MHT CET Biology (Botany) Syllabus

Define plasticity in plant growth with an example.

Plasticity is the ability of plants to follow different growth pathways in response to environment or life phases. Example: heterophylly in cotton/buttercup where leaves differ in juvenile vs adult/aquatic vs terrestrial conditions.

Which plant hormone promotes cell elongation and apical dominance, and who discovered it?

Auxin (IAA) promotes cell elongation and apical dominance. It was discovered through studies by Charles Darwin and F.W. Went (who isolated it from coleoptile tips of oats).

Name the plant hormone responsible for breaking seed/bud dormancy, bolting, and internode elongation.

Gibberellin (GA3). It causes bolting (internode elongation in rosette plants), breaks dormancy, promotes seed germination, and increases fruit length.

Which hormone is called the 'stress hormone' and promotes stomatal closure?

Abscisic acid (ABA). It induces seed dormancy, promotes stomatal closure during water stress, and acts as a general growth inhibitor (antagonist to GA).

What is the role of ethylene in plants?

Ethylene is a gaseous hormone that promotes fruit ripening, senescence, abscission of leaves/flowers/fruits, breaks dormancy, and induces flowering in mango/pineapple. Source: ripening fruits, senescing tissues.

Define photoperiodism and name the three categories of plants based on it.

Photoperiodism is the response of plants to the relative length of day and night for flowering. Categories: short-day plants, long-day plants, and day-neutral plants.

Define vernalization.

Vernalization is the promotion of flowering by exposure to low temperature (cold treatment). It prevents premature flowering and helps plants adjust to environmental conditions (e.g., winter wheat).

What is the structure and ploidy of the typical mature angiosperm female gametophyte (embryo sac)?

Typically 7-celled, 8-nucleate: one egg cell + two synergids (egg apparatus) at micropylar end, three antipodals at chalazal end, and one central cell with two polar nuclei. All cells are haploid (n) except the diploid central cell after fusion.

Describe the process of double fertilization in angiosperms.

One male gamete fuses with the egg cell (syngamy) -> diploid zygote (2n). The second male gamete fuses with the two polar nuclei (triple fusion) -> triploid primary endosperm nucleus (3n). Both fusions = double fertilization.

What is the ploidy of the zygote, endosperm, and nucellus in an angiosperm seed?

Zygote: diploid (2n). Endosperm: triploid (3n). Nucellus: diploid (2n).

Define pollination and distinguish autogamy, geitonogamy, and xenogamy.

Pollination is transfer of pollen to stigma. Autogamy: pollen to stigma of same flower. Geitonogamy: pollen to another flower of the same plant (genetically autogamy). Xenogamy: pollen to a flower of a different plant (cross-pollination).

What is apomixis and what is polyembryony?

Apomixis is the formation of seeds without fertilization (asexual reproduction mimicking sexual). Polyembryony is the occurrence of more than one embryo in a single seed (e.g., citrus, mango).

Name the parts of the male gametophyte (pollen grain) and the typical cells of a mature pollen grain.

A mature pollen grain is 2-celled: a large vegetative (tube) cell and a small generative cell. In some plants it is 3-celled when shed (generative cell divides into two male gametes). Wall: outer exine (sporopollenin), inner intine.

State Mendel's Law of Segregation.

Law of Segregation: the two alleles of a gene separate (segregate) during gamete formation so that each gamete carries only one allele of each gene; alleles unite randomly at fertilization.

State Mendel's Law of Independent Assortment.

During gamete formation, the segregation of alleles of one gene is independent of the segregation of alleles of another gene (applies to genes on different chromosomes). Gives 9:3:3:1 dihybrid ratio.

What phenotypic and genotypic ratios result from a monohybrid cross (F2 generation)?

Phenotypic ratio: 3:1 (dominant:recessive). Genotypic ratio: 1:2:1 (homozygous dominant : heterozygous : homozygous recessive).

Define incomplete dominance and codominance with an example each.

Incomplete dominance: heterozygote shows an intermediate phenotype (e.g., pink flowers in Snapdragon/Mirabilis, F2 ratio 1:2:1). Codominance: both alleles express fully in heterozygote (e.g., AB blood group, MN blood group).

What is pleiotropy? Give an example.

Pleiotropy is a single gene affecting multiple phenotypic traits. Example: phenylketonuria (one gene mutation causes mental retardation, reduced hair/skin pigmentation), or starch synthesis affecting seed shape and starch grain size in pea.

What is the chromosomal basis of sex determination in humans (XX-XY) and in birds (ZZ-ZW)?

Humans: females XX (homogametic), males XY (heterogametic). Birds: males ZZ (homogametic), females ZW (heterogametic).

What experiments established DNA as the genetic material?

Griffith's transformation experiment (1928) showed a 'transforming principle'; Avery, MacLeod & McCarty identified it as DNA; Hershey-Chase experiment (1952) using radioactive 32P (DNA) and 35S (protein) on bacteriophages confirmed DNA is the genetic material.

State the salient features of the Watson-Crick DNA double helix model.

Two antiparallel polynucleotide strands coiled in a right-handed helix; sugar-phosphate backbone outside, bases inside; A=T (2 H-bonds), G≡C (3 H-bonds); pitch 3.4 nm with 10 bp/turn; distance between adjacent base pairs 0.34 nm.

State Chargaff's rule.

In double-stranded DNA, the amount of adenine equals thymine (A = T) and guanine equals cytosine (G = C). Therefore purines (A+G) = pyrimidines (T+C), and A+G = T+C.

What is semiconservative DNA replication and who demonstrated it?

Each new DNA molecule has one old (parental) strand and one newly synthesized strand. Demonstrated by Meselson and Stahl (1958) using 15N labeling in E. coli.

Define the central dogma of molecular biology.

The flow of genetic information: DNA -> (transcription) -> RNA -> (translation) -> Protein. Proposed by Francis Crick. Reverse transcription (RNA -> DNA) is an exception seen in retroviruses.

What are the key features of the genetic code?

It is a triplet code (codons), degenerate (multiple codons per amino acid), unambiguous, universal, non-overlapping, and commaless. AUG is the start codon (methionine); UAA, UAG, UGA are stop codons.

Describe the lac operon and its components.

The lac operon (Jacob & Monod) has a regulatory gene (i), promoter (p), operator (o), and three structural genes z, y, a (β-galactosidase, permease, transacetylase). Lactose acts as inducer; in its absence the repressor binds the operator and switches off transcription.

List the key steps/tools of recombinant DNA technology.

Steps: (1) isolation of DNA, (2) cutting with restriction enzymes, (3) ligation into a vector (plasmid), (4) transformation into host, (5) selection and culturing of transformants. Tools: restriction enzymes, DNA ligase, vectors, host cells.

What are restriction enzymes and what are sticky ends?

Restriction endonucleases are 'molecular scissors' that cut DNA at specific palindromic recognition sequences. When they cut in a staggered manner they leave single-stranded overhangs called sticky (cohesive) ends, which help join DNA fragments.

What is the principle of gel electrophoresis and how do DNA fragments move?

DNA fragments are separated based on size by applying an electric field across an agarose gel. Being negatively charged, DNA moves toward the anode (+); smaller fragments move faster/farther. Bands are visualized using ethidium bromide under UV light.

Define the niche concept and Gause's competitive exclusion principle.

An ecological niche is the functional role and position of a species in its environment. Gause's competitive exclusion principle states that two species competing for the same limiting resources cannot coexist indefinitely; the inferior competitor is eliminated.

Write the logistic (Verhulst-Pearl) population growth equation and define carrying capacity (K).

dN/dt = rN[(K-N)/K], where N = population size, r = intrinsic growth rate, K = carrying capacity (the maximum population the environment can sustain). It produces a sigmoid (S-shaped) curve.

Define an ecosystem and distinguish a food chain from a food web.

An ecosystem is a self-sustaining unit of living organisms (biotic) interacting with their non-living environment (abiotic). A food chain is a single linear sequence of who-eats-whom; a food web is an interconnected network of many food chains.