Module 1: Introduction to Biology

Biology is the scientific study of life.
Biologists explore questions like:
- How does a single cell develop into an organism?
- How does the human mind work?
- How do living things interact in communities?

Order: Living things exhibit complex organization.
Evolutionary Adaptation: Life evolves over time to suit its environment.
Regulation: Living things maintain a stable internal environment (homeostasis).
Energy Processing: Life requires energy and matter to function.
Growth and Development: Living things grow and develop according to genetic information.
Response to the Environment: Life reacts to stimuli from its surroundings.
Reproduction: Living things produce offspring.

Biological hierarchy:
1. The Biosphere
2. Ecosystems
3. Communities
4. Populations
5. Organisms
6. Organs and Organ Systems
7. Tissues
8. Cells
9. Organelles
10. Molecules
Emergent Properties result from the arrangement and interaction of parts within a system.
Biologists use systems biology to analyze interactions within biological systems.

There is a correlation between structure and function at each level of the biological hierarchy.
The Cell: The lowest level of organization that can perform all activities required for life.
Cells are enclosed by a membrane that regulates the passage of materials.

Life’s processes involve the expression and transmission of genetic information.
Chromosomes contain genetic material in the form of DNA (deoxyribonucleic acid).
Genes encode information for building molecules within the cell.
Genes are the units of inheritance.
DNA controls the development and maintenance of organisms.
An organism’s genome is its entire set of genetic instructions.
Genomics is the study of sets of genes within and between species.
Proteomics is the study of whole sets of proteins encoded by the genome (proteomes).
The flow of genetic information:
- DNA $\rightarrow$ mRNA $\rightarrow$ Protein
- Transcription (DNA to mRNA)
- Translation (mRNA to protein)

Evolution accounts for the unity and diversity of life.
Living organisms are modified descendants of common ancestors.
Fossils and other evidence document the evolution of life on Earth.
Taxonomy: Branch of biology that names and classifies species into groups of increasing breadth.

Eukarya: Includes all eukaryotic organisms.
- Plants: Produce their own food by photosynthesis.
- Fungi: Absorb nutrients.
- Animals: Ingest their food.
- Protists: Other eukaryotic organisms formerly grouped into a single kingdom.
Prokarya
- Bacteria
- Archaea

Charles Darwin published "On the Origin of Species by Means of Natural Selection" in 1859.
Darwin's observations:
- Individuals in a population vary in their traits, which are heritable.
- More offspring are produced than survive, and competition is inevitable.
- Species generally suit their environment.
Darwin inferred that the environment "selects" for the propagation of beneficial traits, called “natural selection”.
Natural selection results in the adaptation of organisms to their environment.
Darwin proposed that natural selection could cause an ancestral species to give rise to two or more descendent species.
Evolutionary relationships are often illustrated with treelike diagrams.

Animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers.
Heterotrophs: Animals cannot construct all of their own organic molecules; they ingest them.
- Plants are autotrophic eukaryotes capable of generating organic molecules through photosynthesis.
- Fungi are heterotrophs that grow on or near their food, release enzymes, and feed by absorption.

Animals are eukaryotes and multicellular.
Animals lack cell walls; extracellular proteins (collagen) provide structural support.
Cells of most animals are organized into tissues.
- Muscle and nervous tissue enable movement and nerve impulse conduction.

Most animals reproduce sexually.
Haploid sperm and egg cells are produced by meiotic division.
A small, flagellated sperm fertilizes a larger, nonmotile egg, forming a diploid zygote.
Development
- Zygote undergoes cleavage (mitotic cell divisions) $\rightarrow$ Blastula (hollow ball) $\rightarrow$ Gastrulation (layers of embryonic tissues are produced) $\rightarrow$ Gastrula.
- Life cycles often include a larval stage.
- Larva: Sexually immature form distinct from the adult; undergoes metamorphosis (developmental transformation).
Animals have developmental genes (Hox genes) that regulate gene expression.