Lab 6: Photosynthesis Lab
We have discussed the structural organization of a plant cell and the structural anatomy of the
chloroplast in lecture. We will measure oxygen production in order to understand how plants
react to light intensity.
1. Discuss the process of photosynthesis in plants
2. Discuss the two stages of photosynthesis, and where they happen in the chloroplast of the
3. Learn the structure of the chloroplast by looking at the chloroplast model.
4. Understand the process of transpiration and how it happens in the plants.
5. Understand how plants maintain homeostasis by using stomata.
6. Learn the structure and function of stomata and guard cells.
7. Students will form a hypothesis based on their knowledge of stomata and a plant’s need
for water homeostasis and carbon dioxide for photosynthesis.
8. Students will be asked to explain whether or not their hypothesis was supported by results
9. During follow up discussion students will be asked to verbally explain what they
observed during the experiment and their conclusions related to their hypothesis.
Activity 1: Where does photosynthesis take place in the plant cell?
Write down the overall reaction of photosynthesis
What are the reactants for photosynthesis?
What are the products for photosynthesis?
Where do the light-dependent reactions take place in the chloroplast?
Where does the light-independent reactions take place in the chloroplast?
Watch the “Chloroplast Model Video” and label the following chloroplast diagram.
Chloroplast membranes, thylakoids, stroma, grana (singular: granum)
Activity 2: Stomata and Guard cells
are openings or pores on leaf surfaces that allow plants to take in CO
atmosphere, which is necessary for photosynthesis. Plants also lose water through stomata by
. One way that plants can minimize water loss (or maintain water homeostasis)
while acquiring CO
is to regulate the number of stomata on the upper and lower surfaces of
In this lab, you will compare photosynthesis rates with respect to varying light intensities. The
presence of countless numbers of chloroplasts is critical for plant function. Typically, the plant
epidermis is tightly sealed by a wax-coating which protects the plant body from the relatively dry
atmosphere and UV-rays. At the same time plants must be able to breathe, or exchange carbon
dioxide and oxygen, for photosynthesis and respiration. Stomata act as a gateway for efficient
gas exchange and water movement from the roots through the vasculature to the atmosphere.
(loss of water vapor from plants) via stomata supplies water and minerals to the
entire plant system. Oxygen is also lost via these stomata, allowing us to measure the rate of
photosynthesis under different conditions. When a plant encounters adverse environmental
conditions, such as drought, a plant hormone called
to shut tightly
in order to prevent plants from dehydration and wilting.
The stomata pores are surrounded on both sides by jellybean shaped cells called
guard cells. These cells expand or contract to open or close the stomata. Guard cells also close
when the plant is dehydrated or in dry weather to keep more water in the plant.
Watch the “Leaf Model Video” and label these structures on the following illustration:
Cuticle, Stomata, Vein, Plant cell, Cell Wall, Mesophyll tissue, Central vacuole, Chloroplast.
Activity 3: Study Photosynthesis Rate
In this part of today’s lab, you will study the effect of differing light intensities on the rate of
photosynthesis. Write a hypothesis that answers the following questions.
How do you think light intensity will affect the rate of photosynthesis? Would growing in direct
sunlight vs. shade affect the rate of photosynthesis?
We will use a simulation to answer this question!
You will design and conduct an experiment that studies the rate of photosynthesis in
1) Navigate to the “Photosynthesis Simulation” available in Canvas.
2) Read through the on-screen instructions, and click on the “Instructions” button to
familiarize yourself with the simulation.
3) You will measure the rate of photosynthesis at three light intensities: low, intermediate
The different light intensities are determined by the distance the light is located
from the plant. The greater the distance, the lower the light intensity.
a. Low light intensity correlates to a distance of 180 – 200 cm
b. Intermediate light intensity correlates to a distance of 140 – 160 cm
c. High light intensity correlates to a distance of 100 – 120 cm
4) Drag the slider to your chosen distance.
5) Click “Start” to begin collecting data.
a. You may click the “Instructions” button to learn the different controls.
6) Click on the “Counter” tab once you are reading to begin counting.
7) Click the “+” every time you see a new bubble for
8) Once the minute is up, record your count in the table below.
9) Use the “Back” button to return to the slider.
10) Repeat steps 4 – 9 for the other two intensities
Record your results in this table
Light Intensity (distance)
Bubbles per minute
1. Write the general formula for photosynthesis.
2. Name the two reactions involved in photosynthesis and summarize what happens in those reactions.
3. Define transpiration
4. Define osmosis.
5. What 1 substance enters the leaf through the stomata?
6. What 2 substances exit the leaf through the stomata?
7. How does water enter the plant cells?
8. Why do stomata have the ability to close?
9. How do the guard cells assist the stomata?
10. What gas did you measure in this experiment?
11. What is the benefit of having a waxy coating on the surface of leaves?
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