Introduction
Algae are a diverse group of photosynthetic organisms found in aquatic and moist environments. They range from unicellular microscopic forms like Chlorella to large multicellular forms like seaweeds. Algae are eukaryotic (except for blue-green algae or cyanobacteria, which are prokaryotic) and possess membrane-bound organelles. Understanding their ultrastructure helps in appreciating their ecological roles, photosynthetic efficiency, and commercial importance.
Ultrastructure of Algal Cell
The ultrastructure refers to the internal microscopic structure observed under an electron microscope. While different groups of algae may show some variation, the general structure remains fairly consistent among eukaryotic algae.
1. Cell Wall
- The cell wall provides structural support and shape to the algal cell.
- It is mainly composed of cellulose, pectin, and in some algae, silica (e.g., diatoms).
- Some algae also have a gelatinous covering or mucilage layer.
2. Plasma Membrane
- A selectively permeable membrane that controls the movement of substances in and out of the cell.
3. Cytoplasm
- The matrix that contains all the cell organelles and is the site for many metabolic reactions.
4. Nucleus
- Algae are eukaryotic and hence have a true nucleus surrounded by a nuclear membrane.
- Contains chromosomes and nucleolus, and controls all cellular activities including reproduction.
5. Chloroplasts
- Chloroplasts are the site of photosynthesis.
- They contain pigments like chlorophyll a, b, c, d, and carotenoids depending on the algal group.
- The number, shape, and arrangement of chloroplasts vary (e.g., spiral in Spirogyra, cup-shaped in Chlamydomonas).
6. Pyrenoids
- Located inside the chloroplasts, pyrenoids are centers for carbon fixation and starch storage.
7. Mitochondria
- Powerhouses of the cell where ATP is produced through cellular respiration.
8. Golgi Apparatus and Endoplasmic Reticulum
- Involved in packaging, protein synthesis, and transport.
9. Vacuoles
- Filled with cell sap and help in maintaining cell turgidity.
10. Eyespot (Stigma)
- Present in motile algae like Chlamydomonas.
- Functions as a light-sensitive organelle aiding in phototaxis (movement towards light).
11. Flagella
- Used for locomotion in motile algal cells.
- Usually present as one or more whip-like appendages.
Diagram
Note: For accurate understanding, please refer to your textbook or classroom material for a labeled diagram of an algal cell, especially of a motile type like Chlamydomonas.
The diagram should include:
- Cell wall
- Plasma membrane
- Chloroplast (with pyrenoid)
- Nucleus
- Eyespot
- Flagella
- Vacuole
Conclusion
The ultrastructure of algae reflects their functional efficiency in photosynthesis, storage, and environmental adaptation. Though simple in appearance, their internal organization is highly specialized, especially in photosynthetic machinery. Studying their ultrastructure is important for understanding not only basic biological processes but also their use in biofuels, food, and biotechnology.