Scientific Method and Foundations of Biology

Hypothesis vs. Theory vs. Law

Understanding the distinctions between hypotheses, theories, and laws is fundamental in biology and the scientific method.

• Hypothesis: A tentative answer or explanation for an observation, based on limited evidence. It is testable and falsifiable.

• Theory: A well-substantiated explanation supported by a large body of evidence. Theories are broader in scope than hypotheses (e.g., Theory of Evolution).

• Law: Describes consistent, universal relationships under certain conditions (e.g., Law of Gravity). Laws do not explain why phenomena occur.

Example: Cell Theory (all organisms have at least one cell).

Quantitative vs. Qualitative Data

Data in biology can be classified as:

• Qualitative data: Descriptions or characteristics (e.g., color, texture).

• Quantitative data: Numerical measurements (e.g., height, number of leaves).

Independent vs. Dependent Variables

In experimental design:

• Independent variable: The variable manipulated by the researcher ("cause").

• Dependent variable: The variable measured or observed in response ("effect").

Example: Studying the effect of sunlight on plant growth.

• Independent variable: Amount of sunlight (e.g., 2, 4, 6 hours)

• Dependent variable: Plant growth (e.g., height in cm, number of leaves)

Properties of Life and Biological Organization

What is Life?

Living things exhibit specific properties that distinguish them from non-living things. Viruses are not considered alive because they lack some properties of life (e.g., independent reproduction).

8 Properties of Life

1. Evolutionary adaptations

2. Response to environment

3. Reproduction

4. Growth

5. Development

6. Energy processing

7. Regulation

8. Order

Levels of Biological Organization

Life is organized in a hierarchy from the smallest to the largest scale:

1. Biosphere (all life on Earth)

2. Ecosystem (living and nonliving things in a particular area)

3. Community (populations of different species in an ecosystem)

4. Population (individuals of a species in a specific area)

5. Organism (individual living thing)

6. Organ system

7. Organ

8. Tissues

9. Cells

10. Organelles (e.g., nucleus, mitochondria)

11. Molecules

12. Atoms

13. Subatomic particles

Major Themes in Biology

Theme #1: New Properties Emerge at Each Successive Level

• Emergent properties arise from the arrangement and interaction of parts within a system.

• Example: A functioning bicycle emerges only when all parts are present and correctly arranged.

Theme #2: Organisms Interact with Other Organisms and the Environment

• Organisms interact with both living (biotic) and nonliving (abiotic) components.

• Human activities (e.g., CO2 emissions) impact global systems (e.g., global warming).

• Interactions can be mutualistic, competitive, or predatory.

Theme #3: Life Requires the Transfer and Transformation of Energy & Matter

• Energy flows through ecosystems; matter cycles within them.

• All living organisms require energy for work (growth, reproduction, movement).

• Energy transformations are essential for life (e.g., photosynthesis, cellular respiration).

Theme #4: Structure and Function are Correlated at All Levels

• Biological structures are adapted to their functions (e.g., bird wings for flight).

• Form and function are closely related in biology.

Theme #5: The Cell is the Basic Unit of Structure and Function

• All living organisms are composed of cells.

• Cells are the lowest level of organization that can perform all activities required for life.

• Two main types: Eukaryotic (with nucleus and organelles) and Prokaryotic (no nucleus, simpler structure).

Theme #6: Life's Processes Involve the Expression and Transmission of Genetic Information

• DNA (deoxyribonucleic acid) stores genetic information.

• Genes are units of inheritance, transmitting information from parents to offspring.

• Genomics and bioinformatics are fields that analyze genetic data.

Theme #7: Feedback Mechanisms Regulate Biological Systems

• Positive feedback: The end product speeds up its own production (e.g., blood clotting).

• Negative feedback: The end product slows or stops its own production (e.g., regulation of ATP synthesis).

Theme #8: Evolution, the Overarching Theme of Biology

• Evolution explains the unity and diversity of life.

• Natural selection is a key mechanism of evolution.

• Species adapt to their environments over time.

Basic Chemistry for Biology

Atoms, Elements, and Molecules

• Element: A substance that cannot be broken down by chemical means.

• Atom: The smallest unit of an element that retains its properties.

• Molecule: Two or more atoms held together by covalent bonds.

• Compound: A substance consisting of two or more different elements combined in a fixed ratio.

Atomic Structure

• Protons (+), neutrons (0), and electrons (-) are subatomic particles.

• Atomic number = number of protons.

• Mass number = number of protons + neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

Electron Configuration and Chemical Bonds

• Valence electrons are in the outermost shell and determine chemical reactivity.

• Atoms with incomplete valence shells can share (covalent bonds) or transfer (ionic bonds) electrons.

Water and Its Importance in Biology

Properties of Water

Water is essential for life and exhibits unique properties due to its molecular structure and hydrogen bonding.

• Cohesion: Attraction between water molecules (enables surface tension).

• Adhesion: Attraction between water and other substances (e.g., water and plant cell walls).

• Surface tension: Measure of how difficult it is to break the surface of a liquid.

• High specific heat: Water resists temperature changes, stabilizing environments.

• Heat of vaporization: Large amount of energy required to convert water from liquid to gas.

• Expansion upon freezing: Ice is less dense than liquid water, so it floats.

• Versatility as a solvent: Water dissolves many substances, facilitating chemical reactions.

Table: Properties of Water and Their Biological Significance

Hydrophilic vs. Hydrophobic Substances

• Hydrophilic: Substances that have an affinity for water (e.g., salts, sugars).

• Hydrophobic: Substances that do not have an affinity for water (e.g., oils, fats).

Key Equations and Definitions

• Atomic number: $\text{Atomic number} = \text{number of protons}$

• Mass number: $\text{Mass number} = \text{number of protons} + \text{number of neutrons}$

• Calorie (cal): $1 \text{ cal} = \text{amount of heat required to raise the temperature of 1 g of water by 1^\circ C}$

Summary

• Biology is the study of life, which is organized in hierarchical levels from atoms to the biosphere.

• The scientific method relies on hypotheses, theories, and laws to explain natural phenomena.

• Water's unique properties are essential for life and biological processes.

• Understanding basic chemistry is foundational for studying biological systems.