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Movement in and out of Cells - Active transport

Grade 12A LevelBiology

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

🔑Concepts

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Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient) using energy from respiration.

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The process requires specific carrier proteins embedded in the cell membrane that act as 'pumps'.

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Energy for active transport is provided in the form of Adenosine Triphosphate (ATPATP), which is produced during aerobic respiration in the mitochondria.

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Unlike diffusion and osmosis, active transport is an active process and will stop if the cell is deprived of oxygen or treated with respiratory inhibitors (e.g., cyanide).

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In plants, active transport is used by root hair cells to absorb mineral ions such as nitrates (NO3−NO_3^-) and magnesium (Mg2+Mg^{2+}) from the soil where they are in low concentration.

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In humans, active transport is essential for the absorption of glucose from the lumen of the small intestine (ileum) into the blood, and for the reabsorption of glucose in the kidney tubules.

📐Formulae

ATP+H2O→ADP+Pi+EnergyATP + H_2O \rightarrow ADP + P_i + \text{Energy}

Rate of Active Transport∝Rate of Respiration\text{Rate of Active Transport} \propto \text{Rate of Respiration}

ΔC=Cinternal−Cexternal\Delta C = C_{\text{internal}} - C_{\text{external}} (where transport occurs against this gradient)

💡Examples

Problem 1:

A scientist treats a root hair cell with a chemical that inhibits the production of ATPATP. Predict and explain the effect on the uptake of K+K^+ ions if the soil concentration is 2 mmol/dm32 \text{ mmol/dm}^3 and the cell sap concentration is 25 mmol/dm325 \text{ mmol/dm}^3.

Solution:

The uptake of K+K^+ ions will cease almost immediately.

Explanation:

Because the concentration of K+K^+ is higher inside the cell (25 mmol/dm325 \text{ mmol/dm}^3) than outside (2 mmol/dm32 \text{ mmol/dm}^3), the ions must move against the concentration gradient. This requires active transport, which is dependent on ATPATP. Without ATPATP, the carrier proteins cannot pump the ions into the cell.

Problem 2:

Explain how glucose is absorbed into the bloodstream from the small intestine even when its concentration in the gut is very low.

Solution:

Glucose molecules bind to specific carrier proteins in the cell membrane of the epithelial cells and are moved into the cell using energy from ATPATP.

Explanation:

Even when a concentration gradient exists such that [Glucose]blood>[Glucose]gut[Glucose]_{\text{blood}} > [Glucose]_{\text{gut}}, active transport ensures that all available glucose is absorbed to prevent the loss of nutrients in feces.