If the Casparian strip blocks the apoplast at the endodermis, why bother with the apoplast pathway at all?
Sara Fernandes11th Sample
28 Aug 2026 Β· 1 min read
I was revising after football practice today (muddy knees and all) and got stuck on water uptake by roots, which I thought was an easy chapter.
NCERT: water moves in the root by two pathways, the apoplast (through the cell walls and intercellular spaces, without crossing any membrane) and the symplast (through the cytoplasm, connected by plasmodesmata, crossing the membrane once at entry). Then comes the endodermis, whose walls have the Casparian strip made of suberin, which is impermeable to water.
So if the strip blocks the apoplast, what's the point of the apoplast pathway? Does water just stop there? And how does the strip help the plant?
Second doubt: root pressure and guttation. I know that guttation is the loss of water in liquid form from the margins of leaves, early morning, and root pressure is the positive pressure developed in the xylem by active uptake of ions. But then what does NCERT mean when it says that root pressure can't be the main force for tall trees? What is the main force?
My notes on this are a bit chaotic, since my guitar teacher keeps asking me to practise (separate life crisis). Short and clear answers please π
7 answers & replies
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[+][β]Meera Patel11thSampleΒ· 1mo ago
Water doesn't stop. In the root cortex, apoplast carries most of the water because there's less resistance. When the water reaches the endodermis, the Casparian strip blocks the cell walls, so water has to enter the endodermal cell's protoplast, crossing the plasma membrane, and then it continues via the symplast into the stele.
Why that's useful: the membrane is selective. The plant now controls which minerals and how much water enter the xylem. Think of the Casparian strip as a security gate that forces everyone to show ID (the membrane). It also stops things from leaking back out.
[+][β]Sara Fernandes11thSampleΒ· 1mo agoAuthor
Security gate, I love that. I can see it now. Thanks everyone!
[+][β]Zoya Khan12thSampleΒ· 1mo ago
Guttation vs transpiration is a favourite one. Guttation = liquid water (it contains some dissolved salts) coming out through hydathodes at leaf edges, typically at night or early morning, when soil water is high, transpiration is low (high humidity) and root pressure is high. Transpiration = loss of water as vapour, mainly through stomata. Dew on a leaf is not guttation, it's condensation from air.
[+][β]Harsh Gupta12thSampleΒ· 1mo ago
Guttation is when the plant is crying because it also has board exams, I read. Anyway Sara love the football π
[+][β]Pooja Iyer12thSampleΒ· 1mo ago
Main force in tall trees: transpiration pull, working with cohesion (water molecules stick to each other) and adhesion (water sticks to the xylem walls), which keeps the water column continuous. Root pressure can only push water up a small distance, plus in many plants (especially tall trees) it's absent or very low during the day when transpiration is fast. NCERT mentions that root pressure is "not the main driver" of ascent of sap in tall trees. Cohesion-tension (transpiration pull) is the accepted explanation.
[+][β]Lakshmi TripathiDropperSampleΒ· 1mo ago
Is guttation caused by transpiration at night through open stomata? I thought stomata open at night in some plants.
[+][β]Kavya NaikDropperSampleΒ· 1mo ago
Lakshmi, no. Guttation isn't through stomata, it's through hydathodes, and it's liquid water, which is pushed out because of root pressure. Transpiration is vapour. Some plants like CAM plants open stomata at night, but that's for CO2 uptake and not related to guttation. One-line version: guttation = root pressure + hydathodes + liquid.
