Plastids containing chlorophyll are called. The structure of a plant cell

These are colorless or colored bodies in the protoplasm of plant cells, which are a complex system of internal membranes (membrane organelles) and perform various functions. Colorless plastids are called leukoplasts, differently colored (yellow, orange or red) - chromoplasts, green - chloroplasts. The cell of higher plants contains about 40 chloroplasts in which photosynthesis takes place. They, as already mentioned, are capable of autonomous reproduction, independent of cell division. The size and shape of mitochondria and chloroplasts, the presence of circular double-stranded DNA and their own ribosomes in their matrix make these organelles look like bacterial cells. There is a theory of the symbiotic origin of the eukaryotic cell, according to which the ancestors of modern mitochondria and chloroplasts were once independent prokaryotic organisms.

Plastids are characteristic only for plants. They are not found in fungi and in most animals, with the exception of some photosynthetic protozoa.

Plastid precursors are proplastids, small, usually colorless formations found in dividing root and shoot cells. If the development of proplastids into more differentiated structures is delayed due to lack of light, one or more prolamellar bodies (clusters of tubular membranes) may appear in them. Such colorless plastids are called etioplasts. Etioplasts transform into chloroplasts in the presence of light, and thylakoids form from the membranes of the prolamellar bodies. Depending on the color associated with the presence or absence of certain pigments, there are three main types of plastids (see above) - chloroplasts, chromoplasts and leukoplasts. Usually, only one type of plastid is found in a cell. However, it has been established that some types of plastids can pass into others.

Plastids are relatively large cell formations. The largest of them - chloroplasts - reach 4-10 microns in length in higher plants and are clearly visible in a light microscope. The shape of stained plastids is most often lenticular or elliptical. As a rule, several tens of plastids are found in cells, but in algae, where plastids are often large and diverse in shape, their number is sometimes small (1-5). Such plastids are called chromatophores. Leukoplasts and chromoplasts can have different shapes.

The main function of chloroplasts is photosynthesis. The central role in this process belongs to chlorophyll, more precisely, to several of its modifications. Light reactions of photosynthesis are carried out mainly in the grana, dark - in the stroma

Organelles of general importance, having a two-membrane principle of structure. Found only in plant cells. Plastids were first described by Antonio van Leeuwenhoek in 1676.

Kinds:
1) chloroplasts - green plastids containing a large amount of chlorophyll pigment, as well as carotenoids;
2) chromoplasts - red-yellow plastids containing only pigments from the group of carotenoids (carotene and xanthophyll);
3) leukoplasts - colorless plastids.

Photosynthesis pigments: The main photosynthetic pigments in higher plants and green algae are:

♦ Chlorophyll - A (green-blue) = C55H72O5N4Mg;

♦ Chlorophyll - B (yellow-green) = C55H70O6N4Mg;

Carotenoids:

♦ Carotene (orange-red) = C40H56;

♦ Xanthophyll (yellow) = C40H56O2.

During photosynthesis, these pigments are only able to absorb electromagnetic waves of visible light.

Both chlorophyll - A and B - intensively accumulate the rays of the red spectrum and partially - blue and violet. They are not able to absorb green spectrum radiation, so they reflect such waves and visually appear to be green pigments. Carotenoids absorb blue, green and violet light. Carotenes reflect the "orange rays", therefore they appear as orange inclusions, xanthophylls reflect the radiation of the yellow spectrum, therefore, they are yellow pigments. Under intense light, carotenoids protect chlorophyll molecules from possible photooxidation.

The structure of the chloroplast

Shape: discoid.

Dimensions: width 2 - 4 microns.

1 - outer membrane;
2 - intermembrane space;
3 - inner membrane;
4 - thylakoids;
5 - grains;
6 - plastoglobules;
7 - DNA;
8 - ribosomes;
9 - matrix

The structure of chloroplasts: the chloroplast is delimited by two membranes, and inside is a gelatinous substance - the stroma. The outer membrane is smooth, the inner one forms many folds resembling stacks of coins - grains.

The grains contain pigments, electron acceptors and donors that take part in the light phase of photosynthesis, during which the photophosphorylation reaction occurs and ATP is formed. In addition, the products of the light phase are: O2 and H2O, NADP H2.

As in mitochondria, two spaces are created in chloroplasts: the first is called intermembrane - about 20 - 30 nm, it is filled with watery contents. The second, delimited by the inner membrane, is called the "stroma". The stroma contains its own DNA, ribosomes, enzyme proteins that are directly involved in the dark phase of photosynthesis. The product of the dark phase is glucose - С6Н12О6.

Plastids, like mitochondria, are capable of duplication, have their own apparatus for protein synthesis, and therefore are semi-autonomous organelles of plant cells.

Plastids have functional plasticity and are capable of modification: leukoplasts → chloroplasts → chromoplasts. Leukoplasts can be considered precursors of chloroplasts.

Chloroplasts are the active photosynthetic apparatus of the cell.

Chromoplasts are inactive degenerating plastids.

Functions:

♦ Chloroplasts play an active role in the primary synthesis of carbohydrates (glucose synthesis), which is called photosynthesis. Sometimes they take part in the secondary - the synthesis of starch. Widely represented in the cells of green plant organs (leaves, young stems, unblown buds).

♦ leukoplasts - these plastids are widely represented in the cells of underground plant organs (roots, tubers, bulbs, etc.), as they perform a storage function.

♦ Chromoplasts are found in the cells of flower petals, ripe fruits. By creating a bright color, they help to attract insects for pollination of flowers, animals and birds for the distribution of fruits and seeds in nature.

Plastids are those that make up the structure of a plant cell. They are clearly visible under a microscope, are found in plants. The exceptions are unicellular algae, bacteria and fungi.

The organelles contain the genetic code, they are able to reproduce their own kind by synthesizing DNA and proteins. The role and function of plastids in a cell is determined by their structure. They are able to accumulate nutrients, act as a depot. Some types of plastids perform the function of photosynthesis under the influence of light energy.

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Kinds

Depending on weather conditions, growth phases in plant cells are up to three types of plastids. They are presented in the table.

There are no clear divisions among these types of plastids. They are similar in structure, capable of transformation:

• leukoplasts under the influence of light are reborn into chloroplasts;
• chloroplasts become chromoplasts under the influence of weather factors (length of daylight, temperature);
• under laboratory conditions, chromoplasts turn green again, become chloroplasts;
• chloroplasts are converted into leucoplasts (leaves take root in water).

The structure of plastids

The size of the organelles is small, from 3 to 10 microns. Usually they have a round or oval shape, convex from above, from below.

The structure and functions of plastids change in different phases of growth.

Most have two membranes:

• external (shell):
• internal (immersed in the stroma).

Some highly organized plants have up to four membrane partitions in the structure of plastids. Membrane forms:

• thylakoids - peculiar compartments of various structures;
• grana - columnar or chain accumulations of thylakoids;
• lamellae are elongated thylakoids.

Stroma - viscous content, similar in structure to plastids.

Chloroplasts

Green organoids in structure are found in various shapes, they distinguish:

• oval;
• spiral;
• bladed;
• ellipsoid.

An important component of the stroma is chlorophyll, necessary for photosynthesis.

In complex plastids, structural elements: proteins, fats, pigments, DNA, RNA.

Chromoplasts

Biconvex, have a different structure:

• tubular;
• spherical;
• cubic;
• crystalline.

Chromoplasts contain grains of starch in their structure. The green pigment is completely destroyed in them, other nutritional components of the chloroplast are preserved.

Leucoplasts

According to the structure and composition of the stroma are divided into:

• amyloplasts - storehouses of starch, if necessary, they are transformed into monosaccharides;
• elaioplasts (lipoplasts) they contain fats;
• proteinoplasts are protein storehouses.

They are oval or elliptical in shape.

Functions of plastids

Initially, chloroplasts and leukoplasts are formed. The role of these plastids is photosynthesis, the production of substances that make up plant cells. Under the influence of light, a clear division occurs according to the type of organelles and their function.

The cells of highly organized plant species contain a different number of organelles. There are 10 of them, sometimes the number reaches 200 units. During the period of cooling, the synthesis of certain pigments begins in the leaves. Due to this, the structure of the organoid changes.

The concentration and composition of the dye in plant fruits depends on the DNA code. Color pigments become visible after the destruction of chlorophyll. He is afraid of low temperatures. The plant is getting ready for winter. The role of chromoplasts is attractive and cumulative. Fats, enzymes, proteins, originally contained in leukoplasts, accumulate in the process of growth and ripeness.

The value of chloroplasts

These organelles are responsible for the function of photosynthesis, cell development. They stepwise synthesize glucose from nitrogen dioxide and water. The reaction proceeds with the evolution of oxygen. The process occurs due to chlorophyll - in terms of its component composition, it is a hydrocarbon. By releasing an electron under the influence of light, it changes its function and becomes a reducing agent.

Functions of chromoplasts

In the process of beaming, the structure of organelles changes. In chromoplasts, plastoglobules are formed - accumulations of nutrients. The membranes are changed, destroyed, the cell is compacted. The internal structure affects the functions of the formation: the color becomes more attractive, bright due to an increase in the pigment concentration due to the destruction of the membrane structure of the organoid.

The role of leukoplasts

The functions of the underground part of the plant depend on the type of leukoplast. Depending on the DNA code, the structure of the layers changes. The functions of the cell change, it depends on the component composition - the amount of fats, proteins, sugars, starch of the forming fetus. The shape is mostly round, rarely oval. This is due to the structure of the cell of the eukaryotic species.

Plastid pigments

The structure of cellular organelles includes three groups of pigments:

• chlorophyll - magnesium-porphyrin protein complexes of chromoproteins, giving the leaves and trunk a green color;
• carotenoid - a coloring pigment similar to retinol (vitamin A), depending on the concentration, they acquire an orange or reddish color;
• xanthophyll is essentially oxidized carotene, contained together with p-carotene, has the same functions;
• phycobilin proteins are similar in their component structure to bile pigment-protein compounds. These include: blue phycocyanins, which give color to fruits; red-burgundy phycoerythrins.

Origin of plastids

According to one hypothesis, they originated from cyanobacteria. Later, a theory arose of the natural symbiogenesis of bacteria, which include chlorophyll, and plastid-like microorganisms. This was the explanation for the emergence of mitochondria from eukaryotes.

Scientists paid attention to the pigment structure of plant cells, later they left this version. A hypothesis has emerged that Archaeplastidae plastids originated from green algae and cyanobacteria. Later, thanks to symbiosis, colored protozoan algae were born. They are similar in structure to cell plastids:

• contains chlorophyll;
• pigmented inclusions were found;
• membrane structure.

What color can plastids be?

If we consider the whole plant, three colors stand out:

• yellow, orange, red plastids are located in flowers, fruits, root crops, less often - leaves, trunk;
• the color intensity depends on the concentration of the carotenoid pigment;
• green organelles - chloroplasts, they are involved in the process of photosynthesis; able to transform into chromoplasts of various colors or colorless leucoplasts.

The color of plastids is related to their functionality. What color the organoid of a flower, fruit, root crop will be depends on the DNA model. Information is reproduced during the growth of the plant.

The pigmentation of the flower attracts the attention of insects involved in the honey collection, pollination occurs. The bright color of the fruit serves as a signal for the maturation of seeds, seeds for animals. They distribute seed material over a wide area.

From the school bench. In the course of botany, it is said that in plant cells plastids can be of different shapes, sizes and perform various functions in the cell. This article will remind about the structure of plastids, their types and functions to those who graduated from school long ago, and will be useful to everyone who is interested in biology.

Structure

The picture below schematically shows the structure of plastids in a cell. Regardless of its type, it has an outer and inner membrane that performs a protective function, a stroma is an analogue of the cytoplasm, ribosomes, a DNA molecule, and enzymes.

In chloroplasts there are special structures - grana. Grana are formed from thylakoids, disc-like structures. Thylakoids take part in and oxygen.

In chloroplasts, starch grains are formed as a result of photosynthesis.

Leucoplasts are not pigmented. They do not contain thylakoids, they do not take part in photosynthesis. Most of the leukoplasts are concentrated in the stem and root of the plant.

Chromoplasts have in their composition lipid drops - structures containing lipids necessary to supply the structure of plastids with additional energy.

Plastids can be of different colors, sizes and shapes. Their sizes fluctuate within 5-10 microns. The shape is usually oval or round, but can be any other.

Types of plastids

Plastids can be colorless (leucoplasts), green (chloroplasts), yellow or orange (chromoplasts). Chloroplasts are what give plant leaves their green color.

Another variety is responsible for the yellow, red or orange coloration.

Colorless plastids in the cell act as a storehouse of nutrients. Leukoplasts contain fats, starch, proteins and enzymes. When the plant needs additional energy, starch is broken down into monomers - glucose.

Leucoplasts under certain conditions (under the action of sunlight or by adding chemical substances) can turn into chloroplasts, chloroplasts are converted into chromoplasts when chlorophyll is destroyed, and the coloring pigments of chromoplasts - carotene, anthocyanin or xanthophyll - begin to predominate in color. This transformation is noticeable in autumn, when leaves and many fruits change color due to the destruction of chlorophyll and the manifestation of chromoplast pigments.

Functions

As mentioned above, plastids can be different, and their functions in the plant cell depend on the variety.

Leucoplasts serve mainly to store nutrients and maintain the vital activity of the plant due to the ability to store and synthesize proteins, lipids, and enzymes.

Chloroplasts play key role in the process of photosynthesis. With the participation of the chlorophyll pigment concentrated in plastids, carbon dioxide and water molecules are converted into glucose and oxygen molecules.

Chromoplasts, due to their bright colors, attract insects for pollination of plants. The study of the functions of these plastids is still ongoing.

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3. Plastids: types, origin, structure and functions

Plastids are organelles specific to plant cells (they are found in the cells of all plants, with the exception of most bacteria, fungi, and some algae). In the cells of higher plants there are usually from 10 to 200 plastids 3-10 microns in size ...

Plastids are organelles of plant cells and some photosynthetic protozoa. Animals and fungi do not have plastids.

Plastids are divided into several types. The most important and well-known is the chloroplast, which contains the green pigment chlorophyll, which ensures the process of photosynthesis.

Other types of plastids are multi-colored chromoplasts and colorless leucoplasts.

Also isolated are amyloplasts, lipidoplasts, proteinoplasts, which are often considered varieties of leukoplasts.

All types of plastids are interconnected by a common origin or possible interconversion. Plastids develop from proplastids - smaller organelles of meristematic cells.

The structure of plastids

Most plastids are two-membrane organelles, they have an outer and an inner membrane.

However, there are organisms whose plastids have four membranes, which is associated with the peculiarities of their origin.

In many plastids, especially in chloroplasts, the internal membrane system is well developed, forming structures such as thylakoids, grana (stacks of thylakoids), lamellae - elongated thylakoids connecting neighboring grana. The internal contents of plastids are commonly referred to as the stroma.

Among other things, it contains starch grains.

It is believed that in the process of evolution, plastids appeared similarly to mitochondria - by introducing another prokaryotic cell into the host cell, capable of photosynthesis in this case. Therefore, plastids are considered semi-autonomous organelles.

Plastids and their pigments

They can divide independently of cell divisions, they have their own DNA, RNA, prokaryotic-type ribosomes, that is, their own protein-synthesizing apparatus. This does not mean that proteins and RNA from the cytoplasm do not enter plastids. Part of the genes that control their functioning is located just in the nucleus.

Functions of plastids

The functions of plastids depend on their type.

Chloroplasts perform a photosynthetic function. Spare nutrients accumulate in leukoplasts: starch in amyloplasts, fats in elaioplasts (lipidoplasts), proteins in proteinoplasts.

Chromoplasts, due to the carotenoid pigments they contain, color various parts of plants - flowers, fruits, roots, autumn leaves, etc.

Bright color often serves as a kind of signal for pollinating animals and distributors of fruits and seeds.

In the degenerating green parts of plants, chloroplasts turn into chromoplasts. The chlorophyll pigment is destroyed, so the rest of the pigments, despite the small amount, become noticeable in the plastids and color the same foliage in yellow-red shades.

plastids- these are membrane organelles found in photosynthetic eukaryotic organisms (higher plants, lower algae, some unicellular organisms).

They perform various functions, mainly related to the synthesis of organic substances. Depending on the color due to the presence of pigments, there are three main types of plastids:

• chloroplasts,
• chromoplasts,
• leukoplasts.

Chloroplasts are green plastids containing the green pigment chlorophyll and small amounts of carotene and xanthophyll.

The main function of chloroplasts is photosynthesis, which results in the formation of energy-rich organic substances. Chlorophyll synthesis usually occurs only in the light, so plants grown in the dark or with a lack of light turn pale yellow and are called etiolated. Instead of typical chloroplasts, etioplasts are formed in them.

In the cells of lower plants (algae), chloroplasts are large and few (one or several). They have a variety of shapes (lamellar, star-shaped, ribbon, etc.). Such chloroplasts are called chromatophores.

Chromoplasts are plastids containing pigments from the group of carotenoids, have a yellow, orange or red color.

Carotenoids include the widespread carotenes (orange) and xanthophylls (yellow). Chromoplasts have a variety of shapes. They are formed in autumn leaves, roots (carrots), mature fruits, etc. Unlike chloroplasts, the shape of chromoplasts is very variable, but species-specific, which is explained by their origin and the state of pigments in them.

Leukoplasts are small colorless plastids of spherical, ovoid or spindle-shaped form. They are usually found in the cells of organs hidden from sunlight: in rhizomes, tubers, roots, seeds, core of stems, and very rarely - in the cells of the illuminated parts of the plant (in the cells of the epidermis).

Often leukoplasts gather around the nucleus, surrounding it from all sides. The activity of leukoplasts is specialized and is associated with the formation of reserve substances. Some of them accumulate mainly starch (amyloplasts), others - proteins (proteoplasts or aleuroplasts), and still others - oils (oleoplasts).

Plastids are surrounded by two membranes, their matrix has its own genomic system, the functions of plastids are associated with the energy supply of the cell, which goes to the needs of photosynthesis.

What are plastids: structure and function

In higher plants, a whole set of different plastids was found (chloroplast, leukoplast, amyloplast, chromoplast), which are a series of mutual transformations of one type of plastid into another. The main structure that carries out photosynthetic processes is the chloroplast.

In higher plants, division of mature chloroplasts also occurs, but very rarely.

An increase in the number of chloroplasts and the formation of other forms of plastids (leucoplasts and chromoplasts) should be considered as a pathway for the transformation of precursor structures, proplastids.

The whole process of development of various plastids can be represented as a monotropic (going in one direction) series of changes in forms:

Many studies have established the irreversible nature of the ontogenetic transitions of plastids. In higher plants, the emergence and development of chloroplasts occur through changes in proplastids.

Proplastids are small (0.4-1 μm) two-membrane vesicles that do not have distinctive features of their internal structure. They differ from cytoplasmic vacuoles in their denser content and the presence of two delimiting membranes, external and internal.

The inner membrane may give small folds or form small vacuoles. Proplastids are most often found in dividing plant tissues (cells of the meristem of the root, leaves, at the growth points of stems, etc.). In all likelihood, an increase in their number occurs through division or budding, separation of small two-membrane vesicles from the proplastid body.

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plastids

The structure of plastids: 1 - outer membrane; 2 - inner membrane; 3 - stroma; 4 - thylakoid; 5 - grain; 6 - lamellae; 7 - grains of starch; 8 - lipid drops.

Plastids are found only in plant cells. Distinguish three main types of plastids: leukoplasts - colorless plastids in the cells of unstained parts of plants, chromoplasts - colored plastids are usually yellow, red and orange, chloroplasts - green plastids.

Chloroplasts. In the cells of higher plants, chloroplasts have the shape of a biconvex lens.

The length of chloroplasts ranges from 5 to 10 microns, the diameter is from 2 to 4 microns. Chloroplasts are bounded by two membranes. The outer membrane (1) is smooth, the inner (2) has a complex folded structure. The smallest fold is called thylakoid(4). A group of thylakoids stacked like a stack of coins is called faceted(5). The chloroplast contains an average of 40–60 grains arranged in a checkerboard pattern.

The granules are connected to each other by flattened channels - lamellae(6). The thylakoid membranes contain photosynthetic pigments and enzymes that provide ATP synthesis. The main photosynthetic pigment is chlorophyll, which is responsible for green color chloroplasts.

The inner space of chloroplasts is filled stroma (3).

The stroma contains circular naked DNA, 70S-type ribosomes, Calvin cycle enzymes, and starch grains (7). Inside each thylakoid there is a proton reservoir, there is an accumulation of H +. Chloroplasts, like mitochondria, are capable of autonomous reproduction by dividing in two. They are found in the cells of the green parts of higher plants, especially many chloroplasts in leaves and green fruits. The chloroplasts of lower plants are called chromatophores.

Function of chloroplasts: photosynthesis.

It is believed that chloroplasts originated from ancient endosymbiotic cyanobacteria (symbiogenesis theory). The basis for this assumption is the similarity of chloroplasts and modern bacteria in a number of ways (circular, "naked" DNA, 70S-type ribosomes, mode of reproduction).

Leukoplasts. The shape varies (spherical, rounded, cupped, etc.).

Leucoplasts are bounded by two membranes. The outer membrane is smooth, the inner one forms small thylakoids. The stroma contains circular "naked" DNA, 70S-type ribosomes, enzymes for the synthesis and hydrolysis of reserve nutrients.

There are no pigments. Especially many leukoplasts have cells of the underground organs of the plant (roots, tubers, rhizomes, etc.).

21. Plastids of higher and lower plants

Function of leukoplasts: synthesis, accumulation and storage of reserve nutrients. Amyloplasts- leukoplasts that synthesize and accumulate starch, elaioplasts- oils, proteinoplasts- proteins.

Different substances can accumulate in the same leukoplast.

Chromoplasts. Limited by two membranes.

The outer membrane is smooth, the inner or also smooth, or forms single thylakoids. The stroma contains circular DNA and pigments - carotenoids, which give the chromoplasts a yellow, red or orange color. The form of accumulation of pigments is different: in the form of crystals, dissolved in lipid drops (8), etc. Contained in the cells of mature fruits, petals, autumn leaves, rarely - root crops.

Chromoplasts are considered the final stage of plastid development.

Function of chromoplasts: coloring of flowers and fruits and thereby attracting pollinators and seed dispersers.

All types of plastids can be formed from proplastids. proplastids- small organelles contained in meristematic tissues. Since plastids have a common origin, interconversions are possible between them. Leukoplasts can turn into chloroplasts (greening of potato tubers in the light), chloroplasts - into chromoplasts (yellowing of leaves and reddening of fruits).

The transformation of chromoplasts into leukoplasts or chloroplasts is considered impossible.

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Plastids are the organelles of plant cells. One of the types of plastids are photosynthetic chloroplasts. Other common varieties are chromoplasts and leucoplasts.

All of them are united by the unity of origin and the general plan of the structure. Distinguishes - the predominance of certain pigments and the functions performed.

Plastids develop from proplastids, which are present in the cells of the educational tissue and are significantly smaller in size than the mature organoid. In addition, plastids are capable of dividing in two by constriction, which is similar to the division of bacteria.

In the structure of plastids, the outer and inner membranes are isolated, the inner contents are the stroma, the inner membrane system, which is especially developed in chloroplasts, where it forms thylakoids, grana and lamellae.

The stroma contains DNA, ribosomes, various types of RNA.

Plastids containing the pigment chlorophyll

Thus, like mitochondria, plastids are capable of independent synthesis of some of the necessary protein molecules. It is believed that in the process of evolution, plastids and mitochondria appeared as a result of a symbiosis of various prokaryotic organisms, one of which became the host cell, while others became its organelles.

The functions of plastids depend on their type:

• chloroplasts→ photosynthesis,
• chromoplasts→ coloring of plant parts,
• leucoplasts→ supply of nutrients.

Plant cells contain predominantly one type of plastid.

The pigment chlorophyll predominates in chloroplasts, therefore the cells containing them are green. Chromoplasts contain carotenoid pigments that give color from yellow through orange to red. Leucoplasts are colorless.

Coloring of flowers and fruits of the plant in bright colors by chromoplasts attracts pollinating insects and seed dispersal animals. In autumn leaves, the destruction of chlorophyll occurs, as a result, the color is determined by carotenoids.

Because of this, the foliage acquires the appropriate color. In this case, chloroplasts turn into chromoplasts, which are often considered as the final stage of plastid development.

Leukoplasts, when illuminated, are able to turn into chloroplasts. This can be observed in potato tubers when they begin to turn green in the light.

There are several types of leukoplasts depending on the type of substances accumulated in them:

• proteinoplasts→ squirrels,
• elaioplasts, or lipidoplasts, → fats,
• amyloplasts→ carbohydrates, usually in the form of starch.