Definition
Nucleus: control centre, holds chromatin/chromosomes (DNA); the nucleolus inside it assembles ribosomes.
Ribosomes: protein synthesis — free in the cytoplasm or attached to rough endoplasmic reticulum.
Endoplasmic reticulum (ER): rough ER (ribosomes attached) makes proteins; smooth ER makes lipids and detoxifies harmful substances.
Golgi complex: packages and modifies proteins from the ER before they're sent to their destination.
Lysosome: contains digestive enzymes that break down waste, worn-out organelles and lipids.
Mitochondrion: site of cellular respiration (energy production); its folded inner membrane (cristae) increases surface area for this. It can divide on its own.
Chloroplast: site of photosynthesis in plant cells.
Remember
If lysosomal enzymes stop working, waste and damaged parts build up inside the cell instead of being broken down — this is exactly the kind of failure behind certain genetic "storage" diseases.
Definition
The fluid mosaic model describes the cell membrane as a flexible double layer of phospholipids with proteins floating and moving within it, like objects scattered in a fluid — controlling what enters and leaves the cell.
The cell wall (in plant cells, not animal cells) is a rigid layer outside the membrane, giving the cell shape and support.
Remember
Turgor pressure develops when a plant cell's large central vacuole fills with water, pushing the cell contents against the rigid cell wall — this is what keeps a healthy plant firm rather than wilting.
Rule
Plant cells have: a cell wall, chloroplasts, and one large central vacuole.
Animal cells have: a centriole (helps with cell division) and typically several small vacuoles instead of one large one — and no cell wall or chloroplasts.
In a multicellular organism, different cells specialize for different jobs (a nerve cell sends signals, a leaf cell photosynthesizes) rather than every cell doing everything — this division of labour makes the whole organism more efficient, the same principle as specialists dividing work in a workplace.
Quick Recap
- ●Nucleus: control + DNA. Ribosomes: protein synthesis. Rough ER: protein-making. Smooth ER: lipids + detox
- ●Golgi: packages/modifies proteins. Lysosome: digests waste. Mitochondrion: respiration/energy. Chloroplast: photosynthesis
- ●Fluid mosaic model: membrane = flexible phospholipid bilayer with floating proteins
- ●Plant cells: cell wall, chloroplast, one big vacuole. Animal cells: centriole, small vacuoles, no wall/chloroplast
- ●Cell specialization = division of labour among a multicellular organism's cells
