2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 368 questions
Chromatography is a technique used to separate molecules by their solubility. The diagram shows one apparatus used for this technique. absorbent paper solvent a mixture containing one or more types of molecules As the solvent rises up the paper, the molecules with the greatest solubility in the solvent travel a fixed distance up the paper. When the solvent reaches the top of the paper, the paper is removed, dried and sprayed with a dye. The different molecules appear as coloured spots. Chromatography was carried out on four different carbohydrates; sucrose, cellulose, the products of hydrolysis of sucrose and the products of hydrolysis of cellulose. Which diagram shows the presence of the products of sucrose digestion?
9700_w14_qp_13
MCQ
2014
Paper 1, Variant 3
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Glycogen is a highly branched polysaccharide molecule that is stored in the liver, kidney and muscles of mammals. shows a small part of a molecule of glycogen. CH2OH C O O H H C H OH H C C C O CH2OH CH2 C O H H C H OH H C C C O CH2OH C O O H H C H OH H C C C O C O H H C H OH H C CH2OH C O H OH H H C H OH H OH H OH H OH H OH H C C C O C C O X Name the bond at X. State the advantages for a mammal of having a storage molecule that is highly branched. State two ways in which the structure of cellulose differs from the structure of glycogen. 1. 2. Glycogen from animals and starch from plants form a large part of the energy intake of humans. is a flow chart that shows the energy input, in one growing season, into a field of a cereal crop which is processed to provide animal feed. solar energy = 9 × 107 kJ energy absorbed by cereal plants in photosynthesis processing to produce 140 kg of animal feed energy in the cereal crop harvested = 4 500 000 kJ energy in feed = 2 000 000 kJ initial mass of animals = 25 kg final mass of animals = 75 kg mass gain in 12 weeks = 50 kg energy in 50 kg of animals for human consumption = 385 000 kJ Calculate the percentage of the energy in animal feed that is converted into energy available for human consumption. Show your working. answer Explain why the energy available to humans from feeding on animal products is much less than if the energy came directly from crop plants, such as cereals.
9700_w15_qp_23
THEORY
2015
Paper 2, Variant 3
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shows the structure of sucrose, a disaccharide produced by plant cells. CH2OH CH2OH H H HO OH H HOCH2 H OH H H H OH HO H O O O Name the covalent bond that joins the two monomers in sucrose. Sucrose is hydrolysed by the enzyme sucrase in the human digestive system. The products of this hydrolysis reaction are the monosaccharides α-glucose and fructose. Complete the diagram to show the hydrolysis of sucrose to form α-glucose and fructose. CH2OH CH2OH H H HO OH H HOCH2 H OH H H H OH HO H O O O Plants transport sucrose from a source to a sink. is a scanning electron micrograph (SEM) of a transverse section through a plant tissue used to transport sucrose. X Name the structure labelled X in . A scientist carried out an experiment to study carbohydrate transport in the stem of a woody plant. shows a plan diagram of a transverse section of the stem studied by the scientist. The position of the xylem tissue in the stem is shown. outer stem tissues xylem tissue pith The scientist carried out a set of experiments using plants of the same species. Sucrose is a sweet-tasting sugar found in many foods. Some people become ill when they have sucrose in their diet. These people have a gene mutation in the gene coding for sucrase and cannot hydrolyse sucrose in the digestive system. Scientists studying the DNA of people with this condition identified a deletion mutation in the gene coding for sucrase. Suggest and explain why a person with this deletion mutation cannot digest sucrose.
9700_w24_qp_21
THEORY
2024
Paper 2, Variant 1
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Both sorghum and maize are important food crops in dry regions of the world, but sorghum is able to produce higher yields than maize in very dry conditions. This is partly because sorghum plants have a smaller leaf area than maize, and also because sorghum leaves have rows of motor cells along the midrib of the upper surface of the leaf, allowing the leaves to roll up. Explain how these two features adapt sorghum plants for growth in very dry conditions. Sorghum is a staple food in Africa, but the major storage protein that it contains, kaffirin, is not easily digested by protease enzymes. The main cause of this is cross-linking between kaffirin molecules. The digestibility of the protein in five varieties of sorghum was measured when raw, and after cooking. Digestibility was measured as the percentage of the protein that would be broken down to amino acids during digestion. The results are shown in . HDI Macia Seredo variety of sorghum NK8828 Sudan digestibility (percentage of proteins broken down to amino acids) Key raw cooked With reference to compare the digestibility of raw and cooked sorghum protein using your knowledge of protein structure and enzyme activity, suggest reasons for the differences you have described in .
9700_s11_qp_41
THEORY
2011
Paper 4, Variant 1
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Glycogen and cellulose are polymers. shows small, representative regions of a glycogen molecule and a cellulose molecule. CH2OH CH2OH CH2OH H O H H OH CH2 O H OH H H O H H OH O H OH H H O O H H OH O H H O H H OH O H OH H OH H O glycogen cellulose OH H H CH2OH H O H H OH O H OH H O H OH CH2OH O H H O H OH H H CH2OH H O H H OH O OH H OH CH2OH O H H Describe three ways, visible in , in which the molecule of glycogen differs from the molecule of cellulose. Glycogen is found in the form of granules in mammalian liver and muscle cells. is a diagram of part of a molecule of glycogen isolated from a glycogen granule. Explain how the structure of glycogen is related to its function in cells. Explain how the arrangement of cellulose molecules in plant cell walls is related to their function.
9700_s23_qp_21
THEORY
2023
Paper 2, Variant 1
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Questions Discovered
368