Revision Notes

8.2 Water Uptake

Root Hair Cells

  • Root hairs are single-celled extensions of epidermis cells in the root
  • They grow between soil particles and absorb water and minerals from the soil
  • Water enters the root hair cells by osmosis
  • This happens because soil water has a higher water potential than the cytoplasm of the root hair cell


Structure of the root, IGCSE & GCSE Biology revision notesStructure of the root

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How the Large Surface Area of a Root Hair Cell is Useful

  • The root hair increases the surface area of the cells significantly
  • This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport

Pathway of Water through Roof to Leaf

  • Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels:


Pathway of water into and across a root, IGCSE & GCSE Biology revision notesPathway of water into and across a root

  • Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells
  • So the pathway is:

root hair cell → root cortex cells → xylem → leaf mesophyll cells

  • The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)
  • After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery
  • If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem – these are the xylem vessels


Investigating water movement in plants using a stain, IGCSE & GCSE Biology revision notesInvestigating water movement in plants using a stain

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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