Which tissue carries water upward and is made of dead lignified cells?
Xylem
Which tissue carries sugar from source to sink and is made of living sieve tubes?
Phloem
What is the Casparian strip and its function?
A waterproof suberin band in the root endodermis that blocks the apoplast, forcing water through cell membranes for filtering.
Why does the root epidermis lack a cuticle?
A cuticle would block water absorption; roots need water to enter.
How is xylem arranged in a dicot root vs a dicot stem?
Root = central star; stem = ring of bundles (xylem inside each bundle, phloem outside).
Which mesophyll layer does most photosynthesis and why is it on top?
Palisade mesophyll; it is packed with chloroplasts near the light source at the top.
What is the role of spongy mesophyll?
Provides air spaces for CO₂ diffusion to photosynthetic cells.
What structures control gas exchange in the leaf and where are they mostly found?
Stomata with guard cells, mostly on the lower epidermis.
Name the three tissue systems of a plant.
Dermal, ground, and vascular tissue.
Which layer gives rise to lateral roots?
The pericycle.
Why are stem vascular bundles arranged in a peripheral ring?
Placing stiff tissue far from the centre resists bending (mechanical strength).
Recall Feynman: explain to a 12-year-old
A plant is like a house. The root is the basement with pipes going into the ground to suck up water — its walls have a special waterproof seal (Casparian strip) so dirty water can't just leak in; it must go through a "security door." The stem is the walls with pipes running up like a straw, arranged near the edges so the house doesn't bend over. The leaf is the solar-panel roof: the top is packed with green light-catchers (palisade), the bottom has tiny air-mouths (stomata) to breathe. Same pipes everywhere: one carries water up, one carries food down.
Dekho, poore plant mein sirf teen tissue systems hote hain — dermal (bahar ki skin), ground (packing/storage/photosynthesis), aur vascular (plumbing: xylem aur phloem). Root, stem aur leaf koi alag-alag magic nahi hain — yahi teen tissues alag-alag tareeke se arrange ho jaate hain, kyunki har organ ka kaam alag hai. Xylem paani ko upar le jaata hai (dead, lignified pipes), aur phloem sugar ko source se sink tak.
Root ka kaam paani absorb karna hai, isliye epidermis pe cuticle nahi hoti (warna paani andar nahi aata) aur root hairs banti hain surface badhane ke liye. Root mein xylem beech mein star shape mein hota hai — kyunki root ko kheencha jaata hai, aur central rope jaisi strength chahiye. Endodermis mein ek waterproof Casparian strip hoti hai jo apoplast route ko block karke paani ko cell membrane se guzarne par majboor karti hai — matlab ek security checkpoint.
Stem ko bend hone se bachna hota hai, isliye vascular bundles ek ring mein bahar ki taraf lagte hain (jaise bamboo strong hota hai). Har bundle mein xylem andar, phloem bahar. Leaf solar panel hai: upar palisade mesophyll (chloroplasts se bhara, kyunki light upar se aati hai), neeche spongy mesophyll (air spaces se CO₂ diffuse hota hai), aur neeche stomata gas exchange ke liye. Bas ek line yaad rakho: same parts, different blueprint, decided by the force/job.
