Cell Organelles | Class VIII/IX

A small organ-like structure present inside the cell is called a cell organelle. It has a particular structural makeup and performs a specific function. Depending upon the presence or absence of membrane, cell organelles can be classified into three categories, namely:

  • Without membrane: Some cell organelles like ribosomes are not bounded by any membrane. They are present in prokaryotic as well as eukaryotic organisms.
  • Single membrane-bound: Some organelles are bounded by a single membrane. For example, vacuole, lysosome, Golgi Apparatus, Endoplasmic Reticulum etc. They are present only in a eukaryotic cell.
  • Double membrane-bound: Cell organelles like mitochondria and chloroplast are double membrane-bound organelles. They are present only in a eukaryotic cell.

Structure and Functions of Cells

Structure and functions of different cell inclusions are as follows-

Cell Organelle Occurrence/ Characteristic & Structure Function
Cell Membrane/ Plasma Membrane
  • Present in both plant cell and animal cell.
  • Selectively Permeable: Allows the materials in and out of the cell according to the requirement of the cell.

  • Encloses the contents of the cell.
  • Provides shape: animal cell.
  • Allows transport: by Diffusion and Osmosis.
Cell Wall
  • Present only in a plant cell.
  • Hard and rigid.
  • Fully permeable.
  • Made up of cellulose in plant
  • Protection
  • Gives shape and turgidity.
Cytoplasm
  • Contains 80-90% water and many organic and inorganic compounds.
  • Colloidal, viscous, jelly like fluid inside the cell.
  • Contains enzymes responsible for all the metabolic activity taking place inside the cell.
Nucleus

(Director/ Brain of the Cell)

 

  • Covered by a double membranous nuclear membrane in a Eukaryotic Cell.
  • Contains DNA, RNA, Protein, nucleolus, and Chromatin network.

  • Controls the activity of the cell.
  • Starts cell division.
  • It has the chromosomes or DNA which controls the hereditary characters
Mitochondria (The Power House of The Cell / Storage Batteries)
  • Double membranous structure.
  • Autonomous body as contains its own DNA.
  • Self-duplicates.

  • The main seat of respiration.
  • Stores energy in the form of ATP molecules.
Golgi Bodies

(Shipping Department of Cell)

  • Discovered by Camillo Golgi in 1898.
  • Originates from RER.
  • Contains Sac like Cisternae and Vesicles.
  • Has two faces – cis face or receiving face and trans face or supplying face.

  • Modification, Packaging, and transport of materials
  • Synthesis of lysosomes, plasma membrane
Endoplasmic Reticulum

(Framework of Cell)

  • A network of membranes.
  • RER bears ribosomes and appears rough
  • SER does not have ribosomes

  • Forms the skeletal framework of the cell.
  • Transport of materials from one cell to other.
  • Provides a surface for the synthesis of material – Proteins in RER and Lipids in SER.
  • Formation of lysosomes, Golgi bodies andvacuoles
  • Membrane Biogenesis
  • Detoxification of harmful substances in the liver.
Vacuole
  • Arise from ER and GB
  • Surrounded by tonoplast and filled with cell sap
  • Store cell sap which may be liquid or solid food, toxic byproduct.
  • Provide rigidity and turgidity to plant cell
Lysosomes (Suicidal bags of Cell, natural scavenger, cellular housekeeper)
  • Membrane-bound organelles
  • Present in all animal cells and few plant cells
  • Tiny circular single membrane-bound structures filled with digestive enzymes
  • Intracellular digestion of food in unicellular organisms.
Ribosomes (Protein Factories)
  • Without a membrane
  • Consist of two subunits – 60S and 40S in eukaryote both made up of RNA

  • Synthesis of Proteins
Plastids
  • Double membrane-bound

Types-

  1. Leucoplast –Colourless plastid;
  2. Chromoplast –Coloured Plastid – blue, red, yellow
  3. Chloroplast – Green plastid
  • Autonomous self-duplicating body

  • Chloroplast – Perform Photosynthesis – Helps in the release of oxygen
  • Chromoplast – impart colour to flowers which help in pollination
  • Leucoplast – Storage
  • Amyloplast –Store starch
  • Aleuroplast – Store Protein
  • Elaioplast – Store fat

 

 

Solved Exercise

Question 1: Write the name of different plant parts in which chromoplast, chloroplast and leucoplast are present.

Answer:

  • Chloroplast are present in green parts of the plant like leaves, the stem of cactus, raw mango fruit etc
  • Chromoplast are present in colourful parts of the plant like flowers, fruits etc
  • Leucoplast is present in parts not exposed to sunlight like roots, potato etc.

Question 2: Name the organelles which show the analogy written as under

Answer:

  1. Transporting channels of the cell- Endoplasmic Reticulum
  2. Powerhouse of the cell- Mitochondria
  3. Packaging and dispatching unit of the cell- Golgi Body
  4. Digestive bag of the cell (Suicidal)- Lysosomes
  5. Storage sacs of the cell- Vacuole
  6. Kitchen of the cell- Chloroplast
  7. Control room of the cell- Nucleus

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