Form and functionIB Biology SL: Topic test

20 questions, 54 marks

IB Biology SL

Form and function topic test

Total 54 marks

Name

Class

Date

1
A food scientist analyses the fatty acid composition and melting behaviour of two fats. Fat P, extracted from beef tallow, is 52% saturated fatty acids and 44% monounsaturated, and remains solid at room temperature (20 °C), melting only above about 45 °C. Fat Q, extracted from sunflower seeds, is 66% polyunsaturated fatty acids and only 11% saturated, and is liquid at room temperature, only solidifying below about −17 °C.
(a)
Which feature of the fatty acids in fat Q best explains its much lower melting point compared with fat P?
[1 mark]
AFat Q has more C=C double bonds, which introduce kinks that prevent the fatty acid chains from packing closely together
BFat Q has a higher proportion of glycerol, which lowers melting point
CFat Q molecules are smaller than those in fat P, so they melt more easily
DFat Q contains phosphate groups that make it more soluble in water
(b)
Fat P is an important long-term energy store for an endothermic mammal. Which property of triglycerides makes them well suited to this role, compared with using glycogen as the sole energy store?
[1 mark]
ATriglycerides are hydrophilic, so they dissolve readily and can be mobilised quickly
BTriglycerides yield less energy per gram than glycogen when oxidised
CTriglycerides are more reduced and non-polar/insoluble, so they store more energy per gram without drawing in water by osmosis
DTriglycerides can be hydrolysed directly by amylase, releasing energy faster than glycogen
(c)
Explain, in terms of molecular packing, why fat P is solid at room temperature but fat Q is liquid at the same temperature.
[2 marks]
Total for question 1: 4 marks
2
A researcher compares two types of cultured kidney cells placed in a hypotonic solution (lower solute concentration than the cytoplasm). Cell type R has a normal density of aquaporin channel proteins in its plasma membrane. Cell type S has been genetically modified to produce almost no aquaporins. Both cell types have the same lipid bilayer composition. After 2 minutes in the hypotonic solution, cell type R has swollen substantially, while cell type S shows only a small increase in volume.
(a)
Which statement best explains why cell type R swells more than cell type S in the same time?
[1 mark]
ACell type R has a thicker phospholipid bilayer, slowing water loss
BCell type R has more channel proteins (aquaporins), which increase the rate of water movement by facilitated diffusion across the membrane
CCell type R actively pumps water in using ATP, while cell type S cannot
DCell type R has a lower concentration of solutes in its cytoplasm than cell type S
(b)
Which statement about the movement of water into both cell types is correct?
[1 mark]
AWater moves against its concentration gradient in cell type S because it has fewer aquaporins
BWater requires ATP to cross the plasma membrane in both cell types
CWater can only cross the membrane in cell type R, because cell type S has no aquaporins at all
DWater moves down its concentration gradient by osmosis in both cell types, but more slowly through the bilayer alone in cell type S
(c)
Explain why some water still enters cell type S despite it having almost no aquaporins.
[2 marks]
Total for question 2: 4 marks
3
A biology class compares the gas-exchange surfaces of two organisms. Surface X, from a mammalian lung, consists of a single layer of flattened cells about 0.2 μm thick, is kept moist by a thin fluid layer, is surrounded by a dense network of capillaries, and has a total surface area of around 70 m² in an adult human. Surface Y, from a leaf, consists of loosely packed spongy mesophyll cells surrounded by air spaces that connect to the atmosphere through small pores in the lower epidermis, each pore flanked by two guard cells.
(a)
Identify one feature shared by surface X and surface Y that maintains a fast rate of diffusion, and outline the role of the network of capillaries in maintaining a concentration gradient at surface X.
[3 marks]
(b)
Explain how the thinness of surface X and the arrangement of the air spaces at surface Y each help to maintain efficient gas exchange, and state one feature both surfaces share to keep the exchange surface functional.
[4 marks]
Total for question 3: 7 marks
4
A macrophage engulfs a bacterium by phagocytosis, enclosing it within a phagocytic vacuole. Lysosomes then fuse with this vacuole, releasing digestive enzymes into it. The fluid inside the resulting vacuole has a pH of about 4.5, considerably more acidic than the pH of 7.2 typical of the surrounding cytoplasm. Among the digestive enzymes released is a protease, whose optimum activity is at pH 4.5 but whose activity falls sharply above pH 6.
(a)
State what is meant by denaturation, and explain why the protease is adapted to function at the acidic pH of the phagocytic vacuole rather than at the near-neutral pH of the cytoplasm.
[6 marks]
(b)
Explain, using this example, the advantages to the cell of compartmentalizing digestive enzymes within lysosomes and phagocytic vacuoles rather than releasing them directly into the cytoplasm.
[6 marks]
Total for question 4: 12 marks
5
A student models cells using solid cubes made of agar jelly, with side lengths of 1 mm, 2 mm and 4 mm. For each cube she calculates the total surface area, the volume, and the surface area-to-volume (SA:V) ratio.
(a)
Which cube has the largest surface area-to-volume ratio?
[1 mark]
AThe 4 mm cube
BThe 1 mm cube
CThe 2 mm cube
DAll three cubes have the same ratio
(b)
A real cell needs a certain rate of exchange of materials (e.g. oxygen, nutrients) with its environment in proportion to its volume, but exchange itself occurs across its surface. Based on the model, which statement is correct?
[1 mark]
AA very large cell can always exchange materials fast enough, because a larger surface area always provides more absolute exchange capacity
BSurface area and volume increase by the same factor as a cell's side length increases, keeping the SA:V ratio constant
CSmall cells cannot exchange materials efficiently because their surface area is too small in absolute terms
DAs a cell increases in size, its surface area-to-volume ratio decreases, so exchange of materials per unit volume becomes more limited
(c)
Using the data, calculate the surface area-to-volume ratio of the 2 mm cube, showing your working, and state why real organisms cannot simply keep increasing in size as a single cell without other adaptations.
[2 marks]
Total for question 5: 4 marks
6
An ecologist records the mean annual temperature and mean annual rainfall for four sites. Site 1: 27 °C, 2200 mm rainfall, spread fairly evenly through the year. Site 2: 24 °C, 150 mm rainfall, occurring almost entirely in a short wet season. Site 3: 12 °C, 750 mm rainfall, spread through the year. Site 4: −5 °C, 200 mm rainfall (mostly as snow).
(a)
Which biome is site 1 most likely to represent?
[1 mark]
ATundra
BHot desert
CTropical forest
DTaiga
(b)
Which biome is site 2 most likely to represent?
[1 mark]
AHot desert or a seasonal grassland, given the low, highly seasonal rainfall
BTemperate forest, given the moderate rainfall
CTundra, given the low temperature
DTropical forest, given the high temperature
(c)
State the biome most likely represented by site 4, and identify the single abiotic variable given in the data that provides the strongest evidence for your answer.
[2 marks]
Total for question 6: 4 marks
7
A histologist examines cross-sections of two blood vessels of similar overall diameter taken from the same region of the leg. Vessel A has a wall about 1.0 mm thick, made of thick layers of smooth muscle and elastic tissue, surrounding a lumen of internal diameter 4 mm. Vessel B has a wall about 0.2 mm thick, with much less muscle and elastic tissue, a lumen of internal diameter 7 mm, and small flap-like structures projecting into the lumen at intervals along its length.
(a)
Identify vessel A and vessel B, and explain how the thickness and composition of vessel A's wall suit it to its function.
[3 marks]
(b)
Explain the function of the flap-like structures found in vessel B, and describe two further ways, other than these structures, in which vessel B's structure suits it to the transport of blood back to the heart.
[4 marks]
Total for question 7: 7 marks
8
Two species of barnacle, species J and species K, are studied on a rocky shore. In laboratory experiments, species J can survive and grow across the whole vertical range of the shore, from the low-tide line to well above the high-tide line, when species K is absent. In the field, where both species are present together, species J is only ever found in the upper part of the shore, above where species K occurs, while species K occupies the lower and middle parts of the shore.
(a)
Using the terms fundamental niche and realized niche, explain the distribution of species J shown by the laboratory and field observations.
[6 marks]
(b)
Explain, in terms of range of tolerance to an abiotic factor, why species K is not found on the upper shore even where species J is not present to compete with it, and describe how a transect could be used to test the hypothesis that this abiotic factor limits species K's upper distribution limit.
[6 marks]
Total for question 8: 12 marks

End of questions