Every organism of the living world has a basic building block called a cell. The cells are responsible for the growth and development of the organism. The Class 11 Biology syllabus comprises a detailed chapter on cell cycle and cell division which explains the concept of a cell in detail regarding its life cycle, types of divisions, and phases. If you are studying this chapter and are looking for a comprehensive summary of the major points covered, then you have come to the right place. Through this blog, we have summarized the chapter on Cell Cycle and Cell Division in Class 11 to help you understand its key concepts.
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Cell Cycle and Cell Division
The chapter on cell cycle and cell division in the class 11 syllabus explains that a cell cycle is a process of producing daughter cells. Cell division is a part of the cell cycle. The cell cycle comprises a series of growth stages that take place in a coordinated way for the correct cell division.
Phases of a Cell Cycle
A complete cell cycle requires a cell to grow, duplicate its content and split into two daughter cells. In eukaryotic cells, this happens in two phases, i.e. Interphase and Mitosis. These two phases are elaborated in detail in the chapter on cell cycle and cell division in class 11. Interphase is divided into three stages – Gap 1 (G1), Synthesis (S), and Gap 2 (G2); mitosis is further divided into four stages – prophase, metaphase, anaphase, and telophase. Mitosis is also referred to as the M phase.
Given below is the brief explanation of different phases of a cell cycle as mentioned in the chapter on cell cycle and cell division of class 11:
- Interphase is the phase between the two successive M phases; the actual cell division occurs in the M phase.
- Also known as the preparatory phase. In the first gap (G1) of the interphase, the cell grows and accumulates the energy required for replication.
- After G1, comes the S phase or the synthesis phase of the interphase. Here the identical pairs of DNA molecules are formed through the process of DNA replication. These identical molecules are referred to as sister-chromatids. The protein is also synthesised here for mitosis.
- The sister-chromatids are now two independent cells and start accumulating the energy to enter the preparatory phase.
- However, some cells do not enter the preparatory phase again as they do not need further division or some need occasional division. In this case, these cells enter the inactive stage called G0 or the quiescent stage.
The M Phase or Stages in Mitosis
As mentioned earlier, this phase is central to the process of the actual cell division. It is also referred to as the equational division.
The M phase is also divided into four stages explained as follows:
- Prophase – It is the first stage of the M phase and comprises S and G2 phases of the interphase. In this stage, the chromosomes condense and the nuclear envelope breaks down. The spindle fibres emerge from the centrosomes and the nucleolus disappears.
- Metaphase – Each sister chromatid is attached to the spindle fibre that originated from the opposite pole.
- Anaphase – After attaching to the spindle fibre from the opposite pole in metaphase, the cohesion protein of sister chromatids breaks down. Due to this, the sister chromatids are pulled towards the opposite poles.
- Telophase – In this stage, the chromosomes arrive at the opposite poles and begin to decondense. The nuclear envelope surrounds each set of chromosomes and the mitotic spindle breaks down.
Cytokinesis comes after mitosis and is the division of cytoplasm. The chapter on Cell Cycle and Cell Division in Class 11 also studies Cytonkinesis which occurs differently in animal and plant cells. In animal cells, a cleavage furrow separates the daughter cells. In-plant cells, a new cell wall called the cell plate separates the two daughter cells.
Mitosis and Meiosis
As explained in the chapter on cell cycle and cell division of class 11, mitosis and meiosis are two types of cell division. In mitosis, the cell undergoes the duplication process where it duplicates its chromosomes and then splits into two identical daughter cells. However, in meiosis, the cell reduces the number of chromosomes during the division process in the daughter cells. Go through the following sections to understand the difference between these two cell divisions.
What is Mitosis?
Restricted to just diploid cells, Mitosis happens when a parent cell splits to create two identical daughter cells. Studying Cell Cycle and Cell Division in Class 11, you will also get to learn about its significance in terms of cell division during the life of an organism. The main aim of mitosis is to facilitate growth and replace those cells which are worn out and not essential for the life of an organism.
Significance of Mitosis
After explaining the concept of mitosis, the chapter on cell cycle and cell division of class 11 mentions the main features of its significance:
- Mitosis produces daughter cells with identical genetics. This helps in the growth and development of both the cells and the organism.
- The continuous division of cells to maintain the nucleo-cytoplasmic ratio plays an essential role in cell repair.
- The continuous growth of the plants is the result of mitotic division.
- Since meiosis does not cause any genetic variation, it maintains the originality of the organism type from generation to generation.
The chapter on Cell Cycle and Cell Division in class 11 describes the process of meiosis as a specialized kind of cell division through which the number of chromosomes is reduced to half, resulting in the production of 4 haploid cells.
The process involves two sequential cycles of nuclear and cell division namely:
Meiosis I – This meiotic division is subdivided into prophase I, metaphase I, anaphase I and telophase I
Meiosis II – This meiotic division is subdivided into prophase II, metaphase II, anaphase II and telophase II
Significance of Meiosis
Moving to the next section of Cell Cycle and Cell Division in Class 11, you will get to learn about the significance of Meiosis which is as follows:
- The chromosome number is maintained among sexually reproducing organisms.
- The crossing-over produces a new combination of chromosomes, increasing the genetic variability in every generation.
- It also allows genetic mutation and the beneficial mutations are carried out by the process of natural selection.
- The maternal and paternal processes are independent of each other. Therefore, the traits that are controlled by chromosomes are rearranged after every reproduction.
Given below are some of the crucial questions which you must study while going through the revision notes on Cell Cycle and Cell Division in class 11:
- What is cell division? Differentiate between mitosis and meiosis.
- Explain the phases of mitosis.
- What is the significance of mitosis and meiosis?
- How many stages are there in a cell cycle? What is the G0 or quiescent phase?
- What is cytokinesis?
- When does crossing over occur in a cell cycle?
- What is the average cell cycle span of a mammalian cell?
- Explain different stages of meiosis I and meiosis II.
- Explain and differentiate the terms haploid and diploid.
- Define the terms: chiasmata, homologous chromosomes, karyokinesis, and sister chromatids.
The study of cell cycle and cell division is complex and requires patience and practice to master. However, the chapter on cell cycle and cell division of class 11 introduce the topic step-by-step to ensure better understanding. Want to pursue a course in biology after 12th? Reach out to our experts at Leverage Edu and we will help you in choosing the perfect course and university for a degree in biology. Sign up for a free counselling session today!