Investigating transpiration

Investigating Transpiration

• Stomata are holes in the surface and underside of a leaf that can be made to open or close by changes in the turgidity of guard cells.
• Guard cells regulate the opening and closing of stomata by swelling with water to open the stomatal opening and losing water to close it.
• Transpiration is the process by which plant leaves lose water vapor by evaporating at the mesophyll cell surfaces and then diffusing through the stomata.
• Only a small amount of water taken up by the roots is used by the plant for growth and metabolism (less than 10%); plants lose over 90% of the water they take in by transpiration.
• Water moves up the xylem from the plant's roots into its leaves to replace the water lost through transpiration.

Measuring Transpiration

• A weight-potometer measures the amount of water lost through transpiration by weighing the system at the start and end of an experiment.
• A bubble potometer measures the amount of water lost through transpiration by tracking the movement of an air bubble in a capillary tube.

Factors Affecting Transpiration

• High temperature increases the rate of transpiration due to increased kinetic energy of particles, but if the temperature gets too high, the stomata close to prevent water loss.
• Increasing light intensity opens more stomata, facilitating photosynthetic gas exchange and increasing the rate of transpiration.
• High humidity reduces the rate of transpiration by reducing the concentration gradient between the leaf and the air.
• Wind can increase the rate of transpiration by removing water vapor from the air surrounding the leaf.

Translocation of Materials in Plants

• Phloem vessels are responsible for the transport of sucrose and amino acids, the plant's food sources.
• Sucrose and amino acids are produced in the leaves (the source) and transported to the non-photosynthesizing stems and roots through the phloem tissue.
• The cells of the phloem are connected end to end and contain sieve plates, which facilitate the movement of substances from one cell to another.
• Sucrose can be converted back to glucose for respiration, used to make other molecules for growth, or converted to starch for storage.

Transport in Phloem

• Transport in the phloem can go in different directions depending on the needs of the plant.
• Transport is always from source to sink, with the source being the place where the substance is produced or stored, and the sink being the place where the substance is needed.
• Examples of sinks include growing tips of the root and shoot, flowers, and storage organs like tubers.

Vascular Tissue and Plants

• Vascular tissue, including xylem and phloem, is used to move carbohydrates, nutrients, and water in plants.
• True stems, roots, and leaves are structures found in vascular plants.
• Vascular tissues enabled terrestrial adaptation during land colonization and led to a wide range of shapes and ecological adaptations.

Importance of Vascular Plants

• Vascular plants are primary producers and form the foundation of food webs on land.
• They establish structure and habitat, and impact carbon, water, and nutrient cycles through biogeochemical cycles.
• Vascular plants have economic importance in agriculture, forestry, and medicine.
• They are vital to the health of an ecosystem, and conservation is crucial to prevent the loss of biodiversity and endangered species.