The Scientific Method

1. The Scientific Method

2. The Scientific Method
• The method that scientists use to make new
discoveries about natural phenomena
• Involves several steps:
1. Making observations
2. Forming and testing hypotheses
3. Experimentation
4. Analyzing results
5. Making conclusions

3. Step 1. Making Observations
• Data is any recorded observations.
• Qualitative data describes phenomena.
– Example: Color and formation of product in
chemical reaction
• Quantitative data gives numerical
measurements.
– Example: Height of plant, today’s temperature

4. Question
• Identify the following as qualitative or
quantitative data.
1. The barometric pressure is 760mmHg.
2. A solution of sodium chloride conducts
electricity.
3. A plant grown in sunlight reaches 23.6cm in a
week.

5. Step 2. Forming and Testing
Hypotheses
• A question can be formed from an
observation.
• A tentative answer to the question is known
as hypothesis.

6. Example
• Observation: A plant grown in soil A produces
orange flowers, while the same plant grown in
soil B produces white flowers.
• Possible question: Does the soil have any
effect on the color of the flowers?
• Possible hypothesis: The iron content of soil
has an effect on the color of the flowers.

7. Question
• The following observation was made: A plant
flowers from May 15-Jun 15. What is a
possible question?
A. Could the amount of sunlight have an effect
on the flowering?
B. Could the soil have an effect on the
flowering?
C. Could the location of the plant in the garden
have an effect on the flowering?

8. Question
• What could be a possible hypothesis?
A. Less sunlight causes plants not to flower.
B. The phosphorus content of the soil causes
plants not to flower.
C. The crowdiness of a garden causes plants not
to flower.

9. Step 3. Experimentation
• The hypothesis is proven true or false by
selecting methods that prove or disprove the
hypothesis.
• The different techniques will be taught during
the various sessions.

10. Step 4. Analyzing Results
• Data may be given in tabular or graphical
form.
• Qualitative data is usually reported in tabular
form, whereas quantitative data is usually
reported in either tabular or graphical form.

11. Presenting data in tabular form
• The following data
was given for growth
of plant: Day 1, 1cm;
Day 2, 2cm; Day 3,
3cm; Day 4, 4cm.
Day Length of
plant (cm)
1 1
2 2
3 3
4 4

12. Presenting data in graphical form
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Day 1 Day 2 Day 3 Day 4
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Day 1 Day 2 Day 3 Day 4

13. Step 5. Making Conclusions
• A conclusion is a statement that can be
derived from the data.
• Do not exaggerate the conclusion.

14. Basic Chemistry in Biology

15. Matter
• Matter is anything that takes up space and has
mass.
• Elements cannot be broken down into other
substances by chemical reactions.
• Compounds are composed of two or more
elements combined in a fixed ratio.
• Essential elements are needed by an organism’s
body to be healthy.
• Trace elements are required only in minute
quantities.

16. The Atomic Theory of Matter
• An atom is the smallest unit of matter that
retains the properties of an element. It
contains the following subatomic particles:
– Neutrons have no charge.
– Electrons have a negative charge.
– Protons have a positive charge.
– Protons and neutrons are found in the nucleus.
• The dalton (Da) or atomic mass unit (amu) is the
unit used for subatomic particles.

17. The Atomic Theory of Matter
• The atomic number is the number of protons
of an element and is unique to the element.
• The mass number is the sum of the number of
protons and the number of neutrons and is an
approximation of the atomic mass.
• Some elements have different forms with
more neutrons, which are known as isotopes.
• The atomic mass is the mass reported in the
periodic table based on the availabilities of
the different isotopes .

18. The Atomic Theory of Matter
• The number of electrons is similar to the
number of protons in neutral elements.
• The number of electrons depends on the
charge of the element if it is an ion.
• A positive ion is called a cation and has less
electrons, and a negative ion is called an anion
and has more electrons.

19. Question
• Na+ has mass number 23 and 11 protons.
Identify the number of neutrons and
electrons.
• Solution: Since mass number=number of
neutrons + number of protons, number of
neutrons= 23-11=12.
• Since the ion has charge +1, number of
electrons is 1 less than the number of protons,
resulting in 10 electrons.

20. Technique: Radioactive Isotopes
• A radioactive isotope has its nucleus decaying
spontaneously, resulting in formation of
particles and energy.
• Several radioactive isotopes may be used,
such as 3H, 13C, 14C, 32P, 35S, 59Fe, 125I, and 131I.
• Step 1. One ingredient that cells use to make
certain molecules is labeled with one of the
radioactive isotopes.

21. Technique: Radioactive Isotopes
• Step 2: The ingredients are added to the cells in
culture and incubated in various parameters (pH,
temperature, etc.)
• Step 3: Once the cells have synthesized the
molecules of interest, the molecules are isolated
from the cells.
• Step 4. Scintillation fluid is added to the
molecules. As the radioactive isotope decays, the
radiation emitted excites the chemicals in the
fluid, giving off light.
• Step 5. Light is then measured by a scintillation
counter.

22. Question
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
pH 1 pH 3 pH 5 pH 7
• Suppose that the
following is a graph of
DNA samples labeled
with 3H and measured
with a scintillation
counter. At what pH is
the cell living optimally?

23. Energy
• Energy is the capacity to cause change.
• Potential energy is energy that matter
possesses due to location or structure.
• Electron shells are the possible locations of an
electron, forming concentric circles around
the nucleus, each with a characteristic average
distance and energy level.
• Electrons farther from the nucleus have higher
potential energies.

24. Electron Distribution
• Valence electrons are the electrons found in the
outermost electron shell, and the electron shell
containing them is the valence shell.
• Elements with a complete set of valence
electrons in the valence shell are chemically
unreactive.
• The first electron shell contains only two
electrons, while succeeding electron shells
contain eight electrons.
• However, since electrons are constantly moving
around, the electron shells were soon replaced by
orbitals.

25. Chemical Bonds
• Orbitals are three-dimensional regions where an
electron is found 90% of the time and may only
contain two electrons at any given time.
• Atoms are usually held together by chemical
bonds to complete their valence shell.
• Covalent bonds share electrons with the atoms
involved, while ionic bonds transfer electrons
from one atom to the other.
• Ionic compounds are called salts.
• A single bond represents two electrons being
shared. Atoms may also have double bonds or
triple bonds.

26. Electronegativity
• Electronegativity is the strength of attraction of a
shared covalent bond to a certain atom.
• Nonpolar covalent bonds occur when the two
atoms bonded have similar electronegativities,
while polar covalent bonds occur when the two
atoms bonded have different electronegativities.
• Ionic bonds occur when the two atoms bonded
have very high difference in electronegativities.
• Electronegativity increases from left to right in
the periodic table and from bottom to top.

27. Question
• The valence electron of K is 1, and the valence
electron of Cl is 7.
A. What compound is formed by the two
elements?
B. Is the compound covalent or ionic?
• In the molecule O2,
A. Is the covalent bond polar or nonpolar?
B. How many bonds do they share?

28. Weak Bonds
• Weak bonds are not covalent chemical bonds and
may occur only temporarily between molecules
that are in close proximity.
• Hydrogen bonds occur between hydrogen and
oxygen, sulfur, or nitrogen.
• Van der Waals interactions occur between two
nonpolar molecules due to occasional dipole
moments.
• Molecular shape often determines function in
biology, as this allows for specificity of reactions.

29. Question
• What weak bonds can occur between the
following molecules, if any?
A. H2S, NH3
B. O2, H2
C. CO2, SO2

30. Chemical Reactions
• Chemical reactions involve the breaking and
formation of new chemical bonds.
• The starting materials are called reactants,
while the new molecules formed are called
products.
• Most chemical reactions are reversible to a
certain extent.
• Chemical equilibrium is achieved when the
forward and reverse reactions balance each
other.

31. Properties of Water
• Weak bonding between similar molecules results
in a phenomenon called cohesion.
• Weak bonding between different molecules
results in a phenomenon called adhesion.
• Cohesion between water molecules and adhesion
between water molecules and the plant cells are
responsible for water transport against gravity in
plants.
• Another phenomenon due to weak bonding is
surface tension, which is a measure of how
difficult it is to stretch or break the surface of a
liquid.