Plant Body

Embryophytes, in general, have two major organ systems: (1) shoot system and (2) root system. The shoot system includes body parts that are located in the upper portion of the plant whereas the root system consists of body parts found in the lower portion. The shoot system may include plant organs such as stems, branches, leaves, flowers, and fruits. They are often found above the ground. The root system includes roots, tubers, and rhizomes. They are often found underground.

The tissues of plants are:

• Embryonic or meristematic tissues – plant tissues made up of undifferentiated and mitotically active cells. Examples are apical meristem and cambium
• Permanent tissues – plant tissues that consist of differentiated cells. The permanent tissues may be further classified into fundamental (e.g. parenchyma, collenchyma, sclerenchyma) and complex (e.g. phloem and xylem tissues)
• Reproductive tissues – plant tissues that are involved in reproduction. Example is the sporogenous tissues

The cells of the plants are eukaryotic, i.e. with well-defined nucleus. The nucleus contains the chromosomes that bear genes. Apart from the nucleus, the other organelles are endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and plastids. The plastids may be classified based on the pigments: chloroplasts (with chlorophyll, green pigment), chromoplasts (with pigments apart from green), and leucoplasts (colorless plastids). The large structure inside the plant cell is the vacuole. It is responsible for the regulation of turgor pressure.

The plasma membrane surrounds the cytoplasm where these organelles are suspended. Apart from the plasma membrane, the cell has an additional layer called the cell wall. The cell wall, though, is not exclusive to embryophytes. Other organisms such as fungi, algae, and certain bacteria have cell walls. The cell wall of embryophytes is made up of primary and secondary cell walls. A primary cell wall contains cellulose, hemicelluloses, and pectin. A secondary cell wall is a thicker layer. It is rich in lignin that strengthens and waterproofs the wall. The cell wall has many important roles and one of them is to help resist osmotic pressure.

When a plant cell is placed in a hypertonic solution, water moves into the cell and causes the cell to swell. The presence of the cell wall prevents the cell from bursting during excessive osmosis. Conversely, when a plant cell is placed in a hypotonic solution, water diffuses out of the cell, and turgor pressure is lost causing the cell to become flaccid. Further loss of water will result in plasmolysis, and finally to cytorrhysis, the complete collapse of the cell wall.

Apart from osmoregulation, the fundamental physiological processes that plants carry out include photosynthesis, respiration, transpiration, tropisms, nastic movements, photoperiodism, circadian rhythms, seed germination, and dormancy.