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Cell Organelles, Animals Cell and Plants Cells, Levels of Organisation in Organisms- Biology Guide for Class 8

Information about Cell Organelles, Animal Cell and Plant Cells

Title

Cell Organelles, Animals Cell and Plants Cells and Level of Organisation in Organisms

Class

Class 8

Subject

Class 8 Biology

Topics Covered

  • Plastids
  • Mitochondria
  • Endoplasmic Reticulum (ER)
  • Golgi Complex
  • Vacuole
  • Ribosomes
  • Cilia and Flagella
  • Organisation in an Organisms
  • Difference between Plant and Animal Cells


Some cells exist as unicellular organisms (single-celled individuals) while others are a part of multicellular organisms. Certain basic functions, like nutrition, respiration, growth, development and reproduction, are performed by the cells in all organisms. These functions are essential for the survival of the organisms. The cell as the basic structural as well as functional unit of all living organisms.

Cell organelles

Many small living structures are present in the cell. These are equivalent to the organs of the body. Hence, they are named as 'cell organelles'.
  1. Plastids
  2. Mitochondria
  3. Endoplasmic Reticulum
  4. Golgi Complex
  5. Vacuole
  6. Ribosomes
  7. Cilia and Flagella

Plastids

  • These are large cell organelles, characteristic of plant cells.
  • These may contain pigments that provide colour to the cell.
  • The green-coloured plastids are called chloroplasts.
  • They manufacture food for green plants by the process of photosynthesis.
  • The plastids, associated with the different coloured parts of the plants (like fruits, vegetables and flowers) are called chromoplasts.
  • They are responsible for imparting colour (other than green) to the different parts of the plant.
  • Plants also contain some colourless plastids called leucoplasts; these provide space to store starch, proteins, oils, etc.

Mitochondria

  • These are rod-shaped or spherical structures.
  • They are present in large numbers in cells engaged in different physiological activities.
  • They are responsible for cellular respiration and for generation of energy for different activities of life. 
  • Hence, they are also called the powerhouse of the cell.

Endoplasmic Reticulum (ER)

  • It is a network of membranes.
  • It provides channels for transport of materials in a cell.
  • ER is of two types:
    (i) Rough ER : This type of ER has a rough appearance as it is studded with ribosomes. It plays a vital role in synthesis of proteins.
    (ii) Smooth ER: This type of ER does not have ribosomes attached to it; it, therefore, has a smooth appearance. It helps in the synthesis of fats.

Golgi Complex

  • They are sac-like structures stacked one above the other.
  • They are involved in the processing and packaging of materials produced by the cell.

Vacuole

  • It appears as an empty space in the cytoplasm.
  • It is generally large in plant cells.
  • It stores excess of water and waste products.
  • In Amoeba, food materials are held in its food vacuoles for digestion.

Ribosomes

  • These are tiny granules present in the cytoplasm and on the rough ER.
  • They help in protein synthesis.

Cilia and flagella

  • Some cells have these small extensions on their cell membrane.
  • They help in locomotion and collection of food.
  • Unicellular organisms, like Paramoecium, have numerous cilia while Euglena has a single flagellum.

All these cell organelles work together to perform different functions of the cell. 

Levels of Organisation in an Organism


  • In unicellular organisms, like Amoeba, a single cell performs all the necessary functions.
  • It captures and digests food, respires, excretes, grows and reproduces.
  • Multicellular organisms have cells that are specialised to perform specific functions.
  • A group of cells, performing a specialised function, forms a tissue (for example, nervous tissue).
  • A group of tissues, performing a specific function, forms an organ (for example, kidney).
  • A number of such organs work together to form an organ system (for example, digestive system).

The following organ systems work in the human body:
  1. Digestive
  2. Respiratory
  3. Circulatory
  4. Excretory
  5. Skeletal
  6. Muscular
  7. Nervous
  8. Reproductive
  9. Endocrine
  10. Integumentary
  • All the cells have some common features.
  • They can appear different in different parts of the organism. For example, the blood and liver cells (in animals), the root or leave cells (in plants) have different appearances.
  • The plant and animal cells, however, have some major differences between them.

Comparison Between Plant and Animal Cells 

  • Plant cells generally have a definite shape due to a rigid cell wall around them. In comparison, animal cells have a cell membrane as their outer cover. This provides flexibility to animal cells; hence they can show a large variation in their shapes.
  • Plant cells have plastids; these are absent in animal cells.
  • Plant cells generally have large vacuoles; animal cells, on the other hand, either lack vacuoles, or have very small vacuoles.

Difference between a Plant and an Animal Cell 

Components/Characters

Plant Cell

Animal Cell

Shape

Fixed

Irregular/Not fixed

Cell Wall

Present

Absent

Plastids

Present

Absent

Vacuoles

One large vacuole is present

Vacuoles are either absent or are present only as small vacuoles.


Keywords:
  1. cell: basic structural and functional unit of life. 
  2. cell membrane: a thin membrane that surrounds the protoplasm of every cell. 
  3. cell organelles: a specialised sub-unit, within a cell, that has a specific function. 
  4. chromosomes: thread-like structures found in the nucleus; responsible for the inheritance of characters. 
  5. cytoplasm: portion of protoplasm, lying between the cell membrane and the nuclear membrane. 
  6. cilia and flagella: extensions on the cell membrane, these help in locomotion and procurement of food in organisms like Amoeba and Paramoecium. 
  7. endoplasmic reticulum: network of membranes which provides channels for transport of materials in the cell and helps in synthesis of proteins.
  8. genes: unit of inheritance which gets transferred from one generation to the next.
  9. golgi complex: sac-like structures; these help in processing and packaging of materials produced by the cell. 
  10. mitochondria: rod-shaped structures inside a cell; these help in cellular respiration and production of energy. 
  11. nucleus: a specialised structure in the cells, bound by the nuclear membrane; responsible for controlling all cellular activities. 
  12. plastids: cell organelles found in plant cells. These may contain pigments which help in photosynthesis and are responsible for imparting colour to fruits, vegetables and flowers.
  13. protoplasm: gel-like living matter present inside the cell membrane.
  14. ribosomes: tiny granular structures found in the cytoplasm and on the endoplasmic reticulum; they help in protein synthesis.
  15. tissue: group of cells performing a specialised function.
  16. vacuole: sac-like membrane bound structures in cells; used for storing various materials. 
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