Introduction to Biology: Properties of Life

• Biology is the science that studies life.
• Defining life is challenging; viruses, for example, possess some life characteristics but not all.

Key Questions in Biology

• What shared properties define something as "alive"?
• How do living things function?
• How can we organize the diversity of life to understand it better?
• How did life's diversity arise and continue to evolve?

Properties of Life

• All living organisms share order, sensitivity, reproduction, adaptation, growth and development, regulation/homeostasis, energy processing, and evolution.
• These eight characteristics together define life.

Order

• Organisms are highly organized, from single-celled organisms to multicellular ones, with cells, molecules, and organelles.
• Multicellularity allows for cell specialization and can benefit the organism as a whole.

Sensitivity or Response to Stimuli

• Organisms respond to various stimuli, moving toward (positive response) or away from (negative response) chemicals (chemotaxis) or light (phototaxis).

Reproduction

• Single-celled organisms reproduce by duplicating DNA and dividing.
• Multicellular organisms use specialized reproductive cells to form new individuals, passing on DNA and genes.

Adaptation

• Adaptation is the "fit" of living organisms to their environment, resulting from evolution by natural selection.
• Adaptations include heat resistance in archaea and tongue length in nectar-feeding moths.

Growth and Development

• Organisms grow and develop according to instructions coded in their genes.

Regulation/Homeostasis

• Homeostasis is maintaining a stable internal environment.
• Organisms use regulatory mechanisms, such as thermoregulation, to maintain conditions like temperature and pH, despite external changes.

Energy Processing

• All organisms require an energy source for metabolic activities.
• Some capture energy from the sun, while others use chemical energy from ingested molecules.

Evolution

• Evolution drives the diversity of life through mutations and adaptation to changing environments, subject to natural selection.

Levels of Organization of Living Things

• Living things are organized in a hierarchy: atoms, molecules, macromolecules, organelles, cells, tissues, organs, organ systems, organisms, populations, communities, ecosystems, and the biosphere.
• Atoms are fundamental units of matter.
• Molecules are structures of two or more atoms held by chemical bonds.
• Macromolecules are large molecules made of smaller monomer units, such as DNA.
• Organelles are structures within cells performing specialized functions.
• Cells are the basic unit of life, classified as prokaryotic (no nucleus) or eukaryotic (with a nucleus).
• Tissues are groups of similar cells performing the same function.
• Organs are collections of tissues with a common function.
• Organ systems are functionally related organs.
• Organisms are individual living entities.
• A population is all the individuals of a species living in a specific area.
• A community is a set of populations inhabiting a particular area.
• An ecosystem includes living things and non-living parts of the environment.
• The biosphere is the collection of all ecosystems, representing zones of life on Earth.

The Diversity of Life

• Evolution drives the diversity of life, leading to new species arising from older ones.
• Carl Linnaeus created a hierarchical taxonomy for organizing species.

Taxonomic System

• The taxonomic system has eight levels: species, genus, family, order, class, phylum, kingdom, and domain.
• The domain is the highest level and a relatively recent addition.

Three Domains of Life

• Eukarya: Organisms with cells containing nuclei, including fungi, plants, animals, and protists.
• Archaea: Single-celled organisms without nuclei, many extremophiles in harsh environments.
• Bacteria: Another group of single-celled organisms lacking nuclei.
• Archaea and Bacteria are prokaryotes (cells without nuclei).

Binomial Naming System

• Linnaeus created the binomial naming system using two unique names for each organism.
• The binomial name consists of the capitalized genus name and the lowercase species name, both italicized.

Carl Woese and the Phylogenetic Tree

• A phylogenetic tree shows evolutionary relationships among species, based on genetic or physical traits.
• Carl Woese's work in the 1970s showed that life evolved along three lineages: Bacteria, Archaea, and Eukarya.
• Woese used genetic relationships to construct his tree, using universally distributed, conserved genes.

Branches of Biological Study

• Molecular biology studies biological processes at the molecular level, including interactions of DNA, RNA, and proteins.
• Microbiology studies the structure and function of microorganisms, including microbial physiology, ecology, and genetics.
• Neurobiology studies the biology of the nervous system, using molecular, cellular, developmental, medical, and computational approaches.
• Paleontology uses fossils to study life's history.
• Zoology and botany study animals and plants, respectively.
• Other specializations: biotechnologists, ecologists, and physiologists.

Forensic Scientist

• Forensic science applies science to legal questions.
• Forensic scientists analyze trace materials from crime scenes, including hair, blood, body fluids, and DNA.

Scientific Ethics

• Scientists must ensure their work does not harm humans, animals, or the environment, and must avoid bias.
• Bioethics is an evolving field that defines guidelines for research practices, considering new developments and technologies.
• Example: The Tuskegee syphilis study was unethical, as treatment was withheld from African American men with syphilis wihout their knowledge.
• Bioethicists examine implications of technologies like gene editing, balancing positive outcomes with potential harm.
• Henrietta Lacks' cells (HeLa cell line) were taken without her knowledge and have contributed greatly to medical research.
• Now, harvesting tissue or organs without consent is unethical and illegal.