Tetiana Chychkovska · Transcript · · Updated
Одноклітинні евкаріоти – мешканці прісних та морських водойм – Transcript
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- Euglena viridis is a common single-cell organism found in small bodies of water with polluted water that can cause water blooms.
- Chlamydomonas is a unicellular green alga that reacts to light, chemical substances, and mechanical influences.
- The cell wall of diatoms consists of an inner pectin layer and an outer silica layer called a frustule.
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Glad to welcome you to the channel. Today we continue our overview of single cell eukaryotes, and today we will talk about unicellular organisms that are capable of photosynthesis, subdomain excavata.
Besides parasitic unicellular organisms, specifically Giardia, Trepanosoma, and Leishminia, this group also includes free living forms, for example, euglena viridis. Euglena is a common in small bodies of water, with polluted water, where they multiply massively and cause water blooms.
The body of the euglena is an oblong green cell, up to 2.2 mm in size, covered by a membrane called a pellicle. The pellicle provides shape, but allows for compression and the euglena becomes shorter and wider in the process.
The posterior end of the body is pointed, the anterior is rounded, and has two flagella. One is short and reduced, while the second is long, thin, and serves for locomotion. The flagella moves in a screw-like motion.
The euglena rotates around its own axis and performs translational movements. In the cytoplasm, one can distinguish a large nucleus, about 20 chloroplasts, nutrient inclusions which serve as food storage, as well as an eye spot, a special light-sensitive organ.
Euglena possesses positive phototaxis, swimming in the direction of light. Near the eye spot is a contractile vacuole that rids the euglena of excess water and harmful substances. Euglena has characteristics of both plants and animals.
Since the cell contains chlorophyll, euglena feeds autotrophically in the light through the process of photosynthesis. In the dark and with an excess of organic food, euglena feeds heterotrophically, absorbing organic particles through osmosis, or with the help of a cytostome located at the base of the flagella.
Such nutrition is called mixotrophic. Mixo means mixed trophos means to feed. It occurs by longitude no division.
Under unfavorable conditions, such as winter or the drying up of a body of water, the euglena is capable of forming a cyst. The cell becomes spherical, losing water, and the flagellum. It covers itself with a strong membrane, and in this form can remain in a state of dormancy for a long time.
Subdomain diaphoretics say kingdom archiplastida. In nature in small puddles after rain, often on clay soil or in bodies of water contaminated with organic substances, one can find the unicellular green alga chlamydomonas.
Chlamydomonas has an elongated ellipsoid shape with a slightly pointed anterior end which faces forward during movement. The cell has two flagella for movement. Building the cell membrane is a cell wall which is built from complex proteins and pectin.
Closer to the anterior end of the body is a pulsating contractile vacuole. Next to it is a red-eye spot. Chlamydomonas has one cup-shaped chloroplast which is called a chromatophore.
Starch is deposited in it. In the center of the chromatophore, a protein body called a pyrenoid is visible. Nucleus is located under the chromatophore. Besides the fact that chlamydomonas reacts to light with the help of the eye-spot, phototaxis, it is also characterized by chemotaxis, a reaction to chemical substances, and mechanotaxis, a reaction to mechanical influences.
Like the euglena, it feeds mixotrophically. Chlamydomonas reproduces in two ways, asexually and sexually. Asexual reproduction occurs under favorable conditions. The cell loses its flagella, its contents divide into four eighths, motile, zoospores, and over time they grow to the size of the mother cell.
When the temperature drops or water bodies dry up, the mother cell divides to form gametes, meaning it begins sexual reproduction. The gametes fuse in pairs. This process is called fertilization.
As a result of gamete fusion, a zygote is formed. It covers itself with a dense shell and survives unfavorable conditions this way. When favorable conditions return, the cell nucleus divides, four cells are formed from which new chlamydomonas grow.
Subdomain diaphoretics, kingdom archaea, plastida. Another widely distributed unicellular green alga is chlorella. It is found in moist soil on tree trunks in fresh water and on underwater objects.
Chlorella has a spherical shape. The nucleus and a cup-shaped chromatophore are clearly visible in the cytoplasm. On my chlamydomonas, chlorella is immobile. It lacks vagilla and an eye spot. It feeds only autotrophically in the process of photosynthesis.
Chlorella reproduces only asexually. The cell divides into several parts, which acquire a spherical shape, rupture the mother cell wall and enter the environment. Under unfavorable conditions, the chlorella shell thickens.
Subdomain diaphoretics, kingdom archaea, plastida. Among unicellular green algae is the giant alga acetabil area, which inhabits shallow tropical seas such as the Mediterranean or the Caribbean.
Acetabil area looks like a stock up to six centimeters long, covered by an umbrella, up to one centimeter in diameter. It attaches to the substrate via a branching stalk called a rhizoid.
The nucleus is located in the lower part of the acetabil area stock. This alga is an excellent object as it is convenient for studying regeneration processes. The life cycle of acetabil area lasts three years.
In the spring, gametes emerge from the over-wintering cysts each, having two flagella. They fuse in pairs to form a zygote. A stalk with a rhizoid forms from it.
Before the cold, the stalk dries up and the rhizoid overwinters using stored nutrients. The following spring, a new stalk with an umbrella primordium grows from the rhizoid. A real one only grows in the third year.
At the same time, the nucleus divides multiple times, and small nuclei move into the umbrella, where they gather into cysts that overwinter again. Subdomain diaphoretics supergroups S.A.R.
In addition to heterotrophic unicellular organisms, the SARS supergroup includes a very distinct group of diatoms. In nature, they can be found on the surface of underwater objects in the water column, on the surface of moist rocks and in the soil.
In freshwater bodies, they are found at shallow depths of up to 24 meters and in marine ones, from the surface to a depth of 350 meters. The cell wall of diatoms consists of two independent layers, an inner pectin layer that fits tightly against the outer one, which consists of silica.
This layer is called a frustule and consists of two halves, valves. One overlaps the other, similar to how a lid fits onto a box. On the surface of the frustule, there are thickenings in the form of darts or ribs.
A rough runs along the body of the alga. This is a slit in the cell wall through which mucus is secreted, enabling movement by crawling. For instance, pinularia looks like an elongated ellipse with a small thickening in the middle, one a vicula, has the shape of a small boat.
The reproduction of these alga is interesting. They reproduce by cell division. Before division, the cell valves push apart and the cell contents divide in half. The valves separate. Each one becomes a lid, that is, the upper valve.