8th, Science, Notes, 10.2 Cell and Cell Organelles

 8th, Science, Notes, 

10.2  Cell and Cell Organelles 

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🚃 Endoplasmic Reticulum (ER)

The organelle that conducts various substances inside the cell is called endoplasmic reticulum. E.R. has a net-like structure consisting of interconnected miniature tubes and sheets filled with fluid.

The E.R. is connected to the nucleus from the inside to the plasma membrane from the outside.

Rough ER has ribosome granules on its outer surface.

Functions of ER

1. It is the framework that supports cell.

2. Conduction of proteins.

3. Toxins that have entered the body through food, air, and water are made water-soluble by the ER and then flushed out of the body.

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🚐 Golgi Complex:

Functions

1. The Golgi complex is the secretory organ of the cell.

2. It modifies, sorts and packs materials synthesized in the cell (enzymes, mucus, proteins, pigments, etc.) and dispatches them to various targets like plasma membrane, lysosomes, etc.

3. It produces vacuoles and secretory vesicles.

4. It helps in the formation of cell walls, plasma membranes, and lysosomes.

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🚡 Lysosomes:

Due to various metabolic activities in the cell, organic waste is generated. Lysosomes digest the waste.

Lysosomes are simple, single membrane-bound sacs filled with digestive enzymes.

Functions

1. Immune system—It destroys viruses and bacteria that

attack the cell.

2. Demolition squads—It destroys worn-out cellular organelles and organic debris (autolysis).

3. Suicide Bags—When a cell becomes old or is damaged, lysosomes burst, and enzymes digest their own cells.

4. During starvation, lysosomes digest stored proteins and fats.

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🎻 Mitochondria:

The outer membrane of mitochondria is porous, and the inner membrane is deeply folded. These folds are called ‘cristae.’ The inner cavity is filled with a proteinaceous gel-like matrix containing ribosomes, phosphate granules, and DNA. Therefore, it can produce its own proteins. 

With the help of enzymes, mitochondria oxidize carbohydrates and fats in the cell. The energy released in this process is stored in the mitochondria in the form of ATP (adenosine triphosphate). 

Plant cells have fewer mitochondria than animal cells.

Functions

1. To produce an energy-rich compound—ATP.

2. Synthesis of proteins, carbohydrates, lipids, etc. by using the energy in ATP.

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🎺 Vacuoles:

Vacuoles are the storage sacs for solid or liquid contents.

They don’t have any typical shape or size. 

The structure of the vacuole changes according to the need of the cell. 

A vacuole is bound by a single membrane.

Functions

1. To maintain the osmotic pressure of the cell.

2. To store metabolic byproducts and end products. (Glycogen, proteins, water, etc.).

3. In animal cells, they store waste products and food, while in amoebas, they store food before digestion.

4. In plant cells, vacuoles are full of cell sap and provide turgidity and rigidity to them.

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🎹 Plastids: 

Why are plant leaves green and flowers red, yellow, orange, or blue? The organelle

which gives such colours is present only in the plant cells—it is called plastid. 

Plastids have double membrane and are of two types

1. Leucoplasts—White or colourless plastids

2. Chromoplasts - Coloured plastids Chloroplasts can get converted into other types of chromoplasts. E.g., raw green tomatoes turn red due to the breakdown of chlorophyll and synthesis of lycopene.

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Colour of the plant part            Pigment              

Green (e.g., leaves)                  Chlorophyll

Orange (ex. Carrot)                 Carotene

Yellow                                       Xanthophyll

                                               

Purple, blue                            Anthocyanin

Dark pink (e.g., beet)            Betalains

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🎸  Chloroplast:

• Chloroplasts are important for the photosynthesis process that takes place in the leaves. 
• Chlorophyll in chloroplast traps solar energy and converts it to chemical energy.
• Stroma in the chloroplast contains enzymes, DNA, ribosomes, and carbohydrates that are necessary for photosynthesis.

Functions:

1. Chloroplasts convert solar energy to chemical energy (food).

2. Chromoplasts give different colours to flowers and fruits.

3. Leucoplasts are involved in the synthesis and storage of food like starch, oils, and proteins.

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🎷 Mitochondria and plastids can produce proteins as well as replicate themselves, as they

have their own DNA and ribosomes.

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Difference between Eukaryotic Cell and Prokaryotic Cell:

🎾 Eukaryotic cell 

1.  Size—5-100 micrometer
2.  Number of chromosomes—more than one
3.  Nucleus—with nuclear membrane, nucleolus and nucleoplasm
4.  Mitochondria and plastids—present
5.  Examples—Present in highly evolved unicellular and multicellular plants and animals.

🏀 Prokaryotic cell:

1.  1-10 micrometer.
2.  Only one.
3.  Nucleoid resembling nucleus
4.  They don’t have membrane-bound cell organelles
5.  Bacteria

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