Cell Structure and Organization
Easy Overview
Your body has around 37 trillion cells. This chapter is about what each one of those tiny units looks like inside. It's like zooming into a city — every organelle has a job, and nothing's there by accident.
Cell Theory
Three big ideas: (1) All living things are made of cells. (2) The cell is the basic unit of life. (3) All cells come from pre-existing cells. That's it. This theory is the foundation of all biology. Credit goes to Schleiden, Schwann, and Virchow.
Prokaryotic vs. Eukaryotic Cells
Prokaryotes (bacteria) have no nucleus — their DNA just floats around. Eukaryotes (plants, animals, fungi) have a proper nucleus. Think of a prokaryote as a studio apartment — everything in one room. A eukaryote is a house with separate rooms for different jobs.
Cell Membrane and Cell Wall
The cell membrane is a flexible outer layer that controls what goes in and out. It's selectively permeable — not everything gets through. Plant cells have an extra layer outside: the cell wall. It's rigid and gives them structure. That's why plants don't flop over.
Cytoplasm and Organelles
Cytoplasm is the jelly-like stuff filling the cell. Floating in it are organelles — tiny structures with specific jobs. Mitochondria make energy. Ribosomes make proteins. The ER is like the cell's factory floor. Golgi body packages things up. It's a whole economy in there.
Nucleus — The Brain
The nucleus is the control center. It holds DNA — the instructions for everything. It's surrounded by a nuclear membrane with pores. Inside is the nucleolus where ribosomes are made. No nucleus in prokaryotes — their DNA just hangs out in the nucleoid region.
Mitochondria and Chloroplasts
Mitochondria are the powerhouses — they burn glucose to make ATP (energy). Chloroplasts are found in plants and do photosynthesis. Both have their own DNA and double membranes. Scientists think they were once independent bacteria that got swallowed by bigger cells.
Key Points
- •Cell theory: all living things made of cells, cell is basic unit, cells come from cells.
- •Prokaryotes have no nucleus; eukaryotes have a membrane-bound nucleus.
- •Cell membrane is selectively permeable; cell wall provides structural support.
- •Cytoplasm contains organelles — each with a specific function.
- •Nucleus contains DNA and controls cell activities.
- •Mitochondria produce ATP (energy); chloroplasts do photosynthesis.
- •Ribosomes make proteins; ER modifies and transports them.
- •Golgi body packages and ships proteins out of the cell.
Practice Questions
- State the cell theory. Who proposed it?
- Differentiate between prokaryotic and eukaryotic cells.
- Draw a labeled diagram of a plant cell.
- What is the function of mitochondria? Why are they called the powerhouse of the cell?
- Explain the structure and function of the nucleus.