Cell: The Unit of Life - Cell organelles (Mitochondria, Ribosomes, Golgi bodies, etc.)

Mitochondria: Known as the 'powerhouse of the cell', these are double membrane-bound organelles. The inner membrane forms numerous infoldings called cristae to increase the surface area for $ATP$ (Adenosine Triphosphate) production through aerobic respiration.

Ribosomes: Granular structures composed of ribonucleic acid ($rRNA$) and proteins. Eukaryotic ribosomes are $80S$ (subunits $60S$ and $40S$), while prokaryotic and organellar ribosomes are $70S$ (subunits $50S$ and $30S$). The 'S' stands for Svedberg's Unit (sedimentation coefficient).

Golgi Apparatus: Consists of flat, disc-shaped sacs or cisternae. It has a distinct polarity with a convex $cis$ (forming) face and a concave $trans$ (maturing) face. It is the primary site for the formation of glycoproteins and glycolipids.

Endoplasmic Reticulum (ER): A network of tiny tubular structures. Rough ER ($RER$) bears ribosomes on its surface and is involved in protein synthesis and secretion. Smooth ER ($SER$) lacks ribosomes and is the major site for lipid synthesis and detoxification.

Lysosomes: Membrane-bound vesicular structures formed by the Golgi apparatus. They are rich in hydrolytic enzymes (hydrolases - lipases, proteases, carbohydrases) which are optimally active at an acidic $pH$.

Plastids: Found in all plant cells. Chloroplasts contain chlorophyll and carotenoids which trap light energy for photosynthesis. The matrix is called the stroma, containing flattened sacs called thylakoids, which stack to form grana.

Vacuoles: Membrane-bound space found in the cytoplasm, bound by a single membrane called the tonoplast. In plant cells, it can occupy up to $90\%$ of the volume and maintains turgor pressure.