A2.2.11 Drawing and annotation based on electron micrographs Notes

Key Organelles and Cell Structures to Draw and Annotate

1. Nucleus

1. Seen in EM: Spherical or oval, double membrane with pores.
2. Annotation: Contains chromosomes (DNA + histones); site of transcription and mRNA production; controls cell activities.

2. Chromosomes

1. Seen in EM: Dense, darkly staining regions in the nucleus (when condensed).
2. Annotation: Carry genetic information in the form of DNA; become visible during cell division.

3. Mitochondria

1. Seen in EM: Oval, double membrane with inner folded cristae.
2. Annotation: Site of aerobic respiration; generates ATP; contains its own DNA and ribosomes.

4. Chloroplasts (plants only)

1. Seen in EM: Oval, double membrane, thylakoid stacks (grana), stroma.
2. Annotation: Site of photosynthesis; thylakoids for light-dependent reactions; stroma for Calvin cycle; starch grains visible after photosynthesis.

5. Sap Vacuole (plants only)

1. Seen in EM: Large clear space bounded by tonoplast.
2. Annotation: Maintains turgor pressure; stores ions, sugars, pigments, waste products.

6. Rough Endoplasmic Reticulum (rER)

1. Seen in EM: Flattened cisternae studded with ribosomes.
2. Annotation: Synthesizes proteins for secretion or membrane insertion; transports proteins to Golgi.

7. Smooth Endoplasmic Reticulum (sER)

1. Seen in EM: Tubular membranes, no ribosomes.
2. Annotation: Synthesizes lipids and steroids; detoxifies harmful substances; stores calcium (in muscle).

8. Golgi Apparatus

1. Seen in EM: Curved cisternae with many vesicles nearby.
2. Annotation: Modifies and packages proteins and lipids; forms lysosomes; directs vesicle transport.

9. Lysosomes / Secretory Vesicles

1. Seen in EM: Small spherical structures, darker than vacuoles.
2. Annotation: Contain digestive enzymes (lysosomes); used for secretion or transport (vesicles).

10. Cell Wall (plants, fungi, prokaryotes)

1. Seen in EM: Rigid outer layer outside plasma membrane.
2. Annotation: Provides structural support, prevents lysis, and is composed of cellulose in plants.

11. Plasma Membrane

1. Seen in EM: Thin bilayer enclosing cytoplasm.
2. Annotation: Selectively permeable barrier; regulates entry and exit of molecules.

12. Ribosomes (80S in eukaryotes, 70S in prokaryotes)

1. Seen in EM: Dark granules, free in cytoplasm or attached to rER.
2. Annotation: Site of translation and protein synthesis.

13. Microvilli (animals only, e.g., intestine)

1. Seen in EM: Finger-like extensions of plasma membrane.
2. Annotation: Increase surface area for absorption.