General Biology Study Guide: Essential Characteristics of Life & Chemistry of Biology

Chapter 1: The Science of Biology

Essential Characteristics of Life

Biologists identify several essential characteristics that define living organisms. These features distinguish living things from non-living matter and are fundamental to the study of biology.

Characteristic	Definition	Example
Order	The highly organized and symmetrical structure of living organisms.	A honeycomb built by bees is composed of an intricate pattern of precise, repeating hexagons used to store honey and pollen as well as place eggs, which are all essential to the colony's survival and productivity.
Evolutionary adaptation	When an organism changes over time, typically through many generations, to better adapt to its environment and achieve reproductive success.	The peppered moth became darker in color during the Industrial Revolution, as trees near factories got covered in soot. Even though their original color was lighter, when their environment changed, they had to adapt along with it to survive.
Regulation	The capability of living organisms to consistently maintain a stable internal environment.	When exercising, a human's body temperature gets higher, so to cool down, they sweat (from sweat glands), which eventually evaporates and lowers the temperature of their body, going back to their constant and stable internal temperature.
Energy processing	When an organism acquires and converts energy from the environment for the proper functioning of its body.	Plants take sunlight by absorbing it and changing it into food (sugar or glucose), which is then used to energize themselves.
Growth & development	The inherited genes or information of an organism control the way it grows and develops.	A caterpillar transforms into a butterfly after going through a process known as metamorphosis (creating a cocoon), which is orchestrated with the help of genetic information (genes).
Response to the environment	The way an organism reacts to external changes in its environment.	A chameleon changes its skin color when the environment they are in changes (depends on the presence of predators and potential mates, to name a few).
Reproduction	When an organism produces another of its own kind in the form of an offspring, either sexually or asexually.	A mother panda gives birth to a baby panda, an offspring of its own kind sexually (usually during breeding or mating season).

• Non-essential characteristics: Some features, such as multicellularity or organ systems, are not present in all living organisms. For example, prokaryotes like bacteria lack organelles and are single-celled, yet are still considered alive.

Levels of Biological Organization

Life is organized in a hierarchical manner, from the smallest chemical units to the entire biosphere.

• Atom: The basic unit of matter.

• Molecule: A group of atoms bonded together.

• Organelle: Specialized structures within a cell.

• Cell: The basic unit of life.

• Tissue: A group of similar cells performing a specific function.

• Organ: A body part made up of multiple tissues with specific functions.

• Organ system: Multiple organs working together.

• Organism: An individual living thing.

• Population: All individuals of a species in a defined area.

• Community: All organisms in a particular area.

• Ecosystem: All living things and their environment in a particular area.

• Biosphere: All life on Earth and everywhere it exists.

Homeostasis

Homeostasis is the ability of an organism to maintain a stable internal environment despite external changes.

• Example: Blood sugar regulation by the insulin hormone. After eating, blood glucose rises, stimulating insulin production, which lowers glucose levels by promoting uptake into cells. This is an example of negative feedback.

Energy and Matter in Ecosystems

Energy flows through ecosystems, while matter cycles within them.

• Energy flow: Sunlight is converted to chemical energy by producers (plants), which is then transferred to consumers and decomposers.

• Matter cycling: Matter (such as carbon, nitrogen) cycles through living and nonliving components of the ecosystem.

Cells: The Basic Unit of Life

Cells are the smallest unit of life, capable of performing all activities required for life. All living organisms are composed of cells.

Prokaryotic vs. Eukaryotic Cells

	Prokaryotic	Eukaryotic
No nucleus	✔	✘ (has a nucleus)
Lacks organelles	✔	✘ (contains membrane-enclosed organelles)
Generally smaller	✔	✘ (generally bigger)

DNA: The Universal Genetic Code

DNA (deoxyribonucleic acid) stores genetic information in all living organisms. It is inherited from parents and directs cellular activities.

• Structure: Double helix, encodes instructions for protein synthesis.

• Universal code: All organisms use DNA as their genetic material.

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product (usually a protein).

• Transcription: DNA is transcribed into messenger RNA (mRNA).

• Translation: mRNA is translated into a protein.

Equations:

• Transcription: $\text{DNA} \rightarrow \text{mRNA}$

• Translation: $\text{mRNA} \rightarrow \text{protein}$

Natural Selection and Adaptation

Natural selection is the process by which organisms with advantageous traits survive and reproduce more successfully, leading to evolutionary adaptation.

• Variation: Individuals in a population vary in their traits.

• Inheritance: Traits are passed from parents to offspring.

• Differential survival: Some individuals are more likely to survive and reproduce.

• Example: Bacteria exposed to antibiotics may develop resistance, and resistant bacteria become more common over time.

Chapter 2: Chemistry of Biology

Definitions: Matter, Element, Compound, Isotope

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

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

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

• Isotope: Atoms of a given element that have more neutrons than other atoms of the same element. Isotopes have the same number of protons but different numbers of neutrons.

Common Elements in Life

• Carbon (C)

• Hydrogen (H)

• Oxygen (O)

• Nitrogen (N)

Atomic Structure

Particle	Location	Mass	Charge
Proton	In the nucleus	1 amu (or 1 Dalton)	+ (positive)
Neutron	In the nucleus	1 amu (or 1 Dalton)	0 (neutral)
Electron	Outside of the nucleus (in electron shells/orbitals), forming a "cloud"	0	- (negative)

Atomic Number, Mass Number, and Isotopes

• Atomic number: Number of protons in the nucleus; determines the element's identity.

• Mass number: Sum of protons and neutrons in the nucleus.

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

Element Table (Sample)

Element Name	Atomic Number	Number of Protons	Number of Neutrons	Number of Electrons in Neutral Atom	Mass Number
Carbon	6	6	6	6	12
Oxygen	8	8	8	8	16
Hydrogen	1	1	0	1	1
Carbon (isotope)	6	6	8	6	14
Nitrogen	7	7	7	7	14
Hydrogen (isotope)	1	1	1	1	2
Chlorine	17	17	18	17	35

Electron Configuration

• Carbon: 6 electrons; configuration: 2, 4 (2 in the first shell, 4 in the second shell)

Additional info: These notes expand on the original study guide by providing definitions, examples, and context for each concept, as well as formatted tables and equations for clarity.