General Q&A for Class 12 · Page 69
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What are the different parts of the female reproductive system?
The female reproductive system includes: Ovaries: Paired organs that produce eggs (ova) and female hormones (estrogen and progesterone) Fallopian tubes (Oviducts): Tubes where fertilization typically occurs Uterus: Muscular organ where the embryo implants and develops during pregnancy Cervix: Lower part of the uterus that opens into the vagina Vagina: Bir
- GeneralClass 12All
What is external fertilization and why do these organisms produce many gametes?
External fertilization occurs when gametes fuse outside the parent's body, typically in water environments. Fish, frogs, and many aquatic organisms use this reproduction method. These organisms produce thousands to millions of gametes because: Many gametes are dispersed by water currents and never meet Predators consume a significant number of eggs and sperm Environmental factors may destroy gametes before fertilization
- GeneralClass 12All
How many sperm and eggs are produced in humans?
The production of gametes differs significantly between males and females: Sperm: Males produce millions of sperm continuously from puberty onward. A single ejaculation can contain 200-500 million sperm cells Eggs (Ova): Females typically release one egg per month during ovulation, from puberty to menopause. Women are born with all their eggs (approximately 1-2 million), but only about 400-500 mature and are released
- GeneralClass 12All
What are sperm cells and where are they produced?
Sperm (also called spermatozoa) are the male gametes produced in the testes (specifically within structures called seminiferous tubules). Each sperm cell consists of three main parts: Head: Contains the nucleus with genetic material (DNA) and an acrosome with enzymes to penetrate the egg Middle piece: Packed with mitochondria that provide energy for movement Tail (flagellum)
- GeneralClass 12All
Which process is essential for living organisms to continue their species?
Reproduction is the essential biological process that ensures the continuation of species across generations. This fundamental life process allows organisms to produce offspring, passing on genetic information from parent to progeny. Without reproduction, species would become extinct within a single generation. Both simple organisms like bacteria and complex organisms like humans rely on reproduction to maintain their populations and ensure species survival over time.
- GeneralClass 12All
What is the difference between asexual and sexual reproduction?
Asexual reproduction produces offspring that are genetically identical to the parent organism, creating exact copies or clones. This occurs through processes like binary fission, budding, fragmentation, or regeneration without involving gametes (sex cells). In contrast, sexual reproduction involves the fusion of male and female gametes, creating offspring with genetic variation that combines characteristics from both parents. While asexual reproduction is fas
- GeneralClass 12All
Why is sexual reproduction considered better than asexual reproduction?
Sexual reproduction offers significant evolutionary advantages despite being more complex and time-consuming. It creates genetic variation through the combination of DNA from two parents, producing offspring with unique characteristics. This diversity enables species to adapt to environmental changes, resist diseases, and evolve over time. Populations with genetic variation have better survival chances when faced with challenges like climate change or new pathogens. However,
- GeneralClass 12All
What are the different modes of asexual reproduction in animals?
Animals reproduce asexually through several distinct methods: Binary Fission: The parent organism divides into two equal halves (seen in amoeba) Budding: A small outgrowth develops on the parent and eventually detaches (observed in hydra and yeast) Fragmentation: The organism breaks into fragments, each developing into a complete organism (starfish) Regeneration: Lost body parts re
- GeneralClass 12All
What are the two essential components of sexual reproduction?
The two fundamental components required for sexual reproduction are: Gametes (Sex Cells): Specialized reproductive cells including sperm (male gametes) and ova/eggs (female gametes) that carry half the genetic material Fertilization: The process where male and female gametes fuse to form a zygote, combining genetic information from both parents These components ensure genetic recombination and variation in offspring, d
- GeneralClass 12All
Which animals can undergo complete regeneration?
Planaria (flatworms) and Hydra are classic examples of animals capable of complete regeneration. These organisms can regenerate entire bodies from small fragments. If a planaria is cut into multiple pieces, each piece can develop into a complete organism with all necessary organs and structures. This remarkable ability is due to the presence of specialized stem cells that can differentiate into any cell type needed for regeneration. Starfish also show signifi
- GeneralClass 12All
Why are offspring from asexual reproduction called clones?
Offspring produced through asexual reproduction are termed clones because they are genetically identical to their parent organism. Since asexual reproduction involves only one parent and no fusion of gametes, the offspring receives an exact copy of the parent's DNA without any genetic recombination. This means clones share 100% of their genetic material with the parent, making them essentially biological photocopies. Examples include bacteria dividing through binary fission o
- GeneralClass 12All
Name two structures present only in plant cells and two present only in animal cells.
Structures found ONLY in plant cells: Cell wall: A rigid outer layer made of cellulose that provides structural support and protection Chloroplasts: Organelles containing chlorophyll that carry out photosynthesis Structures found ONLY in animal cells: Centrioles: Cylindrical structures that play a crucial role in cell division by organizing spindle fiber
- GeneralClass 12All
Why are chloroplasts found only in plant cells?
Chloroplasts are found exclusively in plant cells (and some protists) because: Energy source: Plants are autotrophs that produce their own food through photosynthesis, which requires chloroplasts Survival strategy: Unlike animals that obtain energy by consuming other organisms, plants must manufacture glucose using sunlight Evolutionary adaptation: Plants evolved chloroplasts to convert light energy into che
- GeneralClass 12All
Which structure is called the "little nucleus" and what is its role?
The nucleolus is often referred to as the "little nucleus" because it appears as a small, dense structure within the nucleus. Its primary roles include: Ribosome production: Manufacturing and assembling ribosomal RNA (rRNA) and ribosomal proteins Ribosome assembly: Combining rRNA with proteins to form ribosomal subunits RNA processing: Modifying and processing various types of RNA </ul
- GeneralClass 12All
What is the Golgi apparatus called in plant cells?
In plant cells, the Golgi apparatus is also known as the Golgi body or dictyosome. The term "dictyosome" specifically refers to the individual stacks of flattened membrane-bound sacs that make up the Golgi apparatus in plant cells. This organelle plays a crucial role in modifying, packaging, and distributing proteins and lipids produced by the cell, essentially functioning as the cell's processing and shipping center.
- GeneralClass 12All
What do chloroplasts contain?
Chloroplasts contain several important components: Chlorophyll: The green pigment that absorbs light energy for photosynthesis Other pigments: Including carotenoids that assist in light absorption DNA: Their own genetic material, allowing them to reproduce independently Ribosomes: For protein synthesis Enzymes: Necessary for the photosynthesis process</li
- GeneralClass 12All
Which organelle in plant cells is responsible for photosynthesis?
Chloroplasts are the organelles where photosynthesis takes place in plant cells. These green-colored structures contain chlorophyll, the pigment that captures light energy from the sun. During photosynthesis, chloroplasts convert light energy, carbon dioxide, and water into glucose (food) and oxygen. This process is fundamental to life on Earth, as it provides energy for plants and produces the oxygen we breathe.
- GeneralClass 12All
How are Amoeba and earthworm different from a cellular point of view?
From a cellular perspective, Amoeba and earthworms differ significantly in their organization: Amoeba is a unicellular organism, meaning its entire body consists of just one cell that performs all life functions independently, including feeding, respiration, excretion, and reproduction. Earthworm is a multicellular organism, composed of millions of specialized cells organized into tissues and organs t
- GeneralClass 12All
Why is the plasma membrane called a differentially permeable membrane?
The plasma membrane is termed a differentially permeable (or selectively permeable) membrane because it does not allow all substances to pass through equally. Instead, it selectively permits certain molecules to cross while blocking others based on factors like: Size of the molecule Chemical nature (water-soluble vs. fat-soluble) Charge of the particle Concentration gradient For example, the membrane easily allows s
- GeneralClass 12All
What is a cell and who discovered it?
A cell is the basic structural and functional unit of all living organisms. The term "cell" was first coined by scientist Robert Hooke in 1665 when he observed a thin slice of cork through a microscope. He noticed tiny compartments that resembled small rooms or cells in a monastery, which led him to name these structures "cells." This groundbreaking discovery laid the foundation for modern cell biology and our understanding of how living organisms are structured at the micros