Exploration: Water: an Essential for Life

Biology Lesson Activities Student Answer Sheet

Exploration: Water: An Essential for Life

Directions You will evaluate some of these activities yourself, and your teacher may evaluate others. Please save this document before beginning the lesson and keep the document open for reference during the lesson. Type your answers directly in this document for all activities. ______

Self-Checked Activities

Read the instructions for the following activities and type in your responses. At the end of the lesson, click the link on the Summary screen to open the Student Answer Sheet. Use the answers or sample responses to evaluate your own work.

1. Water: True or False?

Which of these statements are true and which ones are false?

a. Liquid water is denser than ice.

b. More objects can be dissolved in water than in sulfuric acid.

c. You can float a needle on water.

d. Water will take more time to boil on Mount Everest than on a California beach.

e. Water can “defy gravity” and climb uphill.

f. Water regulates the earth's temperature.

g. The water that came from your faucet could contain molecules that Neanderthals drank.

h. The overall amount of water on our planet has remained about the same for two billion years.

i. The total amount of water in an average adult human body is four gallons.

1 © 2013 EDMENTUM, INC. Answer a. True b. True c. True d. False. Water will take less time to boil on Mount Everest than on a California beach. e. True, although this is more a case of “working against” gravity rather than “defying” it. Gravity is a basic law of physics that can’t be broken. f. True g. True h. True i. False. The total amount of water in an average adult human body is about 10 gallons.

2. Capillary Action

Read each experiment and write down what you think will happen—this is your hypothesis. Do the experiments and then note your observations after the time specified.

a. Experiment 1

Procedure 1. Take two glasses, fill one with water and leave the other empty. Place them side by side. 2. Fold a paper towel lengthwise and put one end into the water in the glass with water. 3. Stick the other end of the paper towel in the empty glass. 4. Wait 30 minutes and record your observations.

Hypothesis:

Observations:

Answer The entire paper towel becomes wet. Water begins dripping from the paper towel into the empty glass, transferring some of the water from the full glass.

b. Experiment 2

Procedure 1. Mix some red color in a glass of water (or fill a glass with a dark red juice such as cranberry juice). 2. Put a celery stalk in the colored water. 3. Wait 1 to 2 hours. 4. Remove the celery stalk, then cut it in half lengthwise and record your observations.

Hypothesis:

Observations:

Answer Streaks of red appear in the center of the celery stalk. They rise above the line where the surface of the red water (or juice) was, and even above the height of the glass.

2 3. The Properties of Water Table As you complete the experiments in this lesson, you will fill in the table below with information about the behaviors and properties of water. You will begin with Surface Tension, and then return to fill it in for other behaviors and properties as you progress through the lesson. Ask yourself the following questions about each behavior and record your answers in the table below:

 Which property does this experiment demonstrate? Why does water behave this way?  How does this behavior of water affect life?

The first row of the table, Capillary Action, has been filled in as an example.

Properties of Water Which water property? How does this behavior Behavior Why does it behave this way? of water affect life? • Polarity, cohesion, and adhesion • Water, mixed with other • The polarity of a water molecule minerals, is drawn through the helps it to “cohere” to nearby water small “capillary tubes” in plant molecules and to “adhere” to polar roots, stems, and leaves plant material in capillary walls. sustaining the plant’s life. Capillary Action In a very narrow tube, the surface • Water is also drawn into small tension (cohesion) of the water is openings such as those high compared to its weight. So is between grains of sand or soil, the adhesive force pulling it toward helping water to spread beyond the wall and up the tube. its immediate source. Answer • Polarity and cohesion • In the middle of a group of water molecules, each molecule is pulled equally by all the other polar water Answer molecules around it. • Surface tension enables some Surface Tension But, at the edge of that group of objects to float on top of water. water molecules, on the surface of • The tension contributes to the the water, molecules below the phenomenon of capillary action surface are pulling on the surface (see above). molecules, with no opposing force. This binds the molecules on the surface closer together and creates the tension you see on the surface of water.

3 Which water property? How does this behavior Behavior Why does it behave this way? of water affect life? Answer Answer • Polarity • Water can dissolve and transport • Water is attracted to other polar a variety of substances, such as Solvent Behavior compounds like alcohol and ionic nutrients for plants. Fortunately, it compounds like salt. Water does not dissolve non-polar dissolves these compounds. Water substances, such as those and non-polar compounds like oil compounds that compose our cell are not attracted to each other, so walls. they do not dissolve well. Answer Answer • Because ice floats on water, it can • Density of ice is lower than the form a protective layer that keeps density of liquid water the water below warmer than the Density • The hydrogen bonds in water form air. This free-flowing water a rigid, six-sided crystal as water provides a habitat for various freezes. This structure takes up animals throughout winter. more room than liquid water. As a • Ice floating on water forms result, ice has a lower density than icebergs and the arctic ice shelf, liquid water. providing a habitat for various polar animals. Answer • High heat capacity Answer • A higher temperature means more • The oceans and other bodies of molecular movement in liquid Heating water heat up and cool down water. Water’s polar bonds are slowly, moderating temperature very strong and resist molecular changes and impacting both the movement. So water needs to immediate ecosystem and the absorb a lot of heat energy to broader climate. “speed up” its molecules and raise its temperature. Answer Answer • High heat of vaporization • Evaporation is a cooling • The polar bonds between mechanism for animals, plants, Evaporating molecules of water are very strong. and even for the environment It takes a lot of heat to break those itself. When you perspire, for bonds and free water molecules instance, the sweat on your skin completely from the liquid phase, evaporates into the air, using up allowing those molecules to escape heat energy and cooling your as a gas. body.

4 4. Surface Tension

Read the experiment and write down what you think will happen as your hypothesis. Then, conduct the experiment and note your observations. Compare these to your hypothesis.

Procedure 1. Fill a small bowl with 1-2 inches of water. 2. Take a sewing needle and place it on a tissue paper. 3. Place the tissue paper with the needle on the water in the flat dish. 4. Let the tissue sink to the bottom of the bowl and record your observations of the needle.

Hypothesis: Will the needle float or sink to the bottom of the dish?

Observations: Answer The tissue sank to the bottom of the dish, but the needle remained floating on the water. There was a slight depression or halo around the needle in the water.

5. Solvent Behavior

Read the experiment procedure. Note your hypothesis about what will happen. Do the experiment and then note your observations.

Procedure 1. Make a list of five things that you can find in or around your house in powder or liquid form, such as salt, sugar, cooking oil, food color, vinegar, ground spices, dishwasher liquid, soil, and sand. 2. Type yes in the hypothesis column of the table below next to those you think will dissolve in water, and type no next to those you think won’t. 3. Mix the first substance in a glass of water. 4. Evaluate how well the item dissolved in the water. 5. Note down your observation for the item you mixed in the water. 6. Discard the mix, and try the next substance. 7. Repeat steps 3 – 6 for each substance on your list.

Hypothesis and Observation: Use the table below to record your hypothesis about whether the substance will dissolve (Yes if you think it will, no if you think it won’t). After completing the experiment, write down your observation.

Substance Hypothesis Observation Salt (replace with whatever you use)

5 Conclusions Review your observations and compare them to your hypotheses. How well did you predict the result? Are there more Yeses than Nos in your observation list?

Answer It is clear that a wide range of items, such as salt and vinegar, dissolve in water. Others, such as oil or sand, do not.

Return to the Properties of Water Table above and answer the questions for the Solvent Behavior of water.

6. Density

Read the procedures below, then answer the questions in the hypothesis section before you do the two experiments. After completing the experiments, record your observations.

a. Experiment 1 Procedure 1.Pour water into a large metal bowl 2.Put the bowl in the freezer 3.Wait two hours and observe the bowl. 4.Describe the formation of ice in the bowl in your observation area.

Hypothesis: Will the water freeze from the top down or the bottom up? Observations

Answer: The water freezes from the top down. The bottom is still liquid water, but the top layer has frozen.

b. Experiment 2 Procedure 1. Drop some ice cubes into a glass of water. 2. In your observation area, describe how the ice cubes behave in the glass of water.

Hypothesis: Will the ice cubes float on the top or sink to the bottom?

Observation:

Answer The ice cubes float at the very top. They don’t sink at all. They simply sit at the top of the glass and slowly melt.

Conclusions: Compare your hypotheses to what you observed. What does this tell you about the density of water compared to ice, the solid form of water?

6 Answer Water in a bowl freezes from the top down. An important conclusion from both experiments is that ice is lighter than water; that is, solid water is less dense than liquid water. It may not be what you expect, but that’s what you should have observed.

Return to the Properties of Water Table above and answer the questions for the Density section.