4.1. Fluid mosaic membranes
A subsection of Biology, 9700, through 4. Cell membranes and transport
Listing 10 of 134 questions
is a transmission electron micrograph of a transverse section through a blood capillary that is surrounded by actively respiring cells. cell Q fluid R Identify cell Q shown in . Fluid R is formed from blood in the blood capillary. State and explain one difference between the composition of fluid R and the composition of the blood in the capillary. difference explanation The cell surface membranes of the respiring cells have a role in regulating the exchange of substances between the cells of the body and the blood. Draw a diagram in the space below to show the arrangement of phospholipid molecules in the cell surface membrane. Cholesterol is a molecule found in the cell surface membrane. Describe one role of cholesterol in the cell surface membrane. Nicotine is one of the components of tobacco smoke. Nicotine can cross cell surface membranes and enter the bloodstream. Describe the short-term effects of nicotine on the cardiovascular system. Nicotine is absorbed from the blood plasma into the cells of the capillary wall. Scientists have suggested that nicotine is transported from the blood plasma into these cells using a type of co-transporter mechanism. shows how nicotine may be transported from the blood plasma into a cell. co-transport protein blood plasma cytoplasm of the cell cell surface membrane nicotine is transported against its concentration gradient into the cell H+ ions move down their concentration gradient out of the cell The co-transporter mechanism shown in is different from the co-transporter mechanism that moves sucrose into the cytoplasm of a companion cell in phloem tissue. Outline the similarities and differences between the co-transport of nicotine and the co-transport of sucrose.
9700_w21_qp_21
THEORY
2021
Paper 2, Variant 1
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Cell surface membranes are involved with the movement of substances into and out of cells. Calcium pumps in cell surface membranes maintain a concentration of calcium ions inside the cytoplasm that is a thousand times lower than outside the cell. shows the movement of calcium ions across a cell surface membrane. cytoplasm outside cell calcium ion With reference to , explain why calcium ions do not pass through the phospholipid bilayer; name and describe the process by which calcium ions are moved across the membrane. name description Phagocytosis is the process by which bacteria are ingested by cells. Describe the role of the cell surface membrane during phagocytosis. Phagocytic cells contain many lysosomes. Describe the function of lysosomes in destroying ingested bacterial cells.
9700_w09_qp_22
THEORY
2009
Paper 2, Variant 2
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Cathelicidin LL-37 is a cell signalling compound that stimulates many different cells in humans. One role of cathelicidin LL-37 is stimulating the production of endothelial cells in the formation of capillaries during wound healing. Explain how it is possible for many different cell types to respond to the same cell signalling compound. Describe the appearance of the endothelial cells of a capillary. Cathelicidin LL-37 is a protein composed of 37 amino acids. Table 5.1 shows: • the sequence of the first 10 amino acids in the primary structure of cathelicidin LL-37 • DNA triplets in the non-transcribed strand in the gene that codes for the first 10 amino acids in the primary structure of cathelicidin LL-37. Table 5.1 amino acid position amino acid leu leu gly asp phe phe arg lys ser lys DNA triplet CTG CTG GGT GAT TTC TTC CGG AAA TCT AAA Table 5.2 shows the triplets of bases in DNA and the amino acids for which they code. Table 5.2 first base second base third base cys stop stop his gln asp lys asp ala val met ile ile leu leu phe thr pro ser glu try tyr arg ser arg gly T T C A G C A G T C A G T C A G T C A G T C A G TTT TCT TAT TGT TCC TAC TGC TCA TAA TGA TCG TAG TGG CCT CAT CGT CCC CAC CGC CCA CAA CGA CCG CAG CGG ACT AAT AGT ACC AAC AGC ACA AAA AGA ACG AAG AGG GCT GAT GGT GCC GAC GGC GCA GAA GGA GCG GAG GGG TTC TTA TTG CTT CTC CTA CTG ATT ATC ATA ATG GTT GTC GTA GTG Mutations of DNA base sequences in a gene can affect the primary structure of proteins. Use the information in Table 5.1 and Table 5.2 to suggest the effect on the primary structure of cathelicidin LL-37 of: the substitution of the base T with the base A in the middle of the triplet at position 5 the deletion of base T in the triplet at position 2 the insertion of base G between bases G and T in the triplet at position 3. The genetic code is described as universal. Explain why the genetic code is described as universal. Use Table 5.2 to explain why some mutations have no effect on the primary structure of a protein.
9700_w22_qp_23
THEORY
2022
Paper 2, Variant 3
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Questions Discovered
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