CBSE Class 12 Biology Syllabus

What is the function of the placenta? Name two hormones it produces.

The placenta facilitates exchange of nutrients, gases, and wastes between mother and fetus; it produces hormones such as hCG, hPL, estrogen, and progesterone.

What hormone is the basis of pregnancy detection tests and where is it produced?

Human chorionic gonadotropin (hCG), produced by the placenta (trophoblast), is detected in urine for pregnancy tests.

What is parturition and which hormone triggers it?

Parturition is the process of childbirth; it is triggered by oxytocin (from the maternal pituitary), which causes uterine contractions, along with a neuroendocrine reflex.

What is lactation and which hormone stimulates milk production?

Lactation is milk production by the mammary glands after childbirth; prolactin stimulates milk synthesis. The first milk (colostrum) is rich in antibodies.

What does the abbreviation ART stand for, and give two examples of ART techniques.

ART stands for Assisted Reproductive Technologies. Examples include IVF (in vitro fertilisation), ZIFT, GIFT, ICSI, and IUI.

Differentiate ZIFT from GIFT.

ZIFT (Zygote Intra Fallopian Transfer): a zygote/early embryo (up to 8 blastomeres) is transferred into the fallopian tube. GIFT (Gamete Intra Fallopian Transfer): an ovum collected from a donor is transferred into the fallopian tube of a recipient.

What is the difference between a barrier method and an IUD as contraceptives? Give an example of each.

Barrier methods physically prevent sperm-egg meeting (e.g., condoms, diaphragms). IUDs are intra-uterine devices placed in the uterus that prevent fertilisation/implantation (e.g., Copper-T, LNG-20).

Name a common surgical (sterilization) contraceptive method for males and females.

Vasectomy for males (cutting/tying vas deferens) and tubectomy for females (cutting/tying fallopian tubes).

Name three sexually transmitted infections (STIs).

Examples include gonorrhoea, syphilis, chlamydiasis, genital herpes, hepatitis-B, and HIV/AIDS.

What is amniocentesis and why is it sometimes misused?

Amniocentesis is a prenatal test analyzing amniotic fluid to detect genetic/chromosomal disorders; it is misused for illegal sex determination and female foeticide, hence legally banned for sex determination.

State Mendel's Law of Segregation.

The two alleles of a gene separate (segregate) during gamete formation so that each gamete receives only one allele of each pair.

State Mendel's Law of Independent Assortment.

During gamete formation, the alleles of different genes assort independently of one another (applies to genes on different chromosomes).

What is the phenotypic ratio of a typical monohybrid cross and a dihybrid cross in the F2 generation?

Monohybrid F2 ratio is 3:1; dihybrid F2 ratio is 9:3:3:1.

What is incomplete dominance? Give an example.

Incomplete dominance is when the heterozygote shows an intermediate phenotype between the two homozygotes, e.g., pink flowers in Snapdragon (Antirrhinum) from red x white cross.

What is co-dominance? Give an example.

Co-dominance is when both alleles express themselves fully in the heterozygote, e.g., the AB blood group, where both A and B antigens are expressed.

How many alleles control the ABO blood group, and which is recessive?

Three alleles (I^A, I^B, and i); the i allele is recessive. I^A and I^B are co-dominant and both dominant over i.

What is pleiotropy? Give an example.

Pleiotropy is when a single gene affects multiple phenotypic traits, e.g., phenylketonuria or sickle-cell anaemia affecting several characteristics.

Why are red-green colour blindness and haemophilia called sex-linked (X-linked) recessive disorders?

Their genes are located on the X chromosome and are recessive, so they appear more frequently in males (XY) who have only one X chromosome.

What is the chromosomal basis of Down's syndrome?

Down's syndrome (trisomy 21) is caused by an extra copy of chromosome 21 (47 chromosomes total) due to non-disjunction.

Give the karyotypes for Klinefelter's syndrome and Turner's syndrome.

Klinefelter's syndrome: 47, XXY (male). Turner's syndrome: 45, X0 (female, missing one X).

What is the molecular cause of sickle-cell anaemia?

A point mutation substituting glutamic acid with valine at the 6th position of the beta-globin chain of haemoglobin, due to GAG to GUG codon change. It is autosomal recessive.

State Chargaff's rule for DNA base composition.

In a DNA molecule, the amount of adenine equals thymine (A=T) and guanine equals cytosine (G=C); thus purines equal pyrimidines.

What experiment established that DNA replication is semi-conservative, and in which organism?

The Meselson and Stahl experiment (1958) using E. coli grown in heavy nitrogen (15N) then 14N, demonstrated semi-conservative replication.

Who demonstrated that DNA, not protein, is the genetic material in bacteriophages?

Alfred Hershey and Martha Chase (1952), using radioactively labelled bacteriophages (32P for DNA, 35S for protein).

What are the three main features (salient features) of the genetic code?

The genetic code is triplet (codon of 3 bases), degenerate (more than one codon per amino acid), non-overlapping, comma-less, and nearly universal; it has start (AUG) and stop codons.

Name the start codon and the three stop codons in the genetic code.

Start codon: AUG (also codes for methionine). Stop codons: UAA, UAG, and UGA.

In the lac operon, what role does the inducer (lactose/allolactose) play?

The inducer binds to and inactivates the repressor protein, allowing RNA polymerase to transcribe the structural genes (z, y, a) for lactose metabolism.

What is the main goal of the Human Genome Project (HGP), and approximately how many genes were found?

The HGP aimed to sequence all base pairs in the human genome (about 3 billion bp); it found approximately 20,000-25,000 genes.

What is the difference between transcription and translation?

Transcription is synthesis of RNA from a DNA template (in the nucleus in eukaryotes). Translation is synthesis of a polypeptide (protein) from mRNA on ribosomes.

What did the Miller-Urey experiment demonstrate about the origin of life?

It demonstrated chemical (abiogenic) origin of life: passing electric sparks through a mixture of CH4, NH3, H2, and water vapour produced amino acids, supporting Oparin-Haldane's theory.

Differentiate homologous organs from analogous organs, with one example each.

Homologous organs have similar structure/origin but different functions (e.g., forelimbs of mammals) showing divergent evolution. Analogous organs have similar function but different structure/origin (e.g., wings of birds and insects) showing convergent evolution.

What is the Hardy-Weinberg principle, and what equation describes allele frequencies?

It states that allele and genotype frequencies in a population remain constant across generations in the absence of evolutionary influences. Equation: p^2 + 2pq + q^2 = 1, where p + q = 1.

Name the five factors that can disturb Hardy-Weinberg equilibrium (cause evolution).

Gene migration (gene flow), genetic drift, mutation, genetic recombination, and natural selection.

What does the example of industrial melanism in the peppered moth (Biston betularia) illustrate?

It illustrates natural selection: dark moths increased in industrial (soot-covered) areas because they were better camouflaged from predators, demonstrating adaptation to environment.

Differentiate innate (non-specific) immunity from acquired (specific) immunity.

Innate immunity is present from birth, non-specific (e.g., skin, phagocytes, inflammation). Acquired immunity is pathogen-specific, develops after exposure, and has memory (e.g., antibody-mediated and cell-mediated responses).

Differentiate active immunity from passive immunity.

Active immunity: the body produces its own antibodies after exposure to antigen/vaccine (slow, long-lasting). Passive immunity: ready-made antibodies are given directly (e.g., mother's milk, antiserum) (fast, short-lived).

Name the causative organism and a key feature for malaria.

Malaria is caused by Plasmodium (e.g., P. vivax, P. falciparum), transmitted by female Anopheles mosquito; it causes recurring chills and high fever due to release of haemozoin.

Which cells does HIV primarily attack, and what disease results?

HIV attacks helper T-lymphocytes (CD4+ T cells), leading to AIDS (Acquired Immuno Deficiency Syndrome) by weakening the immune system.

What is the difference between a benign tumour and a malignant tumour?

Benign tumours remain confined to their site and do not spread. Malignant tumours grow rapidly, invade surrounding tissues, and spread to distant sites via metastasis.

Define inbreeding and inbreeding depression in animal husbandry.

Inbreeding is mating between closely related individuals of the same breed for 4-6 generations. Inbreeding depression is the reduced fertility and productivity resulting from continued inbreeding.

What is heterosis (hybrid vigour)?

Heterosis is the superiority of crossbred/hybrid offspring over their parents in qualities like growth, yield, and disease resistance, achieved through outbreeding.

What is the difference between somatic hybridisation and micropropagation in plant breeding?

Somatic hybridisation is fusion of protoplasts of two different plants to form a hybrid (somatic hybrid). Micropropagation is producing many plants through tissue culture, yielding genetically identical somaclones.

What is single cell protein (SCP)? Give an example organism.

SCP is protein obtained from microbial biomass used as food/feed supplement, e.g., from Spirulina, mushrooms, or yeast (Saccharomyces).

What is biofortification?

Biofortification is breeding crops with higher levels of vitamins, minerals, proteins, or healthier fats to improve public nutritional quality (e.g., vitamin-A enriched carrots/spinach).

Which microorganism is used to make curd from milk, and what does it produce?

Lactic Acid Bacteria (LAB), e.g., Lactobacillus, convert milk to curd by producing lactic acid, which coagulates and partially digests milk proteins.

Which microorganism is used in baking bread and brewing, and what is it called?

Saccharomyces cerevisiae (brewer's/baker's yeast); it ferments sugars producing CO2 (for bread rising) and ethanol (in brewing).

Name the organisms that produce the antibiotic penicillin and the drug cyclosporin A.

Penicillin is produced by the fungus Penicillium notatum (discovered by Alexander Fleming). Cyclosporin A (an immunosuppressant) is produced by the fungus Trichoderma polysporum.

What are biogas, its main constituent, and the microbes involved?

Biogas is a mixture of gases (mainly methane) produced by microbial activity (methanogens, e.g., Methanobacterium) on organic waste/sewage; it is used as fuel.

Name two microbes used as biofertilizers and the nutrient they provide.

Rhizobium (symbiotic) and Azotobacter/Azospirillum (free-living) fix atmospheric nitrogen; mycorrhiza (Glomus) helps absorb phosphorus.

What is a biocontrol agent? Give one example used against insect pests.

A biocontrol agent is a biological organism used to control pests/pathogens. Example: Bacillus thuringiensis (Bt) used against butterfly caterpillars; ladybird beetles against aphids.