CBSE Class 12 Biology Notes: Important Chapters

CBSE Class 12 Biology Notes 2025: Having Biology notes handy is the most important step to score good marks in the CBSE Class 12th exam. Having the CBSE Bio notes helps students to have a quick and thorough revision of all the important topics. Furthermore, it helps students to complete studying the syllabus in a very short period of time. As CBSE 12th Biology contains both theory-based and diagram-based questions, it is very important that the students prepare notes for every chapter.

To help students have a quick glance at all the topics of important chapters, we have gathered the notes of the important chapters of CBSE Class 12 Biology. Rather than feeling tense in the last-minute, students can choose to refer to the notes and study from them to score good marks effortlessly. Keep reading to get access to the CBSE Class 12 Biology notes 2024-25.

CBSE Class 12 Biology Notes: Overview

Before going into the details of CBSE Class 12 Biology notes, let us have an overview of the number of chapters in CBSE Class 12 Biology 2025:

CBSE Class 12 Biology Notes

Below-mentioned are the notes provided for the important chapters of CBSE Class 12 Biology. Going through them helps students to acquire knowledge required to master the exams and score good marks in the CBSE class 12th exam.

To make studying easier and effortless, students can go through the chapter-wise notes mentioned below in the article.

Chapter 1: Reproduction in Organisms

Reproduction can be defined as the biological process of formation of a new organism from an already-existing organism. There are two types of reproduction: Sexual and Asexual

• If the offspring is generated by single parents, irrespective of the gamete formation, it is known as asexual reproduction
• If there is an involvement or fusion of both male and female gametes, it is known as sexual reproduction
• Binary Fision is a method of asexual reproduction where a cell divides into two halves and rapidly grows into an adult. Example: Amoeba, Paramecium.
• Budding is also one of the methods of asexual reproduction where small buds are produced that remain attached initially with parents and get separated on maturation. Example: Yeast
• Diffferent phases of sexual reproduction involve juvenile phase and reproductive phase
• Diffrerent events of sexual reproduction involve pre-fertilisation, fertilisation and post-fertilisation

Chapter 2: Sexual Reproduction in Flowering Plants

• Flower is a modified stem that works as a reproductive organ and produces ova and/or pollen. An angiosperm flower contains four whorls of floral appendages attached on the receptacle namely calyx, corolla, androecium (male reproductive organ consisting of stamens) and gynoecium (composed of ovary, style and stigma)
• Various changes such as structural and hormonal changes lead to formation and development of the floral primordium. Inflorescence is formed that bears floral buds and then flower
• In the flowers, androecium and gynoecium are developed from which male and female gametes are produced
• Pollen grain represents the male gametophytes and it has two layered walls: Exine which is made of sporopollenin, intine which is a thin and continuous layer, germ pores and a plasma membrane.

Chapter 3: Human Reproduction

• Humans are sexually reproducing and viviparous. 
• Reproductive events in humans include formation of gametes (gametogenesis), i.e., sperms in males and ovum in females, transfer of sperms into the female genital tract (insemination) and fusion of male and female gametes (fertilization) leading to formation of zygote. 
• This is followed by formation and development of blastocyst and its attachment to the uterine wall (implantation), embryonic development (gestation) and delivery of the baby (parturition)
• The Male Reproductive System consists of primary sex organs which is a pair of testes, secondary sex organs which is a pair of ducts and external genitalia
• The Female Reproductive System consists of primary sex organs which is a pair of ovaries, secondary sex organs which is the duct system containing pair of fallopian tubule, uterus, cervix and vagina, external genitalia and mammary glands
• The process of formation of male and female gametes in testes and ovary respectively is called Gametogenesis

Chapter 4: Reproductive Health

• Reproductive health in a society is one of the most crucial parts of general health
• Health and education of young people and marriage and child bearing during more mature stages of life are significant attributes to the reproductive health of a society
• Amniocentesis is a technique that is used to find out chromosomal abnormalities in embryo development with the help of amniotic fluid
• Decline in death rate, MMR (maternal mortality rate) and IMR (infant mortality rate) and increase in population of reproductive age is the major reason for population explosion
• Measures for population control include contraceptive methods, educating people, Increasing the marriageable age of female and male and delivering incentives to the parents bearing 1 or 2 children
• Sexually Transmitted Disease (STDs): Gonorrhea, syphilis, genital herpes, chlamydiasis, genital warts, trichomoniasis, hepatitis-Ba and AIDS are some of the common STDs

Chapter 5: Principles of Inheritance and Variation

• Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity
• Variation is the degree by which progeny differ from their parents. Variation may be in terms of morphology, physiology, cytology and behavioristic traits of individuals belonging to the same species.
• Variation is caused due to reshuffling of genes/chromosomes, crossing over or recombination and mutation and effect of environment
• Selection of pea plant: Mendel conducted artificial hybridization/cross pollination using true breeding pea lines. True breeding lines are those that undergo continuous self-pollination and show stable trait inheritance.
• Hybridization includes emasculation (removal of anther) and transfer of pollen (pollination).
• Test cross is the cross between an individual with dominant trait and a recessive organism to find out whether the dominant trait is homozygous or heterozygous.
• Incomplete dominance is the phenomenon of neither of the two alleles being dominant so that expression in the hybrid is a fine mixture or intermediate between the expressions of two alleles.
• It is the phenomenon of two alleles lacking dominance-recessive relationship and both expressing themselves in the organism.

Students can download the CBSE Class 12 Biology syllabus here. To get good marks in exam students should also solve CBSE Class 12 Sample Papers.

FAQs on CBSE Class 12 Biology Notes

Below-mentioned are some of the frequently asked questions related to Class 12 Bio notes.

Q.1: What are the types of reproduction?
Ans: There are two types of reproduction – Sexual and Asexual. Asexual reproduction is when the offspring is produced by single parents with or without the involvement of gamete formation

Q.2: What is Inheritance and Variation?
Ans: Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity. Variation is the degree by which progeny differ from their parents. Variation may be in terms of morphology, physiology, cytology and behavioristic traits of individuals belonging to the same species.

Q.3: Name some Sexually Transmitted Disease (STDs)
Ans: Gonorrhea, syphilis, genital herpes, chlamydiasis, genital warts, trichomoniasis, hepatitis-Ba and AIDS are some of the common STDs

Q.4: What is Gametogenesis?
Ans: The process of formation of male and female gametes in testes and ovary respectively is called Gametogenesis

Q.5: What is a test cross?
Ans: Test cross is the cross between an individual with a dominant trait and a recessive.

Students should try to attempt CBSE Class 12 previous year question papers after completing CBSE Class 12 Biology Notes.

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