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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 31. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. What are the two basic systems that form the bodies of all plants?       
  2. What three tissues are responsible for all plant organs?
  3. What three organs are responsible for plant structure?
  4. In what region of the plant does photosynthesis occur?
  5. How do materials absorbed from the soil contribute to the mass of a plant?
  6. When did scientists first suspect that plants obtained materials from the air?
  7. How are the materials absorbed at the roots distributed to the other regions of the plant?
  8. How are the sugars produced during photosynthesis distributed to the other regions of the plant?
  9. Why have some plants become adapted to consume animals?

A Guide to the Reading

When exploring the content in Chapter 31 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Plant Tissues and Organs

Plants are formed from three basic tissues, which combine to form roots, stems, and leaves, the three basic plant organs. Despite the obvious differences in appearance among plants, all plant features can be shown to be modifications of these simple elements. All plant structures contain the same three basic tissues. Dermal tissue is typically organized as a single layer of cells in contact with the external environment. Dermal cells are modified for specific functions. In stems and leaves, for example, where evaporation can be a problem, dermal tissues form a waxy cuticle that reduces water loss. Dermal cells often have outgrowths called trichomes that perform various tasks depending upon their location. Ground tissue, located immediately beneath the dermal layer, has many essential roles. It is here that most photosynthesis occurs.  The third type of plant tissue is vascular tissue. Two types exist: phloem, which is formed from living cells and transports photosynthetic products, and xylem, which is formed from dead cells and transports water.
Roots perform the essential functions of anchoring the plant, absorption of water and nutrients, and, in some plants, food storage. The efficiency of anchoring and absorption is improved with root hairs, a type of trichome that increases root surface area. Two types of root systems are found in plants, taproot systems and fibrous root systems. A taproot has a single dominant root growing directly downward beneath the plant. A fibrous root system lacks a dominant root, but has many roots that form a mat below the plant. Fibrous roots tend to hold the plant in place more firmly than do taproots. Stems show many structural similarities to roots. They have an outer layer of dermal cells, abundant ground tissue, and one or more associations of phloem and xylem, called vascular bundles. The position of the vascular bundles within the stem varies within the flowering plants; the bundles are either randomly scattered or arranged in a ring as shown in Figure 31.8.   Leaves are the primary sites for photosynthesis, although some stem cells also produce food. In the leaf, we encounter another modified dermal cell. Called guard cells, these cells control gas exchange, allowing carbon dioxide to enter, but minimizing the loss of water.

For more information on this concept, be sure to focus on:

  • Section 31.2, The Three Plant Tissue Types
  • Section 31.3, The Three Plant Organs and
  • Figure 31.5, Vascular Tissue Transports Food and Water
  • Figure 31.7, Two Kinds of Root Systems
  • Figure 31.8, Stems Support the Plant

How Plants Obtain Nutrients

Scientists had long wondered if plants could obtain all their nutrients from soil. Investigators performed several clever experiments in the 1700s which suggested that the answer was no.  Eventually it was shown that most of the dry mass of the plant came from the air, specifically carbon dioxide, with materials removed from the soil making only a small contribution. Although small, nutrients extracted from the soil are absolutely critical for growth. As you will discover in the next chapter, shortages of soil nutrients often limit plant growth. Nutrients are separated into two categories, the macronutrients, which plants use in relatively large quantities, and micronutrients, which are used in much smaller amounts.  Nutrients enter plants through the root system in one of two different pathways. The most common pathway begins when a nutrient crosses the cell membrane of a root hair. Because adjacent plant cells are connected to one another by openings, called plasmodesmata, in their cell walls, once a nutrient reaches the cytosol of any cell, it can freely move between cells since the cytosol is continuous.  Eventually, the nutrient reaches the xylem and is dispersed throughout the plant. In the alternative pathway, nutrients move between cells until reaching an impassible layer of ground tissue that surrounds each vascular bundle. Termed a Casparian strip, it functions like the plasma membrane of the root hair cell in blocking the entry of harmful materials. Accumulating nutrients at concentrations higher than the surrounding soil requires active transport and the use of cellular energy. Plants obtain their energy from sunlight so, as you would expect, plants kept in the dark quickly lose nutrients. 

For more information on this concept, be sure to focus on:

  • Section 31.4, How Plants Obtain Nutrients
  • Figure 31.10, How Plants Get Raw Materials for Growth
  • Figure 31.12, How Plants Absorb Nutrients from Soil

How Plants Transport Food and Water

The function of the heart and the animal circulatory system was first described in the 1600s. It’s not surprising that biologists anticipated that a similar pumping mechanism would be involved in the circulation of plants, but this is not the case. The pressures required to raise water to the top of an average tree are tremendously greater than those seen in animals. Plants do not have pumps, but rather use a very different system for moving water within their bodies. Recall that xylem forms numerous hollow tubes that are continuous from root to leaf. Because water molecules are polar, each forms a hydrogen bond with an adjacent molecule. In the xylem, water molecules orient to form a continuous column. The evaporation of a water molecule at a leaf surface causes the column to first be stretched and eventually pulled upward, one molecule at a time. The nutrients entering the root when water is absorbed travel with the column, eventually reaching those tissues where it is needed. During photosynthesis water and carbon dioxide are combined to produce sugar within the leaf. Transporting the sugars results from the interplay between active transport, osmosis, and diffusion. Phloem cells accumulate sugar by active transport. As the sugar concentration increases within phloem cells, water enters by osmosis. If phloem cells were typical, this would simply cause the cell to swell, but recall that, because of the plasmodesmata, phloem cells share their cytosol with neighboring cells. In non-photosynthetic areas, sugars and water diffuse from the phloem into the surrounding tissues. Thus, a pressure gradient forms within the phloem that is high at the leaf and lower elsewhere. In response to this pressure gradient, sugar and water flow from the leaves to the plant tissues that are using sugars for energy.

For more information on this concept, be sure to focus on:

  • Section 31.6, How Plants Transport Food and Water
  • Figure 31.14, How Food is Transported in Phloem Tissue
  • Figure 31.15, How Plants Move Water in Xylem Tissue

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

An Overview of the Plant Body

  • Chapter 3 – Section 3.4, The Plantae: Pioneers of Life on Land
  • Chapter 32 – Section 32.1, How Plants Grow: Modularity

Plant Tissues and Organs

  • Chapter 3 – in Section 3.4, Vascular systems allowed ferns and their allies to grow to great heights
  • Chapter 32 – Section 32.1, How Plants Grow: Primary and Secondary Growth

How Plants Obtain Nutrients

  • Chapter 6 – Section 6.1, The Plasma Membrane Is Both Gate and Gatekeeper
  • Chapter 37 – Section 37.4, Nutrient Cycles
  • Chapter 38 – Section 38.3, Changes in the Global Nitrogen Cycle
  • Chapter 38 – Section 38.4, Changes in the Global Carbon Cycle

How Plants Transport Food and Water

  • Chapter 8 – Section 8.2, Photosynthesis: Capturing Energy from Sunlight

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