Introduction to General Biology: Scientific Thinking, Life, and the Chemical Basis of Life

Biology: The Study of Life

Definition and Scope

Biology is the scientific study of life and living organisms. It encompasses a wide range of topics, from the molecular mechanisms within cells to the interactions of organisms within ecosystems.

• Biology investigates the structure, function, growth, origin, evolution, and distribution of living things.

• Major subfields include cell and molecular biology, physiology, and ecology.

• Biology connects the smallest units of life (atoms and molecules) to the largest (biosphere).

• Evolution is a unifying concept in biology, explaining the diversity and adaptation of organisms.

Example: Studying how a plant grows involves understanding its cellular processes, its physiological responses, and its role in the ecosystem.

Levels of Biological Organization

Hierarchy from Atoms to Biosphere

Life is organized in a hierarchical structure, with each level building upon the previous one. Understanding these levels is fundamental to studying biology.

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

• Molecule: Two or more atoms bonded together.

• Organelle: Specialized structures within a cell that perform specific functions.

• Cell: The basic unit of life; can be unicellular or multicellular.

• Tissue: Groups of similar cells that perform a specific function.

• Organ: Structures composed of different tissues working together.

• Organism: An individual living entity.

• Population: A group of organisms of the same species in a given area.

• Community (Biocenosis): Different populations living together in an area.

• Ecosystem: A community and its physical environment.

• Biosphere: All ecosystems on Earth; the global sum of all life.

Example: A human is an organism made up of organs, which are made of tissues, which are made of cells, and so on.

The Scientific Method and Scientific Thinking

Principles of Scientific Inquiry

Science is a systematic approach to understanding the natural world through observation, experimentation, and evidence-based reasoning.

• Evidence-based arguments: Scientific claims must be supported by empirical evidence.

• Consensus: Progress in science relies on agreement about what constitutes valid evidence and methods.

• Reproducibility: Experiments and observations must be repeatable by others.

• Objectivity: Personal beliefs or opinions should not influence scientific conclusions.

• Critical thinking: Scientists question assumptions and test hypotheses.

Example: The theory of evolution is supported by extensive fossil evidence, genetic data, and observed natural selection.

The Chemical Basis of Life

Atoms, Elements, and the Periodic Table

All matter, including living organisms, is composed of atoms. Atoms combine to form elements, which are organized in the periodic table.

• Atom: Consists of a nucleus (protons and neutrons) and electrons in a cloud around the nucleus.

• Element: A substance that cannot be broken down into simpler substances by chemical means. Each element is defined by its number of protons (atomic number).

• Atomic mass: The sum of protons and neutrons in an atom.

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

Example: Carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14.

Table: Major Elements in the Human Body

The following table summarizes the main elements that make up the human body and their approximate percentage by mass (including water):

Element	Symbol	Percentage of Body Mass
Oxygen	O	65.0%
Carbon	C	18.5%
Hydrogen	H	9.5%
Nitrogen	N	3.3%
Phosphorus	P	1.0%
Potassium	K	0.4%
Sulfur	S	0.3%
Sodium	Na	0.2%
Chlorine	Cl	0.2%
Magnesium	Mg	0.1%
Trace elements	-	<0.01%

Additional info: Trace elements include boron, chromium, cobalt, copper, fluorine, iodine, iron, manganese, molybdenum, selenium, silicon, tin, vanadium, and zinc.

Isotopes and Their Applications

Isotopes are variants of elements with the same number of protons but different numbers of neutrons. Some isotopes are stable, while others are radioactive and decay over time.

• Stable isotopes: Do not change over time (e.g., carbon-12, carbon-13).

• Radioactive isotopes: Unstable and decay, emitting radiation (e.g., carbon-14).

• Applications:

  • Radioactive tracers: Used in medicine to track substances in the body.

  • Radiometric dating: Used to determine the age of rocks and fossils by measuring isotope ratios and calculating elapsed time using the concept of half-life.

Example: Carbon-14 dating is used to estimate the age of archaeological samples.

Equation for half-life:

$N(t) = N_0 \left(\frac{1}{2}\right)^{t/T_{1/2}}$

Where $N(t)$ is the amount remaining after time $t$, $N_0$ is the initial amount, and $T_{1/2}$ is the half-life.

Origin of Elements and the Universe

Formation of Elements

The elements that make up living organisms originated from cosmic processes.

• Big Bang Nucleosynthesis: Formed hydrogen and helium within the first few minutes after the Big Bang.

• Stellar Nucleosynthesis: Heavier elements (carbon, oxygen, etc.) were formed in stars and distributed by supernovae.

• "We are made of star stuff": Most elements in our bodies were forged in stars billions of years ago.

Example: The carbon in your body was created in the core of a star that exploded before the solar system formed.

Key Goals of Studying Biology

Learning Objectives

• Develop the ability to think like a scientist and apply scientific reasoning to biological questions.

• Understand the chemical and physical basis of life, including the role of atoms, molecules, and energy.

• Recognize the importance of structure-function relationships in biology.

• Appreciate the vast spatial and temporal scales involved in biological processes.

• Apply knowledge of biology to understand life on Earth and the potential for life elsewhere.

Additional info: The course will emphasize the connection between molecular processes and larger biological systems, and the importance of evidence-based scientific inquiry.