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33 Cards in this Set
- Front
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Describe the ultrastructure of prokaryotic cells. |
Small cells (1-10μm) Small ribosomes (20nm diameter) Peptidoglycan cell wall No microtubules Single, circular DNA which isn't associated with histones ie it's naked DNA is found in nucleoid No membrane-bound organelles Sometimes has a slimy outer capsule Plasmids usually present. |
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Describe the ultrastructure of eukaryotic cells. |
Larger cells (10-100μm) Larger ribosomes (25nm diameter) Cellulose/chitin cell wall No plasmids No capsule Membrane-bound organelles DNA associated with proteins and found in the nucleus Microtubules present and organised as centrioles. |
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Explain the nucleus. |
Bordered by a double membrane known as the nuclear envelope. The nuclear envelope has pores which allow the movement of large molecules between the cytoplastm and the nucleoplasm. The outer membrane is encrusted with ribosomes and is outfolded to form the rough endoplasmic reticulum. The nucleolus contains the cells genetic material (chromatin) which consists of heterochromatin (dark, condensed, inactive and found near the nuclear envelope) and euchromatin (lighter, unwound, active and found near the centre of the nucleus). The nucleus contains the nucleolus which synthesises ribosomes which are then attached to the membrane of the rough endoplasmic reticulum. |
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Explain the smooth endoplasmic reticulum. |
The smooth ER is a system of membrane-lined flattened cavities (cisternae). They do not have ribosomes. Their main function is the synthesis and transport of proteins. |
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Explain the rough endoplasmic reticulum. |
The rough ER is a system of membrane-lined, flattened cavities (cisternae). Ribosomes are attached to the membrane of the ER. The rough ER is a system of membrane-lined, flattened cavities (cisternae). Ribosomes are attached to the membrane of the ER. Synthesised proteins are passed through the membrane and are accumulated in the vesicles.The vesicles are pinched off the rough ER and transport them to the golgi apparatus. |
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Explain ribosomes. |
They are a mixture of proteins and ribosomal RNA. They are the site of protein synthesis. |
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Explain golgi apparatus. |
Vesicles, containing synthesised proteins, are pinched off the rough ER and transport them to the golgi apparatus. They join with the formative face of the golgi apparatus, which consists of a stack of membrane-lined flattened cavities (cisternae). Within the golgi apparatus, the proteins are modified and carbohydrate is added to form a glycoprotein, this stabilises the protein. The vesicles, containing the modified protein are then pinched off the mature face of the golgi apparatus. |
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Explain secretory vesicles. |
Vesicles are small, spherical and bound by a single membrane. Vesicles, containing the glycoprotein, moves towards the cell surface membrane. On arriving at the cell surface membrane, the membrane of the vesical fuses with the membrane of the cell. The contents of the vesicle are secreted to the exterior of the cell, ie exocytosis. Following exocytosis, the membrane of the vesicle is incorporated into the cell surface membrane as they have the same basic structure (the phospholipid bilayer). |
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Explain lysosomes. |
Lysosomes can be found in animal and fungal cells not not plant cells. They are a special type of vesicle produced by the golgi apparatus. They contain powerful hydrolytic (lytic) enzymes known as lysozymes. Lysosomes are involved in the digestion of degenerate cells eg mitochondria which is called intracellular digestion as it takes place inside the cell. Sometimes lysosomes release their enzymes inside the cell which results in the digestion of the whole cell ie autolysis. Lysosomes play a very important part in phagocytes and amoeba. In phagocytes, enzymes from lysosomes digest the bacteria. In amoeba, enzymes from lysosomes digest food that has been previously digested by amoeba. |
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Explain mitochondria. |
Bordered by a double-membrane. The inner membrane is folded to form finger like projections known as cristae (increase surface area available for reactions). Aerobic respiration takes place on the mitochondria and ATP is produced. The matrix contains small ribosomes and circular DNA. Aerobic respiration involves; - The Krebbs Cycle (takes place on membrane which has enzymes to control Krebbs Cycle) - Electron Transport Chain/ETC (takes place on cristae). |
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Explain chloroplasts. |
Chloroplasts are surrounded by a double membrane. It consists of an internal system of membranes called lamellae. Lamellae are organised into thylakoids and stack to from grana. Lamellae contain chlorophyll which is used to trap light energy. The chloroplast matrix is called the stroma and contains small ribosomes, circular DNA, starch grains and lipid droplets. There are two stages of photosynthesis; - The light-dependant stage (takes place on the lamellae/thylakoids). - The light-independent stage (takes place on the stroma as it contains enzymes for this particular stage). |
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Explain microtubules. |
Tubular structures made from a protein called tubulin and they occur within centrioles. Centrioles (found in animal cells) are organelles that are responsible for producing the spindle during cell division. |
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Explain plasmodesmata. |
Plasmodesmata creates gaps that connect plant cells. These occur at plant cell to cell junctions. At the plasmodesmata, there are channels of interconnecting cytoplasm. These allow direct movement between plant cells. |
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Explain vacuoles. |
Plants usually have a vacuole. These are responsible for support. The sap vacuole is surrounded by a membrane called the tonoplast. Vacuoles store nutrients and excretory products. |
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Define membrane. |
Structure surrounding cells and contribute to their internal structure. |
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Explain the structure of the phospholipid bilayer. |
Theu consist of phosphate head which are outermost, polar and hydrophilic, and hydrocarbon chains which are innermost, non-polar and hydrophobic. |
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Why is it known as the fluid mosaic model? |
Fluid - movement Mosaic - variety of different structures Model - a theory. |
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What proteins may the membrane contain? |
Extrinsic (attached to the bilayer) Intrinsic (embedded into one layer) Transmembranal (spans both layers). |
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What else may the membrane contain? |
Glycoproteins - carbohydrate/polysaccharide attached to a protein. Glycolipid - carbohydrate/polysaccharide attached to a lipid. (Glycoprotein + glycolipid = glycocalyx). Cholesterol may be found between the hydrocarbon chains in animal cells and it contributes to membrane stability. |
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What is the function of proteins in a membrane? |
Antigens Enzymes Receptor molecules Stability Support Carriers for facilitated diffusion and active transport Hydrophilic protein carriers. |
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What are the functions of other membrane components? |
Glycocalyx allows the cells to remember each other so they can group together to form tissue. Cholesterol increases fluidity at low temperatures and decreases fluidity at high temperatures. |
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Name 3 cells which are eukaryotic. |
Plant, animal and fungal cells. |
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Explain the eukaryotic cell structure of plant cells. |
Cellulose cell wall One nucleus Permanent vacuole Chloroplasts No centrioles Cellulose cell wall One nucleus Permanent vacuoleChloroplasts No centriolesEukaryotic - membrane bound organelles No cholesterol in cell membrane Cellulose cell wall One nucleus Permanent vacuoleChloroplasts No centriolesEukaryotic - membrane bound organelles No cholesterol in cell membrane Cellulose cell wall One nucleus Permanent vacuoleChloroplasts No centriolesEukaryotic - membrane bound organelles No cholesterol in cell membrane Cellulose cell wall One nucleus Permanent vacuoleChloroplasts No centriolesEukaryotic - membrane bound organelles No cholesterol in cell membrane Cellulose cell wall One nucleus Permanent vacuoleChloroplasts No centriolesEukaryotic - membrane bound organelles No cholesterol in cell membrane Eukaryotic - membrane bound organelles No cholesterol in cell membrane |
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Explain the eukaryotic cell structure of fungal cells. |
Chitin cell wall Multi-nucleate (many nuclei) Temporary vacuoles No chloroplasts No centrioles Eukaryotic - membrane bound organelles No cholesterol in cell membrane |
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Explain the eukaryotic cell structure of animal cells. |
No cell wall One nucleus No vacuole No chloroplasts Centrioles Eukaryotic - membrane bound organelles Cholesterol in cell membrane |
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Name the two types of microscopes used when examining cell structure. |
Light microscope and electron microscope. |
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Explain Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). |
The Transmission Electron Microscope uses the same basic principles as the Light Microscope only it uses electrons instead of light. The electromagnetic lenses focus the electrons into a thin beam, and the electron beam travels through the specimen you want to study. The Scanning Electron Microscope is similar to the TEM only the specimen is covered in a film of gold and the electron beam reflects off the surface to create a 3-Dimensional effect image. |
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What are the advantages and disadvantages of using an electron microscope? |
+ Greater magnification. + Greater resolving power. + Greater resolution. - The interior is a vacuum so specimens must be dead. |
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What are the advantages and disadvantages of using a light microscope? |
+ Livin organisms can be studied (so living processes eg mitosis can be studied). - Poor resolution of images. |
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Compare the light microscope with the TEM. |
Light microscope Uses light: wavelength 450-700nm Light refracted by glass lenses Low resolution: 200nm Low magnification: X1500 max Image formed on the retina of the eye or recorded on photographic film Limited intracellular detail that is revealed Transmission Electron Microscope Uses electrons: wavelength 0.01nm Electron beams refrected by electromagnetic lenses High resolution: 0.1nm High magnification: X1000000 max Image formed on florescent screen or recorded on film Specimens must be dead |
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Explain what artifacts are. |
This is something in a biological specimen that is not found naturally but has been introduced or produced during the procedure. |
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Convert 1mm to μm. |
1mm = 1000μm 1μm = 1000nm |
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What is the calculation of microscopy? |
O=MN (observed size = magnification natural size) |
