01Two kinds of cells
Prokaryotes (bacteria, archaea) have no nucleus and no membrane-bound organelles. Their DNA sits in a region called the nucleoid. Eukaryotes (plants, animals, fungi, protists) wrap their DNA in a nucleus and divide the cell into membrane-bound compartments.
Both kinds share four things: a plasma membrane, cytoplasm, ribosomes, and DNA. If an exam asks what ALL cells have, those are the answer.
02The parts and what they do
Ribosomes — made of rRNA and protein, they build proteins. Free ribosomes make proteins used in the cytosol; ribosomes bound to the rough ER make proteins that will be secreted or placed in membranes.
Endoplasmic reticulum — the rough ER (studded with ribosomes) folds and modifies proteins; the smooth ER makes lipids, detoxifies drugs, and stores calcium.
Golgi complex — receives vesicles from the ER, modifies proteins (for example, adding sugar tags), sorts them and ships them out in new vesicles.
Mitochondria — the site of aerobic respiration, making most of the cell's ATP. Chloroplasts (plants/algae) carry out photosynthesis.
Lysosomes — sacs of digestive enzymes that break down worn-out parts and engulfed material. Vacuoles store water and materials; the plant central vacuole keeps the cell firm (turgor).
03Notebook box
Protein secretion pathway: nucleus (mRNA) → rough ER ribosome → ER lumen (folding) → transport vesicle → Golgi (modify, sort) → secretory vesicle → plasma membrane (exocytosis).
Worked example: A cell makes huge amounts of digestive enzymes to export. Which organelles will be unusually abundant? → Rough ER and Golgi, because secreted proteins are built on bound ribosomes and packaged by the Golgi.