Copy of Ericka Cathlyne De Vera - Lab 5 Photosynthesis
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Global Higher Secondary School & Degree College Danyore Gilgit *
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Course
101
Subject
Biology
Date
Nov 24, 2024
Type
Pages
14
Uploaded by BailiffSalmon3617
Name:
Ericka Cathlyne L. de Vera
Date:
12/11/2023
Investigation: What Factors Affect Photosynthesis
Background and PreLab
Photosynthesis fuels ecosystems and replenishes the Earth's atmosphere with oxygen. Like all enzyme-driven
reactions, the rate of photosynthesis can be measured by either the disappearance of substrate, or the
accumulation of products. The equation for photosynthesis is:
6CO
2 + 6H
2
O ------light--------> C
6
H
12
O
6 + 6O
2 + H
2
0
The rate of photosynthesis can be measured by: 1) measuring O
2
production
2) measuring CO
2
consumption
Leaf Structure and Function
The leaf is composed of layers of cells. The spongy mesophyll layer is normally infused with glasses, oxygen
and carbon dioxide. Leaves (or disks cut from leaves) will normally float in water because of these gasses. If
you draw the gasses out from the spaces, then the leaves will sink because they become more dense than
water. If this leaf disk is placed in a solution with an alternate source of carbon dioxide in the form of
bicarbonate ions, then photosynthesis can occur in a sunken leaf disk. As photosynthesis proceeds, oxygen
accumulates in the air spaces of the spongy mesophyll and the leaf becomes buoyant and floats. Oxygen and
carbon dioxide are exchanged through openings in the leaf called stoma (or stomata).
While this is going on, the leaf is also carrying out cellular respiration. This respiration will consume the oxygen
that has accumulated and possibly cause the plant disks to sink. The measurement tool that can be used to
observe these counteracting processes is the floating (or sinking) of the plant disks. In other words, the
buoyancy of the leaf disks is actually an indirect measurement of the net rate of photosynthesis
occurring in the leaf tissue
.
Learning Objectives:
1) To design and conduct an experiment to explore factors that affect photosynthesis. 2) To connect and apply concepts, including the relationship between cell structure and function, strategies for
capture and stores of energy, and the diffusion of gasses across membranes.
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Experimental Question: What factors affect the rate of photosynthesis?
Pre Lab Questions - these should be completed BEFORE the scheduled lab
1. How can the rate of photosynthesis be measured?
The rate of photosynthesis can be determined by enclosing a leaf in a closed,
transparent chamber and monitoring the drop in carbon dioxide concentration
as a function of time.
2. What is the function of the stomata?
The stomata help a plant to take in carbon dioxide, which is required for
photosynthesis.
3. Where in the leaf can you find air spaces? What will happen if you remove the air
from these spaces?
Air spaces can be found in the spongy mesophyll layer of the leaf. When the
gasses are drawn out of the spaces, the leaves sink because they become
denser than water.
How will air return to these spaces?
Through the process of diffusion caused by variations in atmospheric pressure,
air will return to these spaces.
4. Instead of carbon dioxide, what will be used as the reactant in this lab?
In this lab, water will be used as the reactant instead of carbon dioxide.
5. Write the equation for photosynthesis.
6CO
2
+ 6H
2
O → C
6
H
12
O
6
+ 6O
2
6. List any factors that you think may affect the rate of photosynthesis. Consider environmental factors that
you could manipulate during the lab.
Light intensity, carbon dioxide content, and temperature are all elements that can influence the rate of
photosynthesis.
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Part 1: Basic Procedure for Measuring the Rate of Photosynthesis
Materials
:
baking soda, DI Water, plastic syringes, spinach leaf, hole punch or straws, beakers, timer, light source
1. Collect leaf disks by cutting holes in the leaf (try to get them between the veins) using a straw, you will need 10 leaf
circles. 2. Make a solution of sodium bicarbonate by mixing 200 ml of DI water to a pinch of baking soda 3. Place 10 leaf disks into the syringe and fill halfway with bicarbonate solution.
4. Push out most of the air, but do not crush your leaves. 5. Create a vacuum by covering the tip of the syringe with your finger. Draw back on the plunger. 6. Release the vacuum and the leaf disks should sink. You may need to gently tap the syringe to dislodge discs from the
sides or suction the disks again to remove the air. The goal is to get all 10 to sink. . 7. Place disks back into the beaker (they should sink to the bottom)
and expose the disks to light.
8. Start a timer and record how many of the disks are floating at 30
sec intervals. (See data table.) Troubleshooting:
Gently swirl solution to dislodge disks which may
become stuck at the bottom.
Place your beaker as close to the light as possible! 9. Control Group: Repeat your setup from above, but this time do
not place baking soda in the beaker. Place another set of sunken
disks into this solution and record data on the table. 10. Both the experimental group and the control should run until all
the discs are floating. Data Table
Time (min)
1
2
3
4
5
6
7
8
9
10
# of floating disks (bicarbonate, water)
0
0
0
1
2
5
6
8
10
10
# of floating disks (control)
( only water )
0
0
0
0
1
1
1
1
1
1
Analyzing Data
To make comparisons between experiments, a standard point of reference is needed. Repeated testing of this
procedure has shown that the point at which 50% of the disks are floating (the median or ET
50
) is a reliable and
repeatable point of reference. In this case, the disks floating are counted at the end of each time interval.
ET50, the estimated time for 50% of the disks to rise.
Graph your data for the experimental group. Determine the ET
50
for your leaf disks and determine the ET
50
for
your data.
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What is the relationship between sodium bicarbonate and photosynthesis rate?
This is your
CLAIM
.
The combined use of red light and sodium bicarbonate (water + baking soda + dishwashing
soap) increases photosynthesis faster than the use of sodium bicarbonate (water + baking soda
+ dishwashing soap) only.
Provide
evidence
that supports this claim; summarize data by referencing ET
50
.
In comparison to the bicarbonate solution without light or the water solution under red light, more
leaf disks floated in the bicarbonate solution throughout the experiment. This implies that under
red light, more photosynthesis happened in the bicarbonate solution.
The time it takes for 50% of the leaf disks to float is known as ET50. Following that, only 4 leaf
disks floated for bicarbonate (baking soda), 4 leaf disks float for water + soap with red light, and
0 leaf disks float for water + soap + bicarbonate (baking soda) after 4 minutes of pouring leaf
disks. After 11 minutes, 0 leaf disks float for water + soap + bicarbonate (baking soda), 5 leaf
disks float for bicarbonate (baking soda), and 5 leaf disks float for water + soap. 20 minutes later,
5 leaf disks float for water + soap + bicarbonate (baking soda), 10 leaf disks float for bicarbonate
(baking soda), and 5 leaf disks float for water + soap. This demonstrates that the ET50 in
red-colored light happens more quickly than the ET50 in no colored light. The red-colored
sodium bicarbonate had a significant impact on the rate of photosynthesis.
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Provide
reasoning
that links the evidence and the claim and explains why this relationship exists.
Consider how photosynthesis occurs and what is used and created during the reaction.
The most effective wavelength of light for photosynthesis is red. This is due to the fact that red
light is most effectively absorbed by chlorophyll, the green pigment found in plants that uses light
for photosynthesis. Carbon dioxide is a source of sodium bicarbonate and is also an essential
reactant for photosynthesis. Consequently, the plant has both the essential reactants and the
most effective light wavelength for photosynthesis when red light and sodium bicarbonate are
combined. The rate of photosynthesis speeds up as a result.
.
Part 2: Design and Conduct Your Own Investigation
(with lab report)
Now that you have mastered the floating disk technique, you will design an experiment to test another
variable that may affect the rate of photosynthesis. Choose from the list of variables below to
investigate. (If you have another variable that you would like to try, check with your instructor first.)
light intensity or distance from the light | amount of sodium bicarbonate
water temperature | size of leaf disks or shape of leaf disks | color of light Experimental Question: What factors affect the rate of photosynthesis?
Experimental Design Notes
factor to investigate: color of light
Our experiment was to test what would happen to the number of leaf disks when putting them with
another variable, a red-colored light now, to see how it would affect the rate of photosynthesis. We
wanted to test how many leaf disks would float to the top of the beaker that have red color and the
one that doesn't have color beaker. We put the two different beakers on the light bulb and we waited
to see how many leaf disks would float for every minute up to twenty. After 4 minutes of pouring leaf
disks, only 4 leaf disks floated for bicarbonate (baking soda) + water + soap with red colored light,
and 0 leaf disk for water + soap + bicarbonate (baking soda) with no colored light. After 11 minutes, 5
leaf disks floated for bicarbonate (baking soda) + water + soap with red colored light, and 0 leaf disk
for water + soap + bicarbonate (baking soda) with no colored light. After 20 minutes, 10 leaf disks
floated for bicarbonate (baking soda) + water + soap with red colored light, and 5 leaf disks for water
+ soap + bicarbonate (baking soda) with no colored light.
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Data
Time (minutes)
# of floating disks ( bicarbonate,
water + soap) + red-colored
light
# of floating disks (control)
(bicarbonate, water + soap) +
no colored light
1
0
0
2
0
0
3
0
0
4
1
0
5
1
0
6
1
0
7
1
0
8
2
0
9
3
0
10
4
0
11
5
0
12
6
0
13
7
1
14
7
1
15
8
2
16
8
3
17
8
3
18
9
4
19
9
4
20
10
5
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LAB REPORT
INTRODUCTION:
An essential process for the growth and survival of plants is photosynthesis. The
purpose of this experiment is to look at how sodium bicarbonate and red light
affect the rate of photosynthesis.
Hypothesis: The combined use of red light and sodium bicarbonate (water +
baking soda + dishwashing soap) increases photosynthesis faster than the use of
sodium bicarbonate (water + baking soda + dishwashing soap) with no colored
light.
Null hypothesis: Sodium bicarbonate and red light have no effect together to
speed up photosynthesis.
Background information: Plants use a chemical process called photosynthesis to
produce glucose and oxygen from carbon dioxide, water, and sunshine. The rate
of photosynthesis is affected by a number of factors, such as temperature,
carbon dioxide content, light intensity, and light wavelength; in this case, the rate
of photosynthesis will be determined by the influence of light color (red).
PROCEDURE:
Materials: 2g baking soda (1g each beaker), 200ml distilled water (100ml each
beaker), 2 drops of dishwashing soap (1 drop each beaker), plastic syringes,
spinach leaf, hole punch, 2 beakers, 2 glass containers, timer, and red-light
source (red food coloring)
1. Cut 10 leaf disks or circles from the leaf and try to get them between the
veins with a hole punch.
2. Mix 100 ml of DI water with 1g of baking soda and 1 drop of dishwashing
soap to make a sodium bicarbonate solution.
3. Ten leaf disks should be placed inside the syringe, and the bicarbonate
solution should be poured halfway.
4. Push out most of the air but be sure not to smash your leaves.
5. Put your finger over the syringe's tip to create a vacuum. Pull the plunger
back.
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6. Release the vacuum and the leaf disks should sink. To release the discs
from the sides of the syringe, you might need to gently tap it or suction the
disks once more to eliminate any remaining air. Entire ten leaf disks must
sink to achieve the desired result.
7. The disks should drop to the bottom of the beaker if you put them back in.
Swirl the mixture gently to loosen any disks that could be lodged at the
bottom.
8. Fill the small glass container with 5cc of water and 2 drops of red food
coloring. After that, place it atop the beaker.
9. Repeat the procedure above for the control group, but don't add red food
coloring to the small glass container that goes to the top of the beaker this
time.
10.
Put the two beakers as near to the light as you can to expose the leaf
disks to the light.
11.
Set a timer, and after every minute, note how many disks are floating.
12.
The control group and the experimental group should continue until all of
the discs are floating.
DATA TABLES and GRAPHS:
Time (minutes)
# of floating disks ( bicarbonate,
water + soap) + red-colored
light
# of floating disks (control)
(bicarbonate, water + soap) +
no colored light
1
0
0
2
0
0
3
0
0
4
1
0
5
1
0
6
1
0
7
1
0
8
2
0
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9
3
0
10
4
0
11
5
0
12
6
0
13
7
1
14
7
1
15
8
2
16
8
3
17
8
3
18
9
4
19
9
4
20
10
5
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SUMMARY AND CONCLUSIONS:
The experiment's findings support the hypothesis that sodium bicarbonate and
red light together boost photosynthesis more quickly than sodium bicarbonate
alone.
In comparison to the bicarbonate solution without light and the bicarbonate
solution under red light, more leaf disks floated in the bicarbonate solution with
red light during the experiment (Graph 1). This shows that under red light, more
photosynthesis happened in the bicarbonate solution.
The time it takes for 50% of the leaf disks to float is known as ET
50
. Following
that, in Graph 1, only 1 leaf disk floats for water + soap + bicarbonate (baking
soda) with red-colored light, and 0 leaf disks float for water + soap + bicarbonate
(baking soda) with no colored light after 4 minutes of pouring leaf disks. After 11
minutes, 0 leaf disks float for water + soap + bicarbonate (baking soda) with no
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colored light, while 5 leaf disks float for water + soap + bicarbonate (baking soda)
with red-colored light, which is the ET
50
for bicarbonate solution with red-colored
light that can be seen in Graph 2. 20 minutes later, 5 leaf disks float for water +
soap + bicarbonate (baking soda) with no colored light, which can be seen in
Graph 2, and 10 leaf disks float for water + soap + bicarbonate (baking soda)
with red-colored light. This demonstrates that the ET
50
in red-colored light
happens more quickly than the ET
50
in no colored light. The red-colored sodium
bicarbonate had a significant impact on the rate of photosynthesis.
The most effective wavelength of light for photosynthesis is red. This is due to
the fact that red light is most effectively absorbed by chlorophyll, the green
pigment found in plants that uses light for photosynthesis. Carbon dioxide is a
source of sodium bicarbonate and is also an essential reactant for
photosynthesis. Consequently, the plant has both the essential reactants and the
most effective light wavelength for photosynthesis when red light and sodium
bicarbonate are combined. The rate of photosynthesis speeds up as a result.
DISCUSSION:
The results of the experiment emphasize how crucial light color and the
availability of carbon dioxide are to the best possible photosynthesis. The effects
of varying light intensities on the combined effects of red light and sodium
bicarbonate, the impact of additional environmental factors, such as humidity and
temperature, on the observed results, and the possible advantages of applying
this knowledge to other plant species could all be investigated in more detail.
It is important to take into consideration the limitations of this experiment, which
include the following: the use of leaf disks rather than entire plants could not
precisely represent the natural process of photosynthesis; the experiment's
relatively short (20-minute) duration might have missed the full effects of the
treatments on long-term photosynthesis rates; and the concentration of sodium
bicarbonate may not have been best for increasing the rate of photosynthesis.
Therefore, there are a number of ways to improve the experiment: making it
longer; substituting whole plants for leaf disks; changing the concentration of
sodium bicarbonate; measuring more parameters; controlling more variables;
repeating the experiment; experimenting with different light sources; and looking
into the mechanism underlying the observed effect. This would lead to improved
methods for improving plant growth and productivity by giving a more precise and
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thorough understanding of the relationship between red light, sodium
bicarbonate, and photosynthesis.
Rubric
3 pts
2 pts
1 pt
Problem
Definition
The problem is stated
clearly. Clear identification
of independent and
dependent variables.
Grammar and wording are
appropriate.
The problem is stated adequately.
Adequate identification of
independent and dependent
variables. May have minor issues
with grammar and wording.
The problem is poorly stated.
Poor identification of
independent and dependent
variables.
Experimental
Design
The experiment matches
the stated problem.
Variables are controlled.
The procedures are clear,
complete and replicable. A
control is included when
appropriate.
The experimental design generally
matches the stated problem.
Attempts at controlling variables
are made. Procedures are
generally complete. Minor
modifications or clarifications may
be needed.
The experimental design
matches the stated problem to
some extent. Little attempt to
control variables. Procedures
are incomplete. Major
modifications or clarifications
may be needed.
Data
Presentation
Data are accurate,
complete, well-organized
and presented in an
appropriate manner. All
graphs and tables have
appropriate labels.
Data is
easy to read at a glance.
Data are generally accurate,
complete, organized and
presented in an appropriate
manner. Minor errors or omissions
may be present.
Data are somewhat inaccurate,
incomplete, poorly organized
and presented in an
inappropriate manner. Major
errors or omissions may be
present.
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Conclusions
Conclusions are related to
the stated problem and
fully supported by the data.
Validity of conclusions is
thoroughly discussed and
includes reasoning linked to
an understanding of
photosynthesis (CER) and
other biological principles.
Conclusions are generally related
to the stated problem and fully
supported by the data. Minor
errors in the interpretation of the
results may be present. Reasoning
is not very well developed or there
is little explanation for WHY the
results were obtained or
connections to biological
principles.
Conclusions are related to the
stated problem and supported
by the data to a limited extent.
Major errors in interpretation of
results may be present. Little
discussion of the validity of
conclusions, or reasoning is not
well developed.
Discussion
Thoughtful reflection about
the lab. Connection to
practical science or how or
understanding of the
process can improve human
lives (science and society),
discussion of experimental
errors or ways to improve
experimental design
Discussion is missing one of the
elements listed above (reflection,
practical application,
errors/design), though does show
thoughtful reflection about the
experiment.
Discussion is missing most of
the elements listed above, not
presented in a thoughtful way.
Overall
Display
Report is typed, is
organized into sections with
headings included, creative
use of images or tables,
grammar and sentence
structure is appropriate.
Report is typed, but not well
organized, with some issues with
grammar or sentence structure.
Report is not typed, not well
organized, difficult to follow or
has major grammatical errors
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