Some bacteria (myxobacteria) move due to the secretion of mucus (“reactive” movement).

Some bacteria (myxobacteria) move due to the secretion of mucus (“reactive” movement).

In the dorsal part of the shell is the body of the mollusk, from which the leg departs. The wings of the shell and the folds of the mantle in the back do not fit snugly together. In this place two openings, or siphons are formed. Water enters the mantle cavity continuously through the inlet (lower) siphon due to the movement of numerous cilia covering the surface of the body, the inner sides of the mantle folds, the gills and other organs of the mantle cavity. Undigested food residues and metabolic products are removed from the mantle cavity through the outlet (upper) siphon.

Toothless nutrition. Along with water, bacteria, algae, simple and small remains of plants and animals enter the mantle cavity through the inlet siphon. Larger food particles cannot enter the mantle cavity because they are not allowed by the lattice gill plates covered with ciliated epithelium.

The flow of water brings this food to the mouth of the toothless, which is surrounded by two blades and placed in the mantle cavity at the front end of the body, at the base; legs. From the mouth through the short esophagus food enters the stomach, which opens the duct of the liver, a long medium! a gut forming several loops, and a short rectum, or posterior, gut, which opens into the mantle cavity.

The edentulous respiratory organs are represented by gills, which are permeated with numerous blood vessels. They receive oxygen from the water that washes the gills, and carbon dioxide is released into the https://123helpme.me/write-my-lab-report/ water.

The toothless heart consists of two atria and one ventricle. The circulatory system is not closed.

The excretory system is represented by two kidneys, the ducts of which open into the mantle cavity.

The edentulous nervous system is represented by three pairs of nerve nodes. One pair (main ganglia) is located on the sides of the mouth near the end of the shoulder blades, the second – under the hindgut near the posterior sphincter, and the third – in the leg. Nerve nodes are interconnected by nerve jumpers. Due to low mobility and passive nutrition, the nervous system of bivalves (compared to gastropods) is somewhat simplified, and the senses are poorly developed. At the base of the gills are a pair of chemical senses (osphadium), and at the foot – two statocysts (equilibrium organs). There are many tangential cells on the mouth blades and the edges of the mantle. There are no main tentacles, and often organs of sight.

Toothless – heterosexual animals. In appearance, males do not differ from females. The gonads are paired, located at the top of the leg. Males emit sperm into the water. With water, spermatozoa penetrate into the mantle cavity of females, where they fertilize eggs. From them larvae with toothed leaves develop.

Through the outlet siphon, the larvae are released into the water and attached to the body of the fish, where they develop for 1-2 months. At this point, the fish develop a tumor. After maturation, the toothless tears the skin of the fish and falls to the bottom. Due to the parasitic way of life in the early stages of its development, sedentary toothless people can get to new (often very remote) places of life.

Marine bivalves are typical benthic animals that can bury themselves in the sand. They often form large clusters at the bottom (mussel, oyster, and other “plantations”). The weight of the largest bivalves can reach 250 kg, and the length of their shell – 1.5 m or more.

Some bivalve molluscs (such as the ship worm) can grind wood and stone, causing great damage to the wooden hulls of ships and the shore structures of ports.

Many bivalves are of practical importance. Pearls and mother-of-pearl are extracted from them; oysters, mussels, scallops, etc. are used in food.

Cephalopod class

Modern cephalopods live exclusively in oceans and seas with high salinity. They are not found in the seas of Ukraine. Cephalopods are more complex than other classes. In terms of the development of behavior and senses, they have no equal among invertebrates. Cephalopods have a complex brain, protected by a kind of cartilaginous membrane – “skull”. In captivity, they quickly begin to recognize the person who cares for them, capable of complex behavior.

Most modern cephalopods do not have an outer shell (it is found only in the nautilus). The body is covered with a mantle, on its sides there may be fins. Under the mantle on the dorsal side are the remains of a shell. The head is separated from the body (squid, cuttlefish) or fused with it (octopus). On the head are tentacles with suckers that surround the mouth.

At the base of the head is a funnel – a muscular tube, one end directed to the mantle cavity. This is the main organ of reactive movement of cephalopods.

All cephalopods are predators, they catch prey with their tentacles and tear it into small pieces with a chitinous beak.

Man eats squid, cuttlefish and octopus meat. From the contents of the ink bag of cuttlefish and squid produce paint (sepia), as well as natural Chinese mascara. Fossils of fossil cephalopods are used as “guiding minerals”. Cephalopods are a food base for marine animals, including pinnipeds and toothed whales.

05.01.2012

Bacteria: structure and forms of cells, methods of nutrition. Abstract

General characteristics of crumbs, their classification. Cyanobacteria. The structure and shape of the cells of real bacteria. Methods of feeding and reproduction of bacteria

Bacteria are among the simplest organisms that can only be seen at high magnification under a microscope. They are traditionally studied by botany, but they are pre-nuclear organisms (prokaryotes), which together with the blue-green algae make up the kingdom

Crumbs. The size of the bacteria largely depends on external conditions and ranges from micrometer particles to several micrometers. Their length is 1-10 microns (rarely more), width – 0.2-1 microns. Most of them are unicellular, but there are also filamentous multicellular species.

The form of unicellular bacteria is divided into:

cocci, or spherical; cylindrical rods (bacilli); vibrios in the form of a comma; spirals – spirally curved sticks.

Some bacteria have the ability to move with the help of flagella, which are larger than the cell itself and are thin outgrowths of the cytoplasm. The number of flagella in different species varies (one, two or more). Some bacteria (myxobacteria) move due to the secretion of mucus (“reactive” movement). Spirals are characterized by translational, pendulum, corkscrew and wave-like movements.

The bacterial cell is surrounded by a dense shell, which consists of hemicellulose and pectin, and sometimes of proteins. For the most part, the shell is covered with a mucous capsule that protects the bacterium from adverse environmental conditions. Under the shell is the cytoplasmic membrane that surrounds the cytoplasm of the cell.

The cytoplasm of bacteria contains carbohydrates – glycogen and starch, fats, proteins, minerals, ribosomes, a large number of membranes and membrane structures and more. Bacterial DNA is located in a special nuclear zone of a cell called a nucleoid. No nuclear membrane is formed around the nucleoid. Cocci have one such “core” and bacilli – two or more. Not all bacteria have a nucleolus.

Most bacteria are colorless, some of them are red, green and purple, which is due to the presence of specific bacteriochlorophyll and bacteriopurpurin.

Fig. 1. Forms of bacteria (a) and the structure of the bacterial cell (b):

1 – bacilli; 2 – spirals; 3 – cocci; 4 – vibrios; 5 – shell; 6 – nucleoid; 7 – dispute; 8 – a layer of mucus; 9 – cytoplasmic membrane; 10 – flagella; 11 – inclusion; 12 – RNA particles most), in turn, are divided into saprophytes and symbionts.

Saprophytic bacteria feed on organic remains of dead plants and animals, human food. They cause putrefaction and fermentation (fermentation) of organic matter.

Decay is the breakdown of proteins, fats and other nitrogen-containing compounds by putrefactive bacteria. As a result of decay, nitrogen- and sulfur-containing compounds are released, which have an unpleasant odor. This process plays a huge role in nature, as it cleanses the Earth’s surface of animal carcasses and plant debris. Toxins formed during decay can cause poisoning or even death of humans and animals.

In this regard, it is forbidden to use in food or animal feed products that have signs of rot (specific odor, in particular). To prevent rotting of products and green mass, they are sterilized, dried, marinated, smoked, salted, frozen, ensiled, etc. These treatments kill putrefactive bacteria and their spores and (or) create conditions under which bacteria do not multiply.

Fermentation, or fermentation, is the anaerobic breakdown of carbohydrates by bacterial enzymes. This process has long been known to people. For thousands of years, people have been making wine using alcoholic fermentation, fermenting fruits and vegetables using lactic acid fermentation, and so on.

Bacterial parasites (one of the forms of symbiosis) live at the expense of living organisms. Some of them are pathogenic and can cause animal and human diseases (plague, typhus, tuberculosis, peritonitis, meningitis, sore throat, botulism, gas gangrene, etc.), others are the cause of plant diseases. These bacteria form spores that can retain their ability to infect for a long time (decades).

Some heterotrophic bacteria in the process of evolution have developed the ability to symbiosis (mutualism) with higher plants. These are, for example, nitrogen-fixing bacteria that live on the roots of legumes – nodule bacteria. They absorb nitrogen from the soil and air and convert it into compounds available for use by legumes, which in turn supply bacteria with carbohydrates and mineral salts. During one growing season, nodule bacteria accumulate up to 100 kg of nitrogen per 1 ha. This is taken into account when making crop rotation plans.

Autotrophic bacteria are bacteria that can synthesize organic substances from inorganic ones as a result of photosynthesis (phototroft) or chemosynthesis (chemograph). Phototrophic include purple and green sulfur bacteria, which synthesize components of their body from minerals and carbon dioxide, and use light energy.

Chemotrophic bacteria, or chemosynthetics, feed on chemosynthesis because organic matter is synthesized from inorganic energy due to chemical reactions.