Plant Anatomy and Structure

As we learned in our study of human anatomy and physiology, life begins with cells, which

can then organize into tissues, which can then assemble into organs and organ systems,

and this organizational hierarchy applies to plants just as it does to humans.

In plants, especially vascular plants, there are two organ systems.

Those are the root system and the shoot system.

The root system includes all of the parts of a plant that grow below the ground.

These include roots, tubers, and rhizomes.

The roots are branching structures that extend into spaces in the soil and absorb water and

mineral nutrients, delivering them to the rest of the plant.

Some plant roots also include pockets for bacteria or fungal colonies to live in.

The fungi living in these pockets are called mycorrhizae, and they form symbiotic relationships

with plants, providing mineral nutrients to the plant in exchange for sugars from photosynthesis.

Legume plants, like beans and peas, form similar relationships with bacteria living in nodules

on their roots.

These bacteria specifically help legumes collect nitrogen, which is often a scarce resource

in the soil, and its scarcity can limit plant growth.

Many plants also use their roots as a place to store starches, a convenient form of long-term

energy storage made of complex polysaccharides, which we learned about in the biochemistry series.

However, other plants like potatoes store their starch in underground organs called tubers.

Starch storage in tubers is important for plants that grow year after year, called perennials,

because the energy in the starch allows the plant to grow before its leaves and photosynthetic

abilities are functional at the beginning of the growing season.

This explains why if you’ve ever left a potato on your counter for too long, it will

actually start growing buds and shoots of its own.

The last part of the root organ system in plants is the rhizome.

Just like tubers, not all plants have rhizomes.

But the ones that do have an advantage, because rhizomes can do multiple beneficial things

for a plant.

A rhizome is basically a secondary plant stem that grows out horizontally under the ground.

This provides stability to the plant, especially if the rhizome also grows small supplemental roots.

Rhizomes can also grow new plant shoots up out of the soil, so a rhizome can allow a

plant to create clones of itself and grow over a much wider area, potentially outcompeting

other plants trying to grow in the same space.

This strategy is called clonal reproduction, and is common in certain types of plants like grasses.

So that covers the root system, which is the underground portion of a plant.

The other portion is the above-ground organ system, or the shoot system.

The shoot system includes the vegetative or structural parts of the plant, and also the

reproductive parts of the plant.

The vegetative parts of a plant include organs like the stem and leaves.