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Biology - Organization of the organism (Cell structure and organization)

Grade 9IGCSE

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

🔑Concepts

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Cell Structures: All living organisms are made of cells. Eukaryotic cells (plant and animal) contain a nucleus and membrane-bound organelles, while prokaryotic cells (bacteria) lack a nucleus and have free-floating DNA in a circular chromosome or plasmids.

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Organelles: The nucleus contains genetic material (DNA); cytoplasm is where chemical reactions occur; the cell membrane controls the entry and exit of substances; ribosomes are the site of protein synthesis; and mitochondria are the site of aerobic respiration where energy is released as ATPATP via the reaction C6H12O6+6O2→6CO2+6H2OC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O.

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Plant-Specific Features: Plant cells possess a cell wall made of cellulose for support, chloroplasts containing chlorophyll for photosynthesis (6CO2+6H2O→C6H12O6+6O26CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2), and a large permanent vacuole containing cell sap.

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Specialized Cells: Cells are adapted for specific functions. Examples include: Root hair cells (large surface area for water uptake), Xylem vessels (lignified walls for support and water transport), and Red blood cells (contain hemoglobin to carry O2O_2 and have no nucleus to maximize space).

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Levels of Organization: The hierarchy of biological complexity is: Cells →\rightarrow Tissues (groups of similar cells) →\rightarrow Organs (groups of tissues working together) →\rightarrow Organ systems →\rightarrow Organism.

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Unit Conversion: In microscopy, units must be consistent. 1 mm=103 μm1\text{ mm} = 10^3\text{ }\mu\text{m} and 1 μm=103 nm1\text{ }\mu\text{m} = 10^3\text{ nm}.

📐Formulae

Magnification(M)=Image size (I)Actual size (A)Magnification (M) = \frac{\text{Image size (I)}}{\text{Actual size (A)}}

Actual size (A)=Image size (I)Magnification (M)\text{Actual size (A)} = \frac{\text{Image size (I)}}{\text{Magnification (M)}}

1 mm=1000 μm1\text{ mm} = 1000\text{ }\mu\text{m}

💡Examples

Problem 1:

A micrograph of a plant cell shows a chloroplast that measures 15 mm15\text{ mm} in length. If the actual size of the chloroplast is 5 μm5\text{ }\mu\text{m}, calculate the magnification of the image.

Solution:

M=15×1000 μm5 μm=3000×M = \frac{15 \times 1000\text{ }\mu\text{m}}{5\text{ }\mu\text{m}} = 3000\times

Explanation:

First, convert the image size from millimeters to micrometers so the units match: 15 mm×1000=15000 μm15\text{ mm} \times 1000 = 15000\text{ }\mu\text{m}. Then, divide the image size by the actual size to find the magnification.

Problem 2:

A student views a red blood cell under a microscope with a magnification of 400×400\times. The image diameter is 2.8 mm2.8\text{ mm}. Calculate the actual diameter of the cell in μm\mu\text{m}.

Solution:

A=2.8×1000400=7 μmA = \frac{2.8 \times 1000}{400} = 7\text{ }\mu\text{m}

Explanation:

Convert the image size to micrometers: 2.8 mm=2800 μm2.8\text{ mm} = 2800\text{ }\mu\text{m}. Use the formula A=I/MA = I / M to find the actual size: 2800/400=7 μm2800 / 400 = 7\text{ }\mu\text{m}.

Organization of the organism (Cell structure and organization) Revision - Grade 9 Science IGCSE