Unit 9: Plants                                                               1   2   3   4   5   6

3. Structure of plants

All spermatophytes are divided in three basic parts: root, stem and leaves.

These organs are responsible for nutrition and interaction.

Flowers are the organs responsible for reproduction.

3.1. The vegetative organs of Spermatophytes

a) The root

The root grows in the opposite direction to the stem and it is usually an underground organ.

The functions of the root are:

   - To attach the plant to the ground.

   - To absorb the water and the mineral salts.

   - Sometimes, to store reserve substances.

There is a main root (tap-root) which has several secondary roots.

All of them have absorbent root hairs. Protecting the end of the roots, there is a structure called root cap.

There are two types of root systems:

     - Primary (one tap root and several secondary roots)

     - Fibrous (many roots all of the same size)

b) The stem

The stem is the axis of the plant. On it, there are nodes where branches and leaves grow and internodes which are the zones between two nodes. Buds are the shoots of the stem. Terminal buds are responsible for the longitudinal growth and axillary buds produce new branches, leaves and flowers.

The functions of the stem are:

   - To support the leaves and the flowers.

   - To transport substances between roots and leaves.

There are several ways to classify stems:

   - How long they last (annual or perennial)

   - How rigid they are (woody or herbaceous)

   - Where they grow (aerial, aquatic or underground)

c) The leaf

Leaves are usually flat and green organs and grow from the trunk or the branches.

The functions of leaves are:

   - To carry out photosynthesis

   - To control the gaseous exchange.

   - To regulate the loss of water (transpiration)

The blade is the flat wide part of the leaf. It is crossed by veins (conductive vessels). The petiole is the stalk that joins the leaf to the stem.

Animation: Parts of a flowering plant (Tutorvista)

3.1. Relate every type of root with their characteristics and their picture.

3.2. Complete the sketch: