Biology Chapter on Ageing and Cell Growth
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Questions and Answers

What is the primary function of the centrosome during mitosis?

  • To act as a microtubule organizing center (correct)
  • To coordinate the cell's metabolic activities
  • To separate the nucleolus from the chromatin
  • To produce the chromosomes

    • How do centrosomes facilitate chromatid separation?

  • By producing ribosomes
  • By enhancing the nuclear envelope
  • By directly pulling apart the chromosomes
  • By forming a spindle made of microtubules (correct)

    • Which structure is NOT involved in animal cell mitosis?

  • Centromeres
  • Microtubules
  • Chloroplasts (correct)
  • Centrosomes

    • What distinguishes plant mitosis from animal mitosis in terms of centrosomes?

    <p>Plant mitosis occurs without centrosomes</p> Signup and view all the answers

    In which stage of mitosis are the spindle fibers clearly visible?

    <p>Prophase</p> Signup and view all the answers

    What role do the proteins surrounding the centrioles perform?

    <p>Controlling microtubule production</p> Signup and view all the answers

    Which phase directly follows metaphase in the mitotic cell cycle?

    <p>Early anaphase</p> Signup and view all the answers

    How many centrioles are typically found in a centrosome during animal cell mitosis?

    <p>Two</p> Signup and view all the answers

    What is the primary reason the nucleus divides before cell division in multicellular organisms?

    <p>To ensure each new cell has an identical nucleus</p> Signup and view all the answers

    What are telomeres, and what is their function?

    <p>They are protective sequences that prevent chromosome degradation</p> Signup and view all the answers

    How do telomeres affect the ageing process in organisms?

    <p>They shorten with each cell division, contributing to ageing</p> Signup and view all the answers

    Which enzyme is associated with the replenishment of telomeres?

    <p>Telomerase</p> Signup and view all the answers

    What important issue arises if the ageing process could be slowed or prevented?

    <p>Significant moral and ethical issues would need to be addressed</p> Signup and view all the answers

    What misconception about the aims of alchemists was challenged by 20th-century scientists?

    <p>Life can be prolonged indefinitely by external means</p> Signup and view all the answers

    What is the primary significance of mitosis in multicellular organisms?

    <p>It produces genetically identical daughter cells.</p> Signup and view all the answers

    Which structure is most recognized in eukaryotic cells according to the content provided?

    <p>Nucleus</p> Signup and view all the answers

    What happens to the length of telomeres when a cell divides?

    <p>They experience gradual shortening</p> Signup and view all the answers

    In which parts of plants is growth mainly confined?

    <p>Meristems</p> Signup and view all the answers

    How does mitosis contribute to tissue repair?

    <p>By replacing damaged or dead cells</p> Signup and view all the answers

    Which statement about asexual reproduction is true?

    <p>It is based on mitosis.</p> Signup and view all the answers

    Which of the following organisms can regenerate whole parts of their body through mitosis?

    <p>Starfish</p> Signup and view all the answers

    What happens to the chromosomes during mitosis?

    <p>They condense and line up before division.</p> Signup and view all the answers

    Why is cell replacement rapid in certain areas of the human body?

    <p>These areas experience constant wear and need replenishment.</p> Signup and view all the answers

    Which of the following best describes a key characteristic of offspring produced via asexual reproduction?

    <p>They are genetically identical to the parent.</p> Signup and view all the answers

    How many chromatids are present in a human cell as it enters mitosis?

    <p>92</p> Signup and view all the answers

    What role do centromeres play during nuclear division?

    <p>They serve as attachment points for spindle fibers.</p> Signup and view all the answers

    How many DNA molecules are present in a human cell at the start of mitosis?

    <p>92</p> Signup and view all the answers

    What is the primary purpose of mitosis in the immune response?

    <p>To clone B- and T-lymphocytes.</p> Signup and view all the answers

    During which phase of mitosis would you find chromosomes aligned at the equatorial plane?

    <p>Metaphase</p> Signup and view all the answers

    How many kinetochores are present in a human cell during metaphase of mitosis?

    <p>92</p> Signup and view all the answers

    What is the approximate length of the cell cycle in mouse liver cells if mitosis lasts one hour and 9 out of 75,000 cells are in mitosis?

    <p>3 days</p> Signup and view all the answers

    What defines the regions of growth in plants known as meristems?

    <p>They contain undifferentiated cells for growth.</p> Signup and view all the answers

    What is a characteristic of cancerous cells?

    <p>They divide rapidly and change characteristics.</p> Signup and view all the answers

    During which process do tumor cells invade other tissues?

    <p>Metastasis</p> Signup and view all the answers

    What supplies tumors with necessary nutrients?

    <p>Blood and lymph vessels</p> Signup and view all the answers

    What is the initial change observed in cells undergoing cancerous transformations?

    <p>They begin to look different under the microscope.</p> Signup and view all the answers

    What is one outcome of rapid mitosis in cancerous cells?

    <p>Increased tumor size.</p> Signup and view all the answers

    What technique can help in understanding the stages of mitosis?

    <p>Creating models with colors to represent chromosomes</p> Signup and view all the answers

    Which of the following is NOT true about tumors?

    <p>They cannot alter the characteristics of cells.</p> Signup and view all the answers

    What do cells do when they become cancerous?

    <p>They continue to divide uncontrollably.</p> Signup and view all the answers

    What role do centrosomes play during metaphase?

    <p>They help organize the production of the spindle.</p> Signup and view all the answers

    During which phase do chromatids start to be pulled apart by microtubules?

    <p>Anaphase</p> Signup and view all the answers

    What happens to the spindle during telophase?

    <p>It starts to break down.</p> Signup and view all the answers

    What occurs during cytokinesis?

    <p>The cytoplasm and cell divide.</p> Signup and view all the answers

    How do chromatids move during anaphase?

    <p>They are pulled apart by microtubules with centromeres first.</p> Signup and view all the answers

    What is re-formed during telophase?

    <p>The nuclear envelope and nucleolus.</p> Signup and view all the answers

    What occurs to the chromatids after they reach the poles of the spindle?

    <p>They uncoil and will replicate during interphase.</p> Signup and view all the answers

    What is the function of microtubules during mitosis?

    <p>They form the structure of the spindle and pull chromatids apart.</p> Signup and view all the answers

    When does the cytoplasm start to divide?

    <p>During cytokinesis.</p> Signup and view all the answers

    Which of the following is not involved in the pulling apart of chromatids?

    <p>Cytoplasm</p> Signup and view all the answers

    Study Notes

    Why Grow Old?

    • Scientists are now challenging the idea that ageing is inevitable
    • Studying telomeres led to the discovery that the shortening of these protective sequences at the ends of chromosomes leads to gradual organism degeneration and ageing.
    • Telomerase is an enzyme that replenishes telomeres
    • It is thought that cancer cells can do this and so remain immortal.
    • Some scientists are exploring the possibility of preventing ageing of normal cells by keeping the telomerase enzyme active.

    Growth and Reproduction

    • All living organisms grow and reproduce, and this means that cells must also be able to grow and reproduce too.
    • Cells reproduce by dividing and passing on copies of their genes to 'daughter' cells.
    • The process needs to be very precisely controlled to ensure that no genetic information is lost.
    • The process of mitosis produces genetically identical cells, crucial for growth and repair

    Chromosomes

    • Chromosomes are thread-like structures that become visible in the nucleus just before a eukaryotic cell divides.
    • They are easily visible under a microscope because they stain intensely with certain stains.
    • Chromosomes are composed of two identical chromatids joined together at a narrow region called the centromere.
    • Each chromatid contains one DNA molecule
    • There are genes for different characteristics on each chromosome.
    • The total length of DNA in a human cell's 46 chromosomes is about 1.8 metres.
    • The DNA is wound around histone protein molecules to fit into the nucleus.

    The Mitotic Cell Cycle

    • The cell cycle is the sequence of events between one cell division and the next.
    • The cycle includes interphase, nuclear division (mitosis) and cell division (cytokinesis).
    • Interphase is the period of growth between cell divisions, including the S phase where DNA replicate.
    • Mitosis is the division of the nucleus.
    • Cytokinesis is the division of the cytoplasm and cell into two daughter cells.

    Mitosis

    • Mitosis is the nuclear division that produces two genetically identical daughter nuclei, each containing the same number of chromosomes as the parent nucleus.
    • It is part of a precisely controlled process called the cell cycle.
    • The cell cycle has phases, or stages, that need to follow each other in the right order to prevent problems

    Telomeres

    • Telomeres are protective sequences of nucleotides at the ends of chromosomes.
    • They shorten with each cell division, eventually leading to cell ageing.
    • The enzyme telomerase can add bases to the telomeres.
    • The loss of genes during cell division and preventing continued replication results in cell death

    Stem Cells

    • Stem cells are cells that can divide an unlimited number of times.
    • When they divide, the new cells can either remain stem cells or differentiate into specialized cells (such as blood or muscle cells).
    • Stem cells are crucial for growth from zygote to adult.
    • Stem cells are also important for cell replacement and tissue repair in the adult.

    Cancer

    • Cancer is a group of diseases arising from uncontrolled cell division, thus resulting in tumours in the body.
    • Cancerous cells divide repeatedly and form tumours, which are irregular masses of cells.
    • Mutations in genes that control cell division can cause cancer.

    Immune Response

    • The cloning of B- and T- lymphocytes during the immune response is dependent on mitosis.

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    Description

    Explore the fascinating scientific concepts surrounding ageing, telomeres, and cell reproduction. This quiz delves into the roles of telomerase and chromosomes in growth and the potential for preventing ageing. Test your understanding of these critical biological processes.

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