(a) Differentiate between Active Absorption and Passive Absorption.

**OR**

(b) Explain the Photosynthetic Carbon Reduction Cycle.

Question

(a) Differentiate between Active Absorption and Passive Absorption.

**OR**

(b) Explain the Photosynthetic Carbon Reduction Cycle.

Accepted Answer

>

> [!TLDR]
> Active absorption is a metabolically driven, energy-requiring uptake process; passive absorption is a purely physical process driven by transpirational pull, requiring no metabolic energy from the root.
>
> | Feature | Active Absorption | Passive Absorption |
> |---|---|---|
> | Energy requirement | Requires metabolic energy (ATP) generated by root cell respiration | Does not require metabolic energy from the root; driven by a physical force |
> | Driving force | Active, energy-dependent transport processes in living root cells | Transpiration pull created by water evaporating from leaf mesophyll cells, pulling a continuous water column up through the xylem (the cohesion-tension mechanism) |
> | Direction relative to gradient | Can move water/ions against a concentration/water-potential gradient | Moves along the gradient created by transpiration (from high to low water potential) |
> | Role of the root | The root is an active, living participant, doing metabolic work | The root acts largely as a passive pathway/conduit; living root cells are not the driving force |
> | Effect of metabolic inhibitors | Significantly reduced or stopped by respiratory inhibitors (e.g. cyanide), low oxygen, or low temperature, since it depends on respiration | Largely unaffected by metabolic inhibitors, since it does not depend on root metabolism |
> | When dominant | More significant in slowly transpiring or non-transpiring plants (e.g. at night, or in plants in humid/dark conditions) | Dominant in actively, rapidly transpiring plants (e.g. during a hot, sunny day) — accounts for the great majority of total water absorbed |
> …

Q.(a) Differentiate between Active Absorption and Passive Absorption. OR

Concept understanding — Active and Passive Absorption of Water

Feature	Active Absorption	Passive Absorption
Energy requirement	Requires metabolic energy (ATP) generated by root cell respiration	Does not require metabolic energy from the root; driven by a physical force
Driving force	Active, energy-dependent transport processes in living root cells	Transpiration pull created by water evaporating from leaf mesophyll cells, pulling a continuous water column up through the xylem (the cohesion-tension mechanism)
Direction relative to gradient	Can move water/ions against a concentration/water-potential gradient	Moves along the gradient created by transpiration (from high to low water potential)
Role of the root	The root is an active, living participant, doing metabolic work	The root acts largely as a passive pathway/conduit; living root cells are not the driving force
Effect of metabolic inhibitors	Significantly reduced or stopped by respiratory inhibitors (e.g. cyanide), low oxygen, or low temperature, since it depends on respiration	Largely unaffected by metabolic inhibitors, since it does not depend on root metabolism
When dominant	More significant in slowly transpiring or non-transpiring plants (e.g. at night, or in plants in humid/dark conditions)	Dominant in actively, rapidly transpiring plants (e.g. during a hot, sunny day) — accounts for the great majority of total water absorbed
…

Q.(a) Differentiate between Active Absorption and Passive Absorption. OR

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