1. What are the three main types of tissues?
Dermal, ground, and vascular tissues.
2. What is the major role of dermal tissue?
Dermal tissue protects against environmental stressors, such as extremes of light, temperature, water, and dryness, and controls gas exchange.
3. What function do you think the ground tissue provides to keep plants healthy?
Ground tissue carries out photosynthesis, stores nutrients, and gives support.
4. What is the function of vascular tissue in plants?
Vascular tissue transports water, nutrients, and organic compounds throughout the plant.
5. Why is it important to understand the plant tissue system?
The understanding of the plant tissue system enables us to know how plants grow, develop, and adapt to their environments.
6. How does secondary growth modify the structure of woody stems?
Secondary growth results in the formation of secondary xylem (wood) and secondary phloem, increasing the stem's diameter. It also leads to the development of bark, which includes all tissues outside the vascular cambium.
7. What adaptations in tissue structure allow desert plants to conserve water?
Desert plants often have a thick cuticle, sunken stomata, and a compact arrangement of photosynthetic cells to reduce water loss. They may also have extensive water storage tissue and modified leaves (like spines) to minimize transpiration.
8. How does the arrangement of collenchyma tissue in stems provide both support and flexibility?
Collenchyma tissue is often arranged in continuous strands or cylinders beneath the epidermis. This arrangement provides longitudinal support while allowing for stem flexibility, which is crucial for plants to bend without breaking in response to wind or other forces.
9. What is the function of bundle sheath cells in leaves?
Bundle sheath cells surround the vascular bundles in leaves. They play a crucial role in controlling the movement of substances between the vascular tissue and the mesophyll, and in C4 plants, they are specialized for carbon fixation.
10. How do trichomes contribute to plant survival?
Trichomes are hair-like structures on the plant surface that serve various functions, including: reducing water loss, reflecting excess light, secreting substances to deter herbivores, and in some cases, aiding in seed dispersal.
11. How do meristems contribute to the development of plant tissue systems?
Meristems are regions of actively dividing cells that give rise to all plant tissues. Apical meristems at shoot and root tips produce primary tissues, while lateral meristems (vascular cambium and cork cambium) are responsible for secondary growth.
12. How does the structure of sieve tube elements facilitate the transport of organic compounds?
Sieve tube elements have perforated end walls called sieve plates. These allow for the continuous flow of cytoplasm and organic compounds between connected cells. The lack of a nucleus and most organelles in mature sieve tube elements maximizes space for transport.
13. What is the role of transfer cells in plant tissue systems?
Transfer cells are specialized parenchyma cells with ingrowths in their cell walls, increasing the surface area for transport. They are often found at interfaces between different tissues and play a crucial role in the short-distance transport of solutes.
14. How do plant tissue systems contribute to mechanical support in herbaceous plants versus woody plants?
In herbaceous plants, mechanical support comes primarily from turgid parenchyma cells, collenchyma tissue, and the arrangement of vascular bundles. In woody plants, the extensive development of secondary xylem (wood) provides the main structural support.
15. What is the role of idioblasts in plant tissue systems?
Idioblasts are specialized cells that differ markedly from surrounding cells in structure and function. They may contain crystals, oils, or other substances and often play a role in plant defense or mineral balance.
16. What are the three types of ground tissue and their primary functions?
The three types of ground tissue are: 1) Parenchyma (for storage and photosynthesis), 2) Collenchyma (for support in growing parts), and 3) Sclerenchyma (for mechanical support in mature parts).
17. What is the significance of pith in herbaceous stems?
Pith is the central region of ground tissue in herbaceous stems. It primarily consists of parenchyma cells and serves for storage of nutrients and water. In some plants, it may break down to form a hollow stem, providing structural support with minimal tissue.
18. How does the structure of collenchyma cells relate to their function?
Collenchyma cells have unevenly thickened cell walls, which provide flexibility and strength. This allows them to support growing parts of the plant while still allowing for cell elongation and plant growth.
19. Why are sclerenchyma cells often called "dead cells" even though they're part of a living plant?
Sclerenchyma cells, when mature, lose their cellular contents and become filled with lignin, a tough compound that strengthens cell walls. Although the cells are no longer alive, they continue to provide mechanical support to the plant.
20. What is the difference between fibers and sclereids in sclerenchyma tissue?
Fibers are long, slender cells that provide tensile strength, while sclereids are shorter, irregularly shaped cells that provide compression strength. Both contribute to the overall mechanical support of the plant.
21. What are the main components of xylem tissue and their functions?
The main components of xylem are: 1) Tracheids and vessels (for water conduction), 2) Xylem parenchyma (for storage and lateral transport), and 3) Xylem fibers (for mechanical support).
22. How does the structure of vessel elements in xylem contribute to efficient water transport?
Vessel elements are shorter, wider cells with perforated end walls. They form long, continuous tubes called vessels, which allow for more efficient water transport compared to the narrower, overlapping tracheids.
23. What is the significance of lignin in xylem cells?
Lignin is a complex polymer that impregnates the cell walls of xylem cells, particularly vessels and tracheids. It provides mechanical strength, prevents the collapse of cells under negative pressure during water transport, and makes the cells waterproof.
24. What is the role of companion cells in phloem tissue?
Companion cells are closely associated with sieve tube elements and perform metabolic functions for them. They load sugars into the sieve tubes, maintain the sieve tubes' cellular functions, and provide energy through their mitochondria.
25. How does phloem tissue differ structurally from xylem tissue?
Unlike xylem, phloem tissue consists of living cells at maturity. The main conducting cells, sieve tube elements, retain their cytoplasm but lose their nuclei. They are connected end-to-end and supported by companion cells.
26. What is the function of stomata in the dermal tissue system?
Stomata are tiny pores in the epidermis that regulate gas exchange and water loss through transpiration. They allow carbon dioxide to enter for photosynthesis and oxygen to exit as a byproduct, while also controlling water vapor release.
27. How does the dermal tissue system differ in structure between young and mature plants?
In young plants, the dermal tissue system consists of a single layer of cells called the epidermis. In mature woody plants, the outer protective layer is replaced by a multi-layered tissue called periderm, which includes cork cells.
28. How does the structure of root hairs contribute to their function?
Root hairs are extensions of epidermal cells in the root. Their tubular shape greatly increases the surface area for water and nutrient absorption. Their thin cell walls allow for easy passage of water and dissolved minerals into the root.
29. What is the function of lenticels in woody stems?
Lenticels are porous structures in the periderm of woody stems that allow gas exchange between the internal tissues and the atmosphere. They replace the function of stomata in older, woody parts of the plant.
30. How does the structure of guard cells enable them to control stomatal opening and closing?
Guard cells have an uneven thickening of their cell walls. When they take up water and become turgid, their unique shape causes them to bow outward, opening the stomatal pore. When they lose water and become flaccid, the pore closes.
31. What are the three main types of plant tissue systems?
The three main types of plant tissue systems are: 1) Dermal tissue system (forms the outer protective covering), 2) Ground tissue system (makes up the bulk of the plant body), and 3) Vascular tissue system (responsible for transport of water, nutrients, and photosynthetic products).
32. How do the tissue systems in a leaf blade differ from those in a petiole?
The leaf blade typically has a dorsiventral arrangement with distinct upper and lower epidermis, palisade and spongy mesophyll, and vascular bundles. The petiole has a more stem-like structure with a ring of vascular bundles and often collenchyma for support.
33. How does the arrangement of tissues in a typical dicot root differ from that in a typical monocot root?
In dicot roots, the vascular tissue forms a central cylinder with distinct xylem and phloem regions. In monocot roots, the vascular tissue is arranged in a ring around a central pith, with alternating xylem and phloem bundles.
34. How do dicot and monocot stems differ in their vascular bundle arrangement?
In dicot stems, vascular bundles are typically arranged in a ring, while in monocot stems, they are scattered throughout the ground tissue. This difference affects the potential for secondary growth in these plant types.
35. What is the role of the Casparian strip in the endodermis?
The Casparian strip is a band of suberin in the radial and transverse walls of endodermal cells. It forms a barrier that prevents water and dissolved substances from freely entering the vascular cylinder, forcing them to pass through the selective membranes of endodermal cells.
36. How do xylem and phloem work together in the vascular tissue system?
Xylem transports water and dissolved minerals upward from the roots to other parts of the plant, while phloem transports organic compounds (mainly sugars) produced during photosynthesis from leaves to other parts of the plant, including roots.
37. What is the significance of the endodermis in roots?
The endodermis is a specialized layer of cells in roots that forms a selective barrier between the cortex and the vascular cylinder. Its Casparian strip regulates the movement of water and minerals into the vascular tissue, providing control over nutrient uptake.
38. How do plant tissue systems contribute to the overall water balance in plants?
The dermal system controls water loss through the cuticle and stomata. The ground tissue stores water and facilitates its movement. The vascular system transports water throughout the plant, with xylem moving water upward and phloem redistributing it as needed.
39. What is the difference between primary and secondary plant body?
The primary plant body develops from the apical meristems and consists of primary tissues. The secondary plant body develops from lateral meristems (vascular cambium and cork cambium) and results in an increase in girth through secondary growth.
40. What is the role of plasmodesmata in plant tissue systems?
Plasmodesmata are channels that connect the cytoplasm of adjacent plant cells. They allow for direct communication and transport of molecules between cells, creating a continuum called the symplast, which is crucial for coordinated cellular activities in plant tissues.
41. What is the significance of aerenchyma tissue in aquatic plants?
Aerenchyma is a spongy tissue with large air spaces. In aquatic plants, it provides buoyancy and allows for the storage and movement of gases throughout the plant, which is crucial for respiration in underwater parts.
42. How do reaction wood tissues help trees maintain upright growth?
Reaction wood forms in response to mechanical stress. In gymnosperms, compression wood forms on the lower side of leaning stems, while in angiosperms, tension wood forms on the upper side. These specialized tissues help to reorient stems to a vertical position.
43. What is the role of stone cells (sclereids) in fruit tissues?
Stone cells, or sclereids, are heavily lignified cells found in some fruits. They provide mechanical support and protection, and contribute to the texture of fruits. In pears, for example, they give the characteristic gritty texture.
44. How does the structure of velamen tissue in orchid roots contribute to water absorption?
Velamen is a spongy tissue covering aerial roots of epiphytic orchids. Its dead cells can quickly absorb water from the air or from brief contacts with wet surfaces. The tissue also reduces water loss and provides mechanical protection to the root.
45. How does the pressure flow hypothesis explain the movement of substances in phloem?
The pressure flow hypothesis suggests that sugars are actively loaded into sieve tubes at the source (e.g., leaves), creating a high concentration and drawing water in by osmosis. This creates high pressure, pushing the sugar solution towards areas of lower pressure (sinks) where sugars are unloaded.
46. What is the function of vascular rays in woody plants?
Vascular rays are horizontal bands of parenchyma cells that extend radially in woody stems and roots. They facilitate the lateral transport of water and nutrients between the bark and inner wood, and serve as storage tissue.
47. How do hydathodes contribute to the water balance in plants?
Hydathodes are specialized structures, usually at leaf margins, that secrete water and dissolved minerals. This process, called guttation, helps maintain water balance and internal pressure, especially when transpiration is low.
48. What is the function of resin ducts in conifer needles?
Resin ducts are specialized channels that produce and store resin, a sticky substance that helps protect the plant against herbivores and pathogens. In conifer needles, they also play a role in reducing water loss.
49. How does the structure of spongy mesophyll contribute to efficient gas exchange in leaves?
Spongy mesophyll cells are loosely arranged with large intercellular spaces. This arrangement creates a large surface area for gas exchange and allows for the rapid diffusion of carbon dioxide to the photosynthetic cells.
50. What is the role of passage cells in the endodermis?
Passage cells are endodermal cells that lack a Casparian strip and suberin lamella. They allow for a direct pathway for water and solutes to move from the cortex into the vascular cylinder, bypassing the selective barrier of other endodermal cells.
51. How do bulliform cells in grass leaves contribute to drought resistance?
Bulliform cells are large, thin-walled cells in the upper epidermis of grass leaves. During water stress, they lose turgor and cause the leaf to roll or fold, reducing the surface area exposed to sun and wind, thus minimizing water loss.
52. What is the function of transfusion tissue in gymnosperm leaves?
Transfusion tissue consists of parenchyma and tracheids surrounding the vascular bundles in gymnosperm leaves. It facilitates the lateral distribution of water and solutes from the xylem to the photosynthetic tissue, compensating for the lack of extensive venation.
53. What is the role of secretory cavities in citrus fruit peels?
Secretory cavities in citrus peels are specialized structures that produce and store essential oils. These oils serve as a defense against herbivores and pathogens, and contribute to the characteristic aroma of the fruit.
54. How does the arrangement of vascular bundles in a monocot leaf contribute to its strength and flexibility?
In monocot leaves, vascular bundles run parallel to each other along the length of the leaf. This arrangement, combined with supporting sclerenchyma fibers, provides strength while allowing the leaf to bend easily in one plane, which is advantageous in wind.
55. What is the function of bundle cap fibers in leaves?
Bundle cap fibers are sclerenchyma cells that often occur above and below vascular bundles in leaves. They provide mechanical support to the leaf, protect the vascular tissue, and help prevent the collapse of the leaf during water stress.
