Transpiration in Plants

Transpiration

• Transpiration is the loss of water vapor from plants, primarily through stomata in leaves.
• It's a vital process for plants, driving the upward movement of water and nutrients from the roots to the leaves.
• Stomata regulate the rate of transpiration, opening and closing in response to environmental conditions like light intensity, temperature, and humidity.
• Factors influencing transpiration rate: light intensity, temperature, humidity, wind speed, and soil water availability.
• Light stimulates stomata opening, hence increasing transpiration rate.
• Temperature has a positive correlation with transpiration rate; warmer temperatures increase the rate of evaporation.
• High humidity reduces transpiration rate.
• Wind speed affects transpiration; faster wind speeds lead to increased transpiration rates.
• Low soil water availability reduces the transpiration rate to conserve water.
• Transpiration is crucial for cooling the leaves, with the evaporation of water absorbing heat.
• Guard cells control the opening and closing of stomata, regulating water loss.
• The cohesion-tension theory explains the movement of water through the plant. Cohesion (water molecules stick together) and adhesion (water molecules attach to cell walls) contribute to the continuous water column.
• Transpiration stream is the movement of water through the xylem.
• Xerophytes, plants adapted to dry environments, have reduced leaf surface areas, smaller stomata, thick cuticles, and specialized water storage tissues.
• Transpiration creates a tension in the xylem, drawing water upwards.

Support in Plants

• Plants require support to stand upright against gravity and to support the weight of their leaves, flowers, and fruits.
• Support systems vary dramatically among different plant species, dictated by their size and structure.
• In herbaceous plants, support is often provided by turgor pressure exerted by water within the cells.
• The cells maintain a high internal pressure, thus pushing against their cell walls, providing structural rigidity.
• Plants in arid environments may store water in their tissues to maintain turgidity and support.
• Woody plants have lignified tissues (wood), which provide strong support.
• Lignin forms a rigid polymer that greatly strengthens the plant's structure.
• The arrangement of vascular bundles and the thickness of stem and trunk cell walls also contribute significantly to support.
• Herbaceous plants lack these supportive tissues, depending on turgor pressure more in their support structures
• Roots anchor plants firmly to the ground, providing support against wind and other external forces.
• Root systems, and their intricate structure, can vary greatly between plant species and habitats.
• Different species have unique adaptations and support structures. For example, some vines use tendrils to climb, utilizing external structures for support compared to their roots and stems.
• Other plants have thick stems (e.g., cacti) or woody trunks to support their weight and withstand environmental stresses and support large amounts of leaves or fruit.
• Different parts of a plant contribute to its overall support in specific ways. For example, the stem supports the leaves, branches, flowers and fruits. Roots anchor the entire plant in the ground and absorb water and nutrients.
• Water and mineral transportation, by the xylem, also contributes to the overall structural support in plants.