Biology: An Introduction

Biology: An Introduction

• Biology is the scientific study of life and living organisms.
• It encompasses the structure, function, growth, evolution, distribution, identification, and taxonomy of living things.

Branches of Biology

• Molecular biology explores the interactions between biological molecules.
• Botany focuses on the study of plants.
• Cellular biology delves into the structure and function of cells, the fundamental building blocks of life.
• Physiology examines the physical and chemical functions of tissues, organs, and organ systems.
• Evolutionary biology investigates the processes that led to the diversity of life on Earth.
• Ecology studies how organisms interact with each other and their environment.
• Biochemistry examines the essential chemistry of life.

Characteristics of Living Organisms

• Made of Cells: All living organisms are composed of one or more cells.
• Require Energy: Organisms need energy (often obtained through food) to sustain life processes.
• Reproduce: Living things reproduce to create offspring and perpetuate their species.
• Maintain Homeostasis: Organisms regulate their internal environment to maintain a stable state.
• Organized: Living organisms exhibit a hierarchical level of organization, from cells to tissues, organs, and systems.
• Respond to Environment: Organisms react to stimuli and changes in their surroundings.
• Grow and Develop: Living things increase in size and complexity over time.
• Exchange Materials with Surroundings: Organisms take in nutrients and water, and release waste products.

Levels of Organization of Life

• Nonliving Levels:
  • Atoms: Elements like carbon, hydrogen, and oxygen.
  • Molecules: Compounds formed from two or more atoms, such as carbohydrates and proteins.
  • Organelles: Specialized structures within cells, such as the nucleus, endoplasmic reticulum, and Golgi apparatus.
• Living Levels:
  • Cells: The basic unit of life, making up all organisms.
  • Tissues: Groups of similar cells working together to perform a specific function.
  • Organs: Structures composed of different tissues that work together to carry out a complex function (e.g., heart, brain, stomach).
  • Organ Systems: Groups of organs that work together to perform a major bodily function (e.g., digestive system, circulatory system).

Cell Theory

• Fundamental Principles:
  • All living organisms are made up of one or more cells.
  • The cell is the basic unit of life.
  • All cells arise from pre-existing cells through biogenesis (cell division).
• Modern Additions:
  • Energy flow (metabolism and biochemistry) takes place within cells.
  • Hereditary information (DNA) is passed from cell to cell.
  • All cells of similar species share a basic chemical composition.

Cell Structure

• Basic Components of All Cells:
  • Cell Membrane: A selectively permeable barrier that separates the cell's interior from its surroundings.
  • DNA-containing Region: Houses the genetic instructions for cellular processes (DNA in prokaryotes, nucleus in eukaryotes).
  • Cytoplasm: A semi-fluid region containing the cell's machinery.
• Eukaryotic Cells:
  • Nucleus: Contains the cell's genetic material (DNA) within chromosomes.
  • Cytoplasm: Contains organelles (membrane-bound structures) that perform specialized functions.

Cell Size

• Limits on Cell Size: Cells are limited in size due to the ratio of their surface area to volume.
• Surface Area to Volume Ratio: As a cell grows larger, its volume increases more rapidly than its surface area.
• Nutrient and Waste Transport: A larger surface area is needed for efficient nutrient uptake and waste removal.

Cell Shape

• Diversity in Shape: Cells come in various shapes, reflecting their functions.

Prokaryotic Cells

• Characteristics:
  • Lack a membrane-bound nucleus.
  • Generally smaller than eukaryotic cells.
  • Found in bacteria and archaea.

Prokaryotic Cell Organelles

• Capsule: A slimy or gummy layer that protects the cell and helps bacteria adhere to surfaces.
• Cell Wall: A rigid structure that provides shape and protection, often composed of peptidoglycan.
• Periplasmic Space: A gap between the cell wall and cell membrane, containing enzymes and transport proteins.
• Cell Membrane: Controls the passage of substances into and out of the cell.
• Cytoplasm: Contains the cell's genetic material (DNA) located in the nucleoid region.
• Ribosomes: Sites of protein synthesis.
• Flagella: Tail-like structures that enable movement.
• Pili: Hair-like structures that aid in attachment and communication.

Eukaryotic Cells

• Characteristics:
  • Possess a membrane-bound nucleus.
  • Generally larger and more complex than prokaryotic cells.
  • Found in plants, animals, fungi, and protists.

Eukaryotic Cell Organelles

• Cell Wall (in some): A rigid structure that provides support and protection, often composed of cellulose (plants) or chitin (fungi).
• Cell Membrane: Controls the movement of substances into and out of the cell.
• Cytoplasm: Contains the cell's machinery, including organelles.
• Nucleus: Contains the cell's genetic material (DNA).
  • Nuclear Envelope: Double membrane that surrounds the nucleus, with pores for transport.
  • Nucleolus: Site of ribosome assembly.
• Mitochondria: Powerhouse of the cell, responsible for cellular respiration and energy production.
• Chloroplasts (in plants): Sites of photosynthesis; convert light energy into chemical energy.
• Ribosomes: Sites of protein synthesis.
• Endoplasmic Reticulum (ER): Network of interconnected membranes involved in protein and lipid synthesis and transport.
• Golgi Apparatus: Processes and packages proteins and lipids for secretion.
• Lysosomes: Contain digestive enzymes for breaking down cellular waste products.
• Peroxisomes: Contain enzymes that break down fatty acids and detoxify harmful substances.
• Vacuoles: Storage compartments for water, nutrients, and waste products.
• Flagella: Whip-like structures used for movement.

Reproduction

• General Reproduction: The process by which living organisms create offspring.
  • Asexual Reproduction: Involves a single parent producing offspring that are genetically identical.
  • Sexual Reproduction: Involves two parents contributing genetic material to create offspring with a unique combination of genes.

Interrelationship of Organisms

• Ecosystems: Communities of living organisms interacting with their nonliving environment.
• Food Webs: Interconnected networks of organisms that show feeding relationships.

Heredity and Evolution

• Heredity: The passing of traits from parents to offspring.
• Evolution: The gradual change in the genetic makeup of a population over time, leading to the development of new species.

Elements of Ecology and Types of Habitats

• Ecology: The study of how organisms interact with their environment.
• Habitats: Specific environments where organisms live.