NAKED EGG

PURPOSE : To demonstrate the semi-permeability of a cell membrane.

MATERIALS : 1 raw egg in its shell
                           1 Jar with a lid ( the egg must fit inside the jar )
                           Clear vinegar
                           Flexible measuring tape

PROCEDURE :

• Measure and record the circumference around the center of the egg.
• Record the apperance of the egg.
• Place the egg inside the jar. Do not crack the shell.
• Cover the egg with vinegar.
• Close the lid.
• Observe immediately and then periodically for the next 72 hours.
• Remove the egg after 72 hours and measure its circumference.
• Compare the appearence of the egg before and after being in the vinegar.
• How has the egg changed in appearence and size?

RESULTS : The egg has a hard shell on the outside and the circumference will vary. Bubbles start forming on the surface of the egg's shell immediately and increase in number with time. After 72 hours the shell will be gone and portions of it may be seen floating on the surface of the vinegar. The egg remains intact because of the thin see-through membrane. The size of the egg has increased.

WHY ? The shell of the egg is made of calcium carbonate, commonly called limestone. When vinegar reacts with the limestone, one of the products is carbon dioxide gsa, those bubbles seen on the egg.The membrane around the egg does not dissolve in vinegar, but becomes more rubbery. The increased size is due to osmosis, the movement of water through a cell membrane. The water in the vinegar moves through the thin membrane onto the egg because the water inside the egg has more materials dissolved in it than does the vinegar. Water will always move through a membrane in the direction where there are more dissolved materials. The contents of the egg stayed inside the membrane because these molecules were too large to pass through the tiny holes. This selectiveness of materials moving through the membrane is called semi-permeability.  

BACTERIAL GROWTH

PURPOSE : To demonstrate the effect that temperature has on the growth of bacteria.

MATERIALS : Milk

                        Measuring cup (250ml)

                        2 (500 ml) jars

                        Refrigerator

PROCEDURE : 

• Put a cup of milk in each jar
• Close each jar.
• Place one jar in the refrigerator.
• Place the second jar in a warm place.
• Examine the milk in each jar once for 7 days.

RESULTS : The warm milk has thick, white lumps in it and smell sour. The cold milk looks and smells like drinkable milk.

WHY ? Warm temperature promote the growth of bacteria that can cause food to spoil. Cooler temperature slow down the bacteria growth, but milk will eventually spoil if left in the refrigerator long enough. The bacteria are present and grow very slowly when cold, but they do grow.

LIGHTS OUT

PURPOSE : To determine the effect of sunlight on plant survival.

MATERIALS : House plant 

                          Black construction paper

                          Scissors

                          Tape (cellophane)

 PROCEDURE :

• Cut two piece of black construction paper large enough to civer one leaf on the plant.
• Sandwich the leaf between the two paper pieces.
• Tape the paper together. It is important that the leaf not receive any sunlight.
• Wait 7 days.
• Uncover the leaf and observe its color.

RESULTS : The leaf is much paler than the other leaves on the plant.

WHY ? A green chemical called chlorophyll gives leaves their green color. In the absence of sunlight the green pigment is used up and not replenished in the leaf resulting in a light colored leaf. Since chlorophyll is necessary for plant survival the leaf will die without sunlight.

WHAT'S STOMATA?

PURPOSE : To determine which side of the plant leaf takes in gases.

MATERIALS : Potted plant

                          Vaseline

PROCEDURE :

• Coat the top of four leaves with a heavy layer of vaseline.
• Coat the under side of four leaves with a heavy layer of vaseline.
• Observe the leaves daily for one week.
• Is there any difference in the two sets of leaves ?

RESULTS : The leaves that had vaseline coated on the underside died. The other leaves remained unchanged.

WHY ? Openings on the under side of the plant leaves called stomata allow gases to move into and out of the leaves. The vaseline plugged the openings and the leaf was not able to receive necessary carbon dioxide gas or eliminate excess oxygen gas. 

FOOD PRODUCERS

PURPOSE : To demonstrate that starch, a food substance, is produced in leaves.

MATERIALS : Paper towels

                          Tincture of iodine

                          Leaf ( pale green )

                          Rubbing alcohol

                          Shallow dish

                          ( 500 ml ) jar with lid

                           Measuring cup ( 250 ml )

PROCEDURE : 

• Place the pale green leaf in the jar. The paler the leaf , the easier it will be to extract the green pigment, chlorophyll.
• Pour one cup of alcohol into the jar. Put the lid on the jar.
• Allow the jar to stand for one day.
• Remove the leaf and dry it by blotting with a paper towel.
• Lay the leaf in the shallow dish.
• Add enough iodine to cover the leaf.

RESULTS : Dark areas appear on the leaf.

WHY ? Photosynthesis is an energy producing reaction that occurs in the leaves of plants. Starch, a food substance is one of the product of this reaction. Soaking the leaf in alcohol removes the wax coating on the leaf plus it partially removes the green pigment chlorophyll. It is easier to see the result of the starch test without the presence of the green chlorophyll. Iodine combines with starch particles to form a dark purple to black color. 

LEAF STRAW

PURPOSE : To demonstrate that the leave and stem of plants can act like a straw.

MATERIALS : Glass soda bottle

                           Ivy leaf and stem

                          Clay

                          Straw

                          Pencil

                          Mirror

PROCEDURE :

• Fill the bottle to within an inch of its top.
• Wrap the clay around the stem near the leaf.
• Place the stem into bottle. The end of the stem must be below the surface of the water.
• Cover the mouth of the bottle with the clay.
• Push the pencil through the clay to make an opening for the straw.
• Insert the straw so that its opening is in the air space at the top of the bottle.
• Squeeze the clay around the straw.
• Stand in front of the mirror and look at the mirror image of the bottle while you suck the air out of the bottle through the straw.This should be difficult if there are no leaks in the clay so use a lots of suction.

RESULTS : Bubbles start forming at the bottom of the stem.

WHY ? There are holes in the leaf called stomata, and tiny tubes called xylem run down the stem. The leaf and stem acted like a straw. As you sucked air out of the straw through the leaf straw. It is through these tubes and holes that water moves in a plant.

WATER FLOW

PURPOSE : To demonstrate how water is transported through plant stems.


MATERIALS : Measuring cup (250 ML)

                           2 Glasses

                           1 White carnation with long stem ( purchase at a floral shop )

                            Red and yellow food coloring 

PROCEDURE :  

• Cut the stem in half lengthwise from the bottom to about half way up toward the flower.
• Pour 1/2 cup of water into each glass. 
• Add enough food coloring to make the water in each glass a deep color, one will be red and the other yellow.
• Place one end of the flower stem in the red water and the other end in the yellow water.

• Leave the flower standing in the water for 48 hours.

RESULTS : After 48 hours , the flower will have changed color. One side will be red and the other yellow.

WHY ? Tiny tubes, called xylem run up the stalk to the flower petals. The colored water moves through the xylem allowing the color to be distributed throughout the cells in the petals causing their color to change. Minerals in the soil are carried to plant cell in this way providing in water as did the red and yellow coloring and the solution is carried up to the leaves and flowers where the dissolved material is left as was the red and yellow dye.