CHAPTER 32 Summary

• Nearly all plants share the same basic structure: an aboveground shoot system that includes the stem and photosynthetic leaves, and an underground root system that anchors the plant in the soil and absorbs water and nutrients.
• All plant cells are surrounded by a cell wall made of the complex carbohydrate cellulose. A central water-filled vacuole creates turgor pressure against the cell wall and helps a plant stand up.
• Some plant tissues have cells with an additional inner cell wall made of cellulose and lignin. Lignin is extremely durable and is what makes plant tissues woody.
• Plants have a vascular system. Xylem transports water and dissolved nutrients from the roots to the shoots. Phloem transports dissolved sugars throughout the plant body.
• Water transport is powered by evaporation through stomata in leaves, a process known as transpiration. Plants have mechanisms to control the amount of water lost by transpiration.
• Plants undergo primary (vertical) and secondary (horizontal) growth. Secondary growth is mostly growth of xylem tissue. Tree rings reflect the growth of xylem tissue from season to season.
• Plants are autotrophs, able to make their food from sunlight and carbon dioxide absorbed from the air by photosynthesis. They also require a few additional nutrients from the soil, including water, nitrogen, phosphorus, and sulfur.
• Bacteria in the soil convert nitrogen into a usable form that plants can absorb. In nutrient-poor soils, some plants obtain nitrogen by trapping and digesting insects.
• Some plants have adapted to hot, dry climates, keeping their stomata closed during the day and collecting carbon dioxide for photosynthesis primarily at night.
• A variety of pigments assist with photosynthesis. Chlorophyll is the most predominant and is responsible for the green color of plant leaves. Other pigments contribute to photosynthesis and are visible in the fall, after chlorophyll has broken down.
• Many plants reproduce sexually and have male and female sexual organs that produce haploid gametes.
• Some plants rely on pollinators such as insects to deliver male pollen to female reproductive structures. Other plants depend on the wind to deliver pollen to the female structures.
• Seed-bearing plants (gymnosperms and angiosperms) produce embryonic plants encased within a protective seed that can disperse a great distance from the parent plant.
• Plants respond to their environment by various tropisms. Phototropism is growth toward light; gravitropism is growth in response to gravity; thigmotropism is growth in response to touch or wind.
• Plants produce hormones that contribute to growth and development: ethylene contributes to fruit ripening; gibberellins and ABA regulate germination and stem growth; auxin controls cell elongation.
• Plants have physical defenses (e.g., thorns) and chemical defenses (e.g., toxins) that fend off herbivores. Humans make use of chemical defenses in developing pharmaceuticals.

• MORE TO EXPLORE

  • Chamovitz, D. (2013) What a Plant Knows: A Field Guide the Senses. New York: Scientific American/Farrar, Straus, Giroux.
  • Coursera, What a Plant Knows (and other things you didn’t know about plants) https://www.coursera.org/course/plantknows
  • U.S. Forest Service, Ethnobotany http://www.fs.fed.us/wildflowers/ethnobotany/
  • PBS, Nature, What Plants Talk About (2013) http://www.pbs.org/wnet/nature/episodes/what-plants-talk-about/video-full-episode/8243/
  • PBS, Nature, The Seedy Side of Plants (1999) http://www.pbs.org/wnet/nature/episodes/the-seedy-side-of-plants/introduction/1268/