5 HIGH SCHOOL BIOLOGY EXPERIMENTS - BIOLOGY - 2025

High school biology experiments are a tool used to teach some important processes in living things in an interesting and dynamic way.

Bacteria, protozoa, fungi, plants and animals form the 5 kingdoms of life and share many characteristics of living beings. With these easy experiments you can learn in a practical and entertaining way.

5 biology experiments for high school students

- Experiment 1. DNA extraction from strawberries

DNA stands that specify the Á acid D esoxirribo N ucleico, this is the molecule that contains all the genetic information of an organism. DNA is present in all organisms, from the smallest bacteria to the largest mammal.

Structurally, DNA is a very long and strong microscopic fiber. In most organisms, DNA is made up of two strands that come together in a small twist.

The genetic information contained in DNA is used to produce the proteins of an organism. Thus, strawberry DNA has the genetic information to produce strawberry proteins.

materials

• 3 ripe strawberries
• ½ cup of tap water
• 1 mortar
• 1 plastic container
• 2 teaspoons of liquid detergent
• 2 teaspoons of salt
• 1 paper filter
• 1/3 cup rubbing alcohol (from the pharmacy)
• 1 glass rod
• 1 wooden pallet
• 1 plastic bag

Experimental procedure

1-In ½ cup of tap water mix the liquid detergent and salt. This will be the mixture to break the cell wall, cell membrane and nuclear membrane of the strawberry. Thus the DNA of the strawberry, which is in the nucleus, can be extracted in the following steps.

2-Completely crush the strawberries in the mortar, in this way the effect of the previous mixture (extraction mixture) is facilitated. It is important not to leave large pieces of the fruit without crushing.

3-Add 2 tablespoons of the extraction mixture to the strawberry crush, shake gently with the glass rod. Let stand 10 minutes.

4-Filter this mixture with the paper filter and pour the resulting liquid into the plastic container.

5-Add the same volume of isopropyl alcohol (cold) to the plastic container. For example, if there is 100 ml of strawberry extract, add 100 ml of alcohol. Do not shake or stir.

6-After a few seconds, observe the formation of a whitish cloudy substance (DNA) on the surface of the liquid. Tilt the container and collect the DNA with the wooden paddle.

7-If desired, you can repeat the process with other fruits and make comparisons.

- Experiment 2. Effect of heat on vitamins

In this experiment, students will discover whether cooking foods destroys the vitamins they contain. In this case, vitamin C from citrus fruits will be studied. However, students can extend the experiment to other foods and vitamins.

Vitamin C is present in citrus fruits such as: lemons, oranges, grapefruits, etc. Chemically, vitamin C is ascorbic acid and it is a very important molecule for the body.

This vitamin participates in several metabolic processes essential for health and its deficiency causes a disease called scurvy.

materials

• Citrus (oranges, lemons, etc.)
• 1 tablespoon cornstarch (cornstarch)
• Iodine
• Water
• 2 glass containers
• Bunsen burner (or a stove)
• Pipette (or dropper)
• Several test tubes with shelf
• Heat resistant gloves
• A white sheet of paper
• Pencil
• Notes blog

Experimental procedure

Preparation of the iodine indicator

1-Mix the tablespoon of cornstarch with a small volume of water, mix to form a paste.

2-Add 250 ml of water and boil for approximately 5 minutes.

3-With the pipette, add 10 drops of the boiled solution to 75 ml of water.

4-Add iodine to the mixture until it turns a dark purple color.

Comparing vitamin C levels

1-Squeeze the juice of the chosen citrus fruits into 2 separate containers.

2-One container will be marked as "heated" and the other as "unheated".

3-Heat the one marked "heated" until it boils.

4-With gloves, carefully remove from heat.

5-Using the dropper, add 5 ml of iodine indicator solution to a standard 15 ml test tube.

6-Using a clean dropper (to avoid contamination), add 10 drops of the cooked juice to the test tube. Clean the dropper and repeat with the sample in the "unheated" container.

7-Observe which one produces a darker color. The darker color means that there is less vitamin C present in that particular sample. Compare the results and analyze.

- Experiment 3. Effect of salt on lettuce seeds

It is widely known that plants need water to germinate, grow and live. However, there are many countries in the world that suffer to grow their food because the soils contain a lot of salt.

The goal of this experiment is to determine if plants die when irrigated with salt water. If they did, at what salinity level would plants stop growing and dying?

This is very important because depending on the tolerance to salt, it is possible to grow some plants in these conditions.

materials

• 30 lettuce seeds
• 3 planting pots
• Water
• Salt
• Balance
• Stirring rod

Experimental procedure

1-Prepare two solutions of salt water as follows: one with a concentration of 30g of salt per liter of water (30g / L) and the other at half the concentration of salt: (15g / L).

2-The control solution is pure water, it does not contain salt.

3-Divide the seeds into three groups of 10 seeds each.

4-Sow 10 seeds in each pot. There should be 3 pots with 10 seeds each.

5-Label each pot: pot 1 -> (Sal 30), pot 2 -> (Sal 15) and pot 3 (control).

6-Place the pots outside where they receive sunlight.

7-Water the pots daily each one with its corresponding solution: pot 1 with solution 30, pot 2 with solution 15 and pot 3 with pure water. Do not confuse!

8-Maintain the experiment for 2 weeks and record the observations as they occur. Compare the results and analyze.

- Experiment 4. The fermentation of yeasts

Yeasts are very important microorganisms for humans. These help to produce bread, wines, beers, among other products for human consumption through a process called fermentation.

For example, yeast is commonly used in cooking for bread dough to expand. But what exactly does yeast do?

To answer this, yeast must be recognized as a living organism, which needs nutrients to live. The main source of energy for yeasts are sugars, which are degraded by fermentation.

materials

• Yeast
• 3 clear glass containers
• 3 small plates
• 2 teaspoons of sugar
• Water (hot and cold)
• Permanent marker

Experimental procedure

1-Add a little cold water to the 3 small plates.

2-Place each glass container on each plate, label each container as: 1, 2 and 3.

3-In container 1 mix: 1 teaspoon of yeast, ¼ cup of warm water and two teaspoons of sugar.

4-In container 2, mix a teaspoon of yeast with ¼ cup of warm water.

5-In container 3, place a teaspoon of yeast and nothing else.

6-Observe what happens in each container. Do different reactions occur in each container? In this experiment, in addition to sight, smell is very important.

7-Compare the results and analyze.

Experiment 5: The 5 Second Rule

It is common to hear that if food falls on the ground it takes germs 5 seconds to contaminate the food. The five-second rule states that food taken off the ground will be safe to eat as long as it is picked up within 5 seconds of falling.

This experiment will evaluate if there is any truth to this theory. The main objective is to determine if collecting dropped food in less than 5 seconds effectively prevents contamination with soil bacteria.

materials

• Food you want to try (one wet and one dry, to compare)
• Sterile hisopos
• Sterile gloves
• Chronometer
• 6 Petri dishes with nutrient agar
• Notes blog
• Pencil

Experimental procedure

1-Place the wet food (ex: raw meat) on the ground, wait 4 seconds and remove it from the ground.

2-With sterile gloves on, clean the piece of meat with a sterile swab. Do not touch anything else with the swab!

3-In a sterile environment (a fume hood) remove the lid from the Petri dish and gently swipe the swab back and forth in a zigzag pattern across the entire surface of the agar. Avoid touching the same area of ​​the agar twice.

4-Carefully place the lid on the Petri dish, label.

5-Carry out steps 1-4 with dry food (eg bread).

6-Carry out steps 1-4 for the control, that is, with sterile swabs (without having previously touched any object) make the zigzag pattern on two Petri dishes containing the same nutrient agar.

7-Place all the Petri dishes in an environment at 37ºC, which is the optimum temperature for bacterial growth. Make sure that all the Petri dishes are located in the same place.

8-Make observations at 24h, 36h, 48h, 60h and 72h. Count the bacterial colonies on each plate and at each time interval.

9-Represent the results in a graph and analyze them.

General steps for conducting an experiment

To carry out a scientific experiment, the first thing that is done is to write an introduction proposing what to do. The aim of the experiment and its importance are clearly described below.

The experiments are based on previous observations, therefore, it is essential to describe the hypothesis of the experiment. Basically, the hypothesis is what the researcher hopes to obtain from her experiment.

Subsequently, a list of the materials that will be used in the experiment is made and what is going to be done is described in detail, this is the experimental procedure. The idea is that anyone can repeat the experiment with the instructions given.

Finally, the results are described, analyzed and compared with similar ones, and conclusions are drawn.

References

1. All Science Fair Projects. Recovered from: all-science-fair projects.com.
2. Biology Science Fair Projects. Recovered from: learning-center.homesciencetools.com.
3. High School Science Fair Project. Recovered from: education.com.
4. High School Biology Science Fair Projects. Recovered from: projects.juliantrubin.com.
5. High School Science Fair Projects. Recovered from: livescience.com.