1.1.2 Animal and Plant Cells

In our exploration of cellular biology, it is crucial to understand the sub-cellular structures that contribute to the functions and characteristics of animal and plant cells. Each organelle within a cell plays a specific role, enabling cells to carry out vital processes necessary for life.

Animal Cells

• Nucleus: The nucleus is a prominent organelle within animal cells. It houses the cell’s genetic material, including DNA, which carries instructions for cellular processes.
• Cytoplasm: The cytoplasm is a gel-like substance that fills the cell and surrounds the organelles. It provides a medium for cellular processes and serves as a site for many metabolic reactions.
• Cell Membrane: The cell membrane, also known as the plasma membrane, forms the outer boundary of animal cells. It regulates the passage of substances in and out of the cell and provides structural support.
• Mitochondria: Mitochondria are energy-producing organelles present in animal cells. They generate ATP (adenosine triphosphate), the energy currency of the cell, through cellular respiration.
• Ribosomes: Ribosomes are small, granular organelles responsible for protein synthesis. They can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum.

Plant Cells

In addition to animal cell components, plant cells also have:

• Chloroplasts: Chloroplasts are organelles unique to plant cells. They contain chlorophyll, a pigment responsible for capturing light energy during photosynthesis. Chloroplasts convert light energy into chemical energy, producing glucose and oxygen.
• Permanent Vacuole: Plant cells typically have a large, central vacuole that occupies a significant portion of the cell’s interior. The vacuole stores water, nutrients, pigments, and waste materials, maintaining cell turgidity and providing structural support.
• Cell Wall: Plant cells, as well as algal cells, possess a cell wall made of cellulose. The cell wall provides structural support, protection, and rigidity to the cell, enhancing its overall strength.

Importance of Estimations

Cells and their sub-cellular structures are typically too small to be directly measured with conventional laboratory tools. Estimations allow us to make reasonable assessments and comparisons based on available information. They help us understand the relative size or area of sub-cellular structures within cells. 

When to Use Estimations

• Nucleus: As a rough estimation, the diameter of a typical eukaryotic cell nucleus is often in the range of 5 to 10 micrometres (µm), while the diameter of the entire eukaryotic cell can range from 10 to 30 µm or more. This means that the nucleus is a significant but relatively small part of the cell’s overall volume.
• Mitochondria and Chloroplasts: Mitochondria are generally larger than chloroplasts. The typical size of a mitochondrion is about 1 to 10 micrometres (μm) in length and 0.5 to 1.0 μm in width. In comparison, chloroplasts are usually smaller, with dimensions ranging from 2 to 5 μm in length and 1 to 2 μm in width.
• Vacuoles: In plant cells, vacuoles can be quite large and are often considered one of the largest cellular structures. They can occupy a significant portion of the cell’s volume. In some plant cells, a single large central vacuole can occupy up to 90% of the cell’s volume. These central vacuoles can vary in size but are typically larger than mitochondria and chloroplasts.

Conclusion

Animal cells possess essential organelles like the nucleus, cell membrane, mitochondria, and ribosomes, which facilitate vital cellular processes. Plant cells, in addition to these components, contain chloroplasts for photosynthesis, a permanent vacuole for storage, and a cellulose-based cell wall for structural support. Estimations enable us to judge the relative size or area of sub-cellular structures. Through estimations, we can compare and appreciate the significance of these structures within cells, even without direct measurement.