CBSE class 8 Science – Structure of a Cell

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CBSE class 8 Science Structure of a Cell
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CBSE class 8 Science Structure of a cell

• Science is the study of life itself. Science, is
  a vast subject, with many sub-disciplines that
  concentrate on specific aspects of biology,
  physics and chemistry.. Learning Science could be
  a difficult job if you dont create an effective
  method to memorize the hundreds of definitions
  and terminologies involved. In this Article, we
  are going to explain CBSE class 8 Science -
  Structure of a cell. A building block or basic
  structural unit of life
• Structure of a Cell
• All the plant and animal cells have three main
  parts cell wall (in plants) or cell membrane
  (in animals) and cytoplasm and Nucleus.
• Cell Wall this is the most rigid, protective,
  outermost covering found in plant cells only. It
  provides shape and rigidity to the plant cell.
• Cell Membrane - this is also called the plasma
  membrane. It is a very thin layer covering the
  cell. There are very thin tiny holes in the cell
  membranes.
• The cell membrane or plasma membrane performs the
  following functions
• It protects the cell
• It provides shape to the cell.
• It allows materials to enter and leave the cell
  through the tiny holes.

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CBSE class 8 Science Structure of a cell

• Cytoplasm (kytos hollow, plasm liquid)
  present inside the cell and filled with
  jelly-like substance. It occupies the space
  between the cell membrane and the nucleus. It has
  several different structures called cell
  organelles which perform the various life
  functions.
• Nucleus -This is a dense body found in the centre
  of the cell which control all the activities of
  the cell. The Nucleus is made up of the following
  parts-
• Nuclear membrane it is the porous membrane which
  separates the contents of a nucleus from the
  cytoplasm.
• Nucleoplasm the fluid present in the nucleus is
  called nucleoplasm.
• Nucleolus Small spherical body made up of
  nucleoprotein. RNA are also present in nucleolus.
• Chromosome Nucleoplasm contains certain
  threadlike structures called chromosomes. These
  carry genes which are responsible for the passage
  of traits from one generation to another.

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CBSE class 8 Science Structure of a cell

• CELL ORGANELLES
• These are extremely small structure present in
  the cytoplasm. Cytoplasm is composed of many
  living and non-living parts called cell
  organelles which are concerned with cell
  function.
• Mitochondria Mitochondria ( singular
  mitochondrion) are oval or rod shaped organelles
  commonly called Powerhouse of the cell because
  the production of energy from food takes place
  here.
• Endoplasmic Reticulum It synthesizes, stores and
  transports material within the cell.
• Golgi Complex it secretes enzymes, proteins and
  hormones.
• Lysosome All cells contain enzymes which help in
  breaking down the various material. They are also
  called suicidal bags. Plant cells do not have
  Lysosome.
• Ribosomes it is the site of protein synthesis.
• Valcuole The space within the cytoplasm of the
  plant cell containing cell sap is called
  vacuoles.

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CBSE class 8 Science Structure of a cell

• Prokaryotic and Eukaryotic cells
• The nucleus of animals and plants differ in
  structure. The nucleus in bacteria is not well
  organized. There is no nuclear membrane. Whereas
  in the cells of animals and plant nucleus is well
  defined with nuclear membrane.
• Prokaryotic (Pro primitive, karyon nucleus)
  these cells are bacteria and blue green algae.
• Eukaryotic ( Eu true, karyon nuceus) These
  cells are found in all organisms except bacteria
  and blue green algae.
• The following are the major differences between
  plant and animal cells

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CBSE class 8 Science Structure of a cell
Plant Cell Animal Cell
A rigid cell wall is present. The Cell wall is absent.
Chloroplasts are present. Chloroplasts are absent.
Large Vacuoles are present and occupy a large portion of the cell. Vacuoles are either absent or very small and few in number.
Centrosomes are absent. Centrosomes are present.
Lysosomes are absent. Lysosomes are present.
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CBSE class 8 Science Structure of a cell

• Division of a Cell and Growth
• Plants and human beings start their life as a
  single cell. This single cell produces billions
  of cells. A small seed grows into big plant or
  small baby grows into full grown human being. How
  does this happen? A cell grows and then divides
  into two, increasing the number of cells. The
  process is called cell division.
• The cells resulting from the cell division of a
  parent cell are called daughter cells. The
  daughter cells resemble the parental cell in a
  number of characters. Daughter cells grow in
  their maturity and divide again. New cells are
  required in our body not only for growth, but
  also for replacement of old worn out or damaged
  cells. Skin cell continues to divide throughout
  life. But nerve cells do not divide after a
  certain age.
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