This section covers the following topics

• Bryophytes
• Vascular tissues (xylem and phloem)
• Gymnosperms
• Angiosperms
  • Flower structure
  • Angiosperm reproduction
• Plant hormones
• Responses to the environment

Section Summary

Bryophytes (such as mosses) are one of the most basic groups of plants, lacking vascular tissue of any sort. Bryophytes and tracheophytes both exhibit alternation of generations. The gametophyte generation of a plant reproduces by creating gametes which fuse to create sporophyte plants. Sporophytes produce spores that grow into gametophytes.

Tracheophytes have vascular tissues. Xylem, which is divided into tracheids and vessel elements, carries water and minerals while the sieve tube elements that make up phloem transport nutrients. Sieve tube elements are supported by companion cells.

Growth in plants occurs when undifferentiated cells called meristems divide. Division of apical meristems found at the tips of stems results in primary, or vertical, growth. Lateral meristems increase the diameter of plants and cause secondary growth, producing vascular and cork cambium.

Gymnosperms, such as pine trees, have “naked seeds” that are generally enclosed in cone-like structures.

Angiosperms, in contrast, are flowering plants. Flowers are reproductive organs with both male and female components: the anther produces pollen while the ovary and eggs are contained within the pistil. Angiosperms’ sexual reproduction involves double fertilization, which creates both a zygote and endosperm to serve as food for the new plant. Important structures within the seeds themselves include the cotyledons (first leaves), epicotyl (develops into stems and leaves) and the hypocotyl (develops into roots).

Notable plant hormones include auxin, gibberellins, ethylene, cytokinins and abscisic acid. Plants respond to their environment by exhibiting photoperiodism,... Sign up to continue reading Plant Structure and Function >

• << Diversity of Organisms
• Circulation, Respiration, Digestion, and Excretion >>