7th Grade Science Student ebook

14.2 ROOTS, STEMS, AND LEAVES

CHAPTER 14: PLANTS

The root system

Functions of the

root system

The main functions of the root

system are to collect minerals and

water from the soil and to anchor

the plant. Roots also help support the

part of the plant that is above ground.

In addition, some roots store food

produced from photosynthesis. The

root system consists of a larger

primary root and thinner secondary

roots that branch off of the primary

root. The photo (right) shows the root

system of a carrot plant. The primary

root of the carrot stores food.

Structure of roots The layer of cells that covers the surface of roots is called the
epidermis. Some epidermal cells grow outward into root hairs. Root
hairs increase the surface area and maximize the amount of
substances a plant can absorb. A plant’s root system may contain
billions of root hairs! Once absorbed, water and minerals diffuse
through a layer of cells called the cortex and into the center of the
root which contains the vascular tissues (xylem and phloem). The
vascular tissues transport water and minerals to the rest of the
plant. Figure 14.11 shows a cutaway and a cross section of a root.

Roots and

osmosis

Plants use osmosis to take in water. When there is plenty of water

in the soil, osmosis rapidly draws water into the root hairs. This

happens because the concentration of water is greater on the

outside of the root than on the inside. From there, water passes

into the vascular tissues through osmosis. If the concentration of

water is less outside the root than inside, the plant may lose water.

Figure 14.11: The structure of a

root.

epidermis - the layer of cells that

covers the surface of roots.