The push from below

The idea

Root cells actively take up ions from the soil, creating a concentration difference, so water moves into the root and a column of water is steadily pushed up the interconnected xylem vessels and tracheids.

Water into the roots

Roots sit in damp soil. Water has to get from the soil into the plant.

What do you think makes water move into the root?

• A difference in concentration of ions
• The leaves pushing it down
• The roots drinking by mouth

Root cell at work

Press Next step.

A push from the roots

Root cells in the soil actively take up ions. That makes the root richer in ions than the soil, so water moves into the root to remove the difference. The steady entry of water into the root xylem creates a column of water that is pushed upwards through the xylem vessels and tracheids. On its own this push is unlikely to be enough for the heights that plants reach.

Root cells actively take up ions from the soil, creating a concentration difference, so water moves into the root and a column of water is steadily pushed up the interconnected xylem vessels and tracheids.

Notes

Root cells actively take up ions, so water moves into the root and a column of water is pushed up the xylem: root pressure.

Check yourself

What do root cells in contact with the soil actively take up?

Why does water move into the root from the soil?

What is steadily pushed upwards in the root xylem?

Through which channels is the column of water pushed up?

• Starch. Starch is the internal energy reserve that plants make from carbohydrates.
• Chlorophyll. Chlorophyll is the green substance in chloroplasts that absorbs light energy.
• Ions — correct. Yes!
• To eliminate the difference in the concentration of ions — correct. Yes!
• Because the leaves push it down into the root. Water moves into the root because of the difference in ion concentration between the root and the soil.
• Because the soil has more ions than the root. The root cells take up ions actively, so the root has more ions than the soil.
• A column of starch. The pushing of a column of water is due to the steady movement of water into the root xylem.
• A column of water — correct. Yes!
• A column of air. The xylem vessels and tracheids are water-conducting channels.
• The sieve tubes of the phloem. Sieve tubes belong to the phloem, which transports the products of photosynthesis.
• The stomata. Stomata are tiny pores on the leaves that allow gas exchange.
• The interconnected xylem vessels and tracheids — correct. Yes!