CELL BIOLOGY Living organisms are made up of basic microscopic units called cells. Cells are prokaryotic and eukaryotic, wherein the latter is more complex and contains nuclear material. Plants and animals are made up of cells and though most of the cell organelles are the same, they do have their differences. This article provides information about the different cell organelles present in the animal cell, along with the diagram and functions. The labeled animal cell diagram will help understand the parts of the animal cell. Cell Membrane Cell membrane or plasma membrane is a membrane common to both plant and animal cells. As observed in the labeled animal cell diagram, the cell membrane forms the confining factor of the cell, that is it envelopes the cell constituents together and gives the cell its shape, form and existence. Cell membrane is made up of lipids and proteins and forms a barrier between the extracellular liquid bathing all cells on the exterior and the cell organelles floating in the cell's cytoplasm. This membrane is semi-permeable, thus, it allows only selected substances to pass through it into the cell's interior. Cytoplasm Cytoplasm or Cytosol is nothing but the jelly-like substance filling the cell. To be more precise, it is that fluid material present outside the nucleus and within the cell membrane, into which various cell organelles are scattered. The jelly-like substance is made of dissolved nutrients and helps different materials move throughout the cell, by a process called cytoplasmic streaming. Cytoplasm comprises a network of cytoplasmic filaments, that are responsible for the shape of the cell. Moreover, they also help the cell move. Read more on structure and functions of cytoplasm. Cell Nucleus The cell nucleus is the trademark of any eukaryotic cell. Plant and animal cells are eukaryotic cells, which means they possess a true nucleus. The cell nucleus is a spherical shaped body encompassing a nucleolus, chromosomes with DNA and some other organelles with the help of a nuclear membrane. This nucleus consists of highly specialized cell organelles that take care of storing the cell's hereditary material (DNA) and also coordination of different cell activities like protein synthesis, cell division, growth, etc. Read more on cell nucleus: structure and functions. Mitochondrion Mitochondria (singular - mitochondrion) are double membrane bound cells, scattered in the cell's cytoplasm. The double membrane comprises one outer smooth membrane and one inner convoluted membrane, forming loops called cristae. Both these membranes together form the outer double membrane and keep the fluid-filled matrix within the mitochondria from mingling with the cytoplasm of the cell. Mitochondria is popularly called 'power house of the cell' as it furnishes the cell with all the energy required (ATP) for locomotion, cell division, production of secretory products, etc. The number of mitochondria present in cells may vary depending on the cell's activity. Read more on mitochondrial DNA. Centriole Centrioles are self-replicating, cylindrical bodies comprising 9 triplet bundles of microtubules, which means each bundle has 3 microtubules and there are such 9 bundles. Centrioles are present only in animal cells and each animal cell contains two centrioles arranged perpendicular to each other. Their main function is assisting in the organization of cell division process. When animal cells divide, the centrosome of the cell divides into two and the centriole replicates. Thus, the new centrosome halves have a pair of centrioles each and form new independent daughter cells. Endoplasmic Reticulum (ER) ER is a vast network of membranous tubules and sacs called cisternae in the cell's cytoplasm. There exists two types of ER: Rough ER and Smooth ER. Rough ER features several ribosomes attached to its surface, thereby conducing to its rough appearance. The function of rough ER is protein synthesis and transport of nutrients. The smooth ER unlike the rough one does not have ribosomes attached to their surface, thereby giving them the smooth appearance. Its function is lipid synthesis, carbohydrate metabolism and detoxification of poisons and other harmful substances. Golgi Apparatus Also known as golgi complex, these are piles of flattened sacs layered one above the other. One can observe the golgi apparatus in the labeled animal cell parts diagram. The golgi apparatus is situated near the cell nucleus and besides the stacked sacs, it also contains large number of vesicles. The main function of this golgi complex to receive proteins synthesized in the ER and transformed it into more complex proteins. The vesicles in the apparatus are used to send molecules to the cellular membrane, from where excretion takes place. Lysosomes Lysosomes are produced by the Golgi apparatus and appear like small spherical bodies featuring a single membrane confining it. Their prime function is breaking down of cellular waste substances from the cell into simplified substances. The simplified versions are then transferred to the cytoplasm of the animal cell for building new cell materials. Lysosomes are able to do this with the help of over three dozen types of hydrolytic enzymes like lipases, nucleases, proteases, polysaccharidases, etc. Thus, lysosomes are responsible for digestion of nutrients in animal cells. Ribosomes Ribosomes are small, spherical organelles comprising 65% ribosomal RNA and 35% ribosomal proteins. These organelles are sites of protein assemblage and are responsible for protein synthesis. They occur scattered in the cytoplasm and are also found adhering to the surface of ER. Animal cells contain ribosomes with four strands of RNA. Vacuole Vacuoles are fluid-filled cavities encompassed by a membrane present within the cell itself. These vacuoles act as storage areas for the cells and play significant roles in release of cellular waste substances and intracellular digestion. Vacuoles present in animal cells are small as compared to plant cell vacuole. Plants are highly evolved, eukaryotic organisms that contain membrane-bound cell organelles. Even though plants and animals belong to eukaryotes, they differ in certain characteristic features. For example, a plant cell possesses a well-developed cell wall and large vacuoles, while an animal cell lacks such structural parts. Besides these structural differences, a plant cell lacks centrioles and intermediate filaments, which are present in an animal cell. A typical plant cell is made up of cytoplasm and organelles. In fact, all the organelles (except nucleus) and subcellular structures are present in the cytoplasm, which is enclosed by protective layers (the cell wall and cell membrane). Scientific studies have been done regarding the cell organelles and their functions. Each of the organelles of a plant cell has specific functions, without which the cell cannot operate properly. List of Plant Cell Organelles The plant cell is protected from the surrounding environment by the cell wall and cell membrane. Note that these two are surface structures and not cell organelles. They not only give shape, support, and strength to the cell, but also aid in transportation. When it comes to the organelles found in a plant cell, they are more or less similar to animal cells, except that the latter lacks chloroplasts, that are responsible for photosynthesis. Following is a list of organelles found in plant cell. Nucleus Nucleus (plural nuclei) is a highly specialized cell organelle, which stores the genetic component (chromosomes) of the particular cell. It serves as the main administrative center of the cell by coordinating the metabolic processes like cell growth, cell division, and protein synthesis. Together, the nucleus along with its contents is referred to as nucleoplasm. Plastids (Chloroplasts) Plastids are a collective term for organelles that carry pigments. In a plant cell, chloroplasts are the most prominent forms of plastids that contain the green chlorophyll pigment. Because of these chloroplast plastids, a plant cell has the ability to undergo photosynthesis in the presence of sunlight, water, and carbon dioxide to synthesize its own food. Ribosomes Ribosomes are plant organelles that comprise proteins (40 percent) and ribonucleic acid or RNA (60 percent). They are responsible for the synthesis of proteins. Inside the cell, a ribosome may occur freely (free ribosome) or it may be attached to another organelle, endoplasmic reticulum (bound ribosome). Each ribosome consists of two parts, a larger subunit and a smaller subunit. Mitochondria Mitochondria (singular mitochondrion) are large, spherical or rod-shaped organelles present in the cytoplasm of the plant cell. They break down the complex carbohydrates and sugars into usable forms for the plant. A mitochondrion contains certain enzymes that are essential for supply of energy to the plant cell. Hence, these cell organelles also known as the powerhouse of the cell. Golgi Body A golgi body is also referred to as golgi complex or golgi apparatus. It plays a major role in transporting chemical substances in and out of the cell. After the endoplasmic reticulum synthesizes lipids and proteins, golgi body alters and prepares them for exporting outside the cell. Arranged in a saclike pattern, this organelle is located near the cell nucleus. Endoplasmic Reticulum Endoplasmic reticulum (ER) is the connecting link between the nucleus and cytoplasm of the plant cell. Basically, it is a network of interconnected, convoluted sacs present in the cytoplasm. Based on the presence or absence of ribosomes, ER can be of smooth or rough types. The former type lacks ribosomes, while the latter is covered with ribosomes. Overall, endoplasmic reticulum serves as a manufacturing, storing, and transporting structure for glycogen, proteins, steroids, and other compounds. Vacuoles Vacuoles are the membrane-bound, storage organelles that help in regulating turgor pressure of the plant cell. In a plant cell, there can be more than one vacuole. However, the centrally located vacuole is larger than others, which stores all sorts of chemical compounds. Vacuoles also assist in intracellular digestion of complex molecules and excretion of waste products. Peroxisomes Peroxisomes are cytoplasmic organelles of the plant cell, which contains certain oxidative enzymes. These enzymes are used for the metabolic breakdown of fatty acids into simple sugar forms. Another important function of peroxisomes is to help chloroplasts in undergoing photorespiration process. Read more on plant cell structure and parts. Well! This was a brief information regarding plant cell organelles, their structure, and specific functions. Other parts of the plant cell include microfilaments (structural component), microtubules (cytoskeleton component), and plasmodesmata (connecting tube between cells). As we have seen above, the coordination of cell organelles is crucial for carrying out the physiological and biochemical functionalities of the plant.
