Seat No: ________
Name: ____________________ ______________________________ ____________ __
Section:___________ Section:___________ Date:_______ Date:_______
CHAPTER 7 Review Questions 1.
The “Concepts” section of this chapter states that most roots have three functions. What are they? Some roots have other functions in addition to these three, or instead of them. Name an example of at least one species in which roots do the following: a.
Store carbohydrate during winter
b.
Produce shoot buds that can act as new plants
c.
Grow out of the trunk and harden into spines
d. Acts as holdfasts e. 2.
Attack other plants and draw water and nutrients out of them
What are the two types of root systems? Give several examples of plants that have each type. Which type is associated with nutrient storage in biennial species like carrots and beets? Which is associated with rhizomes and stolon?
3.
Roots must have an enormous absorptive surface. Why do plants have a highly branched root system instead of just one long root?
4.
Even before a seed germinates, it already has a root; what is the name of this embryonic root? In eudicots, what does this embryonic root usually develop into? In most monocots, this embryonic root does a str ange thing during or immediately after germination. What does it do?
5.
What is an adventitious root? In a monocot rhizome such as that of irises and bamboo, are adventitious roots common or rare? If a bamboo rhizome grows 100 feet undergro und and then sends up an aerial branch, where does that branch get its water – water – from the roots 100 feet away or from adventitious roots right at its base (Figure 7-5e)?
6.
What does the root cap do? Do you think this structure would have evolved if roots all grew in air like shoots do, rat her than growing through dirt?
7.
Roots have localized growth; the only parts of the root that become longer are the root apical meristem and the ________________ of _______________, a region only a few millimetres long within which the cells undergo division and expansion.
8.
What would happen to root hairs if they formed in the zone of elongation? Would this happen if the roots were growing in air or in water?
9.
Root hairs greatly increase the root’s surface area. In rye, a single plant has been found to have ______________________ lateral roots with ___________km of root length and a surface area 2
of ___________m . Convert the length to miles (1mile=1.6 km) and the area to square feet (1 foot=0.3 m).
10. Root hairs are narrower than roots. A root is usually at least _________mm in diameter, but root hairs are only approximately ________μm in diameter. Look at Figure 7-9. Could either roots or root hairs enter the pores represented by the red part of the chart? Could either or both enter the gray part? The white part? Most roots grow near the soil surface, in the upper 20 cm, where most of the soil pores are between 0.2 to 60 μm wide. If a root did not produce any root hairs at all, could the plant obtain water and minerals from these abundant, narrow pores?
11. Which part of the root detects gravity? Which organelles enable them to do this? 12. The use of radioactive precursor of DNA can demonstrate that the central c ells of the root apical meristem are not synthesizing DNA. This mitotically inactive central region is called the ______________ ______________. It is now believed that the central cells act primarily as a reserve of ______________ _____________. 13. If you could examine a transverse section through the zone of elongation in a root, would you see any mature cells? Would there be any fully differentiated epidermis cells or vascular tissues? What would the outermost cells be called, if not epidermis? In the center of the zone of elongation, what would be the tissue t hat would later differentiate into xylem and phloem?
14. Examine Figure 7-13. What are the four diffusion paths that a molecule might follow as it tr avels through the root epidermis and cortex? Why does this diagram stop at the endodermis? What happens at the endodermis?
15. Describe the shape of the endodermis. Is it a flat plane, a cylinder a single ring o f cells? What are the Casparian strips, and on w hich cell walls are located?
16. Draw cross-sections of a root showing its structure at three levels: the mature region, the root hair zone, and the zone of elongation. At w hich level is the endodermis complete with Ca sparian strips?
17. Because Casparian strips are impermeable, minerals can cross t he endodermis only if the endodermal _____________ _____________ absorb them from the intercellular spaces or from cortical cells. Many _____________ minerals can be excluded by the endodermis. 18. Examine Figure 7-14. The roots of e udicots are usually noticeably different from those of monocots in transverse section. Which has a relatively wide set of vascular tissues? Which has endodermis cells with very thick walls? Which has ground tissues in the center, and which metaxylem in the center?
19. Which part of the root produces primordia for lateral roots? How does the vascular tissue o f the lateral root connect with that of the parent root?
20. Some perennial plants store significant amounts of nutrients in the stem during winter, but roots offer certain advantages. Describe two of these advantages.
21. Animals typically use fats in adipose tissues for long-term energy stor age, whereas plants use starch in roots. How do animals benefit from using fat? How do plant benefit from using starch? Name two plants that store energy fo r many years. How is long-term storage for these species? What two plant parts often use fats and why? Storage tissue in enlarged roots is vascularized. How is that important to the plant?
22. Look at the prop roots of screwpine in Figure 7.17d (screwpine is a monocot)because the branches produced their own adventitious roots (the prop roots), can the branches obtain water and minerals without depending on the xylem in the trunk (Think about Question 5)
23. Look at the prop roots of banyan trees in Figure 7-18. These prop roots supply extra water to the branch, but how else do they help the branches?
24. What are contractile roots? They are specially common in plants with what types of shoots (e.g., in rhizomes, vines, or what)?
25. What is a mycorrhizal association? What benefit does the plant derive from association?
26. Describe the structure of a nitrogen-fixing nodule; consider especially the relationship with the plant's vascular tissue.
27. Roots nodules are ________________ associations. Plants and bacteria both benefit. The bacteria are not ______________ ______ the plants, nor are the plants __________________________ the bacteria. 28. Many plants are parasitic on other plants. These parasitic plants have modified roots called ________________. Describe some of the ways that this parasitic root penetrates the host stem or root. Do these parasitic roots have a root cap, a root apical meristem, or a cortex?
29. Except when it produces flowers, what is the body of the parasitic plant Tristerix? W hat tissues does this plant body lack, except when it produces flowers?
30. Imagine a plant that has ten roots, each 1 cm long. What is the total length of the root system? Imagine that at the tip of each root are ten lateral roots, each 1 cm long. Now what is the total length of root system? What is the maximum distance a water molecule must travel from the farthest root tip to the base of the shoot? Distance traveled increases as a simple addition, but total absorbing capacity increases exponentially. Why is the length that is traveled important? Consider the friction of moving through tracheids and vessel e lements.
