How does chloroform destroy cell membranes

Chapter 06.04: The cell membrane and cellular processes

Source image: CC-By-SA 3.0 by Wikikommonsusers Dhatfield and LadyofHats, Marina Ruiz, Creative CommonsAttribution-Share Alike 3.0 Unported; Thank you! https://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_4.svg

The cell membrane

Every cell, regardless of whether it is animal or vegetable, is encased by a cell membrane. A large number of different proteins, which in turn fulfill a wide variety of functions, are embedded in this membrane.

Many are channel proteins for the passage of e.g. ions or other soluble substances. Others represent transmembrane receptors for various substances in the environment.

This image of a yeast cell was prepared using the freeze fracture method and shows how densely these proteins are stored in the membrane. (Magnification 22,000x)

Source picture: EM recordings with the kind permission of Prof. Dr. This email address is being protected from spam bots! To display JavaScript must be turned on! et al, Ulm University, https://www.uni-ulm.de/elektronenmikoskopie/

Biomembranes: The cell membrane

Cells, but also their organelles, are surrounded by biomembranes. Cell membranes enclose the cytoplasm and demarcate it from the outside. Cell membranes are very thin and much less stable compared to the cell wall.

  • The cell membrane limits the plasma to the outside (plasmalemma).
  • In plant cells, the cell membrane passes over plasma bridges (plasmodesmata) between the cells continuously into the membrane of the neighboring cell. Such connections serve the exchange of substances and communication.
  • The many organelles such as vacuoles and plastids (chloroplasts and mitochondria) are also surrounded by a membrane (= tonoplast)
  • Membranes allow substances (e.g. water and salts) through. Smaller molecules often passive, larger ones active (=> selectively permeable)
  • In contrast, simple membranes are only selectively permeable, that is, they are permeable to water, which acts as a solvent, but not to dissolved larger particles (larger molecules and charged particles = ions).
  • The outside of the cell membrane is covered with various receptors and surface proteins.
  • The cell membrane is usually not visible in the light microscope because the elastic, deformable and stable membrane is only 6 to 9 nm thick.

Structure of biomembranes:

Lipids and proteins and often small amounts of carbohydrates are found as components in all biomembranes.

Membrane components: lipids

  • Lipids are fatty and fat-like substances
  • In the biomembrane one finds mainly phospholipids (lipids which contain a phosphate group) as well as glycolipids (lipids which have bound carbohydrates).
  • Lecithin is one of the most common membrane proteins. It's a phospholipid.
  • Lipids form a double lipid layer, the polar (hydrophilic) ends of which protrude towards the aqueous environment, while the apolar, lipophilic tails face each other,
  • All lipids are readily soluble in fat and organic solvents, but insoluble in water

Lecithin - a common membrane lipid

As a complex molecule, lecithin essentially consists of five chemical components:
Choline, phosphate, glycerin and 2 fatty acids.

Phosphoglycerides have both phosphate (PO4)3- as well as two fatty acids bound. The phosphoglyceride “lecithin” also has a choline bound to the phosphate.

Membranes consist of a lipid bilayer and contain proteins

There are two types of proteins:

a) Peripheral proteins (= surface proteins) adhere electrostatically to the membrane from the outside

b) Integral proteins are bound into the lipid bilayer and some of them are also visible from the outside. As transport proteins (also called tunnel proteins), they can form a fine channel that allows small molecules and water to enter and exit.

The transformation and movement processes of the membrane are referred to as membrane flow, since all components belong to the same system and can move freely. Membranes are not static and do not have a fixed structure; they can move against each other

The ratio of lipids to proteins is from 1: 4 to 4: 1. It depends on the type of metabolic activity of the associated cells.

The cell membrane in detail:

Source graphic: Public domain based on the graphic by Lady Of Hats, Marina Ruiz; https://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_en.svg - Muchas Gracias

Tasks:

1. Discuss to what extent a vessel filled with marbles at the bottom is similar to a membrane?

2. Try to develop a better membrane model.

Functions of membrane proteins

Membrane proteins have different roles. They are specially manufactured by the cell for their respective purpose:

  • Transport of substances through the membrane: tunnel proteins, carriers, channel proteins
  • Docking points for substances: receptor proteins (recognize, for example, hormones or foreign substances according to the lock and key principle)
  • Glycoproteins are membrane proteins that have bound carbohydrates. They are used for communication between cells (especially in immune cells and hormone receptor cells) and make some cell surfaces more slippery. There are more glycoproteins in membranes than proteins that have not bound any carbohydrates.

The cell membrane is a double membrane

The membrane contains many proteins. These run through them e.g. as channels or can be found on the surface. In addition, there are glycolipids (phosphate-free membrane lipids) and cholesterol molecules on the membranes. In addition, the cell membrane is supported from the inside by filaments (threads) of the cytoskeleton.

The membrane is constructed as a double lipid layer. It is therefore hydrophilic on the outside and hydrophobic on the inside. More detailed explanations in the chapter on the cell membrane.

Membrane structures for connecting cells

Desmosomes

Desmosomes are so-called "sticking points" that are located on cell membranes. Above all, they hold the cells together, which are located in mechanically stressed tissues (especially in epithelia or muscle cells). Deformation energy acting on the tissue, such as when stretching and pulling, is distributed more evenly and the tissue holds together more tightly and does not tear. The adhesive plate itself has a stabilizing connection to the cytoskeleton.

Tight junctions

Tight junctions connect neighboring cells with membrane protein fibers (occludin & claudin). They are like belts around epithelial and endothelial cells so that the cells hold together tightly. The main effect is thus a restriction of the membrane flow so that other proteins stay in place. At the same time, a diffusion barrier is formed in this way.

Gap junctions

Gap junctions are tunnel-like connections between cells, which occur mainly in nerve cells, sensory cells and muscle cells. They allow molecules to be exchanged between cells more quickly than the usual membrane transport proteins. They can also be closed.

Plasmodesma

In plants, the cytoplasm of two neighboring cells is not only separated from one another by the cell membrane, but also by the cell walls of each of the two cells. That makes the exchange of substances difficult and slow. Plasmodesmata are tube-like connections that are large enough that even ER can be threaded through them.

Diffusion through membranes

1. Neutral red test in the test tube:

Oil and water are placed in a test tube and then dissolved in neutral red. The predominantly lipophilic neutral red dissolves mainly in the oil, which takes on a red color. The water is colored orange at best. Now you add acid and the water turns red, whereas the oil becomes discolored.

S: The neutral red dye does not dissolve well in water because it is a fat-soluble (= lipophilic) dye. The acid protonates the lipophilic substance neutral red, which turns it into neutral rotation (with a positive charge due to the added proton). As an ion, it is hydrophilic and dissolves in water.

2. Neutral red solution is added to onion cells.

B: The vacuoles of the onion cells turn red

S: The substance neutral red, as a lipophilic substance, can penetrate the lipid bilayer of the cell membrane and the vacuole membrane (tonoplast) well. In the vacuole, however, there is a slightly acidic environment and there is water. Only water-soluble substances can dissolve in the vacuole. The acid causes protonation (again as in V1). The neutral rotation occurs, which can be easily dissolved in the water and the hydrophilic environment of the vacuole. The vacuole turns red.

The neutral red dye can also no longer escape from the vacuole, since neutral rotions are hydrophilic and cannot easily penetrate the lipophilic layers of the vacuole membranes.

Lipophilic substances can penetrate membranes. Hydrophilic substances can only penetrate the membrane if they are very small or if there are special ion channels or carriers for them.

Neither applies to the fabric neutral red. It's a fairly large molecule.
The vacuole has thus become an ion trap for neutral red.

tasks

  1. The experiment described above for staining the vacuoles only works if tap water is used. If deionized (or distilled) water is present, only the cell walls (but not the vacuoles) turn red. The entry of the dye does not take place. Explain why that is.

    The following values ​​serve as an aid for explanation:
    pH tap water> 8 -> basic
    pH distilled water pH <6 -> acidic)

    Components of the cell wall such as pectin carry negative charges.

Transport of substances through biomembranes

If you look at cell membranes under an electron microscope, you can see that there are many proteins on and in the membrane. Up to 100,000 different types of protein can be found in a cell. They enable a variety of reactions, such as the transport of substances into the cell.

However, the proteins are not firmly anchored, such as plants that grow firmly on a wall. The membrane can be imagined more like a liquid in which the integral proteins “swim”. In doing so, they can form “pores”.

Proteins are in and on the membrane.

Substance transport in and out of the cells: There are now several possibilities for substances to get into and out of the cell. Some are always running, others are controlled by the cell exactly as required.

1. Free diffusion:

With regard to permeability, different processes can be observed in membranes:

Free diffusion is an often found way of entering cells. In order to understand them, one has to know that in living systems membranes are mostly only partially permeable (= selectively permeable). This means that the biomembrane is an obstacle for larger molecules (many salts, large ions, organic substances such as sugar, etc.) to enter the cell. It is much more difficult for these large molecules than small ones, as they cannot “smuggle their way through” the phospholipids of the membrane.

Small particles such as water, oxygen, carbon dioxide and glycerine can usually easily enter the cell. Because of the natural vibration1 of the molecules, it is possible for them to tremble through the lipid bilayer, so to speak, and thus to get into the cell.

Water (H.2O), oxygen (O2), Carbon dioxide (CO2) and small molecules like glycerin (C3H5(OH)3) easily get into cells by simply crossing the biomembrane.

Fat-soluble (= lipophilic) substances, such as the harmful solvent benzene, do this even though they are quite large molecules. They can, so to speak, dissolve through the lipid bilayer. This process is comparatively slow.

A comparison to the entry of fat-soluble molecules: Many people stand in front of the stage at a concert. However, smaller viewers can persistently "push" their way through the crowd to the first rows.

But what is the reason why molecules and ions get into the cell in the first place?

The driving force is solely the difference in concentration (i.e. the concentration gradient, also known as the gradient) between the outside and the inside of the cell. The transport takes place voluntarily (i.e. without energy demand (without ATP consumption)) from the place of high concentration to the place of low concentration. This compensation always takes place.

The voluntary transfer of substances into and out of cells is called free diffusion. The cell has no way of controlling the uptake and release of substances. Energy is not required for this!
The uptake and release of molecules through free diffusion depends, among other things, on the size and charge of the particles to be taken up. The membrane is therefore selectively permeable.

In order, for example, to prevent the leaves from giving off water on hot summer days, the cells must find another option. For this purpose, plants often have a waxy insulating layer on the leaves, the cuticula.

2. More specific Transport through membranes:

There are two forms of specific (controlled and selective) transport:

a) Passive transport (= facilitated diffusion) through biomembranes:

As with free diffusion, the driving force behind facilitated diffusion is a difference in concentration between the inside and outside of the cell. The difference is in how molecules get into the cell.

Selected molecules enter the cell faster through existing entry openings (including carriers (also called translocators) and channel proteins) than with free diffusion. No energy is used in this process.

If there are many molecules of one type (e.g. the ions of a salt solution), this entry method is very fast, as the chance that an ion will hit the appropriate channel is quite high. If but very If there are many molecules (i.e. more molecules than there are translocators!) and all small channels are occupied, the entry speed does not increase any further because all small channels are "occupied". The "saturation value" has been reached.

Example: the ion transport through nerves and muscle cells is maintained by passive transport.

b) Active transport through biomembranes:

It is not always the case that ions have to be transported from the place of high concentration to the place of low concentration. Against a concentration gradient (i.e. from a place of low concentration to a place of high concentration!), Molecules can also be transported (only with ATP / energy consumption). The energy carrier ATP is broken down into ADP + P. This decomposition releases energy.

Here, too, carriers and channel proteins as well as the so-called ion pumps are used:

Specific transport by carrier

So-called translocators (= carriers) are tunnel-like proteins that are located in the membrane and run through it. One speaks of integral proteins. They can bind substances and convey them through the membrane. In doing so, they change their shape.

Advantages of this method:

- the uptake is faster than with free diffusion

- the carriers are substrate-specific, i.e. they specialize in certain molecules. The cell can thus control what it takes in.

Disadvantage:

- During active transport, carriers consume energy in the form of ATP. The ATP is formed by the mitochondria and is produced by cell respiration, during which, for example, blood sugar is oxidized with oxygen to form water and carbon dioxide.

Transport through membranes

Schematic arrangement of possible integral membrane proteins:

Source graphic: Public domain based on the graphic by Lady Of Hats, Marina Ruiz; https://commons.wikimedia.org/wiki/File:Scheme_facilitated_diffusion_in_cell_membrane-en.svg; https://commons.wikimedia.org/wiki/File:Scheme_secundary_active_transport-en.svg - Muchas Gracias

We know three different carriers (specific transports)

Transport through membranes can be done by translocators. This is mostly done passively, that is, without the need for energy.

1. Uniport:

A particle is only going through in one direction
the carrier / channel protein (translocator)
transported.

2. Symport

Two substrates are made at the same time, in one direction
transported in one direction by the channel protein.

3. Antiport

Two substrates are turned into opposite one another at the same time
Direction transported. A substance gets into the

Cell, the other out. This is usually accompanied by energy
necessary in the form of ATP.

Endo- and exocytosis

Membrane flow:

The membrane and its components are not a rigid, but a dynamic, moving system. There is a lot of exchange between the individual membrane systems. The transformation and movement processes of the membrane are called Membrane flow because all components belong to the same system and can move freely against each other. One can imagine that the phospholipids but also the proteins can slide past each other.

Endo- and exocytosis - phenomena of biology:

Cells release substances:

- tear fluid

- digestive enzymes

- saliva

- sweat

Cells take up large substances:

- Viruses and bacteria are absorbed by phagocytes

- Tar from cigarettes is absorbed by lung cells in the lungs

- Protozoa ingest food particles

The question is how cells can absorb or release such large substances without opening the cell membrane and causing the cell to leak. Uptake via channel proteins / carriers is also ruled out, as these substances can only be absorbed in the maximum molecular size.

Exocytosis (release of secretions from cells):

If vesicles (= membrane vesicles) pinch off from the ER inside the cell and become a Golgi apparatus, which in turn can form vesicles (Golgi vesicles are usually filled with secretions and fluids), these can also become the cell membrane wander and unite with it. This is not a problem, since all membranes consist of the same building blocks and these are interchangeable.

The vesicles of the Golgi apparatus contain secretions (enclosed by membranes). Upon contact with the cell membrane, the vesicle membrane becomes the cell membrane. In this way the liquid can get to the outside (=Exocytosis).

Endocytosis (absorption of solids and liquids in cells):

In the reverse process, vesicles become detached from the cell membrane and move into the interior of the cell. If solid particles (e.g. plant residues, bacteria, starch grains) are absorbed, one speaks of Phagocytosis (phagein, gr. = eat; cytos, gr. = cell). In the case of liquids, the process is also called Pinocytosis.

A third process is receptor-controlled uptake. For this purpose, certain receptors are located on the membrane, which, when in contact with certain (desired) substances, trigger the inversion of the membrane. The resulting vesicles have a rough surface because the proteins are still on them. They are called "coated vesicles".
Liquids in particular are absorbed through the receptor-controlled endocytosis.

All three processes of endocytosis take place in many membrane sections (=> many constrictions). For example, amoeba can ingest smaller protozoa as food through phagocytosis. The paramecium has a special field, the so-called mouth field, for feeding through phagocytosis. In this way, fat is also absorbed (= absorbed) in the intestine.

Overview - endo- and exocytosis

Processes such as endo- and exocytosis remove or re-add material to the membrane. The membrane is therefore always changing and remodeling!

Membranes are therefore not to be regarded as static, but rather always in motion and "flowing".

Lysosomes

Small vesicles in which substances are enclosed are called vesicles. In this case, for example, products of the Golgi apparatus can be enclosed, or they can also be food absorbed by single cells through endocytosis and then enclosed by a membrane.

Why do hands wrinkle when bathing?

When swimming, bathing and washing up, the skin becomes wrinkled after a while. The cause is on the one hand water penetrating into the cells through passive membrane processes.

On the other hand, our cells on the fingers and toes are also heavily covered by dead corneas. It contains so-called horn cells. The cornea also absorbs water! Although it does not suck in the water, the cornea swells as it penetrates the cells and intercellular spaces. However, the cornea is still partially bound to the underlying subcutaneous tissue. However, due to the inconsistent connection, the swelling is now not regular.

Since only the hands and feet contain up to 40 layers of horny cells, the wrinkles can only be seen in these places.

Preliminary experiments for a deeper understanding of diffusion

V: A petri dish is placed on the overhead projector, and then one of a grain of potassium permanganate in water is added.

B: The dye appears to distribute itself. After a while, it is finely distributed throughout the vessel.

S: Due to the Brownian molecular movement (= own trembling movement of all particles!) Particles collide again and again and are thus distributed in the available space. An undirected concentration compensation occurs.

The warmer a solution is, the stronger the natural movement of the particles.

Osmosis & Diffusion

1. Change in volume and weight of a chicken egg in different solutions

Under the lime shell of the chicken egg there is a selectively permeable membrane (= membrane that is only permeable in one direction). In order to examine this membrane, the calcareous shell is removed.

V: The lime shell of the egg is removed by placing it in 10% acetic acid for about 6 hours. The egg is then weighed and placed in distilled water (= hypotonic solution).

After about 20 minutes, the egg is weighed again and then placed in a saturated saline solution (hypertonic solution). After about 20 minutes, the egg is weighed again.

B:

solution

Weight

hypotonic (distilled water)

heavy

"Normal" state

normal

Hypertonic (saline solution)

lighter

Conclusion: (see explanation in the following experiment with the onion cells.)

2nd attempt at plasmolysis - deplasmolysis:

The material used is cells from a red onion (from the outer, single-layer epidermis of an onion skin) or cells from the pulp of privet berries. The privet cells are obtained by scraping off some of the pulp with a scalpel

attempt

observation

1. The cells of the onion membrane are placed on a microscope slide, a cover slip is placed over it and observed under the microscope

The reddish colored cell sap vacuoles take up almost the entire cell volume.

2. A hypertonic solution (e.g. concentrated saline solution) is dripped onto the edge of the cover slip and sucked under the cover slip with a piece of filter paper.

The cell sap vacuole becomes smaller and becomes darker in color. The vacuole shrinks immediately after the saline solution has been sucked through.

3. Now a few drops of distilled water are placed on the slide and sucked under the cover slip

The cell sap vacuoles return to their original size and color after a short time.

Onion cells before adding the salt water:

Plasmolysis - isotonic solution

Onion cells shortly after adding d. Salt water:


Enlargement:

What do you guess from which side the salt water was added and why not all cells show plasmolysis?

Frontier plasmolysis

In this state, turning back is no longer possible! The cell has lost too much water, the vacuoles often tear, are damaged and lose their function. The cell dies!

Frontier plasmolysis


Conclusions:
In order to understand what is going on, you have to know what diffusion is:
The diffusion is a process in which atoms or molecules in liquids or gases spread freely. Diffusion is based on Brownian molecular motion (= proper motion of atoms and molecules).

However, free diffusion cannot take place in onion cells because the membrane hinders free diffusion. Living cell membranes are selectively permeable (a somewhat older expression is also semipermeable) for water and smaller ions. This means that it is permeable to some components such as water and small ions, but not to large ions!

If a living cell is brought into a solution in which there is a higher concentration of ions on the outside than in the cell sap vacuole, water diffuses from the vacuole through the cell membrane into the surrounding solution (since more water molecules now collide with the vacuole membrane from the inside than from the outside ).

The decrease in volume of the vacuole associated with the leakage of water initially leads to a decrease in the cell turgor (= wall pressure the cell against the cell wall - the pressure is triggered by a vacuole bulging with liquid), then to a detachment of the protoplast from the cell wall (=Plasmolysis). This process is reversible (the reverse is called Deplasmolysis).

Source image: Public domain by wikicommonsuser LadyofHats, Marina Ruiz - Muchas Gracias; https://commons.wikimedia.org/wiki/Media:Plasmolyse_Pflanzenzelle.svg

Under Plasmolysis one understands the detachment of the vacuole membrane from the cell membrane. Cause is the decrease in volume of the vacuole associated with the leakage of water. It arises from a higher external concentration of ions compared to the concentration in the cell.

Deplasmolysis is the reverse process!
In this way, water diffuses from the vacuole through the cell membrane into the surrounding solution.

The “driving force” of plasmolysis is the difference in concentration between the inside and the outside. Plasmolysis is limited to living cell membranes.

Under osmosis one understands the process of diffusion of a solvent through a selectively permeable (= partially permeable) membrane.

Danger: In some books, plasmolysis is described as the movement of water. But this is basically only the osmosis or the osmotic penetration / leakage of the water.

The prerequisite for osmosis is that two solutions of different concentrations (or a solution and the pure solvent, e.g. water) are adjacent on both sides of the membrane. From the side of the more concentrated solution, on average fewer solvent molecules collide with the selectively permeable membrane than from the less concentrated solution. As a result, a lot penetrate more Molecules of the highly concentrated solution cross the membrane, as conversely, from the weakly concentrated solution to the highly concentrated one.

3. Experiment on the selective permeability of living membranes:

V: 3 potato halves are hollowed out inside, so that an approx. 1 cm deep and 1 cm wide indentation is created. One of the potato halves is cooked for a few minutes. Table salt is poured into the recess of the boiled potato and one recess of the raw potato. The second raw potato is left without the addition of salt. The three potato halves are placed in a Petri dish filled with water.

observation:

After about 30-40 minutes, the cavity of the raw potato, which contained salt, is filled with water. In the case of the boiled potato, no water has accumulated in the recess, as is the case with the raw potato without added salt.

conclusion:

1. In the raw potato, water is osmotically extracted from the surrounding cells by the salt.

2. In the raw potato without the addition of salt, on the other hand, there is no leakage of water from the cells of the potato.

3. The observation that in the boiled potato, despite the presence of highly concentrated salt, no water accumulates in the recess, shows the restriction of the selective permeability of living cells. Cooking destroys the proteins in the cell membrane and thus the channels for water to escape from the cell.

4th attempt: "Potato - Osmometer"

The "potato osmometer" is a simple, clear example of an osmometer, as it is constructed according to Stocke (Stocke`s device with Pfeffer cell).

To set it up, a hole is drilled in a potato with a cork drill, this is filled with salt and sealed with a rubber stopper. A thin riser pipe is inserted into the hole in the rubber stopper. This “apparatus” is then immersed in water.

Explanation: The high salt concentration inside the potato has a strong osmotic effect and removes water from the potato tissue. The tissue in turn absorbs water from the environment. The uptake of water is visible in the riser pipe. The water rises until the hydrostatic pressure of the water column in the riser compensates for the effect of the concentration gradient. The potato tissue corresponds to the selectively permeable membrane of a Pfeffer cell.

Summary osmosis:

Basically, in nature there is always an equalization of concentration from the place of high concentration to the place of low concentration. If there is a selectively permeable membrane, which is only permeable to water, then between the dissolved substances on both sides of the membrane no direct concentration compensation take place!
Instead, water molecules penetrate the membrane and thus ensure a dilution on the part of the high concentration. This also leads to the equalization of the difference in concentration.

This movement of water particles can be found in many areas of nature:

If people eat salty foods, the body compensates for this with body water and becomes dehydrated in the process. He gets thirsty and has to take in new water.

Tasks:

1. Explain the following terms: plasmolysis, turgor, selectively permeable, osmosis, diffusion

2. Seafarers were previously warned not to drink seawater in distress, even if they were dying of thirst. Can you explain why?

3. Warn athletes: After exercising, one should not drink strong coffee (at least not exclusively!), As this dehydrates the body. Show the connection of water requirements through competitive sport and coffee enjoyment.

Osmosis as the mainspring of plasmolysis

In the beginning there is a highly concentrated saline solution outside of cells or tissue. As a result, the protoplast (= living part of the cell) becomes detached from the cell wall after a short time. The vacuole becomes smaller until the protoplast is completely detached from the cell wall and spheres off.

The strength of the contraction of the protoplast depends largely on the concentration of the saline solution used!

Root cause:

The water inside the cell is less concentrated than the water outside. Such imbalances automatically balance each other out in nature (if possible!). water diffused So out of the cell plasma and the cell sap vacuole. The mainspring of this concentration equalization taking place here are the different concentrations of dissolved salts between the solution outside and inside.

The balance now comes mainly through that Diffuse of water through the cell membrane. All of this is only possible because biomembranes are primarily permeable to water, but not to dissolved substances. They say the membrane is selectively permeable.

As a result, the more hypotonic (i.e. less dissolved particles) solution inside the cell is balanced with the hypertonic (i.e. more dissolved particles) solution outside the cell.

The diffusion of water that takes place through a selectively permeable membrane is also called osmosis.

A comparison for understanding:

If you evaporate water in a saucepan, a lime (salt) coating forms on the bottom.

But if you take the pot off the stove shortly beforehand, the remaining water is much more salty than the original water.

=> The release of water from the cell (during plasmolysis) actually increases the salt concentration inside the cell, which is thus the concentration of the external medium (and this is additionally diluted by the water flowing out of the cell)

Further information:

https://de.wikipedia.org/wiki/Plasmolyse

Turgor and wall print

A normal cell has a wall pressure of = 0. This means that the suction tension is equal to the osmotic value of the cell plasma.

When water is absorbed, the wall pressure is greater than 0, the suction tension will consequently decrease (as the dilution inside continues to increase)!

This goes so far until the suction tension becomes less and less due to further water absorption, until the cell can no longer absorb water. This condition is called "turgescent".

The osmotic equation of state for cells is: S = O - W
S = suction force;

O = osmotic value;

W = wall pressure is

Osmosis and plasmolysis tasks

1. Blood cells must be in a so-called isotonic saline solution if they are observed under a microscope, for example. Can you explain why with the help of the graphic?

Source image: Public domain by Wikicommonsuser LadyofHats, Marina Ruiz Muchas Gracias; https://commons.wikimedia.org, /wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg

2. Paramecia living in fresh water have pulsating vesicles, ciliates living in the sea do not. What are the causes?

3. Roadside plants often die when road salt is used in winter. Name and explain the causes.

4. A meadow is accidentally fertilized twice in a short time with mineral salt fertilizer. The lawn gets light spots and seems to be drying up. Explain!

5. Rain makes ripe cherries burst. Explain why this is so.

6. Strong, caffeinated tea (and coffee) with sugar make you want to urinate more than if you had drunk the same amount of water. Explain!

Absorption of toxins into the tissues

The absorption of toxins into the human body occurs through the cells of the skin, particularly through inhalation of vapors, contact with the skin, ingestion or conscious ingestion. Depending on the route, the toxins usually reach the lungs, blood, kidneys and intestines first.

A small selection of pollutants follows. Some are now restricted or prohibited in their use. Others are sometimes deliberately added to oneself.

  • Pesticides
  • Hydrocarbon compounds (especially the chlorinated hydrocarbons)
  • DDT
  • Heavy metal compounds
  • Formaldehyde vapors
  • Mold toxins
  • Combustion residues (burnt sausage!)

The uptake into the cells takes place via the mechanisms that have been learned up to now.
All of the following substances have in common that they influence the normal function of cells and are therefore harmful.

You can read more information on this topic in the “Drugs” chapter!

Methods of investigation of cell membranes

a) Electrophoresis:

A substance to be examined (e.g. a lipid) is applied to a gel plate and a direct voltage is applied to both ends of the gel plate. The polar components are drawn to the corresponding poles, the non-polar ones stay in the middle. (Electrophoresis is also used to study proteins.)

b) Fat proofs

- Evidence of grease stains

- Thin layer chromatography of lipids

- chemical detection (with Sudan (III) glycerine)

c) Electron microscopic evidence - TEM (Transmission Electron Microscope)

The resolution limit of the eye is around 0.1mm. With the light microscope a maximum resolution of about 500nm can be achieved (1 nm = 1 / 1000mm), with a TEM, which has an electron beam instead of a light beam & electromagnetic lenses instead of optical lenses) the resolution is about 0.3nm.

If you look at the magnification, you can achieve a magnification of about 2000 times with the light microscope and about 1,000,000 with a TEM. The reason for this lies in the wavelength, which for visible light is at least 380 nm, but for electrons (at 100 kV) is only 0.0038 nm.

However, in comparison to the light microscope, with the TEM you cannot look at living objects. The samples must first be specially prepared, either by chemical fixation or by freezing (cryopreparation). In addition, the objects for the TEM have to be very thin (max.100nm).

d) Electron microscopic evidence - SEM (scanning electron microscope)

The SEM works on a similar principle, in which an electron beam is guided over the object and interactions between the electrons and the object are used to generate an image of the object. The maximum theoretical magnification factor is around 1: 500,000.

The scanning electron microscope is based on scanning the object surface using a finely focused electron beam. The entire process usually takes place in a high vacuum to avoid interactions with atoms and molecules in the air.

The electron beam is generated in a field emission electron gun. For example, tungsten wires are used, which are heated and release electrons in the process. This electron beam is focused on a point on the object with the help of magnetic coils.

e) myelin figures

V & B: Oil and water (the water phase can be colored) are mixed. Two phases are formed. Then you add lecithin.  An emulsion is formed

S: There are substances that cannot be mixed with one another. Fats are lipophilic and float on the watery layer. This is called lipophobic or hydrophilic. Only the addition of an emulsifier (like lecithin here) can the two phases mix with one another. The mediating effect of the emulsifier only takes place at the interfaces. For this reason, shaking it well helps because so many interfaces are created. As a result, the emulsion usually turns white-cloudy.

Observation of an oil stain on a water surface

V: Fill a petri dish with water and put an oil stain on the surface. What happens when you add some dish soap?

What is the difference between fatty acids, fats and lipids?

Lipid is a collective name for Fats and fat-like substances (lipoids) with a non-uniform organic-chemical structure. They are insoluble in water, but soluble in organic solvents such as gasoline, benzene, ether, chloroform, methanol or acetone.

Lipids are an important part of the diet.

- 1 gram of fat contains 39 kJ = 9 kcal of energy. 1 gram of sugar only 4 kcal.

- So lipids are a very high-energy source of food

- There are some lipids in food that humans cannot make themselves.

- Essential lipids e.g. E.g .: linoleic and linolenic acid

  • Lipids as triglycerides are an important storage material for energy (sugar, on the other hand, is stored in much smaller quantities in the form of glycogen in the liver.)
  • Lipids in the skin protect against injuries because they have a cushioning function. Important organs can also be protected by a layer of fat. They are also good protection against the cold in the skin
  • Lipids are an important part of cell membranes. (often modified lidids or compound lipids such as cholesterol, tocopherol (= vitamin E), phospholipids or glycolipids (= lipids with sugar content)
  • As bile acids, lipids facilitate fat digestion. (Emulsifier effect)
  • Lipoproteins (= fat protein compounds) facilitate the transport of fat in the blood, as they form small spheres around the completely water-insoluble triglycerides.
  • Fatty acids are special organic acids (unbranched monocarboxylic acids), which are made up of a - COOH group (= carboxyl group) and a hydrocarbon chain of different lengths (= remainder, e.g. R.1)consist.
  • Natural fatty acids usually consist of an even number of carbon atoms and are unbranched. Fatty acids differ in the number of carbon atoms (chain length) and the number and position of their double bonds. Fatty acids without double bonds are called saturated. Unsaturated fatty acids have one or more Double bonds between the carbon atoms of the chain. Essential fatty acids are those that an organism cannot synthesize from other food.
  • The sodium or potassium salts of the higher fatty acids are the soaps.

Fatty acid molecule and shorthand notation

Review questions cytology and cell organelles and cell structure:

Membranes and membrane processes

  1. How are membranes constructed. Create a model.
  2. What kind of proteins are there associated with membranes?
  3. What are their tasks?
  4. In middle school, you might have extracted chlorophyll from leaves. To do this, you first boiled the leaves and then put them in alcohol. Explain why both steps are necessary.
  5. What are surface proteins, what are their tasks?
  6. Make a map of ways for solids and liquids to get into and out of cells. What are “translocators” in this context? What is “endocytosis” / “exocytosis” in this context?
  7. What is plasmolysis (deplasmolysis). Explain exactly with a good sketch and a description of all processes?
  8. What happens to tar in the lungs after a while? Where is it with heavy smokers?
  9. Why are watered plants plumper and tighter than "thirsty" ones?
  10. How can organ rejection occur after a transplant?
  11. To describe blood groups, they are divided into the AB0 system (A, B, AB and 0). Two different surface proteins of the red blood cells are hidden behind the letters.
    a) Explain why there can be four blood groups with only two different surface proteins (if necessary: ​​https://de.wikipedia.org/wiki/Blutgruppen)
    b) White blood cells clump together foreign proteins in the immune defense reaction. Explain how deadly blood infusions can occur? (In other words: why do you have to pay attention to your blood type when donating?)
    c) Which blood groups are suitable for someone who has blood group A? (or at?)
    d) What is meant by universal donor blood and universal recipient?
  12. Strong caffeinated tea (like coffee) (especially with sugar) is not regarded by nutrition biologists as a "fluid donor" for the body. Both also lead to an increased urge to urinate (especially in comparison with the same amount of water). Explain why nutritional biologists agree.
  13. If you add heavy sugar to ripe, firm strawberries, they lose juice and after a day they are very soft. Explain the context.
  14. What are the effects of nicotine and what effects does cigarette tar have on the human body?
  15. Explain how toxins such as heavy metals enter the body.

Experiment on amoeba:

a) An amoeba is cut in half in the middle. (The piece containing the cell nucleus lives on). The second dies after a few days. Explain

b) If the nucleus of another amoeba is planted in the seedless piece, the fragment lives on and develops normally. Explain