Biology Topic 3A

• Magnification is the measure of how much bigger the image you see is when compared to the real life subject.
• Resolution is a measure of how far apart two objects must be before we see them separately.
• Light microscope is a tool that uses a beam of light and optical lenses to magnify specimens up to 1500 times life size.
• Actual size of specimen = Image size / Magnification
• Always measure in milimetres (mm) but the unit usually requires is micrometres (µm).
• Electron microscope is a tool that uses a beam of electrons and magnetic lenses to magnify specimens up to 500,000 times life size.
• An advantage of the light microscope is that they are relatively cheap and therefore accessible for schools, universities and hospitals.
• An advantage of the light microscope is that you can see the lining of plant or animal cells, this means that you can compare slides with living tissue.
• A disadvantage of the light microscope is that there is limited resolution powers and magnification ability.
• An advantage of electron microscopes is they have huge magnification and resolution powers. Details of the cell structure is clear and very useful.
• A disadvantage of the electron microscope is that all specimens are examined in a vacuum, therefore it is impossible to observe living material - all specimens are dead.
• A disadvantage of the electron microscope is that extremely expensive and therefore not accessible to everyone including schools.
• A disadvantage of the electron microscope is that the instrument is very large and must be kept at a constant temperature and pressure.
• Staining is used to make it easier to identify types of cells under the microscope. Examples include haematoxylin (stains nuclei purple/blue/brown), methylene blue (stains nuclei in animal cells blue), acetocarmine (stains chromosomes in divinding nuclei) and iodine (stains starch in plants blue/black).
• Scanning Electron Micrographs (SEMs) produce 3D images whereas Transmission Electron Micrographs (TEMs) produce 2D images.
• The nucleus contains genetic material which is found on chromosomes. (Before chromosomes, genetic material is found on chromatid).
• The nucleolus is involved in the production of ribosomes, as well as playing a part in the control of cell growth and division.
• Mitochondria's role is to produce ATP from aerobic respiration. They have a double membrane (outer and inner). The inner membrane folds to form cristae which gives a large surface area which is surrounded by a fluid matrix.
• Centrioles are involved in cell division - produce spindle of microtubules that are involved in the movement of chromosomes.
• Lysosomes contain a powerful mix of digestive hydrolytic enzymes to break down unwanted organelles or food (in single-celled protists).
• The golgi apparatus modifies and packages (folds) proteins. It is also involved in producing materials for plant and fungal cell walls and insect cuticles.
• Ribsomes' role is protein synthesis. Eukaryotic cells contain 80s ribsomes and prokaryotic cells contain 70s.
• The cell membrane regulates the movement of substances in and out of the cell.
• The Smooth Endoplasmic Recticulum (sER) is involved in synthesis and transports steriods and lipids. It is found in testes (which make steriod hormone testosterone) and is found in the liver (which metabolises cholestrol and other lipids).
• Rough Endoplasmic Recticulum (rER) are involved in protein synthesis and stores, and transports the proteins within the cell after they have been made. rER has a large surface area due to granule shape. Cells that secrete materials have large amount of rER.
• Nuclear envelope allows chemical substances to pass in and out of the nucleus, as well as RNA.This double membrane contains nuclear pores.
• Steps of protein synthesis: nucleous - produces ribsomes, nucleus - contains DNA to create mRNA, rER - covered in ribosomes, ribsomes - site of synthesis, vesicles - carry protein chain to golgi apparatus, at golgi apparatus - protein modfies and folded. Vesicle leaves by binding to cell membrane and protein exits by exocytosis.
• Prokaryotic cells do not contain membrane-bound organelles, they are typically unicellular and are usually same size as mitochondria or chloroplasts.
• Prokaryotic cells will always have a cell wall, cell membrane, cytoplasm, circular DNA, food store and 70s ribosomes.
• Prokaryotic cells sometimes have pili, flagellium, capsule, plasmid and infloded cell membrane called mesosones.
• Cell wall in prokaryotic cells: prevents cell from bursting, maintains shape and all have have a layer of peptidoglycan that consist of many parallel polysaccaride chains and short peptide cross-linkage.
• The capsules (slime layer): surrounds the cell wall, protects cell from phagocytosis, covers receptors which help identify cell (immune system struggle to recognise it) and prevents it from drying out.
• Pili: thread-like, helps attach to other cells (host cells), used in reproduction, yet make bacteria more susceptible to viral infections.
• Flagellum: made of many strands of the protein flagellum and rotates quickly to move the bacteria.
• Cell surface membrane in prokaryotic cells: made from phospholipid bilayer and have mesosomes.
• Gram staining is a method of staining bacteria that uses a dye to highlight the cell wall.
• Gram-positive bacteria have thick layer of peptidoglycan so are resistant to decolouring when dehydrated by alchohol and appear purple.
• Gram-negative bacteria have thin layer of peptidoglycan and the outer layer is made out of lipolysaccharides - this layer dissolves when bacteria are dehydrated in ethanol. Purple is washed aways and cell appears red.
• Obligate aerobes are organisms that need oxygen for respiration.
• Facultative anaerobes use oxygen if is available but can respire and survive without it.