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:

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:

Closed vascular bundles lack:

1. Ground tissue

2. Conjuctive tissue

3. Cambium

4. Pith

Companion cells are closely associated with:

Lenticels are involved in:

Vascular bundles in monocotyledons are considered closed because: