Review #8

Question 1

Explain transpiration.

Answer 1

Transpiration is the loss of water vapor from the leaves (and stems) of plants through stomata/pores (more on the lower leaf surface). The water in the spongy mesophyll evaporates out of stomata (water goes down a concentration gradient). Stomata open for gas exchange in photosynthesis (so transpiration rates are affected by and are an inevitable consequence of photosynthesis). In transpiration, water is bonded to other molecules (cohesion) in a chain ALL the way down the xylem of a plant. Water in the xylem is “pulled” upward and new water molecules enter the roots (negative pressure). Water molecules also hydrogen bind to xylem tissue (adhesion), which facilitates transpiration due to its cells lacking a membrane (water enters freely), layer of inner dead cells (continuous tube), outer layer containing pores (water moves through to the leaves easily), and lignin rings (strengthens tissue).

Answer 2

Site of production: Salivary glands.
Site of action: Mouth and esophagus.
pH: 7 (neutral).
Substrate: Starch (amylose).
Product: Maltose.