Simply cut off the bottom of a t-shirt to make it shorter if it is too long, or make it into a crop top length. Cut evenly all the way around the bottom of the shirt to accomplish this.  Each t-shirt will be different depending on the size and how it fits on your own body. Cut away a smaller amount than you think you want, then try it on. Make additional cuts if you want it shorter, and keep trying it on to check the length. You can also create a pattern at the hem of your t-shirt, whether or not you cut it shorter for a crop top. Try cutting strips for a fringe hemline, or cut shapes like diamonds just above the hemline for a cute cutout look. Convert a t-shirt to a tank top or muscle tee. Cut along the armhole seams for a regular tank top, or further down the sides of the shirt for a wide-armed muscle tee look.  You may also want to cut a wider neckline for a classic tank, but this is not necessary. For a muscle tee, you can cut in a straight or slightly angled line down from the shoulder to the side of the shirt. Try it on between cuts to make sure you like how much of the side is open. You can also cut all the way down through the bottom hemline of the shirt and tie the ends together at the bottom for a cute side-tie look. Cut off the collar of any t-shirt to make it wider or just get rid of the typical crew neckband. Remember to cut less at first, then try it on to check the neckline before cutting any more.  To make sure the front and back of your neckline are symmetrical, fold the shirt so that the shoulder seams line up and the neckband is folded evenly on itself. Then cut below the band, following the original curve of it.  Create a v-neck neckline by folding the shirt in the same way with the shoulder seams lined up. Then use a diagonal cut for the front part of the shirt so that it ends in a point instead of a curve. Make “fish gills” in the sides of a shirt by simply cutting even horizontal strips down each side. Or create the same effect by making the strips down the back of the shirt instead.  Stretch out the slits after cutting to make the fabric relax and roll up slightly. Anywhere you create slits will provide some extra stretch in the fabric, which is a great way to make a too-small t-shirt fit a little better. You can also make slits vertically just to the inside of the front or back of your neckline to create more interest and stretch in those areas as well. Create an easy peek-a-boo shoulder by simply cutting a half-circle out of each arm of the t-shirt. This will create a round cutout shape on the shoulders when worn.  Lay the t-shirt flat and find where the shoulder seams meet with the armhole seams. This is where you will make a cut on each side. Cut a piece out of one shoulder, then save the piece you cut away and lay it on the other shoulder to use as a guide. This will ensure both sides look even.
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One-sentence summary -- Cut your t-shirt into a crop top. Make a tank top or muscle tee. Create a wider neckline. Cut slits into the sides or back. Make shoulder cutouts.


Here are a few options:  You can use a styrofoam cell base. Craft or art stores and will have styrofoam balls (if making an animal cell) roughly the size of a basketball or a styrofoam rectangular cube (if making a plant cell). Cardstock can be used to form a number of cell structures, such as the Golgi apparatus or rough endoplasmic reticulum. Straws or small hoses can be used to form tube-like structures. The microtubules could be constructed out of stirring straws, while flexible straws or tubes can be used to model the smooth endoplasmic reticulum. Use beads of various sizes and shapes as other cell structures, such as mitochondria or chloroplasts. Try to keep them on an appropriate scale compared to the other structures in the model cell. Modeling clay can be used to create any structure that is difficult to replicate using preexisting materials. Paint can be used to fill in the cytoplasm and differentiate between it and the exterior of the cell. You can also paint any clay structures you have created. Measure the base and make dots at the points that equal half the length of a side. Draw lines showing where to cut. Then use an exacto knife or something similar to cut and remove a 1/4 section.  For the plant cell, do this by drawing the center line on any two adjoining sides and continue those lines all the way around until they circle back. If doing this for the animal cell, draw the lines like you were making the equator and the meridians on a globe. Paint the inside of the 1/4 section in order to help your cell parts stand out. You can also paint the outside in a different color to contrast it with the cytoplasm. Create them from the craft items listed above. The trickiest of these will be the parts that you must model out of clay. Keep these structures as simple as possible while remaining true to the basic structure you are modeling. It may be best to only make the simplest of structures out of clay and leave more complex parts--say, the smooth endoplasmic reticulum--to be replicated using tubes or some other item. Add the parts to your cell base (the styrofoam). This can be done by using hot glue, regular glue, toothpicks, pins, staples, or a number of other methods. In some cases you may also need to literally dig or carve out space in the styrofoam to fit in the parts. The Golgi apparatus and rough endoplasmic reticulum can be shaped out of cardstock using your hands. In this case, make slices into the styrofoam and slide pieces of cardstock in to form the folded shapes of these structures. After you've added your cell pieces, write up a list of what part of a cell each item corresponds to.  You'll probably need to be able to tell people about the parts of your cell later on.
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One-sentence summary --
Obtain the materials. Cut out a 1/4 section of the styrofoam base. Paint it. Make the cell parts. Add the cell parts. Make a table or key that defines each part.