SHORT QUESTIONS OF STRUCTURE OF PLANT PARTS
1. Differentiate between tap and adventitious roots.
Ans: Tap root arise from the embryo. Adventitious root develops from other mature tissues of plant like stem etc.
2. What are root hairs? Give their functions.
Ans: A root hair starts its growth as a small papilla on the outer wall. The nucleus and cytoplasm migrate into the papilla. The papilla grows and attains maximum size. Its wall becomes rigid due to deposition of pectic substances.
3. What is endodermis and Casparian strips?
Ans: The inner most layer of the cortex is distinct and well developed in primary roots. It is called endodermis. The cells of this layer are rectangular in outline. A band of suberin develops all around the cell in the middle of the transverse and radial walls. This suberin band is called casparian strip.
4. What is pericycle?
Ans: The outer most part of the stele consists of one or more layers of parenchymatous cells. The outer laer of this parenchyma is called pericycle.
5. What type of phloem are found in roots?
Ans: The phloem strands alternate with the ridge of the xylem and have the same number. In each phloem, the protophloem elements are present towards the outside and metaphloem are present towards the inner side. Phloem consists of Sieve tube elements, parenchyma and few fibers.
6. What is root cap?
Ans: Root cap is present at the tip of the root. It protects the underlying apical meristem. Root caps also help in penetration of root in soil. Root cap also controls the geotropic response of root. Central cells of root caps in many parts form a constant stricture called columella.
7. What is Cork cambium or phellogen?
Ans: The stress of secondary growth ruptures the whole cortex. Therefore, the cork cambium arises in the pericycle. Sometimes, new cork cambium arises in deeper layers. It sloughs off the old periderm in the form of bark. Lenticels are not produced in the,periderm of roots.
8. What is phelloderm?
Ans: The cork cambium also produces some phelloderm (Parenchyma cells) towards the inner side. But this phelloderm is not clearly differentiated. It merges with outer part of the non-functional phloem and remaining pericycle.
9. What are medullary rays? Give their function.
Ans: The strips of ground tissues between the adjacent vascular are called medullary rays or pith rays. Medullary rays connect the pith with cortex.
10. Differentiate between Collateral and Bicollateral xylem.
Ans: Collateral: In this case, xylem is present towards the inner side and phloem is present towards the outer side of vascular bundle. Bicollateral: In this case, phloem is present on both side of xylem.
11. What are Concentric bundles?
Ans: In this case, on type of vascular tissue (xylem or phloem) completely surround the other type of tissue.
12. Differentiate between Amphicribral and Amphivasal.
Ans: Amphicribral: In this case, xylem is completely surrounded by phloem. These vessels are found in fruits, flowers and ovules of certain plants. Amphivasal: In this case. phloem is completely surrounded by xylem. These vessels are found in certain member of family Liliaceae.
13. Differentiate between protophloem and metaphloem.
Ans: The phloem present towards the outside are called protophloem. The sieve tubes of protophloem are narrow and stretched. They are often non-functional. The phloem present towards the inner side is called metaphloem. They are functional.
14. What is open type vascular bundle?
Ans: .Vascular bundles having cambium between xylem and phloem are called open type.
15. What is vascular cambium? Give its function.
Ans: A narrow strip of meristematic cells is present between the xylem and phloem in the vascular bundles of dicots and gymnosperms. This strip of meristematic cells is called vascular cambium. This cambium becomes active at the start of secondary growth.
16. What is fascicular cambium?
Ans: The fascicular cambium is present between xylem and phloem tissues. The vascular cambium of the bundles is not continuous with adjacent kindles. The parenchyma cells of the medullary rays are present in between the• fascicular cambium.
17. What are fusiform and ray initials?
Ans: Fusiform initials: They are wedge like. They are many times longer than broad. and have narrow pointed ends. Ray initials: They are nearly isodiametric. They are found in vertical rows. The derivatives of ray initials give rise to rays.
18. Differentiate between sap and heart woods.
Ans: Sap wood: The narrow peripheral functional part of the secondary xylem is called sap wood. Heart wood: The major central nonfunctional part forms the heart wood. The elements of heartwood undergo certain morphological changes. These changes include deposition of tannins and lignification of their walls.
19. What are annual rings? How are they formed?
Ans: The activity of the vascular cambium is not of uniform throughout the years in many plants. The cambium is most active during the spring. It produces wide and loosely dispersed tracheal elements. It is called spring wood. The activity of cambium slows down during the autumn. It produces narrow and closely placed tracheal elements. It forms autumn wood. This difference of spring wood and autumn wood produces annual rings.
20. What is periderm?
Ans: The continuous secondary growth cause rupturing of the protective layer or epidermis. A secondary protective tissue is produced on the surface of the stem. This protective tissue is called periderm.
21. What are lenticels? How are they formed?
Ans: The phellogen produces a group of loosely placed cells at certain points. These loosely placed cells are called lenticels. They have no or slight suberization on their walls. Lenticels Vary in size from minute microscopic to clearly visible spots.
22. Differentiate between Biracial and Isolateral leaves.
Ans: In flattened leaves, the palisade layer is restricted to the upper side. Such leaves are called bifacial or dorsiventral. If the palisade is present on both sides of the spongy tissue, then the leaf is called isolateral.
23. What are centric leaves?
Ans: The palisade forms a continuous ring around the spongy tissue in narrow and cylindrical leaves. Such leaves are called centric leaves.
24. Differentiate between apical and intercalary meristems.
Ans: The meristems present at the tips of roots and shoot are called apical meristems. The meristem situated at the bases of internodes is called intercalary meristem.
25. Differentiate between protoderm and procambium.
Ans: Protoderm: This is the surface layer. Its cells are differentiated into epidermal systems. Procambium: They are also called provascular tissues. Their cells form different parts of vascular systems at maturity.
26. What is Lateral Meristems? Where is it present.
Ans: The cylinders of dividing cells present in the vascular and cork tissue of the plants are called lateral meristems. Lateral meristems are present in dicots and gymnosperms. Vascular and cork cambium are the example of lateral meristem.
27. Differentiate between pericinal and anticlinal divisions.
Ans: Periclinai: In this case, cell division is parallel to the axis. these divisions are also called tangential. Anticlinal: In this case, cell division occurs at right angles to the surface.
28. What is Histogen theory?
Ans: This theory was put forward by Hanstein. According to this theory the apical meristematic tissues are divided into three zones: Dermatogens. Periblem and Plerome.
29. What is Tunica-Corpus theory?
Ans: This theory was given by Schmidt. Histogen theory was discarded due to lack of cytological proof. Therefore, Tunica corpus theory was put forward. According to this concept, the dividing cells in the apical meristem are arranged in two zones: Tunica, Corpus.