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Transcript
Tissues, organs and functioning organ systems within an organism In order to ensure an organism made from many millions of cells survives, the cells’ activities and functions needs to be organised. The level of organisation within multicellular organisms can be described under three main headings: Tissues A collection of cells that are similar to each other and perform a common function. These may be attached to each other but may not be. Examples include phloem and xylem in plants, and epithelial and nervous tissues in animals Organs A collection of tissues working together to perform a particular function. Examples include the leaves of plants and the liver in animals Organ systems Made up of several organs working together to perform an overall life function. Examples include the excretory system and the reproductive system EPITHELIAL TISSUES IN ANIMALS Animal tissues in general are grouped under four main categories: epithelial tissue – layers and linings connective tissue – hold structures together and provide support muscle tissue – cells specialised to contract and move certain body parts nervous tissue – cells that convert certain stimuli into electrical impulses and conduct those impulses Epithelial tissues form sheets which cover surfaces. Almost all organs in the body have some kind of epithelial tissue involved. Simple epithelia are one cell thick. Cells rest on a basement membrane (a network of collagen and glycoprotein, secreted by the underlying cells and that holds the epithelial cells in position). Squamous (pavement) epithelia cover many surfaces in the body including the cheeks, blood vessels and alveoli. The individual cells are smooth, flat and very thin. They fit closely together to provide a low-friction surface. Their thinness allows for rapid diffusion. Ciliated epithelia have cilia. Cells can be cubodial, as in the bronchioles, of columnar, as in the oviduct. The cells with cilia waft rhythmically, moving material over the surface, for example to move the egg along the oviduct. There are also mucus-secreting goblet cells present. In breathing tubes, the mucus traps dirt and microbes whilst cilia move it upwards. TISSUES IN A LEAF 1 – Upper epidermis: secretes a waxy cuticle to protect against pathogens and prevent dramatic water loss. Transparent to allow the light to reach palisade layer 2 – Palisade mesophyll: many chloroplasts circulating the cells for photosynthesis – long and thin cells mean fewer cell walls for light to pass through 3 – Spongy mesophyll: spread out to provide air spaces for uptake of CO2 for palisade cells and excretion of O2 4 – Lower epidermis: as upper epidermis, but also has stomata for gas exchange, controlled by guard cells www.asbiology101.wordpress.com TRANSPORT TISSUES IN PLANTS Plants need to move water and minerals from the soil through their roots and stems and up into their leaves. They also need to be able to move the products of photosynthesis around the plant to be used for growth or stored in other places for later use. In a plant, meristems are points at which meristem cells are produced. These are the only undifferentiated cells in a plant which can specialise into any other form of cell needed. Meristem regions are the root, shoot tips and a ring around the stem or trunk. Meristem cells can become cells which can become part of the transport tissues needed for the above functions. Some meristem cells produce small cells which elongate to become xylem cells. The xylem vessel walls are reinforced and made waterproof by deposits of lignin. The lignin kills the cell contents and breaks down the ends of the cells so that the stack of cells becomes one long hollow tube, with a wide lumen. Xylem tissue is used to transport water and minerals up the plant. Phloem Phloem tissue consists of sieve tubes and companion cells. The meristem tissue produces cells which elongate and Xylem line up end-to-end to form a long tube. Their ends do not completely break down, but form sieve plates between the cells. The plates allow the movement of materials up or down the tubes. Next to each sieve tube is a companion cell. These are very metabolically active. They move the products of photosynthesis up and down the plant. www.asbiology101.wordpress.com