7.2. Transport mechanisms
A subsection of Biology, 9700, through 7. Transport in plants
Listing 10 of 310 questions
shows one section of the nitrogen (N) cycle. Some details of the water cycle are also included. water and nitrate ions in roots water and nitrogen-containing organic compounds in leaves water vapour in atmosphere X Y transport in xylem uptake death death decomposition and ammonification water and nitrate ions in soil nitrogen-containing organic compounds in soil ammonium ions Name processes X and Y. X Y Name one organism involved in process Y. Explain why process X occurs, even if it is a disadvantage to a plant. State two examples of how the leaves of xerophytic plants are adapted to reduce the loss of water vapour to the atmosphere. 1. 2. Nitrate ions are taken up by root hair cells. Outline the role of the cell surface membrane of root hair cells in the uptake of nitrate ions. Describe and explain how water and nitrate ions are transported in the xylem from roots to leaves. One use of the nitrogen in the nitrate ions is for the synthesis of organic molecules such as RNA. State where nitrogen is found within an RNA molecule.
9700_w14_qp_22
THEORY
2014
Paper 2, Variant 2
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Asparagus, Asparagus officinalis, is a green vegetable plant grown in many parts of the world. shows some asparagus shoots. The shoots are usually cooked and then eaten hot or cold. Asparagus contains many mineral ions which have important roles in the bodies of mammals. Complete Table 6.1 to summarise some of these roles. Table 6.1 ion role type of cell Fe2+ red blood cell Na+ co-transport in the kidney Ca+ neurone When asparagus is digested, some of the compounds produced pass quickly into the urine to give a characteristic odour that only 22% of people can detect. The compounds bind to specific chemoreceptors in the nasal cavities of these people. Complete the sentence below by using the most appropriate scientific term. The chemoreceptors will send impulses to the brain only if the potential is reached. Outline how molecules, such as the compounds from the digestion of asparagus, pass from the blood to become part of the glomerular filtrate.
9700_w14_qp_43
THEORY
2014
Paper 4, Variant 3
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is a transmission electron micrograph of the bacterium that causes cholera, Vibrio cholerae. The flagellum shown in allows movement of the bacterium within the gut and may also function to help it to bind to an intestinal epithelial cell. The organism does not enter the cell but the toxin it releases can enter and cause damage. Large quantities of water, chloride ions and sodium ions are lost from the cell. flagellum magnification ×6000 People with symptoms of cholera have severe watery diarrhoea and as a result can become very dehydrated. Explain how a loss of chloride ions and sodium ions from the intestinal epithelial cell will cause a loss of water from the cell. The main treatment for cholera is oral rehydration therapy (ORT) using oral rehydration salts (ORS). This involves drinking a solution of electrolytes (mineral ions) and glucose. summarises the movement of glucose and sodium ions across an intestinal epithelial cell. includes three different types of cell surface membrane proteins: • SGLT1 is a cotransporter protein • GLUT2 and Na+/K+ pump are two types of carrier protein. water water glucose glucose glucose Na+ Na+ 3Na+ to capillary Na+ Na+ / K+ pump GLUT2 SGLT1 2K+ water water ADP ATP ORS lumen of intestine The first rehydrating solution developed for the treatment of cholera did not contain glucose. Using ORS, patients absorb a higher concentration of sodium ions and there is an increase in water uptake. With reference to : • outline the transport mechanisms that result in the movement of glucose and sodium ions across the intestinal epithelial cell • suggest how the movement of glucose and sodium ions increases water uptake by the cell. In severe cases of cholera, the rehydrating solution is given intravenously, as a drip directly into a vein. Suggest one reason why the rehydrating solution is given as a drip directly into a vein rather than into an artery. In very severe cases of cholera, antibiotics are also prescribed. The preferred antibiotic for treatment of cholera is a single dose of doxycycline, a form of tetracycline antibiotic. Tetracycline binds to a ribosomal subunit. Suggest what effect this will have on the metabolism of V. cholerae. A study was carried out to compare the effectiveness of the antibiotic tetracycline in the treatment of 118 patients with cholera. The patients were divided into four different treatment groups: • Group A, given one dose of 1 g tetracycline • Group B, given one dose of 2 g tetracycline • Group C, given a multiple dose (one dose of 500 mg tetracycline every 6 hours for 24 hours) • Group D, no antibiotic given. Following treatment, the volume of diarrhoea collected from each patient was measured every 16 hours for 128 hours. shows the mean volume collected for each group. time after treatment / h mean volume of diarrhoea / dm3 one dose of 1 g tetracycline Key one dose of 2 g tetracycline multiple dose (one dose of 500 mg tetracycline given every 6 hours for 24 hours) no antibiotic Describe the trends shown in . Explain whether the results support, or do not support, treating very severe cases of cholera with tetracycline. Some strains of V. cholerae are antibiotic resistant. Explain why this means that medical practitioners prefer to treat cholera with a single dose of antibiotic, rather than a multiple dose of the same antibiotic. Most people who have recovered from cholera rarely become ill again from the disease. In these people, antibodies have been identified that will bind either to the cholera toxin, or to the bacterial flagellum, or to the main bacterial cell. Explain why the antibodies are different, each one specific to its target. Evidence suggests that newborn babies of mothers who have had cholera have immunity to the disease. State precisely the type of immunity these babies are likely to have.
9700_w17_qp_22
THEORY
2017
Paper 2, Variant 2
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Ammonium ions, NH4 +, can enter the xylem of plant roots by two pathways. ● In the apoplast pathway, ammonium ions move through cell walls until this pathway is blocked by the Casparian strip. Ammonium ions then enter the cytoplasm of root cells. ● In the symplast pathway, ammonium ions move through the cytoplasm of root cells. A scientist measured the uptake of ammonium ions into the xylem of Arabidopsis thaliana. The sgn3 mutant of A. thaliana does not have a Casparian strip. In the sgn3 mutant, ammonium ions can enter the xylem without entering the cytoplasm of root cells. The bar charts show the scientist’s results. non- mutant sgn3 mutant low concentration NH4 + plant variety non- mutant sgn3 mutant high concentration NH4 + uptake of NH4 + into xylem / μmol g–1 h–1 Which conclusion is correct?
9700_w23_qp_13
MCQ
2023
Paper 1, Variant 3
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The transport of water from the soil solution to the xylem of roots occurs by the apoplast and symplast pathways. Mineral ions can be transported dissolved in water. Describe the transport of water from the soil solution to the endodermis of roots by the apoplast pathway and explain why this pathway cannot continue at the endodermis. Researchers investigated the mechanism of transport used for the uptake of potassium ions (K+) into root epidermal cells at different concentrations of K+ in the soil solution. Complete Table 6.1 to provide information about the two different transport mechanisms that were identified by the researchers. Table 6.1 net movement of K+ membrane protein needed (yes or no) ATP used (yes or no) name of transport mechanism against the concentration gradient down the concentration gradient
9700_w24_qp_22
THEORY
2024
Paper 2, Variant 2
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Questions Discovered
310