Plant Cell http://henabio.wordpress.com/cell-structure-and-function/ Structure of a plant cell… • Nucleus. • Nucleolus. • Golgi bodies. • Ribosomes. • Lysosomes. • Rough and smooth endoplasmic reticulum. • Mitochondria. Cytoplasm. • Plasma membrane. • Plastids. • Vacuole. • Chloroplasts. • Microtubules. Cell wall. The cell wall is a semi-rigid structure which is made of microfi brils of cellulose chains arranged in layers. It is located outside the plasma membrane. It is 0.1 micro -metres to several micro-metres thick. The cell wall is composed of mainly cellulose which supports the cell and limits its volume. The cell wall is one of the features that plant cells have to differ them from animal cells. Cell walls are usually quite porous. However the cell wall itself does not have much to do with the entry and exit of substances, although it is strong and slightly elastic. The nucleus. The nucleus controls the cell and carries the genetic code. The nucleus is the most obvious organelle in the cell and can be seen easily when using a microscope. The nucleus consists of three main parts: The nuclear envelope: The nuclear envelope is made up of a double membrane. On the nucleus side there is a layer of protein which helps to maintain the shape of the nucleus. It is perforated by holes called pores. At the lip of each pore, the inner and outer membrane are fused in some way. These pores then control the entry and exit of the large molecules and particles that need to go in and out of the nucleus. Chromatin (chromosomes): Chromatin are made of DNA. When a cell is about to divide, the chromatin coils to form chromosomes. These then carry out genetic inheritance. The nucleolus: The nucleolus’ function is in the synthesis of Ribosomes. In some cells there are two or more nucleoli. However the nucleoli become disorganised when a cell is about to divide. Then after cell division has completed, they reappear again in special areas of chromosomes called nucleolar organisers. The plasma membrane. The plasma membrane is located inside the cell in plants and keeps it separate from the outside medium. The membrane is semi-permeable and controls what goes in and out of the cell. The plasma membrane is 3 to 10 nm thick. The plasma membrane receives information about changes in its surroundings and then responds to these changes. The membrane has a structural and chemical relationship with neighbouring cells. The general structure of a membrane is a mosaic of different protein molecules, bobbing in a double fluid layer (bilayer) of phospholipids. Under the electron microscope the plasma membrane appears as two dark bands with a clear area in between. Chloroplast. A chloroplast is a specialised plastid which contains the green pigment chlorophyll. They contain dense stacks of membranes (grana) within a colourless stroma. Chloroplasts’ are the site for photosynthesis and occur mainly in leaves. They are large, oval organelles. Starch granule. Starch granules are carbohydrates stored in amyloplasts (amyloplasts are plastids specialised for storage). Plastids are unique to plants, meaning that only plants have a starch granule. http://cdavies.files.wordpress.com/2006/10/cartoo n-starch-granule.jpg Lysosomes. Lysosomes are tough membranous bags which contain digestive enzymes. They have been called ‘suicide bags’ because they could potentially digest the cell itself. http://library.thinkquest.org/06aug/01942/plcells/thinkquest/lysoso mes.jpg Rough and smooth endoplasmic reticulum. The endoplasmic reticulum consists of a network of tubes. These form fluid-filled spaces surrounded by membranes. In most cells the spaces seem to be inter connected. The ER acts as a transport system, the synthesis of certain compounds takes place on the membranes. Smooth ER: The smooth ER has a smooth outer surface on it. It produces steroids, plays a role in calcium storage in muscle cells and affects muscle cells and affects muscle contraction, functions in cell sections. Rough ER: Rough ER is especially numerous in cells that secrete proteins. It is used to secrete proteins. Golgi bodies. Golgi bodies consist of a stack of flat disc like membranous sacs. These sacs are called cisternae. The Golgi apparatus is like a manufacturing warehouse, plus sorting and shipping. Here the products of the ER (endoplasmic reticulum) are stored, then modified by having other molecules attached to the proteins, and finally are sent out to their destinations. http://www.bact.wisc.edu/Microtextbook/images/book_4/chapter_2/ 2-59.gif Microtubules. Microtubules are thick, they consist of straight, hollow tubes made from globular proteins forming a spiral tube. They have an important role in the cilia, flagella and centrioles. http://www.quantumconsciousness.org/penrose- hameroff/orchOR_files/or_04.gif Ribosomes. Ribosomes are the site of protein synthesis. They are assembled in the nucleus and pass out through the nuclear pores. Ribosomes are made out of protein and RNA. They function in 2 places: 1. Some are free in the cytoplasm. 2. Others are attached to the outer membrane of the endoplasmic reticulum (ER). These are known as bound Ribosomes. The free Ribosomes tend to make proteins for use inside the cell cytoplasm. However the bound Ribosomes tend to make proteins to be secreted by the cell or used in membranes. Mitochondria. Mitochondria convert energy from food into a form that a cell can use ATP (adensoine tripphosphate). It is the site of aerobic respiration. E.g. a cell that has a lot of energy requirement has a lot of mitochondria. The mitochondria consists of a double membrane. Each membrane is a phospholipid bilayer with particular proteins embedded on it. http://www.cartage.org.lb/en/themes/sciences/zoology/AnimalPhysiology/Anatomy/AnimalCellStru cture/Mitochondria/mitochondria.jpg Vacuole. Plants have a large central vacuole. This is usually filled with an aqueous solution if ions. Vacuoles are prominent in plants and function in storage, waste disposal and growth. Some facts about the vacuole: • The vacuole takes up the whole of a mature cell. • They provide a place to store organic compounds and non organic ions. • The vacuole contains the enzymes usually held by the Lysosomes. • Some store metabolic wastes that would be poisonous to the cell. • Some vacuoles contain the pigments that colour the petals of flowers or the stems of plants. • Some store poisons as a defence against a herbivore eating them. • The large vacuole acts as a fluid skeleton, by inflating when full of water and becoming flaccid and floppy when the water is low. Cytoplasm. The cytoplasm appears as a watery solution. The cytoplasm is the place where most cellular activities are done. It contains dissolved substances, enzymes and also holds the cell organelles and structures. Also carried out in the cytoplasm are the functions which help the cell grow, expand and replicate. Plastids. Plastids are membrane bound structures which includes the green chloroplasts that carry out photosynthesis. There are three different types of plastids, they are: • Leucoplasts – these are starch stored plastids. • Chromoplasts – these contain pigments of colour which then give the colour to flowers etc. • Chloroplasts – these are large, oval shaped organelles. They are found in the green parts of plants and are the site of photosynthesis. How the cell works as a whole… A cell is like a factory, all of the different parts carry out different functions, each function is very important to the running of the cell. The cell wall holds everything together, and keeps the plant cells shape. The cell membrane makes sure that nothing bad gets into the cell. The nucleus is like the boss of the cell, it controls what goes on in the cell and also holds the genetic code. Ribosome's are the place where protein synthesis happens. The mitochondria is what turns the stuff that the plant cell eats into a form that the cell can use to function. Microtubules help to make up the flagella, cilia and centrioles which in turn, helps the cell to move etc. the Golgi Bodies are like the manufacturing warehouse, where the products of the ER are stored and shipped out (etc). The ER acts as a transport system around the cell. The lysosomes contain digestive enzymes. Only plant cells have starch granules. Starch granules are carbohydrates stored in amyloplasts. The plant cell needs each and every part of it to survive, this is because each part of the cell carries out specific jobs which help to make the cell a whole. Again, it is like a factory. The factory needs the boss, the workers and all the people to ship their products.