TEAS Ready🧬 Science · Biology · Lesson 1 of 7 · 5 min
Cell structure and organelles
🔬 Every patient you will ever care for is tens of trillions of cells working together. Knowing what each part of a cell does makes the rest of biology click.
💡 Key idea
Nucleus = DNA control center, ribosomes = protein builders, mitochondria = ATP, and only plant cells have a cell wall, chloroplasts and a large central vacuole.
🧠 The idea
All living things are made of cells. PROKARYOTES (bacteria and archaea) are small and have no nucleus and no membrane-bound organelles; their DNA sits in a region called the nucleoid. EUKARYOTES (animals, plants, fungi, protists) keep their DNA inside a NUCLEUS and have ORGANELLES. The cell membrane controls what enters and leaves. Ribosomes build proteins (prokaryotes have them too). The rough endoplasmic reticulum is studded with ribosomes and makes proteins for export; the smooth ER makes lipids and detoxifies. The Golgi apparatus modifies, sorts and packages proteins. MITOCHONDRIA make most of the cell's ATP through cellular respiration. Lysosomes digest worn-out parts and debris. Plant cells add a cell wall made of cellulose, chloroplasts for photosynthesis, and a large central vacuole; animal cells have centrioles and no cell wall.
✏️ Worked example
A microscope slide shows a cell with a rigid outer wall, ribosomes and no nucleus. Step 1: no nucleus means prokaryote, so it cannot be a plant cell even though it has a wall. Step 2: a wall plus ribosomes without a nucleus fits a bacterium. Step 3: a second cell has a wall, a nucleus and chloroplasts, so it is a plant cell. Sort by the nucleus first, then by wall and chloroplasts.
📌 Takeaways
- Prokaryotes: no nucleus, no membrane-bound organelles, but they do have ribosomes.
- Rough ER makes proteins, Golgi packages them, lysosomes digest, mitochondria make ATP.
- Plant cells add a cellulose cell wall, chloroplasts and a large central vacuole.
📖 Terms in this lesson
Organelle: A specialized structure inside a cell that performs a specific job; for example, mitochondria release energy from food molecules.
✅ Check yourself
Question 1 of 3
Which organelle produces most of the ATP in a human muscle cell?
- Golgi apparatus
- Mitochondrion
- Lysosome
- Smooth endoplasmic reticulum
Show the answer and rationale
Answer: B
Mitochondria carry out aerobic cellular respiration and make most of the cell's ATP. The Golgi apparatus packages proteins, lysosomes digest material, and smooth ER makes lipids; none of them is the main ATP source.
Question 2 of 3
Which structure is found in BOTH prokaryotic and eukaryotic cells?
- Ribosomes
- Golgi apparatus
- Mitochondria
- Nucleus
Show the answer and rationale
Answer: A
Ribosomes build proteins in every cell, so both prokaryotes and eukaryotes have them. A nucleus, mitochondria and a Golgi apparatus are membrane-bound structures found only in eukaryotes.
Question 3 of 3
A cell has a cell wall, chloroplasts and a large central vacuole. What kind of cell is it most likely?
- A virus
- A red blood cell
- A plant cell
- An animal cell
Show the answer and rationale
Answer: C
A cell wall, chloroplasts and a large central vacuole together identify a plant cell. Animal cells, including red blood cells, lack all three, and a virus is not a cell at all.
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