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Unit 4: Maintaining life

Plants And Water — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 7 of 10 2 quizzes

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Plants and water — HIA INTERNATIONAL notes: Explain how root hairs absorb water and how xylem carries it to the leaves, and why plants need water.Photosynthesis — water is a reactant, changed with carbon dioxide to glucose and oxygen.Support — cells full of water are firm and pre…

  • Chemical reactions
  • Large surface area
  • Entry of water
  • Mineral ions
  • No chloroplasts
  • Transpiration stream

Part 1 of 6Why plants need water

Photosynthesis
  • Photosynthesis water is a reactant, changed with carbon dioxide to glucose and oxygen.
Support
  • Support cells full of water are firm and press on each other, holding the plant upright.
Transport
  • Transport water carries dissolved mineral salts through the xylem to all parts.
Cooling
  • Cooling water evaporating from leaf cells takes heat away.
Chemical reactions
  • Chemical reactions living things need water to dissolve chemicals inside cells.

Part 2 of 6Root hair cells

Soil
  • Soil made of rock particles with spaces filled with air and water.
Root hairs
  • Root hairs cells growing out of the root surface, each hair part of a single cell.
Large surface area
  • Large surface area root hairs give a big surface to absorb water and mineral ions.
Entry of water
  • Entry of water water moves from the soil through the cell wall and cell membrane into the cytoplasm and vacuole.
Mineral ions
  • Mineral ions nitrate and magnesium ions dissolved in the soil water enter along with it.
No chloroplasts
  • No chloroplasts root hair cells are underground and do not photosynthesise.

Part 3 of 6Xylem vessels

Xylem vessels
Position
  • Position in the centre of the root, forming a cross-shaped area, and in stems.
Structure
  • Structure long tube-like cells that are dead, with no cytoplasm or nucleus and end walls gone, forming hollow tubes.
Function
  • Function they transport water and mineral salts from the roots to the top of the plant.
Wood
  • Wood the wood in a tree trunk is made of xylem vessels.
Phloem
  • Phloem a different tissue that carries dissolved sugars around the plant.

Part 4 of 6Path of water

1
Water enters a root hair cell from the soil.
2
It moves across the root towards the centre.
3
It enters the xylem vessels.
4
It travels up the xylem in the stem.
5
It reaches the leaves.
  • Transpiration stream
    • loss of water from the leaves pulls more water up the xylem.

Part 5 of 6Investigating transport in celery

1
Put 1–2 cm of coloured water in a container.
2
Cut the lower end of a celery stalk cleanly and stand it in the water.
3
Check every five minutes for dye moving up the stalk.
4
Rinse the stalk and cut across it halfway up.
5
Observe the coloured spots, which are the xylem vessels.
Safety
  • Safety cut away from you on a non-slip surface.
Plan
  • Plan temperature could be tested as the independent variable.

Part 6 of 6Wilting

Cause
  • Cause cells with too little water become soft and floppy.
Result
  • Result the plant collapses and is said to have wilted.
Desert plants
  • Desert plants have adaptations such as a waxy cuticle and fewer stomata to conserve water.

Key terms

TermMeaning
Root hair cellA root cell with a long extension that absorbs water and mineral ions.
Xylem vesselA hollow dead tube carrying water and minerals up the plant.
Mineral ionsDissolved nutrients such as nitrate and magnesium.
WiltingCollapse of a plant when its cells lack water.
Cell sapThe solution in the vacuole of a plant cell.
PhloemTissue that carries dissolved sugars.

Avoid these mistakes

1
Plants take in water through leaves — they absorb it through root hairs.
2
Xylem vessels are living cells — they are dead and hollow.
3
Water moves up the plant in phloem — it moves in xylem; phloem carries sugars.
4
Wilting happens when a plant has too much water — it happens when cells lack water.

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