4. Cell membranes and transport
A section of Biology, 9700
Listing 10 of 418 questions
A scientist carried out an experiment to separate the organelles in an animal cell by mass. The scientist mixed the cells with a buffer solution which had the same water potential as the cells. He then broke the cells open with a blender to release the organelles. The extracted mixture was filtered and then spun in a centrifuge at a speed to separate the heaviest organelle. This sank to the bottom, forming a solid pellet, 1. solid pellet liquid above pellet The liquid above pellet 1 was poured into a clean centrifuge tube and spun in the centrifuge at a higher speed to separate the next heaviest organelle. This organelle sank to the bottom, to form a solid pellet, 2. He repeated this procedure twice more to obtain pellet 3 and pellet 4, each containing a single organelle. What is the function of the organelle extracted in pellet 3?
9700_s17_qp_11
MCQ
2017
Paper 1, Variant 1
View
A person who is exposed to tobacco smoke is at greater risk of lung cancer and chronic obstructive pulmonary disease (COPD). Many people with COPD have both chronic bronchitis and emphysema. These diseases cause changes in the gas exchange system. For example, changes occur in the total lung surface area to volume ratio (SA:. Tar in tobacco smoke has a number of effects on the cells lining the gas exchange system. State the main effects of tar on the cells lining the gas exchange system that are related to lung cancer and to chronic bronchitis. lung cancer chronic bronchitis A student investigated the effect of SA:V on diffusion. Agar was prepared with Universal Indicator solution and sodium hydroxide solution. The agar was coloured blue. Three cubes, A, B, and C, were cut from a solid block of blue agar. Each cube was a different size. Universal Indicator solution changes to a red colour in the presence of acid. The student prepared Table 4.1 to show the sizes and SA:V of each cube. Table 4.1 cube length of each side / cm total surface area / cm2 volume / SA:V A 6:1 B 3:1 C 2:1 Complete Table 4.1 by: • writing the correct units for volume • calculating the total surface area, and volume, of cube C. Cubes A, B and C were placed in a small beaker. At time 0 seconds, dilute hydrochloric acid was added to the beaker to cover the cubes. The student timed how long it took for each cube to change colour completely. Complete to show the results that were obtained. shortest time to change colour completely longest time to change colour completely cube cube cube Some people with emphysema may be offered lung volume reduction surgery (LVRS), in which diseased lung tissue is surgically removed. One expected outcome of the surgery is an improvement in total lung surface area to volume ratio (total lung SA:. Suggest why there is an improvement in total lung SA:V after the surgery has been carried out. In humans, blood that becomes oxygenated in the lungs reaches body tissues without coming into contact with blood that is deoxygenated. Explain how the blood that becomes oxygenated in the lungs is kept separate from blood that is deoxygenated.
9700_s21_qp_22
THEORY
2021
Paper 2, Variant 2
View
A scientist carried out an experiment to separate the organelles in an animal cell by mass. The scientist mixed the cells with a buffer solution which had the same water potential as the cells. The cells were broken open with a blender to release the organelles. The extracted mixture was filtered and then spun in a centrifuge at a high speed to separate the heaviest type of organelle. These sank to the bottom, forming solid pellet 1. solid pellet liquid above pellet The liquid above pellet 1 was poured into a clean centrifuge tube and spun in the centrifuge at a higher speed to separate the next heaviest type of organelle. These organelles sank to the bottom, forming solid pellet 2. This procedure was repeated twice more to obtain pellet 3 and pellet 4, each containing a single type of organelle. What is the main function of the type of organelle extracted in pellet 2?
9700_s23_qp_12
MCQ
2023
Paper 1, Variant 2
View
An experiment was performed to find the effect of surface area:volume ratio on the rate of osmosis. Pieces of yam were cut into cubes of the following sizes: • 2 cm × 2 cm × 2 cm (surface area = 24 cm2, volume = 8 cm3) • 1 cm × 1 cm × 1 cm (surface area = 6 cm2, volume = 1 cm3) The cubes were carefully blotted dry, weighed and their fresh masses recorded. One cube, 2 cm × 2 cm × 2 cm, was put into a beaker and covered with distilled water. Eight cubes each measuring 1 cm × 1 cm × 1 cm were put into another beaker of distilled water, making sure that they were all covered with distilled water. At intervals for a period of 45 hours, the cubes were removed from the beakers, blotted dry, reweighed and then replaced into fresh distilled water. The percentage increase in mass was calculated for the eight cubes of side 1 cm and the one cube of side 2 cm. The results are shown in . key time / hours percentage increase in mass 8 cubes of side 1 cm x 1 cm x 1 cm 1 cube of side 2 cm x 2 cm x 2 cm 1 cm 2 cm Use [T Explain why eight cubes of side 1 cm × 1 cm × 1 cm were used in this experiment. Describe the results shown in . Explain, in terms of water potential, why all the cubes of yam gained in mass. Explain why the percentage increase in mass for the eight cubes of side 1 cm was faster than that of the cube of sides 2 cm.
9700_w05_qp_2
THEORY
2005
Paper 2, Variant 0
View
Strips of plant tissue were immersed in a range of sucrose solutions of different concentrations. Their lengths were measured before immersion and after 30 minutes. The graph shows the ratio of initial length to final length. 1.4 1.2 1.0 0.8 0.6 0.4 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 sucrose concentration / mol dm–3 initial length final length What is a correct description of the change in the cells and in their water potential as the sucrose concentration increases?
9700_w07_qp_1
MCQ
2007
Paper 1, Variant 0
View
Enzymes are globular proteins that catalyse metabolic reactions. Describe the features of globular proteins. Enzymes can be used to remove cell walls from plant and fungal cells. The cells are incubated in a solution that contains a mixture of enzymes. Suggest an explanation for the fact that a different mixture of enzymes is required to remove the walls of plant cells compared to the walls of fungal cells. Explain why, when plant cells are incubated with enzymes to remove their cell walls, it is important to maintain an optimum pH. A student carried out an investigation into osmosis using red blood cells. Red blood cells were placed in sodium chloride solutions at five different concentrations. For each concentration, a sample was added immediately to a microscope slide and the cells were viewed using a light microscope for a period of time. The observations recorded are shown in Table 3.1. Table 3.1 concentration of salt solution / % observation of red blood cells 0.0 swell and burst, numbers decrease 0.4 increase in size 0.9 remain the same size 1.5 decrease in size 3.0 smaller and shrivelled Explain, in terms of water potential and osmosis, the results that the student obtained. The student also carried out a similar investigation using plant cells with cell walls removed. These cells were suspended in a 12% mannitol solution so that the water potential inside and outside of the cells was equal. is a photomicrograph of these cells. The student removed a sample of these cells. The sample was placed into distilled water and was viewed using a light microscope. Describe what you would expect the student to observe and explain why this would not occur with normal plant cells.
9700_w10_qp_22
THEORY
2010
Paper 2, Variant 2
View
Agar cubes can be used to demonstrate the effect of changing surface area to volume ratio on diffusion. Three different agar cubes made using a dilute acid were placed into an indicator solution that diffused into the cubes. When the indicator came into contact with the acid it changed colour. The cubes were 1 cm3, 2 cm3 and 3 cm3 and were left in the indicator solution for 10 minutes. All other variables were kept the same. The results were recorded as diagrams. The results for the 2 cm3 cube are shown...
9700_w18_qp_12
MCQ
2018
Paper 1, Variant 2
View
Questions Discovered
418