Question 76

A plant left unwatered on a hot windowsill droops and its leaves go limp. Which statement explains the drooping?

The plant has used up the food that was stored in its soil
Its leaves have stopped photosynthesising, so they collapse
The stem has lost the lignin that held it up
It is losing water faster than its roots can replace itCorrect answer

Explanation

Cells hold a leaf out while they are full of water, and a plant droops once the water leaving the leaves outruns what the roots can replace, so the cells go slack and stop supporting the leaf. Soil supplies moisture and dissolved minerals rather than food, so an explanation built on running out of food in the soil misidentifies both what soil supplies and what keeps a leaf firm.

Explanation

Continue with this test