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Transcript
CELLS The cell is the basic unit of life. All living organisms are composed of cells and their products. Under a microscope, the human body is seen to be composed of many different cells; muscle cells, brain cells, liver cells - all of which are quite dissimilar. Yet the differences, while important, should not obscure the many similarities in structure(how something is made) which exist. Virtually all living cells have an outer cell or plasma membrane (a thin structure), cytosol (fluid content of the cell); many small structures called organelles and a quantity of DNA (deoxyribo nucleic acid) which controls the activities of the cell. In Unit 2 you will examine a variety of cells under a light microscope. It is important that you are able to identify the various structures, which are present. You are not expected to know, in fine detail, what the function(what something does) of the cellular structures you observe. This will be covered during Unit 3. Cells are made up of a: Nucleus a dense area inside the cell; Cytosol a semi transparent fluid surrounding the nucleus; Organelles(including the nucleus) and a Cell membrane a thin covering which holds the cell together and separates it from other cells and from the cell's environment. Cytoplasm – This is the cytosol and all organelles excluding the nucleus. PLANT CELLS 1-8 Not all plant cells possess these structures. ANIMAL CELLS Animal cell viewed under an electron microscope 1-8 Plant cell viewed under an electron microscope STRUCTURE & FUNCTION(S) OF ORGANELLES / MEMBRANES CELL STRUCTURE Mitochondrion 1-8 SKETCH &/OR DESCRIPTION A cigar-shaped structure bound by a double membrane, the inner one tucked and folded inside. FUNCTION Spherical in shape containing DNA, chromosomes and the nucleolus. Bound by a double membrane. Found in virtually all living cells. Nucleus A dense, solid structure found in the nucleus. Nucleolus CELL STRUCTURE SKETCH &/OR DESCRIPTION A membrane penetrated by holes (nuclear pores). Nuclear Membrane & Nuclear pore 1-8 FUNCTION A network of tubes and flattened sacs continuous with the cell membrane. 'Smooth' in appearance. Often looking like a series of channels. Smooth Endoplasmic Reticulum(SER) A network of tubes and flattened sacs continuous with the cell membrane. Ribosomes are attached giving the structure a 'rough' texture. Rough Endoplasmic Reticulum(RER) Cell Wall 1-8 Found in plant cells on the 'outside'. Composed of cellulose. A structure variable in shape and size containing dense sets of membranes like a stack of coins separated by loosely arranged membranes. Chloroplast A set of paired rods enclosed by a belt of large molecules. Difficult to see unless using an electron microscope. Centriole CELL STRUCTURE SKETCH &/OR DESCRIPTION A membrane often tucked and folded and leading off into the endoplasmic reticulum. Cell/Plasma Membrane 1-8 FUNCTION A series of flattened disc-shaped sacs, stacked one on top of the other and connected to the endoplasmic reticulum. Vesicles(look like small balloons) appear to pinch off from the body. Golgi Body/Apparatus Small ‘grains’ when viewed under an electron microscope. Difficult to detect their internal structure. Found in the cytoplasm and on rough endoplasmic reticulum(RER). Only visible with an electron microscope. Unlike the diagrams below, they are not truly spherical. Ribosome Generally spherical, thin-walled sac showing little internal structure but often containing fragments of material being broken down. Lysosome Vacuole 1-8 Simple organelles that are simply membranebound sacs. They may occupy the majority of plant cells. If present in animals they are usually small. Vesicle Smaller than vacuoles but similar in appearance. Often seen 'pinching off' Golgi, endoplasmic reticulum and cell membranes. Contains the cytosol(fluid within a cell) and all organelles with the exception of the nucleus. Cytoplasm Plastids(chloroplasts, chromoplasts and leucoplasts) Chloroplasts have already been discussed. Leucoplasts are found in underground storage organs of plants. They lack coloured pigments (translucent). Chromoplasts are yellow, red or orange in colour. DIFFERENCES BETWEEN PLANT AND ANIMAL CELLS Although there are many similarities between plant and animal cells there are some important differences. Animal cells do not possess Higher plants(not mosses) do not possess Plastids(chloroplasts, leucoplasts and chromoplasts. Centrioles. Cell walls Asters Large permanent vacuoles COMPOUNDS IN CELLS Carbohydrates(C, H & O) 1-8 Monosaccharides = one sugar e.g. glucose. Disaccharides = two sugars e.g. sucrose = glucose + fructose. maltose = 2 glucose molecules. Polysaccharides = many sugars e.g. cellulose and starch in plants, glycogen in animals(all contain many glucose molecules joined together).Cellulose is found in the cell walls of plants. Other carbohydrates are found in the cytoplasm; little carbohydrate is found with the vacuole. Proteins(C, H, O, N & S + P in some proteins) Made up of many amino acids. Peptide linkages join the amino acids. Examples of proteins: enzymes, some hormones and structural proteins(e.g. hair). Proteins are found in the cytoplasm and in cellular membranes. Lipids(Fats & Oils; C, H & O) Possess a lower proportion of oxygen than carbohydrates. Structural units = fatty acids and glycerol. Found in the cytoplasm and membranes. Nucleic acids Genetic material of all organisms 2 types: DNA (deoxyribonucleic acid) & RNA (ribonucleic acid) Both made of long chains of subunits call nucleotides. Nucleotides made up of a phosphate group, sugar group and a base. Vitamins Organic molecules required by animals in small amounts for normal functioning. Some vitamins can be synthesised by animals – others must be obtained in their diet. 2 categories: water soluble and lipid soluble (water soluble must be consumed regularly as they cannot be stored in the body). 1-8