BOT2603
Assignment 2
Semester 1
DUE: 9 APRIL 2026
, UNIVERSITY OF SOUTH AFRICA
UNISA
ASSIGNMENT ANSWERS
Plant Physiology - Mineral Nutrition & Transport
© UNISA 2026
Total Marks: 70
, QUESTION 1
1.1 Explanation of Terms
1.1.1 Essential Element
An essential element is a mineral nutrient that is indispensable for the normal growth,
development, and completion of the life cycle of a plant. Arnon and Stout (1939)
established three criteria that must ALL be met for a mineral to be classified as
essential:
• The plant cannot complete its life cycle in the absence of that element.
• The role of the element must be specific no other element can substitute for it
entirely.
• The element must be directly involved in the plant's metabolism (i.e., it functions
as a component of an essential metabolite or is required for a specific
biochemical or physiological process).
Essential elements are further subdivided into macronutrients (required in larger
quantities, e.g., N, P, K, Ca, Mg, S) and micronutrients or trace elements (required in
smaller quantities, e.g., Fe, Mn, Cu, Zn, Mo, B, Cl, Ni). The distinction is based on the
concentration at which they are required rather than their functional importance.
1.1.2 Carbon Partitioning
Carbon partitioning refers to the process by which fixed carbon (primarily as sucrose
or other assimilates) synthesised during photosynthesis in source organs (e.g., mature
leaves) is distributed and allocated to various sink organs (e.g., roots, developing
leaves, fruits, seeds, and meristems) within the plant. The term encompasses both the
regulation of carbon flow between source and sink tissues and the relative proportion
of assimilates directed to each sink.
Partitioning is regulated by source strength (the capacity of the source to supply
assimilates), sink strength (the capacity of the sink to attract and utilise assimilates),
and the phloem transport pathway connecting them. Ultimately, carbon partitioning
determines growth patterns, reproductive yield, and the plant's response to
environmental stress.
1.1.3 Sink Activity
Assignment 2
Semester 1
DUE: 9 APRIL 2026
, UNIVERSITY OF SOUTH AFRICA
UNISA
ASSIGNMENT ANSWERS
Plant Physiology - Mineral Nutrition & Transport
© UNISA 2026
Total Marks: 70
, QUESTION 1
1.1 Explanation of Terms
1.1.1 Essential Element
An essential element is a mineral nutrient that is indispensable for the normal growth,
development, and completion of the life cycle of a plant. Arnon and Stout (1939)
established three criteria that must ALL be met for a mineral to be classified as
essential:
• The plant cannot complete its life cycle in the absence of that element.
• The role of the element must be specific no other element can substitute for it
entirely.
• The element must be directly involved in the plant's metabolism (i.e., it functions
as a component of an essential metabolite or is required for a specific
biochemical or physiological process).
Essential elements are further subdivided into macronutrients (required in larger
quantities, e.g., N, P, K, Ca, Mg, S) and micronutrients or trace elements (required in
smaller quantities, e.g., Fe, Mn, Cu, Zn, Mo, B, Cl, Ni). The distinction is based on the
concentration at which they are required rather than their functional importance.
1.1.2 Carbon Partitioning
Carbon partitioning refers to the process by which fixed carbon (primarily as sucrose
or other assimilates) synthesised during photosynthesis in source organs (e.g., mature
leaves) is distributed and allocated to various sink organs (e.g., roots, developing
leaves, fruits, seeds, and meristems) within the plant. The term encompasses both the
regulation of carbon flow between source and sink tissues and the relative proportion
of assimilates directed to each sink.
Partitioning is regulated by source strength (the capacity of the source to supply
assimilates), sink strength (the capacity of the sink to attract and utilise assimilates),
and the phloem transport pathway connecting them. Ultimately, carbon partitioning
determines growth patterns, reproductive yield, and the plant's response to
environmental stress.
1.1.3 Sink Activity
