AP Biology 7.7 Common Ancestry Study Notes - New Syllabus Effective 2025
AP Biology 7.7 Common Ancestry Study Notes – New syllabus
AP Biology 7.7 Common Ancestry Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Describe structural and functional evidence on cellular and molecular levels that provides evidence for the common ancestry of all eukaryotes.
Key Concepts:
- Common Ancestry
7.7.A — Structural and Functional Evidence for Common Ancestry in Eukaryotes
🧠 Big Idea:
Even though eukaryotic organisms look different (like plants 🌿, fungi 🍄, and animals 🐒), all eukaryotes share basic cell structures and functions. This shows we all came from a common ancestor long ago.
🔬 Structural Evidence (What the Cells Look Like):
- Membrane-bound organelles: All eukaryotic cells have organelles like the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, etc. These organelles are enclosed in membranes and help the cell do different jobs.
- Linear chromosomes: Eukaryotic DNA is organized into linear (straight) chromosomes, unlike circular chromosomes in bacteria.
- Cytoskeleton: Eukaryotic cells have a cytoskeleton made of microtubules and microfilaments. It helps with shape, movement, and division of the cell.
⚙️ Functional Evidence (How the Cells Work):
- Similar DNA replication and repair systems: All eukaryotes copy their DNA using almost the same enzymes (like DNA polymerase). The way they fix DNA damage is also very similar.
- Similar gene expression (transcription & translation): Eukaryotes all use RNA polymerase, splicing, and ribosomes to make proteins. Even the process of turning genes “on” or “off” is nearly the same.
- Energy-related organelles (mitochondria & chloroplasts): Mitochondria (in all eukaryotes) and chloroplasts (in plants/algae) have their own DNA and double membranes. This supports the endosymbiotic theory: these organelles came from ancient prokaryotes that were “swallowed” and became part of the cell.
🧬 So What Does This Mean?
- These similarities in cell parts and how they function are not random.
- They are inherited from a common ancestor — the original eukaryotic cell that existed billions of years ago.
7.7.A.1 – Structural & Functional Evidence of Common Ancestry in Eukaryotes
🧱 Membrane-Bound Organelles
- Every eukaryotic cell has membrane-wrapped organelles, like:
- Nucleus (holds DNA)
- Mitochondria (makes energy 🔋)
- ER & Golgi (packaging and transport)
- This kind of complex internal structure is not found in prokaryotes – only eukaryotes have it.
- 🧩 So, this feature supports the idea of a shared evolutionary origin among all eukaryotes.
🧬 Linear Chromosomes
- Eukaryotic DNA is arranged in linear (straight) chromosomes, not circular like in bacteria.
- These chromosomes are stored in the nucleus.
- They have special end caps called telomeres to protect them.
- ✅ This structure is common in all eukaryotes, which means it likely evolved once in their common ancestor.
🧩 Genes That Contain Introns
- Eukaryotic genes often have introns – pieces of DNA that are cut out before making proteins.
- Prokaryotic genes usually don’t have introns.
- All eukaryotes do – from amoebas to elephants.
- 🔄 This “splicing” step is part of the complex RNA processing system that all eukaryotes use.
- 📌 Again, this points to a shared origin.
🎯 Summary:
| Feature | Found in All Eukaryotes | Not in Prokaryotes | Shows… |
|---|---|---|---|
| Membrane-bound organelles | ✅ Yes | ❌ No | Common origin |
| Linear chromosomes | ✅ Yes | ❌ No | Shared evolutionary trait |
| Genes with introns | ✅ Yes | ❌ No | Advanced gene processing |