Fundamentally, animal and plant cells share several key components. A nucleus housing DNA, mitochondria for energy production, and cytoplasm and organelles for conducting various cellular metabolism. However, the unique lifestyles of high-speed flying birds and stationary plants are not only evident in macroscopic world but also profoundly reflected at microscopic world, that is the cellular level.
Cell Wall
Rice field ripple golden waves in rustic farmland. Their non-skeleton stalks are so thin, so how can they sway in the wind? This is because they are wrapped by a cell wall that doesn’t need to be as hard as steel, but must be elastic. The cell wall during juvenile period is indeed relatively thin and contains more pectin, a water-soluble and soft gelling polysaccharide. It acts like natural glue to stick adjacent neighbors. These characteristics make young cells somewhat flexible and expandable to accommodate their rapid growth. More cellulose is found in mature plant cell walls that can withstand stronger external forces. Trees also contain lignin. An organic compound makes them as hard as rock and able to resist extreme pressure. This is why trees can support their massive weight without a skeleton. Owing to a sturdy shell, plant cells have regular shapes, such as square or hexagonal. They stack like building blocks and try to fill their surrounding space.
Although cell walls provide protection and support, they also restrict movement. Freely moving tissues such as blood and muscle didn’t evolve in plants. Animal cells, on the other hand, are much more flexible. A phospholipid bilayer embedded with proteins is the outmost shell. It is precisely controlled to match external environment with the help of cytoskeleton. Their shapes are generally round or irregular.
Central Vacuole in Plants
If you forget to water a peace lily on a hot summer day, its leaves will droop listlessly. This is your plant telling you it lacks moisture. After absorbing enough water, you will be surprised to discover the leaves perk up again. Why does this happen? It turns out that all of this is dominated by plant central vacuole.
A juicy central vacuole occupies most of the cytoplasm volume, sometimes up to 90%. They expand outward and press against cell wall. Water is an incompressible fluid, and could withstand strong external pressure. At this point, the cell is turgid to make plant leaves upright. When it’s thirsty, water is released from vacuole for photosynthesis and transpiration. The decreased turgor pressure leads to a loss of support, and stems and leaves wilt as a result.
The central vacuole is not just a reservoir but also involved in regulating many life activities, such as maintaining ion balance, storing nutrients, and metabolizing waste. Liquid in vacuole is called cell sap that contains various complex organic and inorganic substances. Sugars, salts, organic acids, tannins, alkaloids, and pigments is the common content. Grape juice taste sweet due to abundant fructose and sucrose. The most magical part is how plants like Mimosa and insectivorous plants control their leaf. Ions are released from vacuole rapidly when touched. Loss of ions leads to a decreased osmotic pressure, and water flows out of the vacuole to shrink it.
For almost all animal, vacuoles are meaningless because they lack cell wall and can’t resist turgor. Absorbing too much water will burst them. Freshwater protozoa have vacuole-like contractile vacuoles to expel excess water and control osmotic pressure.
Chloroplasts
Chlorophyll in chloroplasts makes your houseplants green. They are the sites where plants absorb sunlight to produce organic matter. They are also known as food producers or photosynthesis factories. Autotrophic characteristics make it unnecessary for plant to be subjected to intense predation. Most plants are fixed in one place to bask in the warm sunshine. Animal don’t contain chloroplasts and they must consume other organisms for survival. This defines them as consumers in ecosystem. Therefore, animals need more mitochondria to provide energy for their rapid movement.
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell-to-cell communication | Plasmodesmata allows communication and molecular transport between cells. | No plasmodesmata, communication occurs through direct contact, gap junctions or nerve system. |
| waste management | peroxisomes, vacuoles | lysosomes, peroxisomes |
| Structures for movement | Cilia or flagella usually present only in reproductive cells, such as sperm. | cilia or flagella |
| Storage of nutrients | starch | glycogen |