2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 368 questions
is a transmission electron micrograph showing parts of two plant cells. The function of the middle lamella is cell‑to‑cell adhesion. The middle lamella is composed of a polysaccharide known as pectin. Pectin interacts with the polysaccharides cellulose and hemicellulose in the cell walls of the plant cells so that the cell walls are held close together, as shown in . Golgi body middle lamella X Cell structure X in is a cytoplasmic channel with strands of cytoplasm passing through the cell walls of the two cells. Name cell structure X and state one function of this cell structure. name function Researchers have discovered that pectin is synthesised within the Golgi body. Golgi vesicles containing pectin are moved to the cell surface membrane for release. Suggest why researchers would not have investigated ribosomes as being the possible location for the synthesis of pectin. Name the mechanism that is used to transport pectin out of the cell. Juices that are extracted commercially from fruits can be made less cloudy by the breakdown of the cell wall using the enzymes cellulase, pectinase and xylanase: • cellulase hydrolyses cellulose • pectinase hydrolyses pectin • xylanase hydrolyses hemicellulose. is a graph showing the effect of cellulose concentration on the activity of cellulase, which is used in making fruit juice less cloudy. rate of reaction / mg product cm–3 min–1 cellulose concentration / mg cm–3 Describe and explain the curve shown in . Ultrasound is one possible method that can be used to destroy microorganisms that contaminate fruit juices. Ultrasound is the term given to sound waves that are out of the range of human hearing. An investigation was carried out into the effect of ultrasound on the activity of cellulase, pectinase and xylanase used in fruit juice manufacture. For each enzyme, the effect of ultrasound was compared with no ultrasound on the: • maximum rate of reaction (Vma• Michaelis‑Menten constant (Km) • catalytic efficiency (Vmax / Km) Table 5.1 summarises the results. A higher Vmax / Km indicates a higher catalytic efficiency. Table 5.1 enzyme method comparison of Vmax comparison of Km Vmax / Km / min–1 cellulase ultrasound higher higher no ultrasound lower lower pectinase ultrasound same lower no ultrasound same higher xylanase ultrasound higher same no ultrasound lower same In terms of changes in the interaction between enzyme and substrate when ultrasound is used, suggest explanations for the lower Km for pectinase and the higher Vmax for xylanase, as shown in Table 5.1. Explain whether the data shown in Table 5.1 supports the recommendation that ultrasound can be used in the manufacture of fruit juices.
9700_s21_qp_22
THEORY
2021
Paper 2, Variant 2
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Bacterial cells are prokaryotic. The cells of plants are described as eukaryotic. Complete the passage comparing a bacterial cell with a plant cell. A bacterial cell and a plant cell have a cell wall, but the main component of the bacterial cell wall is and not cellulose. The same organelle is used for protein synthesis in both cell types, but a bacterial cell only has smaller, 70S, . A bacterial cell does not have a large surrounded by a tonoplast. Protoplasts are plant cells that have had their cell walls removed by treatment with enzymes. Scientists often use protoplasts when researching ways to improve the yield of crop plants. is a scanning electron micrograph of protoplasts of cells from the tobacco plant, Nicotiana tabacum. magnification ×256 external solution at same water potential as protoplasts cell surface membrane Explain why scientists keep the protoplasts in a solution that has the same water potential as the cell. After protoplast treatment, the cells can be stimulated to synthesise new cell wall material. is at a higher magnification than and shows a scanning electron micrograph of part of a protoplast in an early stage of cell wall synthesis. magnification ×3075 cellulose microfibrils chloroplasts visible below the cell surface membrane The cellulose microfibrils visible in will form cellulose fibres. Each microfibril is formed from cellulose molecules. Each cellulose molecule is a polymer of β-glucose. Describe the structure of a cellulose molecule and a cellulose microfibril. Name one substance that may be added to the network formed by the cellulose microfibrils in the formation of a cell wall. Name the type of plant cell that could have been used to produce the protoplast shown in .
9700_s22_qp_23
THEORY
2022
Paper 2, Variant 3
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Cellulose is a polysaccharide. shows three sub-units from a molecule of cellulose. CH2OH C C C O C C H OH H H H OH H CH2OH C C C O C C H OH H H H OH H CH2OH C C C O O C C H OH H H H OH H O O Name the sub-unit molecule of cellulose. Name the bonds that attach the sub-unit molecules together within cellulose. Cellulose has high mechanical strength which makes it suitable for the cell walls of plants. Explain how cellulose has such a high mechanical strength making it suitable for the cell walls of plants. Plant cell walls consist of cellulose that is embedded in a matrix of compounds, such as pectins and proteins. Cell wall material is synthesised inside the cell and transported to the cell surface membrane as shown in the drawing made from an electron micrograph in . A L K J H G F E D C B Locate the parts of the cell labelled in which apply to each of the following statements. You must only give one letter in each case. You may use each letter once, more than once or not at all. The first answer has been completed for you. statement letter from organelle that contains DNA H transports cell wall material to the cell surface membrane site of transcription site of ribosome synthesis site of photosynthesis Enzymes known as expansins are found in the matrix of cell walls to help the growth of cells. Use the information in to describe how proteins made by the ribosomes reach the matrix of the cell wall.
9700_w10_qp_21
THEORY
2010
Paper 2, Variant 1
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Describe the structure of a cellulose molecule and explain how cellulose is a suitable material for the cell walls of plants. description explanation Animals do not have the ability to produce enzymes to digest cellulose. Most herbivores have bacteria in their digestive systems that can digest cellulose. shows the results of a study on 24 different herbivores. The percentage of cell wall material that was digested by each animal was determined. The time taken for the plant material to pass through the digestive system, the retention time, was also recorded. percentage of cell wall material digested retention time / h With reference to , describe the results of this study. Explain, in terms of energy flow in ecosystems, the importance of the results in . Digested material in animals is absorbed using both facilitated diffusion and active transport. State two similarities and two differences between facilitated diffusion and active transport. similarities: 1. 2. differences: 1. 2. Question 6 starts on page 12
9700_w13_qp_23
THEORY
2013
Paper 2, Variant 3
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Table 1.1 shows some features of four biological molecules that are all polymers. Complete Table 1.1 by using a tick (3) to indicate the features that apply to each polymer. Table 1.1 feature amylopectin cellulose RNA polypeptide synthesised from amino acid monomers contains glycosidic bonds polymer is branched contains nitrogen can be found in both animal and plant cells is a simple diagram of a phospholipid molecule. Explain how the structure of a phospholipid molecule makes it suitable for its function in cell membranes. You may label and annotate as part of your answer. State two components of a cell surface membrane other than phospholipid molecules and describe their function. component 1 function component 2 function
9700_w16_qp_23
THEORY
2016
Paper 2, Variant 3
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is a transmission electron micrograph showing two adjacent cells in a leaf. cell wall Cellulose is the main polysaccharide in cell walls of plants. Describe the structure of cellulose. State one feature visible in , other than the cell wall, that identifies the cells as plant cells. Outline the role of ATP in a leaf cell. Water is a main component of plant cells. shows two water molecules linked by a hydrogen bond. O H H O H H hydrogen bond Explain how hydrogen bonding occurs between water molecules. Suggest why water is an excellent solvent for ions.
9700_w18_qp_21
THEORY
2018
Paper 2, Variant 1
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Questions Discovered
368