Biology Final 🧬

🌿Photosynthesis

Purpose: Plants make their own food (glucose) using sunlight, water, and carbon dioxide.

🌞Light-Dependent Reactions

• Where: Thylakoid membranes in chloroplasts

• Needs: Sunlight and water

• What happens:

  • Sunlight hits chlorophyll → excites electrons

  • Water splits (H₂O → H⁺ + e⁻ + O₂)

  • Energy is stored in ATP and NADPH

  • Oxygen is released as a byproduct

🍃Light-Independent Reactions (Calvin Cycle)

• Where: Stroma (fluid part of chloroplast)

• Needs: ATP + NADPH + CO₂

• What happens:

  • Carbon dioxide is “fixed” into a sugar

  • Uses energy from ATP and NADPH to build glucose (C₆H₁₂O₆)

🔋Cellular Respiration

Purpose: Converts glucose into ATP (energy cells can use)

🔷1. Glycolysis

(anaerobic, happens in all cells)

• Where: Cytoplasm

• Breaks down glucose (6C) into 2 pyruvate (3C)

• Net gain: 2 ATP + 2 NADH

🔷2. Krebs Cycle

(aerobic, in mitochondria)

• Pyruvate → broken down fully into CO₂

• Produces: 2 ATP, NADH, and FADH₂

• NADH and FADH₂ carry electrons to next step

🔷3. Electron Transport Chain (ETC)

• Where: Inner mitochondrial membrane

• Uses oxygen to pull electrons through proteins

• Makes ~32 ATP

• Oxygen is final electron acceptor → makes water

⚡Aerobic Respiration (with oxygen):

• Glycolysis → Krebs → ETC

• Total ATP: ~36 per glucose

🚫Anaerobic Respiration (without oxygen):

• Glycolysis + Fermentation

• Lactic acid fermentation (in muscles): Pyruvate → Lactic acid

• Alcoholic fermentation (in yeast): Pyruvate → Alcohol + CO₂

• Only makes 2 ATP

🧫 Cell Organelles

🚪 Cell Membrane Transport

🟢 Passive Transport (No energy needed)

• Diffusion: Particles move high → low concentration

• Osmosis: Water moves through a membrane from high to low

• Facilitated Diffusion: Uses protein channels to help bigger molecules (like glucose) pass through

🔴 Active Transport (Requires energy)

• Moves substances against the gradient (low → high)

• Uses ATP and protein pumps

• Endocytosis: Cell engulfs material (enters the cell)

• Phagocytosis: “Eating” solids

• Pinocytosis: “Drinking” liquids

• Exocytosis: Cell expels materials (exits the cell)

🧬 DNA & RNA

DNA:

• Double helix

• Bases: A-T, C-G

• Sugar: Deoxyribose

• Cannot leave nucleus

RNA:

• Single strand

• Bases: A-U (Uracil), C-G

• Sugar: Ribose

• Can leave nucleus

🧪 Protein Synthesis

🧾 1. Transcription (in nucleus)

• DNA → mRNA

• Enzyme RNA polymerase unzips DNA and builds mRNA

• mRNA is a copy of the gene

🔧 2. Translation (in ribosome)

• mRNA → Protein

• mRNA codons are read (3 bases = 1 amino acid)

• tRNA brings the correct amino acids

• Each tRNA has an anticodon that matches the mRNA codon

🧰 Important Enzymes:

• Helicase: Unzips DNA strands during replication

• DNA Polymerase: Adds new bases during replication

• Ligase: Seals DNA strands (like glue)

• RNA Polymerase: Builds mRNA during transcription

🔁 Mitosis

Purpose: Make two identical cells (for growth/repair)

Stages:

1. Prophase: Chromosomes appear, nucleus dissolves

2. Metaphase: Chromosomes line up in the middle

3. Anaphase: Sister chromatids pulled apart

4. Telophase: Nuclei reform

5. Cytokinesis: Cell splits into 2

🦎 Natural Selection

• Organisms with advantageous traits survive and reproduce more

• Over time, helpful traits become more common

• Example: Peppered moths during the Industrial Revolution

🧬 Mechanisms of Microevolution

1. Mutation: New traits from DNA changes

2. Gene Flow: Genes move between populations

3. Genetic Drift: Random changes in small populations

4. Natural Selection: Best traits survive

5. Non-random Mating: Traits selected by mates

📚 Evidence of Evolution

• Fossils: Show changes over time

• Homologous Structures: Same structure, different function (like arm bones in humans, cats, whales)

• DNA similarities: Show common ancestry

• Embryos: Similar early development

• Biogeography: Species’ locations match patterns of evolution

🌳 Phylogenetics

• Study of evolutionary relationships

• Phylogenetic trees show who’s related

• Branch points = common ancestors

• Closer branches = more related

👥 Population Ecology

• Study of populations (same species in an area)

• Key terms:

• Carrying Capacity: Max number environment can support

• Limiting factors: Food, water, space, disease

• Growth rate: How fast population grows

• Exponential growth: Fast, J-shaped curve

• Logistic growth: Growth slows as it reaches carrying capacity

🌎 Community Ecology

• Interactions between different species:

• Predation: One eats another

• Competition: Both want same resource

• Mutualism: Both benefit

• Commensalism: One benefits, other unaffected

• Parasitism: One benefits, other harmed

🔗 Food Chains and Food Webs

• Food chain: Simple flow (e.g. grass → rabbit → fox)

• Food web: Complex network of all food chains

Trophic Levels:

1. Producers (plants)

2. Primary consumers (herbivores)

3. Secondary consumers (eat herbivores)

4. Tertiary consumers (top predators)

• Only 10% of energy passes to the next level; rest is lost as heat.