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Organization of the Organism - Cell structure and organisation

Grade 11IGCSEBiology

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

🔑Concepts

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Cell structures found in both plant and animal cells include the cell membrane, cytoplasm, nucleus, ribosomes, and mitochondria. The cell membrane controls the entry and exit of substances, while the nucleus contains the genetic material (DNADNA).

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Plant cells possess additional structures: a cell wall made of cellulose for structural support, chloroplasts containing chlorophyll for photosynthesis, and a large permanent vacuole containing cell sap.

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The mitochondria are the site of aerobic respiration. The overall equation for aerobic respiration is: C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O.

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Specialized cells are adapted for specific functions: Red blood cells lack a nucleus to transport more oxygen via hemoglobin; Root hair cells have long extensions to increase the surface area (SASA) for water absorption; Xylem vessels are lignified for support and water transport.

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Levels of organization: Cells →\rightarrow Tissues →\rightarrow Organs →\rightarrow Organ Systems →\rightarrow Organism. A tissue is a group of cells with similar structures working together to perform a shared function.

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Microscopy units: Biology often requires conversion between millimeters (mmmm) and micrometers (μm\mu m). 1 mm=1000 μm1\text{ mm} = 1000\text{ }\mu m, or 1 mm=103 μm1\text{ mm} = 10^3\text{ }\mu m.

📐Formulae

Magnification=Measured Size of ImageActual Size of ObjectMagnification = \frac{\text{Measured Size of Image}}{\text{Actual Size of Object}}

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

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

💡Examples

Problem 1:

An image of a plant cell in a textbook measures 45 mm45\text{ mm} in length. The actual size of the cell is 0.15 mm0.15\text{ mm}. Calculate the magnification of the image.

Solution:

Magnification=45 mm0.15 mm=300×Magnification = \frac{45\text{ mm}}{0.15\text{ mm}} = 300\times

Explanation:

Using the magnification formula M=I/AM = I/A, we divide the image size by the actual size. Since both units are in mmmm, no initial conversion is required.

Problem 2:

A bacterial cell has an actual length of 2 μm2\text{ }\mu m. If it is viewed under a microscope with a magnification of 5000×5000\times, what is the size of the image in mmmm?

Solution:

Image Size=2 μm×5000=10000 μm\text{Image Size} = 2\text{ }\mu m \times 5000 = 10000\text{ }\mu m Image Size in mm=100001000=10 mm\text{Image Size in mm} = \frac{10000}{1000} = 10\text{ mm}

Explanation:

First, calculate the image size in micrometers using I=A×MI = A \times M. Then, convert the result from μm\mu m to mmmm by dividing by 10001000.

Cell structure and organisation - Revision Notes & Key Diagrams | IGCSE Grade 11 Biology