Water uptake and movement to the xylem
Introduced| English | Meaning |
|---|---|
| root hair cell/ruːt heə sel/ | A specialised root epidermal cell with a long extension that increases the surface area for absorbing water and mineral ions. |
| osmosis/ɒzˈməʊsɪs/ | The net movement of water molecules through a partially permeable membrane from higher to lower water potential. |
| apoplast/ˈæpəplæst/ | Through cell walls (fast). |
| symplast/ˈsɪmplæst/ | symplast |
| plasmodesmata/ˌplæzməʊdˈsmɑːtə/ | Channels through plant cell walls that connect the cytoplasm of neighbouring cells. |
| Casparian strip/kæˈspeərɪən strɪp/ | A water-resistant band in root endodermal cell walls that blocks uncontrolled movement through the cell-wall pathway. |
| endodermis/ˈendəʊdəmɪs/ | The innermost layer of root cortex that regulates movement of water and dissolved substances into the vascular tissue. |
| suberin/ˈsʌbərɪn/ | A water-resistant material deposited in some plant cell walls, including cork and parts of root barriers. |
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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 ______.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
Apoplast = through the cell walls and spaces (fast); symplast = through the cytoplasm via plasmodesmata.
Match each term to its description.
Difficulty 2/5 · 140 coins + a small bonus on first completion today
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:
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Difficulty 1/5 · 100 coins + a small bonus on first completion today
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.
Difficulty 3/5 · 200 coins + a small bonus on first completion today
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