Foundations of Biology: Structure, Diversity, and Chemical Basis of Life

Biology: The Scientific Study of Life

Introduction to Biology

Biology is the scientific study of life, focusing on the structure, function, growth, origin, evolution, and distribution of living organisms. Biologists seek to answer fundamental questions about how life works and evolves.

• Key Questions:

  • How does a single cell develop into an organism?

  • How does the human mind work?

  • How do different forms of life in a forest interact?

  • Interdisciplinary approach and collaborative work are essential in biology.

Reductionism and Emergent Properties

Biologists use reductionism to simplify complex systems into manageable components, but also recognize emergent properties—novel features that arise at each level of organization and are absent from the preceding one.

• Reductionism: Breaking down systems to study their parts.

• Emergent Properties: New characteristics that appear at higher levels of organization (e.g., consciousness in the brain).

• Example: Photosynthesis emerges from the interaction of molecules in chloroplasts, not from the molecules alone.

Unity and Diversity of Life

Evolution and Classification

Life on Earth has existed for approximately 3.5 billion years, with an estimated 10,000,000 species. Evolution is the process by which organisms gradually accumulate differences from their ancestors, leading to diversity.

• Three Domains of Life:

  • Bacteria: Most diverse and widespread prokaryotes, classified into multiple kingdoms.

  • Archaea: Prokaryotes often found in extreme environments (e.g., salty lakes, hot springs).

  • Eukarya: Includes kingdoms Plantae (photosynthetic multicellular organisms), Fungi (nutritional mode by absorption), Protista (mostly unicellular), and Animalia (multicellular organisms that ingest food).

• DNA: Deoxyribonucleic acid is the universal genetic language for all organisms.

The Cell: Basic Unit of Structure and Function

The cell is the smallest unit of life capable of performing all activities required for life. Cells share certain characteristics, such as being enclosed by a membrane.

• Prokaryotic Cells:

  • Generally smaller (0.1–5.0 μm)

  • Lack a nucleus

  • Lack membrane-bound organelles

• Eukaryotic Cells:

  • Membrane-enclosed organelles

  • DNA-containing nucleus

  • Quite big (10–100 μm)

Chemical Basis of Life

Elements and Compounds

All living organisms are carbon-based and require liquid water. Understanding the chemical characteristics of water and other substances is central to biology.

• Matter: Anything that has mass and takes up space.

• Element: A substance that cannot be broken down into other substances by chemical reactions.

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

• Emergent Properties: Compounds have characteristics different from those of their elements.

• Example: $\mathrm{H}_2 + \mathrm{O}_2 \rightarrow \mathrm{H}_2\mathrm{O}$ (water is different from hydrogen and oxygen alone)

Essential Elements of Life

Of 94 natural elements, about 25% are essential elements needed for life and reproduction. Four elements make up approximately 96% of living matter: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

• Trace Elements: Required in minute quantities (e.g., boron, copper, iron, iodine, manganese, zinc).

• Function: Zinc, manganese, and iron are necessary for brain function and growth. Trace metals are important for metalloproteins in neurons and glial cells.

• Deficiency: Decreased concentration can result in neurodegenerative diseases (e.g., Alzheimer's, Parkinson's).

Atomic Structure and Properties

Each element consists of a certain type of atom, which is composed of subatomic particles: protons, neutrons, and electrons.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Number of protons plus neutrons.

• Number of Neutrons: $\text{Mass Number} - \text{Atomic Number}$

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

Isotopes and Radioactivity

Isotopes have the same number of protons but differ in the number of neutrons. Some isotopes are radioactive and decay spontaneously, emitting particles and energy.

Isotope	Protons	Neutrons	Status
Carbon-12	6	6	Stable
Carbon-13	6	7	Stable
Carbon-14	6	8	Radioactive

• Applications: Radioactive isotopes are used in biological research, dating fossils (carbon dating), drug development, and tracing activity in the body (e.g., fast-dividing cancer cells).

Summary of Key Concepts

• Biology studies the structure, function, growth, origin, evolution, and distribution of living organisms.

• Emergent properties arise at each step up the biological hierarchy.

• Structure and function are correlated at all levels of organization.

• Cells are the basic unit of life; eukaryotic cells have a nucleus, prokaryotic cells do not.

• Three domains of life: Bacteria, Archaea, Eukarya.

• Matter is made up of elements; compounds are combinations of elements in fixed ratios.

• Four elements (O, C, H, N) make up most living matter; trace elements are required in small amounts.

• Atoms are made of protons, neutrons, and electrons; isotopes differ in neutron number.

• Radioactive isotopes have many scientific and medical applications.