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Angiosperms, or flowering plants are incredibly diverse. This group of plants contains between 250,000 and 400,000 different species. Although flowering plants are diverse in size, shape, color, and habitat, all angiosperms have the following four structures: the root, the stem, the leaf, and the flower. Each structures in comprised of one or more different types of tissues. In this lab activity we will learn more about angiosperm structures and tissues.

Angiosperm Tissues

Flowering plants contain three main types of tissues in the roots, stems, and leaves. Each tissue has a specific function as described below:

1. Dermal tissue: protects the outside of the plant.
2. Ground tissue: used for photosynthesis and storage. An internal plant tissue.
3. Vascular tissue: used for transport of water and sugars. Xylem transports water and phloem transports sugars.

Unlike animals, angiosperms increase in size their entire life because of meristematic tissue. Meristematic tissue continues to divide and create new cells through photosynthesis increasing the height and width of flowering plants. Plants have two types of meristems, as described below:

1. Apical meristem: located at the tip of the shoot and the tip of the root. The apical meristem lengthens up and down. It is responsible for primary growth.
2. Lateral meristem: located at branches to increase plant girth. It is responsible for secondary growth.

Angiosperm Body Plan

View the representative plants on display in the lab. Notice that the plants have aboveground and below-ground portions. The shoot system is aboveground. What components of the plan comprise the shoot system?

The root system is below ground. State two functions of plant roots.

Angiosperms are divided into two different groups, monocots and eudicots. These groups differ based on tissue organization in the seed, root, stem, leaf and flowers. For example, monocots have leaf veins that form a parallel patter and flower parts in multiples of threes. Eudicots have leaf veins in a net pattern and flower parts in multiples of fours or fives.

Using this information, identify the live plants on display as either monocots or eudicots using a table similar to the one below.

Root

There are two main root arrangements. Most monocots have a fibrous root system where all of the roots are about the same size. Many eudicots have a taproot system with one very large main root and smaller roots branching off. A carrot is an example of a taproot.

View the monocot and eudicot roots models on display and the cross section slides of the monocot and eudicot root. Identify the following structures:

• Root cap 
• Root hairs 
• Zone of cell division 
• Zone of elongation 
• Zone of maturation 
• Xylem 
• Cortex
• Endodermis
• Pith
• Pericycle
• Epidermis
• Phloem

Stem

The stem provides aboveground support for flowers and leaves. Some stems are herbaceous or nonwoody while others are woody. Herbaceous stems increase in length via the apical meristem but they do not increase in girth through secondary growth.

View the cross section slides of the eudicot herbaceous stem and the monocot herbaceous stem. Identify the following tissues in both slides and notice that they have different arrangements of the xylem and phloem.

• Cortex
• Xylem
• Phloem
• Pith
• Epidermis

Many plants have modified stems to assist with food storage or for vegetative reproduction. Some examples include:

1. Rhizome: horizontal underground stem
2. Corm: underground fleshy stem, used for storage
3. Stolon: underground horizontal stem
4. Runner: aboveground horizontal stem
5. Tuber: underground storage stem
6. Bulb: underground storage stem with fleshy leaves

View the stems on display and identify which ones below to the categories described above. You may see more than one example of some and no examples of others.

Leaf

The main function of the leaf is photosynthesis. Therefore, it contains many chloroplasts and is thin to facilitate gas and water transport. View the leaf model and the leaf cross section slide. Make sure you can identify the following components:

• Epidermis (upper and lower) 
• Cuticle 
• Spongy Mesophyll 
• Palisade Mesophyll 
• Xylem
• Phloem
• Stomata (stoma singular)
• Guard Cells

The main, flat portion of the leaf is called the blade and it attaches to the stem via the petiole stalk. There are two main arrangements for the leaf blade. Leaves can either be simple or compound. A simple leaf has a single blade. A compound leaf has a blade divded into leaflets. All of the leaflets share the same auxiliary bud which is the source of new growth. The auxiliary bud is located at the base of the petiole.

There are two arrangements of compound leaves. Palmately compound leaves have all leaflets attached at the same point at the end of the petiole. Pinnately compound leaves have leaflets attached at intervals along the peitole.

View the preserved leaf specimens. Choose six to identify as simple or compound. If the leaf is compound, state if it is palmately or pinnately compound. Record your findings in a table similar to the one below.