WESTLAKE HIGH SCHOOL
BIOLOGY SUMMER ASSIGNMENT
Dear Future Biology Student,
Hello! The Biology Team at Westlake High School is pleased to know that you are going
to be a part of Biology in August! This is a challenging class, but it can be very rewarding if you
put in the effort. You can understand the nature of science and the human impact on the
environment. Biology is a hands on/inquiry course. We will support you in every way that we can
and do our best to offer up exciting and engaging lessons. At the end of the school year, you will
be expected to take the EOC test in Biology which accounts for 20% of your grade. Throughout
the year, we will prepare you for the exam. We’re in this together and expect you to give your
very best!
**** Please complete the summer assignment below. Read the Biology content then
complete the questions. The summer assignment will be graded as a formative assessment.
Class supplies
2 Composition notebooks
4 pk of notecards
Tape
Highlighters
Pens, pencils
Thank you
THE BIOLOGY TEAM!
Water and pH
The importance of water to life, and
therefore biology, cannot be understated. It covers over 70% of the Earth and is
the most abundant compound in living things. All living things on Earth depend
upon water to survive. Water is required for many essential reactions within cells,
such as cell respiration and photosynthesis, which we will discuss in a later module.
Navigate to the sidebar and download the Properties of Water and pH Reading
Guide accompanying this lesson.
Water is a simple but unique molecule that is tasteless, odorless, and transparent.
Its chemical formula is H2O. It has hydrogen atoms that are covalently bonded to
an oxygen atom. What makes water unique, and so important for life, are the
interesting characteristics, or properties, that water displays as a result of its
structure. First, we will discuss the structure of the water molecule, and then its
unique properties.
The Water Molecule
Water is a neutral molecule, meaning that it has the same number of protons as
electrons. Look at the images that shows a water molecule above. The red
represents oxygen and the white hydrogen.
Even though water is neutral, its electrons are unequally distributed among the
oxygen and hydrogens that make it up. The oxygen atom, with its eight positively
charged protons, has a strong pull on the negatively charged electrons; this makes
the probability of finding those electrons near the oxygen greater than finding them
near the hydrogen atoms.
Look at the picture below. You can see that the oxygen end of the water molecule
takes on a slightly negative charge and the hydrogen ends of the water molecule
take on slightly positive charges. Water is therefore a polar molecule.
Properties of Water
Have you ever wondered why a water bug can walk across the water, but a frog
cannot? It's an interesting question that relates directly to properties of water!
Many of the properties of water are related to each other. All of the properties we
will discuss are important to life on Earth. Read on to learn more, and visit the
sidebar for more resources on water's properties.
Polarity
Remember how a water molecule has an unequal distribution of charges? We call
this phenomenon polarity because the molecule has a positive pole on one end and
negative pole on the other. Water molecules' positive and negative charges cause
opposite ends of water molecules to attract each other like tiny magnets. Polarity of
water is important to life on Earth in a number of ways, which are explained below.
Hydrogen Bonding
Hydrogen Bonding is a unique feature of water that is made possible by polarity.
Hydrogen bonds are weak, attractive bonds that exist between individual water
molecules. Hydrogen bonds are easily broken and re-formed. The picture below
shows water forming hydrogen bonds with itself. Hydrogen bonding of water
molecules allows for several unique chemical properties important for life:
Water is called the "Universal Solvent"
Water's polarity also makes it a very good solvent. This is biologically helpful
because it means that water can transport or hold onto dissolved substances for
organisms (salt, food).
Because water is polar itself, when it comes into contact with other polar or ionic
substances, it is able to fit in between the atoms that make up that substance,
dissolving it. In other words, these substances can mix. Salt or rubbing alcohol will
dissolve in water and are therefore called hydrophilic, or "water loving." Take a look
at what happens when table salt (NaCl) is mixed with water:
In the above salt solution, water is the solvent while salt (NaCl) is the solute.
Water cannot dissolve non-polar substances, such as oil, or fats, and will often
show a separation from them acting as if it is "squeezing" them together. This is
called the hydrophobic effect ("water fearing"). This effect is very important in the
formation of cell membranes.
Solid Water is Less Dense than Liquid Water
Hydrogen bonds between water molecules expand as the water freezes. This
creates extra "space" in solid water (ice) and makes it less dense than liquid water.
Translation: ice floats
This property is significant to living things because it means that bodies of water do
not freeze solid. Instead, a layer of solid water (ice) forms nearer the top,
insulating the organisms at the lower layers. Take a look at the diagram below to
see this temperature separation:
High Heat of Vaporization
Liquid water does not evaporate until it reaches relatively higher temperatures that
can break the hydrogen bonds within it. This makes it a good cooling agent for
living things; as water evaporates it carries heat away.
High Specific Heat
Water has a high specific heat, which means that it is slow to undergo changes in
temperature. This allows very large bodies of water to maintain their temperatures
to sustain living things despite weather changes. It also helps your body to
maintain a relatively stable temperature.
Large bodies of water (lakes and oceans) help regulate temperatures of nearby land
masses. This is the reason why winters are colder in the middle of the U.S.
compared to coastal cities.
Acids, Bases and pH
Water molecules can dissociate, or come apart, into two ions:
H2O → H+ + OHwater → hydrogen ion + hydroxide ion
Scientists have devised a scale to measure the concentration of hydrogen ions (H+)
and hydroxide ions (OH-) that exist in solutions. The scale is called the pH scale.
The pH scale ranges from 0 to 14.
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Neutral solutions have equal amounts of H+ and OH- ions. Neutral
solutions have a pH of 7.
Acids, or acidic solutions, have a greater amount of H+, and are
assigned a number between 0 and 7 on the pH scale. The lower the
number, the more acidic the solution.
Bases, or basic solutions, have a greater amount of OH-, (or less H+)
and are assigned a number between 7 and 14 on the pH scale. The
higher the number, the more basic the solution.
pH is measured on a logarithmic scale. This means that the difference of one pH
unit (example: between 3 and 4) means that there is a tenfold difference in H+ or
OH- concentration.
Take a look at the picture on the right that shows the pH scale and common
substances with each pH level.
All living organisms have a set range of pH levels that are optimal for their growth
and development. Sudden changes in pH levels can harm organisms. The pH inside
human cells must be kept close to neutral in the range of 6.5 to 7.5. If a chemical
with a lower or higher pH enters the cell, it could disrupt chemical reactions and
cells' homeostasis. Substances with a very low (strong acid) or very high (strong
base) pH cause chemical burns. To combat this, cells contain weak acids and weak
bases called buffers which work to neutralize substances inside cells that are too
acidic or too basic.
Acid rain is is a concern for biologists because it can harm living things. It damages
trees at higher elevations and can create an acidic environment for organisms in
streams and lakes. It results when rain combines with waste chemicals in the
atmosphere from cars or power plants (sulfur dioxides or nitrogen oxides). Acid rain
has a pH around 4. Take a look at what acid rain can do to a forest with the
scenario below.
Properties of Water and pH
Reading Guide
Answer the following questions after reviewing the information in the Properties of Water and pH
Lesson. Use this as a study resource for the Properties of Water and pH Quiz.
The Water Molecule
1. Draw a picture of a water molecule showing oxygen and two hydrogens
bonded together.
2. Why is a water molecule polar? Indicate the location of charges on the
molecule you have drawn.
3. Is the following sentence true or false? A water molecule is neutral.
4. What causes water molecules to be attracted to each other?
5. Which of the following statements are true about hydrogen bonds?
❏ A hydrogen bond is stronger than an ionic bond.
❏ The attraction between the hydrogen atom on one water molecule and the oxygen atom on
another water molecule is an example.
❏ A hydrogen bond is stronger than a covalent bond.
❏ They are the strongest bonds that form between molecules.
6. Distinguish between cohesion and adhesion.
7. Look at the picture of liquid in a glass tube (burette) at the right. What property of
water is represented?
8. Why is capillary action important for plants?
9. What makes water a good solvent?
10. Sugar is dissolved in water to make a sugar solution. What is the solvent? What is the solute?
11. Which type(s) of substances can water dissolve? (check all that apply)
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❏
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polar
non-polar
ionic
hydrophilic
hydrophobic
12. Why does ice float in liquid water?
13. How does the density of solid water help living organisms in lakes?
14. Water’s high heat of vaporization makes it a good ___________________________.
15. Why is water’s high specific heat good for living things?
Acids, Bases, and pH
16. Water molecules can dissociate to form what two ions?
17. Why is water neutral despite the production of hydrogen ions and hydroxide ions?
18. What does the pH scale indicate?
19. Complete the table to review pH:
Substance
pH range
Acid
amount of OH- and H+
Examples
more H+ than OH-
Base
Water
7
20. How many more H + ions does a solution with a pH of 4 have than a solution with a pH of 5?
21. Why is a change in pH dangerous for cells?
22. What are buffers?