Mr. ChapmanBiology 20

Roots and Stems

Plants are Weird

Unlike animals and other living organisms, plants can grow for their entire lives. A plant will continue to grow in the direction that allows it to reach resources. For roots, this means growing downward.

You are familiar with roots, they are (as we know them) the stringy, fibrous things that hang from the bottom of a plant. Roots, though, come in all kinds of shapes and sizes.

What is a Root?

Roots have several important functions, and these include:

1. Anchoring the plant to the ground

2. Absorbing water, minerals, and other nutrients for the plant.

3. Transporting and storing nutrients for the plant.

4. Roots sometimes make up over half the body of a plant.

Why Are Roots Useful?

Vascular cylinder – composed of xylem and phloem tissues. The vascular cylinder is surrounded by ground tissue, which itself is covered by dermal tissue.

Apical meristem – meristem cells are not specialized, similar to parenchyma cells. However, when they divide they have the ability to become specialized. Apical meristem lengthens the tips of roots and stems.

Root cap – the root cap covers the bottom of the root, protecting it as it grows downward into the soil.

A Root is Composed of the Following Structures....

Root StructureRoot hairs should be mentioned here!

There are 2 main types of roots that we discuss in this class:

Fibrous roots: These are the roots that we are the most familiar with, and they form extensive networks underground with fine branches. Most of the roots are the same size.

Taproots: These are long, thick, vertical roots with smaller root branches coming off of them. Carrots are examples of taproots that you can eat.

Types of Roots

Types of Roots

Why would a plant ever want to have a taproot instead of a fibrous root, are there any advantages?

Stems are seemingly the most boring portion of a plant. Nothing seems particularly interesting about the stem, so we just won’t talk about it...

Stems

Stems are obviously well known for providing support to the plant, but they also have other functions:

Food storageContain the majority of the vascular systemCan store food and waterIn some plants, like green cacti, the stems can

photosynthesize, producing food for the plant.

Just Kidding!

Some stems are herbaceous stems, which means that they contain little or no wood. These plants are usually soft and do not contain very many rigid xylem cells.

These plants do not ever grow to be more than 2 meters tall. Can you think of why?

Herbaceous stems are often green and may conduct photosynthesis.

Herbaceous or Woody?

Stems can also be woody. Usually the stems that have wood are dicots, such as pines and fir trees. Tree trunks are woody stems.

Recall the difference between monocots and dicots in terms of vascular tissue...

Herbaceous or Woody?

Unlike other living organisms, plants are capable of growth as long as they are alive. In order to continue to grow, a plant must be able to obtain enough nutrients to do so.

Plant growth depends on the location of the meristem within the plant. Recall that the meristem is the non-specialized type of cell capable of division and specializiation.

Stem Growth

Location of meristem determines which type of growth occurs in a plant.

Tree rings form due to uneven growth during the seasons. In years where the tree grew more, there is a larger gap between the tree rings.

Obviously, when the tree grew less, the rings are smaller. Tree rings can provide valuable meteorological data from the past, can you explain how?

Tree Rings