4.2. Movement into and out of cells
A subsection of Biology, 9700, through 4. Cell membranes and transport
Listing 10 of 284 questions
Paramecium is a ciliated, unicellular protoctist. The cilia are similar in structure to those found in the trachea of a human. The cilia beat to move Paramecium through the water in which it lives. shows Paramecium. Paramecium has anterior and posterior ends. Generally the cilia beat so that the organism is moved forwards. Sometimes reverse movement is needed, for example when the Paramecium meets an obstacle. • The direction of beating of the cilia is linked to the difference in concentration of calcium ions inside and outside the cell. • There is usually a higher concentration of calcium ions outside than inside the cell. • When Paramecium touches an object, its cell surface membrane becomes deformed. • The membrane potential becomes more positive inside the cell. • The organism moves backwards for a short time. Suggest the sequence of events that occurs to cause the Paramecium to move backwards when it touches an object. Suggest how Paramecium ensures that there is usually a higher concentration of calcium ions in the surrounding water than inside the cell. Paramecium has a contractile vacuole that fills up with water. When it is full, the contractile vacuole contracts to expel the water. The rate of contraction of the vacuole depends on the water potential of the surrounding water. Name the process by which water enters Paramecium. Suggest the relationship between the rate of contraction of the contractile vacuole and the water potential of the surrounding water. Describe how the DNA of Paramecium differs from that of a prokaryotic cell.
9700_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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The cells in the roots of beetroot plants contain a red pigment. When pieces of root tissue are soaked in cold water, some of the red pigment leaks out of the cells into the water. An experiment was carried out to investigate the effect of temperature on the loss of red pigment from the root cells. It was found that the higher the temperature of the water, the higher the rate of loss of red pigment from the root cells. Which of these statements could explain this trend?
9700_m17_qp_12
MCQ
2017
Paper 1, Variant 2
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is a transmission electron micrograph of a plant parenchyma cell. X Y tonoplast cytosol (fluid part of cytoplasm) cell sap in vacuole The external environment of the parenchyma cell has a higher water potential than the internal environment of the cell. One function of parenchyma cells is to provide support to the plant. With reference to , suggest how parenchyma cells provide support to the plant. The image shown in is at a higher magnification than can be obtained using a typical light microscope. Explain what is meant by the term magnification. The actual diameter of the parenchyma cell in along the line X—Y is 35 µm. Calculate the magnification of the image. magnification = × The cell sap in the vacuole of the cell shown in has a pH of 5.0. The cytosol has a pH of 7.2. The tonoplast controls the passage of hydrogen ions from the cytosol into the vacuole. The low pH created by the entry of hydrogen ions is optimum for the action of acid hydrolase enzymes in the vacuole. Acid hydrolase enzymes are also found in lysosomes in animal cells. Suggest which transport mechanism is used to move hydrogen ions from the cytosol of the parenchyma cell into the vacuole. Explain your choice. transport mechanism explanation Suggest how the structure of the tonoplast allows hydrogen ions to be transported into the vacuole, but does not allow the ions to leave the vacuole. The acid hydrolases in the vacuole cannot function in neutral conditions (pH 7.0) or alkaline conditions. Explain the advantage to the plant cell of having acid hydrolases that cannot function in neutral, near neutral or alkaline conditions.
9700_m20_qp_22
THEORY
2020
Paper 2, Variant 2
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Questions Discovered
284