Grade 12 Biology - Exam Notes

Biology Notes: Grade 12

Applications of Biology in Daily Life

  • Nature: Encompasses physical world phenomena, including plants, animals, and landscapes.
  • Biology enhances understanding of living organisms, their functions, evolution and interactions, providing food, air, and water.
  • Conservation: Maintenance and wise use of natural resources to prevent their disappearance; vital for protecting the environment.
  • Natural resources are classified as renewable (e.g., plants, trees) and non-renewable (e.g., metals, fossil fuels).
  • Biology helps promote awareness of natural resources conservation and sustainable development.
  • Food Security: Exists when everyone has physical, social, and economic access to sufficient, safe, and nutritious food to maintain an active and healthy life.
  • Biology is key to producing high-nutrient crops and developing food production processes.
  • Conscious Citizen: Values human life and the relationship with all living things, takes responsibility for ethical decision-making to improve life on the planet.
  • Citizens can expand awareness of social, global, and environmental conditions.
  • Career Development: Involves setting goals and acquiring skills for personal and career improvement.
  • Biology graduates can pursue careers in research, medicine, biotechnology, and environmental sciences.
  • Medicine: Biology is applied in fast diagnosis. Contributions towards public and global health needs, effective diagnostics, prevention, novel drugs, recombinant vaccines and treatment measures.
  • Waste Treatment: Biotechnological processes are used for wastewater treatment and renewable energy production, such as bio-fuels and hydrogen.
  • Biotechnology : Harnesses biological systems, organisms, or their derivatives to make or modify products or processes for specific use, for the benefit of people.

Microorganisms

  • Microorganisms (microbes) are life forms too small to be seen without magnification, are diverse in form and function, and inhabit every environment supporting life.
  • Most microorganisms are harmless or beneficial, essential for nutrient recycling, producing oxygen, and aiding digestion.
  • Types of microorganisms: Eubacteria, Archaea, Fungi, Viruses, and Protozoa.
Eubacteria
  • Simple, single-celled prokaryotes with genetic material not enclosed in a nuclear membrane.
  • Classified by shape: Cocci (spherical), Bacilli (rod-shaped), and Spirochaetes (spiral).
  • Also classified by cell wall composition using Gram staining: Gram-positive (purple) and Gram-negative (red).
Archaea
  • Extremophiles that thrive in extreme conditions (high temperatures, salinity, or pH).
  • Used in commercial applications, including enzymes in detergents and converting cornstarch to dextrin.
Fungi
  • Eukaryotic organisms with cells having a distinct nucleus.
  • Can be unicellular (yeasts) or multicellular (molds).
  • Obtain nourishment by absorbing organic materials from their environment.
  • Decomposers and recyclers, but also cause diseases.
Protozoa
  • Unicellular eukaryotic microorganisms that are either free-living or parasitic.
  • Classified by motility (flagella, cilia, or pseudopodia).
  • Can cause diseases like malaria, amoebiasis, and trypanosomiasis; beneficial by improving water quality.
Viruses
  • Small parasitic particles that replicate within host cells.
  • Contain either DNA or RNA and a protein coat (capsid).
  • Cause diseases and range in size from 20-250nm.

Energy Transformation

Energy
  • All living things require energy for life processes.
  • Cells convert energy from one form to another via metabolism, organized into metabolic pathways.
Carbohydrates
  • Classified into monosaccharides, oligosaccharides, and polysaccharides.
  • Monosaccharides (simple sugars): cannot be broken down into smaller carbohydrates.
  • Disaccharides consist of two monosaccharide units linked by a glycosidic bond.
  • Polysaccharides: are long polymers of monosaccharides.
Lipids
  • Contain carbon, hydrogen, and oxygen -- with less oxygen than in carbohydrates, are and are soluble in organic solvents but not in water.
  • Used for energy storage, cell membrane components, insulation, and hormone production.
  • Classified as simple, compound, or derived lipids.
Cellular Metabolism
  • Chemical reactions that transform energy in cells, organized into metabolic pathways.
  • Metabolism categorized into anabolism (synthesis) and catabolism (degradation).
Photosynthesis
  • Process by which plants, algae, and some microbes convert solar energy into chemical energy.
  • Occurs in two stages: light-dependent and light-independent reactions (Calvin cycle).
  • C3, C4, and CAM plants use different carbon fixation pathways.
Cellular Respiration
  • Metabolic pathways that extract energy from glucose and convert it into ATP.
  • Stages include glycolysis, pyruvate oxidation, Krebs cycle, and electron transport chain.
  • Can be aerobic (with oxygen) or anaerobic (fermentation).
Fermentation
  • Anaerobic pathway that regenerates NAD+NAD+ from NADH, allowing glycolysis to continue.
  • Types include alcohol fermentation and lactic acid fermentation.

Evolution

Theories of the Origin of Life
  • Evolution: Gradual genetic change in a population over generations.
  • Special Creationism: Life was divinely created.
  • Spontaneous Generation: Life arises from non-living objects (disproved).
    • Eternity of Life: Claims there is no beginning and no end to life on Earth. Cosmozoan Theory: Life originated from cosmos through resistant spores. Biochemical Origin: Life evolved abiogenically through biochemical reactions.
Theories of Evolution
  • Lamarckism: Inheritance of acquired characteristics (disproved).
  • Darwinism: Evolution through natural selection; survival of the fittest.
  • Neo-Darwinism: Combines Darwin's theory with genetics.
Evidence for Evolution
  • Comparative Anatomy: Homologous structures (shared ancestry) vs. analogous structures (convergent evolution).
  • Embryology: Similarities in early development suggest common ancestry.
  • Palaeontology: Fossils provide a record of past life and evolutionary changes.
  • Biochemistry: Similarities in DNA and proteins indicate evolutionary relationships.
Mechanisms of Evolution
  • Natural Selection: Traits that enhance survival become more common.
  • Types of Selection: Directional, stabilizing, and disruptive.
  • Genetic Drift: Random changes in allele frequencies.
  • Bottleneck Effect: Population size reduction leads to loss of genetic diversity.
  • Founder Effect: Small group establishes a new colony.
  • Gene Flow: Movement of genes between populations altering allele frequencies.
  • Causes of Species Extinction: Natural disasters & anthropogenic effects.
Human Evolution
  • Humans (Homo sapiens) are distinct from other primates.
  • Modern humans have large brain and bipedalism.
  • Fossil discoveries in Ethiopia (e.g., Lucy, Ardi) have been key to study human evolution.
  • Focus on the importance of specific finds, Ardi vs Australopithecus.

Human Body System

Nervous System
  • Definition: Rapid, coordinated response system.
  • Types: Central Nervous System (CNS), Peripheral Nervous System (PNS).
  • Central Nervous System (CNS): Brain and spinal cord.
    -The brain: is a delicate mass of nervous tissue, protected by membrane inside of the skull in a space known as cranium. is the spinal cord
  • Peripheral Nervous System (PNS): Somatic (voluntary) and Autonomic (involuntary).
    -The neurons: are connected together in Neural Junctions(Synapses).
  • Neuron Structure: Cell body, axon, and dendrites.
  • Neurons: classified as Sensory (affector)or Motor (effector)Neurons including Interneurons.
    Nerve impulse and transmission: depend on action porential of a cell
  • Drug Abuse: Affects nervous system and causes addiction and mental changes.
Sense Organs
  • Skin: Provides touch, temperature, pain senses; protects against water loss, etc. Has epidermis, dermis, and hypodermis tissues.
  • Tongue: Contains taste buds for sweet, sour, bitter, salty, and umami.
  • Nose: Olfactory receptors detect smells for food identification and warnings.
    Eyes: Detect visual stimuli; includes cornea, iris, lens, retina. The Lens: are flexibale disk that help focus light on the retina.The iris functions to control the diammeter of the pupil. Rods are cells in the retina respond to light and cones are cells in the retina function bright light with color
    Ears: are specialized for hearing and balance; include outer, middle, and inner ear.
  • Side effects of drugs: Harmful for the normal operation of the nervous systems of the sense of organs.
    Endocrine System: Glands secrete hormones directly into the bloodstream. hormones interact with nervous system to coordinate body activities. Examples: Pineal gland,Testisis.
    Exocrine glands: secrete hormones outside. Examples: Sweat glands, Salivary glands