Complete Biology notes on Reproduction Growth and Heredity for BPSC and Other Competitive Exams in 2025
General Science- 20 (Biology)
Reproduction Growth and Heredity
These three biological processes are fundamental to life, ensuring the continuation of species, the development of organisms, and the transmission of traits across generations.
1. Reproduction
Definition: Reproduction is a fundamental biological process by which new individual organisms (offspring) are produced from their parents. It is essential for the continuation and survival of species, preventing their extinction.
Purpose:
- Perpetuation of Species: Ensures that life continues from one generation to the next.
- Introduction of Variation (in sexual reproduction): Creates genetic diversity, which is crucial for adaptation and evolution.
Types of Reproduction:
A. Asexual Reproduction:
- Definition: A single parent produces offspring that are genetically identical to itself. There is no fusion of gametes.
- Characteristics:
- Involves a single parent.
- Offspring are genetically identical (clones) to the parent.
- Faster process, produces many offspring quickly.
- Common in unicellular organisms, some plants, and lower animals.
- Methods of Asexual Reproduction:
- Fission: Parent organism divides into two or more new organisms.
- Binary Fission: Parent divides into two equal halves. (e.g., Amoeba, Paramecium, Bacteria).
- Multiple Fission: Parent divides into many daughter cells simultaneously. (e.g., Plasmodium – the malarial parasite).
- Budding: A small outgrowth (bud) forms on the parent body, detaches, and develops into a new individual. (e.g., Hydra, Yeast).
- Fragmentation: The body of the parent breaks into fragments, and each fragment develops into a new complete individual. (e.g., Spirogyra, Planaria).
- Spore Formation: Organisms produce spores, which are asexual reproductive units that can develop into new individuals under favorable conditions. (e.g., Fungi like Bread Mould, Ferns).
- Vegetative Propagation (in Plants): New plants are grown from vegetative parts of the parent plant (root, stem, leaves) without seeds.
- Natural Methods: Roots (e.g., sweet potato), Stems (e.g., potato tubers, ginger rhizomes, onion bulbs, grass runners), Leaves (e.g., Bryophyllum).
- Artificial Methods: Cutting (e.g., rose, sugarcane), Layering (e.g., jasmine), Grafting (e.g., mango, apple).
B. Sexual Reproduction:
- Definition: Involves the fusion of two specialized reproductive cells (gametes) from (usually) two different parents, leading to the formation of a zygote.
- Characteristics:
- Typically involves two parents (male and female).
- Involves the formation and fusion of gametes (sperm and egg).
- Offspring are genetically different from both parents (due to recombination of genetic material), leading to variation.
- Common in most animals and higher plants.
- Sexual Reproduction in Humans:
- Gametes: Male gamete (sperm) produced in testes; Female gamete (egg/ovum) produced in ovaries.
- Fertilization: Fusion of sperm and egg, usually in the fallopian tube, to form a zygote.
- Development: The zygote undergoes cell division (mitosis) and develops into an embryo, then a fetus, and eventually a baby.
- Sexual Reproduction in Flowering Plants (Angiosperms):
- Flower: The reproductive organ. Contains male parts (stamens – anther produces pollen) and female parts (carpel/pistil – stigma, style, ovary containing ovules).
- Pollination: Transfer of pollen grains from the anther to the stigma. Can be self-pollination or cross-pollination.
- Fertilization: Fusion of male gamete (from pollen) with the female gamete (in the ovule).
- Seed and Fruit Formation: The fertilized ovule develops into a seed, and the ovary develops into a fruit (which encloses the seeds).
2. Growth
Definition: Growth is an irreversible increase in the size, mass, or volume of an organism or its parts. It is a fundamental characteristic of living organisms.
Mechanism of Growth:
Growth occurs primarily due to:
- Cell Division (Mitosis): Increase in the number of cells.
- Cell Enlargement: Increase in the size of individual cells.
- Accumulation of Intercellular Material: Non-living substances outside the cells.
Types of Growth:
- Determinate Growth: Organisms (like most animals) grow to a certain size and then stop growing.
- Indeterminate Growth: Organisms (like most plants) continue to grow throughout their lifespan due to the presence of meristematic tissues.
Growth in Plants:
- Plants exhibit continuous growth from specific regions called meristems.
- Apical Meristems: Located at the tips of roots and shoots, responsible for increasing the length of the plant (primary growth).
- Lateral Meristems (Cambium): Found in the stem and root, responsible for increasing the girth/thickness of the plant (secondary growth).
- Growth in plants also involves cell differentiation, where cells specialize to form different tissues (e.g., xylem, phloem).
Growth in Animals:
- Animals generally exhibit determinate growth, growing to a specific size and then ceasing to grow in length, although some tissues (e.g., skin, blood cells) continue to undergo cell division for repair and replacement.
- Growth in animals is highly regulated by hormones (e.g., growth hormone, thyroid hormones) and nutrient availability.
Factors Affecting Growth:
- Genetic Factors: Genes determine the potential growth limits.
- Nutrition: Adequate supply of essential nutrients (proteins, vitamins, minerals) is vital for proper growth.
- Hormones: Regulatory chemicals that control growth processes.
- Environmental Factors: Temperature, light, availability of water and oxygen.
3. Heredity
Definition: Heredity is the passing of traits or characteristics from parents to their offspring. It is the reason why offspring tend to resemble their parents, but also exhibit variations.
Basis of Heredity:
The fundamental basis of heredity is DNA (Deoxyribonucleic Acid), which carries the genetic information.
Key Concepts in Heredity:
- Genes:
- The basic unit of heredity.
- Segments of DNA that contain the instructions for building specific proteins, which in turn determine specific traits.
- Located on chromosomes.
- Chromosomes:
- Thread-like structures found in the nucleus of eukaryotic cells.
- Composed of DNA tightly coiled around proteins (histones).
- Humans have 23 pairs of chromosomes (46 total): 22 pairs of autosomes and 1 pair of sex chromosomes (XX for female, XY for male).
- DNA (Deoxyribonucleic Acid):
- The genetic material of almost all living organisms.
- Forms a double helix structure, resembling a twisted ladder.
- The sequence of nitrogenous bases (Adenine, Thymine, Guanine, Cytosine) along the DNA strand carries the genetic code.
- Traits (Characteristics):
- Observable features or qualities of an organism that are inherited.
- Can be physical (e.g., eye color, height, blood group) or behavioral.
- Alleles:
- Different forms or versions of a single gene.
- For example, a gene for eye color might have an allele for blue eyes and an allele for brown eyes.
- Dominant and Recessive Traits:
- Based on Gregor Mendel’s laws of inheritance.
- Dominant Trait: An allele that expresses its phenotype even when only one copy is present (e.g., brown eyes are dominant over blue eyes).
- Recessive Trait: An allele that expresses its phenotype only when two copies are present (i.e., homozygous recessive), and the dominant allele is absent.
- Genotype vs. Phenotype:
- Genotype: The genetic makeup of an individual; the set of genes or alleles an individual possesses (e.g., Tt, TT, tt for height).
- Phenotype: The observable physical or biochemical characteristics of an individual, resulting from the interaction of its genotype and the environment (e.g., tall, short).
- Variation:
- Differences among individuals of the same species.
- Crucial for evolution and adaptation to changing environments.
- Sources of variation: Sexual reproduction (crossing over, independent assortment, random fertilization), and mutation.
- Mutation:
- A sudden, random, and heritable change in the DNA sequence of an organism.
- Can be spontaneous or induced by mutagens (e.g., radiation, certain chemicals).
- Mutations are a primary source of genetic variation.
- Sex Determination (in Humans):
- Determined by sex chromosomes.
- Females have two X chromosomes (XX).
- Males have one X and one Y chromosome (XY).
- The male gamete (sperm) determines the sex of the offspring (sperm can carry either an X or a Y chromosome, while the egg always carries an X chromosome).
Practice Questions
- Which type of reproduction results in offspring that are genetically identical to the single parent?
- A) Sexual reproduction
- B) Fertilization
- C) Asexual reproduction
- D) Cross-pollination
- Rationale: Asexual reproduction produces clones of the parent.
- The process by which an Amoeba reproduces by dividing into two equal halves is called:
- A) Budding
- B) Fragmentation
- C) Multiple fission
- D) Binary fission
- Rationale: Binary fission is the division of a parent organism into two identical daughter organisms.
- In flowering plants, the process of transfer of pollen grains from the anther to the stigma is known as:
- A) Fertilization
- B) Germination
- C) Pollination
- D) Budding
- Rationale: Pollination is the crucial first step in sexual reproduction of flowering plants, involving pollen transfer.
- Which of the following is a method of vegetative propagation?
- A) Spore formation in fungi
- B) Binary fission in bacteria
- C) Cutting of a rose stem
- D) Budding in Hydra
- Rationale: Growing a new plant from a cut stem is a common artificial vegetative propagation method.
- The irreversible increase in the size or mass of an organism is called:
- A) Reproduction
- B) Development
- C) Growth
- D) Heredity
- Rationale: Growth is defined as an irreversible increase in size/mass.
- In plants, the increase in the length of the stem and roots is primarily due to the activity of:
- A) Lateral meristems
- B) Vascular cambium
- C) Apical meristems
- D) Intercalary meristems
- Rationale: Apical meristems are located at the tips of shoots and roots and are responsible for primary (length-wise) growth.
- Which of the following is NOT a primary mechanism contributing to growth in multicellular organisms?
- A) Increase in cell number
- B) Increase in cell size
- C) Accumulation of intercellular material
- D) Decrease in cell metabolism
- Rationale: A decrease in cell metabolism would hinder, not promote, growth.
- The basic unit of heredity, a segment of DNA that codes for a specific trait, is called a:
- A) Chromosome
- B) Nucleus
- C) Gene
- D) Protein
- Rationale: Genes are the fundamental units of inheritance.
- In humans, the sex of a child is determined by the chromosomes contributed by the:
- A) Mother only
- B) Father only
- C) Both mother and father equally
- D) Random genetic mutation
- Rationale: Males have XY chromosomes and contribute either an X or a Y sperm, while females only contribute an X egg. Therefore, the father’s sperm determines the sex.
- What is the term for the observable physical or biochemical characteristics of an individual, resulting from their genetic makeup and environmental influences?
- A) Genotype
- B) Allele
- C) Chromosome
- D) Phenotype
- Rationale: Phenotype refers to the outward expression of traits.
- A sudden, random, and heritable change in the DNA sequence of an organism is known as a:
- A) Recombination
- B) Adaptation
- C) Mutation
- D) Variation
- Rationale: Mutation is a change in the genetic material.
Good