Study the function of cell membrane and chloroplast

Cell is the most basic unit of life. But what else is in this cell? Plant cells include chloroplasts (mostly), nuclei, cytoplasm, mitochondria, cell membranes and cell walls.

Then what I want to discuss is the function of chloroplast and cell membrane.

Let's start with chloroplasts. According to what I read in the book before, chloroplasts have photosynthesis, that is, chloroplasts react with sunlight to convert sunlight into binding energy and supply it to cells. Then my guess is that the function of chloroplasts is to convert energy. So how to design an experiment to prove it?

The tentative idea of the experiment is verified by the control experiment. I use an animal cell and a plant cell and put them in the sun at the same time. If plant cells are photosynthetic with the sun, then plant cells will survive. Animal cells, without chloroplasts and energy sources, will die earlier.

The purpose of the experiment is whether chloroplasts have the function of transforming energy.

But it suddenly occurred to me that no, even if the final result is that plant cells survive and animal cells die. That can't prove that chloroplasts are transforming energy.

There are many small tissues in cells. Could it be that mitochondria played a role? Nuclei are also possible. So this experiment can't prove that chlorophyll produces energy. The second point is that animal cells will not die without chlorophyll, which may be caused by other reasons.

The problem of the experiment is that the single factor variable is not well controlled, and what can and cannot be changed should be that one has chlorophyll and the other has no chlorophyll. They are the same plant. And the environment should be the same.

To put it another way, chloroplasts can be converted into energy during photosynthesis, and oxygen can be discharged. Can we detect the presence of oxygen or increase its concentration?

Objective: Does chloroplast have the function of transforming energy?

The second experimental idea is: because chlorophyll will emit oxygen when it produces photosynthesis again, the purity of oxygen discharged from the group with chlorophyll will be improved. Enough to rekindle the extinguished match. Then we can design the control group and the experimental group.

The plant cells in the control group have no chloroplasts, while the plant cells in the experimental group contain chloroplasts, so the oxygen purity in the experimental group space will be improved. We can put chlorophyll into the oxygen release space with extinguished matches. If the match is rekindled, and the group without chlorophyll is not rekindled. It can be proved that chlorophyll can transform energy. (Thought experiment, no instrument)

Experimental materials: radish plant cells, sealed bottles, sunlight, chlorophyll extractor. Extinguished matches

Experimental steps: Chlorophyll was extracted from the plant cells of the control group with an extractor, and the two groups of plant cells of the plant were covered with different bottles and placed in the sun. Leave it for a period of time and put the extinguished matches into two groups of experiments respectively.

I didn't really do this experiment, but I think there are two possibilities for his experiment. )

The first possibility is that the matches in the experimental group are rekindled, while the matches in the control group are not rekindled.

The second possibility is that the experimental group did not rekindle and the matches in the control group did not rekindle.

Ideological conclusion: The first possible conclusion is that chloroplasts have the function of producing oxygen.

The conclusion of the second possible result is that chloroplasts have no oxygen-producing function.

Query on the experiment: He has many problems in this experiment. The first question is, is the oxygen released by chlorophyll in the experimental group enough for the match to be rekindled? I don't think it is enough to produce oxygen only by that small amount of chlorophyll. This will only lead to problems in the experimental results.

The second point: oxygen containing oxygen is in a glass bottle, because there is oxygen in the air. (Otherwise, how can human beings live? Even if the oxygen in the air is not enough to rekindle the match, whether the rigor of this experiment remains to be questioned. The purpose of this experiment is not to make univariate factors the same. This experiment is not perfect enough.

For the sake of rigor, I said that there are two possibilities for these thought experiments, but in fact we can think from another angle. Because someone has done such an experiment, if our experimental ideas, experimental purposes, experimental materials and experimental steps are the same as his, then the result of his final experiment is also our experimental result. The result of the real experiment is that the match does not rekindle, because there are too few chloroplasts and the oxygen produced is not enough to rekindle the match.

Then there is something wrong with this experiment. As I just questioned, the number of chloroplasts is not enough. So this experiment is not good enough. Maybe you can put these chloroplasts for 30 years until enough matches are put in, and the sudden oxygen is proved, but this experimental exploration is too time-consuming and not good enough.

Is there a third experiment: the experiment of the same univariate variable? There must be.

The experimental idea of an experiment is very important, but the experimental materials of an experiment are equally important. If you choose the right materials, your experiment will become very simple. We can't improve our experimental thinking any more, so we will change the choice of experimental materials.

What we want to prove is whether chloroplasts can produce oxygen, so can we find a creature that likes oxygen? If this creature likes oxygen, then this creature should be adsorbed on chloroplasts. So can we observe whether this creature is adsorbed on chloroplasts through a microscope? If this organism is adsorbed on chloroplast and observed by microscope, can it be concluded that chloroplast has the function of producing oxygen, that is, transforming energy? Then there may be a problem in this experiment, that is, will this creature be too big, which will affect whether the organism under the observation microscope is adsorbed on the chloroplast.

There are such creatures in the world. This creature is an aerobic bacterium. It is a kind of bacteria, very small, which can avoid what I just said. Because bacteria are not as big as cells. This creature likes oxygen very much. If you like oxygen at this time, it will be adsorbed on chloroplasts. We can use it according to the idea just now.

Objective: Whether chloroplasts can produce oxygen. (Does chloroplast have the function of transforming energy? )

Experimental idea: put aerobic bacteria on plant cells, and then observe whether the bacteria are distributed on chloroplasts.

Experimental materials: plant cells with chloroplasts, aerobic bacteria, microscope and cover glass.

Experimental steps: Aerobic bacteria are placed on plant cells. Leave it for a while and observe the chloroplast with a microscope. Compared with the chloroplast before the release of aerobic bacteria.

The results showed that aerobic bacteria were attached to chloroplasts through microscope observation.

Experimental conclusion: Chloroplast has the function of producing oxygen and transforming energy.

The logic of this experiment is correct, the univariate factor is the same and the experimental steps are simple. This experiment is possible, no doubt.

Next, we will study the cell membrane.

What is the first guess about cell membrane?

My first guess is that it is isolated from the outside world, which is a stable environment for the inside and easier to operate in cells.

The second guess is protection, which is secondary. Because for plant cells, it has the protection of cell wall, and cell membrane may also play a protective role. But the impact is not great. There are animal cells, animal cells, it has only one layer of cell membrane, it has no cell wall. Its cell membrane is also very fragile. Can't play a very good protective role. So the function of cell membrane is to isolate from the outside world.

This conjecture is self-evident, because the cell membrane does separate the internal environment from the external environment, which can be observed through a microscope.

I think the cell membrane should have another function, because cells will absorb nutrients and some beneficial substances. Then there are some substances that are not beneficial to cells. How can cells avoid them? For example, if a virus invades a cell, it will command the cell to produce countless viruses like it. The virus will attack all the tissues in your body, which is not only bad for the cell, but also harmful. The virus will attack the cells in your body. And it's not good for your whole body Then the cell membrane will definitely evolve a function, which is the function of detection. It can detect which substances are good for it and which substances are not. If it is intentional, the cell membrane will open its cell membrane and let substances in. That useless substance, the edge of the cell membrane will not open its membrane. Therefore, the cell membrane surface should have recognition function. To sum up, the cell membrane is selective for the entry and exit of substances. So how do we prove our conjecture? -Experiment.

Objective: To prove that the cell membrane is selective for the entry and exit of substances.

Experimental thinking: We put a cell into different substances, and the weight of these substances is the same, so is the cell we put in. The weight of cells is very small, which will not affect the results very much. There are no other substances in the environment of Petri dishes, only the substances to be tested, and the environment is the same. These three substances are placed at the same time. The summary is that single variables have the same factors. When cells are put into different substances, they will absorb some substances and then take them out. At this point, we will compare the weight of the substance before and after absorption. If the substance is reduced, this part of the substance will be absorbed by the cell, and which of these substances has the greatest difference from the weight before being put into the cell, and which substance is most needed by the cell.

Experimental materials: Petri dishes, three 100g X Y Z substances, tomato cells and gravimeter.

Experimental steps: put a tomato cell in three Petri dishes, and there are three different substances in the three Petri dishes, which we define as X Y Z substances. The weight of the three substances is 100g g, and there is no other substance in the Petri dish except the experimental substance. Then put tomato cells into three Petri dishes respectively. Let it stand for a while.

Experimental results: the weight of substance X is 96g, that of substance Y is 94g, and that of substance Z is 98g.

X: 100-96=4？ y: 100-94 = 6z: 100-98 = 26 > 4 > 2。

Analysis: Compared with before, substance Y is absorbed by cells the most, so the weight difference is also the biggest, so it is concluded that tomato cells need substance Y more.

Experimental conclusion: Cell membrane is selective to substances.

This experiment has the same univariate factors, correct logic and rigorous experiment. The experiment is normal

The interaction between cell membrane and chloroplast is explored. After designing many experiments, what are the main points to follow in the principle of an experiment?

The first point I think is very important, that is, univariate factors are the same. If the univariate factors are different, it means that your experiment is not rigorous enough, and there are many other possibilities. Because of the different univariate factors, many experiments I have done are not rigorous enough. So no matter what experiment you do, you must first reach the same univariate factor. Second, your logic is correct and can be proved by induction. Experiments need to be compared. Only through comparison and difference can we see what its function is.

Another suggestion is to design an experiment. When designing an experiment, we always think about how to be simple and focus on the experimental ideas, but he can actually have another way, that is, on the selection of materials for your experiment. If you choose the right materials, your experiment will become very simple. This material can be many things and should not be limited to all our materials. For example, my working medium experiment, my experimental materials were not very good at first, and its function was proved by comparative experiments. But later I found that the experimental materials are aerobic bacteria and chloroplasts ... In this experiment, the most important material is aerobic bacteria, because this kind of bacteria can be directly adsorbed on chloroplasts, and you only need to observe whether aerobic bacteria are adsorbed on chloroplasts. In this way, this time will become very simple.

Finally, I want to extend like water and sugar. These substances are good for cells, so will water and sugar automatically enter cells? This is impossible, because water, he is not a living body, he has no independent consciousness, he may have been pushed into the cell by external forces, and the cell just opened the door of the cell membrane to let water in. Maybe there is a pool of water around the cell, and too many water molecules gather together, so the water molecules will squeeze some water molecules into the cell. Then if the concentration of water molecules is not very high, it may be floating around the cell. So what will he do if the cells have no nutrition at this time? At this time, the cell changes from passive absorption to active absorption, and the cell has to send some substances to bring water molecules into the cell.

This is my inquiry.