Learn About Plant Cell Structures and Organelles

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What Is a Plant Cell?

Plant cell
Mariana Ruiz / Modified by Dhatfield

Plant cells are eukaryotic cells, or cells with a membrane-bound nucleus. Unlike prokaryotic cells, the DNA in a plant cell is housed within a nucleus that is enveloped by a membrane. In addition to having a nucleus, plant cells also contain other membrane-bound organelles (tiny cellular structures) that carry out specific functions necessary for normal cellular operation. Organelles have a wide range of responsibilities that include everything from producing hormones and enzymes to providing energy for a plant cell.

Plant cells are similar to animal cells in that they are both eukaryotic cells and have similar organelles. However, there are a number of differences between plant and animal cells. Plant cells are generally larger than animal cells. While animal cells come in various sizes and tend to have irregular shapes, plant cells are more similar in size and are typically rectangular or cube shaped. A plant cell also contains structures not found in an animal cell. Some of these include a cell wall, a large vacuole, and plastids. Plastids, such as chloroplasts, assist in storing and harvesting needed substances for the plant. Animal cells also contain structures such as centrioles, lysosomes, and cilia and flagella that are not typically found in plant cells.

 

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Structures and Organelles

The Cell: Golgi Apparatus Model
The Golgi Apparatus Model. David Gunn / Getty Images

The following are examples of structures and organelles that can be found in typical plant cells:

  • Cell (Plasma) Membrane - a thin, semi-permeable membrane that surrounds the cytoplasm of a cell, enclosing its contents.
  • Cell Wall - outer covering of the cell that protects the plant cell and gives it shape.
  • Chloroplast - the sites of photosynthesis in a plant cell. They contain chlorophyll, a green pigment that absorbs energy from sunlight.
  • Cytoplasm - gel-like substance within the cell membrane containing water, enzymes, salts, organelles, and various organic molecules.
  • Cytoskeleton - a network of fibers throughout the cytoplasm that helps the cell maintain its shape and gives support to the cell.
  • Endoplasmic Reticulum (ER) - extensive network of membranes composed of both regions with ribosomes (rough ER) and regions without ribosomes (smooth ER). The ER synthesizes proteins and lipids.
  • Golgi Complex - responsible for manufacturing, storing and shipping certain cellular products including proteins.
  • Microtubules - hollow rods that function primarily to help support and shape the cell. They are important for chromosome movement in mitosis and meiosis, as well as cytosol movement within a cell.
  • Mitochondria - these organelles generates energy for the cell by converting glucose (produced by photosynthesis) and oxygen to ATP. This process is known as respiration.
  • Nucleus - membrane bound structure that contains the cell's hereditary information (DNA).
    • Nucleolus - structure within the nucleus that helps in the synthesis of ribosomes.
    • Nucleopore - tiny hole within the nuclear membrane that allows nucleic acids and proteins to move into and out of the nucleus.
  • Peroxisomes - tiny structures bound by a single membrane that contain enzymes that produce hydrogen peroxide as a by-product. These structures are involved in plant processes such as photorespiration.
  • Plasmodesmata - pores or channels between plant cell walls that allow molecules and communication signals to pass between individual plant cells.
  • Ribosomes - consisting of RNA and proteins, ribosomes are responsible for protein assembly. They can be found either attached to the rough ER or free in the cytoplasm.
  • Vacuole - structure in a plant cell that provides support and participates in a variety of cellular functions including storage, detoxification, protection, and growth. When a plant cell matures, it typically contains one large liquid-filled vacuole.

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Types of Plant Cells

Plant Tissue Stem
This is a typical dicotyledon stem (Buttercup). At center is an oval vascular bundle embedded in parenchyma cells (yellow) of the cortex of the stem. Some parenchyma cells contain chloroplasts (green). The vascular bundle contains large xylem vessels (center right) which serve to conduct water; the nutrient conducting phloem is orange. At the outer edge of the vascular bundle is sclerenchyma tissue which supports the vascular bundle. POWER AND SYRED/SCIENCE PHOTO LIBRARY/Getty Images

As a plant matures, its cells become specialized in order to perform certain functions necessary for survival. Some plant cells synthesize and store organic products, while others help to transport nutrients throughout the plant. Some examples of specialized plant cell types include:

Parenchyma Cells

Parenchyma cells are usually depicted as the typical plant cell because they are not very specialized. These cells synthesize (by photosynthesis) and store organic products in the plant. Most of the plant's metabolism takes place in these cells. Parenchyma cells compose the middle layer of leaves as well as the outer and inner layers of stems and roots. The soft tissue of fruits is also composed of parenchyma cells.

Collenchyma Cells

Collenchyma cells have a support function in plants, particularly in young plants. These cells help to support plants while not restraining growth due to their lack of secondary cell walls and the absence of a hardening agent in their primary cell walls. 

Sclerenchyma Cells

Sclerenchyma cells also have a support function in plants, but unlike collenchyma cells, they have a hardening agent and are much more rigid. These cells are thick and contain various shapes. Sclerenchyma cells form the hard outer shell of nuts and seeds. They are found in stems, roots, and leaf vascular bundles.

Water Conducting Cells

Water conducting cells of xylem also have a support function in plants but unlike collenchyma cells, they have a hardening agent and are much more rigid. Two types of cells compose xylem. They are narrow, hollow cells called tracheids and vessel members. Gymnosperms and seedless vascular plants contain tracheids, while angiosperms contain both tracheids and vessel members.

Sieve Tube Members

Sieve tube cells of phloem conduct organic nutrients such as sugar throughout the plant. Other cell types found in phloem include companion cells, phloem fibres, and parenchyma cells.

Plant cells are grouped together into various tissues. These tissues can be simple, consisting of a single cell type, or complex, consisting of more than one cell type. Above and beyond tissues, plants also have a higher level of structure called plant tissue systems. There are three types of tissue systems: dermal tissue, vascular tissue, and ground tissue systems.