Introduction to Biology

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

Core Principles of Biology

• Cell theory: All living organisms are composed of cells
• Gene theory: Hereditary information is encoded in DNA and genes
• Evolution: All life forms have evolved from a common ancestor through natural selection
• Homeostasis: Living organisms maintain a stable internal environment

Levels of Biological Organization

• Molecules: Atoms combine to form molecules, such as DNA and proteins
• Cells: The basic unit of life, consisting of organelles and other structures enclosed by a membrane
• Tissues: Groups of similar cells performing a specific function
• Organs: Structures composed of different tissues working together
• Organ systems: Groups of organs that cooperate to perform major bodily functions
• Organisms: Individual living beings consisting of one or more organ systems
• Populations: Groups of individuals of the same species living in the same area
• Communities: Populations of different species interacting with each other
• Ecosystems: Communities interacting with their physical environment
• Biosphere: The sum of all ecosystems on Earth

Cell Structure and Function

• Cells are the basic structural and functional units of life
• Two main types of cells: prokaryotic and eukaryotic
• Prokaryotic cells: Simple cells lacking a nucleus and other membrane-bound organelles (e.g., bacteria)
• Eukaryotic cells: Complex cells with a nucleus and other membrane-bound organelles (e.g., animal, plant, fungi, and protist cells)
• Key cell structures:
  • Plasma membrane: Outer boundary of the cell that controls the movement of substances in and out
  • Nucleus: Contains the cell's DNA and controls cell activities
  • Cytoplasm: Gel-like substance within the cell containing organelles
  • Ribosomes: Sites of protein synthesis
  • Mitochondria: Powerhouses of the cell, generating ATP through cellular respiration
  • Endoplasmic reticulum (ER): Network of membranes involved in protein and lipid synthesis
  • Golgi apparatus: Modifies, sorts, and packages proteins
  • Lysosomes: Contain enzymes for breaking down cellular waste and debris
  • Vacuoles: Storage structures for water, nutrients, and waste

Genetics and Heredity

• Genetics: The study of genes, heredity, and variation in living organisms
• Genes: Units of heredity that contain instructions for building proteins
• DNA (deoxyribonucleic acid): The molecule that carries genetic information in the form of a double helix
• Chromosomes: Structures made of DNA that contain genes
• Genotype: The genetic makeup of an organism
• Phenotype: The observable characteristics of an organism
• Heredity: The passing of traits from parents to offspring
• Mendelian genetics: Principles of inheritance based on the work of Gregor Mendel
  • Law of segregation: Allele pairs separate during gamete formation
  • Law of independent assortment: Alleles of different genes assort independently during gamete formation
• Mutations: Changes in the DNA sequence that can lead to genetic variation

Evolution

• Evolution: The process of change in the heritable characteristics of biological populations over successive generations
• Natural selection: The mechanism of evolution in which individuals with advantageous traits are more likely to survive and reproduce
• Adaptation: Traits that enhance an organism's survival and reproduction in its environment
• Evidence for evolution:
  • Fossil record: Shows the history of life on Earth and the transition of species over time
  • Comparative anatomy: Similarities in the anatomy of different species due to common ancestry
  • Embryology: Similarities in the embryonic development of different species
  • Molecular biology: Similarities in the DNA and protein sequences of different species
  • Biogeography: The distribution of species around the world
• Mechanisms of evolution:
  • Mutation: Introduction of new genetic variation
  • Gene flow: Transfer of genes between populations
  • Genetic drift: Random changes in allele frequencies in small populations
  • Natural selection: Differential survival and reproduction based on heritable traits

Ecology

• Ecology: The study of the interactions between organisms and their environment
• Ecosystem: A community of living organisms (biotic factors) interacting with their physical environment (abiotic factors)
• Population ecology: Studies the dynamics of populations, including their size, density, distribution, and growth rate
• Community ecology: Studies the interactions between different species in a community
• Ecosystem ecology: Studies the flow of energy and nutrients through an ecosystem
• Trophic levels: The position an organism occupies in a food chain or food web
• Producers (autotrophs): Organisms that produce their own food through photosynthesis (e.g., plants)
• Consumers (heterotrophs): Organisms that obtain energy by consuming other organisms
  • Primary consumers (herbivores): Eat producers
  • Secondary consumers (carnivores): Eat primary consumers
  • Tertiary consumers: Eat secondary consumers
• Decomposers (detritivores): Break down dead organic matter and release nutrients back into the environment
• Food chains and food webs: Models that show the flow of energy and nutrients through an ecosystem
• Biogeochemical cycles: The cycling of nutrients (e.g., carbon, nitrogen, phosphorus) through the biotic and abiotic components of an ecosystem

Plant Biology

• Plants are multicellular, eukaryotic organisms that belong to the kingdom Plantae
• Key characteristics:
  • Autotrophic: Produce their own food through photosynthesis
  • Cell walls made of cellulose
  • Adaptations to terrestrial life, such as vascular tissues and roots
• Plant structures:
  • Roots: Anchor the plant and absorb water and nutrients from the soil
  • Stems: Support the plant and transport water, nutrients, and sugars
  • Leaves: Primary sites of photosynthesis
  • Flowers: Reproductive structures of angiosperms (flowering plants)
• Photosynthesis: The process by which plants convert light energy into chemical energy in the form of glucose
  • Occurs in chloroplasts, which contain chlorophyll
  • Carbon dioxide + Water --(light energy)--> Glucose + Oxygen
• Plant reproduction:
  • Sexual reproduction: Involves the fusion of gametes (sperm and egg)
  • Asexual reproduction: Production of new plants from vegetative parts (e.g., stems, roots, leaves)
• Plant hormones: Chemical signals that regulate plant growth and development

Animal Biology

• Animals are multicellular, eukaryotic organisms that belong to the kingdom Animalia
• Key characteristics:
  • Heterotrophic: Obtain energy by consuming other organisms
  • Lack cell walls
  • Capable of movement
  • Respond to stimuli
• Animal tissues:
  • Epithelial tissue: Covers surfaces and lines body cavities
  • Connective tissue: Provides support, connects tissues, and transports substances
  • Muscle tissue: Responsible for movement
  • Nervous tissue: Transmits electrical signals
• Organ systems: Groups of organs that cooperate to perform major bodily functions
  • Digestive system: Processes food and absorbs nutrients
  • Respiratory system: Exchanges gases (oxygen and carbon dioxide)
  • Circulatory system: Transports blood, nutrients, and gases throughout the body
  • Excretory system: Removes waste products from the body
  • Nervous system: Controls and coordinates body activities through electrical and chemical signals
  • Endocrine system: Regulates body functions through hormones
  • Immune system: Protects the body from pathogens
  • Reproductive system: Enables reproduction
• Animal development:
  • Fertilization: Fusion of sperm and egg to form a zygote
  • Cleavage: Rapid cell division of the zygote
  • Gastrulation: Formation of the three primary germ layers (ectoderm, mesoderm, and endoderm)
  • Organogenesis: Development of organs and organ systems from the germ layers