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Organisation of the Organism - Cell structure and organisation

Grade 12IGCSEBiology

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

🔑Concepts

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Cell Membrane and Wall: The cell membrane controls the entry and exit of substances. Plant cells possess a cell wall made of cellulose (C6H10O5)n(C_6H_{10}O_5)_n, providing structural support.

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The Nucleus: Acts as the control center, containing DNADNA organized into chromosomes. It governs cell division and protein synthesis.

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Cytoplasm and Organelles: The cytoplasm is a jelly-like substance where metabolic reactions occur. Key organelles include Mitochondria for aerobic respiration: C6H12O6+6O2→6CO2+6H2O+EnergyC_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + Energy.

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Ribosomes and RER: Ribosomes are the site of protein synthesis. Rough Endoplasmic Reticulum (RER) transports proteins synthesized by the attached ribosomes.

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Chloroplasts: Found in photosynthetic plant cells, they contain chlorophyll to catalyze: 6CO2+6H2O→lightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6 + 6O_2.

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Vacuoles: Plant cells have a large permanent vacuole containing cell sap to maintain turgor pressure (P = rac{F}{A}). Animal cells have small, temporary vacuoles.

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Specialized Cells: Adaptation to function. E.g., Root hair cells increase surface area for osmosis; Red blood cells lack a nucleus to maximize HbHb (hemoglobin) for O2O_2 transport.

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Levels of Organization: Cells →\rightarrow Tissues →\rightarrow Organs →\rightarrow Organ Systems →\rightarrow Organism.

📐Formulae

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

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

1 mm=103 μm=106 nm1\ mm = 10^3\ \mu m = 10^6\ nm

💡Examples

Problem 1:

A micrograph shows a plant cell with an image length of 80 mm80\ mm. If the actual length of the cell is 200 μm200\ \mu m, calculate the magnification.

Solution:

M=80,000 μm200 μm=400×M = \frac{80,000\ \mu m}{200\ \mu m} = 400\times

Explanation:

To calculate magnification, units must be consistent. Convert 80 mm80\ mm to μm\mu m by multiplying by 10001000 (80×1000=80,000 μm80 \times 1000 = 80,000\ \mu m). Then use M=IAM = \frac{I}{A}.

Problem 2:

The diameter of a nucleus in a drawing is 15 mm15\ mm. The magnification is 1500×1500\times. Find the actual diameter in μm\mu m.

Solution:

A=15,000 μm1500=10 μmA = \frac{15,000\ \mu m}{1500} = 10\ \mu m

Explanation:

Convert image size to micrometers: 15 mm=15,000 μm15\ mm = 15,000\ \mu m. Divide by magnification: 15,000/1500=1015,000 / 1500 = 10. The actual size is 10 μm10\ \mu m.

Cell structure and organisation - Revision Notes & Key Diagrams | IGCSE Grade 12 Biology