Biology 8th Guide: 300 Simplified Terms and Energy Processes

Scientific Method & Characteristics of Life

• Observation: Using senses to gather information.

• Hypothesis: An educated guess that can be tested.

• Experiment: A test to check if the hypothesis is correct.

• Independent Variable: The factor you change in an experiment.

• Dependent Variable: What you measure in the experiment.

• Control Group: The group that doesn’t get the experimental treatment.

• Constants: Things kept the same for all groups.

• Theory: A well-tested explanation.

• Biology: The study of life.

• Organism: Any living thing.

• Cell: Basic unit of life.

• Homeostasis: Keeping internal conditions stable.

• Metabolism: All chemical reactions in an organism.

• Reproduction: Making more of the same organism.

• Growth: Getting bigger or more cells.

• Development: Changes that happen as an organism matures.

• Response to Stimuli: Reacting to the environment.

• Adaptation: Inherited trait that helps survival.

• Evolution: Change in species over time.

Biochemistry

• Atom: Basic unit of matter.

• Element: Substance made of one type of atom.

• Molecule: Group of atoms bonded together.

• Compound: A substance made from different elements.

• Covalent Bond: Atoms share electrons.

• Ionic Bond: Electrons are transferred between atoms.

• Water (H2O): Most important molecule for life.

• Polarity: Molecule has a positive and negative end.

• Hydrogen Bond: Weak bond between water molecules.

• Cohesion: Water sticks to water.

• Adhesion: Water sticks to other things.

• Solvent: A substance that dissolves other substances.

• pH Scale: Measures acidity (0-14).

• Acid: Below 7 on pH scale.

• Base: Above 7 on pH scale.

• Buffer: Keeps pH stable.

• Organic Molecule: Has carbon and hydrogen.

• Macromolecule: Big molecules like carbs, proteins, lipids, nucleic acids.

• Carbohydrate: Main energy source (sugars, starch).

• Monosaccharide: Simple sugar (glucose).

• Polysaccharide: Complex sugar (starch, cellulose).

• Lipid: Fats and oils; store energy.

• Fatty Acid: Building block of lipids.

• Protein: Made of amino acids; build structures and enzymes.

• Amino Acid: Building block of proteins.

• Enzyme: Speeds up chemical reactions.

• Substrate: What an enzyme acts on.

• Nucleic Acid: DNA and RNA.

• Nucleotide: Building block of DNA/RNA.

Cells

• Cell Theory: All living things are made of cells.

• Prokaryote: Simple cells without nucleus (bacteria).

• Eukaryote: Cells with nucleus (plants, animals).

• Nucleus: Holds DNA in eukaryotic cells.

• Cytoplasm: Gel inside the cell.

• Cell Membrane: Controls what goes in/out of the cell.

• Cell Wall: Rigid outer layer in plants/bacteria.

• Ribosome: Makes proteins.

• Endoplasmic Reticulum (ER): Moves materials in cell.

• Golgi Apparatus: Packages and ships proteins.

• Mitochondria: Makes energy (ATP).

• Chloroplast: Where photosynthesis happens (plants).

• Vacuole: Stores stuff (big in plant cells).

• Lysosome: Breaks down waste.

• Cilia/Flagella: Help cells move.

• Cytoskeleton: Gives shape/support to cell.

• Peroxisome: Breaks down fats and toxins.

Cell Transport

• Diffusion: Movement from high to low concentration.

• Osmosis: Water moving across membrane.

• Passive Transport: No energy needed.

• Active Transport: Needs energy (ATP).

• Endocytosis: Cell takes in materials.

• Exocytosis: Cell releases materials.

• Isotonic: Same solute concentration inside and out.

• Hypotonic: Lower solute outside; cell swells.

• Hypertonic: Higher solute outside; cell shrinks.

Photosynthesis & Respiration

• Photosynthesis: Plants use sunlight to make food.

• Chlorophyll: Green pigment in chloroplasts.

• Light Reaction: First part of photosynthesis.

• Calvin Cycle: Second part of photosynthesis.

• Cellular Respiration: Breaks down food for energy.

• Glycolysis: First step; happens in cytoplasm.

• Krebs Cycle: Second step; makes CO2.

• Electron Transport Chain (ETC): Final step; makes most ATP.

• ATP: Energy molecule.

• Anaerobic: No oxygen needed.

• Aerobic: Needs oxygen.

• Fermentation: Makes energy without oxygen.

Cell Division & Genetics

• Mitosis: Cell division for growth/repair.

• Meiosis: Makes sex cells (sperm, egg).

• Chromosome: DNA wrapped up.

• Gene: Section of DNA with instructions.

• DNA: Holds genetic info.

• RNA: Helps make proteins.

• Replication: Copying DNA.

• Transcription: DNA to RNA.

• Translation: RNA to protein.

• Mutation: Change in DNA.

• Allele: Different versions of a gene.

• Genotype: Genetic makeup.

• Phenotype: Physical traits.

• Homozygous: Same alleles.

• Heterozygous: Different alleles.

• Dominant: Shows up if present.

• Recessive: Hidden if dominant is present.

• Punnett Square: Shows possible gene combinations.

• Gregor Mendel: Father of genetics.

Ecology

• Ecology: Study of interactions between organisms and environment.

• Ecosystem: All living and nonliving things in an area.

• Biotic: Living things.

• Abiotic: Nonliving things.

• Producer: Makes own food (plants).

• Consumer: Eats other organisms.

• Herbivore: Eats plants.

• Carnivore: Eats animals.

• Omnivore: Eats plants and animals.

• Decomposer: Breaks down dead stuff.

• Food Chain: Steps in energy transfer.

• Food Web: All connected food chains.

• Trophic Level: Energy level in food chain.

• Energy Pyramid: Shows energy loss in food chain.

• Habitat: Where an organism lives.

• Niche: Role in ecosystem.

• Population: Same species in an area.

• Community: All organisms in an area.

• Biodiversity: Variety of life.

• Carrying Capacity: Max number of organisms an area can support.

• Limiting Factor: Stops population growth.

• Symbiosis: Relationship between species.

• Mutualism: Both benefit.

• Parasitism: One benefits, one harmed.

• Commensalism: One benefits, one unaffected.

Evolution

• Natural Selection: Best traits survive and reproduce.

• Charles Darwin: Came up with natural selection.

• Variation: Differences in traits.

• Adaptation: Helps survival.

• Fossil: Remains of old organisms.

• Speciation: Formation of new species.

• Extinction: Species dies out.

• Homologous Structures: Similar structures, different functions.

• Analogous Structures: Different structures, same function.

• Vestigial Structure: Leftover from evolution.

• Embryology: Study of embryos.

• Genetic Drift: Random changes in genes.

• Gene Flow: Genes move between populations.

• Artificial Selection: Humans choose traits to breed.

Photosynthesis & Cellular Respiration (Detailed Flow Charts, Molecule Counts, and Diagrams)

Photosynthesis (in plants, in chloroplasts):

Overall Reaction: 6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂

Step 1: Light Reactions (Thylakoid Membranes)

• Input: Light + H₂O + ADP + NADP⁺

• Output: O₂ (waste) + ATP + NADPH

• Water is split (photolysis) to release electrons, H⁺, and O₂.

• Electron Transport Chain creates ATP and reduces NADP⁺ → NADPH.

Step 2: Calvin Cycle (Stroma)

• Input: CO₂ + ATP + NADPH

• Output: Glucose (C₆H₁₂O₆) + ADP + NADP⁺

• 6 CO₂ enter; with energy from ATP and NADPH, glucose is produced.

Flow Chart for Photosynthesis:

Light + H₂O → [Light Reactions] → O₂ + ATP + NADPH

CO₂ + ATP + NADPH → [Calvin Cycle] → C₆H₁₂O₆

Cellular Respiration (in all eukaryotes, in mitochondria):

Overall Reaction: C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + ~36-38 ATP

Step 1: Glycolysis (Cytoplasm)

• Input: Glucose (C₆H₁₂O₆)

• Output: 2 Pyruvate + 2 ATP + 2 NADH

• No oxygen required.

Step 2: Krebs Cycle (Mitochondrial Matrix)

• Input: 2 Pyruvate → converted to Acetyl-CoA

• Output (per glucose): 6 CO₂ + 2 ATP + 8 NADH + 2 FADH₂

Step 3: Electron Transport Chain (Inner Mitochondrial Membrane)

• Input: NADH + FADH₂ + O₂

• Output: ~32-34 ATP + H₂O

• Oxygen is the final electron acceptor → forms water.

Flow Chart for Cellular Respiration:

C₆H₁₂O₆ → [Glycolysis] → 2 Pyruvate + 2 ATP + 2 NADH

→ [Krebs Cycle] → 6 CO₂ + 2 ATP + NADH + FADH₂

→ [ETC] + O₂ → H₂O + ~32-34 ATP

Total ATP: ~36-38 per glucose

Anaerobic Respiration (Fermentation):

• Happens when no oxygen is present.

• Produces less ATP (~2 total).

• Lactic Acid Fermentation: Glucose → Lactic Acid + 2 ATP

• Alcoholic Fermentation (yeast): Glucose → Ethanol + CO₂ + 2 ATP

What Are NADH and FADH₂?

• NADH (Nicotinamide adenine dinucleotide): An energy-carrying molecule made during glycolysis and the Krebs cycle. Carries high-energy electrons to the electron transport chain.

• FADH₂ (Flavin adenine dinucleotide): Similar to NADH, it carries electrons from the Krebs cycle to the electron transport chain, but contributes slightly less ATP.