Plant Cell PDF

The Plant Cell  Plant Cell  Plants, like any multicellular organisms, are made of cells that show a complex division of labour.  Plants have different types of cells.  Plants have different types of tissues and organs.  Plant cells, have properties and structures t...

The Plant Cell  Plant Cell  Plants, like any multicellular organisms, are made of cells that show a complex division of labour.  Plants have different types of cells.  Plants have different types of tissues and organs.  Plant cells, have properties and structures that make it different from those of other life forms.  Plants are composed of Eukaryotic cells.  Plant Cell A plant is a multi-cellular organism composed of millions of cells with specialized functions. All plant cells have the same basic organisation. They contain a nucleus, a cytoplasm, a sub-cellular organelles enclosed in membranes. Plant Cell  Plant Cell Cell Wall In plants, the cell wall protects the cell, maintains its shape, and prevents excessive uptake of water. It also supports the plant against the force of gravity. The thickness and chemical composition of cell walls differs from species to species and among cell types. The basic design consists of microfibrils of cellulose embedded in a matrix of proteins and other polysaccharides. This is like steel-reinforced concrete or fiberglass. A mature cell wall consists of a primary cell wall, a middle lamella with sticky polysaccharides that holds cell together, and layers of secondary cell wall. Plant Cell Cell Wall  Plant Cell Biological membranes All cells are enclosed in a membrane that serves of their boundary. This plasma membrane also called plasmalemma, it allows the cell to take up and retain certain substances and exclude others. Biological membranes are phospholipid bilayers that contain proteins. According to the fluid-mosaic-model, all biological membranes have the same basic molecule organization. They consist of double layers (bilayer) of phospholipids in which proteins are embedded.  Plant Cell Biological membranes Proteins: The protein associated with the lipid bilayer are of 2 main types: integral, and peripheral.  Plant Cell Biological membranes  Plant Cell Biological membranes A eukaryotic cell has extensive and elaborate internal membranes, which partition the cell into compartments. These membranes also participate in metabolism as many enzymes are built into membranes. The barriers created by membranes provide different local environments that facilitate specific metabolic functions. Each type of membrane has a unique combination of lipids and proteins for its specific functions. For example, those in the membranes of mitochondria function in cellular respiration.  Plant Cell The Nucleus The nucleus contains most of the genetic material of the cell. It is responsible for regulating the metabolism, growth, and differentiation of the cells.  Plant Cell The Nucleus In the nucleus is a region of densely stained fibers and granules adjoining chromatin, the nucleolus. In the nucleolus, ribosomal RNA (rRNA) is synthesized and assembled with proteins from the cytoplasm to form ribosomal subunits. The subunits pass from the nuclear pores to the cytoplasm where they combine to form ribosomes. The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA). The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific polypeptide.  Plant Cell The Endoplasmic Reticulum (ER) The ER is a network of internal membranes. There are two types of ER: 1- Smooth ER: NO RIBOSOMES, it functions as a major site of lipid synthesis and membranes assembly. 2- Rough ER: Covered by ribosomes that are engaged in protein synthesis.  Plant Cell The Endoplasmic Reticulum (ER) The endoplasmic reticulum (ER) accounts for half the membranes in a eukaryotic cell. The smooth ER is rich in enzymes and plays a role in a variety of metabolic processes. Enzymes of smooth ER synthesize lipids, including oils, phospholipids, and steroids. Rough ER is especially abundant in those cells that secrete proteins. As a polypeptide is synthesized by the ribosome, it is threaded into the cisternal space through a pore formed by a protein in the ER membrane. Many of these polypeptides are glycoproteins, a polypeptide to which an oligosaccharide is attached.  Plant Cell Golgi Apparatus The Golgi apparatus typically appears in electron microscope as stack of 3-10 flattened membrane sacs. Golgi sacs produce and distribute secretary products. Proteins and polysaccharides destined for secretion are processed on the Golgi apparatus.  Plant Cell Central Vacuole The membrane surrounding the central vacuole, the tonoplast, is selective in its transport of solutes into the central vacuole. The functions of the central vacuole include stockpiling proteins or inorganic ions, depositing metabolic byproducts, storing pigments, and storing defensive compounds against herbivores. It also increases surface to volume ratio for the whole cell.  Plant Cell Mitochondria & Chloroplasts Mitochondria and Chloroplasts are the sites of energy conversion. A typical plant cell has 2 types of energy providing organelles: mitochondria and chloroplasts. Both are separated from cytosol by double membranes.  Plant Cell Mitochondria & Chloroplasts Mitochondria (singular mitochondrion) are the cellular sites for respiration: the process in which the energy released from sugar metabolism is used for the synthesis of ATP.  Plant Cell Mitochondria & Chloroplasts Chloroplasts have also double membranes. Chloroplast membranes contain chlorophyll and associated proteins and are the sites of Photosynthesis.  Plant Cell Mitochondria & Chloroplasts In addition to their inner and outer membranes, they contain a third system of membranes called thylakoids. A stack of thylakoids forms a granum (plural grana). The fluid compartment surrounding the thylakoids is called the stroma. Adjacent grana are connected by unstacked membranes called stroma lamellae (singular lamella).  Plant Cell Cytoskeleton The cytoskeleton is a network of fibers extending throughout the cytoplasm. The cytoskeleton organizes the structures and activities of the cell. In plant cells, actin-myosin interactions and sol-gel transformations drive cytoplasmic streaming. This creates a circular flow of cytoplasm in the cell. This speeds the distribution of materials within the cell.