Everywhere you look there are different kinds of plants.  The grass on your lawn, the trees and flowers in the park, and the vegetables in your garden or on your plate are all plants.  Plants are incredibly varied and diverse; recent information says there are almost three hundred thousand species of plants on Earth (This information comes from Science Daily.  To learn more go to www.sciencedaily.com)! Of course we know that plants are alive, but they are also very different from us.  For instance, we know plants grow from seeds, but how does the plant go from a seed to the leafy green that we see?  How is a plant born? 

Nearly every plant you see around you, from the blades of grass to the largest trees, came from a seed.  When a plant reproduces (that is, when it has its babies), it puts them in a hard capsule along with enough food for them to live on and grow until they can start making food for themselves.  Now, the seeds from different types of plants are also very different from each other; some seeds are as tiny as the head of a pin, and some are as large as a grown man’s fist—the largest seed in the world is from a palm tree called the Coco de Mer, is 15-20 inches in diameter, and can weigh up to 60 pounds!  However, every seed no matter its size has to have three things: 1) the baby plant, called the embryo; 2) a food source for the embryo to use until it can make its own food (this is sometimes called the endosperm, or sometimes the cotyledons, depending on the type of seed); and 3) a hard shell to protect the embryo, called the seed coat.  If we could look inside your bean seeds, we would see these things.

When the embryo is inside the seed it is dormant, meaning asleep, and is not growing.  Being in this state of deep sleep is good for the embryo; it means that if conditions in the environment are not good for the plant to grow, it can stay dormant inside its seed until the conditions are right.  For our seeds, that means they need water (which means they will be able to take up nutrients from their environment), and warmth (which means sunlight)!  Once the seed finds these conditions, the seed coat will take up water and rupture, to let the embryo out. 

The embryo will use the food in its cotyledons and begin growing. 

This process when the embryo first begins to grow and come out of its seed is called germination.  If we provide water and warmth to our seeds, we can get them to germinate for us!

Here's what you'll need:

1.     10 Bean seeds

2.     Paper towels

3.     2 small plates

4.     A journal to write down all your observations

Here's what you need to do:

1.     Take two paper towels and soak them in water. Lay them flat on a plate, one on top of the other. 

2.     Fold the soaked paper towels in half.

3.     Take five bean seeds, and place them at one end of the folded, wet paper towels.

4.     Fold the other end of the paper towels over the seeds.  Place the wet paper towels with the seeds on the plate, and keep them in a warm place (a sunny window sill would work very well). 

5.     Now take two more paper towels, and repeat the procedure from above, but this time do not get the paper towels wet!  Put these paper towels and seeds on the other plate, and keep them in the same place as the seeds in the wet paper towels.

6.     Check the seeds every day, making sure the paper towels for the first set of seeds stay wet by adding one or two tablespoons of water each day.  After 5-7 days, there should be a small white shoot coming out of the seeds in the wet paper towels.  This means they have germinated!


How long did it take your seeds to germinate?  When the seeds germinated, what did they look like?

What do the seeds in the dry paper towels look like?  Did they germinate? Why or why not?

Be sure to write down all your observations!!


MAKE UP YOUR OWN EXPERIMENT!

What else could affect the plants’ germination?  They must have water and warmth, but what about nutrients?  If you added a little sugar to the water you use to soak the paper towels, would they germinate faster?  Try the experiment again using different liquids to soak the paper towels (try sugar water, soda, coffee...be creative)!  Be sure to germinate a few seeds in water alone too, so that you have something to compare your test to.  Also remember to write down all your observations in your journal!

When you hear the words “invisible ink”, you probably think of James Bond, magic shows, and secretive government operations.  While the idea seems complex, reserved for individuals with access to fancy and expensive tools, it is actually quite an old and often simple idea.  Writing messages that cannot be seen at first but appear later when the paper is developed (that is, treated in some special way) is a very old idea going back 2,000 years, and you can use some pretty mundane techniques to do it.   In fact, invisible ink is not so mysterious, once you stop thinking of it as “ink”.

Invisible ink is usually not ink at all.  What we think of as ink is a fluid containing a pigment or a dye, which is usually permanent.  Invisible ink does not use dye to produce writing or images, but instead uses chemistry.  This means you can write a message on paper (or sometimes on other surfaces) and it won’t be visible until it is developed, depending on what the invisible ink is that you used. 

There are basically three types of invisible ink.  Each type is defined by how the message can be developed in order to be seen.

1.        Heat: The fluid used oxidizes when heated (that is, the compounds that make up the liquid lose some electrons therefore changing their chemical makeup), and this oxidation turns the compounds brown.  Acids work well for this type of ink, because they not only may oxidize themselves, but they change the chemical makeup of the paper also, causing it to burn and char more easily.

2.       Chemical Reactions: The fluid used as ink will be exposed to another chemical, either in liquid or gas form, in order to be developed.  This exposure will cause a chemical reaction to occur, which changes the color of the original ink, making it visible.  Some of these inks are also acids or bases, but others are metal compounds like iron sulfate (developed using sodium carbonate) and cerium oxalate (developed using hydrogen peroxide, according to Kristi Macrakis, et al). 

3.       UV Light: The fluid does not have any color visible to the naked eye, but will fluoresce (give off light) when put under a UV light.  Many organic compounds do this, as do laundry detergents and sunscreens. 

Of the three types of invisible ink, those developed by heat are the easiest and the safest to use (developing chemicals used for the second type and UV light for the third type can be very dangerous).  Let’s explore more carefully what these invisible inks are really doing.

Paper is made up of a compound called cellulose, which comes from wood and consists of a long chain of linked sugar molecules.  The cellulose fibers are pressed together and dried, leaving a thin flexible sheet behind.  This flexible sheet is your sheet of paper.

One type of invisible ink developed by heat is weak acid, like lemon juice or cola.  When these are brushed on the paper they are not visible, but they slowly begin to change the chemical composition of the paper by breaking down the cellulose the paper is made of.  The compounds created by this breakdown oxidize more easily than the original cellulose, and when they oxidize they turn brown.  Heat speeds up chemical reactions, so heating these compounds makes them turn brown faster (give them enough time and they will turn brown without heat...that’s why old books sometimes look yellow, they have acid in the paper!).

Other types of heat-developed invisible ink contain sugar, which caramelizes when heat is applied (for more information on caramelization, see our blog about methods of cooking). 

TRY IT!

Here’s what you’ll need:

1.       Lemon juice, at least one tablespoon

2.       Cotton-tipped applicators or a small paint brush

3.       White sheets of paper

4.       A cloths iron, one with a high setting like linen

5.       An ironing board or a bath towel

Here’s what to do:

1.       Dip the cotton applicator in the lemon juice.

2.       Write a message on a piece of paper using the juice.  Don’t use too much juice, or the paper will get wrinkled spots!

3.       Allow the paper to dry completely.  The message should not be visible.

4.       Place your paper with the message face up on your ironing board, or on the bath towel on top of your kitchen table.

4.       Once the paper is dry, use your iron on the linen setting to heat up the paper.  The message should turn darker and become readable!

How long did it take to make your message appear?  Is it easy to read?  How could you improve your message?  How could you make it harder for others to find your message?  Remember to write down all your observations!

HERE ARE SOME OTHER PROJECTS TO TRY:

What other things could make good invisible ink?  Sugar water (remember that sugar caramelizes)?  Milk?  There are records of war prisoners even using their own saliva and sweat as invisible ink! 

If you have a black light, try using laundry detergent as invisible ink by mixing it with some water.   Write your message, and view the message under the black light.  The laundry detergent should fluoresce and show the message!

What else could you write messages on?  How about light colored fabric?  Be sure to use fabric from an old T-shirt or dish towel or handkerchief—something nobody wants to keep any more!

Reference for further reading:

Macrakis, K; Bell, E. B.; Perry, D. L.; Sweeder, R. D. (2012) “Invisible Ink Revealed: Concept, Context and Principles of “Cold War” Writing”, Journal of Chemical Education, 89(4) 529-532.

There's a new arrival at Discovery Express!!  Our new book, "Science Projects for Grades 7 and 8" is now available in our online store!  This book compiles our best and most popular blog topics for middle school kids in one easy-to-use package.  Each lesson includes a hands-on activity, perfect for school and science fair projects.  All lessons also include suggestions for further exploration, references for additional information, and a generous notes section. 

"Science Projects for Grades 7 and 8" is available in paperback, or as a digital PDF download.  Please visit our store for more information!

When you are outside in the summertime, and you go into your house, you probably feel cooler once you are inside.  However, when you are outside in winter you probably feel warmer once you are inside the house (provided you live in a place where it is cold in winter!).  Yet the house is probably always about the same temperature.  Why does it feel warm in winter and cool in summer?

This difference in the way you feel in the house, despite that it is always the same temperature, comes from differences in thermal energy between you and the house.  Thermal energy is that portion of the energy in any body or object that is responsible for its temperature, according to Robert F. Speyer in his Thermal Analysis of Materials.  (In general, energy is just a property of any object or system that can be transferred to another object or system through some interaction.) Therefore, if one object has a higher temperature than another object, this object has more thermal energy. 

Like all forms of energy, thermal energy likes to transfer from an area of higher energy to an area of lower energy, until both areas are equal.  This means that if our boxes above touch, the one with more thermal energy will transfer some of that energy to the other box, until they both have the same amount of energy—that is, until they are at the same temperature.

The same sort of transfer happens between you and the air inside your house.  In winter, because your house has a heating system that is set by the thermostat, the air inside your house is kept warm, say 70°F.  Outside the air is much colder; say around 20°F depending on where you are.  If you are outside, and you enter your house, thermal energy is transferred to you from the air in the house, since you have less thermal energy than the air does. 

In the summer the opposite happens:  you come indoors, and you have more thermal energy on your skin than the air in the house does.  This means some of the thermal energy on your skin will transfer to the air in the house, until your skin and the air in the house are the same temperature. 

This transfer of thermal energy from some other object to you or from you to the other object is responsible for the feeling of warm or cold.  When you touch something that is warmer than you—that is, it has more thermal energy and is therefore at a higher temperature—the flow of energy from the object to you gives you the feeling of becoming warmer.  If you touch an object that is cooler than you, some of the thermal energy in your skin is flowing out and into the other object.  This is why your house at the same temperature can feel warm or cool depending on the time of the year—it all depends on who or what is transferring  thermal energy!

TRY IT!

Here’s what you’ll need:

1.       A large bowl of very warm water, but not hot enough to burn you, about 90°F (like a hot bath)

2.       A large bowl of ice water

3.       A large bowl of water at room temperature

4.       A watch with a sweep second hand, or a stopwatch

Here’s what you need to do:

1.       Place all the bowls of water on a table or counter, ice water and hot water on either side of you, and the room temperature water in front of you.

2.       Place one hand in the hot water, and your other hand in the ice water.

3.       Leave your hands this way for at least 30 seconds, or 60 if you can.

4.       After 30 seconds, pull both hands out of their respective bowls, and place them both in the room temperature water.

What are your hands feeling?  Is there any difference?  Why is that?  Be sure to write down what you feel and observe!

Speyer, R. F. (2012). Thermal Analysis of Materials. Materials Engineering. Marcel Dekker, Inc., New York, New York.

Do you need to wear glasses?  If you do, things probably look a little fuzzy when you take your glasses off.  If you don’t, you’re lucky!  But why do some people need to wear glasses, while others don’t?  What makes the eyes of these people different?

First, let’s take a look at how our eyes work.  The eye is basically a ball filled with a jelly-like substance called the vitreous humor.  At the front of your eye (the part you can see when you look in the mirror) is a thin, rounded dome of tissue called the cornea; this is like a window that lets light pass through the eye.  Once past the cornea, the light passes through the pupil (the black part of your eye), an opening surrounded by the iris (the colored part of your eye).  Inside the pupil is the lens, which focuses the entering light on the tissues at the back of your eye which are called the retina.  The retina turns the light into an electrical signal, which is transmitted by the optic nerve to the brain; the brain then interprets these electrical signals, allowing us to see all the things around us.

So what’s happening if things look blurry to you without glasses?  It depends on which things you see as being blurry.  If you see things far away from you as blurry, but things close to you are in focus, you are nearsighted.  Nearsightedness (or myopia) is generally caused by one of two things: either the eye itself has become too long, causing the focus of the light to fall in front of the retina; or the lens or cornea has become excessively curved, and so does not focus the light at the appropriate distance.  If you are nearsighted, your glasses have concave lenses—that is, they are thinner in the middle than at the edges.  This helps the light focus on the retina as it should.

If you see things near you as blurry, but things far away from you are in focus, you are farsighted.  Farsightedness (or hyperopia) is generally caused by one of two things:  the eye itself has become too short, causing focus of the light to fall behind the retina; or the lens or cornea is less curved than it should be, and so does not focus the light at the appropriate distance.  If you are farsighted, your glasses have convex lenses—that is, they are thicker in the middle than at the edges. 

So how can you tell how good your eyesight is?  One of the easiest and most popular tests of eyesight is called a Snellen Chart (named after Dr. Hermann Snellen who invented it in 1862 (1)). 

This chart is usually hung on a wall, and the person being tested stands 20 feet away.  They try to read as many of the letters in the chart as they can, covering up first one eye, and then the other.  If you can read the eighth row of letters without glasses, you have 20/20 (normal) vision.  If you can only read down to the fifth line without making mistakes, you have 20/50 vision—this means you can see at 20 feet away what a person  with normal vision could see at 50 feet away (2).  This is also called your visual acuity.  If you cannot even see the first letter at the top of the chart, you are considered legally blind!

TEST YOUR EYESIGHT!

NOTE: While this is an easy and usually accurate way to test your eyesight, it is NOT a substitute for getting your eyes checked by a professional!  Only an eye doctor can provide you with the correct prescription for glasses, or diagnose if you have any other problems with your eyes.

Here’s what you’ll need:

1.       Masking tape

2.       A tape measure at least 20 feet long

3.       An accurate Snellen Chart, which you can download and print by clicking here, or go to http://www.i-see.org/block_letter_eye_chart.pdf.

4.       A friend to help you

 

Here’s what to do:

1.       Download and print the Snellen Chart from the link above.  Be sure to disable the printer’s “Fit to Page” option.  The first page contains instructions, the last page we’ll get to later!

2.       Check t o be sure the chart has printed correctly—the letter ‘E’ at the top of the chart should be 3.49 inches (88.7 millimeters) high.

3.       Tape the chart on a wall at eye level, with the largest letter at the top.

4.       Measure 20 feet from the wall using your tape measure, and mark that spot with masking tape.

5.       First cover your left eye, and read the numbers on the chart aloud, starting at the top and reading every line until the letters are too small for you to read.  Have your friend keep track of which line you could not read.

6.       Now cover your right eye, and repeat step 5 with your left eye.

7.       When you have finished, ask your friend which lines were the smallest you could read. 

8.       To calculate your visual acuity for each eye, take the number to the left of the smallest print you could read for that eye, and put it under the number 20.  For instance, if the smallest line you could read was the seventh line from the top letter, your vision in that eye is 20/30—you can see at 30 feet what a person with normal vision can see at 20 feet. 

What is your visual acuity?  Do you wear glasses?  Do you think you should?  If you think you may need glasses, visit an eye doctor to have your eyes professionally checked!


MORE THINGS TO TRY!

The final page of the eye chart is called a Near Vision Test Card, and it tests how good your vision is close up.  Tape this page to a wall and stand 16 inches away, and see how many rows of letters you can read!

If you do need glasses, and you are nearsighted, here’s a really cool trick to try! 

Take a piece of paper (any piece large enough to cover your eye will do), and poke a small hole in it with a pen. 

Close one eye, and hold the paper up to your open eye. 

Look at something far away through the tiny hole in the paper.  Does it look more focused?


References for further reading:

1.       H. Snellen, Probebuchstaben zur Bestimmung der Sehschärfe, Utrecht 1862.

2.       "What Does 20/20 Vision Mean?"  Eye Care Associates of East Texas. http://www.eyecaretyler.com/2020.htm.  Accessed 28 May 2014.