Life, Diversity & Classification Lecture Notes

Defining Life and Living Organisms

• Biology and Life Sciences: Biology, or Life Sciences, is defined as the study of life or living organisms.
• The Challenge of Definition: There is no universal definition of life. Defining life in unequivocal terms remains a challenge. When derived from analyzing known organisms, life is usually defined at the cellular level.
• Conventional Definition: Scientists often disagree on whether certain entities, like viruses, are alive. Currently, the consensus is that life is a characteristic of organisms exhibiting all or most of the following seven phenomena:
  1. Homeostasis: Regulation of the internal environment to maintain a constant state. Examples include maintaining constant internal temperature, carbon dioxide levels, and sugar levels.
  2. Organization:
     • In Physical Science: All matter consists of atoms, the smallest unit of matter, which join to form molecules.
     • In Life Sciences: The smallest unit of life is the cell.
     • Unicellular: Organisms consisting of a single cell.
     • Multicellular: Organisms consisting of many cells.
     • Hierarchy of Organization:
       • Tissues: Groups of similar cells performing the same function (e.g., bone, muscle, or nerve tissue).
       • Organs: Different types of tissue grouped to perform a specific function (e.g., heart, kidney, leaf).
       • Systems: Different organs grouped to form a functional unit (e.g., digestive or circulatory system).
       • Organism: A collection of different systems forming a single living entity.
  3. Metabolism: This includes photosynthesis, nutrition, respiration, and excretion. Energy is required to maintain homeostasis and produce life-associated phenomena.
     • Anabolism: The process of producing larger molecules from smaller ones (e.g., sugars from water and carbon dioxide).
     • Catabolism: The process of breaking large molecules down into smaller ones.
  4. Growth: A growing organism increases in size in all its parts rather than just accumulating matter. This occurs through an increase in the number of cells and/or an increase in the size of individual cells.
  5. Adaptation: The ability to change over time in response to the environment. This is fundamental to evolution and is determined by heredity, metabolized substances, and external factors.
  6. Response to Stimuli: The ability to detect and respond to environmental changes. Responses range from a unicellular organism contracting to chemicals to complex sensory reactions in higher animals. Motion is a common expression (e.g., leaves turning toward the sun).
  7. Reproduction: The ability to produce new organisms. It can be simple cell division to form two new cells.
     • Asexual Reproduction: Production of a new individual from a single parent.
     • Sexual Reproduction: Production of a new individual from at least two differing parent organisms.

Energy and Life

• Requirement for Energy: Energy is essential for all seven characteristics of life.
• Sources of Energy:
  • The Sun: The most important source of energy for life on Earth.
  • The Earth's Core: Causes tectonic plate movement, earthquakes, and volcanoes.
  • Atomic Energy: Energy within the atom (protons and neutrons in the nucleus). Utilized by humans for electricity generation since the Second World War.
  • Chemical Bonds: Some ancient bacteria (Archaea) use energy stored in molecular bonds (e.g., hydrogen sulphide or methane).
• Chemical Potential Energy: Living organisms cannot use solar energy directly; it must be converted into chemical potential energy, referred to as food.
• ATP (Adenosine Triphosphate): The specific form of energy that cells use for their living functions. Energy from food is released into this usable form through respiration.

Photosynthesis: Producing Food

• Definition: Photosynthesis is the process where chlorophyll-containing organisms use water ($H_2O$), carbon dioxide ($CO_2$), and radiant energy from the sun to manufacture glucose ($C_6H_{12}O_6$), releasing oxygen ($O_2$) as a by-product.
• Producers: Organisms capable of producing food.
  • Include large plants.
  • Include unicellular organisms: bacteria and protists like phytoplankton.
• Photosynthetic Pigment: Chlorophyll is required to absorb sunlight energy.
  • In plants: Found in organelles called chloroplasts.
  • In bacteria: Found in thylakoids within the cytoplasm.
• Balanced Chemical Equation:
  • $6CO_2 + 6H_2O \xrightarrow{\text{sunlight and chlorophyll}} C_6H_{12}O_6 + 6O_2$
• Raw Materials (Reagents):
  • Water: Obtained from soil via roots in land plants or from the surrounding water for aquatic bacteria and protists.
  • Carbon Dioxide: Absorbed from the air through stomata (tiny leaf openings) in land plants or dissolved in water for aquatic organisms.
• Storage of Energy: Glucose is soluble and potentially dangerous to the plant cell's osmotic balance. It is converted into starch, a larger insoluble molecule, for safe storage. Plants also convert glucose into oils, proteins, and cellulose for cell walls.
• Testing for Photosynthesis (Starch Test):
  1. Boil leaf in water: Softens cell walls and breaks the waxy cuticle.
  2. Boil in ethanol (water bath): Flammable ethanol removes green chlorophyll so color changes are visible. The leaf becomes white and brittle.
  3. Rinse in water: Softens the leaf and removes ethanol.
  4. Add Iodine solution: Red-brown iodine turns blue-black in the presence of starch.

Respiration: Releasing Energy

• Definition: The process where energy-rich molecules (glucose) are broken down gradually to release chemical potential energy. It is a form of combustion controlled by enzymes.
• Balanced Chemical Equation:
  • $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{energy (ATP)}$
• Site of Respiration: Occurs in organelles called mitochondria (found in all organisms except bacteria).
• Aerobic vs. Anaerobic:
  • Aerobic: Respiration in the presence of oxygen.
  • Anaerobic: Respiration without oxygen.
    • In plants and yeasts: Forms alcohol.
    • In animal cells: Forms lactic acid.
• Metabolic Water: Water produced as an end-product of respiration. It is vital for desert animals. For example, camels store fat in their humps; breaking down this fat for energy produces metabolic water to keep the camel hydrated.
• Reciprocity: The equations for photosynthesis and respiration are the reverse of one another.

Biodiversity and Classification

• Biodiversity: Refers to the variety of living organisms in an area, their habitats, and their interrelationships (e.g., ecology).
  • 1.4 million species are named; estimates exceed 30 million.
• Taxonomy: The process of grouping organisms and naming them based on similar characteristics to build "The Tree of Life."
• Binomial System: Developed by Carl Linnaeus (c. 1753).
  • Consists of two Latin names: Genus (starts with a capital) and species (lower case).
  • Format: Italics in print, underlined separately when handwritten (e.g., Canis familiaris).
• Species Definition: A group of organisms living in the same habitat that look alike, can reproduce with each other, and produce fertile offspring.
• The Hierarchy of Classification (8 Ranks):
  1. Domain
  2. Kingdom
  3. Phylum
  4. Class
  5. Order
  6. Family
  7. Genus
  8. Species
• Example: The Lion classification:
  • Domain: Eukaryota (true nucleus)
  • Kingdom: Animalia (all animals)
  • Phylum: Chordata (notochord present)
  • Subphylum: Vertebrata (skull and vertebrae)
  • Class: Mammalia (young fed with milk)
  • Order: Carnivora (meat eaters)
  • Family: Felidae (all cats)
  • Genus: Panthera (large cats)
  • Species: Panthera leo (lions)

The Five Kingdom System vs. Three Domains

• Five Kingdom System:
  1. Animalia: Multicellular, heterotrophic (cannot produce food), no cell wall, eukaryotic.
  2. Plantae: Multicellular, autotrophic (photosynthetic), cellulose cell walls, eukaryotic.
  3. Fungi: Heterotrophic (feed on decaying matter), non-motile, chitin cell walls, eukaryotic.
  4. Protista: Microscopic, mostly unicellular, eukaryotic. Includes Amoeba and seaweeds.
  5. Monera: Microscopic, prokaryotic (no true nucleus), peptidoglycan cell walls, circular DNA. (e.g., bacteria).
• Three-Domain System: The modern classification system:
  1. Eukaryota: Kingdoms Protista, Fungi, Plants, and Animals.
  2. Eubacteria: True bacteria.
  3. Archaea: Ancient single-celled prokaryotes.

Archaea: Extreme Life

• Characteristics: Single-celled, lack nuclei, lack peptidoglycan in cell walls. More closely related to Eukaryotes than Bacteria.
• Methanogens: Largest group of Archaea. Produce methane as a metabolic byproduct. Found in wetlands (marsh gas) and animal guts. A cow's gut can produce up to $100\,\text{liters}$ of methane daily.
• Extremophiles: Require extreme conditions to survive.
  • Thermophiles: Require temperatures above $45^{\circ}\text{C}$ ($113^{\circ}\text{F}$) to survive.
  • Halophiles: Require salinity greater than $9\%$ to maintain cell wall integrity.

Viruses: Akaryotic Entities

• Structure: Viruses are akaryotic (no cell, no nucleus, no cytoplasm). They consist of nucleic acid (DNA or RNA) inside a protein coat (capsid).
• Living or Non-living?: Viruses do not possess characteristics like growth, feeding, or excretion. They only replicate inside a host cell, making them obligatory parasites.
• Discovery: Discovered in 1900 by Dutch professor Beijernick via experiments with tobacco mosaic disease. He realized the infectious agent was smaller than bacteria and called it "virus" (Latin for poison).
• Key Medical Terms:
  • Endemic: Disease found among a particular group or local region.
  • Epidemic: Disease occurring in many individuals in a community at the same time.
  • Pandemic: Disease affecting people worldwide.
• Transmission:
  • Vector: Organism carrying a pathogen (e.g., mosquitoes, fleas, ticks).
  • In Animals: Spread via blood, sputum, excreta, or contact.
  • In Plants: Spread via wind, insects (aphids), or humans (infected seeds/tools).
• Prevention and Treatment:
  • Immune System: First line of defense. Boosted by nutrition, hydration, and sleep.
  • Vaccines: Stimulate antibodies.
  • Mutation: Some viruses are "plastic" and mutate regularly (e.g., Flu, HIV), rendering vaccines less effective.
  • Herd Immunity: Occurs when enough people in a community are immune to prevent a disease from spreading.

Mathematical Application in Biology

• Magnification Calculation:
  • Formula: $\text{Actual Size} = \frac{\text{Drawing Length}}{\text{Magnification}}$
  • Example: A drawing of 160 mm with x50 magnification.
  • Calculation: $\frac{160\,\text{mm}}{50} = 3.2\,\text{mm}$