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Life Processes in Plants - Transport of food

Grade 7CBSE

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

🔑Concepts

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Translocation is the biological process by which the food (organic solutes like sucrose) manufactured in the leaves is transported to other parts of the plant through a specialized vascular tissue called Phloem.

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The phloem consists of sieve tubes and companion cells which work together to facilitate the movement of nutrients.

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Unlike the transport of water in xylem (which is unidirectional), the transport of food in phloem is bi-directional, meaning it can move both upwards (to developing buds/fruits) and downwards (to roots).

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Translocation is an active process that requires energy in the form of ATPATP (Adenosine Triphosphate).

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The movement occurs due to osmotic pressure. When sucrose is loaded into the phloem using ATPATP, the water concentration inside the phloem decreases. Water then moves from the xylem into the phloem via osmosis, creating high pressure that pushes the sap to areas of lower pressure (the 'sink').

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The 'source' is the part of the plant that produces or releases food (e.g., leaves), while the 'sink' is the part that needs or stores it (e.g., roots, fruits, growing tips).

📐Formulae

6CO2+6H2O→Sunlight, ChlorophyllC6H12O6+6O26CO_2 + 6H_2O \xrightarrow{\text{Sunlight, Chlorophyll}} C_6H_{12}O_6 + 6O_2

Sucrose=C12H22O11\text{Sucrose} = C_{12}H_{22}O_{11}

Osmotic Pressure∝Concentration of Solute\text{Osmotic Pressure} \propto \text{Concentration of Solute}

💡Examples

Problem 1:

Explain the role of ATPATP in the transport of food in a plant where the concentration of sucrose in the sieve tube is higher than in the surrounding leaf cells.

Solution:

The plant uses ATPATP to actively transport sucrose against the concentration gradient.

Explanation:

To move food from the leaf (source) into the phloem where the concentration is already high, the plant must perform 'active transport'. This requires energy in the form of ATPATP molecules to load the sucrose into the sieve tubes.

Problem 2:

During the spring season, sugar stored in the root or stem tissue of a plant is transported to the buds. Identify the 'source' and 'sink' in this scenario.

Solution:

Source: Roots/Stem; Sink: Buds.

Explanation:

In spring, the buds need energy to grow but cannot yet perform photosynthesis. Therefore, the stored sugars move from the roots (acting as the source) to the growing buds (acting as the sink) through the phloem.

Problem 3:

A scientist measures the pressure in the phloem near the leaf and finds it to be higher than the pressure near the root. Calculate the pressure difference if the leaf pressure is 15 units15 \text{ units} and the root pressure is 4 units4 \text{ units}.

Solution:

15−411\begin{array}{r} 15 \\ - 4 \\ \hline 11 \end{array} units.

Explanation:

The pressure gradient is what drives the bulk flow of food. The difference in pressure (11 units11 \text{ units}) ensures that the food moves from the high-pressure area (leaf) to the low-pressure area (root).