SRMJEEE Biology (Botany) Syllabus

What is the special type of fertilisation found only in angiosperms and what does it produce?

Double fertilisation: one male gamete fuses with the egg (syngamy) to form the diploid zygote, and the other fuses with two polar nuclei (triple fusion) to form the triploid (3n) primary endosperm nucleus.

Give the key differences between monocots and dicots (seed, venation, vascular bundles, floral parts).

Monocots: one cotyledon, parallel venation, scattered closed vascular bundles, trimerous (multiples of 3) flowers, fibrous roots. Dicots: two cotyledons, reticulate venation, ring of open vascular bundles, tetra/pentamerous flowers, tap root.

Name the three types of root systems and which plants show them.

Tap root system (one main root with branches, in dicots), fibrous root system (cluster of fine roots, in monocots), and adventitious root system (roots arising from parts other than the radicle, e.g. grass, Monstera).

What are the regions of a typical root from tip upward?

Root cap, region of meristematic activity, region of elongation, and region of maturation (bearing root hairs).

Give examples of storage root modifications and the plants showing them.

Tap root storage: carrot (conical), turnip (napiform), radish (fusiform). Adventitious storage root: sweet potato (tuberous).

What are the modifications of stem for storage, and give examples?

Underground stem modifications for storage/perennation: tuber (potato), rhizome (ginger), bulb (onion) and corm (Colocasia/Crocus).

Identify the stem modifications seen in (a) Opuntia, (b) grapevine, (c) Citrus.

(a) Opuntia — phylloclade (flattened green photosynthetic stem). (b) Grapevine — stem tendril for climbing. (c) Citrus/Bougainvillea — stem (axillary) thorn for protection.

Name three types of leaf modifications with an example of each.

Tendrils for climbing (pea), spines for protection/reducing transpiration (cactus, Opuntia), and storage fleshy leaves (onion bulb scales); pitcher (Nepenthes) for insectivory.

Define phyllotaxy and name its three types.

Phyllotaxy is the pattern of arrangement of leaves on the stem: alternate (one leaf per node, e.g. China rose), opposite (two leaves per node, e.g. guava), and whorled (more than two per node, e.g. Alstonia).

What is an inflorescence and what are its two main types?

An inflorescence is the arrangement of flowers on the floral axis. Two main types: racemose (main axis keeps growing, flowers borne laterally in acropetal order) and cymose (main axis ends in a flower, flowers in basipetal order).

Distinguish acropetal and basipetal succession in inflorescences.

Acropetal succession (racemose): older/mature flowers at the base and younger ones toward the apex. Basipetal succession (cymose): older flowers at the apex and younger ones toward the base.

Name the four whorls of a typical flower from outside inward.

Calyx (sepals), Corolla (petals), Androecium (stamens — male), and Gynoecium/Pistil (carpels — female).

Define actinomorphic and zygomorphic flowers with examples.

Actinomorphic = radially symmetrical, can be divided into equal halves by any vertical plane (e.g. mustard, Datura). Zygomorphic = bilaterally symmetrical, divided into equal halves by only one vertical plane (e.g. pea, Cassia).

Define aestivation and name its four common types.

Aestivation is the arrangement of sepals or petals in a floral bud with respect to other members of the same whorl: valvate, twisted (contorted), imbricate, and vexillary (papilionaceous).

What is placentation? Name its main types.

Placentation is the arrangement of ovules within the ovary: marginal (pea), axile (China rose, tomato), parietal (mustard), free central (Dianthus) and basal (sunflower).

Define a tissue and distinguish meristematic from permanent tissue.

A tissue is a group of cells with common origin and function. Meristematic tissue consists of actively dividing cells (apical, intercalary, lateral); permanent tissue is formed from meristem, the cells having lost the ability to divide (simple and complex).

Name the three simple permanent tissues and the distinguishing feature of each.

Parenchyma (thin-walled living cells, storage/photosynthesis), collenchyma (living cells with cellulose thickening at corners, mechanical support in young stems), and sclerenchyma (dead, thick lignified walls — fibres and sclereids, providing rigidity).

What are the two complex tissues and their components?

Xylem (tracheids, vessels, xylem fibres, xylem parenchyma) for water/mineral conduction; Phloem (sieve tube elements, companion cells, phloem fibres, phloem parenchyma) for food translocation.

Name the three tissue systems described by Sachs.

Epidermal tissue system (epidermis, stomata, trichomes), ground (fundamental) tissue system (cortex, pericycle, pith, mesophyll), and vascular tissue system (xylem and phloem).

Differentiate open and closed vascular bundles.

Open vascular bundles have cambium between xylem and phloem and are capable of secondary growth (dicot stems). Closed vascular bundles lack cambium and cannot undergo secondary growth (monocot stems).

What is secondary growth and which meristems bring it about?

Secondary growth is the increase in girth (thickness) of stems and roots due to the activity of two lateral meristems: the vascular cambium (produces secondary xylem and phloem) and the cork cambium (phellogen).

What are annual rings (growth rings) and how do they form?

Annual rings are concentric rings of secondary xylem formed by the differing activity of cambium in favourable (wide, light early/spring wood) and unfavourable (narrow, dark late/autumn wood) seasons; counting them estimates a tree's age (dendrochronology).

Distinguish heartwood from sapwood.

Heartwood (duramen) is the central, dark, dead, non-conducting secondary xylem filled with tannins and resins providing mechanical support; sapwood (alburnum) is the peripheral, lighter, living xylem that actively conducts water and minerals.

What is the bark and what are its components?

Bark is all tissue exterior to the vascular cambium — it includes the secondary phloem, cork cambium (phellogen), cork (phellem) and secondary cortex (phelloderm). Lenticels in the cork allow gas exchange.

Define diffusion and state two factors affecting its rate in plants.

Diffusion is the net movement of molecules/ions from a region of higher concentration to lower concentration along a concentration gradient, without expenditure of energy. Rate increases with steeper concentration gradient, higher temperature, and smaller molecule size/pressure.

Define osmosis and the role of the semipermeable membrane.

Osmosis is the net movement of solvent (water) molecules from a region of higher water potential (dilute/pure water) to lower water potential (concentrated solution) across a selectively (semi) permeable membrane.

Write the equation relating water potential, solute potential and pressure potential.

$$\Psi_w = \Psi_s + \Psi_p$$ where $\Psi_w$ is water potential, $\Psi_s$ (or $\Psi_\pi$) is the solute (osmotic) potential, and $\Psi_p$ is the pressure potential.

What is the water potential of pure water at standard temperature and pressure, and what sign does solute potential always carry?

The water potential of pure water at standard conditions is zero ($\Psi_w = 0$). Solute (osmotic) potential is always negative ($\Psi_s < 0$), since adding solute lowers water potential.

Define plasmolysis and the condition under which it occurs.

Plasmolysis is the shrinkage of the protoplast away from the cell wall when a cell is placed in a hypertonic solution (external solution has lower water potential), causing water to exosmose out of the cell.

Define transpiration and name its three types.

Transpiration is the loss of water in the form of vapour from the aerial parts of a plant. Types: stomatal (~90%, through stomata), cuticular (through the cuticle) and lenticular (through lenticels).

According to the cohesion-tension theory, what forces drive the ascent of sap?

Transpiration pull created at the leaf surface, transmitted down a continuous water column held together by cohesion (water-water hydrogen bonding) and adhesion (water-xylem wall attraction); this transpirational pull is the main driving force for the ascent of sap.

What is the role of guard cells in stomatal opening, and what ion is key?

Stomata open when guard cells become turgid: an influx of $\ce{K+}$ ions lowers water potential, water enters by osmosis, and the unevenly thickened guard cells bow outward opening the pore; loss of $\ce{K+}$ and water closes them.

What are the criteria for an element to be called an 'essential element'?

An element is essential if: it is absolutely necessary for normal growth and reproduction, it is directly involved in plant metabolism, its deficiency cannot be met by another element, and its absence prevents the plant from completing its life cycle.

Differentiate macronutrients and micronutrients with examples.

Macronutrients are required in large amounts (>10 mmol/kg dry matter): C, H, O, N, P, K, Ca, Mg, S. Micronutrients (trace elements) are needed in small amounts (<10 mmol/kg): Fe, Mn, Cu, Zn, B, Mo, Cl, Ni.

Why is nitrogen, phosphorus, potassium and magnesium deficiency seen first in older leaves?

Because N, P, K and Mg are highly mobile elements that are readily remobilised from older (senescing) leaves to young growing tissues; thus their deficiency symptoms appear first in mature/older leaves.

Name the element whose deficiency causes chlorosis appearing in young leaves first, and explain why.

Iron (and also calcium, sulphur, boron, copper) deficiency shows in young leaves first because these elements are relatively immobile and cannot be remobilised from older tissues to the growing apices.

What is chlorosis and which nutrient deficiencies cause it?

Chlorosis is the loss/yellowing due to reduced chlorophyll. It results from deficiency of N, K, Mg, S, Fe, Mn, Zn and Mo (Mg and Fe are central to chlorophyll synthesis).

What is biological nitrogen fixation and which enzyme catalyses it?

Biological nitrogen fixation is the reduction of atmospheric dinitrogen to ammonia by living organisms, catalysed by the enzyme nitrogenase: $$\ce{N2 + 8H+ + 8e- + 16ATP -> 2NH3 + H2 + 16ADP + 16Pi}$$

Write the overall steps of nitrification in the soil.

Nitrification is the oxidation of ammonia to nitrate by soil bacteria: $$\ce{2NH3 + 3O2 -> 2NO2^- + 2H+ + 2H2O}$$ (by Nitrosomonas), then $$\ce{2NO2^- + O2 -> 2NO3^-}$$ (by Nitrobacter).

What is the symbiotic nitrogen-fixing bacterium of leguminous root nodules, and what pigment protects nitrogenase from oxygen?

Rhizobium forms a symbiosis with legume roots, inducing root nodules. The pink pigment leghaemoglobin acts as an oxygen scavenger, protecting the oxygen-sensitive nitrogenase enzyme.

What is the role of GS-GOGAT in nitrogen metabolism (fate of ammonia)?

Ammonia produced by fixation/reduction is assimilated into amino acids: glutamine synthetase (GS) combines ammonia with glutamate to form glutamine, and glutamate synthase (GOGAT) transfers the amide group to 2-oxoglutarate forming two glutamates; amino acids are then made by transamination.