π What is Biology?
Biology is the scientific study of life and living organisms. It explores everything from the smallest molecules inside cells to the vast ecosystems covering our planet. Understanding biology helps us comprehend how organisms grow, function, reproduce, and interact with their environment.
Why Study Biology?
- Medicine & Health: Understanding diseases, treatments, and human body systems
- Environment: Conservation, climate change, and ecosystem management
- Biotechnology: Genetic engineering, pharmaceuticals, and agriculture
- Everyday Life: Nutrition, fitness, and understanding your own body
π― Key Concepts
Characteristics of Life
All living things share these fundamental characteristics:
The 8 Characteristics of Life
- Organization: Made of one or more cells
- Metabolism: Chemical reactions to obtain and use energy
- Homeostasis: Maintaining stable internal conditions
- Growth: Increase in size and/or cell number
- Reproduction: Producing offspring
- Response: Reacting to environmental stimuli
- Adaptation: Evolving over generations
- Movement: Internal or external motion
Levels of Biological Organization
π¬ Cell Biology
Cell Theory
- All living things are made of one or more cells
- The cell is the basic unit of life
- All cells come from pre-existing cells
Prokaryotic vs Eukaryotic Cells
| Feature | Prokaryotic | Eukaryotic |
|---|---|---|
| Nucleus | No (nucleoid region) | Yes (membrane-bound) |
| Size | 1-10 ΞΌm | 10-100 ΞΌm |
| Organelles | No membrane-bound | Membrane-bound present |
| DNA | Circular, in cytoplasm | Linear, in nucleus |
| Examples | Bacteria, Archaea | Animals, Plants, Fungi |
Key Organelles
| Organelle | Function | Found In |
|---|---|---|
| Nucleus | Contains DNA, controls cell activities | Eukaryotes |
| Mitochondria | Cellular respiration, produces ATP | Eukaryotes |
| Chloroplast | Photosynthesis | Plants, Algae |
| Ribosome | Protein synthesis | All cells |
| ER (Rough) | Protein processing & transport | Eukaryotes |
| ER (Smooth) | Lipid synthesis, detoxification | Eukaryotes |
| Golgi Apparatus | Modifies, packages, ships proteins | Eukaryotes |
| Lysosome | Digestion, waste breakdown | Animal cells |
| Vacuole | Storage, maintains turgor pressure | Plants (large central) |
| Cell Wall | Structural support, protection | Plants, Bacteria, Fungi |
Photosynthesis vs Cellular Respiration
6COβ + 6HβO + Light Energy β CβHββOβ + 6Oβ
Plants convert carbon dioxide and water into glucose and oxygen using sunlight.
CβHββOβ + 6Oβ β 6COβ + 6HβO + ATP Energy
Cells break down glucose with oxygen to release energy (ATP).
Photosynthesis and cellular respiration are opposite reactions! What one produces, the other uses.
𧬠Genetics
DNA Structure
The Double Helix
- Sugar-phosphate backbone: Deoxyribose sugar + phosphate groups
- Nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
- Base pairing: A pairs with T, G pairs with C (complementary)
- Hydrogen bonds: A-T has 2 bonds, G-C has 3 bonds
From DNA to Protein
Key Terms
- Replication: DNA makes a copy of itself
- Transcription: DNA β mRNA (occurs in nucleus)
- Translation: mRNA β Protein (occurs at ribosomes)
- Codon: 3-letter mRNA code for one amino acid
- Gene: Segment of DNA that codes for a protein
Mendelian Genetics
Key Vocabulary
- Allele: Different versions of a gene
- Dominant: Allele expressed when present (capital letter, e.g., B)
- Recessive: Allele only expressed when homozygous (lowercase, e.g., b)
- Genotype: Genetic makeup (BB, Bb, or bb)
- Phenotype: Physical expression (what you see)
- Homozygous: Two identical alleles (BB or bb)
- Heterozygous: Two different alleles (Bb)
Cross: Bb Γ Bb (both parents heterozygous)
| B | b | |
| B | BB | Bb |
| b | Bb | bb |
Result: 1 BB : 2 Bb : 1 bb (genotypic ratio 1:2:1)
Phenotype: 3 dominant : 1 recessive (phenotypic ratio 3:1)
Evolution & Natural Selection
Darwin's Four Principles
- Variation: Individuals in a population have different traits
- Inheritance: Traits are passed from parents to offspring
- Selection: Some traits improve survival and reproduction
- Time: Over generations, favorable traits become more common
βοΈ Practice Questions
Answer: UACGGU
Answer: 50% will be short
Together they maintain the carbon and oxygen cycles essential for life!
π‘ Tips & Tricks
Think of a cell like a city: Nucleus = City Hall, Mitochondria = Power Plants, Ribosomes = Factories, Cell Membrane = City Walls
Biology is visual! Sketch cells, DNA, food webs, and cycles. Drawing helps cement concepts in memory.
Biology topics are interconnected. DNA β Genes β Proteins β Traits β Evolution. Understanding relationships makes learning easier.
Always label parents clearly, use capital for dominant/lowercase for recessive, and double-check your work!
Kingdom β Phylum β Class β Order β Family β Genus β Species
β οΈ Common Mistakes to Avoid
DNA has Thymine (T), RNA has Uracil (U). DNA is double-stranded, RNA is single-stranded. DNA stays in nucleus, mRNA travels out.
Dominant doesn't mean "more common" or "better." It just means the trait is expressed when at least one allele is present.
Mitosis: Body cells, 2 identical daughter cells, same chromosome number
Meiosis: Sex cells, 4 different daughter cells, half the chromosomes
Plant cells have cell walls, chloroplasts, and large central vacuoles. Animal cells do NOT have these!
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