yeast respiration experiment variables

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3.1.3 Yeast experiment explained

You’ve seen the results of the yeast experiment, but what do these results mean?

Yeasts are microscopic, single-celled organisms, and are a type of fungus that is found all around us, in water, soil, on plants, on animals and in the air. Like all organisms, when yeasts are put in the right type of environment they will thrive; growing and reproducing.

Your experiments were designed to help you identify which environment promotes the most yeast growth. The first three glasses in your experiment contained different temperature environments (cold water, hot water and body temperature water). At very low temperatures the yeast simply does not grow but it is still alive – if the environment were to warm up a bit, it would gradually begin to grow. At very high temperatures the cells within the yeast become damaged beyond repair and even if the temperature of that environment cooled, the yeast would still be unable to grow. At optimum temperatures the yeast thrives.

Your third and fourth glasses both contained environments at optimum temperature (body temperature) for yeast growth, the difference being, the fourth glass was sealed. The variable between these two experiments was the amount of available oxygen. You may have been surprised by your results here, thinking that a living organism in an environment without oxygen cannot survive? However, you should have found that yeast grew pretty well in both experiments.

To understand why yeast was able to thrive in both conditions we need to understand the chemical process occurring in each glass during the experiment. In the three open glasses, oxygen is readily available, and from the moment you added the yeast to the sugar solution it began to chemically convert the sugar in the water and the oxygen in the air into energy, water, and carbon dioxide in a process called aerobic respiration.

Yeast is a slightly unusual organism – it is a ‘facultative anaerobe’. This means that in oxygen-free environments they can still survive. The yeast simply switches from aerobic respiration (requiring oxygen) to anaerobic respiration (not requiring oxygen) and converts its food without oxygen in a process known as fermentation. Due to the absence of oxygen, the waste products of this chemical reaction are different and this fermentation process results in carbon dioxide and ethanol.

Depending on how long you monitored your experiment for and how much space your yeast had to grow you may have noticed that, with time, the experiment sealed with cling film slowed down. This is for two reasons; firstly because less energy is produced by anaerobic respiration than by aerobic respiration and, secondly, because the ethanol produced is actually toxic to the yeast. As the ethanol concentration in the environment increases, the yeast cells begin to get damaged, slowing their growth.

The ethanol produced is a type of alcohol, so it is this process that allows us to use it to make beer and wine. When used in bread making, the yeast begins by respiring aerobically, the carbon dioxide from which makes the bread rise. Eventually the available oxygen is used up, and the yeast switches to anaerobic respiration producing alcohol and carbon dioxide instead. Do not worry though; this alcohol evaporates during the baking process, so you won’t get drunk at lunchtime from eating your sandwiches.

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8 Chapter 8 – Respiration

Respiration by yeast.

During respiration, yeast undergo metabolic processes to obtain energy from the breakdown of sugars. However, yeast can only metabolize certain types of sugars. In order for yeast to utilize a particular sugar as a food source, it needs to have specific transport mechanisms to bring the sugar molecules into its cells. Additionally, the yeast must possess the necessary enzymes capable of breaking down the chemical bonds in the sugar molecules in a way that can be used for energy production.

Among the various sugars, glucose is an essential source of energy for all living organisms, including yeast. Yeast can metabolize glucose through two different pathways: aerobic respiration and anaerobic fermentation. In aerobic respiration , yeast utilize oxygen to break down glucose molecules completely, resulting in the production of carbon dioxide (CO 2 ) and water (H 2 O) as byproducts. This process is highly efficient and yields a larger amount of energy in the form of ATP (adenosine triphosphate).

On the other hand, yeast can also carry out anaerobic respiration in the absence of oxygen. This process, known as fermentation, allows yeast to partially break down glucose molecules, resulting in the production of ethanol (alcohol) and carbon dioxide as byproducts. Although fermentation provides yeast with energy, it is less efficient compared to aerobic respiration.

In this lab, the objective is to investigate the ability of yeast to metabolize different sugars and observe respiration rate . The four sugars being tested are glucose, sucrose , fructose , and lactose . The experiment involves using a CO 2 Gas Sensor to measure the production of carbon dioxide by yeast as they respire using these sugars. The production of carbon dioxide indicates the metabolic activity of the yeast and provides insight into their ability to utilize the tested sugars as a food source.

By observing the rate and amount of carbon dioxide produced by the yeast when exposed to each sugar, it is possible to determine which sugars can be effectively metabolized by the yeast. This information helps in understanding the metabolic preferences and capabilities of yeast in utilizing different sugars for energy production.

• Respiration rate

 Objectives

• Use a C0 2 Gas Sensor to measure concentrations of carbon dioxide.
• Determine the rate of respiration by yeast while using different sugars.
• Determine which sugars can be used as a food source by yeast.
• Vernier LabQuest 2 device
• Water bath @ 38-40 °C
• Vernier C02 Gas Sensor (2)
• Test tube rack
• Yeast Suspension*
• Deionized water
• 10x100mm test tubes (5)
• 5% Glucose, Sucrose, Lactose, and Fructose sugar solutions
• Disposable pipettes OR p-1000 Micropipettes with tips
• 250ml respiration chamber or Erlenmeyer flask (5)

*Stock solution of yeast: 7g of yeast (1 packet) in 100 mL water prepared fresh for the class, placed in 38-40 °C water bath for 10 minutes.

Pre-Assessment

1. What is the purpose of investigating the ability of yeast to metabolize different sugars in the lab? 2. How does yeast obtain energy from the breakdown of sugars during respiration? 3. What are the specific requirements for yeast to utilize a particular sugar as a food source? 4. Which sugar is considered an essential source of energy for all living organisms, including yeast? 5. What are the two pathways through which yeast can metabolize glucose? 6. Describe the byproducts produced during aerobic respiration of glucose by yeast. 7. What is the difference between aerobic respiration and anaerobic fermentation in yeast? 8. How does the efficiency of energy production differ between aerobic respiration and anaerobic fermentation in yeast? 9. What is the role of the CO 2 Gas Sensor in the lab experiment? 10. How can observing the rate and amount of carbon dioxide produced by yeast when exposed to different sugars help determine their metabolic preferences and capabilities?

• Prepare a water bath for the yeast. A water bath is simply a large reservoir of water at a certain temperature. This ensures that the yeast will remain at a constant and controlled temperature. Make sure the digital water bath has several inches of water in the basin. Turn the water bath on and set the temperature at 38-40°C. Monitor the temperature of the water bath during the experiment.
• Connect the C0 2 Gas Sensor to the LabQuest 2 device: Insert the plug into the CHI port at the left side of the device. Set the sensor switch to low (0 – 10,000 ppm) setting. Turn on the LabQuest 2 by pressing the button at the top left of the device.
• To clear any unwanted data from the device before beginning the experiment, tap ‘File’, then select ‘New’ from the drop down menu. When prompted, tap ‘Discard’.
• Obtain five test tubes and label them G, S, F, L, and W.
• Place 3 mL of the glucose solution in test tube G.
• Place 3 mL of the sucrose solution in test tube S.
• Place 3 mL of the fructose solution in test tube F.
• Place 3 mL of the lactose solution in test tube L.
• Place 3 mL of deionized water in test tube W.
• Obtain 15 mL of the yeast suspension. Gently swirl the yeast suspension to mix the yeast that settles to the bottom.
• Put 2 mL of the yeast suspension into the test tube labeled G (glucose). Gently swirl the test tube to mix the yeast into the solution.
• Set the test tube into the water bath and incubate for 10 minutes.
• When incubation is finished, use a pipet to place 3 mL of the solution from test tube G into the 250 mL respiration chamber or flask. Note the temperature of the water bath and record as the actual temperature in Table 1.
• Quickly place the shaft of the C0 2 Gas Sensor in the opening of the respiration chamber or flask. Gently twist the stopper on the shaft of the C0 2 Gas Sensor into the chamber opening. Do not twist the shaft of the C0 2 Gas Sensor or it could be damaged.
• Begin measuring the carbon dioxide concentration by tapping the green arrow ( at the bottom left of the screen. Collect data for 4 minutes (240 seconds), then press the red square to stop data collection. Pressing the arrow button on the right of the device will also start and stop data collection.
• A graph of C0 2 production over time will be displayed. Move your data to a stored run. To do this, tap on the filing cabinet icon at the top right of the screen.
• When data collection has finished, remove the C0 2 Gas Sensor from the respiration chamber. Use a notebook or notepad to fan air across the openings in the probe shaft of the C0 2 Gas Sensor for 1 minute.
• Repeat Steps 7 – 13 for the other four test tubes. Each run will be graphed a different color with a different shape for the data points (square, triangle, circle). It is a good idea to write down which graph represents which sugar.
• When data for all five tubes has been collected and stored, tap the screen next to the filing cabinet icon where it says ‘Run’. Select ‘All Runs’. The graphs for each sugar tested will be displayed.
• Tap ‘Analyze’ from the top of the screen.
• Select ‘Curve Fit’ from the drop-down menu. Select the square for the first sugar tested.
• Tap the arrow next to ‘Choose Fit’ and select ‘Linear’. The formula for a best fit line will appear (y = mx + b).
• RECORD THE SLOPE OF THE LINE (m) AS THE RATE OF RESPIRATION IN TABLE 1. The rate of respiration given by m on the graph is in ppm/s. This should be converted to ppm/min for Table 1.
• Tap OK at the bottom right. This displays the best fit line on the graph.
• Determine the slope of the line (m) for each of the sugars by repeating steps 1 through 5, selecting the next square for the next sugar tested.
• Name (Bench #) and save your file
• Insert your USB (if LabQuest2 does not register the USB, ensure the USB is inserted properly)
• Highlight your named file and continue.
• It is now safe to remove the USB once exporting is complete.
• Upload your file to a device and make sure the entire group has a copy. You can use this file for data manipulation.
• Upload the data into the Respiration discussion board on Canvas.
• Clear the data by tapping ‘File’ and selecting ‘New’. Tap ‘Discard’ when prompted.
• Press the button on the device with the house icon.
• Select (System’, then ‘Shut Down’.
• Tap ‘OK’ when prompted.
• Return sensors and LabQuest 2 to the cart. Wash all glassware.

DATA ANALYSIS & CRITICAL THINKING QUESTIONS

• (Optional) When all other groups have posted their results on the board, calculate the average rate of respiration for each solution tested. Record the average rate values in Table 2.
• Make a bar graph of rate of respiration vs. sugar type. The rate values should be plotted on the y-axis, and the sugar type on the x-axis. Use the rate values from Table 1.
• Considering the results of this experiment, do yeast equally utilize all sugars? Explain.
• Hypothesize why some sugars were not metabolized while other sugars were.
• Why do you need to incubate the yeast before you start collecting data?
• Yeast live in many different environments. Make a list of some locations where yeast might naturally grow. Estimate the possible food sources at each of these locations.

Licenses and Attributions

Yeast is a type of fungus belonging to the kingdom Fungi. It is a single-celled microorganism that plays a significant role in various biological processes, especially in the context of fermentation and baking. Yeast cells are eukaryotic, meaning they possess a true nucleus and other membrane-bound organelles.

Yeast is widely used in the food and beverage industry, particularly in baking and brewing. It has been utilized by humans for thousands of years for the fermentation of sugars, which results in the production of carbon dioxide, ethanol, and other metabolic byproducts. This fermentation process is essential in the leavening of bread, where carbon dioxide gas produced by yeast causes the dough to rise, resulting in a light and fluffy texture.

The most commonly used species of yeast in baking and brewing is Saccharomyces cerevisiae. It has the ability to metabolize various sugars, including glucose, sucrose, fructose, and lactose, through the process of respiration. Yeast cells break down these sugars to obtain energy in the form of ATP (adenosine triphosphate), which is the primary energy currency of cells.

Apart from its role in fermentation, yeast also serves as a model organism in biological research. Due to its simple and well-studied genetics, yeast has provided valuable insights into various cellular processes and molecular mechanisms. Researchers have used yeast to study fundamental biological phenomena, such as cell cycle regulation, DNA replication, protein synthesis, and aging.

Yeast cells reproduce asexually through a process called budding, where a small bud or protrusion forms on the parent cell and eventually separates to become a new individual. Under certain conditions, yeast can also undergo sexual reproduction, involving the fusion of two yeast cells and the exchange of genetic material.

In summary, yeast is a single-celled fungus that plays a vital role in fermentation, baking, brewing, and scientific research. Its ability to metabolize sugars and produce carbon dioxide and ethanol has made it an indispensable microorganism in the food and beverage industry. Additionally, yeast's genetic simplicity and biological characteristics have made it a valuable model organism for understanding fundamental biological processes.

Glucose is a simple sugar and one of the most important carbohydrates in biological systems. It is a primary source of energy for living organisms and plays a crucial role in cellular metabolism. Glucose is a monosaccharide, which means it consists of a single sugar molecule. Its chemical formula is C6H12O6.

Glucose is found in various forms and sources in nature. Some common examples include:

1. Blood sugar: Glucose is the main sugar found in the bloodstream of animals, including humans. It is transported through the bloodstream to provide energy to cells throughout the body.

2. Plant sap: Glucose is present in the sap of plants, which serves as a nutrient-rich fluid that transports sugars and other substances within the plant's vascular system.

3. Fruits: Many fruits contain glucose, often in combination with other sugars like fructose. Fruits such as grapes, bananas, apples, and oranges are examples of glucose-containing fruits.

4. Honey: Bees produce honey by converting nectar, a sugary liquid found in flowers, into a concentrated solution. Honey contains glucose as well as other sugars.

5. Starches: Glucose molecules are the building blocks of starch, a polysaccharide found in various plant-based foods. Starchy foods like potatoes, rice, wheat, and corn contain glucose in the form of long chains of starch molecules.

6. Sweeteners: Glucose is used as a sweetener in various food products. It is commonly found in syrups like corn syrup and high-fructose corn syrup, which are widely used in the food industry.

7. Metabolism: Glucose is produced through the breakdown of more complex carbohydrates, such as glycogen (the storage form of glucose in animals) and starches, during digestion. It is then used by cells as a fuel source through processes like glycolysis and cellular respiration.

Glucose is an essential energy source for organisms and serves as a fundamental component in many biological processes. Its availability and regulation in the body are crucial for maintaining normal physiological functions.

Aerobic metabolism of sugar refers to the process by which cells, including yeast cells, break down sugar molecules in the presence of oxygen to produce energy. This process is also known as cellular respiration and occurs in several sequential steps.

The first step in aerobic metabolism is glycolysis, which takes place in the cytoplasm of the cell. During glycolysis, a molecule of glucose, a six-carbon sugar, is converted into two molecules of pyruvate, a three-carbon compound. This process involves the breakdown of glucose into smaller molecules, releasing a small amount of ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide, a coenzyme) as byproducts.

After glycolysis, if oxygen is available, the pyruvate molecules produced are transported into the mitochondria, the powerhouses of the cell. In the mitochondria, the pyruvate molecules undergo further oxidation in a process called the citric acid cycle, also known as the Krebs cycle or TCA (tricarboxylic acid) cycle. The citric acid cycle involves a series of chemical reactions that break down the pyruvate molecules, releasing more ATP, NADH, and FADH2 (flavin adenine dinucleotide, another coenzyme).

The NADH and FADH2 molecules produced during glycolysis and the citric acid cycle play a crucial role in the final step of aerobic metabolism: oxidative phosphorylation. Oxidative phosphorylation occurs in the inner mitochondrial membrane and involves the transfer of electrons from NADH and FADH2 to a series of protein complexes known as the electron transport chain (ETC). As electrons pass through the ETC, they release energy that is used to pump protons (H+) across the inner mitochondrial membrane, creating an electrochemical gradient.

The electrochemical gradient created by the ETC drives the synthesis of ATP through a process called chemiosmosis. ATP synthase, an enzyme located in the inner mitochondrial membrane, utilizes the energy from the proton gradient to produce ATP. This process is known as oxidative phosphorylation because it couples the phosphorylation of ADP (adenosine diphosphate) to form ATP with the oxidation of NADH and FADH2.

Overall, aerobic metabolism of sugar provides the most efficient way to produce energy in cells. It yields a large amount of ATP compared to anaerobic processes like fermentation. By utilizing oxygen, cells can fully break down sugar molecules, extracting maximum energy from them and generating carbon dioxide and water as byproducts. This process is essential for the functioning and survival of cells, including yeast cells, in oxygen-rich environments.

Anaerobic metabolism of sugar, also known as fermentation, is a metabolic pathway that allows cells to generate energy from sugar molecules in the absence of oxygen. Unlike aerobic metabolism, which occurs in the presence of oxygen and yields more energy, anaerobic metabolism is less efficient and produces fewer ATP molecules.

There are several types of anaerobic fermentation, but one of the most common forms is alcoholic fermentation, which occurs in yeast and some bacteria. In this process, glucose or other sugars are converted into ethanol (alcohol) and carbon dioxide.

The first step of anaerobic metabolism is glycolysis, which takes place in the cytoplasm of the cell. During glycolysis, a molecule of glucose is broken down into two molecules of pyruvate, similar to the process in aerobic metabolism. This step releases a small amount of ATP and NADH.

In the absence of oxygen, pyruvate molecules undergo further conversion through fermentation. In the case of alcoholic fermentation, pyruvate is decarboxylated, meaning it loses a carbon dioxide molecule, to form acetaldehyde. This reaction is catalyzed by the enzyme pyruvate decarboxylase. Simultaneously, NADH is oxidized back to NAD+ by transferring its electrons to the acetaldehyde, producing NAD+ and NADH. Acetaldehyde then undergoes a second reaction, catalyzed by the enzyme alcohol dehydrogenase, where it is reduced by NADH to produce ethanol. This final step regenerates NAD+ for further glycolysis to continue.

The overall process of anaerobic metabolism of sugar is less efficient than aerobic metabolism because it produces only a small amount of ATP. In addition to ethanol, carbon dioxide is also produced as a byproduct. This is why during alcoholic fermentation, we observe the release of carbon dioxide bubbles.

Anaerobic metabolism is important for organisms that live in environments with low oxygen availability. It allows them to continue producing energy even when oxygen is limited or absent. For example, yeast cells undergo anaerobic metabolism when fermenting sugars in the absence of oxygen, which is utilized in the production of alcoholic beverages and bread-making.

It's important to note that different organisms can undergo other types of anaerobic fermentation, such as lactic acid fermentation in some bacteria and human muscle cells. These processes involve different intermediate compounds and produce lactic acid instead of ethanol as the end product.

Respiration rate refers to the rate at which an organism or a cell undergoes cellular respiration, which is the process of breaking down organic molecules, such as sugars, to produce energy in the form of ATP (adenosine triphosphate). In the case of yeast, respiration rate specifically refers to the rate at which yeast cells carry out the process of cellular respiration.

Yeast cells are capable of metabolizing sugars through aerobic respiration, which occurs in the presence of oxygen, or anaerobic respiration, which occurs in the absence of oxygen. Both forms of respiration involve the breakdown of sugar molecules to release energy.

During aerobic respiration, yeast cells convert glucose, sucrose, fructose, lactose, or other sugars into carbon dioxide (CO2) and water (H2O). This process involves a series of enzymatic reactions that occur in the mitochondria of yeast cells. Oxygen is used as the final electron acceptor in the electron transport chain, allowing for the efficient production of ATP.

In contrast, during anaerobic respiration, yeast cells can metabolize sugars without the presence of oxygen. Instead of utilizing oxygen as the final electron acceptor, yeast cells undergo a process called fermentation. In this process, sugar molecules are partially broken down, producing alcohol (typically ethanol) and carbon dioxide as byproducts. This type of respiration is commonly observed in yeast when they are in an oxygen-deprived environment, such as when fermenting fruits to produce alcoholic beverages or when used in baking to make bread rise.

The respiration rate of yeast can be measured by monitoring the production of carbon dioxide gas. As yeast cells metabolize sugars, they release carbon dioxide as a byproduct, which can be detected and quantified using various methods, such as gas sensors or gas chromatography. By measuring the rate of carbon dioxide production, researchers can assess the metabolic activity and respiration rate of yeast under different conditions, such as varying sugar concentrations, temperatures, or pH levels.

Overall, the respiration rate of yeast provides insights into its metabolic activity, energy production, and ability to utilize different sugars as energy sources. It is an important parameter to consider when studying yeast physiology, fermentation processes, or when using yeast in various applications, such as brewing, winemaking, or biofuel production.

Sucrose is a disaccharide composed of glucose and fructose molecules linked together. It is commonly known as table sugar and is one of the most widely used sweeteners in the world. The chemical formula of sucrose is C12H22O11.

Sucrose is found in various natural sources and is commonly used as a sweetening agent in food and beverages. Here are some common examples of where sucrose is found:

1. Sugarcane: Sucrose is abundantly found in sugarcane plants. Sugarcane juice is extracted from the stalks of the plant and processed to obtain crystalline sucrose, which is further refined to produce table sugar.

2. Sugar beet: Sugar beet is another major commercial source of sucrose. The sucrose content is extracted from the root of the sugar beet plant and processed similarly to sugarcane to obtain sugar.

3. Fruits: Sucrose is naturally present in many fruits, although in varying amounts. Fruits like mangoes, pineapples, oranges, and strawberries contain sucrose along with other sugars like glucose and fructose.

4. Processed foods: Sucrose is widely used as a sweetener in processed foods such as baked goods, candies, desserts, soft drinks, and sauces. It provides sweetness and enhances the flavor of these products.

5. Condiments: Some condiments and spreads, such as jams, jellies, and syrups, contain sucrose to add sweetness and improve the taste.

6. Confectionery: Chocolates, candies, and confectionery products often contain sucrose as a primary sweetener. It contributes to the desirable taste and texture of these treats.

7. Beverages: Many beverages, including soda, energy drinks, and sweetened teas, contain sucrose for sweetening purposes.

Sucrose is widely consumed in the human diet and is a common ingredient in various culinary preparations. However, it is important to consume sucrose in moderation as excessive intake can contribute to health issues like obesity, dental problems, and metabolic disorders.

Fructose is a monosaccharide, or simple sugar, that is naturally occurring in many fruits, vegetables, and sweeteners. It is the sweetest of all naturally occurring sugars and has the same chemical formula as glucose (C6H12O6), but with a different arrangement of atoms.

Here are some key points about fructose and common examples of where it is found:

1. Natural Sources: Fructose is found in varying amounts in a wide range of fruits and vegetables. Some examples include:

- Fruits: Fructose is abundant in fruits such as apples, pears, grapes, cherries, peaches, and mangoes. It contributes to the natural sweetness of these fruits.

- Honey: Honey contains a mixture of fructose and glucose, with fructose being the predominant sugar. Bees convert nectar from flowers into honey, which is a concentrated source of fructose.

- Agave: Agave syrup, derived from the agave plant, is a popular natural sweetener that primarily consists of fructose. It is commonly used as an alternative to table sugar.

2. Processed Foods and Beverages: Fructose is also used as an added sweetener in various processed foods and beverages. High-fructose corn syrup (HFCS) is a common sweetener used in soft drinks, processed snacks, cereals, and baked goods. It is produced by enzymatically converting glucose from cornstarch into fructose, resulting in a sweeter and more economical alternative to sucrose (table sugar).

3. Sweeteners: Crystalline fructose, which is a highly pure form of fructose, is used as a sweetening agent in some food products. It is sweeter than sucrose and can be found in certain beverages, desserts, and low-calorie or sugar-free products.

It is worth noting that excessive consumption of fructose, particularly in the form of added sugars like high-fructose corn syrup, has been associated with potential health risks. High intake of fructose from processed foods and beverages has been linked to increased risk of obesity, type 2 diabetes, and metabolic disorders. As with any sugar, moderation is key when consuming fructose as part of a balanced diet.

Lactose is a disaccharide composed of two sugar molecules, glucose and galactose, linked together. It is commonly referred to as milk sugar because it is the primary sugar found in milk and dairy products. Lactose is unique in that it is primarily found in mammalian milk, including human breast milk.

Here are some key points about lactose and common examples of where it is found:

1. Milk and Dairy Products: Lactose is abundantly present in milk from various mammalian species, including cows, goats, and sheep. It serves as the main carbohydrate source in milk. Dairy products such as yogurt, cheese, butter, and ice cream also contain lactose, although the concentration may vary depending on the specific product.

2. Human Breast Milk: Lactose is an essential component of human breast milk, providing a source of energy for infants. It plays a crucial role in the development and growth of newborns. Human breast milk typically contains higher levels of lactose compared to the milk of other mammalian species.

3. Lactose-Containing Food Products: Lactose is sometimes used as an ingredient in processed food products, especially those aimed at individuals who are lactose intolerant. These products may include lactose-reduced or lactose-free dairy alternatives, lactose-free milk, lactose-free ice cream, and lactose-free yogurts.

4. Medications and Supplements: Lactose is also used as an excipient in some medications and dietary supplements. It can act as a filler or a binding agent in tablet or capsule formulations. Individuals with lactose intolerance or milk allergies should be cautious about consuming such products and may need to seek alternatives.

Lactose intolerance is a common condition where the body lacks sufficient amounts of the enzyme lactase, which is responsible for breaking down lactose into glucose and galactose for absorption in the small intestine. This leads to digestive symptoms, such as bloating, gas, and diarrhea, after consuming lactose-containing foods or beverages. As a result, individuals with lactose intolerance often need to limit or avoid foods high in lactose or use lactase supplements to aid in digestion.

It's important to note that lactose is not naturally present in non-dairy plant-based beverages like soy milk, almond milk, or coconut milk. These products are typically made by grinding or blending the respective plant material with water, without the addition of lactose.

Biology I Cellular Processes Laboratory Manual by The authors & Hillsborough Community College is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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How to Measure Yeast Respiration

Science Project: The Evaporation of Fresh Water Vs. Salt Water

In the beginning of your biology laboratory career it is inevitable that you will run into the yeast respiration experiment. This simple experiment is a starting point many instructors use to introduce their students into the world of biological reactions. In this experiment the yeast, a living organism, feeds off the sugar in the solution and creates a byproduct. This is known as respiration and the product of the yeast is carbon dioxide, or CO 2 .

Fill the 250mL beaker halfway with water and fill the graduated cylinder completely with water. Put your hand on the top of the graduated cylinder and flip it upside down and place it into the beaker. Try to make sure you don’t let any water out because at this point your goal is to make sure the graduated cylinder stays completely full of water. If some air seeps in, don’t worry about it, just mark it down and subtract it from your final amount at the end of the experiment.

Open the packet of yeast and pour it into the flask followed by the quarter cup of warm water. Once both are in the flask place your thumb over the opening of the flask and gently swirl the contents until the yeast has dissolved in the water. Add one tsp. of sugar and swirl the contents once again.

Place the stopper firmly onto the flask and insert the short glass tube into the hole in the top of the stopper. Now attach the rubber hose to the glass tube and place the other end of the tube into the water in the beaker and into the bottom of the graduated cylinder so that any gas that travels through the hose will become stuck in the cylinder.

Wait about fifteen minutes for the reaction to run itself out. During this time you will see the amount of gas in the graduated cylinder increase over time and push the water out of the cylinder. This continues until the yeast uses its entire food source or until it poisons itself with its own waste.

Measure the amount of carbon dioxide that has been created by the yeast. If there was any air that had been trapped in the graduated cylinder before the experiment started then now would be a good time to subtract that amount from your new measurement. You now have your yeast respiration measurement.

Things You'll Need

• Make sure you only use warm water and not hot water.

Once the experiment starts don’t touch the flask because the heat from your hands will cause the gas in the flask to expand and will end up varying your end results. As with most lab experiments you are working with glass so be careful when the lab equipment so you don’t break anything and cut yourself.

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• Once the experiment starts don't touch the flask because the heat from your hands will cause the gas in the flask to expand and will end up varying your end results.
• As with most lab experiments you are working with glass so be careful when the lab equipment so you don't break anything and cut yourself.

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Lab Explained: Carbon Dioxide Production by Yeasts under Different Temperatures

• Lab Explained: Carbon Dioxide Production…

Yeasts undergo aerobic cell respiration if there is sufficient oxygen and releases carbon dioxide as a waste product. Yeasts, like any other cells, have an optimum temperature at which they work most efficiently, including the process of cell respiration. This experiment aims to discover the relation between temperature and the carbon dioxide yield of yeasts to discover the optimum temperature for yeasts’ execution of aerobic cell respiration.

Hypothesis:

It is hypothesized that yeasts carry out aerobic cell respiration most efficiently at high temperatures because high temperature is likely to activate the process at a higher rate. Cells are most active in high temperatures yet within their tolerance of heat, if the temperature exceeds 40 degrees, yeasts, along with their enzymes, will die off or become denatured so they no longer function. On the contrary, low temperature will not activate the yeasts to work as yeasts are not adapted to a cold environment.

• Independent variable: temperatures of 10% glucose solution in which yeasts are placed to carry out aerobic cell respiration (6°C, room temperature, and 30°C are the temperatures investigated, though the actual room temperature at the lab is noted down)
• Dependent variable: Change in CO 2 concentration after yeasts were placed in the glucose solution over time at different temperatures (CO2 concentration in 3 minutes recorded at an interval of 30 seconds)
• Constants/controlled variables: concentration of glucose solution (10%), the mass of glucose solution used at each trial (50 gm of water and 5 gm of glucose), the mass of yeasts used at each trial (250 mg), rate of stirring of the solution on the stirring plate (500 rpm), time to record CO2 concentration after yeasts are put in (30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, 3 minutes), chemicals used (10% glucose solution), apparatus and equipment (test tubes, 100 ml beakers, 50 ml graduated cylinders with an uncertainty of ±0.1 ml, 250 ml Erlenmeyer flasks, balance in g accurate to 2 decimal places, a hot plate that also contains a magnetic stirrer plate and magnetic stirring bar, thermometer range from 0°C to 100°C with an uncertainty of ±0.01°C, CO 2 sensor which connects to an Xplorer GLX machine, test tube racks, timer accurate to 0.01 s, 1 spatula, 1 ice bath consists of a 50 ml beaker and ice cubes, 1 fridge)
• Yeasts 1.5 g
• Glucose 30 g
• 500 ml distilled water
• 4 100 ml beakers, uncertainty ±5 ml
• 1 thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C
• 12 test tubes
• 1 test tube rack that can hold 12 test tubes
• 1 50 ml graduated cylinder with an uncertainty of ±0.1 ml
• 6 250 ml Erlenmeyer flasks, uncertainty is not concerned as they are not used to measure volumes
• 1 Weighing balance in g accurate to 2 decimal places
• 1 hot plate that also contains a magnetic stirrer plate
• 1 magnetic stirring bar
• 1 CO2 sensor charged to the full battery with a stopper binds to the flask
• 1 GLX machine with a full battery
• 1 timer accurate to 0.01 s
• 1 ice bath, including 1 50 ml beaker and 6 ice cubes with a side length of approximately 1 centimeter
• 1 fridge with a refrigerator compartment that refrigerates at a temperature higher than 0°C, approximately 0 to 4°C

Procedures:

6 °C glucose solution preparation:

• 100 ml beaker is filled with distilled water
• 6 ice cubes with side length of approximately 1 centimeter are placed in the 100 ml beaker with distilled water
• The 100 ml beaker is laid aside in the refrigerator compartment with a temperature ranged from 0°C to 4°C but higher than 0°C so water will not freeze in the fridge overnight
• On the second day, 5 g of glucose is weighed on a weighing balance accurate to 2 decimal places
• 5 g glucose is put into a test tube and placed on the test tube rack
• Similarly, 0.25 grams of yeasts are measured by a weighing balance accurate to 2 decimal places and transferred into a test tube, which is placed on the test tube rack
• The 100 ml beaker stored in the fridge is taken out and poured into a 50 ml graduated cylinder with an uncertainty of ±0.1 ml to measure 50 ml of ice water, ice cubes will stay in the beaker
• 50 ml ice water is poured into the 250 ml Erlenmeyer flask
• The Erlenmeyer flask is placed on a hot plate which also functions as a magnetic stirring plate and a magnetic stirring bar is put into the flask
• 5 gram of glucose already measured in the test tube is poured into the water
• The stirring plate is turned on, stirring at a rate of 500 rpm
• The stirring plate is turned off once glucose is fully dissolved
• A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution, at this stage, the ice water is warmed up, the procedure cannot be proceed until the temperature of the solution reaches 6°C
• The CO2 sensor is connected to the GLX machine which displays the CO2 concentration in the air
• The CO2 sensor, which attached to a stopper that binds to the neck of the flask to block the flow of air, is embedded into the flask
• The CO2 concentration will be displayed on the GLX machine and is noted as the original CO2 concentration in the flask
• The CO2 sensor is pulled out and yeasts in the test tube are poured into the flask, CO2 sensor is put back into the flask, the magnetic stirring plate is turned on at a revolution rate of 500 rpm, the stopwatch is ticked off, all this should be done without intervals
• The CO 2 concentration in the flask is recorded every 30 seconds for 3 minutes so 6 numbers will be recorded
• The procedure above is repeated twice more

Room temperature glucose solution preparation:

• The beaker is placed in the lab overnight
• 25 grams of yeasts are weighed on a balance accurate to 2 decimal places
• 25 g yeasts are transferred to a test tube and placed on the test tube rack
• The distilled water in the 100 ml beaker is poured into a 50 ml graduated cylinder with an uncertainty of ±1 ml to measure 50 ml of water at room temperature
• 50 ml water is poured into the 250 ml Erlenmeyer flask
• 5 grams of glucose already measured in the test tube is poured into the water
• A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution, the temperature measured should be the room temperature and is noted for further examination
• Steps 14 to 19 in 6°C glucose solution preparation from the last section are repeated

30°C glucose solution preparation

• 50 ml distilled water is measured with 50 ml graduated cylinder with an uncertainty of ±0.1 ml
• 50 distilled water is transferred to the 250 ml Erlenmeyer flask
• 5 g of glucose is weighed on a weighing balance accurate to 2 decimal places
• 25 g of yeasts are measured by a weighing balance accurate to 2 decimal places
• The yeasts are put into a test tube and placed on the test tube rack
• 5 gram of glucose already measured in the test tube is poured into the water in the flask
• The flask is placed on the top of a hot plate that also functions at a magnetic stirring plate, which is set to 30 degrees and turned on the stirring at a rate of 500 rpm
• A thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C is inserted into the glucose solution to monitor the change in temperature
• Once the temperature reaches 30°C, the thermometer is taken out, hot plate turned off
• Steps 14 to 19 in 6°C glucose solution preparation from the second last section are repeated

Methods of control of variables:

The independent variables are temperatures of 10% glucose solution in which yeasts are placed to carry out aerobic cell respiration. They are 6°C, room temperature, and 30°C respectively.

The methods of how to manipulate the independent variables are explained in the procedure. Briefly, 6°C glucose solution needs to have a distilled water stored in an ice bath and placed in the refrigerator compartment of a fridge. Note that it cannot be put into the freezer compartment, otherwise the distilled water will be frozen so cannot be used. Overnight, the temperature will be close to the temperature of the refrigerator compartment, which should be between 0 to 4°C.

The water will be taken out the second day and its temperature is measured with a thermometer ranged from 0°C to 100°C with an uncertainty of ±0.01°C. The temperature is likely to rise during the process, so once the temperature reaches 6°C, the rest of the procedure can be carried out. The room temperature glucose solution requires a similar setup as the 6°C solution. Distilled water fills the 100ml beaker and is placed in the lab overnight to require water at room temperature.

The exact temperature, however, should be noted for quantitative analysis. The 30°C glucose solution requires a hot plate. Distilled water is heat up on the hot plate set at 30°C and a thermometer is inserted into the flask with distilled water to monitor change in temperature. Once the temperature reaches 30°C, the hot plate is turned off and the rest of the procedure must be carried out immediately so that the water or the glucose solution does not cool down.

The dependent variable is the change in CO 2 concentration after yeasts were placed in the glucose solution over time at different temperatures. One would record the initial CO 2 concentration of the glucose solution before yeasts were put in to obtain the stock concentration of CO 2 in the flask. Then, the CO 2 concentration in the flask is recorded at a 30 seconds interval after yeasts are put in for 3 minutes, so after 30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, and 3 minutes the CO­ 2 concentration are recorded. One would need a timer for this.

The experimenter may wish the record the data and graph them in a graph of CO 2 concentration in the flask over time. With the graph, one would subtract the initial CO 2 concentration from the CO ­2 concentration, the CO­ 2 concentration at 30 seconds from the CO 2 concentration at 1 minute and so on the obtain the difference of CO 2 concentration between each interval to monitor the overall rate of change in CO 2 concentration at different temperatures in which yeasts carry out aerobic cell respiration.

One controlled variable is the concentration of glucose solution, which is kept at 10% by measuring 5 grams of glucose with a weighing balance accurate to 2 decimal places and then the glucose is poured into a 50 ml distilled water measured by a 50 ml graduated cylinder with an uncertainty of ±0.1 ml, mixed by the magnetic stirring plate and bar. This process is carried out in all three temperatures.

Another constant is the mass of glucose solution used at each trial. Similar to the previous one, 50 gm of distilled water are measured by a 50 ml graduated cylinder and 5 gm of glucose are weighed by a weighing balance. They will be mixed using a magnetic stirring plate and a magnetic stirring bar put into the Erlenmeyer flask that contains the distilled water and glucose.

Note that the glucose can be stored in a test tube and put aside and when being poured into the flask containing distilled water, the test tube is knocked lightly to ensure glucose would not stick to the internal surface of the test tube so most if not all 5 gm of glucose will go into the flask.

The mass of yeasts used at each trial – 250 mg – is another controlled variable. Like glucose, yeasts are also measured with a weighing balance accurate to 2 decimal places in grams. Weighing yeasts and transferring them into a test tube can be tricky, extra concentration is required.

The rate of stirring of the solution on the stirring plate is 500 revolutions per minute. The indicator should be switched to 500 rpm with the magnetic bar placed inside the solution and with yeasts, if numbers of rpm are not shown, the revolution rate is switched to medium instead.

Another constant is the time to record CO 2­ concentration after yeasts are put in. The time is 30 seconds, 1 minute, 90 seconds, 2 minutes, 150 seconds, 3 minutes. A stopwatch or a timer is required and also accurate to 0.01 s. At these 30 seconds intervals, the CO­ 2 concentration is displayed on the GLX machine connected to the CO 2 sensor, the number is jogged down by looking at the number displayed in ppm.

The chemicals used, i.e. 10% glucose solution, is another controlled variable.

Remember only glucose, not other sugars, are investigated in this experiment. The apparatus and equipment used are constants as well. They are 12 test tubes, 100 ml beakers, 50 ml graduated cylinders with an uncertainty of ±0.1 ml, 250 ml Erlenmeyer flasks, balance in g accurate to 2 decimal places, a hot plate that also contains a magnetic stirrer plate and magnetic stirring bar, thermometer range from 0°C to 100°C with an uncertainty of ±0.01°C, CO 2 sensor which connects to an Xplorer GLX machine, test tube racks, timer accurate to 0.01 s, 1 spatula, 1 ice bath consists of a 50 ml beaker and ice cubes, 1 fridge.

The numbers of each piece of equipment are listed in the materials section. New equipment can be used if the previous one has a residue of the solution, e.g. glucose solution with yeasts, so the procedure can be carried in a faster fashion.

Equations or methods to collect relevant data:

Data table 1:

Data table 2:

This experiment aims to investigate the relation between the temperature of the solution as an environment in which yeasts carry out aerobic respiration and the carbon dioxide production by yeasts.

The correlation is whether positive or negative yet the optimum temperature for yeasts to carry out aerobic respiration cannot be determined by only investigating 3 temperatures. However, we can infer the property of the correlation by examining and comparing the rates of change in CO 2 concentration at each temperature of the glucose solution.

First, the temperature of the glucose solution placed in the lab overnight which should be equivalent of the room temperature is measured with a thermometer ranged from 0 to 100°C with an uncertainty of ±0.01°C. Then the n value in the first column on both data tables can be filled.

Second, the initial concentration of carbon dioxide in the flask with 10% glucose concentration is recorded using a CO 2 sensor that is inserted into the flask and connected to a GLX device that displays the concentration. This stock concentration acts as a reference to how much carbon dioxide present in the flask in the first place. This concentration is measured in each trial because the CO 2 concentration is likely to fluctuate in each trial and will influence the results of the CO 2 concentration measured later.

Third, after yeasts were put into the flask with glucose solution, the CO 2 sensor is put back on and the timer ticked off. At each interval of 30 seconds, the CO2 concentration is recorded. If the new concentrations rise, it indicates the yeasts are carrying out aerobic cell respiration in which they breathe in oxygen and release carbon dioxide as a waste product.

Because there is abundant oxygen gas present in the flask beforehand, the yeasts are expected to continuously carry out aerobic respiration through the 3-minute trial. On the contrary, if the CO2 concentration remains the same or even starts to decrease, it implies that yeasts are not functioning. It is either because the temperature does not fulfill the requirement of yeasts to work or the yeasts start to die off as enzymes denatured from high temperature.

The CO 2 concentration measured is recorded at 30 seconds, 60 seconds, 90 seconds, 120 seconds, 150 seconds and 180 seconds after yeasts are placed into the glucose solution with CO 2 sensor attached stopper sealed up the neck of the Erlenmeyer flask so air cannot flow. The data acquired should fill the entire data table 1.

Data table 1 consists of raw data only. And data table 2 is filled with processed data.

Fourth, after all raw data are obtained, processed data can be calculated. The change of CO 2 concentration in the flask from the initial concentration to the concentration after 180 seconds since yeasts are put in can be deduced by deducted the stock concentration from the carbon dioxide concentration in the flask after 180 seconds since yeasts are put in the glucose solution. This change of concentration leads to the first speculation of the efficiency of yeasts under these temperatures. The equation is therefore used:

concentration of CO 2 in the flask after yeasts are put in for 180 seconds in ppm – concentration

of initial CO 2 in the flask in ppm = change in CO 2 ­ concentration

Fifth, the CO 2 production per second per gram of yeasts can therefore be calculated by divide the change in CO 2 concentration with 180 seconds and then divide again by 0.25 g of yeasts that had been used. The overall three sets of data representing three trials under different temperatures will be added together and divide by three to determine the average rate of change in CO 2 concentration. The following formula is used:

Average production of CO 2 per second per gram of yeast in ppm/s/g = (change in CO 2 ­ concentration in the first trial in ppm/180 s/0.25 g + change in CO2 ­concentration in the second trial in ppm/180 s/0.25 g + change in CO2 ­concentration in the third trial in ppm/180 s/0.25 g)/3

Once the average rate is calculated in ppm/s/g, the three rates can be compared to determine under which of the three temperatures is the most efficient for yeasts to carry out aerobic cell respiration. The highest one would mean that the related temperature is likely to be closer to the optimum temperature at which yeasts function most efficiently because more carbon dioxide produced per second per gram of yeasts under one temperature means the temperature is more favored by yeasts among the three temperatures examined.

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Practical: Investigating Anaerobic Respiration in Yeast ( Edexcel IGCSE Biology )

Revision note.

Biology Lead

Practical: Investigating Anaerobic Respiration in Yeast

• Yeast can respire anaerobically (without oxygen), breaking down glucose in the absence of oxygen to produce ethanol and carbon dioxide
• Anaerobic respiration in yeast cells is called  fermentation
• Fermentation is economically important in the manufacture of bread (where the production of carbon dioxide makes dough rise) and alcoholic drinks (as ethanol is a type of alcohol)
• It is possible to investigate the effect of temperature on yeast fermentation , by seeing how temperature affects the rate of anaerobic respiration in yeast

The process of anaerobic respiration in yeast

• Boiling tubes
• Capillary tubes
• Sugar solution
• The sugar solution provides the yeast with glucose for anaerobic respiration
• This prevents oxygen from entering the solution ( prevents aerobic respiration in the yeast )
• Using a capillary tube, connect this boiling tube with another boiling tube that is filled with limewater
• The rate that carbon dioxide is produced by yeast can be used to measure the rate of anaerobic respiration (i.e. the rate of fermentation )
• Change the temperature of the water bath and repeat

Experimental set up for investigating anaerobic respiration in yeast

Results and Analysis

• Compare results at different temperatures to find out at which temperature yeast respires fastest
• The higher the temperature , the more bubbles of carbon dioxide should be produced as higher temperatures will be closer to the optimum temperature of enzymes in yeast, increasing enzyme activity
• As respiration is an enzyme controlled reaction , as enzyme activity increases, the rate of anaerobic respiration will increase
• If the temperature is too high (beyond the optimum temperature), the enzymes will denature causing carbon dioxide production to slow down and eventually stop

Applying CORMS to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• C  – We are changing the temperature in each repeat
• O – The type (species) of yeast we are using must be the same
• R – We will repeat the investigation several times at each temperature to make sure our results are reliable
• M1 – We will measure the number of bubbles (of carbon dioxide) produced
• M2 – in a set time period (e.g. 2 minutes)
• S – We will control the concentration, volume and pH of the sugar solution, as well as the mass of yeast added

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Author: Lára

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.