Comprehensive Biology: Evolution, Cell Types, and Molecular Foundations

What is biology?

The scientific study of life, living organisms, and their interactions.

What makes something alive?

Life is identified by a combination of properties; no single property alone necessarily defines life.

What are common properties of life?

Order/organization, response to the environment, reproduction, growth and development, energy processing/metabolism, regulation/homeostasis, and evolutionary adaptation.

How was life categorized from Ancient Greece to the late 1960s?

Early systems often divided organisms into plants and animals; later systems added groups such as Protista and Monera. The exact historical sequence may depend on lecture notes.

What are the three domains of life?

Bacteria, Archaea, and Eukarya.

Why are organisms grouped into the three domains?

They are grouped by evolutionary relationships and major cellular and molecular differences, especially comparisons of ribosomal RNA.

What is LUCA?

The Last Universal Common Ancestor of all life living today; it was not necessarily the first life.

What defines prokaryotic cells?

They lack a membrane-bound nucleus; their DNA is in a nucleoid region.

What defines Eukarya?

Cells with a membrane-bound nucleus and other membrane-bound organelles.

What is the key concept of a phylogenetic tree?

It represents hypotheses about evolutionary relationships and common ancestry.

How are phylogenetic trees organized?

The root represents the ancestral lineage; branches represent lineages; tips represent sampled groups or species.

Why are only three branches red?

This depends on the specific tree or color key shown in class; use the lecture diagram to identify what the red branches represent.

What is the order of the domains from oldest to youngest?

Domains are not usually ranked as a simple oldest-to-youngest list; Bacteria and Archaea are ancient lineages, and Eukarya arose later. Follow your course's specific tree.

How do scientists infer which lineage is oldest?

They compare molecular evidence and fossils/geological context; a living domain is not itself necessarily 'older' than another living domain.

What is the general evolutionary history of life?

Life originated in aquatic environments; early life was microbial and prokaryotic; photosynthesis changed Earth's atmosphere; eukaryotes evolved; multicellular organisms diversified; some lineages later colonized land.

What does it tell us that most species that ever lived are extinct?

Extinction is common, and life on Earth has changed greatly through time.

What is the basic unit of life?

The cell, the smallest unit capable of carrying out life's basic functions.

What are the four key biomolecule groups and their functions?

Carbohydrates provide energy and structure; lipids store energy and form membranes; proteins perform many structural and functional roles; nucleic acids store and transmit genetic information.

What is the broad trajectory for the origin of biomolecules?

Simple chemical compounds may form small organic molecules, which can form larger polymers and eventually systems capable of replication and cellular organization; details remain under investigation.

How do scientists investigate major steps in life's origin?

Through experiments, chemical models, geology, fossils, comparative biology, and evidence from living organisms.

How could simple organic molecules form on early Earth?

They may have formed through abiotic chemical reactions driven by energy sources such as lightning, UV radiation, or hydrothermal chemistry, and possibly arrived from space.

How do scientists infer which molecules were present in prehistoric times?

They study ancient rocks, chemical signatures, fossils, geological conditions, and experimental models.

What are organic molecules?

In biology, carbon-containing molecules, especially those with carbon-hydrogen bonds; definitions in chemistry have some exceptions.

What was the Miller-Urey experiment?

An experiment that simulated proposed early-Earth conditions using water, gases, and electrical sparks; it produced several organic molecules, including amino acids.

What were the Miller-Urey experiment's key variables and conclusion?

The setup included water, a gas mixture, and electrical sparks as an energy source. It showed that some organic molecules can form abiotically under certain simulated conditions.

Did Miller create life or cells?

No. The experiment produced organic molecules, not living cells.

How might genomes have originated?

A leading idea is that self-copying molecules, possibly RNA-like molecules, preceded more complex genetic systems; the full pathway is unresolved.

What is the RNA world hypothesis?

The hypothesis that RNA played an early central role in both storing genetic information and catalyzing chemical reactions before DNA and proteins took on their modern roles.

What is unity of life?

The shared features of living organisms that point to common ancestry.

How do we understand the unity of life?

Shared genetic code, DNA/RNA, ribosomes, ATP-based energy transfer, and common cellular processes.

How did the diversity of life arise?

Mutation, natural selection, genetic drift, gene flow, and speciation generated and shaped diversity over evolutionary time.

What cell types are associated with the three domains?

Bacteria and Archaea are prokaryotic; Eukarya consists of eukaryotic cells.

What does it mean that prokaryotes existed long before eukaryotes?

Complex eukaryotic cells evolved later, after a long period of microbial life.

What is the endosymbiotic theory?

Mitochondria and chloroplasts descended from bacteria that were taken into ancestral eukaryotic cells and formed lasting symbiotic relationships.

How did mitochondria originate according to endosymbiotic theory?

From an ancestral bacterium related to modern alphaproteobacteria that became an endosymbiont inside another cell.

How did chloroplasts originate?

From photosynthetic bacteria related to cyanobacteria that became endosymbionts in ancestral eukaryotic cells.

What do mitochondria do?

They perform many stages of cellular respiration and produce much of a eukaryotic cell's ATP.

What is ATP?

A molecule that transfers usable energy for cellular processes.

What evidence supports endosymbiotic theory?

Mitochondria and chloroplasts have their own circular DNA, bacterial-like ribosomes, divide by fission, have double membranes, and show genetic similarities to bacteria.

What is morphology?

The form and structure of an organism or its parts.

Binary fission vs. mitosis?

Binary fission is a common way prokaryotes divide; mitosis is nuclear division in eukaryotic cells.

What is protein synthesis?

The process of making proteins: transcription makes RNA from DNA, and translation uses mRNA to assemble amino acids into a protein.

What is phylogeny?

The evolutionary history and relationships of a group of organisms.

What is an endosymbiont?

An organism that lives inside another organism's body or cells in a symbiotic relationship.