Plants and animals are both living things, but at first glance, they seem very different. Animals tend to move around, while plants stay rooted in one place. Animals eat their food, while plants convert sunlight into the energy they need. Despite these differences, scientists argue that plants and animals are more similar than they are different. Some living things even blur the line between the plant and animal kingdoms.
Plants and animals share many characteristics, but they are different in some respects. Animals usually move around and find their own food, while plants are usually immobile and create their food via photosynthesis. Plants and animals both have cells that contain DNA, yet the structure of their cells differs. Animal cells absorb nutrients from food, while plant cells use plastids to create energy from sunlight.
Plant and Animal Cellular Structure
Because both plants and animals are living things, they have cells. Cells are the smallest functional units of living organisms, and they make up every part of organism bodies. In some ways, plant and animal cells are similar. In others, they are vastly different.
Both plant and animal cells carry DNA – genetic material that is passed down from one generation to another. Because of DNA, plants and animals can pass on their genes over time and adapt to the environment around them via natural selection. Plant and animal cells both divide. Cell division is how individual animals and plants grow and replace parts of themselves. Human children reach adult height because of cell division, and grass grows for the same reason. Both plant and animal cells absorb nutrients and convert those nutrients into usable energy. Animal cells absorb nutrients from food, while plant cells absorb energy from sunlight via a process called photosynthesis.
Plant and animal cells have their differences, however. Plant cells are surrounded by a stiff cell wall, which helps keep plants rigid and upright, while animal cells are surrounded by a thin, permeable membrane that permits the absorption of outside substances. Plant and animal cells also contain differing organelles – inner-cellular structures. Some animal cells have cilia, the hairlike protrusions that help the cell move around. Plant cells do not have cilia, although most plant cells contain plastids. These organelles, which animal cells lack, contain pigment or food and are necessary for photosynthesis.
Plant and Animal Senses
Human beings have five senses: sight, scent, taste, touch and hearing. In fact, all living things, including plants, have senses, but without eyes, noses, tongues, skin or ears, can plants even sense the world around them? The answer is yes. All living things can sense the world around them, although they do so in different ways.
Most animals have fairly complex central nervous systems. Vertebrates – animals with a brain and spinal cord, such as human beings – have especially developed senses. Even invertebrates usually possess all or most of the five basic senses. Animals' bodies interpret light, chemical signals, pressure and sound waves to understand what is going on around it.
Plants sense their environment in other ways. Instead of sensory organs, they use a combination of hormones and sensory ions to take in information. Plants can sense light, which is important since sunlight is a plant's main source of energy. Plants slowly move over time to lean toward sunlight. Plants can also sense when the sun goes down. Scientists have found that certain plant species open pores on their leaves during the day to take in maximum sunlight, but close the pores at night to prevent moisture loss.
Scientists have recently discovered that plants can even communicate with one another. About 90 percent of plants have mutually beneficial relationships with fungus, which spreads out underground in large webs. These webs can link the roots of several plants together, allowing the plants to send signals and nutrients back and forth. Plants may send beneficial carbon to their neighbors via the "fungal" network or even toxic chemicals if new, competing plants begin to sprout.
Plant or Animal?
Usually, it is easy to tell a plant from an animal simply by looking. Animals move around and find their food. Plants are immobile and create their food. However, some creatures blur the line between plant and animal. These creatures possess characteristics that make classifying them as plants or animals difficult.
For example, coral reefs are colorful, underwater gardens located in warm ocean waters. The coral itself appears rooted in place, entirely immobile. In shades of green, pink and yellow, with round or petal-like shapes, coral resembles flowers. In almost every way, coral looks and behaves like a plant. However, coral is an animal that gathers its own food. Coral reefs are created by millions of tiny coral polyps clustered together, excreting an exoskeleton base to which they cling.
Venus flytraps, easily identified as plants by their green leafy appearance, exhibit behavior that is usually reserved for animals. These plants have "mouths" that clamp shut when insects land inside. The Venus flytrap even lines its mouth pad with a sweet-smelling substance to draw flies and other bugs. Whether this counts as hunting is up for debate, but there is no doubt that Venus flytraps move and eat food in addition to creating energy from sunlight via photosynthesis. Almost no other plants do this.
With thick "stems," bright colors and waving "petals," sea anemones look like beautiful ocean flowers swaying with the tide. At first glance, they appear to be plants, but these creatures are animals, and over periods of days or weeks, they can travel short distances.
Plants and animals have many differences, but many similarities as well. Some animals are so similar to plants and vice versa that they can be difficult to classify at first sight. All living creatures, plants and animals alike, share a common ancestor, which means that we are all related, in spite of the differences in our cells and senses.