In Part 7 of this series on the Simple Cell, we looked vesicles and how they served to contain things for transportation like shipping boxes and for storage like Tupperware. Today we are going to take a look at vacuoles.
When I took biology in high school I was taught that vacuoles are just hollow structures that move water and food particles from the cell membrane to other parts of cell. However, further studies have discovered a number of important functions for the vacuole.
Besides the obvious functions of transporting water and nutrients with the cell, some of the other functions of vacuoles consist of:
- As the different organelles in the cell generate waste products, they are enclosed in vesicles which in turn are taken in by the vacuoles for transportation to the cell wall/membrane where it is excreted from the cell.
- Collect and transport the many different vesicles that contain vital proteins and materials throughout the cell to their needed destinations.
- Different types of cells require different pH concentrations. Vacuoles maintain the proper pH level in the cell, which in most cases is acidic.
- Maintain the turgor and hydrostatic pressure within the cell. This is the internal fluid pressure exerted on the cell wall in plants and membrane in animal cells.
- Any substances that are generated within the cell that may be harmful to the cell are collected into vesicles which are then packed into vacuoles for transportation to the cell wall/membrane for excretion.
- Maintaining a balance between biogenesis and degradation processes within the cell. This process is known as autophagy. Just as cells, organs and living organisms die, so do certain organelles within the cells. When that occurs, the decaying products are encased in vesicles which are then packed into vacuoles for transport to the cell wall/membrane to be excreted.
- Cell immunity against certain bacteria. When harmful bacteria enter a cell, the vacuoles will seek them out, engulf them and destroy them with their internal acidic solution.
- Any other undesirable substances or materials are collected by the vacuoles and taken to the cell wall/membrane where they are excreted.
There are additional functions of vacuoles that are unique to certain types of organisms or cells. Some of these specialized functions include:
- Contractile vacuoles (CV) are unique to organisms that inhabit freshwater environments. These vacuoles expand and contract as necessary to maintain the proper water pressure balance in these organisms. As water enters the cell through osmosis and with nutrients, the contractile vacuole with collect the excess water and remove it from the cell.
- Central vacuole in plants. Up to 80% of the plant cell may be taken up by the central vacuole. Its purpose is to maintain the shape of softer plant structures such as leaves and flower parts. The central vacuole is surrounded by a membrane called the tonoplast which helps the central vacuole to keep its size and internal water pressure. The central vacuole contains a water attracting solution to help it collect and store a large amount of water. This water pressure is what gives the leaves and flower parts their shape. (Have you ever noticed what happens to a plant that is dry and wilting when you water it? The water is collected in the roots, transported up through the xylem up to the leaves and flowers where it is then taken in by the central vacuole. This is when you notice that the leave return to their normal rigid shape. Succulents such as cacti contain huge central vacuoles which stores a large amount of water that can later be used by the plants during dryer times.)
- Fungal vacuoles. Where plants have one central vacuole, fungi cells can contain more than one vacuole. These vacuoles are involved in balancing cell pH, storage of amino acids, and the regulation of water pressure.
What I once thought were just tiny sacs of food and water turn out to be a lot more than what I was initially taught. Now I see vacuoles as functioning like garbage trucks collecting and transporting all of the waste and harmful material out of the cell and like UPS trucks that collect all of the vesicles and transport them to their destinations throughout the cell.
Notice as we learn more and more about the internal workings of the Simple Cell that everything has a purpose and function and is interconnected with everything else in one way or another. Nothing is left to chance but all takes place in a very precise and orderly fashion. And realize that we are not finished with our series on the Simple Cell. I hope you return next Friday when we look at lysosomes.