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CHAPTER 10

PLANT ANATOMY AND PHYSIOLOGY

REVIEW QUESTIONS

PLANT CELL STRUCTURE AND PLANT GROWTH

1. What is plant anatomy and how does it differ from animal anatomy?

Plant anatomy is the study of the tissue and cell structure of plant organs.

In zoology, the term anatomy refers to the study of internal organs; histology is the study of cells and tissues of animals.

2. What is the cell theory and its four tenets?

A unifying theme of biology, entailing:

a) All life is composed of one or more cells.

b) Cells arise only from preexisting cells, occurring either through cell division (meiosis or mitosis) or cell fusion (e.g., fertilization of egg and sperm).

c) Cells are the units of metabolic processes; thus, each cell contains the necessary chemical compounds and cellular components to carry on the biosynthetic pathways needed for basic physiological processes.

d) Each cell contains a set of DNA, the hereditary material that is transferred from one cell to another that codes for the structural and functional features of the organism.

3. Name and give the function of the major components and organelles of a typical plant cell.

Plasma membrane - a phospholipid bilayer with embedded proteins that envelops the cell.

Nucleus - a double-membrane bound organelle that contains DNA, the hereditary material of the cell.

Mitochondria - double membrane-bound organelles, with invaginations called cristae that function in the electron transport reactions of respiration.

Vacuole - a large, internal, membrane-bound sac that functions in storage of compounds such as pigments, acids, or ergastic

substances.

Endoplasmic reticulum - interconnected phospholipid membranes that function as the site of protein synthesis and material transport.

Golgi bodies - parallel stacks of flattened membranes that function in transport and modification of compounds.

Chloroplasts - double membrane-bound with internal thylakoid membranes (composed of lamellae and grana in the green plants), functioning in the reactions of photosynthesis.

Ribosomes - function as the site of protein synthesis.

4. Name the various types of ergastic substances.

Chromoplasts, amyloplasts (starch grains), aleurone grains, tannins, fats, oils, waxes, crytsals.

5. What are chromoplasts and what is their function?

Carotenoid-containing bodies that function to provide yellow, orange, or red pigmentation for a plant organ, as in petals or fruits.

6. What is an amyloplast and what is its chemical composition?

Lamellate deposits of starch (alpha-1,4-glucopyranoside, a polysaccharide polymer of glucose units with alpha-1,4 chemical bonding) which functions as the high-energy storage compound in green plants.

7. Of what is an aleurone grain composed?

Protein.

8. Name four types of crystals based on their shape. What two different substances make up plant crystals?

a) Druses, raphides, styloids, prismatics.

b) Calcium oxalate and silica.

9. Characterize a primary cell wall in terms of development and structure.

The wall secreted outside the plasma membrane during primary growth (before the cell ceases to elongate), consisting of cellulosic microfibrils.

10. How does cellulose differ from starch?

It is a beta-1,4-glucopyranoside (instead of alpha).

11. What are plasmodesmata and what is their function?

Pores in the primary cell wall, allowing for inter-cell communication.

12. Where is the secondary cell wall formed in relation to the plasma membrane and the primary cell wall?

To the outside of the plasma membrane, inside of the primary cell wall.

13. What are the name, properties, and function of the compound (other than cellulose) making up a secondary cell wall?

Lignin - a complex polymer of phenolic compounds that binds the cellulose microfibrils together.

Lignin imparts significant strength and rigidity to the cell wall.

14. What is a pit and what is the function of pit-pairs?

A hole in the secondary cell wall (typically occurring opposite one another, in pit-pairs, in line with plasmodesmata) that functions to enable cell-cell communication.

15. What are meristems and what are the two major types?

Regions of actively dividing cells.

a) Apical meristems - occurring at the tips of roots and shoots.

b) Lateral meristems - developing as cylindrical sheaths of cells, which function in growth that increases width or girth.

16. Explain the processes of cell differentiation.

Cell differentiation refers to the series of changes that a cell undergoes from the point of inception to maturity, involving the transformation of a meristematic cell into one that assumes a specific structure and function.

Differentiation involves two processes: cell expansion, in which the cell grows in size (often by elongation, in which growth in the axial direction is greatest); and maturation or specialization, in which the cell acquires the structural and functional features at maturity. Cell differentiation results in the development of various cell types.

PLANT TISSUES AND SPECIALIZED CELL TYPES

17. What is a tissue and what are the three general tissue types?

A tissue is a group of cells having a common function or structure.

18. How are parenchyma and collenchyma similar and how different with respect to structure and function?

Both consist of cells that have a primary cell wall only and that are living at maturity.

Collenchyma differs in being always elongate and in having pectic-rich, unevenly thickened cells walls, the cells functioning in structural support.

19. What are the characteristics and two general cell types of sclerenchyma?

Sclerenchyma refers to hard, lignified cell walls) are cells that structurally have thick, lignified secondary (2˚) cell walls, which may have pits, and are (usually) dead at maturity.

The two types of sclerenchyma are fibers, which are long, very narrow cells with sharply tapering end walls, and sclereids, which are isodiametric to irregular in shape and often branched

20. What is the function of xylem and why is it a complex tissue?

Xylem functions in water and mineral conduction.

It is composed of tracheary elements plus some parenchyma and sometimes sclerenchyma.

21. What are the names and characteristics of the two types of water-conductive cells of xylem?

There are two types of tracheary elements: tracheids and vessel members.

Tracheids are imperforate, meaning that water and mineral nutrients flow between adjacent cells through pit-pairs, in which there are intermediate primary cell walls. Vessel members are perforate, meaning that there are one or more continuous holes between adjacent cells through which water and minerals may pass.

22. What is the function of phloem and why is it a complex tissue?

Phloem is a tissue composed of specialized cells called sieve elements plus some parenchyma and often some sclerenchyma.

23. What are the names and characteristics of the two types of sugar-conductive cells of phloem?

There are two types of sieve elements: sieve cells and sieve tube members. Sieve cells have only sieve areas (containing callose-lined pores) on both end and side walls. Sieve tube members have both sieve areas and sieve plates. Sieve plates consist of one or more sieve areas at the end wall junction of two sieve tube members; the sieve pores of a sieve plate, however, are significantly larger than are those of sieve areas located on the side wall.

24. What tissue occurs as the outermost cell layer of plant organs?

Epidermis.

25. Describe the characteristics and function of the epidermis, stomata, trichomes, and secretory structures.

Epidermis - usually tabular (flattened, tilelike) in shape; have a cutinized (infiltrated with cutin, a polymer of fatty acids) or suberized (infiltrated with suberin) outer cell wall; secrete a layer of cutin (called a cuticle) outside the cell wall; and are usually living at maturity.

Stomata are epidermal cells specialized for gas exchange.

Trichomes (plant hairs) are cellular appendages that grow from the epidermal cells; may function in providing protection from UV light or herbivory; trichomes of carnivorous plants even function in digestion.

Secretory structures are cells that secrete compounds, either internally (and stored within the cell) or externally, including glandular or stinging (urent) trichomes, nectaries, hydathodes, resin/oil/mucilage ducts or canals, and laticifers.

ROOT STRUCTURE AND FUNCTION

26. From what in an embryo does the first root arise?

Radicle.

27. Distinguish between a primary, lateral, and adventitious root.

Primary root - continues to develop from the radicle after embryo growth.

Lateral - arises from another root.

Adventitious - arise from a nonroot organ (stem or leaf).

28. Name three ways that roots can be distinguished from shoots/stems.

a) The apical meristem is covered on the outside by a rootcap.

b) The epidermal cells proximal to the root tip develop hair-like extensions called root hairs.

c) Roots have no exogenous (externally developing) organs; all lateral roots arise endogenously from the internal tissues of the root.

29. What is a Casparian strip and endodermis and what are their function?

The Casparian strip is a tangential band of suberin that infiltrates the endodermis cell wall. They function as a water-impermeable binding material to the plasma membrane of the endodermal cells, forcing absorbed water and nutrients to flow through the endodermal plasma membrane, selectivity controlling what mineral nutrients are and are not absorbed by the plant; e.g., toxic minerals may be selectively excluded.

30. What is the function of the pericycle?

Functions as the site of development of at least part of the vascular cambium in roots.

31. What is a velamen?

A multi-layered epidermis of many Orchidaceae and Araceae that lacks root hairs and may function in protection, prevention of water loss, or water and mineral absorption.

SHOOT/STEM STRUCTURE AND FUNCTION

32. What is the definition of a shoot?

A stem plus associated leaves.

33. From what in an embryo does the first shoot arise?

Epicotyl.

34. What is a bud primordium and where are buds typically located?

The meristematic cells that will develop into a bud, an immature shoot sytem, typically located in the axiles of leaves.

35. What are three ways that stems differ from roots?

a) The apical meristem of stems is not covered by an outer protective layer (like the root

cap).

b) The epidermal cells of the stem do not form structures resembling root hairs.

c) Stems bear leaves exogenously; no organs are born endogenously (except in cases of adventitious roots potentially arising from the internal parenchyma cells of stems).

36. What is a stele? Name five stele types and distinguish between them.

A particular arrangement of the primary vasculature of stems.

a) protostele, in which there is a central cylinder of vascular tissue, either xylem surrounded by phloem or the two tissues interdigitated.

b) Siphonostele, in which a ring of xylem is surrounded by a continuous layer of phloem, either on the ouside only (an ectophloic siphonostle) or on the outside and inside (an amphiphloic siphonostele = solenostele).

c) Dictyostele - a much dissected siphonostele.

d) Eustele - an arrangment of collateral (or bicollateral) vascular bundles as a single ring.

e) Atactostele - numerous, collateral vascular bundles positioned throughout the stem tissue.

37. Distinguish between protoxylem and metaxylem; between exarch, endarch, and mesarch.

Protoxylem refers to the first xylem that matures in a group of vascular tissue; protoxylem cells are often smaller in diameter.

Metaxylem is the xylem that develops later and usually consists of larger-diameter cells.

Three general types of protoxylem orientation are recognized: (1) exarch, in which the protoxylem is oriented toward the outside relative to metaxylem, as occurs in some protosteles; (2) endarch, in which the protoxylem is oriented toward the center of the stele, relative to the metaxylem, as occurs in eusteles and atactosteles; and (3) mesarch, in which the protoxylem is surrounded by metaxylem within the vascular tissue, as can occur in siphonosteles.

SECONDARY GROWTH

38. What is secondary growth and from what general type of meristem does it arise?

a) Growth in girth or width by means of cells produced not from the apical meristems, but from lateral meristems.

b) From lateral meristems: vascular and cork cambium.

39. Where does the vascular cambium arise?

In eustelic stems the vascular cambium forms from parenchyma cells both between the primary xylem and phloem of vascular bundles and in the adjacent region between the bundles. In woody roots the vascular cambium develops from parenchyma cells between xylem and phloem and from the adjacent pericycle.

40. What two products does the vascular cambium give rise to and in what direction?

Secondary xylem to the inside; secondary phloem to the outside.

41. What is the technical name for wood?

Secondary xylem.

42. Where does the cork cambium form, and what two tissues does it give rise to?

The cork cambium differentiates near the periphery of the stem or root axis. The cork cambium forms cork to the outside and phelloderm to the inside.

43. Describe the adaptive significance of the lateral meristems.

Secondary xylem (wood) produced by the vascular cambium functions in structural support, enabling the plant to grow tall and acquire massive systems of lateral branches.

Cork produced by the cork cambium functions as a thick layer of dermal tissue cells that protects the delicate vascular cambium and secondary phloem from mechanical damage, predation, and desiccation.

44. What is a ray and what is its function?

Radially oriented cells occuring in bandlike strands, functioning in lateral translocation of water, minerals, and sugars.

45. What is an annual ring and what is the structural difference between spring wood and summer wood?

Each annual ring represents the accumulation of secondary xylem (or phloem) over a single growing season.

The tracheary elements of spring wood tend to be larger in diameter with thinner walls; those of summer wood tend to be smaller in diameter with thicker walls.

46. Define and draw the three major sections of wood.

Transverse (cross-sectional).

Radial (longitudinal and ca. parallel to a stem radius).

Tangential (longitudinal and perpendicular to a stem radius).

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47. What is the difference between a softwood and a hardwood?

The term softwood is used for a wood product derived from a conifer.

The term hardwood is used for one derived from a nonmonocotyledonous angiosperm.

48. Distinguish between nonporous, ring-porous, and diffuse-porous wood.

Nonporous - having only tracheids.

Ring-porous - wood in which the vessels may form only in the spring wood, with summer wood either lacking or having relatively small vessels and usually containing mostly fibers.

Diffuse-porous - wood in which vessels develop more or less uniformly throughout the growth season.

49. Distinguish between uniseriate, biseriate, and multiseriate rays.

Uniseriate - with a single, vertical row of cells.

Biseriate - with two vertical rows of cells.

Multiseriate - with many vertical rows of cells.

50. What is dendrochronology and for what can it be used?

The field of study in which wood (both extant and fossil) may be used to trace the history of climatic conditions in a given region.

LEAF STRUCTURE AND FUNCTION

51. What is the difference between a lycophyll and a euphyll?

Lycophylls - leaves of lycophytes, which have a single, generally unbranched vein, lack a leaf gap, and grow by means of an intercalary meristem.

Euphylls - have multiple, branched vascular strands in the leaf blade, possess a leaf gap, in which parenchymatous tissue replaces vascular tissue in the region just distal to the point of departure of the vasculature from stem to leaf, and grow by means of either marginal or apical meristems.

52. What are the structure and function of stomates and of subsidiary cells?

Stomates consist of two chlorophyllous guard cells, between which is an opening, the stomatal pore or stoma. The guard cells can alter turgor pressure by changes in ion gradients, which results in opening or closing the stomatal pore.

Stomates function to regulate gas exchange.

53. What is the name of the leaf cells located between upper and lower epidermal layers? What are the two types called?

a) Mesophyll.

b) Palisade and spongy mesophyll.

PHOTOSYNTHESIS

54. Describe the basic pathway of C3 photosynthesis.

Photosynthesis occurs by the fixation of carbon dioxide in the following net reaction: nCO2 + nH2O → (CH2O)n + nO2, in two interdependent sets of reactions: light and dark.

55. What enzyme functions to fix carbon dioxide in C3 photosynthesis?

Ribulose-bisphosphate carboxylase (rubpcarboxylase).

56. How does C4 photosynthesis differ from C3?

In C4 plants carbon dioxide is initially fixed in the mesophyll cells by a different enzyme, PEP carboxylase. The initial molecule of carbon fixation is a four-carbon molecule, which, in the form of malic acid, is then transported to the bundle sheath cells, where the carbon dioxide is released and fixed by the typical (and ancestral) enzyme, ribulose-bisphosphate carboxylase (RuBP-carboxylase).

57. What is Kranz anatomy?

Kranz anatomy is that in which chloroplasts of the bundle sheath cells are typically much larger than those of the mesophyll cells.

58. What enzyme functions to fix carbon dioxide in C4 photosynthesis?

PEP carboxylase.

59. How does CAM photosynthesis differ from C3 and C4 and how does this function for plants living in dry conditions?

CAM (crassulacean acid metabolism) differs in that the initial fixation of CO2 occurs at night, when (unlike other plants) stomata are open. The CO2 is initially fixed by the enzyme PEP carboxylase to form malic acid, which is temporarily stored within vacuoles of the mesophyll cells. During the day the stomata close and CO2 is released from the vacuoles into the cytoplasm, where it is fixed in the chloroplasts by the Calvin cycle.

CAM minimizes evapotranspiration by allowing the stomates to close during the day.

ANATOMY AND SYSTEMATICS

60. Draw a general cladogram of land plants, illustrating several anatomical apomorphies.

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