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Cell Biology - Organelles and their Functions

Grade 6IB

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

🔑Concepts

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The Cell Theory states that all living organisms are made of cells, and the cell is the basic unit of life.

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The Nucleus acts as the control center of the cell and contains genetic material in the form of DNADNA (Deoxyribonucleic acid).

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Mitochondria are known as the 'powerhouse' of the cell where aerobic respiration occurs to produce energy in the form of ATPATP.

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Chloroplasts are found only in plant cells and some protists; they contain chlorophyll and are the site of photosynthesis where C6H12O6C_6H_{12}O_6 (glucose) is produced.

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The Cell Membrane is a semi-permeable lipid bilayer that controls the movement of substances like H2OH_2O, O2O_2, and CO2CO_2 in and out of the cell.

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The Cell Wall is a rigid outer layer made of cellulose, providing structural support to plant cells; it is absent in animal cells.

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Ribosomes are small organelles responsible for protein synthesis.

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Vacuoles store nutrients and waste products. Plant cells typically have one large central vacuole that maintains turgor pressure using H2OH_2O.

📐Formulae

Total Magnification=Magnification of Eyepiece×Magnification of Objective Lens\text{Total Magnification} = \text{Magnification of Eyepiece} \times \text{Magnification of Objective Lens}

Actual Size=Image SizeMagnification\text{Actual Size} = \frac{\text{Image Size}}{\text{Magnification}}

6CO2+6H2O→light energyC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{light energy}} C_6H_{12}O_6 + 6O_2

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

💡Examples

Problem 1:

A student observes a plant cell under a microscope. The image size of a chloroplast is measured to be 5 mm5\text{ mm}, and the magnification used is 1000×1000\times. Calculate the actual size of the chloroplast in micrometers (μm\mu m).

Solution:

Actual Size=5 mm1000=0.005 mm=5μm\text{Actual Size} = \frac{5\text{ mm}}{1000} = 0.005\text{ mm} = 5\mu m

Explanation:

Using the magnification formula, we divide the image size by the magnification. Since 1 mm=1000μm1\text{ mm} = 1000\mu m, we convert the result to get the final answer in the correct unit.

Problem 2:

Identify which organelle would be most abundant in a muscle cell that requires a high amount of energy to function.

Solution:

The Mitochondria.

Explanation:

Mitochondria are responsible for cellular respiration, represented by the equation C6H12O6+6O2→6CO2+6H2O+ATPC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}. Since muscle cells require significant energy for contraction, they contain a higher density of mitochondria compared to other cells.