(i) Senescence is controlled by plants own genetic programme and death of the plant or plant part consequent to senescence is called Programmed Cell Death.
(ii) In short senescence of an individual cell is called PCD.
(iii) The proteolytic enzymes involving PCD in plants are phytaspases and in animals are caspases.
(iv) The nutrients and other substrates from senescing cells and tissues are remobilized and reallocated to other parts of the plant that survives.
(v) The protoplasts of developing xylem vessels and tracheids die and disappear at maturity to make them functionally efficient to conduct water for transport.
(vi) In aquatic plants, aerenchyma is normally formed in different parts of the plant such as roots and stems which encloses large air spaces that are created through PCD.
(vii) In the development of unisexual flowers, male and female flowers are present in earlier stages, but only one of these two completes its development while other aborts through PCD.

Pentose Phosphate pathway:
(i) It was described by Warburg, Dickens and Lipmann. Hence, it is also called Warburg - Dickens - Lipmann pathway.
(ii) It takes place in cytoplasm of mature plant cells.
(iii) It is an alternate way for breakdown of glucose.
(iv) It is also known as Hexose monophosphate shunt (HMP shunt) or Direct oxidative pathway.
(v) It consists of two phases, Oxidative Phase and non oxidative Phase
Oxidative Events:
(vi) 6 molecules of 6 carbon Glucose - 6 phosphate to 6 molecules of 5 carbon sugar Ribulose - 5 phosphate with loss of 6CO₂ molecules and generation of 12 \(\mathrm{NADPH}+\mathrm{H}^{+}\)
Non-Oxidative Pathway:
(i) Convert Ribulose - 5 - phosphate molecules to various intermediates such as ribose 5 - phosphate (5C), Xylulose - 5 - phosphate (5C), Glyceraldehyde - 3 phosphate (3C), sedoheptulose - 7 - phosphate (7C) and Erythrose 4 - phosphate (4C). Finally 5 molecules of glucose - 6 - phosphate is regenerated.
(ii) The net result of complete oxidation of one glucose - 6 - phosphate yield 6CO₂ and 12 NADPH + H⁺.
(iii) The oxidative pentose phosphate pathway is controlled by glucose - 6 - phosphate dehydrogenase enzyme which is inhibited by high ratio of NADPH to NADP⁺.
The over all reaction is:

(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.

S.No.	Characters	Dicot root	Monocot root
1.	Pericyle	Gives rise to lateral roots, phellogen and a part of vascular cambium.	Gives rise to lateral roots only.
2.	Vascular tissue	Usually limited number of xylem and phloem strips.	Usually more number of xylem and phloem strips.
3.	Conjunctive tissue	Parenchymatous; Its cells are differentiated into vascular cambium.	Mostly sclerenchymatous but sometimes parenchymatous. It is never differentiated in to vascular cambium.
4.	Cambium	It appears as a secondary meristem at the time of secondary growth.	It is altogether absent.
5.	Xylem	Usually tetrach	Usually polyarch

The fruits are derived from single pistil where the pericarp is fleshy, succulent and differentiated into epicarp, mesocarp and endocarp. It is subdivided into the following.
(i) Berry: Fruit develops from bicarpellary or multicarpellary, syncarpous ovary. Here the epicarp is thin, the mesocarp and endocarp remain undifferentiated. They form a pulp in which the seeds are embedded. Eg: Tomato, Grapes, Brinjal.

(ii) Drupe: Fruit develops from monocarpellary, superior ovary. It is usually one seeded. Pericarp is differentiated into outer skinny epicarp, fleshy and pulpy mesocarp and hard and stony endocarp around the seed. Eg: Mango, Coconut.

(iii) Pepo: Fruit develops from tricarpellary inferior ovary. Pericarp turns leathery or woody which encloses, fleshy mesocarp and smooth endocarp. Eg: Cucumber, Watermelon, Bottle gourd, Pumpkin.

(iv) Hesperidium:Fruit develops from multicarpellary, multilocular, syncarpous, superior ovary. The fruit wall is differentiated into leathery epicarp with oil glands, a middle fibrous mesocarp. The endocarp forms distinct chambers, containing juicy hairs. Eg: Orange, Lemon.

(v) Pome: It develops from multicarpellary, syncarpous, inferior ovary. The receptacle also develops along with the ovary and becomes fleshy, enclosing the true fruit. In pome the epicarp is thin skin like and endocarp is cartilaginous. Eg: Apple, Pear.

(vi) Balausta: A fleshy indehiscent fruit developing from multicarpellary, multilocular inferior ovary whose pericarp is tough and leathery. Seeds are attached irregularly with testa being the edible portion. Eg: Pomegranate.

Features of DNA:
1. If one strand runs in the 5'- 3' direction, the other runs in 3'- 5' direction and thus are antiparallel (they run in opposite direction). The 5' end has the phosphate group and 3' end has the OH group.
2. The angle at which the two sugars protrude from the base pairs is about 120°, for the narrow angle and 240° for the wide angle. The narrow-angle between the sugars generates a minor groove and the large angle on the other edge generates major groove.
3. Each base is 0.34 nm apart and a complete turn of the helix comprises 3.4 nm or 10 base pairs per turn in the predominant B form of DNA.
4. DNA helical structure has a diameter of 20 A° and a pitch of about 34 A°. X-ray crystal study of DNA takes a stack of about 10 bp to go completely around the helix (360°).
5. Thermodynamic stability of the helix and specificity of base pairing includes
(i) the hydrogen bonds between the complementary bases of the double helix
(ii) stacking interaction between bases tend to stack about each other perpendicular to the direction of helical axis. Electron cloud interactions ((Π – Π)) between the bases in the helical stacks contribute to the stability of the double helix.
6. The phosphodiester linkages gives an inherent polarity to the DNA helix. They form strong covalent bonds, gives the strength and stability to the polynucleotide chain.
7. Plectonemic coiling - The two strands of the DNA are wrapped around each other in a helix, making it impossible to simply move them apart without breaking the entire structure. Whereas in paranemic coiling the two strands simply lie alongside one another, making them easier to pull apart.
8. Based on the helix and the distance between each turns the DNA is of three forms - A DNA, B DNA and Z DNA.

(i) The symbiotic association between algae and fungi is called lichens.
(ii) The algal partner is called Phycobiont or Photobiont and the fungal partner is called Mycobiont.
(iii) Algae provide nutrition for fungal partner in turn fungi provide protection and also help to fix the thallus to the substratum through rhizinae.
(iv) Asexual reproduction takes place through fragmentation, Soredia and Isidia. Phycobionts reproduce by akinetes, hormogonia, aplanospore, etc., Mycobionts undergo sexual reproduction and produce ascocarps.
Classification:
(i) Based on the habitat lichens are classified into following types: Corticolous (on Bark) Lignicolous (on Wood) Saxicolous (on rocks) Terricolous (on ground) Marine (on siliceous rocks of sea) Fresh water(on siliceous rock of fresh water).
(ii) On the basis of morphology of the thallus they are divided into Leprose (a distinct fungal layer is absent) Crustose-crust like; Foliose-leaf like; Fruticose-branched pendulous shrub like.
(iii) The distribution of algal cells distinguishes lichens into two forms namely Homoiomerous (Algal cells evenly distributed in the thallus) and Heteromerous (a distinct layer of algae and fungi present)
(iv) If the fungal partner of lichen belongs to ascomycetes, it is called Ascolichen and if it is basidiomycetes it is called Basidiolichen.

Factors affecting the rate of enzyme reactions: Enzymes are sensitive to environmental conditions. It could be affected by temperature, pH, substrate concentration and enzyme concentration. The rate of enzyme reaction is measured by the amount of substrate changed or amount of product formed, during a period of time.
1. Temperature: Heating increases molecular motion. Thus the molecules of the substrate and enzyme move more quickly resulting in a greater probability of a reaction occurring. The temperature that promotes maximum activity is referred to as optimum temperature.

2. pH: The optimum pH is that at which the maximum rate of reaction occurs. Thus the pH change leads to an alteration of enzyme shape, including the active site. If extremes of pH are encountered by an enzyme, then it will be denatured.

3. Substrate concentration: For a given enzyme concentration, the rate of an enzyme reaction increases with increasing substrate concentration.

4. Enzyme concentration: The rate of reaction is directly proportional to the enzyme concentration.
5. Michaelis-Menten Concept: When the initial rate of reaction of an enzyme is measured over a range of substrate concentrations (with a fixed amount of enzyme) and the results plotted on a graph. With increasing substrate concentration, the velocity increases - rapidly at lower substrate concentration.
6. Inhibitors of Enzyme: Certain substances present in the cells may react with the enzyme and lower the rate of reaction. These substances are called inhibitors. It is of two types competitive and non-competitive.

Habit : Twining climber
Root : Branched tap root system having nodules.
Stem : Aerial, weak stem and a twiner
Leaf : Imparipinnately compound, alternate, stipulate showing reticulate venation. Leaflets are stipellate. Petiolate and stipels are pulvinated.
Inflorescence : Solitary and axillary
Flower : Bracteate, bracteolate, bracteoles usually large, pedicellate, heterochlamydeous, complete, bisexual, pentamerous, zygomorphic and hypogynous.


Calyx : Sepals 5, synsepalous, green showing valvate aestivation. Odd sepal is anterior in position.
Corolla : Petals 5, white or blue apopetalous, irregular papilionaceous corolla showing descendingly imbricate aestivation.
Androecium : Stamens 10, diadelphous (9)+1 nine stamens fused to form a bundle and the tenth stamen is free. Anthers are dithecous, basifixed, introse and dehiscing by longitudinal slits.
Gynoecium : Monocarpellary, unilocular, with many ovules on marginal placentation, ovary superior, style simple and incurved with feathery stigma.
Fruit : Legume
Seed : Non-endospermous, reniform.

S.No Plant cell Animal cell 1.  Usually they are larger than animal cells Usually smaller than plant cells 2. Cell wall present in addition to plasma membrane and consists of middle lamellae, primary and secondary walls Cell wall absent. 3.  Plasmodesmata present.  Plasmodesmata absent. 4.  Chloroplast present. Chloroplast absent. 5.  Vacuole large and Permanent. Vacuole small and temporary. 6.  Tonoplast present around vacuole.  Tonoplast absent 7.  Centrioles absent except motile cells of lower plants.  Centrioles present 8.  Nucleus present along the periphery of the cell  Nucleus at the centre of the cell 9.  Lysosomes are rare  Lysosomes present. 10.  Storage material is starch grains.  Storage material is a glycogen granules.

S.No Cytokinesis in plant cell Cytokinesis in animal cell 1 Cleavage cytokinesis occurs only in lower plants, higher plant cells show cell plate cytokinesis It occurs through cleavage 2 The middle part of spindle persists during cytokinesis. It forms a complex called phragmoplast Spindle degenerates during cytokinesis 3 A mid body is absent A mid body develops centrally 4 A row of vesicles develops in the equatorial plane in plant cell cytokinesis A row of vesicles does not form in animal cell cytokinesis 5 Vesicles fuse to form cell plate Cell plate is not formed 6 There is little role of microfilaments in plant cell cytokinesis Microfilaments actively involved in animal cell cytokinesis 7 It starts with the formation of cell plate during telophase It starts as a constriction in cell membrane during late anaphase or early telophase 8 The cell plate grows from the centre towards the lateral walls, so centrifugal The furrow depends from periphery towards the centre and meets at the centre so centripetal 9 Wall formation occurs in the region of cytokinesis Wall formation is absent

(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) \(\Psi_{W}=\Psi_{S}+\Psi_{P}\)

Physiological effect:
1) Cytokinin promotes cell division in the presence of auxin (IAA).
2) Induces cell enlargement associated with IAA and gibberellins
3) Cytokinin can break the dormancy of certain light-sensitive seeds like tobacco and induces seed germination.
4) Cytokinin promotes the growth of lateral bud in the presence of apical bud.
5) Application of cytokinin delays the process of aging by nutrient mobilization.
6) It is known as Richmond Lang effect.
7) Cytokinin
(i) increases rate protein synthesis
(ii) induces the formation of inter-fascicular cambium
(iii) overcomes apical dominance
(iv) induces formation of new leaves, chloroplast and lateral shoots.
8) Plants accumulate solutes very actively with the help of cytokinins.

Stages	ATP	NADH2	FADH2	Total ATPs
Glycolysis Link reaction Kreb's cycle	2 - 2	2 \(\times\) 2.5 2 \(\times\) 2.5 6 \(\times\) 2.5	0 - 2 \(\times\) 1.5	7 5 20
	4 ATPs	25 ATPs	3 ATPs	32 ATPs

C₄ plants are more advantageous than C₃ plants because increasing the proportion of C₄ plants on earth could assist biosequestration of CO₂ and represent an important cilmate change avoidance strategy.