Introduction to Biology

• Biology is the scientific study of life.
• It explores living organisms' structure, function, growth, origin, evolution, distribution, and taxonomy.
• Biology includes botany, zoology, microbiology, genetics, and ecology.

Core Principles of Biology

• Cell theory states all living organisms are composed of cells, the basic units of structure and function.
• Gene theory states traits are inherited through genes, specific DNA sequences.
• Evolution is the change in heritable characteristics of populations over generations.
• Homeostasis refers to living organisms maintaining a stable internal environment.
• Thermodynamics: Life depends on the flow of energy, which is governed by the laws of thermodynamics.

Levels of Biological Organization

• Molecules: Atoms combine to form molecules, such as DNA, proteins, and carbohydrates.
• Cells are the basic unit of life, consisting of organelles and other structures enclosed by a membrane.
• Tissues are groups of similar cells performing a specific function.
• Organs are structures composed of different tissues working together.
• Organ Systems: Groups of organs cooperate for major bodily functions.
• Organisms: Individual living entities composed of organ systems.
• Populations are groups of individuals of the same species living in the same area.
• Communities: Populations of different species live and interact.
• Ecosystems: Communities of organisms interact with their physical environment.
• Biosphere: The part of Earth where life exists, including all ecosystems.

Cell Biology

• Cells are the fundamental units of life and are categorized as prokaryotic or eukaryotic.
• Prokaryotic cells (bacteria and archaea) lack a nucleus and other membrane-bound organelles.
• Eukaryotic cells (protists, fungi, plants, and animals) possess a nucleus and membrane-bound organelles.
• Key cell structures are the plasma membrane, cytoplasm, nucleus (in eukaryotes), ribosomes, and various organelles.
• The plasma membrane controls the movement of substances into and out of cells.
• The cytoplasm, a gel-like substance, houses organelles within the cell.
• The nucleus contains DNA and controls cell activities.
• Ribosomes are responsible for protein synthesis.
• Mitochondria generate ATP through cellular respiration.
• The endoplasmic reticulum (ER) is involved in protein synthesis (rough ER) and lipid synthesis (smooth ER).
• The Golgi apparatus modifies, sorts, and packages proteins.
• Lysosomes contain enzymes for breaking down cellular waste.

Genetics

• Genetics is the study of heredity and variation in living organisms.
• Genes are segments of DNA that encode specific traits.
• DNA (deoxyribonucleic acid) carries genetic information.
• DNA is a double helix of nucleotides (adenine, guanine, cytosine, and thymine).
• RNA (ribonucleic acid) is involved in protein synthesis.
• Gene expression uses the information encoded in a gene to synthesize a functional gene product (protein or RNA).
• Transcription synthesizes RNA from a DNA template.
• Translation synthesizes protein from an RNA template (mRNA).
• Mutations are changes in the DNA sequence that can lead to trait variations.
• Mendelian genetics describes the inheritance of traits, based on the work of Gregor Mendel.
• Chromosomes are structures that carry genes; humans have 46 chromosomes (23 pairs).

Evolution

• Evolution is the change in the heritable characteristics of biological populations over successive generations.
• Natural selection is the primary mechanism of evolution; individuals with advantageous traits are likely to survive and reproduce.
• Adaptation allows populations to become better suited to their environment through natural selection.
• Genetic drift is the random change in the frequency of alleles in a population.
• Gene flow is the movement of genes between populations.
• Speciation is the process by which new species arise.
• Evidence for evolution includes fossils, comparative anatomy, embryology, and molecular biology.

Ecology

• Ecology studies the interactions between organisms and their environment.
• Ecosystems consist of communities of organisms interacting with their physical environment.
• Populations are groups of individuals of the same species living in the same area.
• Communities are groups of different species living and interacting in the same area.
• Food chains and food webs describe the flow of energy and nutrients through an ecosystem.
• Trophic levels represent an organism's position in a food chain.
• Producers (autotrophs) produce their own food through photosynthesis or chemosynthesis.
• Consumers (heterotrophs) consume other organisms for energy.
• Decomposers break down dead organic matter, recycling nutrients.
• Biomes are large-scale ecosystems defined by specific climate conditions and plant communities.
• The biosphere is the global sum of all ecosystems.

Plant Biology

• Plants are multicellular, eukaryotic organisms belonging to the kingdom Plantae.
• Plants perform photosynthesis, converting carbon dioxide and water into glucose and oxygen.
• Key plant structures include roots, stems, leaves, and flowers.
• Roots anchor plants and absorb water and nutrients.
• Stems provide support and transport water and nutrients.
• Leaves are the primary sites of photosynthesis.
• Flowers are involved in sexual reproduction, producing seeds and fruits.
• Plant cells have cell walls made of cellulose.
• Vascular tissues (xylem and phloem) transport water, nutrients, and sugars.
• Plant hormones regulate growth, development, and responses to environmental stimuli.

Animal Biology

• Animals are multicellular, eukaryotic organisms belonging to the kingdom Animalia.
• Animals are heterotrophs, obtaining energy by consuming other organisms.
• Key animal tissues include epithelial, connective, muscle, and nervous tissue.
• Organ systems in animals include the digestive, respiratory, circulatory, nervous, and endocrine systems.
• The digestive system breaks down food and absorbs nutrients.
• The respiratory system exchanges gases (oxygen and carbon dioxide).
• The circulatory system transports oxygen, nutrients, and waste products.
• The nervous system coordinates and controls body functions.
• The endocrine system produces hormones that regulate physiological processes.
• Animals exhibit diverse locomotion, including walking, swimming, and flying.
• Animal behavior is influenced by genetic and environmental factors.

Biology is the scientific study of life, exploring the structure, function, growth, origin, evolution, distribution, and taxonomy of living organisms. It encompasses fields like botany, zoology, microbiology, and genetics. Key principles include cell theory, gene theory, evolution, homeostasis, and thermodynamics.