ET #58: What do plants need to
make (their own) food?
Light Energy
Carbon dioxide
Water
ET #58: What is this food?
Glucose (C6H12O6)
Today’s Learning Target
I can:
Identify the reactants and products in
Photosynthesis.
Ch 7: Cells are Busy Places
Lab: Cellular Activities
in Plants
(Photosynthesis)
lab intro
design lab
create data table
Converting Sunlight into
Sugar
What is Photosynthesis?
photo = light synthesis = put together
CO2 + water
Reactants
light
chlorophyll
glucose + O2
Products
CO2
(from air)
O2
Oxygen
H2O
(from ground)
Glucose
(food, growth)
Light
Put Together
Chlorophyll
+
Bromothymol Blue = BTB
• Do Activity Part 1:
Goggles MUST BE WORN!
• BTB is a chemical that changes color in the
presence/absence of CO2
• CO2 in water = carbonic acid (a weak acid).
This changes blue (basic) solution to yellow
(acidic).
• If CO2 is used up (by photosynthesis), yellow
will changes to green then blue.
BTB
CO2 Absent
Carbon Dioxide
Present
Each group will be assigned two
distances. We will share the class data.
Your Experiment:
H2O+
BTB
+ CO2
Put near light
at specific
distances
Variables?
Amounts? (mL)
Distances? (cm)
Rate? (sec)
BTB solution
turns yellow
Add
Elodea
leaf
O2
Glucose
Oxygen
Evidence?
Questions:
•How long will this take?
•How will I know
photosynthesis is
happening?
Is photosynthesis happening?
How do I know if photosynthesis is
happening?
O2 Bubbles!
Air bubbles appear on the
leaves of the plant
Plant is giving off O2!
O2
bubbles
forming
on
Elodea
leaves
Bubbles!
Activity II: Photosynthesis Inquiry Lab
Question: Does the intensity of light affect the
rate of photosynthesis in Elodea leaves?
light intensity = distance (cm) from light source
rate = time (minutes/sec) Manipulated var: _?___
Responding var: _?___
Evidence of photosynthesis?
• Presence of bubbles (O2) on leaf
Hypothesis: If…(MV), then….(RV), because…
(Make a Prediction as to what will happen and why)
•Materials: Include what materials you plan to
use*
*You have the materials listed: 2 beakers,
6 test tubes, etc. You will also have a sheet of
black paper
•Write a detailed Procedure (minimum 10 #’d
steps)
•Need to design a Controlled Experiment (Do
you trust the data? What can you do to ensure
the MV is what’s causing your results? )
•Set up a Data Table with headings
**These things must be done in order to start lab!**
What should your data table look like? How many
columns? How many rows?
What should your data table look like? How many
columns? How many rows?
 Each group will be assigned two distances from the light
source (i.e., two different light intensities) highlighted in
yellow. Some groups will be assigned a control group.
 Data (time it takes for bubbles to first appear on leaves)
will be recorded on the shared “class data” spreadsheet in
Google Docs.
Procedure should includes steps to collect
photosynthesis rate data for all five
distances (5 light intensities) and a control
group even though your group will only be
assigned two of the distances, plus the
control.
We are sharing the data collected as a class.