PHOTOSYNTHESIS LAB: Floating Leaf Disks: AP Biology
Summary
TLDRIn this Madden Science video, we delve into the floating leaf disk assay, a lab experiment exploring factors affecting photosynthesis rates in leaves. The lab is a favorite for its simplicity, affordability, and adaptability. Key variables include light intensity, temperature, and sodium bicarbonate levels. Using a syringe to submerge leaf disks in a carbon dioxide-rich solution, students observe how oxygen production causes the disks to float. The video introduces a pocket lab to measure light intensity, a crucial factor in photosynthesis, and encourages viewers to explore other variables in part two of the experiment.
Takeaways
- πΏ **Lab Introduction**: The video introduces a lab on photosynthesis, specifically the floating leaf disk assay, which is part of the energetics unit in AP Biology.
- π **Objective**: The main goal is to explore the factors affecting the rate of photosynthesis in living leaves, focusing on rates and variables.
- π§ͺ **Materials Needed**: Key materials include a syringe, baking soda solution, a hole punch, a light source, and a heat sink.
- π **Leaf Selection**: The lab uses the hardest leaves available, punched to create discs that are then filled with a solution to sink them.
- π§ **Baking Soda Solution**: Baking soda provides a carbon source for the leaves during photosynthesis, replacing air with carbon dioxide-rich water.
- π **Light as a Variable**: Light intensity is a key environmental variable that can be manipulated by changing the distance or color of the light source.
- π‘οΈ **Temperature Consideration**: Heat can affect the experiment, so a heat sink or cover can be used to regulate temperature.
- π **Data Analysis**: The lab involves observing how many leaf discs float over time, with a focus on the time it takes for half of the discs to float (estimated time 50).
- π **Environmental Variables**: Factors like light intensity, temperature, and pH are considered environmental variables that can affect photosynthesis.
- π¬ **Pocket Lab Usage**: A pocket lab device is used to measure light intensity, providing precise data to correlate with the rate of photosynthesis.
- π **Adaptability**: The lab is noted for its adaptability, allowing for various experiments to be conducted with different variables.
Q & A
What is the main focus of the 'Madden Science' video?
-The main focus of the 'Madden Science' video is exploring photosynthesis, specifically the factors that affect the rate of photosynthesis in living leaves.
What is the name of the lab experiment discussed in the video?
-The lab experiment discussed in the video is often called the 'floating leaf disk assay'.
What are the two main things the lab is investigating?
-The lab is investigating rates and factors that affect the rate of photosynthesis.
What is the purpose of using baking soda solution in the lab?
-The baking soda solution provides a carbon source for the leaves when they undergo photosynthesis.
Why do the leaves float initially in the experiment?
-The leaves float initially because the spongy mesophyll layer inside the leaf is filled with air.
How does the experiment increase the density of the leaf disks to make them sink?
-The experiment increases the density of the leaf disks by replacing the air in the mesophyll layer with water that contains carbon dioxide from the sodium bicarbonate solution.
What happens when the leaf disks are placed under the light source?
-When the leaf disks are placed under the light source, photosynthesis occurs, producing carbohydrates and oxygen, which causes the disks to float due to decreased density.
How is the rate of photosynthesis measured in the lab?
-The rate of photosynthesis is measured by observing how quickly the leaf disks start to float after being placed under the light source.
What is the 'estimated time 50' mentioned in the video?
-The 'estimated time 50' refers to the time it takes for half of the leaf disks (five out of ten) to start floating, indicating the rate of photosynthesis.
What are the three groups of variables that can affect the rate of photosynthesis?
-The three groups of variables that can affect the rate of photosynthesis are environmental variables, plant or leaf variables, and method variables.
How can light intensity be adjusted in the experiment?
-Light intensity can be adjusted in the experiment by changing the distance of the light source or by changing the light color.
What role does the Pocket Lab Voyager play in the experiment?
-The Pocket Lab Voyager is used to measure light intensity, providing precise data on how much sunlight or energy is being fed into the photosynthesis process.
Outlines
πΏ Introduction to Photosynthesis Lab
The script introduces a biology lab focused on photosynthesis, specifically the floating leaf disk assay. It's part of the energetics unit under photosynthesis and is a favorite due to its ability to make the microscopic processes of photosynthesis visible. The lab is easy, quick, and adaptable, focusing on the rates and factors affecting photosynthesis. The script mentions that students will explore variables in part two of the lab, possibly using a pocket lab to measure light intensity. The necessary materials for the lab include a syringe, baking soda solution (to provide carbon for photosynthesis), a hole punch, and a light source. The process involves creating leaf disks, using the syringe to fill them with a carbon dioxide-rich solution to increase their density and cause them to sink, simulating the conditions for photosynthesis.
π Exploring Photosynthesis Rates
This paragraph delves into the experimental setup for measuring photosynthesis rates. The lab uses a light source to simulate sunlight, a solution with sodium bicarbonate to provide carbon dioxide, and spinach cells to carry out photosynthesis. The goal is to observe the production of carbohydrates and oxygen. The script explains how the accumulation of oxygen causes the leaf disks to float, which is a visual indicator of the photosynthesis rate. The analysis involves charting the number of floating disks over time to find the 'estimated time 50', which is the time it takes for half of the disks to float. The paragraph also discusses various factors that can affect the rate of photosynthesis, such as light intensity, temperature, and pH, and introduces the use of a pocket lab to measure light intensity, showing how it changes with the distance from the light source.
Mindmap
Keywords
π‘Photosynthesis
π‘Floating Leaf Disk Assay
π‘Energetics
π‘Variables
π‘Sodium Bicarbonate
π‘Light Intensity
π‘Pocket Lab
π‘Thylakoid
π‘Chlorophyll
π‘Carbon Dioxide
π‘Density
Highlights
Exploring photosynthesis with the AP Biology Lab
Lab focuses on factors affecting the rate of photosynthesis
Floating leaf disk assay demonstrates the microscopic in the macroscopic
Lab is easy, quick, cheap, and adaptable
Variables to be changed in part two of the lab
Use of a pocket lab to measure light intensity
List of materials needed for the lab
Baking soda solution provides carbon source for leaves
Explanation of the floating leaf disc phenomenon
Creating a vacuum to replace air with carbon dioxide-rich water
Increasing leaf density to make them sink
Setting up the lab with a light source and heat sink
Photosynthesis produces carbohydrates and oxygen
Observing oxygen accumulation through leaf disc floating
Analyzing the rate of photosynthesis by charting disk floating over time
Factors affecting photosynthesis include environmental, plant, and method variables
Light intensity as a key factor with the use of a pocket lab
Adjusting light intensity by changing the distance of the light source
Using a pocket lab to measure and track light intensity
Light intensity's impact on the rate of photosynthesis
Transcripts
[Music]
hey everybody welcome to madden science
today we're exploring photosynthesis
with the ap biology lab what factors
affect the rate of photosynthesis in
living leaves this lab is often called
the floating leaf disk assay the lab
falls into unit 3 energetics under 3.5
photosynthesis
it's one of my all-time favorite labs
it brings to life the microscopic into
the macroscopic
allows students to visualize the
biochemistry of photosynthesis
it's also
pretty easy it's rather quick
it's pretty cheap and it's highly
adaptable as the title states we're
investigating factors that affect the
rate of photosynthesis so those are
really the two main things we're looking
at rates and factors so these will be
variables that you can change in part
two of the lab so we'll run through part
one pretty straightforward and then you
at home will be able to run through some
different possibilities with part two
one of those might involve the use of
a pocket lab to measure light intensity
please note that we're always going to
have
extra information and helpful links
below in the description and i'd really
love to hear your feedback and ideas in
the comments below
let's start with the examination of the
formula
the gear materials and then the
procedure
you're going to need a syringe you're
going to need your baking soda solution
again this will be best with 100
milliliters of water
and 1 gram of baking soda
the baking soda is going to be in there
because it will
provide the carbon source for the leaves
when they undergo photosynthesis
you're going to need a hole punch
light source which we can see here
a heat sink
don't need markers anymore
now lab is often called
floating leaf discs
well first you got to get them to sink
so how we're going to do that we're
going to pick out your hardest leaf and
you're going to make
10
hole punches
we're going to put these into
our syringe so i may have a few more
than 10.
now a smaller syringe would work you're
going to want to test it out first
for instance syringe like this is good
but the suction on this one wasn't
working so i got a bigger one
i can then
get as much of the air out as i possibly
can
and pull in
some of the solution
from there
i'm going to get out as much air as i
can
and then i want to create
a suction or a vacuum negative pressure
down
and the reason for this is because the
leaves as you can see they float and the
reason they float is because the spongy
mesophyll layer kind of inside a leaf is
filled with a lot of air
we want to pull that out and replace it
with
water and not just any water but water
that has carbon dioxide in it because
the carbon dioxide
in the sodium bicarbonate the
bicarbonate ion will provide carbon
needed for photosynthesis
so we put our finger thumb on the end
and we
draw back
and this should feel tough and it should
also bounce back
and you'll start to see that indeed
the leaf dis start to sink
this is all a matter of density
i'm your density
i mean
your destiny we are increasing the
density by adding water replacing the
air so that they sink
you ever been in a pool and you're
floating nicely and you
exhale all the air out of your lungs
and you slowly sank to the bottom
that's what we're going to need to do
here
except there's air trapped in the
mesophyll layer of the spinach and then
the lab itself we're going to be doing
quite the opposite so i'm going to try
this one more time try and get those
other ones that are stuck at the top to
come down
and this should be difficult
once i get that tap them
you can see that they sink
once i get them
good to go
i'm going to place 10 of them
in here at this point you're good to go
once you have 10 in here you're going to
place it under
your light source
again if there's too much heat and heat
will be a variable you can
put a glass dish or tupperware above
there so that it absorbs much of the
heat
while letting through the light
so this lamp is our sun
we've got carbon dioxide from
bicarbonate ion and our water
and the plant cell itself the spinach
cell and the thylakoid inside
the chloroplast are going to run through
photosynthesis
and what they're going to make is
carbohydrate and oxygen now if you look
at this to explore the rate of the lab
we could see how much carbon dioxide is
being used
or we could see how much oxygen is being
produced
so as this reaction takes place
we can start to see the accumulation of
oxygen by actually looking at it and
seeing it and you'll start to see that
indeed these discs start to float so as
soon as you set it under here start your
timer
more light equals more photosynthesis
equals more oxygen produced
equals less density
which equals more float
the analysis comes
from taking a look at this and charting
how many disks float versus time so
number of disks on the y-axis and time
on the x-axis now a standard that can be
used across experiments will be
estimated time 50. so
what is the time it takes for half of
those disks
in this case five
to be floating
if we go back to the title of the lab
what factors affect the rate of
photosynthesis in living leaves
we see both rates which we're covering
here again as oxygen is produced and
there's different
factors so take a look at this list
those can come in
one of three groups
environmental variables plant or leaf
variables and method variables go ahead
and pause the video and see how many of
those you can come up with on your own
how many did you get let's reveal and
see which ones are maybe the most common
and the easiest to do
first would be light intensity and
that's what we're going to use pocket
lab form so in order to adjust light
intensity we would simply change the
distance of a light source
we can also change a light color
temperature
how much
sodium bicarbonate you added in there
what's the ph
so my pocket lab voyager is connected to
the ipad and it's recording light
intensity
you can see as it changes on here
as i cover it up i'm going to start
recording on this
we can see as it changes now i'm going
to set it next to my beaker with my leaf
disk
and
turn on my light source you can see it
skyrocket up
now you can adjust that distance now you
can measure that
you can keep track of it as it relates
to
what is your light intensity and what is
the distance and
ultimately what is your estimated time
50 so how long did it take for
50
or 5 out of 10
of your leaf discs
to start floating
you can see that intensity begin to fall
as we get further and farther away
and as we
slowly
get closer and closer
you can see that
it begins to intensify
and so the pocket lab is going to allow
you to get very
close
measurements for your light intensity
and therefore
use that as a good indicator for
how much sunlight or energy
is fed into
the photosynthesis equation
hope this is helpful
take care everybody
[Music]
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