How Plants Work:

Topics in Practical Plant Physiology for Gardeners
Professor Karen Snetselaar

This course is co-sponsored by the Pennsylvania Horticultural Society.  The lectures will be given at the PHS offices, 100 N. 20th Street (20th and Arch Streets), Philadelphia.


  1. Tuesday, January 22, 2013 - Overview of Plant Structure
    Plants are made of cells, and in order to understand how plants grow we need to know a bit more about what cells are made of, how plant cells differ from animal cells, and how the cells function together in tissues like xylem and phloem, and organs like roots, stems, and leaves.
  2. Monday, January 28, 2013 - Photosynthesis
    The class will begin with a quick survey of the two main parts of photosynthesis: the reactions that require light to make cellular energy (light reactions), and the reactions that use that energy to convert carbon dioxide into sugars (dark reactions). This will be followed by a discussion of variations on photosynthesis, including practical aspects such as why some weedy plants grow so quickly.
  3. Monday, February 4, 2013 - Water
    While a small amount of water is needed for the chemical reactions of photosynthesis, most simply moves through the plant, from the root hairs out through the leaves into the air, in a process called transpiration. We will talk about why plants undergo this seemingly wasteful process, and discuss how it impacts plant care.
  4. Monday, February 11, 2013 - Minerals
    Plants need relatively small quantities of a variety of elements, and these are taken up as dissolved salts in the water that enters through the root hairs. We will discuss the roles that various minerals play in plant growth, and talk about different types of fertilizers and other ways that minerals can be made available to plants.
  5. Monday, February 18, 2013 - Hormones
    There are several classes of chemicals produced by plants that influence plant growth, and they interact in complex ways. We'll choose a couple examples of plant hormone activities and discuss how they impact plant growth.
  6. Monday, February 25, 2013 - Putting it all Together: Plant Responses
    The class will have input into the topics discussed for the last lecture. Topics may include plant responses to the challenges of disease-causing organisms and/or how plants respond to changing environmental conditions by making flowers and fruit.

Snow Date: Monday, March 4, 2013

Knowing more about how plants work leads to a better appreciation for their complexity and a better understanding of how to meet their needs. This course will focus on a few topics in plant physiology. The class will examine how plant structure and growth is influenced by the transport of water and minerals and the ability of plants to make many other required chemical compounds. Lectures include numerous photographs and animations that help make the dynamic aspects of plant growth easier to understand.

There will be a website for this course where students can view the lecture presentations and gain access to other online materials and helpful links.

Recommended reading

No textbook is required; the following may be useful.

Botany for Gardeners: 3rd Edition. By Brian Capon. Portland, OR: Timber Press, 2010.

Any introductory college-level botany textbook.

PLEASE NOTE:  The first class will meet on Tuesday, January 22.  PHS is closed on Monday, January 21 in observance of Martin Luther King Day.

This course is full.

To be placed on the waiting list, please call 215-763-6529 x23.




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