Textbook (Raven Biology of Plants, 8th editions) 1. Annuals, Biennials, and Pere
ID: 57662 • Letter: T
Question
Textbook (Raven Biology of Plants, 8th editions)
1. Annuals, Biennials, and Perennials; pp. 614–615; easy
Explain the differences between annuals, biennials, and perennials.
2. The Vascular Cambium; p. 615; difficult
What two types of cells make up the vascular cambium? Explain why these cells must divide anticlinally and periclinally.
3. Effect of Secondary Growth on the Primary Body of the Stem; p. 617; moderate
What is the difference between fascicular and interfascicular cambium. Explain the process by which they develop.
4. Effect of Secondary Growth on the Primary Body of the Stem; pp. 617–619; moderate
Which tissues are produced by the vascular cambium and which by the cork cambium? Describe how the functioning of the cork cambium results from the activity of the vascular cambium.
5. Effect of Secondary Growth on the Primary Body of the Stem; pp. 619-620; easy
What is a lenticel? What function does it play in the plant?
6. Effect of Secondary Growth on the Primary Body of the Stem; pp. 620-622; moderate
What is bark? Explain how the composition of bark changes over time.
7. Effect of Secondary Growth on the Primary Body of the Stem; p. 620; moderate
Explain why less secondary phloem than secondary xylem accumulates in the stem.
8. Effect of Secondary Growth on the Primary Body of the Stem; pp. 620–623; moderate
Distinguish among periderm, cork, and bark. What is the difference between the inner bark and the outer bark?
9. Effect of Secondary Growth on the Primary Body of the Stem; pp. 620-622; difficult
Why is it advantageous for a plant to produce more than one periderm?
10. Wood: Secondary Xylem; pp. 626, 628; moderate
Compare and contrast angiosperm and conifer woods.
11. Wood: Secondary Xylem; pp. 626, 628; difficult
Describe the appearance of conifer wood in transverse, radial, and tangential sections.
12. Wood: Secondary Xylem; pp. 626, 631–632; moderate
Explain the difference between hardwood and softwood, between early wood and late wood, and between heartwood and sapwood.
13. Wood: Secondary Xylem; pp. 628, 630; moderate
What causes growth rings to form? How can growth rings be used to determine past climates?
14. Wood: Secondary Xylem; p. 632; moderate
What is reaction wood? What are the characteristics of the two types of reaction wood?
15. Wood: Secondary Xylem; p. 634; moderate
Distinguish between the specific gravity and the density of wood. What do these properties tell us about the strength of wood?
Explanation / Answer
Q1)Answer:
Annuals: Plants complete life cycle within a year
Biennials: Plant complete their life cycle within two year
Perennials: Plants can survive for many years
Q2).
Answer:
The vascular cambium will be developed by two types of cells:
Periclinal divisions of the initials and their immediate derivatives produce secondary xylem and secondary phloem, where as anticlinal division increases the diameter of the stem.
Q3).
Answer:
Fascicular cambium is found within the vascular bundles, produces secondary xylem and secondary phloem.
Interfascicular cambium arises in the parenchymatous regions between vascular bundles. It produces medullary ray or pith rays between vascular bundles.
Fascicular cambium arises from the procambium that remains undifferentiated between the primary xylem and primary phloem.
Interfascicular cambium arises from parenchyma that occurs in the interfascicular region, which occurs between the vascular bundles or fascicles.
Q4).
Answer:
Vascular cambium produces secondary xylem and secondary phloem.
Cork cambium (Phellogen) produces phellum (cork) on the outside and phelloderm (secondary cortex) on the inner side.
As vascular cambium produces sec. xylem and sec. phloem in stele, it exerts pressure on cortex. Hence, the parenchymatic cells develop as cork cambium produces new cells as mentioned above and form periderm, which can with stand the pressure.
Q5).
Answer:
A lenticel is a present in the large intercellular spaces in the periderm of the stem secondarily thickened organs and the bark (secondary growth) of woody stems and roots of dicotyledonous flowering plants. It mainly helps in gas exchange as stomata
Q6).
Answer:
The bark includes all tissues outside the vascular cambium that is phloem, cortex and periderm (Phellum, phellogen and cork).
At the end of the first year growth, the bark includes any primary tissues still present, the secondary phloem, the periderm, and any dead tissues remaining outside the periderm. Each year new periderm appears in between the old crushed secondary phloem and newer secondary phloem. The first cork cambium may remain active for many years (20 years) as in apples and pears. In most woody roots and stems, additional periderms are formed as the axis increases in circumference. New periderm is formed deeper in the bark from phloem parenchyma cells that become meristematic and are no longer active in transporting materials in the stem. The innermost cork cambium separates the living inner bark from the dead outer bark. With maturation of the suberized cork cells, the tissues outside them are separated from the supply of water and nutrients. Hence, the outer bark consists entirely of dead tissues.
Q7).
Answer:
More secondary xylem is produced, pushing the primary phloem outward and its thin walled cells are destroyed. In elderberry, the primary phloem becomes obliterated and replaced by fibers (sclerenchyma). In basswood, the rays in the secondary phloem become dilated in order to adjust to the increase in girth.
Q8).
Answer:
Distinguish among periderm, cork, and bark. What is the difference between the inner bark and the outer bark?
Periderm= Phellum + Phellogen + Secondary cortex.
Cork: It is a tough substance that replaces the epidermis produced by phellogen.
Bark: Periderm ( Phellum + Phellogen + Secondary cortex) + Secondary phloem.
The part of the inner bark that is engaged in the transport of food is called functional or conducting phloem. With maturation of the suberized cork cells, the tissues outside them are separated from the supply of water and nutrients. Hence, the outer bark consists entirely of dead tissues. It is mainly for protection
Q9).
Answer:
In most woody roots and stems, additional periderms are formed as the axis increases in circumference and also more protective in function. Besides, due to secondary growth, the quality increased of wood and becomes valuable economically
Q10)
Answer:
Angiosperm wood- hardwood, more complex structure, many cell types in the axial system, including vessel elements, tracheids, several types of fibers, and parenchyma cells.
Confier wood- softwood, simple structure, lacks vessels, contains resin ducts
Q11).
Answer:
The transverse or cross section is the plane perpendicular to the long axis of the trunk. It is the same view as you would see if you were looking down at the top of a stump after a tree had been cut down.
The radial section is the vertical plane from the pith at the center of the tree heading out towards the bark.
The tangential section is the plane perpendicular to the long axis of the rays and tangential to the growth rings.
Q12).
Answer:
Softwood lacks vessels. Hardwoods have a greater number of cell types in the axial system, including vessel elements, tracheids, several types of fibers, and parenchyma cells.
Early wood is less dense with wider cells and proportionally thinner walls- produced early in growing season. Late wood is more dense with narrower cells and thicker walls- produced late in growing season.
Sapwood is lighter and conductive and heartwood is darker and nonconductive.
Q13).
Answer:
The periodic activity of the vascular cambium in relation to its production of secondary xylem and phloem (happens every season, or any time there are droughts, etc.)
Q14
Answer:
Reaction wood is modified in its anatomical and chemical properties and is generally formed in response to a non-optimal orientation of the stem or branch caused by prevailing winds, snow, slope, loads, or asymmetric crown shape.
There are two different types of reaction wood.
In angiosperms reaction wood is called tension wood. Tension wood forms on the side of the part of the plant that is under tension, pulling it towards the affecting force (upwards, in the case of a branch). It has a higher proportion of cellulose than normal wood. Tension wood may have as high as 60% cellulose.
In gymnosperms it is called compression wood. Compression wood forms on the side of the plant that is under compression, thereby lengthening/straightening the bend. Compression wood has a higher proportion of lignin than normal wood. Compression wood has only about 30% cellulose compared to 42% in normal softwood. Its lignin content can be as high as 40%
Q15).
Answer:
The specific gravity (SG) of wood is a measure of the amount of structural material a tree species allocates to support and strength. The specific gravity of wood is defined as the density of wood relative to the density of water.
Wood density is actually a measure of the mass of a wood per unit volume (kgm3 or lbft3) and can be measured at any moisture content.
Density is related to growth rate, but the response depends on the species and the range of growth rates involved. The only species group in which density is closely related to growth rate is the ring-porous hardwoods (density increases as growth rate increases). In softwoods and diffuse-porous hardwoods, density is generally not related to growth rate. In softwoods density is directly related to the percentage of latewood in a growth ring (more latewood = higher density). Also generally the fewer the growth rings per unit length in some hardwoods the higher the density. Density decreases as moisture content decreases, but below the fiber saturation point (FSP) the specific gravity increases as the moisture content decreases.
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