Life's complexity unfolds from atoms to the biosphere.
We'll explore the essential
functions of organisms, like homeostasis and reproduction, and how they grow and
adapt. These processes occur across different levels, from molecules to ecosystems.
Understanding life's organization is key to grasping biology. We'll examine how
atoms form molecules, cellscombine into tissues and organs, and organisms interact
in ecosystems. This hierarchical structure reveals the interconnectedness of all
living things.
Characteristics of Life
Essential Functions of Living Organisms
• Homeostasis maintains stable internal conditions within an organism
• Regulates internal environment (temperature, pH, water balance)
• Negative feedback mechanisms return systems to set points
(thermoregulation, blood glucose levels)
• Metabolism includes all chemical reactions involved in maintaining life
• Anabolism builds complex molecules from simpler ones (protein
synthesis)
• Catabolism breaks down complex molecules to release energy (cellular
respiration)
• Reproduction allows organisms to produce offspring
• Asexual reproduction produces genetically identical offspring from a
single parent (binary fission in bacteria)
• Sexual reproduction combines genetic material from two parents to
produce genetically diverse offspring (fertilization in animals and plants)
Growth, Development, and Interaction with Environment
• Growth increases the size and number of cells in an organism
• Cell division and cell expansion contribute to growth (mitosis, stem
cell differentiation)
• Development involves changes in form and function over an organism's
life (metamorphosis in insects, embryogenesis in mammals)
• Adaptation enables organisms to survive and reproduce in their
environment
• Genetic variations that enhance survival are passed to future
generations (antibiotic resistance in bacteria)
• Natural selection favors traits that increase fitness (camouflage in
prey animals)
• Response to stimuli allows organisms to react to changes in their
internal or external environment
• Stimuli can be chemical, physical, or biological (pheromones, touch,
presence of predators)
• Responses can be behavioral, physiological, or developmental (fight-or-
flight response, plant tropisms)
Hierarchical Organization of Living Systems
• Organization refers to the ordered structure of living systems at all
levels
• Atoms form molecules (water, glucose)
• Molecules form organelles and cells (mitochondria, neurons)
• Cells form tissues (muscle tissue, epithelial tissue)
• Tissues form organs (heart, lungs)
• Organs form organ systems (circulatory system, respiratory system)
• Organ systems form organisms (humans, plants)
Levels of Organization
Atoms to Molecules
• Atoms are the basic units of matter
• Consist of protons, neutrons, and electrons (carbon, oxygen, nitrogen)
• Combine to form molecules through chemical bonds (covalent bonds, ionic
bonds)
• Molecules are two or more atoms held together by chemical bonds
• Can be small and simple (water, oxygen) or large and complex (proteins,
DNA)
• Perform specific functions in living organisms (enzymes catalyze
reactions, hormones regulate physiology)
Cells to Organs
• Cells are the basic structural and functional units of life
• Prokaryotic cells lack membrane-bound organelles (bacteria)
• Eukaryotic cells have membrane-bound organelles (animal and plant
cells)
• Tissues are groups of cells with similar structure and function
• Four main types in animals: epithelial, connective, muscle, and nervous
tissue
• Three main types in plants: dermal, ground, and vascular tissue
• Organs are structures composed of multiple tissue types that perform
specific functions
• Examples in animals: heart, liver, lungs, brain
• Examples in plants: leaves, roots, stems, flowers
Organ Systems and Organisms
• Organ systems are groups of organs that work together to perform a
common function
• Examples in animals: digestive system, nervous system, reproductive
system
• Examples in plants: root system, shoot system, vascular system
• Organisms are individual living entities composed of one or more cells
• Can be unicellular (bacteria, protozoa) or multicellular (animals,
plants, fungi)
• Interact with their environment and other organisms (predation,
symbiosis, competition)
Ecological Hierarchy
Populations and Communities
• Populations are groups of individuals of the same species living in a
particular area
• Characterized by density, dispersion, age structure, and sex ratio
(population of lions in a national park)
• Can change over time due to births, deaths, immigration, and emigration
(population growth, population decline)
• Communities are assemblages of populations of different species living
in the same area
• Interact through various relationships (predation, competition,
mutualism)
• Have a specific structure and composition (dominant species, keystone
species)
Ecosystems and the Biosphere
• Ecosystems are communities of organisms and their abiotic environment
• Include both biotic factors (producers, consumers, decomposers) and
abiotic factors (sunlight, water, soil)
• Involve the flow of energy and cycling of nutrients (food chains, food
webs, carbon cycle, nitrogen cycle)
• The biosphere is the global sum of all ecosystems on Earth
• Encompasses all living organisms and their environments (terrestrial,
aquatic, and atmospheric)
• Is a closed system with respect to matter but an open system with
respect to energy (solar energy input, heat loss to space)
