Learning Objectives Regulation of transpiration is achieved primarily through the opening and closing of stomata on the leaf surface. Stomata are surrounded by two specialized cells called guard cells (Figure ). Stomata must open to allow the gas exchange of carbon…
Learning Objective Describe the various adaptations that help plants reduce transpiration rate. Plants have evolved over time to adapt to their local environment and reduce transpiration. Leaves are covered by a waxy cuticle on the outer surface that prevents the loss of…
Learning Objective Define transpiration and identify how environmental factors affect transpiration rate. Less than 1% of the water reaching the leaves is used in photosynthesis and plant growth. Most of it is lost in transpiration, the loss of water vapor to…
Learning Objectives Plants are phenomenal hydraulic engineers. Using only the basic laws of physics and the simple manipulation of potential energy, plants can move water to the top of a tree approaching 116 m (~381 ft, see The Tallest Trees…
Water potential, transpiration, and stomatal regulation influence how water and nutrients are transported in plants. Water potential refers to the potential energy in water, and water moves towards the areas with the lowest water potential. Water is ultimately pulled to the top…
The structure of plant roots, stems, and leaves facilitates the transport of water, nutrients, and photosynthates throughout the plant. The phloem and xylem are the main tissues responsible for this movement. Water and nutrients are absorbed from the soil by…
Plant hormones—naturally occurring compounds synthesized in small amounts—can act both in the cells that produce them and in distant tissues and organs. Auxins are responsible for apical dominance, root growth, directional growth toward light, and many other growth responses. Cytokinins stimulate cell division and counter apical…
Learning Objectives Recent research has discovered a number of compounds that also influence plant development. Their roles are less understood than the effects of the major hormones described so far. Brassinosteroids Brassinosteroids (Figure ) are synthesized primarily in young tissues are important…
Learning Objectives Ethylene differs from other plant hormones in that it is a smaller and simpler molecule that is a volatile gas (Figure ). Hundreds of years ago, when gas street lamps were installed in city streets, trees that grew close…
Learning Objectives The plant hormone abscisic acid (ABA) was was once thought to be responsible for abscission; however, this is now known to be incorrect. Instead, ABA accumulates as a response to stressful environmental conditions, such as dehydration, cold temperatures, or shortened…