Questions & explanations
1. Casparian strips in the endodermis of roots are primarily involved in:
- Facilitating rapid water transport through apoplast
- Blocking the apoplastic movement of water into the stele
- Providing mechanical strength to the endodermis
- Secreting digestive enzymes
Answer: Blocking the apoplastic movement of water into the stele
Casparian strips are suberized bands that seal the endodermal cell walls, forcing water and solutes to cross the plasma membrane (symplastic pathway) before entering the stele, thus regulating water entry. They do not facilitate apoplastic transport, provide mechanical strength, or secrete enzymes.
2. In a dicot root, which layer is the innermost layer of the cortex and is characterized by cells bearing Casparian strips?
- Epidermis (epiblema)
- Cortex
- Endodermis
- Pericycle
Answer: Endodermis
The endodermis is the innermost layer of the cortex and is characterized by Casparian strips, which are suberized bands that regulate water movement. The epidermis is the outermost layer, the cortex lies between epidermis and endodermis, and the pericycle is just inside the endodermis.
3. Primary xylem differs from secondary xylem in that primary xylem:
- Is formed by vascular cambium
- Contains vessels and tracheids
- Is derived from procambium during primary growth
- Has more fibres and less parenchyma
Answer: Is derived from procambium during primary growth
Primary xylem develops from procambium during primary growth, while secondary xylem is formed by vascular cambium during secondary growth. Both contain vessels and tracheids, but secondary xylem typically has more fibres and less parenchyma.
4. Which meristem is responsible for secondary growth (increase in girth) in dicot plants?
- Apical meristem
- Lateral meristem
- Intercalary meristem
- Primary meristem
Answer: Lateral meristem
Lateral meristems, including vascular cambium and cork cambium, are responsible for secondary growth, which increases the girth of stems and roots. Apical and intercalary meristems are involved in primary growth (increase in length).
5. Which of the following is true regarding secondary growth in monocot roots?
- Monocot roots exhibit secondary growth due to vascular cambium
- Monocot roots do not undergo secondary growth
- Monocot roots show secondary growth only in older roots
- Monocot roots have cork cambium but no vascular cambium
Answer: Monocot roots do not undergo secondary growth
Monocot roots lack vascular cambium and cork cambium, so they do not exhibit secondary growth. Dicot roots typically have secondary growth. The other options are incorrect because monocot roots do not have these cambia.
6. Which simple permanent tissue has cells with unevenly thickened cell walls and provides mechanical support?
- Parenchyma
- Collenchyma
- Sclerenchyma
- Xylem
Answer: Collenchyma
Collenchyma cells have unevenly thickened primary cell walls and provide mechanical support to growing stems and leaves. Parenchyma has thin walls, sclerenchyma has thick lignified walls, and xylem is a complex tissue.
7. Which of the following correctly compares dicot and monocot root anatomy?
- Dicot roots have polyarch xylem; monocot roots have diarch to tetrarch xylem
- Dicot roots have a large pith; monocot roots have a small or absent pith
- Dicot roots have a distinct pericycle; monocot roots lack pericycle
- Dicot roots have 2-4 xylem arches; monocot roots have many xylem arches
Answer: Dicot roots have 2-4 xylem arches; monocot roots have many xylem arches
Dicot roots typically have 2-4 xylem arches (diarch to tetrarch), while monocot roots have polyarch xylem (many arches). Monocot roots have a large pith, dicot roots have a small or absent pith. Both have a pericycle.
8. Which of the following are the three tissue systems in flowering plants?
- Epidermal, ground, and vascular
- Dermal, cortical, and medullary
- Epidermal, pericycle, and pith
- Vascular, cambial, and pith
Answer: Epidermal, ground, and vascular
In flowering plants, the three tissue systems are the epidermal (outer covering), ground (fundamental) tissue, and vascular (conducting) tissue systems. The other options mix components of these systems incorrectly.
9. In a temperate region, the annual ring of a tree consists of:
- Spring wood only
- Autumn wood only
- Both spring wood and autumn wood
- Heartwood and sapwood
Answer: Both spring wood and autumn wood
An annual ring is formed by one layer of spring wood (early wood, lighter) and one layer of autumn wood (late wood, darker), representing one year's growth. Dendrochronology uses these rings to determine age.
10. Which of the following is NOT a component of the epidermal tissue system?
- Epidermis
- Cuticle
- Stomata
- Pericycle
Answer: Pericycle
The epidermal tissue system includes the epidermis, cuticle, stomata (guard cells and subsidiary cells), trichomes, and root hairs. The pericycle is part of the ground tissue system, not the epidermal system.
11. Which meristem is responsible for secondary growth in dicot stems?
- Apical meristem
- Intercalary meristem
- Lateral meristem (vascular cambium and cork cambium)
- Primary meristem
Answer: Lateral meristem (vascular cambium and cork cambium)
Lateral meristems, including vascular cambium and cork cambium, are responsible for secondary growth, increasing the girth of stems and roots. Apical and intercalary meristems are involved in primary growth.
12. A vascular bundle consists of:
- Xylem and phloem
- Xylem, phloem, and cambium
- Xylem and cambium
- Phloem and cambium
Answer: Xylem, phloem, and cambium
A vascular bundle typically contains xylem and phloem, and in dicot stems, it also includes cambium. The correct answer includes all three components, as the question does not specify open or closed bundles.