Category: Dissection

Lemon Dissection

7/7/2020

A lemon is actually an amazing fruit, if you stop to think about it. It can heal itself if it gets cut or bruised, it has oils that can be used for several different purposes, and it serves as both seasoning and food for people and animals. Let’s take a closer look at this interesting specimen in a very scientific way - by dissecting it.

Dissection, by the way, does not mean hacking something apart until it is all gross and disgusting. It means to carefully cut something apart so that we can observe it in a scientific way. That way, we can see the various pieces of it, and learn how they work.

Click and expand the tabs below to get started.

What you'll need

Lemon
Butter knife
Cutting board or plate

experimental procedure

Before we start cutting into this lemon, take a really close look at it. Use all of your senses (except taste - let’s save that for later). What do you notice about how it smells, about how the skin of the lemon feels, and about how it looks close up?
Next, let’s identify a couple landmarks. The pointy end of the lemon is called the apex. The end opposite the pointy end is called the pedicel. There may be a small circle there, or even a bit of stem. That is the part where the lemon was attached to the tree that it came from.
Now, let’s cut off a bit of the outside of the lemon, so that we can look at it more closely. We are not going to cut all the way through the lemon yet - just through the outside layer of the skin. This is sometimes called the rind. The scientific name for the outside part of the lemon is the exocarp. The piece that you cut off should be mostly yellow, with some white on the underside of it.
Hold this bit of exocarp up to the light, and bend it in half. Squeeze it gently, and notice what happens! You might see a squirt of something come out of the exocarp! This is an oil coming from the glands of the lemon. This is the stuff that gives a lemon its citrus-y smell and helps the lemon heal itself if it gets cut or bruised while it is growing on the tree. We can also use this oil for a fun trick later on.
Now, let’s get ready to cut the lemon open. Cut it open about halfway between the apex and the pedicel, and separate the two parts.
Do you have seeds in your lemon? If so, notice where they are. They are usually towards the middle of the lemon, because that is where the seeds of the lemon get their food from. When the lemon is ripe, the seeds are ready to grow into new lemons. In fact, you can take the seeds out of your lemon, put them in a pot with some dirt, water them and put the pot in sunlight, and you might just be able to grow your own lemon tree!
Look at half of your lemon. Do you see that it is divided into sort of triangular pieces? These are called segments. Inside each segment are tiny sacs called vesicles. These vesicles hold the juice of the lemon. Count how many segments your lemon has. They usually have somewhere between 8 and 12 segments.
Look at the rind of the lemon again, now that it is cut open. Does the yellow part go all the way through to the vesicles, or is there another part in the middle? Most lemons have an exocarp, an albedo (white part) and an endocarp (where the vesicles and segments are). Is your lemon organized this way?

What's Happening

Scientists sometimes dissect, or cut apart, an organism in order to see how it is put together and how it works. When we cut apart a lemon, we can see that it has many different parts, and that all of those parts work together to keep the lemon healthy and living. The exocarp protects and heals the lemon, the pedicel connects the lemon to the branch of the tree, and the vesicles contain the fluid of the lemon. Can you think of any ways in which these parts of a lemon are similar to parts of your body?

variations and related activities

Of course, now that you have a cut lemon right there in front of you, there are several things that you can do with it. You could make yourself a nice, tall glass of homemade lemonade - no powder needed! Just squeeze all the lemon juice into the glass, add water and as much sugar as you need, and drink up! But, there are also other things to do!

You can use the juice of a lemon to make your own invisible ink for secret messages. Just squeeze some lemon juice into a little cup (you can also use bottled lemon juice), then use a Q-tip swab or small paint brush to write a message with this juice on a piece of plain paper. Let it dry completely and you shouldn't be able to read the message- it's invisible. To reveal the message you must know the secret: heat. With the help of a grownup carefully hold a warm iron above the paper for a few seconds until the message magically appears. You can also carefully hold the paper above a toaster (don't burn your fingers!), or sometimes a hair dryer will also work. What's happening is that the acid juice of the lemon soaks into the paper and damages the fibers a bit. When you heat the paper carbon atoms from the sugars in the juice that was absorbed begin to react with oxygen from the air and actually cause it to burn a little bit or oxidize, turning it brown. The reference links below explain this experiment in more detail if you want to give it a try.

You can make a mini flame thrower out of a lemon peel and a candle! If you want to try this make sure that you have adult supervision to help you light a candle and set it on a table or something to hold it steady. Now cut off a piece of the peel (just the exocarp and some of the albedo, not the fruit inside), then hold it between your thumb and index finger with the exocarp facing away from you. Move it near the candle but not too close, then give it a little squeeze. You should see the flame explode a little (watch the video link below). The peel of citrus fruits, including your lemon, contains an oil called limonene which is the main chemical that gives citrus fruits their citrus-y smell. It's what you've probably squirted in you eye before, and it stings. It is also flammable, and that mist of oil instantly ignites as it hits the candle's flame.

You can also use the lemon’s limonene oil to burst a balloon! Just squirt some of the lemon oil from the exocarp, just as described for the mini flame thrower above, onto an inflated balloon and POP! This happens because the limonene oil in the peel can dissolve the latex rubber in the balloon. This makes the balloon weaker, so it pops! If you try this we should warn you that some balloons may be much more difficult or even impossible to pop this way. That's because they have a different type of rubber or have been processed a little differently that makes them stronger. The video reference link below explains this very nicely. We have found that the cheap little balloons made for filling with water (sometimes called water bombs) work really well for this experiment, and if you do it outside with a water balloon it's even more fun when it pops! Will other citrus fruits (grapefruit, orange, clementine) work? Experiment and find out!

Another interesting experiment is a variation on the classic Cartesian Diver Bottle. This fun little project is usually made with a ketchup packet, a plastic pipette or pen casing, a bit of a straw or even a small balloon (we'll have our own version as a new activity page soon, but for now check out the reference links below). You can also make a diver using a piece of a lemon peel. Just cut a little sliver of the peel (just the exocarp and a little of the albedo) and drop it into an empty plastic soda or water bottle. Fill the bottle completely to the top with water (make sure there is no air left in the bottle) then screw on the lid tightly. The lemon peel should float to the top of the bottle, but when you squeeze the bottle (you might need to squeeze really hard) the peel will sink. If you stop squeezing it will float to the top again. If you're lucky you may be able to repeat this for a few minutes until the peel eventually sinks to the bottom and stays there. You may need to experiment a bit to get just the right size and thickness piece, and you might need to try a fresher or different lemon- it can be finicky. What's happening is that the little pores on the outside of the exocarp trap some air, and this makes the peel less dense than the water and it floats. When you squeeze the bottle, however, the water inside pushes into these little pores making the peel more dense so it sinks. Eventually the air in the pores will escape as tiny bubbles (look closely and you may see them) and the peel can't float any more.

references and links to more information

Some helpful diagrams and labels of parts: