Introduction to Biology

• Biology is the scientific study of life
• It explores the structure, function, growth, origin, evolution, and distribution of living organisms

Characteristics of Life

• Living organisms share several key characteristics
• Organization: They exhibit a high degree of order and complexity, from atoms to biosphere
• Metabolism: They carry out chemical reactions to acquire and use energy
• Growth: They increase in size and complexity
• Reproduction: They produce new organisms, passing on genetic information
• Response to Stimuli: They react to changes in their environment
• Adaptation: They evolve over time to better suit their environment
• Homeostasis: They maintain a stable internal environment

Levels of Biological Organization

• Life is organized in a hierarchy of levels
• Molecules: Atoms combine to form molecules, such as DNA and proteins
• Cells: Molecules are organized into cells, the basic unit of life
• Tissues: Similar cells working together form tissues
• Organs: Different tissues combine to form organs
• Organ Systems: Organs work together in organ systems
• Organisms: Individual living beings composed of organ systems
• Populations: Groups of individuals of the same species living in the same area
• Communities: Different populations interacting with each other in an area
• Ecosystems: Communities interacting with their physical environment
• Biosphere: The part of Earth where life exists

The Cell: The Basic Unit of Life

• The cell theory states that all living things are composed of cells
• The cell is the smallest unit of organization that can perform all life's activities
• There are two main types of cells: prokaryotic and eukaryotic
• Prokaryotic cells lack a nucleus and other membrane-bound organelles
• They are generally smaller and simpler
• Bacteria and archaea are prokaryotes
• Eukaryotic cells have a nucleus and other membrane-bound organelles
• They are generally larger and more complex
• Protists, fungi, plants, and animals are eukaryotes

Genetic Information: DNA

• DNA (deoxyribonucleic acid) is the molecule that carries genetic information
• DNA is a double helix composed of four nucleotide bases: adenine (A), guanine (G), cytosine (C), and thymine (T)
• The sequence of these bases encodes the instructions for building and maintaining an organism
• Genes are specific segments of DNA that code for proteins
• DNA is passed from parents to offspring, allowing for inheritance of traits

Evolution: The Core Theme of Biology

• Evolution is the process of change in the characteristics of a species over time
• Natural selection is the mechanism by which evolution occurs
• Individuals with traits that are better suited to their environment are more likely to survive and reproduce
• Over time, these advantageous traits become more common in the population
• Evolution explains the diversity and unity of life

Classification of Life

• Taxonomy is the science of classifying organisms
• Organisms are grouped into increasingly inclusive categories:
• Species
• Genus
• Family
• Order
• Class
• Phylum
• Kingdom
• Domain
• The three domains of life are:
• Bacteria: Prokaryotic, unicellular organisms
• Archaea: Prokaryotic, unicellular organisms that often live in extreme environments
• Eukarya: Eukaryotic organisms, including protists, fungi, plants, and animals

Energy Flow and Chemical Cycling

• Life requires energy, which flows through ecosystems
• The sun is the primary source of energy for most ecosystems
• Producers (e.g., plants) convert sunlight into chemical energy through photosynthesis
• Consumers (e.g., animals) obtain energy by eating other organisms
• Decomposers (e.g., fungi and bacteria) break down dead organisms, returning nutrients to the environment
• Chemical elements are cycled between living organisms and the environment

Scientific Inquiry

• Biology is a science, and scientists use the scientific method to investigate the natural world
• The scientific method involves:
• Observation: Observing a phenomenon or asking a question
• Hypothesis: Developing a testable explanation for the observation
• Experiment: Designing and conducting an experiment to test the hypothesis
• Data Analysis: Analyzing the data collected during the experiment
• Conclusion: Drawing a conclusion based on the data analysis, and determining whether the hypothesis is supported or rejected
• A scientific theory is a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses

Interdependence in Nature

• Organisms interact with each other and their environment in complex ways
• Ecology is the study of these interactions
• Ecosystems are composed of biotic (living) and abiotic (non-living) factors
• Organisms depend on each other for resources, such as food, water, and shelter
• Human activities can have a significant impact on ecosystems and the environment

The Importance of Biology

• Biology is essential for understanding ourselves and the world around us
• It has applications in medicine, agriculture, biotechnology, and environmental conservation
• By studying biology, we can develop new treatments for diseases, improve food production, and protect our planet
• Understanding biology is crucial for making informed decisions about issues such as climate change, genetic engineering, and public health

Homeostasis

• Maintenance of a stable internal environment despite external changes is crucial for cell function
• Temperature, pH, and solute concentrations are kept within optimal ranges

Reproduction

• Life perpetuates itself through reproduction
• Asexual reproduction: single parent produces identical offspring
• Sexual reproduction: two parents produce genetically diverse offspring

Response to Stimuli

• Organisms react to changes in their environment, enabling survival
• Examples: plants growing towards light or animals fleeing from predators

Adaptation

• Through evolution, populations adapt to their environment over generations
• Inherited traits that enhance survival and reproduction become more common

Metabolism

• All chemical reactions within an organism that produce energy are collectively called metabolism
• Involves building molecules (anabolism) and breaking them down (catabolism)

Growth and Development

• Living things increase in size and complexity during their life cycle
• Controlled by genetic information and environmental factors

Organization

• Living things display a high level of organization, from atoms to ecosystems
• Each level builds upon the previous one, resulting in emergent properties

Scientific Method

• A way to ask and answer questions about the natural world
• Observation leads to questions, which leads to a hypothesis, which leads to experiments, which lead to a conclusion

Central Dogma

• The flow of genetic information in cells, DNA -> RNA -> Protein
• DNA makes RNA through transcription, and RNA makes protein through translation

Viruses

• Biologists consider viruses non-living
• They can only reproduce inside another cells acting as a parasite
• They are essentially genetic material inside of a protein coat