Biology Essentials: Chapter 1 Quick Reference

Viruses are non-living outside a host; they require a host cell to replicate.
Antibiotics do not kill viruses; treatment uses antivirals or symptom suppression.
Viral load correlates with contagiousness; lowering viral load reduces active infection and symptoms.
Transmission occurs via droplets or contact when actively symptomatic; infection risk remains without strong immune defenses.
Some viruses persist and lie dormant, reactivating under stress or poor conditions.
Examples mentioned: common cold, flu, HIV, herpes simplex, mononucleosis (EBV), Epstein–Barr, coronavirus, Ebola, HPV.
Outside host: viruses are abiotic; inside a host, they become biologically active pathogens.

Living things possess cellular life; two main cell types:
- Prokaryotic cells: no true nucleus, no membrane-bound organelles, usually single-celled (bacteria).
- Eukaryotic cells: true nucleus with a nuclear envelope, membrane-bound organelles, often multicellular (plants, animals, fungi) and also single-celled protists (e.g., amoeba).
Amoeba is a single-celled eukaryote (a protist).
All cells have a cell membrane; some have a cell wall (plants and bacteria).
Nucleus acts as the “brain” of the cell; prokaryotes lack a nucleus; their DNA/RNA are in the cytoplasm.

Nucleus: houses DNA/RNA; controls cell activities (present in eukaryotes).
Mitochondria: powerhouse of the cell; produce energy (ATP).
Golgi apparatus: packages and ships proteins/lipids; like the cell's post office.
Cell membrane: controls what enters/leaves the cell; present in all cells.
Cell wall: provides structure; present in plants and bacteria.
Chloroplasts: site of photosynthesis; contain chlorophyll; found in plants/algae.

$ATP$ : the energy currency of the cell; adenosine triphosphate.
Produced in the mitochondria; used for cellular processes; replenished as needed.

Homeostasis = stable internal environment; organisms regulate body conditions.
Local responses (e.g., tearing, sneezing, temperature adjustments) help maintain balance.
If regulation fails severely, death can occur.

Evolution occurs across populations over time via natural selection.
Fitness = number of offspring that survive and reproduce.
Examples: giraffes with long necks favored when food is high; cave-dwellers lose eyes due to perpetual darkness.
Changes occur in populations over generations, not in a single individual.

Three domains: Archaea, Bacteria, and Eukarya.
Within Eukarya: animals, plants, fungi, protists, etc.
Taxonomic ranks (from broad to specific): domain → kingdom → phylum → class → order → family → genus → species.

From smallest to largest: $ext{molecule} ightarrow ext{cell} ightarrow ext{tissue} ightarrow ext{organ} ightarrow ext{organ system} ightarrow ext{organism} ightarrow ext{population} ightarrow ext{community} ightarrow ext{ecosystem} ightarrow ext{biosphere}$
Biomes = ecosystems with characteristic climates (e.g., tundra, desert, rainforest).
Ecosystem = living and nonliving components in an area; biosphere = life on Earth.

Systematic approach to inquiry; include controls, constants, and variables in experiments.
Inductive vs. deductive reasoning; emergent properties arise at higher levels of organization.
Chapter 1 emphasizes hierarchy, taxonomy, and the basics of biology.

Viruses: non-living outside host; treat with antivirals/symptom relief; avoid antibiotics.
Cell types: prokaryotic vs eukaryotic; nucleus presence; organelles.
Energy: $ATP$ as cellular energy currency; mitochondria as the powerhouse.
Hierarchy: domains, kingdoms, and the progression from molecules to biosphere.
Ecosystems vs biomes vs biosphere: definitions and scale.
Evolution: population-level change, fitness defined by offspring count.
Homeostasis: stability and regulation; failure can be fatal.