(i) Mineral deficiency of plant A is due to Molybdenum
(ii) Mineral deficiency of plant B is due to Zinc

(i) Yes. Nitrogen cannot be directly absorbed by plants but they are essential for normal growth and functioning of a plant. Hence they are fixed by bacteria and some fungi.
(ii) It can be utilised only in the form of nitrates (NO₃^-) and nitrites (NO₂^-).

(1) Water potential \(\left(\Psi_{\mathrm{W}}\right)\) can be determined by,
(i) Solute concentration or Solute Potential \(\left(\Psi_{\mathrm{S}}\right)\)
(ii) Pressure potential \(\left(\Psi_{\mathrm{P}}\right)\)
(2) By correlating two factors, water potential is written as,
(3) Water potential = Solute potential + Pressure potential
(4) \(\Psi_{W}=\Psi_{S}+\Psi_{P}\)

In the spring season, because cambium is very active and produces a large number of xylary elements having vessels / tracheids with wide lumen.

(i) If the bark of a tree is damaged by the horn of a deer, the tree first seals the damaged region from microbial infection.
(ii) This happens by altering the chemistry of the affected area by forming a callus, which grows and covers the damaged area.

The cells of sclerenchyma & tracheids become dead because they lack protoplasm

(i) Lateral meristem increases the girth in both stem and root
(ii) Secondary growth in dicots and gymnosperms is brought about by two lateral meristems
(iii) Vascular cambium
(iv) Cork Cambium
(v) Vascular cambium produces the secondary vascular tissues. i.e. Secondary xylem and Secondary phloem.

(i) Sieve tubes are long tube like conducting elements in the phloem.
(ii) These are formed from a series of cells called sieve tube elements.
(iii) The sieve tube elements are arranged one above the other and form vertical sieve tube.
(iv) The end wall contains a number of pores and it looks like a sieve hence called as sieve plate.
(v) These elements show nacreous thickenings on their lateral walls with simple or compound sieve plates.
(vi) The function of sieve tubes are believed to be controlled by companion cells.
(vii) In mature sieve tube, Nucleus is absent and it contains a lining layer of cytoplasm with special protein called slime body in it.
(viii) In mature sieve tubes, the pores in the sieve plate are blocked by a substance called callose.
(ix) The conduction of food material takes place through cytoplasmic strands.
(x) Sieve tubes occur only in Angiosperms.

Sclereids (Stone Cells)
Sclereids are dead cells, usually these are isodiametric but some are elongated too. The cell wall is very thick due to lignification. Lumen is very much reduced. The pits may simple or branched. Sclereids are mechanical in function. They give hard texture to the seed coats, endosperms etc., Sclereids are classified into the folowing types.
Types of Sclereids
(a) Brachysclereids or Stone cells:
Isodiametric sclereids, with hard cell wall. It is found in bark, pith cortex, hard endosperm and fleshy portion of some fruits. Example: Pulp of Pyrus.

(b) Macrosclereids:
Elongated and rod shaped cells, found in the outer seed coat of leguminous plants. Example: Crotalaria and Pisum sativum.

(c) Osteosclereids (Bone cells):
Rod shaped with dilated ends. They occur in leaves and seed coats. Example: seed coat of Pisum and Hakea

(d) Astrosclereids:
Star cells with lobes or arms diverging form a central body. They occur in petioles and leaves. Ex: Tea, Nymphae and Trochodendron.

(e) Trichosclereids:
Hair like thin walled sclereids. Numerous small angular crystals are embedded in the wall of these sclereids, present in stems and leaves of hydrophytes. Example: Nymphaea leaf and Aerial roots of Monstera.

(i) Nitrogen fixation process requires Nitrogenase enzyme complex, Minerals (Mo, Fe and S), anaerobic condition, ATP, electron and glucose 6 phosphate as H⁺ donor.
(ii) Nitrogenase enzyme is active only in anaerobic condition.
(iii) To create this anaerobic condition a pigment known as leghaemoglobin is synthesized in the nodules which acts as oxygen scavenger and removes the oxygen.

1. The discovery of enzyme phosphorylase in guard cells by Hanes (1940) greatly supports the starch-sugar interconversion theory.
2. The enzyme phosphorylase hydrolyses starch into sugar and high pH followed by endosmosis and the opening of stomata during light. The vice versa takes place during the night.

High concentration of salt in the soil leads to high osmotic potential, which may a result in wilting of plants due to following reasons.
(a) This may be due to osmotic withdrawal of water from a cell or system when it is placed in a hypertonic solution called Exosmosis.
(b) Exosmosis in a plant cell leads to plasmolysis. As a result of water loss in the cell protoplasm shrinks and the cell membrane is pulled away from the cell wall and finally the cell becomes flaccid.

(i) The log A will last longer for the merchant.
(ii) In any tree the outer part of the wood is pale in colour, is called Sap Wood, while the centre part is darker called Heart Wood.
(iii) Due to the presence of tyloses and their contents, the heartwood becomes coloured, dead and the hardest part of the wood.
(iv) The heartwood is more durable and more resistant to the attack of microorganisms and insects.