Why are seaweeds not classified as plants

On the other hand, specialized cell types and tissues that assist in the distribution of nutrition within the organism can be found in a number of brown macroalgae. Access to nitrogen is an important limiting factor in seaweed growth, particularly for green algae. The increasing runoff into the oceans of fertilizer-related nitrogen from fields and streams has created favorable conditions for the growth of algae, especially during the summer when it is warm and the days are long.

Omelette tamago-yaki with Nori 1 sheet of nori seaweed 3 eggs mirin sweet rice wine salt and sugar 1. Crack the eggs into a bowl. Add a little salt, sugar, and mirin optional and whisk everything together lightly with a fork.

Heat a pan that has been greased with a tiny amount of fat, preferably one that has virtually no flavor of its own. Pour the egg mixture into the pan a little at a time over low heat. Place the nori sheet on the wooden surface and, using chopsticks or a wooden spatula, fold the set egg mixture together on itself several times to create a flat, layered omelette tamago.

Remove the omelette from the pan and press itinto shape with a bamboo rolling mat, which will imprint a nice surface texture on it. Different species of seaweeds avail themselves of a variety of strategies in order to grow.

In sea lettuce Ulva lactuca , the cells all undergo division more or less randomly throughout the organism. Other species, among them several types of brown algae, have a growth zone at the end of the stipe and at the bottom of the blade; this is where an existing blade grows and new blades are formed.

The oldest blades are outermost, eventually wearing down and falling off as the seaweed ages. As a result, the stipe can be several years old, while the blades are annuals. This growth mechanism allows the seaweed to protect itself from becoming overgrown by smaller algae, called epiphytes, which fasten on to it.

On certain seaweed species, the epiphytes are found overwhelmingly on the stipes, which can become covered with them, while the blades retain a smooth surface as long as they are young and still growing. Finally, some types of seaweeds, such as bladder wrack Fucus vesiculosus and the majority of the red algae, grow at the extremities of the blades. The overall effect of seaweeds on the global ecosystem is enormous.

It is estimated that all algae, including the phytoplankton, are jointly responsible for producing 90 percent of the oxygen in the atmosphere and up to 80 percent of the organic matter on Earth. We can compare their output with that of plants by looking at the amount of organic carbon generated per square meter on an annual basis. Macroalgae can produce between 2 and 14 kilograms, whereas terrestrial plants, such as trees and grasses in temperate climates, and microalgae can generate only about 1 kilogram.

The vast productive capacity of macroalgae can possibly be best illustrated by the fact that the largest brown algae can grow up to half a meter a day. That amounts to a couple of centimeters an hour! Seaweeds are made up of a special combination of substances, which are very different from the ones typically found in terrestrial plants and which allow them to play a distinctive role in human nutrition.

Most notably, the mineral content of seaweeds is 10 times as great as that found in plants grown in soil; as a consequence, people who regularly eat seaweeds seldom suffer from mineral deficiencies. In addition, marine algae are endowed with a wide range of trace elements and vitamins.

Because they contain a large volume of soluble and insoluble dietary fiber, which are either slightly, or else completely, indigestible, seaweeds also have a low calorie count. A wild strain of Chondrus crispus , or Hana-Tsunomata in Japanese, appeals to both the eye and the palate. This seaweed has a distinct crunchy texture and a milder taste than most other sea vegetables. Its flamboyant colors—pink, green, and yellow—are completely natural.

Marine algae possess a fantastic ability to take up and concentrate certain substances from seawater. For example, the iodine concentration in konbu and other types of kelp is up to , times as great in the cells of the seaweeds as in the surrounding water, and the potassium concentration is 20—30 times greater. On the other hand, the sodium content is appreciably lower than that of salt water. Depending on the species, fresh seaweeds are 70—90 percent water by weight. The composition of the dry ingredients in the different types of seaweeds can vary a great deal, but the approximate proportions are about 45—75 percent carbohydrates and fiber, 7—35 percent proteins, less than 5 percent fats, and a large number of different minerals and vitamins.

Broadly speaking, the proteins in seaweeds contain all the important amino acids, especially the essential ones that cannot be synthesized by our bodies and that we therefore have to ingest in our food.

Porphyra has the greatest protein content 35 percent and members of the order Laminariales the lowest 7 percent. Three groups of carbohydrates are found in seaweeds: sugars, soluble dietary fiber, and insoluble dietary fiber. Many of these carbohydrates are different from those that make up terrestrial plants and, furthermore, they vary among the red, the green, and the brown species of algae. The sugars, in which we include sugar alcohols such as mannitol in brown algae and sorbitol in red algae, can constitute up to 20 percent of the seaweeds.

The seaweed cells make use of several types of starch-like carbohydrates for internal energy storage; again, these vary according to species. For example, the brown algae contain laminarin, which is of industrial importance as it can be fermented to make alcohol.

Norwegian winged kelp Alaria esculenta is appearing on the menus of top restaurants. Soluble dietary fiber, which is situated in between the seaweed cells and binds them together, constitutes up to 50 percent of the organism. Composed of three distinct groups of carbohydrates, namely, agar, carrageenan, and alginate, fiber can absorb water in the human stomach and intestines and form gelatinous substances that aid in the digestive process.

Insoluble dietary fiber derived from the stiff cell walls of the seaweeds is present in lesser quantities, typically amounting to between 2 percent and 8 percent of the dry weight. Cellulose is found in all three types of algae and xylan another type of complex carbohydrate in the red and green ones. The primary mineral components in seaweeds are iodine, calcium, phosphorous, magnesium, iron, sodium, potassium, and chlorine. Added to these are many important trace elements such as zinc, copper, manganese, selenium, molybdenum, and chromium.

The mineral composition, especially, varies significantly from one seaweed species to another. Konbu contains more than —1, times as much iodine as nori. Some algae, the diatoms , are single-celled. Others, such as seaweed , are multicellular see Figure below. Why are algae considered plant-like? The main reason is that they contain chloroplasts and produce food through photosynthesis.

However, they lack many other structures of true plants. For example, algae do not have roots, stems, or leaves. Some algae also differ from plants in being motile. They may move with pseudopods or flagella.

Although not plants themselves, algae were probably the ancestors of plants. Algae play significant roles as producers in aquatic ecosystems. Microscopic forms live suspended in the water column.

They are the main component of phytoplankton. As such, they contribute to the food base of most marine ecosystems. Multicellular seaweeds called kelp may grow as large as trees. They are the food base of ecosystems called kelp forests see Figure below.

Atualizado: Jan By Gabrielle Souza. Edited by Katyanne M. When we walk along the beach and see seaweed, we associate it with terrestrial plants.

Afterall, scientific evidence strongly suggests that plants evolved from green algae in the Paleozoic Era. However, they are quite quite different in many ways. Algae, like terrestrial plants, are eukaryotic organisms the cell has several organelles including a nucleus surrounded by a membrane and photosynthetic autotrophs produce their own food through photosynthesis.

The word algae comes from Latin and means "marine plant," but you must be aware that not all algae live in the water. Some live in terrestrial environments associated with fungi, in a mutually beneficial relationship, or symbiosis, forming so-called lichens. Thus, due to the complexity and constant taxonomic changes of these organisms, we will not go into details of classification of this polyphyletic group they do not share a common ancestor called "algae," but we will focus on its general characteristics.

Are they even plants? The shortest answer I can give you is "it depends. In Latin, the word "alga" simply means "seaweed. In fact, without specification, algae may refer to entirely different kingdoms of life including Plantae which is often divided in the broad sense, Archaeplastida and the narrow sense, Viridiplantae , Chromista, Protista, or Bacteria. Caulerpa racemosa , a beautiful green algae. Taxonomy being what it is, these groupings may differ depending on who you ask.

The point I am trying to make here is that algae are quite diverse from an evolutionary standpoint. Even calling them seaweed is a bit misleading as many different species of algae can be found in fresh water as well as growing on land. Take for instance what is referred to as cyanobacteria. Known commonly as blue-green algae, colonies of these photosynthetic bacteria represent some of the earliest evidence of life in the fossil record.