) The chemical reaction (CO2 + H20 → H2CO3) is relatively simple,
and the product – carbonic acid – is what causes the color change. The reason the color change
only goes to yellow-green is because carbonic acid is a weak acid and only lowers the pH to a
slightly acidic level (about pH 6); at that pH we’re seeing about half the BTB molecules in their blue
form and the other half in yellow, so together they blend visually to “green.”
4) If possible, perform demonstration #3 above twice, covering one tightly and leaving the other open
to the air. By the following morning students should observe the closed container has remained
greenish-colored, while the open container has changed back to blue. This is because the carbonic
acid slowly breaks down to water and carbon dioxide, which escapes into the classroom air. The
closed container doesn’t allow carbon dioxide to escape, so it is constantly re-forming carbonic acid
after being released into the small sealed air space.
NOTE THAT ALL OBSERVATIONS HERE ARE QUALITATIVE, and so students will record their
results as “+” for a change and a “–” for no change observed. Compilation of class data in the post-lab
activity will allow for data presentation in percentages; i.e., the percent of the same test throughout the
class with similar results.
DAY 3: Students should be given the lab activity instructions, form groups and plan their experiments. Each
test they perform should have an expected outcome, and thus a hypothesis. The four experiments can be
summarized as follows:
1) High CO2, light, neutral pH
High CO2, no light, neutral pH
2) High CO2, light, acidic pH
High CO2, no light, acidic pH
3) Low CO2, light, neutral
Low CO2, no light, neutral
4) Low CO2, light, acidic
Low CO2, no light, acidic
(If a refrigerator is available another variable, temperature, may also be tested.)
DAY 4: Students will collect data from their trials and organize their results in a table on the handout.
The amount of each material required will be determined by the experiments proposed. Note that the
acidic/neutral option (vinegar/no vinegar) does not relate to the basic reactions of photosynthesis, but is
included as a point of discussion for environmental considerations.
POST-LAB DISCUSSION
Class data can be summarized on a whiteboard/SMART board. Students should record this summary data and
then work in pairs to draw conclusions about the effect of various conditions on the process of photosynthesis.
Student commentary can be summarized as a list for all to critique. Finally, students should be invited to
suggest sources of error suggested by the data or encountered during their tests. These, too, should be
summarized, either as a class activity or, if time is an issue, a lab homework assignment.
Life Science
Lab Activity
NAMES: 1)________________________ 2)__________________________
DATE: ___________ PER: ___
What Conditions Are Needed For Plants to Carry Out Photosynthesis?
LIGHT ENERGY
Water + Carbon dioxide ----------------→
Sugar
H2 0
CO2
C6H12O6
+ oxygen
O2
PHOTOSYNTHESIS
Identify the following components of your experimental design:
Independent Variable: _____________________________
Dependent Variable: ______________________________
Hypothesis: ____________________________________________________________________________
_______________________________________________________________________________________
How will you measure your results? ________________________________________________________
_______________________________________________________________________________________
Describe your procedure:
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________________________________
__________________________________________________________________
Results: Construct a table that shows your results.
Conclusion: ____________________________________________________________________________
_______________________________________________________________________________________
_______________________________________________________________________________________