Glycogen Structure and Function, Exams of Advanced Education

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AQA A-level Biology paper 1 large molecules often contain carbon. why? - they can readily form bonds with other carbon atoms. this forms a 'backbone'. other atoms can then attach. describe benedicts test for reducing sugars - add equal volumes of the sugar sample and benedicts reagent. heat the mixture in a water bath for 5 minutes. brick red precipitate will form. what is a reducing sugar? - a sugar that can reduce (give electrons to) another chemical. describe the benedicts test for non reducing sugars - with food sample, add an equal volume of dilute hydrochloric acid in a test tube. place test tube in water bath for 5 mins. add sodium hydrogencarbonate solution. heat resulting solution with an equal volume of benedicts. solution for 5 minutes. turns orange/brown. what does dilute hydrochloric acid do in the benedicts test for non reducing sugars? - it hydrolyses any disaccharide into monosaccharides, thus also forming reducing sugars. describe the structure of starch - chains of alpha glucose some chains are branched= amylopetcin some chains are coiled= amylose what purpose does the structure of amylose serve? - makes the molecule compact so it is stored more easily. what purpose does the structure of amylopectin serve? - more surface area for enzymes to work on, thus glucose molecules can be released at a much quicker rate. how is the structure of starch suited to its function? - 1. starch is insolube so it doesnt affect water potential 2. it is large enough that it doesnt diffuse out of cells 3. compact enough so that a lot of it can be stored in a small space 4. branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released how is the structure of glycogen suited to its function? - 1. insoluble, so no effect on water potential of cell 2. insoluble, so doesnt diffuse out of cells 3. compact, a lot of it can be stored in a small space 4. very highly branched= each end can simultaneously be acted on by enzymes, so glucose is quickly released why do animals need highly branched glycogen? - because animals metabolic rate is faster than plants and so needs glucose to be released quicker. describe the structure of cellulose - made up of straight chains of beta glucose the chains are parallel to each other, so H bonds form cross-linkages all the H bonds together strengthens the cellulose forms microfibrils draw alpha and beta glucose - how does the structure of triglycerides relate to their properties? - 1. triglycerides have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms, so its a good source of energy. 2. low mass to energy ratio, so theyre good energy storage molecules. 3. large and non-polar, therefore insoluble, therefore don't affect osmosis. what type of bond forms between the phosphate group and deoxyribose sugar in DNA? - phosphodiester bond why is DNA stable? - 1. the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix 2. many hydrogen bonds link the base pairs together, so it adds strength overall. how is DNA adapted to carrying out its function? - 1. it is very stable, thus rarely mutates 2. the H bonds can easily be separated during DNA replication and protein synthesis 3. extremely large, thus carries a lot of genetic information 4. base pairing allows DNA to replicate and transfer info as mRNA. describe semi conservative replication - - DNA helicase unwinds separates the two strands of DNA into single strands by breaking the H bonds between the bases - this therefore forms 2 base templates (the bases on each strand are exposed) - free complimentary nucleotides align with the bases according to complimentary base pairing - they are joined via condensation reaction with DNA polymerase - the new DNA molecule is formed what is meant by resolution - the minimum distance apart that two objects can be in order for them to appear as separate items. before cell fractionation, why is the tissue placed in a cold, isotonic buffer? - cold: reduce enzyme activity that may break down the organelles isotonic: same water potential as tissue, this prevents organelles shrinking/bursting due to osmotic loss/gain of water buffered: so the pH doesn't fluctuate, so that nothing alters the organelle structures or affects enzyme functioning what are the advantages of an electron microscope? - electron beam has a short wavelength and the microscope can therefore has high resolution. the negatively charged beam can be focused using electromagnets. what are the limitations of using a transmission electron microscope? - the whole system must be in vacuum, so living specimens cant be studied. complex staining process the image may contain artefacts what is the function of SER? - synthesises, stores and transports lipids and carbohydrates what is the function of RER? - provides a large surface area to synthesise proteins and glycoproteins provides a transport pathway for materials throughout the cell what is the function of golgi apparatus? - add carbs to proteins to form glycoproteins produce secretory enzymes secrete carbohydrates transport, modify and store lipids form lysosomes what is meant by 'organ'? - a combination of tissues that are coordinated to perform a variety of functions. describe binary fission - the circular DNA molecule replicates and both copies attach to the cell membrane. plasmids also replicate cell membrane grows between the two DNA molecules, dividing the cytoplasm into two. a new cell wall forms between the two DNA molecules. two daughter cells are produced, each with a single copy of circular DNA and a variable number of plasmids. how do viruses replicate? - they attach to their host cell with their attachment proteins. nucleic acids are injected into host cell. the genetic info contains "instructions" for the host cells metabolic processes to start producing the viral components, which are assembled into new viruses. describe cell mediated immunity - 1. phagocytes injest pathogens. 2. the phagocyte places antigens from pathogen on its cell surface membrane, so it becomes an antigen presenting cell. 3. receptors of T-helper cells have a complimentary fit to these antigens. 4. this attachment activates T cells to divide rapidly by mitosis and form a clone of genetically identical cells. 5. the cloned T cells: a. develop into memory cells b. stimulate phagocytosis c. stimulate B cells to divide and secret their antibody d. activate cytotoxic T cells. describe humoral immunity - 1. the surface antigen of a pathogen is taken up by B cell 2. the B cell processes it and presents the antigen on its surface 3. T-helper cells attach to the processed antigens, thus activating the B cell 4. B cells divide by mitosis to produce a clone of plasma cells 5. these secrete the specific antibody that can bind to the pathogens antigen 6. the antigens destroy the pathogen 7. some B cells develop into memory cells what is passive immunity and how is it produced? - produced by the introduction of antibodies into individuals from an outside source. immunity is acquired immediately. no contact with pathogen/s needed. short term immunity: antibodies aren't replaced when broken down, memory cells not formed. e.g. anti-venom -so, diffusion concentration gradient established and maintained across the entire width of the gill lamellae -so, 80% of O2 in water absorbed into fish blood how does the structure of a plant leaf link to gas exchange? - -all cells are close to stomata, and therefore surface, therefore a short diffusion pathway -inter-connecting air spaces in the mesophyll so that gases can readily contact mesophyll cells describe and explain why plant stomata links to gas exchange and its benefits - stomata are like minute pores, on the underside of leaves. each has guard cells, which control the rate of gas exchange guard cells close when water loss is excessive how do insects limit water loss? - -small surface area to volume ratio -waterproof coverings -spiracles which can close how do xerophytes limit water loss? - -thick waxy cuticle -rolled up leaves: traps water vapour -hairy leaves: traps moist air -stomata in pits/grooves: traps moist air -reduced surface area to volume ratio by trapping air, water potential gradient is reduced describe the process of inspiration - external intercostals contract internal intercostals relax ribs move up and outwards, increasing thorax volume diaphragm contracts, further increasing thorax volume air pressure in lungs becomes lower than atmospheric pressure, so air is forced in describe the process of expiration - internal intercostals contract external intercostals relax ribs movie in and downwards diaphragm relaxes this decreases thorax volume air pressure in lungs becomes greater than atmospheric pressure, so air is forced out structure of haemoglobin - 4 polypeptide chains - 2 alpha - 2 beta each chain has a haem group which contains a ferrous Fe2+ ion. what is the vena cava connected to? - right atrium what is aorta connected to? - left ventricle what is pulmonary artery connected to? - right ventricle what is pulmonary vein connected to? - left atrium how is tissue fluid formed - high hydrostatic pressure at arterial end due to contractions of ventricles this causes tissue fluid to be forced out of the blood plasma this is ultrafiltration describe the process of lipid digestion - in small intestine, bile salts combine with fat droplets and break them down smaller (emulsification). lipase enzymes from pancreas hydrolyse lipids into fatty acids, glycerol and monoglycerides. short chain fatty acids: diffuse directly into blood via epithelial cell longer chain fatty acids: combine with bile salts to form micelles, which break down into fatty acids and monoglycerides which diffuse into epithelial cells. once there, they recombine into triglycerides which can form chylomicrons. artery structure - thick muscle layer so that they can dilate and contract to smooth blood flow. thick elastic layer so artery can stretch and recoil with systole and diastole, smoothing blood flow. overall thickness of wall is large so that it doesn't burst under pressure. why do arterioles have thinner elastic layer than arteries? - blood pressure is lower. vein structure - muscle layer is thinner, because they carry blood away from tissues, and so have less need to dilate. elastic layer is thinner because of lower blood pressure, which doesn't need recoil. overall thickness of wall is thinner due to low blood pressure. valves at regular intervals to ensure there's no backflow of blood. why do veins have thinner walls than arteries? - thinner walls because blood is at lower pressure, and so less stretch and recoil with each contraction of ventricles. capillary structure - one cell thick endothelium. allows rapid diffusion. numerous, highly branched, so provides a larger surface area. narrow lumen and diameter. spaces in lining to allow tissue fluid to form. how does water travel into/through plants? - the water particles have higher water potential than the root hair cell, and so they enter the cell by osmosis down a water potential gradient. the water potential of the root hair cell is now higher than the cortex cell, and so water enters the cortex cell by osmosis. describe the process of translation - 1. mRNA associates with a ribosome in the cytoplasm 2. tRNA molecules with complimentary anticodons align with the first 2 mRNA codons 3. peptide bond forms between the amino acid molecules 4. the tRNA that bound to the first codon is free to leave the ribosome 5. the ribosome moves along the mRNA by one codon and now a new tRNA with a complimentary anticodon enters the ribosome 6. this continues until the ribosome reaches a stop codon the 2 mechanisms that mean that meiosis will result in genetic variation - independent segregation crossing over what happens during independent segregation? - during meiosis 1 each chromosome aligns with its homologous partner at the equator of the cell the combination of maternal/paternal chromosomes aligns randomly one chromosome of each pair goes to daughter cell- by chance what happens during crossing over? - when the chromosomes align, the chromatids of each pair become twisted around one another tension is built and portions of chromatids are broken off, which rejoin with the chromatid of the homologous partner so, new genetic combinations of maternal and paternal alleles are produced what is ATP made up of? - adenine ribose 3 phosphates how does ATP store energy? - has 3 phosphates, the bonds between these are unstable and so have a low activation energy, hence easily broke. when they break, they release energy. what does ATP synthase catalyse? - the formation of ATP from ADP in what scenarios is ATP reformed? - during photosynthesis, in chlorophyll containing plants during respiration (oxidative phosphorylation) substrate level phosphorylation why is ATP a good immediate energy source in a cell - the instability of the phosphate bonds. each ATP molecule releases less energy than glucose molecule, and so is smaller and more manageable the hydrolysis of ATP to ADP is a single reaction that releases immediate energy what energy requiring processes need ATP? - metabolic processes movement active transport secretion activation of molecules which has a longer wavelength: light or a beam of electrons? - light what are the two types of electron microscope? - transmission electron microscope scanning electron microscope how does a transmission electron microscope work? - it has an electron gun which produces a beam of electrons this is focused onto a specimen by condenser electromagnets the beam passes through the specimen some parts of the specimen absorb the electrons and appear dark and vice versa an image is produced why cant the highest resolution images not be produced by TEM? - there are difficulties preparing the specimen, which can limit resolution a higher energy electron beam may destroy the specimen how does a scanning electron microscope work? - it directs an electron beam onto a specimen surface rather than penetrating it. the beam is passed back and forth across a specimen in a regular pattern, depending on its contours a computer is used to build up a 3D image how to calibrate an eyepiece graticule? - use a stage micrometer and align it with the eyepiece graticule. then, calculate the length of each subdivision define ecology - the study of the inter-relationships between organisms and their environment, including abiotic and biotic factors. define ecosystem - dynamic systems made up of a community and all the non-living factors of its environment. It includes all the living organisms that interact with one another and also with the physical and non-physical factors present. biotic - living abiotic - non-living define population - a group of individuals that occupy the same habitat at the same time and are potentially able to interbreed. define community - all the populations of different species living and interacting in a particular place at the same time. define habitat - the place where an organism normally lives