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Plants are an incredibly important kingdom of organisms. They are multicellular organisms with the amazing ability to make their own food from carbon dioxide in the atmosphere. They provide the foundation of many food webs and animal life would not exist if plants were not around. The study of plants is known as botany and in this introduction to plants we look at key topics such as the process of photosynthesis, different types of plants and the different parts of a plant such as roots, stems and leaves.

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By using the sun’s energy to fix carbon dioxide, plants are able to produce sugars through a process known as photosynthesis. The sugars produced through photosynthesis provide plants with the energy to survive, grow and reproduce. As plants grow they become a food source for animals and other organisms.

There are over 400,000 species of plants currently on Earth and the majority of them produce flowers and fruit for reproduction. Plants that produce flowers belong to a group called angiosperms.

Other woody plants include a group known as the gymnosperms. This group includes pine trees and their relatives plus other non-flowering trees. Less advanced plants include ferns, lycophytes and mosses.

Plants made the move from water to land around 500 million years ago. Living on land is significantly different to living on water and plants have had to make serious changes to their body plans in order survive on land.

Land plants separated their body plans into roots, stems and leaves. Roots absorb water and nutrients from soil, stems transfer materials between roots and leaves, and leaves produce sugars that provide the plant with energy to survive.

Photosynthesis

Photosynthesis is a key topic for an introduction to plant biology. It is a process that occurs in plant cells that uses the sun’s energy to produce sugars from carbon dioxide and water. The process is simply a series of chemical reactions, probably the most important chemical reactions of Earth.

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The green color of plants is caused by a molecule called chlorophyll a. Chlorophyll a has the ability to absorb light energy from the sun. The energy that is absorbed is used to force reactions with water and carbon dioxide. The result of these reactions is the production sugars and oxygen gas.

The overall reaction looks like this:
energy + water + carbon dioxide → sugar + oxygen

Photosynthesis takes carbon dioxide from the atmosphere, converts it into sugar and releases oxygen back into the atmosphere. Over time photosynthesis changed the atmosphere of the Earth by increasing the amount of oxygen in the air.

Vascular vs. non-vascular

A critical step in the evolution of current plant species was the evolution of vascular tissue. Like humans have vascular tissue that transports blood through our bodies, the majority of species of plants have vascular tissue that transports water and nutrients around their bodies.

Before plants evolved vascular tissue, water was only able to enter into a plant by diffusing through the plant’s cells. This meant plants were unable to grow very large because diffusion is not efficient enough to support large plants. Once plants evolved vascular tissue, they were able to grow much larger and which allowed the evolution of the giant trees that now grace the Earth’s lands.

There are still many species on non-vascular plants but the vast majority of plant species contain vascular tissue. Non-vascular plants include organisms such as mosses and liverworts. Some biologists also consider the green algae to be non-vascular plants. Because non-vascular plants rely on diffusion to absorb water they are typically found in moist environments.

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Vascular plants make up over 90% of all plant species that are currently found on Earth. More primitive vascular plants include lycophytes and ferns. These two groups reproduce with spores rather than seeds and are unable to produce wood.

Gymnosperms and angiosperms are the two most recently evolved groups of vascular plants. They can both produce wood and reproduce with seeds rather than spores.

Plant body plan

Plants have a relatively simple body plan. A plant can be split into two sections: the underground system known as roots and the above ground system referred to as shoots. The shoots typically include stems, branches and leaves.

The evolution of roots was key to the success of plants on land. Roots grow underground in search for water and nutrients in the soil. Often almost half of a plant’s mass is hidden underground in the root system.

Roots also help to anchor a plant to the ground so it doesn’t get blown away in the wind or in a flood. They can also be used to store excess food to be used at a later date.

Stems and branches connect leaves and roots to each other. They are the ‘highways’ that water, nutrients, and sugars travel through to nourish the various parts of a plant.

Branches and stems influence the height and size of a plant which in turn affects how much light it will receive from the sun. A stem and branch can be green and fleshy but in many plants, they are brown, woody and covered in bark.

Leaves are the main place where photosynthesis occurs. The leaves of the plant have the responsibility of producing enough energy to feed the entire plant. Leaves are optimized for this challenge.

A typical leaf is full of a green molecule called chlorophyll a which is the magic ingredient in photosynthesis. Chlorophyll a is able to use energy from the sun to kick start the process of photosynthesis. Leaves are also usually flat and have large surface areas to capture as much light from the sun as possible.

Angiosperms

An angiosperm is any plant that produces flowers, fruit, and seeds. They are the most advanced, diverse and abundant group of plants. Angiosperms include the majority of the plants that most people are familiar with such as grasses, orchids, roses, lavender, magnolias, plus the plants that produce the fruits, vegetables, grains and nuts that we regularly eat.

Flowers and fruit evolved as a part of a plant’s reproduction. Flowers produce pollen and an ovary. Pollen from one flower is delivered to the ovary of another flower – this is known as pollination. A sperm cell found in a pollen grain fertilizes an egg located in an ovary. Once the egg is fertilized, it develops into a seed and the ovary develops into a fruit.

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Angiosperms have a close relationship with animals, in particular insects and birds. The pollination of flowers is most commonly assisted by animals. Flowers provide animals with nutritious foods such as nectar and pollen.

As animals move between flowers feeding on nectar and pollen, they transfer pollen between flowers. The newly delivered pollen then has the ability to fertilize the egg of the new flower.

Many angiosperms and animals have evolved alongside each other and their survival depends on one another. If the angiosperm goes extinct, the animal loses its food source. If the animal goes extinct, the plant loses it pollinator and cannot reproduce.

Gymnosperms

Gymnosperms are the closest relatives of angiosperms. They are a group of woody plants that produce seeds but no flowers or fruit. The seeds of gymnosperms are usually found in cones rather than inside fruit.

The world’s largest, tallest, oldest and widest organisms are all gymnosperms. They are incredible plants and some species are known to survive for over 2000 years.

There are four different groups of gymnosperms. These include the gingko, gnetophyta, cycads and conifers. Conifers contain the majority of species and include the well-known pine trees.

Ferns and lycophytes

Ferns and lycophytes are non-woody plants and also don’t produce seeds, flowers or fruit. Instead, ferns and lycophytes reproduce using tiny structures called spores.

These two groups were once the most common plants of Earth but they have since been outgrown by gymnosperms and angiosperms. Still, around 12,000 species of ferns and 1,200 species of lycophytes remain on Earth.

The main difference between ferns and lycophytes is in the vascular tissue of their leaves. Ferns have fronds with multiple veins whereas the leaves of lycophytes are very simple and only have one vein.

Non-vascular plants

Besides lacking tissue, non-vascular plants also lack wood, roots and flowers. This group of often ignored plants includes mosses, hornworts, liverworts and (depending on who you’re talking to) some algae. Compared to vascular plants, non-vascular plants are small and they struggle to grow taller than a few centimeters.

Mosses are the most common and best known of the non-vascular plants. They include over 14,000 species that are found all around the world.

Liverworts and hornworts are two groups of underappreciated plants. They are flattened plants that are typically only a few millimeters tall but grow sprawling across moist surfaces and are commonly mistaken for mosses and algae.

Video by Frank Gregorio. To see more brilliant videos like this one, check out Greg’s vimeo channel

For a deeper look at the biology of plants check out the plant section of our website:
Plants – Basic Biology

Last edited: 16 December 2016

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Biology

Systems biology, the study of the interactions and behaviour of the components of biological entities, including molecules, cells, organs, and organisms.

The organization and integration of biological systems has long been of interest to scientists. Systems biology as a formal, organized field of study, however, emerged from the genomics revolution, which was catalyzed by the Human Genome Project (HGP; 1990–2003) and the availability to biologists of the DNA sequences of the genomes of humans and many other organisms. The establishment of the field was also influenced heavily by the general recognition that organisms, cells, and other biological entities have an inherently high degree of complexity. Two dominant themes of modern biology are rooted in that new outlook: first, the view that biology is fundamentally an informational science—biological systems, cells, and organisms store and transfer information as their most-fundamental processes—and second, the emergence of new technologies and approaches for studying biological complexity.

Biological organisms are very complex, and their many parts interact in numerous ways. Thus, they can be considered generally as integrated systems. However, whereas an integrated complex system such as that of a modern airliner can be understood from its engineering design and detailed plans, attempting to understand the integrated system that is a biological organism is far more difficult, primarily because the number and strengths of interactions in the system are great and they must all be inferred after the fact from the system’s behaviour. In the same manner, the blueprint for its design must be inferred from its genetic material. That “integrated systems” point of view and all the associated approaches for the investigation of biological cells and organisms are collectively called systems biology.

Complexity and emergent properties

Many of the most-critical aspects of how a cell works result from the collective behaviour of many molecular parts, all acting together. Those collective properties—often called “emergent properties”—are critical attributes of biological systems, as understanding the individual parts alone is insufficient to understand or predict system behaviour. Thus, emergent properties necessarily come from the interactions of the parts of the larger system. As an example, a memory that is stored in the human brain is an emergent property because it cannot be understood as a property of a single neuron or even many neurons considered one at a time. Rather, it is a collective property of a large number of neurons acting together.

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One of the most-important aspects of the individual molecular parts and the complex things they constitute is the information that the parts contain and transmit. In biology information in molecular structures—the chemical properties of molecules that enable them to recognize and bind to one another—is central to the function of all processes. Such information provides a framework for understanding biological systems, the significance of which was captured insightfully by American theoretical physical chemist Linus Pauling and French biologist Emil Zuckerkandl, who stated in a joint paper, “Life is a relationship among molecules and not a property of any one molecule.” In other words, life is defined in terms of interactions, relationships, and collective properties of many molecular systems and their parts.

The central argument concerning information in biology can be seen by considering the heredity of information, or the passing on of information from one generation to the next. For a given species, the information in its genome must persist through reproduction in order to guarantee the species’ survival. DNA is passed on faithfully, enabling a species’ genetic information to endure and, over time, to be acted on by evolutionary forces. The information that exists in living things today has accumulated and has been shaped over the course of more than 3.4 billion years. As a result, focusing on the molecular information in biological systems provides a useful vantage point for understanding how living systems work.

That the emergent properties derived from the collective function of many parts are the key properties of biological systems has been known since at least the first half of the 20th century. They have been considered extensively in cell biology, physiology, developmental biology, and ecology. In ecology, for example, debate regarding the importance of complexity in ecological systems and the relationship between complexity and ecological stability began in the 1950s. Since then, scientists have realized that complexity is a general property of biology, and technologies and methods to understand parts and their interactive behaviours at the molecular level have been developed. Quantitative change in biology, based on biological data and experimental methods, has precipitated profound qualitative change in how biological systems are viewed, analyzed, and understood. The repercussions of that change have been immense, resulting in shifts in how research is carried out and in how biology is understood.

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A comparison with systems engineering can provide useful insight into the nature of systems biology. When engineers design systems, they explore known components that can be put together in such a way as to create a system that behaves in a prescribed fashion, according to the design specifications. When biologists look at a system, on the other hand, their initial tasks are to identify the components and to understand the properties of individual components. They then attempt to identify how interactions between the components ultimately create the system’s observable biological behaviours. The process is more closely aligned with the notion of “systems reverse engineering” than it is with systems design engineering.

The Human Genome Project contributed broadly to that revolution in biology in at least three different ways: (1) by acquiring the genetics “parts list” of all genes in the human genome; (2) by catalyzing the development of high-throughput technology platforms for generating large data sets for DNA, RNA, and proteins; and (3) by inspiring and contributing to the development of the computational and mathematical tools needed for analyzing and understanding large data sets. The project, it could be argued, was the final catalyst that brought about the shift to the systems point of view in biology.

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