29.1 - Adaptations for Acquiring Resources, Campbell Biology in Focus
EVOLUTION-The algal ancestors of land plants absorbed water, minerals, and CO2 directly from the water in which they lived, so transport was simple because every cell was close to the resources.
Tall plants had broad and flat appendages with more surface area that could absorb more light, but also resulted in more evaporation, needing more water.
Large shoots also require more anchorage, which led to multicellular, branching roots.
-As plants grew taller shoots, capability for efficient long-distance transport of materials was favored in natural selection. The xylem that transports water and minerals from roots to shoots, and the phloem that transports products of photosynthesis to where they are needed, make this possible.
-Other important adaptations include structural ones for efficiently acquiring light form the sun, CO2 from the air, and water from the ground.
Shoot Architecture and Light Capture-Stems serve as supporting structures for leaves and as conduits for material transport.
-The height of the shoots and their branching pattern affect light capture.
-Branching enables plants to harvest sunlight for photosynthesis more effectively.However, some plants may not have branching because plants have finite energy for shoot growth and must save energy to prevent being shaded by other plants.
-Phyllotaxy is the arrangement of leaves on a stem. It’s determined by the shoot apical meristem. Most angiosperms have alternate phyllotaxy with leaves arranged in an ascending spiral around the stem.
-The canopy is the leafy portion of all the plants in a community. If a canopy is too thick, the lower leaves will photosynthesize less and undergo programmed cell death and are shed—self-pruning.
-In low light, horizontal leaves capture more light than vertical, but in sunny areas, they may be injured by exposure to intense light. Vertical leaves are parallel to light rays, so...