Article-2⃣8⃣
*Self-practice*
10 th -Science Part 2
Topic 2: *Life Process in Living organisms Part-1*
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Today we are going to learn Mitosis and I need your undivided attention.
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🔹 *Mitosis*
*Meaning:* - In mitosis, a mother cell divides into two identical daughter cells.
Mitos in Latin means thread; osis means action / process. This means the process of splitting the DNA thread.
*Occurance:* - Mitosis occurs in asexual cells such as somatic cells and stem cells.
■ *Steps:* - Mitosis occurs mainly in two steps.
1) *Karyokinesis*: Greek word Karyos means nucleus. Hence it is also called nuclear division.
2) *Cytokinesis*: Cytos means cytoplasm. Hence it is also called splitting of cytoplasm.
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🔹 *Extra but necessary*
*Preparation for cell division*
The cell receives a message through a chemical signal as to when to start and when to stop the cell division process. Preparation begins with the storage of extra energy and nutrients as soon as the message is received. These preparations are represented in three stages.
1) *G1-stage:* - In this gap 1 stage, all the cell organelles except the nucleus are duplicated.
2) *S-Stage:* - In this synthesis stage DNA is replicated.
3) *G2 stage:* - In this gap 2 stage, the required enzymes for cell division are generated.
All three of these stages are collectively referred to as *"interphase"*. The cell then turns to kariokinesis.
*Note* - The above three stages are not mentioned in the textbook. This will not be questioned even in the exam. The cell division process takes about 4 hours to complete. More than half of that time is spent in pre-preparation. Therefore, considering the importance of pre- preparation, this information is given here so that it will help you to understand the process.
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The karyokinesis is completed in the following four steps.
1) Prophase 2) Metaphase 3) Anaphase and 4) Telophase.
🔹1) *Prophase:* -
◆ *Folding of DNA* - In this process DNA strands are wrapped. As a result, they become thick and dense.
◆ *Centriole formation:* -
Centriole in the cell doubles and the two newly formed centrioles move towards the opposite poles of the cell.
◆ *Disappearance of nucleus:* -
Gradually nuclear membrane and nucleus begin to disappear.
🔹 2) *Metaphase:* -
◆ *Sister chromatide formation:* -
The condensation of chromosomes is complete. Coiled original and duplicate DNA are stapled near the centromere. They are called "sister chromatids". Because they have identical genetic information.
◆ *Chromosome arrangment:* -
All the chromosomes are arranged parallel to the equatorial plane (center) of the cell.
◆ *Spindle fibre production:* -
Centrioles produce spindle fibres. These spindle fibres grow and attach to centromere of chromosomes arranged on equator.
We will discuss the remaining two stages and cytokinesis tomorrow. No assignments given today. But read the given information again and again.
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