10.1: Plant Cell Structure and Components

Plant Cells

Figure \(\PageIndex{1}\): A diagram of a plant cell. Plants cells differ from animal cells in that they have a cell wall (which is glued to adjacent cells by the middle lamellae), a large central vacuole, and chloroplasts. Image by LadyofHats, Public domain, via Wikimedia Commons.

Plant Cell Components

Cell Wall, Plasma Membrane, and Middle Lamella

Figure \(\PageIndex{2}\): A diagram of the primary cell wall, including the plasma membrane and middle lamella. The primary wall is composed of crisscrossing cellulose and hemicellulose microfibrils. Strands of pectin and some soluble proteins are also in the mix. Diagram by LadyofHats, Public domain, via Wikimedia Commons.

Figure \(\PageIndex{3}\): A generalized diagram of a plasma membrane. The cell membrane, also called the plasma membrane or plasmalemma, is a semipermeable lipid bilayer common to all living cells. It contains a variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes. It also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall. Diagram by LadyofHats, Public domain, via Wikimedia Commons.

Plasmodesmata are channels through the cell wall and middle lamella where the plasma membrane of adjacent cells (and therefore the cytoplasm) is connected.

Figure \(\PageIndex{4}\): The image above shows cells in the epidermis of a red pepper. Two locations are circled and labeled as plasmodesmata. In each of these circles, there is a section of the cell wall that appears to be missing. This is where a section of the plasma membrane traverses through a channel in the middle lamella and cell walls of both cells. Photo by Maria Morrow, CC BY-NC.

The Nucleus

Figure \(\PageIndex{5}\): A micrograph of a cell nucleus. The nucleolus (A) is a condensed region within the nucleus (B) where ribosomes are synthesized. The nucleus is surrounded by the nuclear envelope (C). Just oustide the nucleus, the rough endoplasmic reticulum (D) is composed of many layers of folded membrane. Image from the public domain, via Wikimedia Commons, labels added by Maria Morrow.

Figure \(\PageIndex{6}\): The large, golden, globose structure is an onion cell nucleus, magnification 3000x. Berkshire Community College Bioscience Image Library, CC0, via Wikimedia Commons.

Plastids

Plastids are organelles that are the result of an endosymbiotic event in the evolutionary history of plants. In plants, plastids have two membranes.

Chloroplasts

Chloroplasts are plastids that contain green pigments called chlorophylls.

Figure \(\PageIndex{7}\): This image shows cells in the leaf of an aquatic plant, Elodea. Each cell is filled with small green discs which often appear to line the edges of the cell. These are chloroplasts (four are indicated and labeled in the image). Photo credit: Melissa Ha, CC BY-NC .

Figure \(\PageIndex{8}\): A diagram of chloroplast anatomy. There are two membranes, the outer and inner membrane, that enclose this structure. Within, there are stacks of flat discs. Each stack is called a granum and each individual disc is a thylakoid. The grana float within a jelly-like matrix called the stroma. Artwork by Nikki Harris, CC BY-NC .

Chromoplasts

Chromoplasts are plastids that do not contain chlorophyll, but do contain other pigments, such as carotenoids. Carotenoid pigments reflect colors like yellow, orange, and red.

Figure \(\PageIndex{9}\): This image shows the cells of a red pepper. There are many small red dots floating within the cells. These dots are chromoplasts that contain carotenoids. The chromoplasts give the pepper its red color. Photo credit: Melissa Ha, CC BY-NC .

Figure \(\PageIndex{10}\): In this image of red pepper epidermal cells, the chromoplasts are larger and easier to distinguish. Each cell is filled with circular, red discs. These are chromoplasts that contain carotenoids. Photo by Maria Morrow, CC BY-NC.

Leucoplasts

Leucoplasts are plastids that do not contain pigments. The main function of leucoplasts is to store starches and oils. Leucoplasts that store starch are called amyloplasts (as in amylose).

Figure \(\PageIndex{11}\): This image shows cells from a potato tuber that have been stained with iodine. When iodine interacts with starch, it turns a blue-black color. This helps us see the amyloplasts inside the cells, which would normally be transparent due to their lack of pigment. In the image, the cell walls of the potato cells can be seen as lighter lines (indicated by the arrows in two places). The amyloplasts are dark, pebble-like structures within the cells. Some of these are less opaque because they have not been in contact with as much of the iodine stain. Photo credit: Melissa Ha, CC BY-NC.

The Central Vacuole

The central vacuole is a large organelle that often fills most of the plant cell. It is filled with liquid and surrounded by a membrane called the tonoplast. Plants can alter the solute concentration in the central vacuole to influence cell structure and movement of water. It is also a place to store pigments, such as anthocyanins, or other secondary metabolites, such as phytotoxins.

Figure \(\PageIndex{12}\): This image shows the same Elodea leaf cells again, this time with the cell wall, cell membrane, and tonoplast of one of the cells labeled. The cell walls are visible as thicker lines between the cells. The plasma membrane and tonoplast locations must be inferred. The plasma membrane is pushed against the cell wall, just to the inside of it. The tonoplast can be seen as the border between the chloroplasts the "empty space" within the cell, as the central vacuole pushes the cytoplasm to the edges of the cell. Photo credit: Melissa Ha, CC BY-NC .

Figure \(\PageIndex{13}\): In this image, the Elodea leaf has been exposed to salt water. This helps us see the plasma membrane and tonoplast more distinctly, as much of the water has left the cell and the central vacuole has shrunk, causing plasmolysis. As the central vacuole shrinks, the plasma membrane collapses inward but the rigid cell wall remains in place. The plasma membrane is surrounding the outside of the chloroplasts, which have been clustered into a ball inside each cell. Just inside the shell of chloroplasts is the tonoplast. The nucleus will also be squished in there somewhere, though it is also transparent. Photo by Maria Morrow, CC BY-NC.