Plant cells are made up of many parts; however, many of us haven’t taken the time to review these specialized organelles since we were in school. Here’s a short refresher for gardeners.
Chloroplast: Chloroplasts’ main job is to conduct photosynthesis; however, they also carry out a number of other functions, including making fatty acids and amino acids, and aiding in plants’ immune responses. Chloroplasts move around within plant cells quite a bit based on the available light; in low-light conditions they may spread out in a sheet to maximize the surface area. In intense light, they sometimes appear to seek shelter by aligning in vertical columns along the plants’ cell wall.
Green parts of vascular plants contain chloroplasts, and the chlorophyll in them is what makes the plant green in the first place. Chloroplasts contain their own DNA, are inherited from one parent, and they reproduce within their parent cells, much like the Cyanobacteria they likely descended from. Gymnosperms, such as pine trees, mostly pass on chloroplasts paternally, while flowering plants often inherit chloroplast maternally.
Endoplasmic reticulum (ER): This system contains a series of flattened sacs that are particularly important in the modification and transport of proteins and lipids. There is a smooth ER and a rough ER. The rough ER is primarily involved with the production of proteins that will be exported from the cell to help build the plant. The smooth ER is involved with the creation, secretion, and storage of lipids, the creation of new membranes, and the metabolism of carbohydrates. The ER also helps regulate large quantities of calcium, which can become toxic if too much is accumulated.
Nucleus: The nucleus stores the plant’s DNA, which controls everything in the plant from the color of its petals to the number of stamens. The nucleus is enclosed by two membranes and some small openings- called nuclear pores – which only let in certain, pre-approved things. A defined nucleus is an advanced feature in a cell and is found in eukaryotic cells but not prokaryotic cells.
Mitochondrion: Mitochondria are known as the “powerhouses” of the cell because they take in carbohydrates and fatty acids, break them down, and create energy. Mitochondria are small organelles that float freely throughout the cell. They also work closely with the endoplasmic reticulum to control the concentration of calcium ions within the cell. Like the chloroplast, mitochondria contain their own bacteria-like DNA and they reproduce by division within the cell’s cytoplasm.
Ribosome: Ribosomes help build proteins, which support cell/plant structure and function. Ribosomes attached to the endoplasmic reticulum make it appear rough, hence the name “Rough ER.”
Cytoplasm: The cytoplasm includes all the material within a living cell, except its nucleus. This includes the organelles, such as the mitochondrion and the chloroplast, and also a gel-like substance called “cytosol” that gives the cell its shape and keeps the organelles more or less organized. The cytoplasm is about 80 percent water and is typically colorless.
Golgi complex: The golgi apparatus, or “complex,” is made up of membrane-bound sacs that look like pancakes, and it can be thought of as the cell’s post office because it modifies, sorts, and packages proteins to be delivered elsewhere. The golgi apparatus gathers up simple molecules, combines them to form more complex molecules, and then packages them into “vesicles” to either store for later or send out of the cell.
Vacuole: Vacuoles are membrane-bound structures filled with fluid that contribute to the rigidity of the plant cell, store nutrients, and break down complex molecules. Different vacuoles within the same cell can contain different chemicals depending on that vacuole’s role. These fluid-filled sacs can occupy anywhere between 30 and 90 percent of the cell by volume.
For gardeners, the state of a plant’s vacuoles is the cue to whether or not it needs to be watered. A cell in which the vacuole contains all the water it needs is called “turgid,” and when a plant wilts it’s said to have “lost its turgor.”
Lysosome: Lysosomes are one of the key organelles involved in digestion and waste removal. Structurally, lysosomes are like a floating garbage bag that contains enzymes capable of digesting molecules. They go to work when the cell absorbs or eats any food. If the cell is starving, lysosomes will even digest other organelles for nutrients.