Published by Patrick Mutisya · 14 days ago
Recognise organelles and other cell structures found in eukaryotic cells and outline their structures and functions.
| Organelle / Structure | Structure | Primary Function(s) |
|---|---|---|
| Cell surface membrane | Phospholipid bilayer with embedded proteins; fluid‑mosaic model. | Regulates passage of substances, cell‑cell communication, maintains cell shape. |
| Nucleus | Large spherical organelle surrounded by a double nuclear envelope; contains nucleoplasm, chromatin and a nucleolus. | Stores genetic material (DNA); coordinates gene expression and cell activities. |
| Nuclear envelope | Two concentric lipid bilayers perforated by nuclear pores. | Controls traffic of molecules between nucleus and cytoplasm. |
| Nucleolus | Dense, non‑membranous region within the nucleus. | Site of ribosomal RNA (rRNA) synthesis and ribosome assembly. |
| Rough endoplasmic reticulum (RER) | Network of flattened sacs studded with ribosomes on the cytoplasmic face. | Synthesises membrane‑bound and secretory proteins; initiates protein folding. |
| Smooth endoplasmic reticulum (SER) | Tubular network lacking ribosomes. | Lipid synthesis, detoxification of drugs and toxins, calcium ion storage. |
| Golgi body (Golgi apparatus) | Stacked, flattened membrane‑bound cisternae with a cis (receiving) and trans (shipping) face. | Modifies, sorts and packages proteins and lipids for secretion or delivery to other organelles. |
| Mitochondrion | Elongated organelle with a double membrane; inner membrane folded into cristae; contains its own small circular DNA. | Site of aerobic respiration; produces ATP via oxidative phosphorylation. |
| Ribosome (80S cytoplasmic, 70S organellar) | Complex of rRNA and proteins; 80S in cytoplasm (eukaryotic), 70S in chloroplasts and mitochondria (prokaryote‑like). | Protein synthesis according to mRNA template. |
| Lysosome | Membrane‑bound vesicle containing hydrolytic enzymes (acidic pH). | Digest macromolecules, old organelles (autophagy) and foreign material. |
| Centrioles and microtubules | Pair of orthogonal barrel‑shaped centrioles; radiating microtubules form the spindle apparatus. | Organise mitotic spindle; assist in cytokinesis and cell movement. |
| Cilia | Hair‑like projections of the plasma membrane containing a core of microtubules (9+2 arrangement). | Move fluid or the cell itself; sensory functions in some cells. |
| Microvilli | Finger‑like extensions of the plasma membrane supported by a core of actin filaments. | Increase surface area for absorption and secretion (e.g., intestinal epithelium). |
| Chloroplast | Double‑membrane organelle with internal thylakoid stacks (grana) and stroma; contains its own small circular DNA. | Site of photosynthesis; converts light energy to chemical energy (glucose). |
| Cell wall (plant) | Rigid layer external to the plasma membrane, mainly cellulose fibres embedded in a matrix of pectins. | Provides structural support, protection and determines cell shape. |
| Plasmodesmata | Microscopic channels traversing the cell wall, linking cytoplasm of adjacent plant cells. | Facilitate intercellular transport of water, nutrients and signalling molecules. |
| Large permanent vacuole (plant) | Membrane‑bound sac (tonoplast) occupying up to 90 % of cell volume. | Stores water, ions, metabolites; maintains turgor pressure; contributes to cell growth. |
| Tonoplast | Vacuolar membrane rich in transport proteins. | Regulates movement of solutes into and out of the vacuole; essential for turgor maintenance. |