Internal Structures of Plant Cells

Plant cells, like animal cells, are eukaryotes, meaning that they contain a nucleus that stores DNA and membrane-bound, internal structures called organelles. Different organelles in plant cells perform a variety of essential functions. Cells from different parts of a plant or different species of plants exhibit many similarities but also some important differences as well. Certain structures, however, are either common in plant cells.

  1. Nucleus

    • The nucleus is the defining characteristic of a eukaryotic cell. It acts as the storehouse for the cell's DNA or genetic code and is surrounded by a double membrane pierced by nuclear pores. Each nuclear pore is formed of a complex of proteins that help to regulate entry and exit of other proteins or compounds. The nuclear membrane breaks down during cell division, or mitosis.

    Mitochondria

    • Mitochondria are the powerhouse of the cell. Cells use adenosine triphosphate, or ATP, as a kind of energy currency or fuel to power most cellular processes. Plant cells break down sugars to release the energy they need to make ATP. Most of the ATP the cell produces is manufactured in the mitochondria.

    Chloroplast

    • Chloroplasts are the organelles where photosynthesis takes place. During photosynthesis the plant uses sunlight to produce sugars it can use for synthesizing organic compounds or producing ATP through cellular respiration. Chloroplasts contain small membrane-enclosed sacs called thylakoids, arranged in stacks called granum. The most distinctive visual feature of the chloroplast is the green color lent them by the chlorophyll pigment.

    Golgi Apparatus

    • The Golgi appartus is a stack of pita-shaped sacs that modifies and sorts proteins destined for secretion or for transport to certain cell organelles. The sacs are called cisternae and are formed by fusion of smaller membrane-enclosed sacs called vesicles that carry proteins to the Golgi from the endoplasmic reticulum. Each of the cisternae moves out toward the cell membrane, where smaller sacs called vesicles will bud off from the cisternae, carrying proteins to their destination.

    Endoplasmic Reticulum

    • Plant cells feature two kinds of endoplasmic reticulum: rough and smooth. Rough ER modifies proteins destined for secretion or for use in certain other organelles. Smooth ER acts as a site for lipid synthesis. Each type is named based on its appearance under the microscope; unlike smooth ER, the surface of rough ER is studded with ribosomes.

    Ribosomes

    • Ribosomes are complexes of proteins and RNAs that catalyze protein synthesis based on instructions encoded in messenger RNAs (mRNAs). In turn, mRNAs are copies or transcripts of genes in the cells DNA, so when ribosomes translate the instructions in an mRNA into a protein, they are in effect translating the instructions encoded in the cell's DNA.

    Cytoskeleton

    • The cytoskeleton is a network of fibers that helps organize other structures in the cell. Cytoskeletal elements can be subdivided into three general classes: microtubules, intermediate filaments and microfilaments. Microtubules are tiny hollow tubes with walls formed from a protein called tubulin; they act as tracks to guide movement of certain other organelles and play a key role in cell division. Intermediate filaments are coiled strands of fibrous proteins that have high tensile strength and are important as a framework for the cytoskeleton. Microfilaments are tiny chains formed from a protein called actin that help to provide structure to the cell and are involved in cytoplasmic streaming, a continuous flow of cytoplasm (the fluid inside the cell) that helps circulate nutrients and other materials.

    Cell Wall

    • Cell walls are tough but flexible structures that encircle the cell membrane. They consist of carbohydrate polymers like cellulose and prevent plant cells from bursting through osmotic pressure (the pressure caused by water diffusing into the cell). They also stiffen the plant and keep it upright against the force of gravity.

    Vacuole

    • The vacuole is often the single largest and most prominent organelle in plant cells. It fulfills a variety of functions, including storage and breakdown of metabolic wastes, helping maintain the right solute concentration and pH inside the cell and maintaining pressure against the cell wall. Some plants also use their vacuole to perform other functions, like storing compounds that poison herbivores who try to eat the plant.

    Peroxisome

    • Hydrogen peroxide is a natural byproduct of certain reactions important in cell metabolism, but it's reactive and can oxidize other molecules in the cell. Some of these reactions take place inside structures called peroxisomes. Peroxisomes keep the hydrogen peroxide contained and break it down into water so other cell components are not damaged. Peroxisomes also play an important part in seedling growth and development; as a seedling grows, specialized peroxisomes called glyoxysomes help convert fatty acids from the seed to sugars that can fuel the plant's growth.

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References

  • Photo Credit Plants image by Degitail Imaging from Fotolia.com

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