Water uptake and movement to the xylem
| English | Chinese | Pinyin |
|---|---|---|
| root hair cell | 根毛细胞 | gēn máo xì bāo |
| osmosis | 渗透 | shèn tòu |
| apoplast | 质外体 | zhì wài tǐ |
| symplast | 共质体 | gòng zhì tǐ |
| plasmodesmata | 胞间连丝 | bāo jiān lián sī |
| Casparian strip | 凯氏带 | kǎi shì dài |
| endodermis | 内皮层 | nèi pí céng |
| suberin | 木栓质 | mù shuān zhì |
Water from soil to xylem
- Water gets in at the root hair cells 根毛细胞.
- It then crosses the root to reach the xylem.
- A clever waterproof barrier lets the plant control what gets through.
Water enters a root hair cell by osmosis because the root hair has:
Water moves down the water-potential gradient, into the root hair which has the lower water potential.
Water enters root hair cells from the soil by ______.
Water moves down a water-potential gradient into the root hair.
Into the root hair
- A root hair cell has a lower water potential than the soil water around it.
- So water enters by osmosis 渗透, down the water-potential gradient.
- Root hairs give a huge surface area for this uptake.
The apoplast and symplast pathways differ because:
Apoplast = through the cell walls and spaces (fast); symplast = through the cytoplasm via plasmodesmata.
Match each term to its description.
Two routes cross the cortex; the Casparian strip then forces water through a membrane for control.
Two pathways across the root
- Apoplast 质外体 pathway: water moves through the cell walls and spaces between cells — without entering the cytoplasm. This is fast.
- Symplast 共质体 pathway: water moves through the cytoplasm, passing cell to cell through the plasmodesmata 胞间连丝.
The apoplast (through walls) and symplast (through cytoplasm) routes; the Casparian strip 凯氏带 blocks the apoplast.
The Casparian strip at the endodermis:
The waterproof suberin band blocks the apoplast, so all water must cross a membrane — giving the plant control.
By forcing water through cell membranes, the Casparian strip lets the plant control what enters the xylem.
Crossing a membrane means selective transport proteins decide what passes — so the plant controls xylem contents.
Put water's journey from soil to leaf in order.
Root hair → cortex → endodermis (membrane) → xylem → up to the leaves.
The endodermis 内皮层 and Casparian strip
- At a ring of cells called the endodermis, the apoplast route is blocked by the Casparian strip — a waterproof band of suberin 木栓质.
- This forces all the water through the cell membranes, so the plant can control what enters the xylem.
The wood of a tree trunk is xylem; each ring is one year of growth.
Water from soil to xylem
Follow water in from the soil. It crosses the root two ways, is forced through a membrane at the endodermis, then enters the xylem.
You've got it
- water enters the root hair by osmosis (root hair has lower water potential than soil)
- apoplast = through cell walls (fast); symplast = through cytoplasm (via plasmodesmata)
- the Casparian strip (suberin) at the endodermis blocks the apoplast
- this forces water through the membranes → the plant controls what enters the xylem