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What is a Plant Study Guide

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Updated on Sep 21, 2011

Introduction

You can usually tell plants from other organisms because they (or parts of their bodies) are green. This is because plants contain a molecule called chlorophyll. Chlorophyll acts as a pigment to give plants their green color, but more importantly, it absorbs sunlight energy in the first step of the process known as photosynthesis. Plants also have chloroplasts and cell walls. This lesson introduces the world of plants.

What is Plant?

Many diverse organisms are classified within the Plant Kingdom, but they usually share certain characteristics that make them recognizable as plants. They are usually green (or part of their body is green), and they do not have the ability of locomotion, so they stay in one spot. They carry out the process known as photosynthesis, which turns carbon dioxide and water into sugars and oxygen gas. This process takes place in structures called chloroplasts. Plant cells have a hard cell wall made of the carbohydrate, cellulose.

Diverse Environments and Plants

Plants are found in nearly every place on Earth. They are located in the ocean and on mountaintops, they are in extremely warm and extremely cold places, and they even exist in very dry places like deserts. Plants are dependent upon light, so their access to a source of light is what limits where they can live. Water is also important to plant growth and development because much of plants' support comes from the water contained within its cells by the cell wall.

Long ago, two major groups of land plants evolved from algae, the bryophytes or nonvascular plants and the tracheophytes or vascular plants.

Bryophytes (Nonvascular Plants)

These plants lack roots, leaves, and stems, but they do have structures called rhizoids (root-like hairs) that absorb water and nutrients. However, the bryophytes have no vessels for conducting water throughout their bodies, so they rely on slow diffusion to distribute water and nutrients. This means that they cannot grow very large because the process of diffusion would be too inefficient to support large bodies. The most representative plants in this grouping are the liverworts and mosses.

Tracheophytes

Trachea refers to tube, and these vascular plants have tubes (vessels) that provide support and a means of transporting water and nutrients throughout their bodies. Vascular plants can thus grow very tall, up to hundreds of feet. This group is further broken down into two types, the seedless vascular plants and the seeded vascular plants.

Seedless vascular plants include club mosses, horsetails, and ferns. These plants must be in moist environments because they need water to reproduce. Millions of years ago, these types of plants dominated the Earth, and they grew to large sizes. Many of these types of plants are still in existence, but the seed plants have become dominant. The remains of the many seedless plants from millions of years ago have been transformed into oil and coal by tremendous heat and pressure.

Seed plants have become dominant today because they have developed pollen and seeds as adaptations. Pollen is a protective structure that ensures that the sperm cell used in pollination survives harsh conditions until it reaches the female part of a flower and can fertilize the egg found there. Seeds are an adaptation that allows these plants to undergo a period of inactivity in their life cycles. The seed contains and protects an immature plant in a state of dormancy. The small plant stays dormant until conditions are favorable, and then it germinates and forms a new plant.

Seeds are also very highly adapted to many ways of being dispersed. Some seeds are distributed by wind, some by water, and others by animals. This dispersal is a way plants can establish themselves in new areas because they cannot transport themselves. Seed plants are divided into two groups, flowering and nonflowering plants.

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