Introduction to Biology

• Biology is the scientific study of life
• Explores the structure, function, growth, origin, evolution, and distribution of living organisms
• Includes taxonomy, classification, and examination of all creatures, extant and extinct

General Concepts

• Biology recognizes the cell as the basic unit of life
• Genes are the basic unit of heredity
• Evolution explains the unity and diversity of life
• Living organisms maintain homeostasis to survive

Branches of Biology

• Biochemistry: Study of the chemical processes within and relating to living organisms
• Botany: Study of plants, including their physiology, structure, genetics, ecology, distribution, classification, and economic importance
• Cell biology: Study of cell structure and function
• Ecology: Study of the interactions of organisms with one another and with their physical and chemical environment
• Evolutionary biology: Study of the evolutionary processes that produced the diversity of life on Earth
• Genetics: Study of heredity and variation in organisms
• Microbiology: Study of microorganisms, including bacteria, viruses, fungi, protozoa, and algae
• Molecular biology: Study of the molecular basis of biological activity
• Physiology: Study of the functions and mechanisms in a living system
• Zoology: Study of animals, including their physiology, structure, genetics, ecology, evolution, classification, and behavior

Cell Biology

• Cell biology is the study of cells and their functions, focusing on the structure, function, and behavior of cells
• Examines cell components and their interactions
• Understanding cell biology is crucial for comprehending tissues, organs, and organisms

Cell Theory

• All living organisms are composed of one or more cells
• The cell is the basic unit of structure and function in organisms
• All cells arise from pre-existing cells

Cell Structures

• Cell membrane: Outer boundary separating the cell's internal environment from the external environment
• Cytoplasm: Gel-like substance within the cell containing organelles
• Nucleus: Control center of the cell containing DNA
• Ribosomes: Sites of protein synthesis
• Endoplasmic reticulum (ER): Network of membranes involved in protein and lipid synthesis
• Golgi apparatus: Modifies, sorts, and packages proteins and lipids
• Lysosomes: Contain enzymes for intracellular digestion
• Mitochondria: Powerhouses of the cell, generating ATP through cellular respiration
• Chloroplasts: (In plant cells) Site of photosynthesis
• Cytoskeleton: Network of protein filaments providing structural support and facilitating movement

Cell Types

• Prokaryotic cells: Lack a nucleus and other membrane-bound organelles
  • Bacteria and Archaea
  • DNA is located in the cytoplasm
• Eukaryotic cells: Possess a nucleus and other membrane-bound organelles
  • Protists, fungi, plants, and animals
  • DNA is contained within the nucleus

Cell Membrane

• Selectively permeable barrier controlling the movement of substances in and out of the cell
• Composed of a phospholipid bilayer with embedded proteins
• Fluid mosaic model describes the dynamic nature of the membrane

Cell Transport

• Passive transport: Does not require energy
  • Diffusion: Movement of molecules from an area of high concentration to an area of low concentration
  • Osmosis: Diffusion of water across a selectively permeable membrane
  • Facilitated diffusion: Movement of molecules across a membrane with the help of transport proteins
• Active transport: Requires energy (ATP)
  • Moves molecules against their concentration gradient
  • Involves transport proteins

Cell Communication

• Cells communicate with each other through chemical signals
• Signaling pathways involve:
  • Reception: Binding of a signaling molecule to a receptor
  • Transduction: Conversion of the signal into a form that can bring about a cellular response
  • Response: Specific cellular change due to the signal

Cell Cycle

• Ordered sequence of events in which a cell duplicates its contents and divides
• Consists of two main phases:
  • Interphase: Cell grows and replicates its DNA
    • G1 phase: Cell growth and preparation for DNA replication
    • S phase: DNA replication
    • G2 phase: Cell growth and preparation for cell division
  • M phase (Mitotic phase): Cell divides
    • Mitosis: Division of the nucleus
      • Prophase
      • Metaphase
      • Anaphase
      • Telophase
    • Cytokinesis: Division of the cytoplasm

Cell Division

• Mitosis: Produces two identical daughter cells
  • Important for growth, repair, and asexual reproduction
• Meiosis: Produces four genetically different daughter cells with half the number of chromosomes
  • Occurs in sexually reproducing organisms to produce gametes (sperm and egg cells)
  • Introduces genetic variation through crossing over and independent assortment

Cell Metabolism

• Sum of all chemical reactions occurring in a cell
• Catabolism: Breakdown of complex molecules into simpler ones, releasing energy
• Anabolism: Synthesis of complex molecules from simpler ones, requiring energy
• Enzymes: Biological catalysts that speed up chemical reactions
• ATP (adenosine triphosphate): Main energy currency of the cell

Cell Respiration

• Process of generating ATP by breaking down glucose and other organic molecules
• Occurs in three main stages:
  • Glycolysis: Breakdown of glucose into pyruvate
  • Citric acid cycle (Krebs cycle): Oxidation of pyruvate to produce ATP, NADH, and FADH2
  • Oxidative phosphorylation: Electron transport chain and chemiosmosis to generate a large amount of ATP

Photosynthesis

• Process by which plants and other organisms convert light energy into chemical energy
• Occurs in chloroplasts
• Two main stages:
  • Light-dependent reactions: Light energy is used to split water and generate ATP and NADPH
  • Light-independent reactions (Calvin cycle): CO2 is fixed and used to synthesize glucose

Apoptosis

• Programmed cell death
• Important for development, tissue homeostasis, and eliminating damaged cells
• Involves a series of biochemical events leading to cell disassembly

Cell Specialization

• Process by which cells become specialized to perform specific functions
• Occurs through differential gene expression
• Different cell types express different sets of genes

Cell Communication Types

• Direct Contact: Communication through gap junctions
• Paracrine Signaling: Local signaling where cells secrete substances that affect nearby cells
• Endocrine Signaling: Long-distance signaling where hormones are secreted into the bloodstream
• Synaptic Signaling: Occurs in the nervous system where neurotransmitters are released

Cell Junctions

• Tight Junctions: Prevent leakage of extracellular fluid
• Adherens Junctions: Provide strong mechanical attachments between cells
• Desmosomes: Similar to adherens junctions but provide even stronger attachments
• Gap Junctions: Allow direct communication between cells through channels