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Mycorrhizae and Symbiotic Root Associations

Biology · Organisms and Populations · NEET

Mycorrhizae (singular: mycorrhiza) are a mutualistic (+/+) association between a fungus and the roots of a higher plant. The fungus helps the plant absorb nutrients (mainly phosphorus) from the soil, and the plant gives the fungus energy-rich carbohydrates. Memory hook: "MY-corrhiza = MY fungus lives on MY root, and we both win."
Mycorrhiza: Fungus + Plant Root Mutualism (+/+)PLANT(higher plantroot)FUNGUS(e.g. Glomus)hyphae insoilcarbohydrates (food) →← phosphorus / nutrientsBoth partners benefit → Mutualism (+/+)
Mycorrhiza is a two-way exchange: the plant root sends carbohydrates to the fungus, and the fungus sends soil phosphorus and other nutrients back to the plant. Because both gain, the sign convention is (+/+), i.e. mutualism.

Your doubts, answered

Is mycorrhiza mutualism, commensalism or parasitism?

It is mutualism (+/+). Both partners benefit: the fungus gets carbohydrates (food) from the plant, and the plant gets soil nutrients from the fungus. It is NOT commensalism (that is +/0, only one benefits) and NOT parasitism (that is +/-, one is harmed). NEET 2017 asked this exact word: 'Mycorrhizae are the example of' and the answer is Mutualism.

What is the difference between mycorrhiza and lichen?

Both are mutualism, but the partners differ. Mycorrhiza = fungus + roots of a higher plant. Lichen = fungus + an alga (or cyanobacteria). A quick trick: lichen has NO higher plant and NO roots; mycorrhiza always involves plant ROOTS. NEET loves to swap these two in match-the-column questions.

Exactly who gives what in mycorrhiza?

The FUNGUS absorbs mineral nutrients from the soil (mainly phosphorus) and passes them to the plant. The PLANT, in return, supplies the fungus with energy-yielding carbohydrates made by photosynthesis. Remember the direction: nutrients flow fungus to plant, carbohydrates flow plant to fungus.

Why can Pinus not grow without mycorrhiza?

Pinus has an obligate (compulsory) association with mycorrhizae. Its seeds cannot germinate and establish without the fungal partner, because the fungus supplies phosphorus and helps the seedling take up nutrients. This is a favourite NEET example of an obligate mutualism.

Which genus of fungi commonly forms mycorrhiza?

Many members of the genus Glomus form mycorrhiza (from NCERT Biology, Microbes in Human Welfare). The fungal symbiont absorbs phosphorus from the soil and passes it to the plant. Extra benefits: resistance to root pathogens, tolerance to salinity and drought, and overall better plant growth.

⚠️ The NEET trap
✗ Marking mycorrhiza as commensalism because 'the fungus just lives on the root'.
✓ Mycorrhiza is mutualism (+/+). Both benefit: fungus gives nutrients, plant gives carbohydrates.
🧠 If BOTH partners get something, it can never be commensalism (+/0). Ask 'does the plant also gain?' Yes it does, so tick mutualism.

Real NEET questions

NEET 2017

Mycorrhizae are the example of

A · Fungistasis
B · Amensalism
C · Antibiosis
D · Mutualism ✓
Solution: Mycorrhizae are associations between fungi and the roots of higher plants. The fungi help the plant absorb essential nutrients (mainly phosphorus) from the soil, while the plant supplies the fungi with energy-yielding carbohydrates. Both partners benefit, so this is mutualism (+/+). NCERT Ch 11, p.201.
NEET 2023 Phase 1

Match List I with List II: List I (Interacting species) A. A Leopard and a Lion in a forest/grassland B. A Cuckoo laying egg in a Crow's nest C. Fungi and root of a higher plant in Mycorrhizae D. A cattle egret and a Cattle in a field List II (Name of Interaction) I. Competition II. Brood parasitism III. Mutualism IV. Commensalism Choose the correct answer:

A · A-I, B-II, C-III, D-IV ✓
B · A-I, B-II, C-IV, D-III
C · A-III, B-IV, C-I, D-II
D · A-II, B-III, C-I, D-IV
Solution: Leopard and Lion compete for the same prey -> Competition (I). Cuckoo laying egg in a crow's nest -> Brood parasitism (II). Fungi and root of a higher plant in Mycorrhizae -> both benefit -> Mutualism (III). Cattle egret and cattle -> egret benefits, cattle unaffected -> Commensalism (IV). So A-I, B-II, C-III, D-IV.

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Frequently asked

What is a mycorrhiza in one line?

A mutualistic association between a fungus and the roots of a higher plant, where the fungus supplies soil nutrients and the plant supplies carbohydrates.

What sign convention does mycorrhiza get in NEET?

(+/+), the same as mutualism, because both species benefit.

Which mineral does the mycorrhizal fungus mainly supply?

Phosphorus. It absorbs phosphorus (and other minerals) from soil and passes it to the plant.

Is mycorrhiza the same as a lichen?

No. Both are mutualism, but mycorrhiza is fungus + plant roots, while a lichen is fungus + alga (or cyanobacteria). Lichen has no roots.

Give an obligate example of mycorrhiza.

Pinus. Its seeds cannot germinate and establish without the mycorrhizal fungus, making the association obligate.

Related concepts:
Mutualism (+/+): Definition and Examples (Lichens, Mycorrhizae)Population Interactions Overview: The +/-/0 Sign TablePlant-Animal Mutualism: Pollination, Fig-Fig Wasp RelationshipSolving 'Match the Population Interaction' Sign Questions (NEET Trick)What is an Ecological Niche?
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Organisms and Populations PYQs