4.2. Movement into and out of cells
A subsection of Biology, 9700, through 4. Cell membranes and transport
Listing 10 of 284 questions
Epithelial cells in the small intestine have cell structures known as microvilli. The microvilli of these cells are found only on the surface that borders the gut lumen. shows images of microvilli of intestinal epithelial cells. These images have been obtained using a scanning electron microscope and a transmission electron microscope. A is at a different magnification to B. A B With reference to , state how it is possible to distinguish between a scanning electron micrograph and a transmission electron micrograph. The approximate length of a microvillus is 1 μm. Outline the method you would use to estimate the magnifications of the images shown in . One role of an intestinal epithelial cell is the absorption of glucose from the gut lumen into the circulatory system. This involves different membrane transport proteins. The events occurring in an intestinal epithelial cell during the absorption of glucose are summarised in . not to scale gut lumen glucose Na+ glucose Na+ K+ tissue fluid capillary • Sodium ions (Na+) are removed from the cell by active transport through a transport protein known as a sodium-potassium (Na+ / K+) pump. • This decreases the concentration of Na+ in the cell compared to the gut lumen. • Glucose molecules are cotransported with Na+ into the cell from the gut lumen. • Glucose molecules are transported out of the cell into the tissue fluid down a concentration gradient. Active transport involves water-soluble substances, such as Na+ and K+, and the use of ATP to provide the energy needed for their transport through carrier proteins. Outline other features of active transport. Glucose molecules enter the cell through a membrane protein. Suggest why glucose molecules need to be cotransported with Na+ when it enters the cell through the membrane protein. Explain how microvilli increase the uptake of glucose into an intestinal epithelial cell. Stem cells are also located in the wall of the small intestine. These cells divide by mitosis continuously. Suggest and explain the importance of mitosis by stem cells in the small intestine.
9700_s22_qp_22
THEORY
2022
Paper 2, Variant 2
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The table compares the surface area to volume ratios of five agar blocks that differ in dimensions but which all have the same volume. The agar blocks can be used to measure the efficiency of diffusion, where efficiency is measured as the time taken for a dye to reach all parts of the block. length / mm width / mm height / mm surface area / mm2 volume / mm3 surface area : volume ratio 0.75 1.3 1.1 0.5 4.1 1.5 Which prediction can be made about the way in which size and dimensions of these blocks affect the efficiency of diffusion?
9700_s23_qp_11
MCQ
2023
Paper 1, Variant 1
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