Question 1 of 8cell membranes
A curated set of real ZIMSEC past paper questions with answers and explanations. The full question bank is in the Danho app.
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The diagram shows the fluid mosaic model of a membrane.
Where in an animal cell is alcohol detoxified?
The following diagrams show the main steps involved in measuring the width of a leaf at the midrib region using a light microscope.
Which of the following properties of water allows homoiotherms to adapt to a range of environments?
The diagram represents a disaccharide.
What is the theoretical number of different dipeptides that can be made using 20 different amino acids?
What is the temperature co-efficient of most enzyme-controlled reactions?
The diagram illustrates enzyme action.
In what ways do polyribosomes make protein synthesis efficient?
Which of the following enzymes protect bacteria from foreign DNA?
The diagram illustrates complementary base pairing in a segment of DNA, where the small rectangles represent pyrimidines and large rectangles represent purines.
Which of the following groups of structures would be clearly seen in a well stained onion epidermal cell under the light microscope at ×400 magnification?
What property of phospholipids makes them ideal in membrane architecture?
On an electron micrograph whose magnification is ×9600, a nucleus measures 58 mm. What is the actual size of the nucleus in μm?
A triglyceride has
Which orientation is likely to favour hydrogen bond formation between water molecules?
The diagram illustrates the buffering effect of an amino acid at pH 5.6.
The following diagram shows a single DNA strand.
Bacteria were grown for several generations in a medium containing ¹⁵N. Some of the resulting bacteria were then grown in ¹⁴N for one generation. Which test tube shows the position of first generation DNA in the density gradient?
A fresh leaf was homogenised and the suspension subjected to differential centrifugation. The procedure is shown in the flow chart below.
The diagrams show cells obtained from different organs.
Which feature in microscopy enables specimens to be viewed in detail?
Which properties explain the role of water in synovial fluid and amnion of a mammal?
Which property of lipids correctly matches its biological function?
What is the function of glycoproteins in cell membranes?
Which statement, about resolution, is not true?
In a calibrated eyepiece graticule, a single division measures 2.5μm.
The diagram shows the structure of a biological molecule.
The table gives a comparison of the light microscope and the electron microscope.
A secretory cell was supplied with radioactively labelled amino acids.
The primary structure of a protein is
A haemoglobin molecule is built from four separate polypeptide chains held together as one functional molecule. Which level of protein structure does this represent?
An adult haemoglobin molecule is made up of
Name the class of enzyme used in genetic engineering to cut a DNA molecule at a specific base sequence.
Bacterial plasmids are
The same restriction enzyme is used to cut both the plasmid and the gene to be transferred because this produces
Meiosis differs from mitosis in that meiosis
During metaphase I of meiosis the bivalents line up at random on the equator. This is important because it
During prophase I of meiosis, non-sister chromatids of homologous chromosomes exchange equivalent lengths of DNA. Name this process.
In Meselson and Stahl's experiment, bacterial cells were first grown in medium containing the heavy nitrogen isotope ¹⁵N, then transferred to medium containing the lighter isotope ¹⁴N. After each generation the DNA was centrifuged and separated into bands of differing density, showing that DNA molecules become progressively lighter as replication proceeds in ¹⁴N medium, with each new DNA molecule retaining exactly one original strand. What process of DNA replication does this experiment demonstrate?
In Meselson and Stahl's experiment, cells were grown in medium containing the heavy isotope ¹⁵N, then transferred to medium containing the light isotope ¹⁴N and allowed to undergo semi-conservative DNA replication. After the DNA had replicated twice in ¹⁴N medium (the 2nd generation), what proportion of the DNA molecules were hybrid (¹⁵N/¹⁴N) compared with fully light (¹⁴N/¹⁴N)?
Fig. 2.1 shows two types of enzyme inhibition. In one type, both the substrate and an inhibitor are able to bind directly to the enzyme's active site, so the inhibitor competes with the substrate for that site. What is this type of inhibition called?
Fig. 2.1 shows two types of enzyme inhibition. In the second type, the substrate still binds normally to the active site, but an inhibitor instead binds to a separate allosteric site on the enzyme, which changes the shape of the active site. What is this type of inhibition called?
In competitive inhibition, the inhibitor competes with the substrate for the enzyme's active site. At a sufficiently high substrate concentration, the reaction rate can eventually reach the same ___ as the uninhibited enzyme, because excess substrate molecules out-compete the inhibitor for the active site.
In genetic engineering, a plasmid and a human gene are cut with the same restriction enzyme so that their cut ends are complementary. Which enzyme is then used to join (splice) the human gene into the cut plasmid to form a recombinant plasmid?
Fig 1.1 is a diagram of protein tertiary structure. The bond labelled A forms by electrostatic attraction between two oppositely charged R-group (side chain) groups on the folded polypeptide chain. Bond A is best classified as a...
During the formation of recombinant DNA, an mRNA molecule for the required gene is isolated and an enzyme is used to synthesise a complementary DNA (cDNA) copy of it. Which enzyme carries out this conversion of mRNA into cDNA?
In a cell surface membrane, water-soluble (polar) substances cannot diffuse freely across the lipid bilayer. Which part of the membrane structure is mainly responsible for restricting this movement?
In an enzyme-catalysed reaction, the potential energy of the substrates at the start of the reaction is 50 kJ, and the maximum potential energy reached along the reaction pathway, with the enzyme present, is 68 kJ. Calculate the activation energy of this catalysed reaction, in kJ.
Red-green colour blindness is inherited as an X-linked recessive trait, with X^B representing the normal (dominant) allele and X^b representing the colour-blind (recessive) allele. What is the genotype of a female who displays the colour-blind phenotype?
Fig 1.1 shows the structure of the cell membrane, with structures labelled A, B and C. What is the name of the molecule labelled A, which forms the bilayer that makes up the basic framework of the membrane?
Globular proteins differ from fibrous proteins in that globular proteins have
Fig. 1.1 is a diagram of a typical mammalian cell. The structure labelled A is the
In Fig. 1.1, A labels the stack of flattened membrane sacs that chemically modifies and packages the proteins made by the cell. Name this organelle.
An organelle of an animal cell, seen under the electron microscope, is bounded by two membranes and its inner membrane is folded inwards into cristae. This organelle is
Fig. 1.1 shows two amino acids, one with a hydrogen atom as its side chain and one with a benzene ring carrying a hydroxyl group. When these two molecules are joined together,
Fats and oils are both triglycerides. They differ in that
In aeroponics the roots of the crop are
One advantage of aeroponics over the water intensive hydroponic system is that aeroponics
A commercial use of the aeroponics system is the
An air-lift fermenter has no mechanical stirrer. The culture is kept mixed because the
The air supplied to a fermenter must be sterile because unsterilised air would
Name the device that should be fitted into the exhaust pipe of an industrial fermenter.
The purpose of the device fitted in a fermenter's exhaust pipe is to
Aeroponically grown plants suffer less root disease than plants grown in a nutrient tank because
A reason for maintaining a gene bank is to
A seed sample in a seed bank falls short of 100 per cent germination because
Discontinuous variation arises because the character is
Which is an example of discontinuous variation in humans?
Endocytosis differs from osmosis in that endocytosis
Name the type of transport in which the cell surface membrane invaginates and pinches off to form a vesicle enclosing extracellular material.
Osmosis is the net movement of water molecules from a region of
At high temperature, cholesterol in a cell surface membrane
Which correctly distinguishes a lysosome from a ribosome?
Besides glycerol, name the two components that make up a phospholipid molecule.
A phospholipid molecule is described as amphipathic because it has
In an aqueous environment, phospholipids spontaneously form a bilayer with
The wall of an artery contains a thick tunica media mainly because it needs to
Unlike an artery, a vein has
The cell body of a sensory neuron is located
A common source of conflict between conservationists and crop farmers is that
In a school practical, 2 cm3 of 2.0M hydrogen peroxide is added to 2 cm3 of an active (unboiled) yeast suspension in a test tube, and a glowing splint is immediately inserted into the tube above the mixture. What happens to the glowing splint?
In the same test (2 cm3 of 2.0M hydrogen peroxide added to 2 cm3 of active, unboiled yeast suspension), what is seen in the reaction mixture itself, separate from the glowing-splint test?
A yeast suspension is boiled for 5 minutes, then cooled under running tap water. Hydrogen peroxide is added and a glowing splint is inserted, exactly as was done with an unboiled sample. What is observed?
Name the enzyme present in yeast that is responsible for breaking down hydrogen peroxide into water and oxygen.
When catalase breaks down hydrogen peroxide in yeast, which gas is produced?
A yeast suspension that was boiled for 5 minutes and then cooled shows no bubbling and does not relight a glowing splint when hydrogen peroxide is added, unlike an unboiled sample of the same yeast suspension. Why?
Specimen Z1 is a stained section of a mammalian ovary showing oogenesis, from an early primary follicle through to a fully developed mature Graafian follicle. What event follows once a mature Graafian follicle has fully developed?
In this investigation catalase activity was measured by timing how long it took manometer fluid to rise 5 cm in a boiling tube containing potato discs, buffer and hydrogen peroxide. After adding the hydrogen peroxide and replacing the bung, the tube was shaken gently. State the reason the tube was shaken.
In this investigation, catalase activity was tested in buffer solutions at pH3, 4, 5, 6, 7 and 8, so that the rate of the reaction could be compared across the different pH values. State why buffer solutions, rather than plain solutions of acid or alkali, were necessary for this investigation.
Catalase activity was measured over the pH range 3 to 8. As the pH rises from pH3 towards pH7, the rate of the reaction increases. What happens to the ionisable groups of catalase's active site as the pH rises over this range?
As the ionisable groups of catalase's active site are modified between pH3 and pH7, what specifically is disrupted, allowing the reaction rate to rise?
Between pH3 and pH7, disruption of the ionic bonding that maintains catalase's shape is linked to a rising reaction rate, without yet denaturing the enzyme. What effect does this disruption have on the active site over this range?
Above pH7 (towards pH8), the rate of the catalase reaction falls. What happens to catalase's ability to form enzyme-substrate (ES) complexes over this range?
Table 1.1 in this practical dilutes a 0.005 mol/dm3 glucose stock solution with distilled water to make five standards, keeping the total volume at 5 cm3. Row 1 mixes 1 cm3 stock with 4 cm3 water (0.001 mol/dm3); row 2 mixes 2 cm3 stock with 3 cm3 water (0.002 mol/dm3); row 3 mixes 3 cm3 stock with 2 cm3 water (0.003 mol/dm3). Following this same pattern, how many cm3 of the 0.005 mol/dm3 glucose stock and how many cm3 of distilled water are needed to make the 0.004 mol/dm3 standard?
Using the same 5 cm3-total dilution series as Table 1.1 (1 cm3 stock + 4 cm3 water = 0.001 mol/dm3, up to 3 cm3 stock + 2 cm3 water = 0.003 mol/dm3), how many cm3 of the 0.005 mol/dm3 glucose stock and how many cm3 of distilled water are needed to make the 0.005 mol/dm3 standard itself?
In a Benedict's test, five glucose standards from 0.001 to 0.005 mol/dm3 are each mixed with Benedict's solution and heated in a boiling water bath for 5 minutes. Which colour is expected for the LOWEST standard, 0.001 mol/dm3?
In a Benedict's test, five glucose standards from 0.001 to 0.005 mol/dm3 are each mixed with Benedict's solution and heated in a boiling water bath for 5 minutes. Which colour is expected for the HIGHEST standard, 0.005 mol/dm3?
In this practical, starch solutions A, B and C were each hydrolysed by solution P then tested with Benedict's solution. The expected results were: tube A, dark orange (concentration greater than 0.005 mol/dm3); tube B, green (0.001 mol/dm3); tube C, yellow (0.0025 mol/dm3). Ranking the three tubes from LOWEST to HIGHEST reducing sugar concentration, what is the correct order?
Starch solutions A, B and C were hydrolysed for 30 minutes by the same enzyme solution P, then tested for reducing sugar. Tube A (highest original starch concentration) produced the most reducing sugar; tube B (lowest original starch concentration) produced the least. Why does a solution with a higher original starch concentration produce more reducing sugar in the same fixed reaction time?