Biology Notes The Cell C.Walsh The Cell The basic unit of life 2 Contents The Light Microscope Electron Microscope The Cell Cell Ultra structure Cell membrane The Cell Wall Mitochondria Plastids Ribosomes Vacuoles Slides of cell types Prokaryotic or Eukaryotic? 3 The Light Microscope 4 Microscope • • Light microscope • The parts of a light microscope include: The stage, to hold the slide The light source 5 The diaphragm, to adjust the brightness of the light The eyepiece The objective lens The total magnification is found by multiplying the magnification of the Light microscope: it focuses light with a combination of objective lens and an eyepiece to a maximum magnification of 1500 1 of 9 Biology Notes The Cell C.Walsh eyepiece with that of the objective lens. 6 Transmitting Electron Microscope (TEM) • Electron microscope: a microscope that magnifies up to 500,000 times by passing beams of electrons through the specimen • A TEM is much more powerful than a light microscope. It reveals the ultra structure of cells because its resolving power is about 1 nm. 7 Scanning Electron Microscope (SEM) • Photographs reflected electros from surfaces and reveals 3D structures. • It has less detail than a TEM but can be used on slightly larger specimens 8 The Cell Cell: the basic unit of life. Cells consist of plasma membrane, cytoplasm, and nucleus (if present). Outside the plasma membrane there may be a cell wall e.g. plant, fungal and bacterial cells. 9 There are two kinds of cell • prokaryotic cells, e.g. bacteria, do not have a true nucleus • eukaryotic cells do have a nucleus. Eukaryotic cells may also have mitochondria and chloroplasts. Plant cells differ from animal cells in having • A cell wall • A large vacuole • Chloroplasts. 10 Prokaryotic Cells Possess nuclear material Do not have a membrane surrounding this genetic material 11 Prokaryotic cells – mixed bacteria 2 of 9 Biology Notes The Cell C.Walsh 12 Eukaryotic Cells Possess a true nucleus 13 Eukaryotic cells - amoeba 14 More eukaryotic cells Paramecium Spirogyra Euglena Chlamydamonas 15 Cell Ultra structure • Cell ultra structure: the cell organisation that is visible under the electron microscope. 3 of 9 Biology Notes The Cell C.Walsh 16 Cell ultra structure 17 Cell Components Cell wall Cytoplasm Nucleus Vacuole Chloroplast Cell membrane Mitochondria Nuclear pores Ribosome DNA 18 Cell Membrane Structure 2D 19 Cell membrane structure 3D 4 of 9 Biology Notes The Cell C.Walsh 20 Phospholipid 21 Phospholipid 22 Cell Membrane • • • • • • Is not solid and is self-sealing if broken open, i.e. it is a fluid, moving barrier. • These glycoproteins and glycolipids are involved in making contact with other cells and in cell protection Forms a bilayer around the perimeter of the cell The heads of the lipid molecules are hydrophilic – attracted to water The tails of the molecules are hydrophobic – repel water 23 Large protein molecules float freely within the bilayer Carbohydrate molecules are often fixed to proteins and lipids on the outer side of the membrane 24 Functions of cell membrane • • • Allow diffusion of gases Allow the passage of water by osmosis Allow the transmission of light 5 of 9 Biology Notes • • • The Cell C.Walsh Actively move specific chemicals from one side to the other Defend the cell against attack Generate nerve impulses (as in nerve cells) 25 The Cell Wall • • • • • Lies outside the cell membrane Composed of tiny microfibrils of cellulose and other polysaccharides Very strong – contributes to strength, protection and shape of the cell Fully permeable Adjacent plant cells glued together by calcium pectate – the middle lamella 26 Mitochondrion structure • • • • Power house of cell Produces ATP Used during respiration 2 or 3 per skin cell 800 per muscle cell 27 Plastids Three types • Chloroplasts (green - chlorophyll) – photosynthesis • Chromoplasts (coloured) – petal colour • Leucoplasts (colourless) – starch storage e.g. potato 28 Ribosomes • • • Thousands found in the cytoplasm of every cell • A single strand of mRNA often passes over several ribosomes Made from protein and RNA Enzymes and proteins made here – DNA in the nucleus sends mRNA to the ribosomes with instructions for protein synthesis 29 Vacuoles • Plant cells have permanent vacuoles 6 of 9 Biology Notes The Cell C.Walsh • • Fluid filled spaces surrounded by a membrane (the tonoplast) • Animal cells have smaller, temporary vacuoles sometimes called vesicles Contain cell sap – a mixture of food, minerals, pigments and water 30 Examples of Animal Cells 31 Examples of Plant cells 32 Drawing of a Root cell - TEM 7 of 9 Biology Notes The Cell C.Walsh 33 Prokaryotic or Eukaryotic? 34 Prokaryotic cells • • Bacteria differ from plants, animal and fungi in the type of cell they possess • Do not have a definite nucleus and have fewer organelles Bacteria have prokaryotic cells – perhaps the type of cell that first appeared millions of years ago 35 Eukaryotic cells • • • Plants, animals and fungi possess eukaryotic cells A more advanced cell type Have a definite nucleus, bounded by a nuclear membrane, and many organelles 36 Prokaryotic Cells V Eukaryotic Cells • No distinct nucleus • No nuclear membrane • Single, circular chromosome of DNA • Have ribosomes • No mitochondria • No plastids • Cell wall contains protein • Small cell size 1 – 10 µm 8 of 9 • Distinct nucleus • Nucleus bounded by a nuclear membrane • Many chromosomes of DNA • Have ribosomes • Have mitochondria • Have plastids • Cell wall contains cellulose or chitin • Larger cell size 10 – 100 µm Biology Notes The Cell 37 Generalised Animal Cell 38 Generalised Plant Cell END 9 of 9 C.Walsh
