Form and functionIB Biology HL: Topic test

20 questions, 54 marks

IB Biology HL

Form and function topic test

Total 54 marks

Name

Class

Date

1
A plant scientist compares the energy stores in the seeds of two plant species. Species P stores most of its seed energy as starch, a polysaccharide of alpha-glucose, making up 60% of dry seed mass with an energy content of about 17 kJ g⁻¹. Species Q stores most of its seed energy as triglyceride oil, making up 45% of dry seed mass with an energy content of about 37 kJ g⁻¹.
(a)
Which property explains why species Q's oil provides more than double the energy per gram of species P's starch?
[1 mark]
AOil molecules contain more hydrogen relative to oxygen, giving a higher proportion of energy-rich C-H and C-C bonds than a carbohydrate of the same mass
BOil is a polymer whereas starch is not
COil dissolves more easily in water, releasing energy faster
DStarch molecules are branched, which lowers their energy content
(b)
Species P's seeds germinate rapidly in wet soil, using their starch reserves within days. Which property of starch makes it well suited to being rapidly mobilised at germination, compared with a lipid store?
[1 mark]
AStarch is completely insoluble and cannot be hydrolysed
BStarch monomers (alpha-glucose) can be added or removed rapidly by condensation and hydrolysis reactions
CStarch contains more carbon-hydrogen bonds than lipid
DStarch is amphipathic, allowing it to form bilayers
(c)
Explain why triglyceride is a better long-term energy store than starch for a seed that must survive many months of dormancy before germinating.
[2 marks]
Total for question 1: 4 marks
2
A researcher purifies two proteins from muscle tissue. Protein M is a single, compact, roughly spherical molecule of 153 amino acids that is soluble in the cytoplasm and catalyses a metabolic reaction. Protein N is a long, rope-like molecule of three intertwined polypeptide chains, is insoluble in water, and provides mechanical strength to connective tissue.
(a)
Which term describes the overall shape of protein N?
[1 mark]
AGlobular
BAmphipathic
CFibrous
DDenatured
(b)
Protein M's hydrophobic amino acids are found mostly in the interior of the molecule while hydrophilic amino acids are found on its surface. What is the most likely explanation for this arrangement?
[1 mark]
AIt maximises the surface area available for hydrogen bonding to other proteins
BIt allows protein M to embed permanently in a lipid bilayer
CIt prevents protein M from forming a tertiary structure
DHydrophobic R-groups cluster away from the surrounding water while hydrophilic R-groups interact with it, folding protein M into a stable, water-soluble globular shape
(c)
Explain, in terms of bonding, how the tertiary structure of protein M could be disrupted if the tissue is heated to 70 °C, and state the effect this would have on protein M's function.
[2 marks]
Total for question 2: 4 marks
3
A researcher compares two membrane samples: sample X is taken from a liver cell membrane, and sample Y is a purified phospholipid bilayer containing no protein. When both are placed in a solution containing glucose and potassium ions, sample X shows measurable movement of both glucose and potassium ions across it, while sample Y shows almost no measurable movement of either substance over the same time.
(a)
Explain why sample Y shows almost no movement of glucose or potassium ions across it.
[3 marks]
(b)
Using the description, explain how the presence of specific membrane proteins in sample X could allow both glucose (which moves down its concentration gradient) and potassium ions (which are pumped against their concentration gradient in some cells) to cross the membrane.
[4 marks]
Total for question 3: 7 marks
4
A climber ascends from sea level, where atmospheric partial pressure of oxygen is about 21 kPa, to a high-altitude camp at 6000 m, where it falls to about 10 kPa. At sea level her resting heart rate is 65 beats per minute and her arterial haemoglobin is 98% saturated with oxygen. After several days at altitude, her resting heart rate has risen to 85 beats per minute, and her arterial haemoglobin saturation, although lower than at sea level, remains above 85% due to increased breathing rate and other physiological changes.
(a)
Explain, using the oxygen dissociation curve and cooperative binding, why her arterial haemoglobin saturation remains above 85% despite oxygen partial pressure falling from 21 kPa to 10 kPa.
[6 marks]
(b)
Explain how the increase in her resting heart rate at altitude, together with adaptations of the circulatory system, helps to maintain oxygen delivery to her tissues despite lower blood oxygen saturation.
[6 marks]
Total for question 4: 12 marks
5
Researchers use an ultracentrifuge to separate organelles from a sample of pancreatic cells by cell fractionation. One fraction contains organelles with a large surface area of cristae and compartmentalised Krebs cycle enzymes in a fluid matrix. Another fraction contains flattened stacks of membrane sacs that receive proteins from the rough endoplasmic reticulum, modify them, and package them for secretion.
(a)
Which organelle is found in the first fraction?
[1 mark]
AMitochondrion
BGolgi apparatus
CNucleus
DRibosome
(b)
What is the main function of the organelle in the second fraction?
[1 mark]
ASynthesis of ATP by aerobic respiration
BProcessing and secretion of proteins
CStorage of the cell's genetic material
DTranslation of mRNA into polypeptides
(c)
Explain one advantage to the pancreatic cell of separating the Krebs cycle enzymes and substrates into the mitochondrial matrix, rather than having them free in the general cytoplasm.
[2 marks]
Total for question 5: 4 marks
6
A biologist compares two human cell types. A cube-shaped model cell of side length 20 µm is used to represent a typical unspecialised cell, giving a surface area of 2400 µm² and a volume of 8000 µm³. A proximal convoluted tubule cell in the nephron has numerous microvilli covering its surface facing the tubule lumen, which increase its effective surface area many times over without increasing its volume.
(a)
What is the surface area-to-volume ratio of the 20 µm cube-shaped model cell?
[1 mark]
A3.0 µm⁻¹
B0.03 µm⁻¹
C0.3 µm⁻¹
D30 µm⁻¹
(b)
Why do microvilli on the proximal convoluted tubule cell increase the rate at which it can exchange materials with the tubule fluid?
[1 mark]
AThey increase the cell's volume, increasing the need for exchange
BThey replace the plasma membrane with a thicker, less permeable layer
CThey reduce the number of transport proteins needed
DThey increase the surface area available for exchange without a corresponding increase in volume, raising the surface area-to-volume ratio
(c)
Explain why a small, unspecialised cell such as the model cube does not usually need adaptations such as microvilli to exchange materials efficiently.
[2 marks]
Total for question 6: 4 marks
7
A physiologist studies a sarcomere from a relaxed human skeletal muscle fibre, measuring it at 2.4 µm long, and again after the muscle has fully contracted, when the same sarcomere measures 1.9 µm. Separately, an ecologist compares two plant species: species R grows on an exposed sand dune with low water availability and high wind exposure, and species S grows in the waterlogged, saline soil of a mangrove swamp.
(a)
Using the sliding filament model, explain how the sarcomere shortens from 2.4 µm to 1.9 µm during contraction.
[3 marks]
(b)
Explain two different adaptations you would expect species R (sand dune) and species S (mangrove swamp) to show to survive the abiotic conditions of their contrasting habitats.
[4 marks]
Total for question 7: 7 marks
8
A desert-dwelling rodent, the kangaroo rat (Dipodomys sp.), lives in a hot desert biome with very low and unpredictable rainfall and extreme daytime temperatures. It obtains almost all of its water metabolically from the oxidation of dry seeds, is active only at night, and shares its desert habitat with a smaller, similarly seed-eating mouse species. Where the two species occur together, the kangaroo rat forages mainly in open, sandy areas, while the mouse is largely restricted to foraging under shrubs.
(a)
Explain how the kangaroo rat's adaptations and behaviour suit it to the abiotic conditions of the hot desert biome.
[6 marks]
(b)
Using the concepts of fundamental and realized niche, and competitive exclusion, explain the difference in foraging areas between the kangaroo rat and the mouse species where they occur together.
[6 marks]
Total for question 8: 12 marks

End of questions