Nature of science:

Use models as representations of the real world—mechanisms involved in water transport in the xylem can be investigated using apparatus and materials that show similarities in structure to plant tissues. (1.10)

• Transpiration is the inevitable consequence of gas exchange in the leaf.
• Plants transport water from the roots to the leaves to replace losses from transpiration.
• The cohesive property of water and the structure of the xylem vessels allow transport under tension.
• The adhesive property of water and evaporation generate tension forces in leaf cell walls.
• Active uptake of mineral ions in the roots causes absorption of water by osmosis.

Applications and skills:

• Application: Adaptations of plants in deserts and in saline soils for water conservation.
• Application: Models of water transport in xylem using simple apparatus including blotting or filter paper, porous pots and capillary tubing.
• Skill: Drawing the structure of primary xylem vessels in sections of stems based on microscope images.
• Skill: Measurement of transpiration rates using potometers. (Practical 7)
• Skill: Design of an experiment to test hypotheses about the effect of temperature or humidity on transpiration rates.

• Syllabus and cross-curricular links:
• Biology
• Topic 2.2 Water
• Topics 2.9 and 8.3 Photosynthesis

Aims:

• Aim 7: The introduction of image processing software and digital microscopes increases further the ability to gather more data to ensure reliability.
• Aim 6: Measurement of stomatal apertures and the distribution of stomata using leaf casts, including replicate measurements to enhance reliability, are possible experiments.