IB Biology SL Theme B: Form and function questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Paper 2Medium16 marks

Cellulose in plant cell walls and glycoproteins on cell surfaces are examples of biological structures associated with different functions.

In a model of cell-surface recognition, probe A binds only to the A antigen and probe B binds only to the B antigen. The probes represent recognition molecules on another cell. A “+” indicates that binding was detected.

Red-cell sample	Probe A binding	Probe B binding
P	+	−
Q	−	+
R	+	+
S	−	−

For this question, a red-cell sample with A antigen only is group A; with B antigen only is group B; with both antigens is group AB; and with neither antigen is group O.

(a)

Explain how the structure of cellulose makes it suitable for its role as a structural polysaccharide in plant cell walls.

[4]

(b)

Use the results in the table to determine the ABO group of each sample, P, Q, R and S.

[4]

(c)

Explain how glycoproteins contribute to cell-cell recognition. Use ABO antigens and the results in the table in your answer.

[8]

Question 2

Paper 2Medium16 marks

A researcher used four model membranes, each consisting of a phospholipid bilayer separating a donor compartment from a receiving compartment. Each donor initially contained one substance at 10.0 mmol dm⁻³; each receiver initially contained none. The donor volume was 20 times the receiver volume. Membrane area and temperature were the same in all four setups. Figure 1 shows the concentration of each substance in the receiving compartment during the experiment.

(a)

At 4 min, identify the substance with the highest concentration in the receiving compartment and state that concentration.

[2]

(b)

Compare the changes in receiving-compartment concentrations of O₂ and CO₂ with those of Na⁺ and glucose over the 8 min. Quote data from Figure 1.

[3]

(c)

Calculate the mean rate of increase in CO₂ concentration in the receiving compartment from 0 to 4 min. Include a unit.

[2]

(d)

Using Figure 1, explain how the structure of the phospholipid bilayer accounts for the pattern of movement of the four substances.

[4]

(e)

A student states: “The bilayer completely blocks Na⁺ and glucose, but allows O₂ and CO₂ to cross.” Assess this statement using Figure 1.

[3]

(f)

The measurements stop at 8 min. Identify one limitation this creates for assessing the movement of Na⁺ and glucose, and suggest a further measurement.

[2]

Question 3

Paper 2Medium16 marks

Adult human bone-marrow stem cells were divided into equal groups of 100 cells. Each group was exposed for seven days to a different set of signals, M or N, from bone-marrow niche cells. Assume that no cells died, differentiated cells did not divide, and all cells present at day 7 were either stem cells or newly differentiated blood cells.

Signal condition	Stem cells at day 7	Newly differentiated blood cells at day 7
M	240	60
N	60	240

(a)

State two properties of stem cells.

[2]

(b)

Name two adult human locations that contain stem-cell niches, and state one role of a niche.

[3]

(c)

Calculate the percentage of counted cells that were stem cells in condition M and condition N.

[3]

(d)

Compare the outcomes for M and N and infer which set of signals favoured maintenance or proliferation of the stem-cell population and which favoured differentiation.

[4]

(e)

A researcher concludes that these results prove that the stem cells can divide endlessly and differentiate along different pathways. Evaluate this conclusion using the data.

[4]

Question 4

Paper 2Medium16 marks

A coastal reserve contains upper sand dunes beside a mangrove swamp. Researchers placed ten randomly positioned 1 m² quadrats at each of four sites. The table shows the mean number of living shoots of marram grass (Ammophila arenaria) and seedlings of the mangrove tree Avicennia marina per quadrat.

Site	Habitat	Soil salinity / g kg⁻¹	Soil water content / %	Marram shoots per quadrat	A. marina seedlings per quadrat
A	Upper dune	2	4	13	0
B	Dune–swamp boundary	14	18	6	4
C	Inner mangrove swamp	28	42	0	16
D	Creek edge	36	55	0	8

Field notes describe the following features: marram leaves roll inward in dry air, enclosing the stomata in a humid space, and its roots spread widely through loose, shifting sand. A. marina has upright pneumatophores that project above the waterlogged sediment, and salt glands on its leaves release salt.

To estimate the number of marram shoots in an 800 m² upper-dune patch, researchers counted the shoots in ten additional randomly placed 1 m² quadrats. The counts were 12, 15, 9, 14, 16, 11, 13, 10, 17 and 13.

Researchers also surveyed an estuarine snail in five pools of similar area, counting snails in 10 m² at each pool. The same search time was used at each pool, and other measured conditions were similar.

Water temperature / °C	Snails counted per 10 m²
14	1
18	7
22	15
26	8
30	0

(a)

State one abiotic variable measured in the plant survey and one measured in the snail survey.

[2]

(b)

Describe how the abundance of the two plant species changes across the sites as soil salinity increases.

[2]

(c)

Estimate the number of marram shoots in the 800 m² upper-dune patch.

[3]

(d)

Explain how the features described in the field notes may help marram and A. marina live in their respective habitats.

[4]

(e)

Describe the pattern in the snail counts, including the observed temperature range of pools in which snails were recorded.

[2]

(f)

A student concludes that soil salinity alone determines which of the two plant species occurs at each site. Evaluate this conclusion, using the plant data and field notes.

[3]

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