PHOTOSYNTHESIS LAB: Floating Leaf Disks: AP Biology

Summary

In 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

• 🌿 **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.
• 🔍 **Objective**: The main goal is to explore the factors affecting the rate of photosynthesis in living leaves, focusing on rates and variables.
• 🧪 **Materials Needed**: Key materials include a syringe, baking soda solution, a hole punch, a light source, and a heat sink.
• 🍃 **Leaf Selection**: The lab uses the hardest leaves available, punched to create discs that are then filled with a solution to sink them.
• 💧 **Baking Soda Solution**: Baking soda provides a carbon source for the leaves during photosynthesis, replacing air with carbon dioxide-rich water.
• 🌞 **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.
• 🌡️ **Temperature Consideration**: Heat can affect the experiment, so a heat sink or cover can be used to regulate temperature.
• 📊 **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).
• 📉 **Environmental Variables**: Factors like light intensity, temperature, and pH are considered environmental variables that can affect photosynthesis.
• 🔬 **Pocket Lab Usage**: A pocket lab device is used to measure light intensity, providing precise data to correlate with the rate of photosynthesis.
• 🌐 **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

00:00

🌿 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.

05:00

🌞 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.

Keywords

💡Photosynthesis

Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods with the help of chlorophyll pigments. In the video, photosynthesis is the central theme, as the lab experiment is designed to explore the rate at which it occurs. The process is visualized through the floating leaf disk assay, where the production of oxygen is a direct result of photosynthesis.

💡Floating Leaf Disk Assay

The floating leaf disk assay is a method used to measure the rate of photosynthesis in living leaves. It involves submerging leaf disks in a solution and observing how they sink or float based on the gas exchange occurring due to photosynthesis. The video describes this assay in detail, emphasizing how the disks' behavior is indicative of the photosynthetic activity.

💡Energetics

Energetics is the study of energy transformations and energy flow in biological systems. In the context of the video, energetics relates to the energy captured during photosynthesis, which is then stored in the form of carbohydrates. The lab falls under the unit of energetics, specifically focusing on how different factors affect the energy production through photosynthesis.

💡Variables

Variables in a scientific experiment are factors that can be changed to observe their effect on the outcome. The video discusses how changing variables such as light intensity, temperature, and sodium bicarbonate concentration can affect the rate of photosynthesis, which is a key aspect of the lab's investigation.

💡Sodium Bicarbonate

Sodium bicarbonate, or baking soda, is used in the lab to provide a carbon source for the leaves undergoing photosynthesis. It is mixed with water to create a solution that the leaf disks are submerged in. The video explains that the bicarbonate ion will provide the carbon needed for photosynthesis.

💡Light Intensity

Light intensity is the measure of the amount of light energy per unit area. It is one of the variables explored in the lab to understand its impact on the rate of photosynthesis. The video mentions using a pocket lab to measure light intensity, showing how it can be adjusted by changing the distance of the light source from the leaf disks.

💡Pocket Lab

A pocket lab is a portable device used to measure and record scientific data. In the video, a pocket lab is used to measure light intensity during the experiment. It is connected to an iPad, allowing for real-time monitoring and recording of the light levels, which is crucial for understanding how light affects photosynthesis.

💡Thylakoid

Thylakoids are membrane-bound compartments within the chloroplasts of plant cells where the light-dependent reactions of photosynthesis occur. The video mentions thylakoids in the context of the photosynthetic process, explaining that they are where the energy from light is converted into chemical energy.

💡Chlorophyll

Chlorophyll is the green pigment in plant cells that plays a crucial role in photosynthesis by capturing light energy. Although not explicitly mentioned in the script, chlorophyll is implied as the key component that enables the process of photosynthesis, which is the focus of the lab.

💡Carbon Dioxide

Carbon dioxide is a gas that plants use as a raw material for photosynthesis. In the video, it is noted that the carbon dioxide in the sodium bicarbonate solution provides the carbon needed for the process. The script explains how replacing air in the leaf disks with carbon dioxide-rich water is essential for photosynthesis to occur.

💡Density

Density is the measure of mass per unit volume of a substance. In the context of the video, density is discussed in relation to how the leaf disks sink or float in the solution. By increasing the density of the leaf disks through the removal of air and replacement with water, the disks are made to sink, facilitating the photosynthetic process.

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]