AP Biology Investigation 6: Cellular Respiration

hi everyone so this is a virtual lab for ap biology investigation 6 which covers the topic of cellular respiration and the way that we do that is using a respirometer so a respirometer and to be honest with you this is probably a lab that has been asking to be made virtual for a very long time i find it to be incredibly complicated to run in a high school lab environment but you know some some teachers do still physically run it you know for me i essentially have always run it virtually um or through a demonstration but the respirometer has several iterations so the old-school respirometers are a large glass file with a stopper at the top and you know inside the stopper a hole is drilled so that you can fit a one mil pipette they've made some newer ones that are smaller micro respirometers i know some people that use them but many people don't still don't use them but you know we're going to run through this in a in a virtual fashion so just imagine and i will have showed you in class for my students what a respirometer is but the important part of it well it's all important but you know inside this glass file you can fit components of the experiment and then this one mil pipette is going to act as a gauge for gas consumption so decreasing volumes of gas can be read on this one mil pipette so you know basically you know if you're going from 0.9 to 0.8 to 0.7 that's a 0.2 milliliter difference so we'll go over that in a minute but you can actually gauge the amount of oxygen gas consumed using this this very simple setup and basically what it is excuse me for the respirometer we're going to take trays of water and submerge the respirometer into the water and what happens is water rushes into the tip of the respirometer up to a certain point and from there on is you know the the air from the glass vial pushing back against that water bubble and so we're going to set up this experiment such that whatever organism where studying the respiration rates of will be in the glass vial and as that organism performs respiration and consumes oxygen the air bubble starts to recede into the respirometer and we can measure we can measure the rate of respiration based on the change in that reading on the one ml pipet okay so for example you know if this is all water right here and this is air as cell respiration proceeds you'd see that bubble proceed in this direction as the volume of gas decreases so the first thing you would need to do is to set up an experiment where you have um we need to set up a control experiment we need to set up an experiment where we're looking at organisms and to do that we need to do a displacement a water displacement to calculate an equal amount of beads that we we will use for our control and we want to do the following so you take 50 milliliters of water in a graduated cylinder and you add 20 or 25 ps um to that so just define what you're doing so we're going to add 25 ps and then you measure the amount of displacement of water so however many milliliters that rises for 25 ps you want to take another graduated cylinder and um also fill it up to 50 and you want to add beads until it equals the same amount of milliliters displaced so that will give us an equal volume of peas and beads to add to our experiment and i'll show you what i mean by that in a moment so this is how we'll construct our respirometer so essentially again it's a glass file with a stopper and a pipette sticking out of it on the back we have these washers to weigh it down because remember you want it to be submerged in water and then inside the respirometer you'll see the following components so you're going to see absorbent cotton balls all the way the back that have a predefined amount of potassium hydroxide added to it so for example you can say 20 drops of potassium hydroxide to this absorbent cotton ball for students and in front of that and i'll explain what potassium hydroxide does in a minute in front of that we put a non-absorbent cotton ball that acts as a barrier between you know the one that has potassium hydroxide and our our organism that we're studying in this case this is the control so there is nothing living here but we have these glass beads okay and the glass beads control is basically going to control for pressure changes that would occur in the environment so we're going to do this experiment side by side with our other experiment in this case we're studying germinating peas so we're going to do it side by side with germinating peas we've controlled for it by having the same amount of volume inside the respirometer so essentially what we've done is we've controlled for pressure changes we're going to control for this air bubble moving in response to pressure changes in the atmosphere so i imagine that in different environments around the world this would be a problem for us here in pennsylvania it's not really a problem but it does allow us to be more precise in our measurements of how the respiration rate how fast the respiration rate is occurring okay and then since this is occurring in water we're going to have a thermometer in the water that shows us you know we're going to keep this water at room temperature for um one part of the study okay so um the the this experiment does a good job of asking students about controls and constants okay so this glass vial this glass bead vial that contains the beads is our control for pressure another thing i'd like to mention that if you were actually doing this experiment you would set up a five minute equilibration uh period where you know the the two vials four vials however many vials you have going would essentially rest on a piece of tape that is the glass vial part where the organism and the control beads are would be submerged in the water to let the organisms acclimate to that environment that temperature where whereas the tips of the respirometer would not be in the water just yet they'd be resting on the side the edge or on a piece of tape so that these experiment doesn't start yet so you want them to adjust to that environment and so there's a five minute adjustment period so i want to go back and explain why we have potassium hydroxide on that absorbent cotton ball so the the experiment is essentially designed to measure the amount of oxygen that an organism like germinating peas would be consuming as it performs cellular respiration to meet its energy needs the problem with that as you recall from the krebs cycle is that they're also putting out another gas in response to that rate of of cell respiration that gas being co2 so if we're creating equal pressures of gases coming in and gas is going out you're not going to see that bubble advance so what we've done is we put potassium hydroxide on the cotton ball and potassium hydroxide can take gaseous carbon dioxide and precipitate it into potassium carbonate so really what we're doing by adding potassium hydroxide is we're dealing with co2 as a gas and removing it from the equation so that oxygen can rush in and so that the the gas bubble the air bubble can be uh can proceed as a measurement for oxygen consumption okay so now that we've removed co2 pushing back um on the air bubble now you can just see the air bubble recede into the pipet as the organism undergoes cellular respiration okay so this is a good lab to consider the ideal gas laws that you learned back in chemistry and i've never really seen the college board actively ask about this question um which is not to say that they won't ever but um you know you should be able to understand the relationship between pressure volume gas number um in this experiment um so we've actually controlled for this and so we really want to see the relationship between temperature pressure and volume in this experiment so the key part for us is if we keep temperature and pressure constant the volume of the gas inside the respirometer is going to be directly proportional to the number of gas molecules so as those um you know as oxygen is consumed in the respirometer you'll get an idea of the number of of gas molecule of oxygen molecules left over so you know essentially by the setup of the experiment we've controlled uh for variables and then you can see the relationship between those components of that equation so again going back to this um you know this this design with the glass beads um you know controlling for pressure changes in the atmosphere and temperature we've controlled for a lot in that experiment okay so now we want to perform uh the experiment so in a second glass file you'll put those p's that we counted the 25 ps will go in and this is where the non-absorbing cotton ball comes into play because potassium hydroxide is caustic and can kill cells inside the peas so we want to protect them by putting that non-absorbent cotton ball so this is going to be our our test subject okay we're going to be testing germinating peas in various temperatures right so where the variable that we're looking at is temperature for these organisms okay so an important note here too a lot of times teachers will run six vials um side by side two controls two germinating uh p two germinated peas one at twenty five one at ten and then some non-germinating peas some dormant peas at twenty five and ten i've removed that from this video um i'll just go ahead and tell you that you know dormant non-germinating peas actually are performing cell respiration at a much slower rate you probably would have hypothesized that anyway but um we're gonna reduce your your workload here and just ask you to analyze um the experimental data for germinating peas at 25 and at 10. okay so how does this work well let's run the experiment for the control that is glass vials containing a glass vial containing glass beads okay so there's nothing living in there cell respiration shouldn't be occurring you shouldn't see advancement of that that water into the pipette so we shouldn't see that um that air bubble recede unless there are pressure changes occurring so we're just watching out in this experiment for pressure changes um in the experiment so i've put in here a table for you to fill out so basically you're going to follow the the air bubble seeing if it changes at all at these time points so when you drop the respirometer into the water not when you drop when you place it into the water you know what is the the reading on the pipette when you put it in there so what is the initial reading and then every five minutes for 20 minutes you're going to take a reading of where that air bubble slash water interface is now i would hypothesize that in our lab you're not going to see this bubble advance very much maybe if a little tiny bit so i'm going to ask you to take those readings here in this column you'll you'll basically you know subtract the change in that bubble's placement over time so let's just go ahead and show you what i mean okay so we're doing our control at 25 degrees celsius which is room temperature i place the respirometer on the water and the water rushes all the way into 0.8 so your initial reading at time 0 would be 0.8 then i'm going to come back to this this pipette tip every five minutes and read it so when i come back five minutes later there it is i'll go ahead and tell you what this is so i've actually done the readings for you for the control this is 0.79 okay so it's it's moved a hundredth space here it is 10 minutes it's moved again a little bit we find ourselves here kind of at .78 15 minutes 20 minutes and here's your table okay so it hasn't really moved a lot this um you know basically there's no respiration going on we haven't really sensed any atmospheric pressure changes um so really our experiment should be pretty pretty much good to be read for the germinating p's now what we'll do is we'll we'll subtract .01 from whatever the the reading is for for ps at that point in time um just to control for that change this change is essentially random change um just you know random moving so to compensate for that we'll subtract that at the end i'll show you that in a moment but um let's go ahead and run our experiment for germinating peas in the respirometer setup at 25 celsius what is your hypothesis what do you think is going to happen in this experiment so go ahead and write that down here's your data table that i want you to fill out so again you're following the readings at every five minutes you're calculating the difference between readings and the corrected difference is you're subtracting um the difference seen in the control glass bead respirometer for each of those time points so you're getting more precise by by subtracting that control data okay so here's your data for germinating peas at 25. you place the respirometer in the water it starts at 0.8 there it is at 5 minutes there it is at 10 minutes 15 minutes and 20 minutes so go ahead and fill out your data table here i'm very specific in what i want you to do here okay so you're going to take this data right here once you have filled out the readings once you've calculated the difference between time points i want you to subtract these numbers from those difference numbers and that's your corrected difference and by the way that's the that's the data that i want you to graph at the end here okay so we're going to continue to run this experiment we're now going to run our control with glass beads in our classic respirometer setup but we're going to do it at 10 degrees celsius so we've lowered the temperature of the water bath that these respirometers are submerged in so again here's your data table and here's your data for the control experiment so there it is five minutes and i forgot to write that but i'll go ahead and say it so you place it in the water at zero that's your initial reading there it is at five minutes there it is at 10 minutes there it is at 15 minutes there it is at 20 minutes so there i've calculated this for you but i do want you to be able to read those so here's your control data for the glass beads experiment and i've calculated the differences there let's go ahead and look at germinating peas at 10 degrees celsius what would you hypothesize would that rate of cellular respiration increase or decrease go ahead and write that down here's the data table i want you to to fill in so here's germinated peas at 10 degrees celsius at time point zero so i put the respirometer in the water bubble goes all the way to 0.75 at 5 minutes at 10 minutes at 15 minutes at 20 minutes so go ahead and calculate your data there and i'm going to give you a head start on your graph as well so looking at this graph and by the way here's an example of a title i'd like to see you know don't don't copy it i guess i am giving you the the debt the a good example of a title but don't copy it come up with your own so i'm calling this reducing temperatures reduces respiration rates and germinating ps in the respirometer lab so i kind of gave away the the data but you could see that coming through the experiment right okay so on the y-axis we're going to um we're going to plot our dependent variable which is oxygen consumed in milliliters so 0.2 0.1 0.2 0.3 0.4 okay and then on the x-axis we're going to examine the experiment over time okay so you should come up with two lines here one line is going to talk about the data you saw for germinating peas at 25 degrees celsius room temperature and the other line is going to show me what happens when you lower that temperature by putting ice literally ice into the water to lower it down to 10 degrees celsius okay so i've given you a head start on that graph i know this is a longer video but um i hope this helped you to get a good head start in understanding respirometer labs and how they can show you cellular respiration rates in various organisms we've been looking at germinating peas in this experiment but really can put anything that undergoes cellular respiration inside that vial and i've seen some people do some some fun and weird stuff where you put crickets and other sorts of organisms in there so get an idea based on what you know about cellular respiration and metabolism rates in general get an idea of you know what you might see if you look at different organisms of different masses different sizes okay and we'll talk about this in class

Channel: Ron Kinser

Views: 741

Rating: 5 out of 5

Keywords: AP Biology, Investigation 6, Cellular Respiration, Respirometer, Germinating Peas, KOH, Control, Independent Variable, Dependent Variable

Id: Z-Mm8sdunpA

Length: 19min 32sec (1172 seconds)

Published: Fri Nov 06 2020