Grass leaves curl inwards during very dry weather. Select the most appropriate reason from the following :
1. Tyloses in vessels
2. Closure of stomata
3. Flaccidity of bulliform cells
4. Shrinkage of air spaces in spongy mesophyll
Phloem in gymnosperms lacks:
1. Both sieve tubes and companion cells
2. Albuminous cells and sieve cells
3. Sieve tubes only
4. Companion cells only
Guard cells help in:
1. | protection against grazing |
2. | transpiration |
3. | guttation |
4. | fighting against infection |
Anatomically, fairly old dicotyledonous root is distinguished from the dicotyledonous stem by:
1. absence of secondary xylem
2. absence of secondary phloem
3. presence of cortex
4. position of protoxylem
The chief water conducting elements of xylem in gymnosperms are:
1. | vessels | 2. | fibres |
3. | transfusion tissue | 4. | tracheids |
Closed vascular bundles lack:
1. Ground tissue
2. Conjuctive tissue
3. Cambium
4. Pith
Companion cells are closely associated with:
1. | Sieve elements | 2. | Vessel elements |
3. | Trichomes | 4. | Guard cells |
Lenticels are involved in:
1. | Gaseous exchange | 2. | Food transfer |
3. | Photosynthesis | 4. | Transpiration |
Vascular bundles in monocotyledons are considered closed because:
1. | a bundle sheath surrounds each bundle |
2. | cambium is absent |
3. | there are no vessels with perforations |
4. | xylem is surrounded all around by phloem |