Comparing Features of Eukaryotic Cells: Animal, Plant, and Fungal Cells
- Plants, fungi, and animals are organisms that seem distinct, yet their cells share a common blueprint: the eukaryotic cell.
- However, the structural differences between animal, plant, and fungal cells reflect their unique roles in nature.
Cell Walls: Strength and Protection
Plant Cells
- The cell wall, made of cellulose, is like a suit of armor.
- It maintains shape, withstands stress, and prevents water-induced bursting.
Despite its rigidity, it is freely permeable to water, gases, and nutrients.
Fungal Cells
- Fungal cell walls are made of chitin, a flexible and strong polymer.
- This composition allows fungi to thrive in diverse environments, from decaying logs to food storage.
- Many students incorrectly assume that fungal cell walls are made of cellulose.
- In fact, they are composed of chitin, a key difference tested in IB examinations.
Animal Cells
- Animal cells lack a cell wall.
- Instead, they depend on a plasma membrane for flexibility, enabling diverse shapes and movements.
Animal cells do not have cell walls, which is why they are more flexible and dynamic compared to the rigid structures of plants and fungi.
Vacuoles: Storage and Pressure Regulation
Plant Cells
- A large central vacuole, often occupying up to 90% of the cell, stores water, nutrients, and waste.
- It also maintains turgor pressure, keeping plants upright and leaves firm.
- When drawing plant cells in IB Biology exams, always include a large central vacuole.
- Omitting it is a common way to lose marks, as this is a key structural feature distinguishing plant cells from animals and fungi.
Fungal Cells
- Vacuoles are also present and often large, but their composition and function vary.
- They are primarily involved in storage, osmoregulation, and recycling of cellular components.
Animal Cells
- Vacuoles are small and temporary.
- They are often involved in isolating waste or engulfing food during processes like endocytosis.
- In plants, the central vacuole can store pigments that give flowers their bright colors or toxins that deter herbivores.
- In fungi, vacuoles might store enzymes for digesting nutrients.
- In animals, a vacuole could temporarily store food particles during digestion.
Plastids: The Power of Photosynthesis (and Beyond)
Definition
Plastid
Plastids are specialized organelles in plant cells that perform functions such as photosynthesis, storage, and pigment synthesis.
Plant Cells
- Plastids, such as chloroplasts, perform photosynthesis.
- Chloroplasts contain chlorophyll, converting sunlight into glucose and oxygen.
- Other plastids include:
- Amyloplasts: Store starch.
- Chromoplasts: Contain pigments for colorful flowers and fruits.
Fungal and Animal Cells
- These lack plastids entirely.
- Animals obtain energy heterotrophically, while fungi absorb nutrients by extracellular digestion.
Think of chloroplasts as solar panels that generate energy for plants, while animals and fungi rely on external "power sources" like food.
Centrioles, Cilia, and Flagella: Movement and Organization
Centrioles
- Animal cells possess centrioles, which organize the spindle apparatus and form the basal bodies of cilia and flagella.
- Plant cells generally lack centrioles, yet they can still form spindle fibres during mitosis and meiosis using other microtubule-organizing centres.
- Fungal cells usually lack centrioles as well, except in species that produce motile gametes.
Cilia and Flagella
- Animal cells commonly possess cilia or flagella, both with the classic 9+2 arrangement of microtubules. Examples include sperm cells (flagella) or respiratory tract epithelial cells (cilia).
- Plant cells rarely possess flagella, except in some motile gametes of lower plants such as mosses and ferns.
- Fungal cells also generally lack motile structures, though some chytrid fungi produce gametes with flagella.
- Not all eukaryotic cells have centrioles, cilia, or flagella.
- These features are specific to certain cells and should not be assumed to be universal.
Key Differences in Eukaryotic Cells
| Feature | Animal cells | Plant cells | Fungal cells |
|---|---|---|---|
| Cell Wall | Absent | Present (cellulose) | Present (chitin) |
| Vacuoles | Small, temporary | Large central vacuole | Small, often multiple |
| Plastids | Absent | Present (e.g., chloroplasts) | Absent |
| Centrioles | Present | Absent (except in motile gametes) | Absent (except in motile gametes) |
| Cilia/Flagella | Often present (e.g., sperm flagella) | Rare (e.g., motile algae gametes) | Rare (e.g., motile spores) |
- How do structural differences in eukaryotic cells reveal how organisms adapt to their environments?
- Could these adaptations predict survival in extreme conditions?
- Why does the absence of a cell wall give animal cells greater flexibility than plant or fungal cells?
- Which structural feature allows plant cells to maintain rigidity without a skeleton?
- What key biochemical difference exists between plant and fungal cell walls?
- Why are plastids only found in plants and not in animals or fungi?
