8th, Science, Notes, 10.1 Cell and Cell Organelles

 8th, Science, Notes, 

10.1  Cell and Cell Organelles 

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              आपल्या विज्ञान विषयाच्या माहितीसाठी खालील 👇लिंकला स्पर्श करा.

माहिती विज्ञानाची 🎷

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1. How many types of cells are found in living organisms?

Ans: Prokaryotic and eukaryotic these are the two types of cells. Plant cell and animal cell these are sub-types of cells.

2. Which instrument had you used to observe cells?

Ans: Compound microscope is used for the study of cell.

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 🎻 Difference between plant cell and animal cell. 

🏈  Animal cell 

1. Cell membrane Present 
2. Cell wall absence 
3. lysosome Present 
4. Plastids absence 
5. Endoplasmic reticulum Present 
6. Vacuoles many and small 
7. Golgi complex Present 
8. Mitochondria present 

🎺  Plant cell

1. Cell membrane Present
2. Cell wall Present
3. lysosome Absent
4. Plastids Present
5. Endoplasmic reticulum Present 
6. Only one vacuole, and in the center.
7. Golgi complex Present 
8. Mitochondria present 

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🏉  Components of a cell

1. Cell wall: 

Cell walls are found around cells of algae, fungi, and plants. 

Animal cells lack a cell wall.

The cell wall is an elastic and strong coat around the cell membrane. 

Composition: The cell wall is mainly composed of carbohydrates like cellulose and pectin. Afterwards, polymers like lignin, suberin, and cutin are added to the cell wall as needed. 

The function of the cell wall is to support and to protect the cell by preventing entry of excess water into the cell.

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2. Plasma membrane/cell membrane: 
It is a thin, fragile, and elastic covering that separates the cell components from the outer environment.
Structure of plasma membrane—
Protein molecules are embedded in two layers of phospholipids.
The plasma membrane is said to be a selectively permeable membrane, as it allows some substances to enter the cell while preventing other substances.
Due to this property, useful molecules of water, salt and oxygen enter the cell and
CO₂ exits the cell.

Homeostasis: If any changes occur outside the cell, the cellular environment does not change due to the plasma membrane. This condition is called homeostasis.

How do substances travel in the cell?

Activities that consume cellular energy

1. Endocytosis—

To gulp/engulf food and other substances from the outer environment.

2. Exocytosis—

To excrete waste materials out of the cell.

🏀 Processes those that don’t consume cellular energy

1. Diffusion—

Entry or exit of small molecules like O₂, CO₂

2. Osmosis—

The travelling of water from a part with more water to a part with less water, through a selectively permeable membrane, is osmosis. 

Osmosis is a physical process.

a. Isotonic solution—

The medium outside and inside the cell has the same proportion of water. doesn’t go in or out.

b. Hypotonic solution—

The cell has less water than the outside medium, so water enters the cell. This is called endomosis. 

E.g., if raisins are kept in water, after some time they swell and become turgid.

c. Hypertonic solution -

If a cell has more water than the outside medium, then water comes out of the cell.

E.g., fruit pieces are kept in a thick saturated sugar solution; the water from the fruit pieces enters the sugar solution. So the fruit pieces shrink after a while. If a plant cell or animal cell is kept in a hypertonic solution, water comes out of the cell by the process of exosmosis, and there is contraction of cytoplasm. This process is called plasmolysis.

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3. Cytoplasm -

1. Cytoplasm is the fluid between the plasma membrane and the nucleus. 
2. Cytoplasm is a moving, sticky substance. 
3. Many cell organelles are suspended in cytoplasm. 
4. Cytoplasm is the medium for cellular chemical reactions. 
5.  Part of the cytoplasm other than organelles is the cytosol.
6. Cytosol stores vital substances like amino acids, glucose, vitamins, etc. 
7. In animal cells, cytoplasm is more granular and dense, while in plant cells, it is thin and mostly pushed to the periphery due to a larger central vacuole.

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🎹 Cell organelles : 

• An organelle is a specialized subunit having a specific function within the cell. 
• They are ‘organs of the cell.’
• Each organelle has its own lipoprotein membrane. 
• Except for the nucleus and chloroplast, all other organelles can be seen only with an electron microscope.

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       🎸  Nucleus 

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The nucleus is covered by a double-layered membrane with small pores. These pores allow

the passage of material in and out of the nucleus.

The nucleus has one round nucleolus and a network of chromatin fibers. Chromatin fibers are thin, thread-like structures, which condense to form short, thick chromosomes at the time of cell division. 

Functional segments on chromosomes are called genes.

Functions of nucleus

1. The Nucleus controls all metabolic activities of the cell and also the cell division.

2. It is involved in the transmission of hereditary characters from parents to offspring.

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🎷 Do you know?

Due to loss of nucleus, large quantity of haemoglobin can be accomodated in the RBC

and thereby a large amount of oxygen can be transported.

• Due to the loss of the nucleus of sieve tubes of the plant phloem, they become hollow, and thereby transportation of food becomes easy.

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✨ टीप:- या पाठात काही शब्दांना गुगल लिंक आहे त्यांना स्पर्श केल्यास त्या शब्दांची जास्तीची माहिती आपणास मिळेल.

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