Comprehensive Study Guide: Living Organisms - Characteristics, Diversity, and Cellular Mechanics

Characteristics of Living Organisms

Criteria for Life: Scientists define life based on a specific list of characteristics. An object must perform all these life processes to be considered alive; otherwise, it is classified as dead or non-living.
The Eight Life Processes: 1. Nutrition: Obtaining food to provide energy for life processes and molecules (proteins, carbohydrates, and lipids) for building living material. 2. Cellular Respiration: The chemical process of releasing energy from substances like glucose. 3. Excretion of Wastes: Removal of metabolic waste products from cells. 4. Response to Surroundings: Sensitivity to stimuli and the ability to respond to avoid danger or access resources. 5. Movement: All living things move; animals often move from place to place (locomotion), while plants move parts of themselves. 6. Control of Internal Conditions (Homeostasis): Maintaining an internal environment within strict limits (e.g., temperature, water content). 7. Reproduction: Producing offspring to ensure the survival of the species, either sexually or asexually. 8. Growth and Development: Permanent increase in size and complexity over time.

Detailed Nutrition and Energy Flow

Autotrophs (Producers): Organisms that produce their own food. * Photosynthesis: Green plants take in water and carbon dioxide to produce sugars and oxygen using light energy. * Photosynthesis Equation: $6CO_2 + 6H_2O + ext{Light} ightarrow C_6H_{12}O_6 + 6O_2$
Heterotrophs (Consumers): Organisms that must eat other organisms to derive energy. They break down complex molecules into simpler units and rebuild them. * Herbivores: Eat plant-based food. * Carnivores: Eat other animals. * Omnivores: Eat both plants and animals.
Macromolecules and Subunits: * Complex Carbohydrates (e.g., Starch): Built from simple sugars like glucose (found in bread). * Proteins: Built from amino acids (found in meat). * Lipids (e.g., Triglycerides): Built from fatty acids and glycerol (found in margarine).
Food Chain Hierarchy: Sun → Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer → Decomposer.

Cellular Respiration and Energy Storage

Cell Respiration vs. Respiration: * Cell Respiration: Releasing energy stored in the chemical bonds of molecules like glucose. * Respiration (Gas Exchange): The physical exchange of $CO_2$ and $O_2$ via respiratory organs like lungs.
Process and Location: Occurs in the mitochondria of most organisms. In bacteria, it occurs on the cell membrane.
ATP (Adenosine Triphosphate): Acts as a biological battery, storing energy released during respiration until it is needed for cellular work.
Aerobic Respiration: Requires oxygen; efficient production of ATP. * Equation: $ext{Glucose} + ext{Oxygen} ightarrow ext{Carbon Dioxide} + ext{Water} + ext{ATP}$
Anaerobic Respiration: Occurs in the absence of oxygen; less efficient. * Yeast/Bacteria Fermentation: $C_6H_{12}O_6 ightarrow 2C_2H_5OH + 2CO_2 + ext{ATP}$ (Produces ethanol and carbon dioxide). * Muscle Cell Fermentation: $C_6H_{12}O_6 ightarrow 2C_3H_6O_3 + ext{ATP}$ (Produces lactic acid). * Lactic Acid Recovery: Lactic acid causes muscle pain; it is carried by blood to the liver, converted back to glucose, and the pain subsides.

Waste Management and Response Systems

Metabolic Reactions: Chemical reactions in cells that change substances into other materials.
Excretion vs. Egestion: * Excretion: Removal of metabolic waste ( $CO_2$ , $O_2$ , urea, water). * Egestion: Elimination of undigested feces from the body.
Examples of Waste: Urea in humans is removed via urine processed by kidneys.
Response Mechanisms: * Animals: Use receptors (eyes, ears, nose) and a nervous system (brain, spinal cord, neurons) for rapid muscle-based responses. * Plants (Tropisms): Slow growth-based responses toward or away from stimuli. * Phototropism: Growth response to light. * Geotropism: Growth response to gravity. * Hydrotropism: Growth response to water. * Thigmotropism: Growth response to touch (e.g., vines wrapping around objects).

Homeostasis and Internal Regulation

Homeostasis: Maintenance of the internal environment within required limits.
Temperature Control: Involves feedback loops using sensors to trigger responses like sweating (to cool) or shivering (to warm).
Water Balance in Plants: * Stomata: Pores on leaves that control gas exchange and water loss (transpiration). * Hot Conditions: Stomata close to prevent water vapor loss and dehydration. * Ample Water: Stomata stay open for gas exchange and excess water loss.

Reproduction, Growth, and Specialized Cells

DNA: Contains genetic information controlling offspring characteristics.
Asexual Reproduction: Single parent; offspring are genetically identical clones (common in unicellular organisms, Hydras, sweet potatoes).
Sexual Reproduction: Two parents; involves sex cells (gametes) and fertilization. Increases genetic variation.
Cell Division Types: * Meiosis: Specialized division producing gametes (sperm and egg). * Mitosis: Division producing two identical daughter cells for growth and repair.
Specialized Cells: 1. Root Hair Cells: Elongated to increase surface area for water absorption. 2. Guard Cells: Control stomata opening through turgidity changes. 3. Red Blood Cells: No nucleus; contain hemoglobin to carry oxygen. 4. Nerve Cells: Elongated fibers to transmit electrical impulses.
Levels of Organization: Organelle → Cell → Tissue → Organ → System → Organism.

Variety and Classification of Living Organisms

Five Kingdom Classification: 1. Monera: Bacteria. 2. Protista: Microscopic single-celled organisms. 3. Fungi: Yeasts, molds, mushrooms. 4. Plantae: Multicellular autotrophs. 5. Animalia: Multicellular heterotrophs.
Taxonomic Distinctions: * Plants: Have chloroplasts, cellulose cell walls, and store carbohydrates as starch or sucrose. * Animals: No chloroplasts or cell walls; often move via locomotion and store sugar as glycogen. * Fungi: Cell walls made of chitin. Body made of hyphae organized into mycelium. Feed via saprotrophic nutrition (extracellular enzymes). * Bacteria: Single-celled with no nucleus (circular DNA/plasmids). Cell walls made of peptidoglycan. Shapes include cocci and bacilli (e.g., E. coli, Streptococcus pneumoniae). * Protista (Protoctista): Diverse "misfit" group. Includes protozoa (Amoeba, Plasmodium) and autotrophs (Chlorella). * Viruses: Non-living parasitic particles. Consist of a protein coat (capsid) and DNA or RNA. Examples: HIV, Coronavirus, Bacteriophages (infect bacteria).
Carbohydrate Chemistry: * Cellulose: Structure of plant walls; human dietary fiber. * Starch: Plant energy storage; made of glucose subunits. * Glycogen: Animal energy storage; made of glucose subunits. * Sucrose: Simple sugar; glucose + fructose; formula $C_{12}H_{22}O_{11}$ .

Cellular Structures and Functions

Organelles: * Nucleus: Houses DNA; contains nucleoplasm, nucleolus (ribosome production), and nuclear pores in the nuclear envelope. * Endoplasmic Reticulum (ER): Rough ER has ribosomes for protein synthesis; Smooth ER synthesizes lipids. * Golgi Apparatus: Packages and ships proteins in vesicles. * Lysosomes: Spherical vesicles with enzymes to digest waste, cellular debris, or pathogens. * Mitochondria: Energy production sites via cellular respiration; contain their own DNA. * Chloroplasts: Found in plants/protists for photosynthesis; contain chlorophyll.
Enzymes: Biological catalysts. Substrates bind to the active site of the enzyme to form an enzyme-substrate complex, resulting in products. They facilitate both synthesis and decomposition.

Movement of Substances

Diffusion: Passive net movement of molecules from high to low concentration. Examples include gas exchange in stomata and alveoli.
Osmosis: Diffusion of water through a partially permeable membrane. * Aquaporins: Protein channels that facilitate water transport. * Turgidity: Water entering plant cells creates pressure against the cell wall, keeping the plant upright.
Active Transport: Movement against a concentration gradient (low to high). Requires ATP and often carrier proteins. * Examples: Mineral ion uptake in roots; glucose reabsorption in kidneys.
Factors Affecting Movement: * Surface Area to Volume Ratio: Higher ratio (e.g., villi in intestines) increases movement rate. * Temperature: Higher temperature increases kinetic energy and molecule speed. * Concentration Gradient: A larger difference in concentration leads to faster net movement.

Questions & Discussion

Is it alive?: How do you decide? (Answer: Check the 8 characteristics of life).
Think About It Questions: 1. What occurs inside cells? (Answer: Respiration, protein synthesis, metabolic reactions). 2. Which organisms are single-celled? (Answer: Bacteria, Amoeba, yeast). 3. Types of cells in plants/animals? (Answer: Nerve cells, red blood cells, root hair cells, guard cells).
Tropisms Inquiry: What part of a plant shows positive vs. negative tropism? Why seek water? Why are sunflowers named so? (Answer: Generally, roots show positive geotropism/hydrotropism; stems show positive phototropism).