Cells,Reproduction and Heredity

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Chapter 1 : Cells, Reproduction and Heredity

Topics covered in this snack-sized chapter:

What are Cells? arrow_upward

  • Cells are the basic structural units of all living organisms.
  • It is smallest unit of life, often called as the building block of life.
  • All living things are composed of cells.
  • Cell biology is also called life fundamental science.
  • Most cells are very small, so small that they can only be seen with the microscope.
  • Our body is composed of billions of cells! Within our body, cells have different functions.
  • We have a variety of cells in our body for example blood cells, skin cells, platelets, etc.
  • Cells found in animals and plants (with just a few exceptions) have these features in common:
    • Cell membrane which serves as a boundary between the cell and the outside environment
    • The Cytoplasm is a gel-like substance within the cell membrane holding all the internal sub-structures of cell.
    • Nucleus is a central structure of a cell that contains DNA inside them.
    • Mitochondrion (plural, mitochondria), where cellular respiration takes place.
    • Cellular respiration: The breakdown of sugar to produce energy for the cell, a process that uses oxygen and produces carbon dioxide and water.
  • Plant cells have some additional features other than the ones listed above:
    • Chloroplast uses light energy to convert carbon dioxide molecules into one organic carbon sugar.
    • Cell wall is outside the cell membrane which provides additional strength.

    Reproduction arrow_upward

    Eukaryotic Cell Reproduction

  • The life of eukaryotic cells is characterized by a cell cycle with two major phases:
    • Interphase
    • Cell Division
  • During the interphase, the cell takes in nutrients, grows, and duplicates its chromosomes.
  • During the cell division phase, the nucleus divides in a process called mitosis and then the divided nuclei are established in separate cells in a process called cytokinesis.

  • Prokaryotic Cell Reproduction

  • Prokaryotic cells reproduce by a process called as binary fission.
  • The DNA in such cells is contained in a single circular chromosome called a plasmid within the cytoplasm.
  • The reproductive process starts with the replication of the chromosome.
  • The new chromosome attaches itself to the plasma membrane and the two chromosomes migrate to opposite ends of the cell.
  • The plasma membrane in the middle of the cell grows inward until it closes to separate the cell into two compartments, each with a full complement of genetic material.
  • The cell then "fissions" at the center, forming two new daughter cells

  • Cell Division arrow_upward

  • Cells are divided and new cell is formed, cells also have life cycle.
  • Cells reproduce themselves by dividing a “mother” cell into two “daughter” cells that are exactly like the mother cell.
  • Mitosis
    • In this process before cell divides the mother cell makes two copies of each chromosome.
    • This means that for a short time the mother cell has four complete pairs of 23 chromosomes.
    • Cells having two pairs of chromosomes are called “diploids”
    • Mother cell does this because when it divides, each daughter cell receives two pairs of chromosome.
    • This cell division is called “mitosis”.
    • Through mitosis, cells keeps on dividing-from one cell all the way to a trillions of cells.
  • Meiosis
    • Some cells have only ONE pair of chromosome, these cells are called “haploid”.
    • Haploid cells are made through a different type of cell division called “meiosis”.
    • Meiosis begins with one diploid mother cell which divides into two daughter cells like mitosis.
    • But in the next process daughter cell divides itself into four haploid cells without copying chromosome pairs. We need haploid cells for reproduction.

    Genetics and Heredity arrow_upward

  • Inside every cell of each living thing (plants or animals) is a set of instructions called genes.
  • The genes provide the instructions on what is the plant or animal, what it looks like, how it should survive, and how it will interact with its surrounding environment.
  • Most living things have pairs of chromosomes (one from each parent).
  • They may have different numbers of chromosomes from another living thing.
  • For example, humans have 23 pairs of chromosomes and the fruit fly has 4 pairs.
  • Genetics deals with molecular structure of genes.
  • All humans look alike yet they are different from one another.
  • Heredity is the process by which an offspring cell or organism acquires or becomes activated to the characteristics of its parent cell or organism.

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