5.3 2.1.4 summary

Summary

Plants are made up of roots, stems, leaves and flowers. The various types of tissues found within plants work together to fulfil functions such as supportand transport of water and nutrients. In this chapter you have learnt about the structure of roots and stems, and found out how they function. Roots consist ofa protective epidermis, a cortex to store food and water, and an endodermis surrounding an inner stele, which is composed of vascular tissue important intransport. Xylem is responsible for transporting water and minerals up from the roots to the stem, while phloem is responsible for transporting food (which theplant has made by photosynthesis) from the leaves to the roots. Similarly, a stem consists of a waterproof cuticle, a protective epidermis, a cortex forstorage, and contains vascular bundles arranged in a ring (in dicotyledonous plants) or scattered throughout the stem (in monocotyledonous plants). The mostimportant force that causes the movement of water through the xylem, from the roots up to the stem and leaves, is transpiration. As water evaporates from thestomata of the leaves during transpiration, it creates a suction force that pulls the water up through the roots. Hot, bright, dry and windy conditions canall lead to an increase in the rate of transpiration. If plants lose too much water and do not replace it, this causes a loss of turgor pressure, and theplant will wilt and eventually die. Water is also required for photosynthesis, which is the process whereby plants use water, carbon dioxide and the energyfrom sunlight to make glucose, and release oxygen as a by-product. Glucose is manufactured mainly in the palisade cells of the leaves, from where it passesinto the phloem and is transported to the rest of the plant. This food may be stored in the roots, stems or fruit.