Plant Cell Structure PDF

 Cell the basic building blocks of all living things Most plant cells and a majority of animal cells are so small unit of measurement used for microscopic objects is usually the micron (um) micron is equivalent to 0.001 millimeter classified: by...

 Cell the basic building blocks of all living things Most plant cells and a majority of animal cells are so small unit of measurement used for microscopic objects is usually the micron (um) micron is equivalent to 0.001 millimeter classified: by fundamental structural elements by the way they obtain their food  Plant Cell “Plant cells are eukaryotic cells with a true nucleus along with specialized structures called organelles that carry out certain specific functions.” Plant cells are eukaryotic cells that vary in several fundamental factors from other eukaryotic organisms. Both plant and animal cells contain a nucleus along with similar organelles. One of the distinctive aspects of a plant cell is the presence of a cell wall outside the cell membrane.  Plant Cell Functions Plant cells are the building blocks of plants. Photosynthesis is the major function performed by plant cells. Photosynthesis occurs in the chloroplasts of the plant cell. It is the process of preparing food by the plants, by utilizing sunlight, carbon dioxide and water. Energy is produced in the form of ATP in the process. A few plant cells help in the transport of water and nutrients from the roots and leaves to different parts of the plants. Plant Cell Diagram Parts of the Plant Cell  Cell Wall the outermost part of a plant cell almost all plant cells have cell walls, except for the sperm cells of some seed plants contain large amounts of polysaccharide, of which cellulose is one  Cell Wall cellulose molecules may crystallize to form an extremely strong microfibril Cellulose microfibrils are packed together by other polysaccharides called hemicelluloses, which are produced in dictyosomes or Golgi bodies and brought to the wall by the dictyosome vesicles  Cell Wall cell wall of one cell is glued to the walls of adjacent cells by an adhesive- like layer, the middle lamella, which is composed mainly of pectic substances All plant cells have cell walls called the primary wall Between the primary wall and the protoplast, a secondary wall may arise  Cell Wall thicker than the primary wall and is impregnated with the compound lignin, making it stronger primary and secondary cell walls are permanent; once deposited, they are never degraded or depolymerized Cell walls can be found in plant and not in animal cells  Cell Membrane known as the plasmalemma (plasma membrane) of the cell, the plasma membrane provides a covering for the cell impermeable to harmful substances and permeable to beneficial ones, which makes it a semi-permeable membrane  Cell Membrane Molecular pumps in the plasma membrane keep substances moving by actively pumping them in and out of the cell composed of a double layer of phospholipids and associated proteins  Cytoplasm It is the largest part of the cell, having many cellular inclusions and organelles surrounded by the plasma membrane function?  Vacuole occupies around 30% of the cell’s volume in a mature plant cell Tonoplast - a membrane that surrounds the central vacuole  Vacuole storage and to sustain turgor pressure against the cell wall cell sap - a mixture of salts, enzymes and other substances  Mitochondria cellular respiration takes place Compounds such as sugars, starches, and amino acids are broken down and the energy released is used to synthesize new compounds that are both highly energetic and very reactive. ATP  Mitochondria Cristae inner membranes of the mitochondria have many tube-like infoldings Its folded nature increases the mitochondrion's inner surface area, providing more space for a number of enzymatic activities favorable to its functions  Mitochondria Matrix Between the cristae is the liquid matrix, the site of moast chemical reactions  Mitochondria Inner Membrane The inner membrane of the mitochondria is the center for ATP synthesis  Mitochondria Outer Membrane smooth, (i.e., having no folds), is readily permeable to solutes Numerous ionic pumps and channels are present, facilitating chemiosmosis *Chemiosmosis refers to the movement of hydrogen ions across the membrane via ATP synthase  Mitochondria Intermembrane Space the region between the inner membrane and the outer membrane of a mitochondrion or chloroplast  Mitochondria Ribosomes and mtDNA have their own ribosomes and DNA, both of which are different from their extra-mitochondrial counterparts can grow in size, like the cell, or grow in number as the demand for respiration increases  Mitochondria Ribosomes and mtDNA They are around 1 um in diameter and 5 um in length, and are capable of division the number of mitochondria per cell increases and may range from 100-1000, depending on the function of the cell morphology of the cell is related to its physiology  Dictyosomes (Golgi bodies) consist of disk-shaped sacs that are stacked-up together in a flat or cup-shaped array tendency of dictyosomes to form stacks is related to their functions receive vesicles from the endoplasmic reticulum  Dictyosomes (Golgi bodies) Once inside the dictyosome, the material is modified in the lumen of the vesicle New material may be synthesized Vesicles then start to swell and are released from the maturing face secretory vesicles are either for export to the outside of the cell or for its own use cell may use its own secretory materials for the repair of its worn-out parts or for the formation of lysosomal vesicles  Endoplasmic Reticulum a system of narrow tubes and sheets of membrane forming a network throughout the cytoplasm most of the cell's ribosomes are attached is called rough endoplasmic reticulum (RER) without attached ribosomes is called smooth endoplasmic reticulum (SER)  Endoplasmic Reticulum smooth ER is involved in lipid synthesis rough ER is in-charge of protein synthesis  Ribosomes common structures found dispersed in the cytoplasm or attached to the ER responsible for protein synthesis in the cell animal cells synthesize more proteins and are richer in ribosomes, particularly those found in the liver, compared to plant cells  Lysosome suicidal bags as they hold digestive enzymes in an enclosed membrane function as cellular waste disposal by digesting worn-out organelles, food particles and foreign bodies in the cell In plants, the role of lysosomes is undertaken by the vacuoles  Microbodies numerous spherical bodies, about 0.5-1.5 um in diameter, found in the cytoplasm two classes of microbodies: the glyoxysomes and the peroxisomes isolate reactions that either produce or use the compound hydrogen peroxide (H2O2)  Microbodies If peroxide escape from the microbodies, it would damage most things it would come in contact with two bodies also contain the enzyme catalase, which detoxifies peroxides through chemical reactions, converting it to oxygen and water  Microbodies Peroxisomes can also detoxify some products of photosynthesis Glyoxysomes are only found in plant cells and are involved in converting stored fats into sugars in plants important in the germination of oily seeds  Plastids have inner and outer membranes, and an inner fluid called stroma have ribosomes and a circular DNA that is not associated with histones grouped into chromoplasts and leucoplasts  Plastids Chromoplasts, which include chloroplasts and carotene, are colored plastids leucoplasts, like the proplastids and amyloplasts, are large, unpigmented plastids All pigments help in the process of photosynthesis, either in storage organelles like amyloplasts, or in photosynthetic organelles like chloroplasts  Plasmodesmata membrane-lined cytoplasmic nanopores that bridge adjacent plant cells enabling direct communication with one another facilitate the exchange of numerous metabolites and signaling molecules between cells and enable connected cells to coordinate their biochemical, physiological, and developmental processes that are required for plants to form and function as complex multicellular organisms  Cytoskeleton a structure that helps cells maintain plant’s shape and internal organization provides mechanical support that enables cells to carry out essential functions like division and movement  Microfilaments are found in almost all cells, protein filaments arranged in bundles play an important role in cyclosis, the streaming movement of the cytoplasm with the microtubules they form a flexible framework within the cytoplasm  Microtubules thin, hollow, tube-like structures that are commonly found just inside the plasma membrane regulate the addition of cellulose to the cell wall also found in the spindle fibers and cell plates of dividing cells  Intermediate Filaments generally strong and ropelike functions are primarily mechanical support less dynamic than actin filaments or microtubules commonly work in tandem with microtubules, providing strength and support for the fragile tubulin structures  Nucleus a membrane-bound structure that is present only in eukaryotic cells vital function of a nucleus is to store DNA or hereditary information required for cell division, metabolism and growth  Nucleus Nuclear Envelope outermost covering of the nucleus composed of a membrane perforated by numerous pores  Nucleus Nuclear Pore a protein-lined channel in the nuclear envelope that regulates the transportation of molecules between the nucleus and the cytoplasm  Nucleus Nucleoplasm the granular fluid inside the nucleus  Nucleus Chromatin darkly-staining bodies inside the nucleus contain the genes, which determine the inherited characteristics of the organism  Nucleus Nucleolus the site of synthesis of ribosomal RNA, which, when transported outside the nucleus, combines with protein to form the ribosomes  Diffusion “the movement of molecules from a region of higher concentration to a region of lower concentration down the concentration gradient.”  Types of Diffusion Simple diffusion A process in which the substance moves through a semipermeable membrane or in a solution without any help from transport proteins. For example, bacteria deliver small nutrients, water and oxygen into the cytoplasm through simple diffusion.  Types of Diffusion Facilitated diffusion a passive movement of molecules across the cell membrane from the region of higher concentration to the region of lower concentration by means of a carrier molecule.  Types of Diffusion Active Transport the assisted movement of a substance from a lower concentration to a higher concentration of that substance. In other words, during active transport, substances move against the concentration gradient. Types of Diffusion  Factors affecting Diffusion Temperature. Area of Interaction. Size of the Particle. Diffusion Pressure Gradient  Examples of Diffusion A tea bag immersed in a cup of hot water will diffuse into the water and change its colour. A spray of perfume or room freshener will get diffused into the air by which we can sense the odour. Sugar gets dissolved evenly and sweetens the water without having to stir it. As we light the incense stick, its smoke gets diffused into the air and spreads throughout the room. By adding boiling water to the dried noodles, the water diffuses causing rehydration and making dried noodles plumper and saturated.  Significance of Diffusion During the process of respiration, this process helps in diffusing the carbon dioxide gas out through the cell membrane into the blood. Diffusion also occurs in plant cells. In all green plants, water present in the soil diffuses into plants through their root hair cells. The movement of ions across the neurons that generates electrical charge is due to diffusion  Significance of Diffusion The exchange of gases through stomata takes place by the process of diffusion. Transpiration occurs by the principle of diffusion. The ions are absorbed by simple diffusion. The food material is translocated by this process. This process keeps the walls of the internal tissues of the plant moist. It is responsible for spreading the ions and molecules throughout the protoplast. Aroma of flowers is due to the diffusion of aromatic compounds to attract insects.  Osmosis the movement of solvent molecules from the region of lower concentration to the region of higher concentration through a semipermeable membrane. Since water is solvent in every living being, biologists define osmosis as the diffusion of water across a selectively permeable membrane. For example, plants take water and minerals from roots with the help of osmosis. Osmosis  Osmosis Osmosis is a passive process and happens without any expenditure of energy. It involves the movement of molecules from a region of higher concentration to lower concentration until the concentrations become equal on either side of the membrane. Any solvent can undergo the process of osmosis including gases and supercritical liquids.  Osmotic Solutions There are three different types of solutions: Isotonic Solution - one that has the same concentration of solutes both inside and outside the cell Hypertonic Solution - one that has a higher solute concentration outside the cell than inside Hypotonic Solution - one that has a higher solute concentration inside the cell than outside Osmotic Solutions  Types of Osmosis Endosmosis– When a substance is placed in a hypotonic solution, the solvent molecules move inside the cell and the cell becomes turgid or undergoes deplasmolysis. Exosmosis– When a substance is placed in a hypertonic solution, the solvent molecules move outside the cell and the cell becomes flaccid or undergoes plasmolysis.  Effect of Osmosis on Cells Osmosis affects the cells differently. An animal cell will lyse when placed in a hypotonic solution compared to a plant cell. The plant cell has thick walls and requires more water. The cells will not burst when placed in a hypotonic solution. In fact, a hypotonic solution is ideal for a plant cell.  Effect of Osmosis on Cells An animal cell survives only in an isotonic solution. In an isotonic solution, the plant cells are no longer turgid and the leaves of the plant droop. The osmotic flow can be stopped or reversed, also called reverse osmosis, by exerting an external pressure to the sides of the solute. The minimum pressure required to stop the solvent transfer is called the osmotic pressure.  Osmotic Pressure the pressure required to stop water from diffusing through a membrane by osmosis. It is determined by the concentration of the solute. Water diffuses into the area of higher concentration from the area of lower concentration. When the concentration of the substances in the two areas in contact is different, the substances will diffuse until the concentration is uniform throughout. Osmotic Pressure  Significance of Osmosis Osmosis influences the transport of nutrients and the release of metabolic waste products It is responsible for the absorption of water from the soil and conducting it to the upper parts of the plant through the xylem. It stabilizes the internal environment of a living organism by maintaining the balance between water and intercellular fluid levels. It maintains the turgidity of cells.  Significance of Osmosis It is a process by which plants maintain their water content despite the constant water loss due to transpiration. This process controls the cell to cell diffusion of water. Osmosis induces cell turgor which regulates the movement of plants and plant parts. Osmosis also controls the dehiscence of fruits and sporangia. Higher osmotic pressure protects the plants against drought injury.  Examples of Osmosis The absorption of water from the soil is due to osmosis. The plant roots have a higher concentration than the soil. Therefore, the water flows into the roots. The guard cells of the plants are also affected by osmosis. When the plant cells are filled with water, the guard cells swell up, and the stomata open. If a freshwater or saltwater fish is placed in the water with different salt concentrations, the fish dies due to the entry or exit of water in the cells of the fish.  Examples of Osmosis Humans suffering from cholera are also affected by osmosis. The bacteria that overpopulate the intestines reverse the flow of absorption and do not allow water to be absorbed by the intestines, which results in dehydration. When the fingers are placed in water for a longer period of time, they become pruney due to the flow of water inside the cells.  Plasmolysis defined as the process of contraction or shrinkage of the protoplasm of a plant cell and is caused due to the loss of water in the cell derived from a Latin and Greek word plasma – the mould and lusis meaning loosening  Stages of Plasmolysis 1. Incipient plasmolysis: It is the initial stage of the plasmolysis, during which, water starts flowing out of the cell; initially, the cell shrinks in volume and cell wall become detectable.  Stages of Plasmolysis 2. Evident plasmolysis: It is the next stage of the plasmolysis, during which, the cell wall has reached its limit of contraction and cytoplasm gets detached from the cell wall attaining the spherical shape.  Stages of Plasmolysis 3. Final plasmolysis: It is the third and the final stage of the plasmolysis, during which the cytoplasm will be completely free from the cell wall and remains in the center of the cell.  How do Water Pass through the Cell Membranes? During the process of Plasmolysis within the plant cell, the cell membrane separates the interiors of the cell from the surrounding. It allows the movement of water molecules, ion and other selective particles across the membrane and stops others. Water molecules travel in and out of the cell across the cell membranes and the water flow is a necessary consequence that enables cells to fetch water. How do Water Pass through the Cell Membranes?  How do Water Pass through the Cell Membranes? The process of plasmolysis can be easily explained in the laboratory by placing a living cell in a strong salt solution. When the plant cells are placed in the concentrated salt solution, because of osmosis, water from the cell sap moves out. Therefore, the water travels through the cell membrane into the neighboring medium. Finally, the protoplasm separates from the cell and assumes a spherical shape.  Types of Plasmolysis There are two different types of plasmolysis and this classification is mainly based on the final structure of the cytoplasm. Concave plasmolysis Convex plasmolysis  Types of Plasmolysis Concave Plasmolysis During the concave plasmolysis, both the cell membrane and protoplasm shrink away and begins to detach from the cell wall, which is caused due to the loss of water. Concave plasmolysis is a reversible process and it can be revised by placing the cell in a hypotonic solution, which helps calls to regain the water back into the cell.  Types of Plasmolysis Convex plasmolysis During the convex plasmolysis, both the cell membrane and protoplasm lose so much water that they completely get detach from the cell wall. Later, the cell wall collapses and results in the destruction of the cell. Convex plasmolysis cannot be reversed, and this happens when a plant wilts and dies from lack of water.  Examples of Plasmolysis Shrinkage of vegetables in hypertonic conditions. Blood cell shrinks when they are placed in the hypertonic conditions. During extreme coastal flooding, ocean water deposits salt onto land. Spraying of weedicides kills weeds in lawns, orchards and agricultural fields. When more amount of salt is added as the preservatives for food like jams, jellies, and pickles. The cells lose water due to higher concentration outside and become less conducive to support the growth of microorganisms.  Deplasmolysis When the plasmolyzed cell is placed in a hypotonic solution, (the solution in which solute concentration is less than the cell sap), the water travels into the cell, due to the higher concentration of water outside the cell. Then the cell swells and becomes turgid. This is known as deplasmolysis.  Imbibition a type of diffusion where the water is absorbed by the solid particles called colloids, causing an enormous increase in volume. The solution is not formed in the process. In other words, water absorption by colloids is known as imbibition. Colloids are hydrophilic in nature.  Imbibition Here, the solid substances are referred to as imbibants and the imbibed liquid is referred to as imbibate. E.g. the absorption of water by seed or dry wood. The capacity of imbibing will differ in different imbibants. For instance consider proteins, since it is a hydrophilic collides it will have maximum imbibing capacity. Compared to this, starch has less capacity and cellulose with least capacity.  Factors Affecting Imbibition pressure texture of the imbibant pH of the medium affinity of the imbibant for the imbibate  Condition Necessary for Imbibition Water potential gradient between imbibate and imbibant Force of attraction between imbibant and imbibate. Imbibation increases with an increase in temperature.  Imbibition In Plants Imbibition causes swelling of seeds and results in the breaking of testa. Imbibition is the initial step in seed germination. The water moves into ovules which are ripening into seeds by imbibition. Imbibition is dominant in the initial stage of water absorption by roots.  Imbibition Pressure This pressure can be of tremendous magnitude and can be shown by a technique that is used by early Egyptians. It was used to break stone blocks. Split rock and insert a wooden stalk that is completely dry in the crevices of the rocks and soak them in water. Different types of organic substances have different imbibing capacities. Proteins have a very high imbibing capacity compared to starch and cellulose has the least. That is why proteinaceous pea seeds swell more on imbibition than starchy wheat seeds.  Significance of Imbibition It facilitates water absorption. It helps in seed germination. It keeps the cells moist.  Imbibition and Diffusion Imbibition Diffusion It refers to the absorption of water by It refers to the movement of general surface. molecules, ions of solids, liquids or gases from the region of higher concentration to lower concentration It takes place both in living and dead It takes place in solids, liquids and cells. gases. It is a reversible process. 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