IB Biology SL Theme B: Form and function questions

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.

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.

Two polypeptides each contain 80 amino acids and the same number of each amino-acid type, but the amino acids are in different orders. Which statement correctly links this difference to a possible effect of a large pH change or high temperature?

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 signal forms a gradient across four adjacent regions of an early embryo. Gene G is expressed only where the signal concentration exceeds 6 arbitrary units. Cells expressing gene G differentiate into specialized cell type P; cells not expressing it differentiate into another type. Which outcome is predicted? [1 mark]

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.

In a plant, the rate of water loss from leaf-cell walls increases. Which change in the xylem and role of cohesion are expected?

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.

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.

The table shows a molar-area index (molar grinding-surface area divided by combined incisor and canine area), measured in the same way for each skull. Diets of the living reference hominids are known from observations. Which inference about the fossil skulls is supported by the data?