General Biology: The Study of Life and Chemical Basis of Life

Biology: The Study of Life

What Does It Mean to Say That Something is Alive?

Biologists define life by a set of fundamental characteristics shared by all living organisms. These criteria help distinguish living things from non-living matter.

• Cells: All organisms are made of membrane-bound cells.

• Replication: All organisms are capable of reproduction.

• Evolution: Populations of organisms evolve over time.

• Information: Organisms process hereditary information encoded in genes and respond to environmental information.

• Energy: All organisms acquire and use energy.

Scientific Hypotheses and Theories

Science relies on forming and testing explanations for natural phenomena. Hypotheses and theories are central to this process.

• Hypothesis: A testable statement that explains something observed.

• Experiment: A test that examines the effect of a single, well-defined factor.

• Prediction: A measurable or observable result expected if a hypothesis is valid.

• Theory: An explanation for a broad pattern in nature, supported by a wide body of evidence.

Cell Theory and Spontaneous Generation

Cell theory states that all organisms are made of cells and that all cells come from preexisting cells. This refuted the idea of spontaneous generation.

• Experiment: Louis Pasteur's experiments showed that cells arise from preexisting cells, not spontaneously.

Life Replicates Through Cell Division

Cells divide to produce new cells, allowing life to continue from one generation to the next.

• Chromosome: A molecule of deoxyribonucleic acid (DNA) that carries genetic information.

• Gene: A segment of DNA that codes for a specific trait or protein. copy information for DNA and help make proteins.

How Life Processes Information and Requires Energy

DNA Structure and Function

DNA is the hereditary material in almost all living organisms. Its structure allows it to store and transmit genetic information.

• Nucleotide: The building block of DNA, consisting of a sugar, phosphate group, and nitrogenous base.

• Bases: Four types: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

• Base Pairing: $A$ pairs with $T$, $C$ pairs with $G$.

• Double Helix: DNA consists of two strands held together by base pairing.

Base	Type
Adenine (A)	Purine
Thymine (T)	Pyrimidine
Cytosine (C)	Pyrimidine
Guanine (G)	Purine

Central Dogma of Molecular Biology

The central dogma describes the flow of genetic information in cells:

• DNA is transcribed into messenger RNA (mRNA).

• mRNA is translated into proteins.

Proteins perform most cellular functions and are required for chemical reactions.

Energy Processing in Cells

Organisms must acquire and use energy to survive. The molecule adenosine triphosphate (ATP) is the primary energy currency in cells.

• Plants and Bacteria: Use energy from sunlight to make ATP via photosynthesis.

• Animals: Obtain energy by consuming other organisms.

Life Evolves

Evolution and Natural Selection

Evolution is the change in characteristics of populations over time. Natural selection is the process by which certain traits become more common in a population due to increased reproductive success.

• Population: Group of individuals of the same species living in the same area at the same time.

• Natural Selection: Individuals with advantageous traits reproduce more successfully.

• Speciation: The formation of new species through evolution.

Phylogeny and Classification

Phylogenetic Trees

Phylogenetic trees illustrate evolutionary relationships among species, with branches representing common ancestry.

• DNA sequence comparisons are used to infer relationships.

• Closely related species have more similar DNA sequences.

Taxonomy and Domains of Life

Taxonomy is the effort to name and classify organisms. The three domains of life are:

• Bacteria

• Archaea

• Eukarya

Domain	Characteristics
Bacteria	Prokaryotic, unicellular
Archaea	Prokaryotic, unicellular, distinct biochemistry
Eukarya	Eukaryotic, unicellular or multicellular

Scientific Method and Experimental Design

Formulating and Testing Hypotheses

Scientific investigations begin with observations, followed by hypotheses and experiments to test predictions.

• Null Hypothesis: States what should be observed if the hypothesis is incorrect.

• Results: Data collected from experiments are analyzed to support or refute hypotheses.

• Conclusion: Experiments must be repeatable and use large sample sizes for reliability.

Chemical Basis of Life

Atoms and Elements

All matter is composed of atoms, which consist of protons, neutrons, and electrons. Elements are substances that cannot be broken down into simpler substances.

• Atomic Number: Number of protons in the nucleus.

• Mass Number: Sum of protons and neutrons.

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

Electron Shells and Chemical Bonds

Electrons occupy shells around the nucleus. The arrangement of electrons determines chemical properties and reactivity.

• Valence Electrons: Electrons in the outermost shell, involved in chemical bonding.

• Covalent Bonds: Atoms share electrons to form molecules.

• Polar Covalent Bonds: Electrons are shared unequally, creating partial charges.

• Hydrogen Bonds: Weak attractions between partially charged regions of molecules.

Water and Carbon: The Chemical Basis of Life

Water is essential for life due to its unique properties, such as cohesion, adhesion, and ability to dissolve many substances. Carbon forms the backbone of organic molecules.

• Polarity: Water molecules have partial positive and negative charges, allowing hydrogen bonding.

• Organic Molecules: Carbon-based compounds are the foundation of life.

Radioactive Isotopes

Some isotopes are unstable and decay over time, releasing energy. These are used in biological research and medicine.

• Example: Carbon-14 is used in radiometric dating.

Summary Table: Types of Chemical Bonds

Bond Type	Description
Covalent	Atoms share electrons
Polar Covalent	Electrons shared unequally, partial charges
Hydrogen	Weak attraction between partial charges

Additional info:

• Some context and definitions have been expanded for clarity and completeness.

• Tables have been recreated to summarize key comparisons and classifications.