In this lesson, we’ll talk about some of the things that make plant cells so different from our cells.
In addition to being mean, green photosynthesizing machines, plant cells have cell walls and central vacuoles to make them unique!
Plant Cells Have Specialized Components
Your friend asked you to watch her plants while she went away for the summer. You know plants need plenty of sunshine and water, so you put them on your windowsill and give them a daily drink. But maybe one day you get home late from work and you just completely forget to water the plants. Today turns into tomorrow, which turns into the next day. Before you know it, you walk by the plants and notice they’ve started to wilt. Whoops!
|endoplasmic reticulum and ribosomes. However, plants have some original cell components that are different than what’s in your cells. For one, plant cells have chloroplasts that help turn light energy into food. In today’s lessons, we’ll talk about two more structures important to plant cells.
Plant Cell Walls
All plant cells have a plasma membrane just like an animal cell, which provides the same barrier and regulates transport. However, plant cells also have a specialized structure called the cell wall. The cell wall is a protective layer surrounding the cell on the outside of the plasma membrane. A cell wall can be up to 800 times thicker than the plasma membrane. It’s composed largely of cellulose, a polysaccharide sugar that provides strength to the cell wall. If you’ve ever noticed how strong the bark of a tree is, that’s because this bark is composed of dead cells with really tough cell walls.The cell wall also grows with the cell, getting bigger as the cell gets bigger.
Although plants aren’t the only organisms with a cell wall, this structure is a characteristic of all plants.
The cell wall serves several purposes. Its Popeye-like toughness provides great protection, strength and shape to the cell, helping a plant cell to be both flexible and rigid. Think about a bouquet of roses.
The stems are strong enough that you need a sharp knife to cut them, but flexible enough that they fit easily into a beautiful vase.
Plant Central Vacuoles
In addition to a cell wall, plant cells also have this very large structure that can take up as much as 80% of the cell’s volume. This is called a central vacuole, a large storage compartment in plant cells. What can this vacuole hold? Well, although other non-plant cells can also have vacuoles, plant cells have these characteristically gigantic vacuoles that are largely a storage place for water. While animal cells are around 70% water, plant cells can be 90% full of water – and they need a place to put it! However, in addition to water, a vacuole can also contain food and other nutrients, as well as waste products.The central vacuole can also contain digestive enzymes like those in animal cell lysosomes. A central vacuole also can help maintain a neutral pH in the cell by pumping hydrogen atoms, or protons, from the cytoplasm into the vacuole.
What happens if you pump a lot of protons into the vacuole? This makes this plant cell component acidic, which also is similar to a lysosome.
Osmosis in Plant Cells
So how does the cell wall and the central vacuole relate to those plants you forgot to water? Remember that cells transport water across their cell membranes through the process of osmosis. When you forget to water the plants, the plant cells are then in a hypertonic environment, or an environment with less water around them and more solutes. This causes water to leave the plant cells. The consequence? A wilting plant! Notice, however, that even in a hypertonic environment, the cell wall helps maintain the shape of the plant cell.
As soon as you started watering the plant regularly, the plants were again in an isotonic, or equal, water environment. As a result, the cell’s central vacuole takes on more water, and the cell can fill the cell wall’s shape. Now, what if you poured on a little too much water to try to make up for lost time? You may have seen a plant wilt when it isn’t watered enough, but have you ever seen a plant explode with water? I doubt it.
That’s because in a hypotonic environment, with more water outside the cell, the central vacuole will swell with water, putting pressure on the cell walls. However, those cell walls will keep the cell rigid and strong. It’ll prevent the cell from bursting.
This pressure that is put on the cell walls is known as turgor pressure. In fact, most healthy plants are in a constant state of turgor pressure, and this is what gives plant their rigid shape.
In summary, we’ve learned more about two important plant cell components today. The first is the cell wall, which is a protective layer surrounding the cell on the outside of the plasma membrane. The cell wall is composed of cellulose, or a polysaccharide sugar that provides strength to the cell wall.
A second structure important to all plant cells is the central vacuole, which is a large storage compartment in plant cells. Both the cell wall and the central vacuole help plant cells regulate water movement, or osmosis, to keep plant cells strong enough to withstand a few days without water.
After watching this lesson, you should be able to: