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The Fundamental Unit of Life - Cell Organelles (ER, Golgi, Mitochondria, Plastids, Vacuoles)

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Endoplasmic Reticulum (ER): A large network of membrane-bound tubes and sheets. Rough ER (RER) has ribosomes attached for protein synthesis, while Smooth ER (SER) is responsible for lipid/fat molecule synthesis and detoxification of poisons and drugs.

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Golgi Apparatus: A system of membrane-bound vesicles arranged parallel to each other in stacks called cisterns. Its functions include the storage, modification, and packaging of products in vesicles, and the formation of lysosomes.

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Mitochondria: Known as the 'Powerhouse of the cell.' They have two membrane coverings: the outer is porous while the inner is deeply folded to increase surface area for ATPATP (Adenosine Triphosphate) generating chemical reactions. They contain their own DNADNA and ribosomes.

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Plastids: Found only in plant cells. Two types: Chromoplasts (colored, e.g., Chloroplasts containing chlorophyll for photosynthesis) and Leucoplasts (white or colorless for storing starch, oils, and protein granules). Like mitochondria, they have their own DNADNA and ribosomes.

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Vacuoles: Storage sacs for solid or liquid contents. In plant cells, they are very large (occupying 50−90%50-90\% of cell volume) and provide turgidity and rigidity by remaining full of cell sap.

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Membrane Biogenesis: The process where proteins and lipids synthesized in the ERER are used to build the cell membrane.

📐Formulae

Cellular Respiration (Mitochondria):C6H12O6+6O2→6CO2+6H2O+Energy (ATP)\text{Cellular Respiration (Mitochondria)}: C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

Photosynthesis (Chloroplasts):6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O2\text{Photosynthesis (Chloroplasts)}: 6CO_2 + 6H_2O \xrightarrow[Chlorophyll]{Sunlight} C_6H_{12}O_6 + 6O_2

Surface Area to Volume Ratio∝1Size of Cell\text{Surface Area to Volume Ratio} \propto \frac{1}{\text{Size of Cell}}

💡Examples

Problem 1:

Why is the inner membrane of the mitochondria deeply folded?

Solution:

The inner membrane is folded into finger-like projections called cristae to increase the surface area available for ATPATP (Adenosine Triphosphate) generating chemical reactions.

Explanation:

A larger surface area allows for more enzymes and respiratory chain components to be packed into the organelle, increasing the efficiency of energy production.

Problem 2:

What would happen to the life of a cell if there was no Golgi apparatus?

Solution:

Without the Golgi apparatus, the material synthesized near the ERER would not be packaged, modified, or dispatched to various targets inside and outside the cell.

Explanation:

The Golgi apparatus acts as a 'post office'; its absence would prevent the formation of lysosomes and the delivery of proteins and lipids required for cell maintenance.

Problem 3:

Identify the organelle that provides turgidity to a plant cell and name the substance filling it.

Solution:

The organelle is the Vacuole, and it is filled with 'cell sap'.

Explanation:

In plants, the large central vacuole exerts pressure against the cell wall, maintaining the cell's shape and structural integrity.