Biology Handwritten Notes In Hindi [ जीव विज्ञान PDF ] / Biology notes / Biology pdf notes / biology 11 class / biology

                                 

Biology Handwritten Notes In Hindi [ जीव विज्ञान PDF ]

Biology Handwritten Notes in Hindi (जीव विज्ञान ) से संबंधित अत्यंत महत्वपूर्ण Notes को लेकर आए है | Free PDF Notes से प्रत्येक प्रतियोगी परीक्षा में बहुत ही Question अक्सर पूछा जाता है| और अधिकतर छात्र छात्राओं को सही जानकारी ना हो पाने के कारण गलत उत्तर का चयन कर देते हैं, जिससे वह परीक्षा में असफल हो जाते हैं| तो आज हम आपको Biology Handwritten Notes in Hindi जीव विज्ञान से संबंधित महत्वपूर्ण PDF को उपलब्थ कराएगे| जिससे अक्सर सभी प्रतियोगी परीक्षाओं में प्रश्न पूछे ही जाते हैं|

Biology Handwritten Notes :

सामान्य विज्ञान (General Science) में Biology के Handwritten Notes PDF को आप सभी छात्रों के लिए लेकर आए है, जो आपके बहुत से परीक्षा की तैयारी करने में मदद करती है, यह नोट्स आपके लिए सभी भर्ती परीक्षाओं जैसे SSC CHSL, CGL, CPO, Bank, Railway D Group, NTPC, UPSC, PCS, NDA, Air-force आदि के लिए अति महत्वपूर्ण है| Biology विषय के सभी टॉपिक्स को बहुत ही आसन भाषा में Biology PDF में दरसाया गया है जिसे अप निचे से डाउनलोड कर सकते है :

Biology Handwritten Notes Book In Hindi Pdf

जीव विज्ञान विषय के महत्कोवपूर्ण Topics को निचे दिए गए लेख के माध्यम से पड़ सकते है और पीडीऍफ़ को आसानी से डाउनलोड कर सकते है :-

• पाचन
• हार्मोन
• यकृत
• पित्ताशय
• पोषण
• ग्लूकोज
• प्रोटीन
• मानव रक्त
• ह्रदय
• कंकाल तंत्र
• रोग
• जीवाणु
• बैक्टीरिया
• वायरस
• पेड़ पोधे

Cell Cycle Definition

The cell cycle is the sequence of events occurring in an ordered fashion which results in cell growth and cell division.

• The cycle begins at the end of each nuclear division and ends with the beginning of the next.
• A cell cycle acts as a unit of biological time that defines the life history of the cell. 
• The cell cycle is a continuous process that includes all significant events of the cell, ranging from duplication of DNA and cell organelles to subsequent partitioning of the cytoplasm.
• In addition, the process of cell growth where the cell absorbs nutrients and prepares for its cell division is also a part of the cell cycle.
• The process of the cell cycle occurs in various phases, all of which are specialized for a particular stage of the cell.
• The overall process and steps of the cell cycle might differ in eukaryotic and prokaryotic organisms as a result of the differences in their cell complexity.
• Three main cycles are involved in the cell cycle; chromosome cycle, cytoplasmic cycle, and centrosome cycle.
  • The chromosome cycle involves DNA synthesis that alternates with mitosis. During this cycle, the double-helical DNA of the cell replicates to form two identical daughter DNA molecules. This is followed by mitosis to separate the cell into two daughter cells.
  • The cytoplasmic cycle involves cell growth that alternates with cytokinesis. During growth, the cell accumulates nutrients and growth factors and doubles the contents of the cytoplasm. Eventually, the cytoplasm divides via cytokinesis to equally divide the cytoplasmic contents into two cells.
  • The final cycle is the centrosome cycle where the centrosome is divided so that it can be inherited reliably and duplicated accordingly to form two poles of the mitotic spindle fibers.
• The cell cycle is regulated by various stimulatory and inhibitory factors that decide whether the cell needs to divide or grow.
• The cell cycle is divided into different phases (according to Howard and Pelc), each of which is defined by various processes.

• Phases of the Cell Cycle

  1. Gap 0 Phase (G0)

  • Gap 0 phase or G0 phase of the cell cycle is a period of time where the cell is present in a quiescent stage or resting phase, as it neither divides nor grows.
  • The G0 phase can be considered either an extended G1 phase or a separate phase-out of the cell cycle.
  • Usually, cells enter the G0 phase when they reach maturity like in the case of muscle cells and nerve cells, but the cells continue to perform their function throughout their life.
  • In some cases, however, cells might enter the G0 phase from the checkpoint in the G1 phase due to the lack of growth factors or nutrients.
  • In the G0 phase, the cell cycle machinery of the cell is dismantled, and the cell continues to remain in the G0 phase until there is a reason for the cell to divide.
  • There are some cells like the parenchymal cells of the liver and kidneys that enter the G0 phase semi-permanently and can be induced to divide.
  • Even though the G0 phase is often associated as senescence, the G0 phase is a reversible stage where a cell can enter the cell cycle again to divide.
  • The cells in the G0 phase have different regulators that ensure the proper functioning of the cell.

  2. Gap 1 Phase(G1)

  • The G1 phase of the cell cycle is a part of the interphase where the cell begins to prepare for cell division.
  • A cell enters the G1 phase after the M phase of the previous cycle, and thus, it is termed as the first gap phase of the first growth phase.
  • In this phase, no DNA synthesis takes place, but RNA synthesis occurs in order to produce proteins required for proper cell growth.
  • G1 phase is considered a time of resumption where the cell finally picks up normal cell metabolism that had slowed down during the M phase of the previous cycle.
  • The process and steps of the G1 phase are highly variable, even within the cells of the same species.
  • The most important event of the G1 phase, however, is the transcription of all three types of RNAs which then undergo translation to form proteins and enzymes necessary for other events in the cell cycle.
  • The duration of the G1 phase is also highly variable among cells. In some cells, it occupies about 50% of the total cell cycle time, whereas, in rapidly dividing cells, the phase is entirely omitted.
  • An important in the G1 phase is the G1/S checkpoint that determines if the cell is ready enough to proceed into the division phase. 
  • At this point, events like the detection of DNA damage and nutrient concentration are performed to ensure that the cell has enough machinery to undergo cell division.

  3. Synthesis Phase (S)

  • The S phase or synthesis phase of the cell cycle is a part of the interphase where important events like DNA replication and formation of histone proteins take place.
  • The processes of the S phase are tightly regulated as the synthesis of proteins and replication of DNA require utmost precision.
  • The production of histone proteins and other proteins are crucial in this phase as the newly replicated DNA molecules require histone proteins to form nucleosomes.
  • The entry into the S phase is regulated by the G1/S checkpoint that only allows cells with enough nutrients and healthy DNA to enter the next phase.
  • The phase is moderately long, occupying about 30% of the total cell cycle time.
  • During this phase, the content of DNA doubles in the cell, but the number of chromosomes remain the same as the division of chromosome doesn’t take place just yet.
  • The regulatory mechanism of the S phase also ensures that the process of DNA synthesis takes place before the M phase and with precision.
  • In order to preserve the epigenetic information, different regions of the DNA are replicated at different times.
  • Similarly, actively expressed genes tend to replicate during the first half of the S phase, whereas inactive genes and structural DNA tend to replicate during the latter half.
  • Therefore, at the end of the S phase, each chromosome of the cell has double the amount of DNA with a double set of genes.

  4. Gap 2 Phase (G2)

  • The G2 phase or Gap Phase 2 or Growth Phase 2 is a phase of the cell cycle where the cell collects nutrients and releases proteins in order to prepare the cell for the M phase.
  • The G2 phase is also a part of the interphase when the cell is still in the resting phase while preparing for cell division.
  • The G2 phase is also important as it checks for DNA damage (during replication) to ensure that the cell is in proper condition to undergo division.
  • The phase might be skipped in some rapidly dividing cells that directly enter the mitotic phase after DNA replication.
  • It is, however, an essential phase that checks for mutations and DNA damage to prevent excessive cell proliferation.
  • Even though information on the regulation and working of the G2 phase has been studied, its role in cancer initiation and development is yet to be determined.
  • DNA repair is a crucial step in the G2 phase as it repairs breaks that might be present in the DNA strand after replication.
  • The entry of the cell from the G2 phase to the M phase is regulated by the G2 checkpoint, where different proteins and complexes are involved.
  • In the case of DNA damage or insufficient nutrients, the cell remains in the G2 phase and is not passed for cell division.

  5. Mitosis Phase (M)

• • The M phase or Mitotic phase of the cell cycle is the most crucial and dramatic phase of the entire cycle where the cell divides to form identical daughter cells.
  • The most important event of this phase is the karyokinesis (nuclear division) where the chromosomes separate into form two distinct cells.
  • The process of mitosis might differ from one organism to another and even from one cell to another.
  • Mitosis begins with the condensation of chromosomes which then separate and move towards opposite poles.
  • A cell entering the M phase has a 4N concentration of genetic material and ends with two cells, each containing a 2N concentration of DNA.
  • Mitotic cell division occurs via four distinct steps; prophase, metaphase, anaphase, and telophase.
  • Prophase is the first stage of mitosis where the chromosome of the cell divides into two chromatids held together by a unique DNA region called the centromere. As the prophase progresses, the chromatids become shorter and thicker. Prophase also includes the division of centriole that move toward the two opposite ends of the cell.
  • Metaphase is the second and the longest stage of cell division where the chromatids are lined up on the metaphase plate. The chromatids are shorter and thicker and are still held together by a centromere. 
  • Anaphase is the next stage of mitosis involving the splitting of each chromosome into sister chromatids to form daughter chromosomes. After splitting, the chromatids are moved towards the pole due to the shortening of the microtubules.
  • Telophase is the final stage of mitosis which involves the reorganization of two nuclei and the entry of the cell into the next phase. During this phase, a nuclear envelope is formed around the chromosomes to form two distinct daughter nuclei.
  • Telophase indicates the end of the M phase, which initiates the division of cell organelles and separation of cytoplasm into two cells (cytokinesis).

  Read More: Mitosis- definition, purpose, stages, applications with diagram

  6. Cytokinesis

  • Cytokinesis is the division of cytoplasm into two halves, indicating the end of cell division.
  • Cytokinesis occurs immediately after the M phase to separate the nucleus, cell membrane and the rest of the cytoplasm into two halves to form two distinct and complete cells.
  • The phase begins with the constriction of the cell membrane, which ultimately leads to cleavage and division.
  • The constriction is first observed during anaphase, which continues to grow deeper to finally cause cleavage.
  • The process and mechanism of cytokinesis might be different in different cells. 
  • In some cases, cytokinesis is often considered to be a part of the M phase, but in the case of animal cells, cytokinesis and mitosis might occur independently.
  • The contraction of the cell membrane during cytokinesis is brought about by the contraction of actin fibres that form a bundle, called a contractile ring.
  • In the case of a plant cell, however, a distinct cell plate is formed at the middle of the dividing cell which separates the cytoplasm and cell organelles into equal halves.
  • Cytokinesis, like the rest of the cell cycle, is also regulated by several factors that are responsible for the initiation of division as well as the termination.