A Unity and Diversity

A1.1 Water

A1.2 Nucleic acids

A2.1 Origins of cells

A2.2 Cell structure

A2.3 Viruses [HL only]

A3.1 Diversity of organisms

A3.2 Classification and cladistics [HL only]

A4.1 Evolution and speciation

A4.2 Conservation of biodiversity

B Form and Function

B1.1 Carbohydrates and lipids

B1.2 Proteins

B2.1 Membranes and membrane transport

B2.2 Organelles and compartmentalization

B2.3 Cell specialization

B3.1 Gas exchange

B3.2 Transport

B3.3 Muscle and motility [HL only]

B4.1 Adaptation to environment

B4.2 Ecological niches

C Interaction and Interdependence

C1.1 Enzymes and metabolism

C1.2 Cell respiration

C1.3 Photosynthesis

C2.1 Chemical signalling [HL only]

C2.2 Neural signalling

C3.1 Integration of body systems

C3.2 Defence against disease

C4.1 Populations and communities

C4.2 Transfers of energy and matter

D Continuity and Change

D1.1 DNA replication

D1.2 Protein synthesis

D1.3 Mutation and gene editing

D2.1 Cell and nuclear division

D2.2 Gene expression [HL only]

D2.3 Water potential

D3.1 Reproduction

D3.2 Inheritance

D3.3 Homeostasis

D4.1 Natural selection

D4.2 Stability and change

D4.3 Climate change

IB Biology HL D2.3 Water potential Question Bank

[Maximum number: 5]

Data was collected on rabbit red blood cells that were exposed to sodium chloride (NaCl) and scorpion venom. Under some osmotic conditions red blood cells swell and burst, releasing hemoglobin (hemolysis). The graph shows the response of red blood cells to different concentrations of sodium chloride, with and without scorpion venom.

(a)

Outline the effect of the venom on the hemolysis of red blood cells.

[ 2 ]

(b)

Describe how the variables would be controlled in an experiment to estimate the osmolarity of plant tissue.

[ 3 ]

[Maximum number: 2]

The micrograph shows part of a cardiac muscle cell.

(a)

Explain the changes that would occur in a cardiac muscle cell placed in a hypotonic solution.

[ 2 ]

[Maximum number: 1]

Red blood cells from a small mammal were immersed in NaCl (sodium chloride) solutions of different concentrations for 2 hours. The graph shows the percentage of hemolysed (ruptured) red blood cells at each concentration.

What can be deduced from the graph?

At Y , the net movement of Na ions between red blood cells and the NaCl solutions is zero.

At X, Na and Cl ions disrupt the structure of cell membranes.

At Y , the hypertonic NaCl solutions diffuse into the red blood cells.

At X , water has moved by osmosis into the red blood cells.

[Maximum number: 1]

The salt concentration inside the Paramecium is 1.8 %. The salt concentration in the surrounding medium suddenly drops to 0.2 %. What will be the likely response?

The cell will lose salt to the medium.

The contractile vacuole will expel more water.

The cell will swell and eventually burst.

The membrane will become more permeable to salt.

[Maximum number: 1]

Which solution has the highest salt concentration?

The original solution

Solution 1

Solution 2

Solution 3

[Maximum number: 1]

Onion (Allium cepa) epidermis was placed in pure water and observed with a light microscope using high magnification.

What would happen to these cells if they were transferred to a hypertonic solution?

Cells would gain mass.

Cells would take in water by osmosis and swell.

Cells would burst open, releasing their content.

Cell membranes would detach from walls at some points.

[Maximum number: 4]

The table shows the percentage of red blood cells that have ruptured (hemolysis) when placed in sodium chloride solutions of different molar concentrations.

(a)

Explain the effect of placing red blood cells in distilled water (0.000 M NaCl).

[ 3 ]

(b)

Deduce with a reason which sodium chloride concentration shown in the table is closest to the osmolarity of the blood cells.

[ 1 ]

[Maximum number: 2]

Vibrio fischeri is a bioluminescent (light-producing) bacterium in the Pacific Ocean. V. fischeri grown in the laboratory often has less luminescence. An investigation was carried out to look at the effect of the external osmolarity (in mOsmol) on the bacterium's luminescence, at different densities of bacteria. V. fischeri cultures were grown in three different concentrations of artificial seawater. Relative luminescence is the total luminescence divided by the density of bacteria.

Key: osmolarity
- 1300 mOsmol
- 810 mOsmol
- 570 mOsmol

(a)

Student osmosis experiments often involve putting plant tissue such as potato cylinders in several salt solutions of different concentrations and measuring the mass before and after immersion. Outline how data collected from such an experiment could be used to estimate the osmolarity of the plant tissues.

[ 2 ]

[Maximum number: 4]

An experiment was carried out to study osmosis in plant cells. Small cylinders of zucchini (Cucurbita pepo) were cut and placed in different sucrose solutions at $25^{\circ} \mathrm{C}$ . The figure shows the percentage changes in mass after 24 hours.

(a)

Estimate the solute concentration of the zucchini cells.

[ 1 ]

(b)

Explain one reason for calculating the percentage changes in mass.

[ 2 ]

(c)

Predict what would happen to a red blood cell placed in distilled water.

[ 1 ]

(a)

This image shows a normal red blood cell.

These images show two red blood cells that have been placed in solutions with different concentrations of solutes.

Deduce, with a reason, which red blood cell has been placed in a hypertonic solution.

[ 1 ]

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