Class 12 Biology Bihar Board Long Answer Questions PDF

# Class 12th Bihar Board Biology ## Chapter 1, 2, 3, 4 - Important Long Answer Questions ### Sexual Reproduction (लौंगक जनन) - **Male (नर) (46)** - Testis (वृषण) - Gametogenesis (युग्मक निर्माण) - Spermatogenesis (शुक्राणु जनन) - Sperm (शुक्राणु) (23) - **Female (माद...

# Class 12th Bihar Board Biology ## Chapter 1, 2, 3, 4 - Important Long Answer Questions ### Sexual Reproduction (लौंगक जनन) - **Male (नर) (46)** - Testis (वृषण) - Gametogenesis (युग्मक निर्माण) - Spermatogenesis (शुक्राणु जनन) - Sperm (शुक्राणु) (23) - **Female (मादा) (46)** - Ovary (अण्डाशय) - Oogenesis (अण्डाणुजनन) - Ovum (अण्डाणु) (23) - **Fertilization (निषेचन)** - Zygote (युग्मनज) ### Embryogenesis (भ्रूण निर्माण) - **(Embyo) भ्रूण निर्माण** - **Gestation time (गर्भकाल)** (270 Days) - **Foetus (गर्भ)** - **Parturation (प्रसव)** - **Infant (नवजातशिशु)** 50%: 50% ### Question 1 **Define reproduction. What are the two types of reproduction in living organisms?** **Answer:** Reproduction is a process in which a cell or organism produces cells or organisms similar to itself. Reproduction is of two types - sexual and asexual. **Sexual Reproduction:** Sexual reproduction occurs in all multicellular organisms. It involves two stages: 1. **Spermatogenesis** in males: This involves the formation of sperm cells. 2. **Oogenesis** in females: This involves the formation of egg cells. During spermatogenesis and oogenesis, the process of meiosis occurs, where the number of chromosomes in the cells is halved. The fusion of sperm and egg, known as **fertilization**, results in a diploid zygote, beginning the process of embryonic development. **Asexual Reproduction:** Asexual reproduction occurs only in single-celled organisms. It only involves **mitosis**, where one cell divides into two identical daughter cells. Thus, both cells have the same number of chromosomes as the parent cell. This process yields clones of the parent cell, which are genetically identical. ### Question 2 **Describe the structure of microsporangium with the help of a labeled diagram.** **Answer:** When the pollen sac (microsporangium) is cut transversely, it appears round and is surrounded by 4 layers: **1. Epidermis (बाह्यत्वचा):** It is the outermost protective layer; the cells have thick walls. **2. Endothecium (एण्डोथीसियम):** This layer is found beneath the epidermis. The cells are thin-walled and shrink due to the loss of water, helping with the dehiscence of the pollen sac. **3. Middle Layer (मध्य आवरण):** This layer has thin-walled cells and is often present in one to five layers. It helps in the nutrition of the developing pollen grains. **4. Tapetum (टेपीटम):** The innermost layer consists of large cells with thick cytoplasm and multiple nuclei. The tapetum is the nutritive tissue that provides nourishment to the developing pollen grains. **Diagram** The diagram shows the structure of a microsporangium, with the following components: - **Anther (परागकोष)** - **Epidermis (बाह्यत्वचा)** - **Endothecium (एण्डोथीसियम)** - **Middle layer (मध्य आवरण)** - **Tapetum (टेपीट)।** - **Pollen grains (परागधानी) (04)** - **Connective tissue (संयोजक)** - **Stomium (स्टोमियम)** - **Xylem & Phloem (जाइलम & फ्लोएम)** - **Cellulose (सेल्यूलोज)** ### Question 3 **What is triple fusion? Where and how does it take place? Explain with a diagram.** **Answer:** Triple fusion is a process that occurs during double fertilization in angiosperms. **Steps of Triple Fusion:** 1. **Pollen tube entry into the embryo sac:** The pollen tube carrying two male gametes enters the embryo sac through the micropyle. 2. **Fusion of one male gamete with the egg cell:** The first male gamete fuses with the egg cell to form a diploid zygote (2n). This is known as **syngamy** or **true fusion**. 3. **Fusion of the second male gamete with the polar nuclei:** The second male gamete fuses with the two polar nuclei (n + n = 2n) present in the central cell of the embryo sac. This fusion results in a triploid (3n) primary endosperm nucleus. This is known as **triple fusion**. **Diagram:** - The diagram illustrates the process of triple fusion, showing the fusion of the second male gamete with the two polar nuclei to form the primary endosperm nucleus (3n). **Conclusion:** Triple fusion is essential for the development of the endosperm, which provides nourishment to the developing embryo. ### Question 4 **What is megasporogenesis? Describe the process with a labeled diagram.** **Answer:** Megasporogenesis refers to the development of the female gametophyte, the embryo sac, inside the ovule of a flower. **Steps of Megasporogenesis:** 1. **Megaspore mother cell:** A single megaspore mother cell (MMC) is located in the nucellus of the ovule. 2. **Meiosis:** The MMC, which is diploid (2n), undergoes meiosis to produce four megaspores. 3. **Degeneration of megaspores:** Three of the four megaspores degenerate. 4. **Megaspore development:** The surviving megaspore undergoes a series of mitotic divisions to form an embryo sac (female gametophyte). 5. **Embryo sac formation:** The embryo sac typically contains 7 cells -- one egg cell, two synergids, three antipodal cells, and a central cell with two polar nuclei. **Diagram:** - The diagram illustrates the steps of megasporogenesis, showing the meiosis of the MMC to form four haploid megaspores, the degeneration of three megaspores, and the development of the surviving megaspore into a mature embryo sac. ### Question 5 **Explain the structure of the male reproductive system in humans with a diagram.** **Answer:** The main parts of the male reproductive system include the **testis**, **accessory ducts**, and **accessory glands**. **Testis (वृषण):** - The testis is a pair of oval-shaped organs located within the scrotum, a pouch-like structure hanging outside the body. - The testis produces sperm cells, which are the male gametes. - The temperature inside the scrotum is slightly lower than the body temperature, which is important for sperm production. **Accessory ducts:** - **Epididymis (अधिवृषण):** It is located on the posterior surface of the testis. The sperm passes from the testis to the epididymis, where it is stored and matures. - **Vas deferens or ductus deferens (शुक्रवाहिका):** They are long, muscular tubes that transport mature sperm from the epididymis to the urethra. - **Urethra (मूत्रमार्ग):** It is the common passageway for urine and sperm, extending from the urinary bladder, through the penis, and opening outwards at the tip of the penis. **Accessory glands:** - **Seminal vesicles (शुक्राशय):** These glands secrete a viscous fluid rich in fructose, which provides energy to sperm cells. - **Prostate gland (पुरस्थ ग्रंथि):** The prostate gland secretes an alkaline fluid that neutralizes the acidity of the urethra and vaginal fluid. - **Bulbourethral gland (बुल्बोयुरेथ्रल ग्रंथि):** This gland secretes a clear, viscous fluid that lubricates the urethra during sexual arousal. **Diagram:** - The diagram shows the male reproductive system, with the main reproductive organs and the accessory ducts and glands. ### Sperm production (शुक्राणुजनन) - **Spermatogonia (s)** - **Sertoli cells** - **Leydig Cells** - **Testosterone** (शुक्राणुजनन) ### Accessory Reproductive Organs - **Epididymis (अधिवृषण)** - **Vas deferens (शुक्रवाहिका)** - **Urinary bladder (मूत्राशय)** - **Urethra (मूत्रमार्ग) ** - **Penis (शिश्न)** - **Scrotum (वृषणकोष)** - **Bulbourethral gland (बुल्बोयुरेथ्रल ग्रंथि)** **Diagram** - The diagram shows the accessory reproductive organs and their locations. ### Function of Accessory Reproductive Organs 1. **Epididymis (अधिवृषण):** The epididymis serves as a storage site for the newly produced sperm, allowing it to mature and gain motility. 2. **Vas deferens (शुक्रवाहिका):** This muscular tube acts as a crucial transport system to convey the mature sperm from the epididymis towards the urethra during ejaculation. 3. **Urinary bladder (मूत्राशय):** While the primary function of the urinary bladder is to store urine, in the male reproductive system, it also serves as a passageway for sperm. 4. **Urethra (मूत्रमार्ग):** This tube facilitates the passage of both urine and sperm, depending on the body's needs. The sperm travels through the urethra to be expelled from the penis during ejaculation. 5. **Penis (शिश्न):** The penis is the external organ involved in sexual intercourse, both for the transport of urine and semen. 6. **Scrotum (वृषणकोष):** The scrotum is a pouch that holds the testes outside the body. It regulates the temperature of the testes, which is vital for sperm production. 7. **Bulbourethral gland (बुल्बोयुरेथ्रल ग्रंथि):** Responsible for secreting a clear, viscous fluid, the bulbourethral gland lubricates the urethra during sexual stimulation, making it easier for the ejaculated semen to be expelled.