Using Poinsettia Leaves as an Acid / Base pH Indicator

Click image to view this resource in my TpT store.

I LOVE this fun holiday activity!

We science teachers know that many plants contain pigments that can be used as pH indicators.  I think we have all created a stink in our homes or labs by boiling red cabbage to use the "juice" as an acid/base indicator!



Did you know that you can do the same with the pigments found in red Poinsettia leaves?

These plants contain anthocyanins, which are water soluble pigments.  These pigments are responsible for the the red, purple, and blue colors seen in flowers, fruits, and vegetables. Anthocyanins respond to changes in pH.  I absolutely love lab activities that use items like this in the lab.  My students are often surprised and excited to discover that household items, such as the Poinsettia or red cabbage, can be used for scientific purposes.  Using the Poinsettia leaves as an acid/base indicator makes for a super fun lab activity around the holidays.

In this lab, the students will use a pigment solution extracted from the leaves of the poinsettia to establish a known pH baseline.  Students will then use this baseline to predict the pH of common household items.

The images below will give you a great idea of all that is involved with this lab. Click on any image below to view this resource in my TpT store.

I hope you find this useful in your science classes.  Enjoy the holiday season!

Helping Students Review and Reinforce Biochemistry and Organic Compounds

Master the Information with this Organic Compounds Mix/Match Game 

It's that time of year again.  Time to teach the dreaded unit on Biochemistry!  (Insert scary music here.)

I love the phrase, "Nothing in Biology makes sense, except in the light of evolution."  I would like to add to that, "...except in the light of evolution and biochemistry."  In my mind, there is simply no way to teach cell physiology, cell division, photosynthesis, enzymatic reactions, or cellular respiration without first teaching a solid unit on biochemistry and organic compounds.

The concepts of biochemistry are difficult, and unfortunately, this is the unit that our biology students are usually faced with at the very beginning of the school year. Teaching strategies, labs, and review activities are especially important at this time. This mix/match review game will provide the review and reinforcement that you are looking for.

The set includes 4 larger cards, each with the name of one of the groups of organic compounds.  There are 75 smaller answer cards. Students must match the answer card statements to the correct group of organic compounds.

One of the things that I love best about this activity is that the game can be customized for different grade levels and ability levels.  An advanced class should use all of the cards.  A younger grade or slower-paced class should use only the answer cards that are appropriate.  Remove any answer cards that you have decided not to use.  The game can be made easy or hard based on your particular students.   It is very easy to differentiate within the same class. By placing the game pieces into small Ziplock bags, you can easily give a "customized" bag to each group of students in your class.

Once the students have completed the card sort, have them record the answer card statements on the student answer sheet.  When students write, it helps them learn and commit the information to memory.  Students can easily do this on their own notebook paper as well.  Blank cards are included so you can add additional answer card statements.

Click image to view product.

I make these cards available to my students before school, after school, and/or during their study hall.  It is a great way to review for the unit test. Best of luck as you teach your unit on biochemistry!  Have a great school year!

If you are looking for a more interactive digital review option, you might also like these biology hidden picture review activities that give students instant feedback as they work.

          👉 Link: biology hidden picture review activities

To give students a hands on way to apply what they have learned about macromolecules, try this organic compounds food testing lab activity using common foods and indicator tests.

How much Vitamin C is in your fruit juice?

Lab: Determining the Amount of Vitamin C in Fruit Juices

I  have been doing this lab every year for a long, long time.  I always enjoy it, and so do my students. I often do this lab with my biology students when teaching about nutrition and digestion, but my favorite use of this lab is with my chemistry classes.  This lab is perfect to introduce the idea of titrations, equivalents, and as a review of dimensional analysis.

In this experiment the student will use a lab procedure known as a titration to determine the amount of Vitamin C found in a 6 ounce serving of various fruit juices.  I most often use orange juice, pineapple juice, and apple juice. 

A titration is the controlled addition and measurement of the amount of a solution of known concentration required to react completely with a measured amount of a solution of unknown concentration.  Titration provides a means of determining the chemically equivalent amounts of two substances.  

The materials list is short and consists of items found in almost all labs..... no fancy equipment required!  You will need:  Spot plate, Thin stemmed or microtip Beral pipets  (or medicine droppers),  White paper for background, Ascorbic acid standard solution,  Apple juice,  Orange juice,  Pineapple juice, Starch solution,  Iodine solution and Plastic Toothpick (stirrer).

In order to determine the amount of Vitamin C in the fruit juice, the student must first do a titration using a vitamin C (ascorbic acid) solution of known concentration.  An iodine/starch complex is used so that a color change can be detected.  The number of drops of iodine added will be used to determine the amount of Vitamin C present in the juice.  

When ascorbic acid (Vitamin C) comes into contact with iodine, it is oxidized to form dehydroascorbic acid.  When Vitamin C and iodine are in solution together, they will form iodide.  As iodine is added during the titration, iodide will continue to be formed until there is no more Vitamin C left in the solution.  At this point, iodine becomes present in the solution and the starch turns a blue-black color.  The starch is used as an indicator because it turns black in the presence of iodine, but not for iodide.  The amount of iodine that is added during the titration can be used to indicate the amount of Vitamin C present in the fruit juice.

Set up for the lab is quick and easy, and does not take a lot of advance preparation.  

This lab is available in my TpT store and can be viewed here:  Determining the Amount of Vitamin C in Fruit Juices.

Why Do Living Cells Need pH Buffers? A Homeostasis Lab for Biology

Why Living Cells Must Maintain Homeostasis

Living cells must carefully regulate their internal environment in order to survive. Many of the chemical reactions that occur inside cells produce byproducts that can change the pH of the cell. Even small changes in pH can disrupt enzyme function, alter protein structure, and interfere with essential biochemical reactions.

Maintaining a stable internal environment is called homeostasis. One critical part of cellular homeostasis is maintaining a nearly constant internal pH. If the pH of a cell shifts too far from its optimal range, the cell can be damaged or even die. To prevent this, living cells produce substances that stabilize internal pH.

These substances are called buffers. This is why living cells need pH buffers to maintain homeostasis and survive in changing conditions.

What Are pH Buffers and How Do They Work?

A buffer is defined as:

“A substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution.”

In simple terms, buffers resist sudden changes in pH. They do this by:

• Accepting hydrogen ions (H⁺) when they are in excess

• Donating hydrogen ions when they have been depleted

This stabilizing action helps maintain internal balance inside cells.

A powerful example of buffering in living systems is human blood. The pH of human blood is approximately 7.4. A person cannot survive for long if blood pH drops to 7.0 or rises to 7.8. Buffer systems in the blood prevent dangerous swings in hydrogen ion concentration and keep the pH within a narrow range.

Most living cells maintain an internal pH close to neutral, typically around 7.2, although this can vary slightly depending on cell type and location.

Even small changes in pH are important in biology because enzymes are highly sensitive to their environment. A slight shift in pH can change the shape of an enzyme and reduce or eliminate its ability to function.

Simple Controlled Experiment: Testing pH Changes in Living Cells

This concept becomes incredibly clear through a simple but powerful lab activity. It is easy to set up, requires minimal equipment, and consistently produces impressive results. 

If you are looking for a ready-to-use biology lab on pH buffers and homeostasis, you can find my complete activity, "Cells and pH: A Biochemistry Homeostasis Enzyme Lab" here.

Part 1: Control With Tap Water

Students begin by placing tap water in a beaker. They add drops of dilute acid one drop at a time and record the pH after each addition. They repeat the procedure using a dilute base.

As expected, the pH drops significantly when acid is added and rises significantly when base is added. This serves as the control. Water does not produce buffers, so there is nothing to resist the pH change.

Part 2: Testing Liver Cells

Next, students test a liver homogenate, which is liver tissue blended with water. When acid or base is added to the liver solution, there is very little change in pH.

Students often assume their pH meter is malfunctioning because the readings barely change. That moment is powerful. It becomes immediately clear that the living cells are producing buffer systems that resist dramatic pH shifts.

Part 3: Testing Plant Cells With Potato

Repeating the procedure with raw potato demonstrates that plant cells also contain buffering systems. Again, the pH changes very little compared to the water control.

This reinforces the idea that buffering is a universal cellular mechanism found in both animal and plant cells.

How This Lab Demonstrates Homeostasis in Action

This lab is a direct model of cellular homeostasis.

Water lacks regulatory systems, so its pH changes dramatically. Living cells, however, contain internal chemical systems that stabilize their environment.

While diffusion and osmosis regulate the movement of substances across membranes, buffer systems regulate the internal chemical balance of the cell. This makes it an excellent reinforcement activity when teaching cell homeostasis, enzyme function, or biological feedback mechanisms. Together, these mechanisms help cells maintain homeostasis and survive in changing conditions.

The minimal pH change observed in liver and potato solutions is clear evidence of biological regulation at work.

Data Collection and Graphing in Biology

One of the strongest aspects of this lab is the emphasis on quantitative data and graphing.

Students:

• Record pH after each drop of acid or base

• Organize large amounts of data in tables

• Graph pH versus number of drops added

• Compare slopes between water and living cell samples

• Analyze trends and explain differences

The contrast between the steep slope of water and the nearly flat slope of liver or potato makes the concept visually obvious. Students are not simply told that buffers work. They see the evidence in their own data.

This lab reinforces graphing skills, data interpretation, and experimental analysis while teaching a core biological concept. For many students, the graph makes the concept of homeostasis more concrete than a textbook definition ever could.

Equipment and Setup

I use a digital pH meter for this lab. The models I have used are affordable, durable, and long lasting. Batteries are easily replaceable and rarely need to be changed.

If pH meters are not available, this lab can also be conducted using pH paper with excellent results.

The materials are simple, the setup is straightforward, and the experiment works consistently every year.

Frequently Asked Questions About pH in Living Cells

Why do all living cells need pH buffers to maintain homeostasis?
Cells need pH buffers to maintain a stable internal environment so enzymes and metabolic reactions can function properly.

What is the pH inside most living cells?
Most cells maintain an internal pH close to neutral, typically around 7.2, although this varies slightly by cell type.

Why are small changes in pH so important in biology?
Even small pH changes can alter protein structure and enzyme activity, disrupting essential chemical reactions.

What substances are produced by cells to prevent sudden changes in pH?
Cells contain buffer systems composed of weak acids and weak bases that resist sharp changes in hydrogen ion concentration.

Why Teachers Love This Lab

This is one of my favorite labs to teach because it:

• Clearly demonstrates the concept of buffers

• Provides a powerful model of homeostasis

• Requires careful lab technique

• Emphasizes data collection and graphing

• Engages students with dramatic, visible results

It is appropriate for Grade 9 and up and fits beautifully into units on cell homeostasis, internal regulation, enzymes, or biochemistry.

If you would like a complete, classroom-ready lab that clearly demonstrates pH regulation and cellular homeostasis, you can view it by clicking the image below.

If you are planning a full biochemistry unit, you may also want to include this biochemistry lab testing foods for organic compounds, which helps students connect macromolecules to the foods they eat.

Catalase Enzyme Lab: Liver and Potato Experiment for High School Biology

This catalase enzyme lab uses liver and potato tissues to demonstrate enzyme activity in a clear and engaging way for high school biology students. In this catalase lab experiment, students observe how catalase breaks down hydrogen peroxide into water and oxygen, producing visible bubbles that show enzyme activity in real time. This enzyme lab is an excellent hands-on activity for teaching enzyme function, enzyme specificity, and biological reactions.

This catalase enzyme lab is an excellent high school biology experiment for teaching enzyme activity, biological catalysts, and biochemical reactions using simple classroom materials. This lab is one of the most popular enzyme experiments for teaching enzyme activity and is easy to set up using common classroom materials.

You can download this free catalase enzyme lab activity here to use with your biology students.

What concepts are covered and reinforced?

1.  Enzymes speed up the rate of biological chemical reactions.

2.  The same enzymes are found in both plant and animal cells.

3.  Enzymes are highly specific for the reaction they catalyze.

4.  Enzymes carry out their functions more efficiently than catalysts.

5.  Enzymes can be denatured by excessive heat.

Why Catalase Is Found in Both Plant and Animal Cells

Catalase is an enzyme that is commonly found in both plant and animal tissues. Its function is to break down hydrogen peroxide, a toxic byproduct of cellular respiration and other metabolic reactions, into water and oxygen. Because hydrogen peroxide is continuously produced inside living cells, catalase plays an essential role in protecting plant and animal cells by preventing harmful buildup of this toxic substance.

Manganese dioxide is a non-biological catalyst. Like enzymes, catalysts speed up chemical reactions, but unlike enzymes, catalysts are not specific to a single reaction. This comparison helps students understand the unique properties of enzymes and how enzyme activity differs from inorganic catalysts.  

This catalase enzyme lab uses common materials to demonstrate enzyme activity in plant and animal tissues.

Materials for the Catalase Enzyme Lab Using Liver and Potato

• Fresh plant and animal tissue (Potato and Liver)
• Boiled animal tissue (Liver)
• 3% hydrogen peroxide
• Manganese dioxide
• Test tubes and test tube rack
• Sand
• Mortar and pestle

Catalase is found in all eukaryotic cells, which is why this enzyme lab works using many types of fresh, living tissues. Liver is an excellent source of catalase from animal cells, and potato tissue provides a reliable source of catalase from plant cells. Comparing catalase activity in liver and potato tissues allows students to observe enzyme activity in both plant and animal cells. This comparison helps students understand that catalase is present in many different living tissues and plays an essential role in protecting cells.

What Happens When Catalase Breaks Down Hydrogen Peroxide?

Students will observe bubbles forming as catalase breaks down hydrogen peroxide into water and oxygen gas. These bubbles are oxygen released during the catalase enzyme reaction. Fresh liver and potato tissues produce a strong bubbling reaction because they contain active catalase, while boiled tissues produce little or no reaction because heat has denatured the enzyme.

Students absolutely love this catalase enzyme lab because they can immediately observe enzyme activity as bubbles of oxygen form during the reaction. 

This free catalase enzyme lab activity includes complete student instructions and a teacher guide to help you easily implement this engaging enzyme experiment in your classroom.

Download the FREE Catalase Enzyme Lab Activity

Frequently Asked Questions About the Catalase Enzyme Lab

Why do both plant and animal cells contain catalase?

Catalase is found in both plant and animal cells because all living cells produce hydrogen peroxide during normal metabolic processes. Catalase protects cells by breaking hydrogen peroxide down into water and oxygen.

Why is liver often used in catalase labs?

Liver cells contain large amounts of catalase because the liver plays a major role in detoxification. This makes liver an excellent tissue for demonstrating catalase enzyme activity in lab experiments.

Why do boiled tissues show little or no catalase activity?
Boiling denatures the catalase enzyme, changing its structure so it can no longer function properly. This prevents catalase from breaking down hydrogen peroxide.

What causes the bubbles in a catalase enzyme lab?
The bubbles are oxygen gas released when catalase breaks down hydrogen peroxide into water and oxygen. This visible reaction demonstrates enzyme activity.

Related Blog Posts About Enzymes and Enzyme Labs:

Everything About Enzymes!

The Affect of the Enzyme Amylase on Starch

Why Do Living Cells Need Buffers? A Homeostasis Lab for Biology

Another engaging activity to include in your biochemistry unit is this food testing lab for organic compounds, where students identify sugars, starches, proteins, and lipids using indicator tests.

Related Enzyme Labs and Biology Activities

These enzyme labs and biology activities help students further explore enzyme function, enzyme activity, and biochemical reactions in living cells.

Enzyme Lab: The Effect of pH on Living Cells

Enzymes: Complete Unit Bundle

Enzyme Graphing Activity

Lab: The Effect of the Enzyme Amylase on Starch

Enzymes Task Cards