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Cell Structure Part 3

Definition of Lysosomes
A membrane bound sacs filled with digestive enzymes is called lysosomes. It is also called as a “suicidal bags” of cell or a “waste disposal bags” of cell because it helps to clean the cell by digesting any foreign material as well as worn out cell organelles.

Function:
  • Digest foreign materials like bacteria or food, as well as old worn out cell organelles with the help of digestive enzymes present in it.
  • Facilitates the entry of sperm into egg.
  • During the disturbance in cellular activities, it burst and digests its own cell.

Definition of Mitochondria:
A double layered cylindrical or granular structure present in cytoplasm is called mitochondria. It is called as “Powerhouse” of cell as it releases energy in form of ATP. The outer membrane of mitochondria is porous and continuous. The inner membrane of mitochondria has many folding called cristae. Inner region of mitochondria is called matrix which contains their own Ribosome and circular DNA.


Function:
  • Synthesis ATP and releases it for various cellular activities
  • Synthesize some proteins

Definition of Plastids:
A double layered tubular shape organelle present only in plant cells is called plastids.


Types of plastids:
1.  Chromoplasts
·  Coloured pigments responsible for various colors in fruits, seeds and flowers.
·  They possess pigments like carotene, Xanthophylls, Anthocyanin etc

2.  Chloroplasts
·  The outer layer is continuous and inner layer has many folds which are called as grana.
·  They possess chlorophyll pigment and important for photosynthesis in plants


3.  Leucoplasts
·  They are while or colorless and don’t contain any pigments
·  They stores food, oils and protein granules and act as a food storing units.

    • Amyloplasts – stores starch
    • Elaioplasts – Stores fat or oil
    • Aleuoplasts – stores protein
·  Inner region except grana is called stroma which contains proteins, ribosome, circular DNA and enzymes require for dark reaction.

Definition of Vacuoles:
A storage sac for solids and liquids without any cytoplasm is called vacuoles.


Plant cell vacuoles:
  • It contains large vacuoles about 50 – 90% of cell volume which is surrounded by a semi-permeable membrane called tonoplast.
  • They are full of cell sap and gives turgidity and rigidity to the cell
  • It stores many important substances like amino acids, sugars, some proteins and various organic acids.

Unicellular organic vacuoles:
  • It stores food items hat unicellular organism has consumed like Amoeba
  • It helps in expelling excess water and some wastes from the cell

Animal cell vacuoles:
  • It contains very small vacuoles or many times it is absent in animal cells.
  • The membrane around animal cell vacuole is made up of lipoproteins.

Introduction of Centriole:
  • It is present only in Animal Cell, Exception – Algae & Fungi
  • It is organized like a wheel containing nine triplets at about 40° angle arranged in peripheral region
  • Each triplet contains three microtubules made up of tubulin and each adjacent triple is inter connected by protein fibers.
  • A proteinaceous hub is present at the centre of triple, which connects triplets by filaments.
  • Normally, two Centriole arranged right angle to each other is seen in animal cells
  • The protoplasm surrounding he Centriole is called centrospheres.
  • Centriole and centrospheres combines and forms Centro some

Function:
  • During cell division, it directs formation of bipolar spindle
  • Helps in formation of basal body, cilia and flagella.

Self study:

Example-1: Match the following

(A) (B)
Lysosomes Power house of cell
Mitochondria Suicidal bags of cell
Vacuoles Directs formation of bipolar spindle during cell division
Centriole Storage sacs for solids and liquids

Answer:
(A) (B)
Lysosomes Suicidal bags of cell
Mitochondria Power house of cell
Vacuoles Storage sacs for solids and liquids
Centriole Directs formation of bipolar spindle during cell division

Example-2:  The protoplasm surrounding the Centriole is called ……….
a)  Centro some
b)  Chromoplasts
c) 
Centrospheres
d)  Chloroplasts

Answer: The protoplasm surrounding the Centriole is called centrospheres.


Example-3: Which of the following is responsible for photosynthesis in plants?
a)  Centro some
b)  Chromoplasts
c)  Centrospheres

d)  Chloroplasts

Answer: Chloroplasts is responsible for photosynthesis in plants.
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