A student conducted an experiment to study the conditions under which microorganisms grow on food, a

What I write is not a standard answer, you can write it with a similar meaning but different expressions.

1) What conclusions can you draw from this experiment?

If there is mold growing on water, the water affects the growth of the mold; If mold grows on waterless bread, water has nothing to do with mold growth.

Or: water affects mold growth, and there is a water environment suitable for mold growth.

2) What variables are involved in this experiment?

In this experiment, a single variable method was used, and the variable was only water.

3) How is the countermeasure controlled in the experiment?

Single variables, the same amount is: bread, mold, temperature, brightness, and the variable is: water.

4) If you want to study whether temperature has an effect on mold growth, what kind of experiment should you design, write your hypothesis and experimental protocol.

Hypothesis: temperature will have an effect on mold growth, the more suitable the temperature for mold growth, the more vigorous the mold growth, too high or too low temperature will inhibit mold growth, steps: put 2 pieces of bread of the same size and thickness in 2 clean Petri dishes; Drip some tap water on two slices of bread and let them sit in the air for about 1 hour; Put 2 slices of bread into a sealed plastic bag respectively, squeeze the bag, drive away the air, seal the bag and seal it with tape paper, one bag is placed in a warm place (25), the other bag is placed in a low temperature place (5), and placed in a dark place together; Observe and record the presence of mold every day; Draw conclusions, contrast hypotheses.

Put each of the two slices of bread into a sealed plastic bag, squeeze the bag to drive away the air, seal the bag and seal it with tape"Why do you need to seal it, mold is aerobic.

The Effect of Moisture on Mold.

Variables: moisture, temperature, air.

If you want to study whether the temperature will have an effect on the growth of mold, do a comparative experiment, 10 degrees, 15 degrees, 20 degrees, 25 degrees.

Step 1: Don't drive the air out of the plastic bag, and don't seal it, because you need air for mold growth.

1) Put dry bread in a Petri dish, put bread moistened with water in Petri dish B, and only put distilled water in Petri dish C, and C was compared with AB respectively, so in this experiment, the C Petri dish played a control role

2) In the experiment, B, put water-moistened bread in the B petri dish, and there was water in B, Xiao Wang found that B Petri dish had the most microorganisms, and it can be concluded that the growth of microorganisms is related to water

3) The reason for food deterioration is the growth and reproduction of microorganisms, so the principle of preserving food is to kill or inhibit the growth and reproduction of microorganisms, such as: remove the water in the food to inhibit its growth and reproduction, low temperature environment preservation, can inhibit its growth and reproduction, food is heated, and then sealed and preserved, which can kill the microorganisms in it at high temperature and stored in plastic bags, there is still a lot of air in it, and microorganisms can still grow and multiply in large quantities, so the food will also spoil so choose b

So the answer is: (1) control.

2) The growth of microorganisms is related to water 3) b

(1) This experiment needs to digest the starch by saliva, so the only variable in the experiment is saliva, and the test tube is specially added with 2ml of water and steamed bread crumbs, which is controlled by the test tube

Starch turns blue when it meets iodine, and maltose does not turn blue when it meets iodine After the water bath, add iodine solution dropwise to the test tube, and the test tube does not change blue, because the saliva contains salivary amylase, which decomposes the starch into maltose under suitable conditions, so the conclusion of the experiment is that saliva has a digestive effect on starch

2) To the digestion of the steamed bread by the chewing of the teeth, the control experiment should be set up with the condition as the variable, that is, the variable of the experiment is whether the steamed bread is chewed or not The test tube is put in 2ml of saliva and steamed bread, so the test tube is selected to be placed in the beaker as a control experiment with the test tube

So the answer is: (1) ; Saliva; Saliva has a digestive effect on starch (2) ; Whether the steamed bun is chewed or not

1) As can be seen from the title, this experiment is to study the optimal temperature required for anaerobic respiration of yeast, due to the energy released by yeast respiration.

Some of it is lost in the form of heat energy, which will increase the temperature in the device, so the results of the chemical reaction during this experiment will change the independent variable of the experiment, the temperature

2) As can be seen from the title, this experiment is to study the optimal temperature required for anaerobic respiration of yeast, and the main purpose of adding water to the test tube is to create an anaerobic environment

3) The purpose of boiling the glucose solution is to remove the influence of bacterial respiration on the experimental results and to exclude oxygen

4) Alcohol will make the acidic potassium dichromate solution change from orange to gray-green, so the acidic potassium dichromate solution is used to identify whether the anaerobic respiration product has alcohol or not

5) Analysis of the curve of the problem map shows that the curve has no peak and cannot achieve the purpose of the experiment. The temperature range should be extended after 25 and the test should be repeated until the temperature corresponding to the peak peak is found

So the answer should be:

1) Lost in the form of heat energy.

2) Create an oxygen-free environment.

3) Remove bacteria and remove oxygen.

4) Potassium dichromate, concentrated sulfuric acid (or acidic potassium dichromate) Orange turns grayish-green.

5) Do not expand the temperature range after 25, repeat the test, and find the temperature corresponding to the peak is the optimal temperature.

d, ethanol should be tested with potassium dichromate, and the experiment did not involve the test of ethanol, so it cannot be a problem in the **d option.

D test question analysis: A When studying the influence of one condition on the research object, the experiment that is carried out with the same conditions except for this condition is called a control experiment This different condition is the variable In the group of experiments A and B, except for the condition with or without moisture, the other conditions should be the same The independent variable is moisture.

b In the group of experiments B and C, except for the difference in the conditions with or without bread, the other conditions should be the same The variable is bread Set up a control experiment to ensure that all other factors are the same except for the different factors studied In this way, the difference in the experimental results can only be caused by variables Make the experimental results convincing The reason why there are a large number of microorganisms growing in B and no microorganisms in C is caused by bread It shows that the growth of microorganisms needs nutrients.

c Analyze the phenomenon and draw conclusions After a week of observation with a magnifying glass, the result is that only a large number of microorganisms grow in B A has no change, indicating that the growth of microorganisms needs water From b and c, it shows that the growth of microorganisms requires certain conditions, such as water, organic matter (nutrients), etc. (viruses can only parasitize in living cells).

d Microorganisms include bacteria, fungi and viruses, and bacteria do not occur naturally but are produced by pre-existing bacteria.

(1) Due to various bacteria, molds and other microorganisms, contact with food, and adhere to it to use the organic matter in the food, growth and mass reproduction During the growth and mass reproduction, a lot of growth metabolites will be produced, resulting in a variety of tastes, such as acid, odor, etc. Therefore, the comparison between B bottle and D bottle shows that food spoilage is caused by the growth and mass reproduction of microorganisms

2) 50ml of mineral water was placed in bottle A, and 50ml of milk cooled after boiling was placed in bottle B, and a large number of microorganisms were found in bottle B, indicating that organic matter is needed for microbial survival

3) 50ml of boiled and cooled milk are put in bottle B and bottle C, and bottle B is cultured under the condition of 25 and bottle C is cultured under the condition of 5, and it is found that there are a large number of microorganisms in bottle B, and it is difficult to find microorganisms in bottle C, indicating that microorganisms need a suitable temperature for survival

So the answer is: (1) growth and reproduction;

2) organic matter;

3) Suitable temperature

A controlled experiment is an experiment in which the conditions are the same except for the different conditions when studying the effect of one condition on the research object We found that group A did not do any treatment, and the conditions for seed germination were met, and it should be the control group Three groups of experiments were set up for this question, which could be composed of two groups of comparisons, a and b, the variables were light, and the variables a and c were air

After a few days, you think that in the 3 cups, the soybeans may germinate A, B, A and B meet the conditions for seed germination, and those that cannot germinate may be C, and the C cup lacks air

1) To prove whether light has an effect on soybean seed germination, the only variable should be: light A and B have this condition, but the result is: after a period of time, most of the seeds in the two cups of A and B germinate It indicates that the germination of soybean seeds is not related to light

2) To prove whether air has an effect on seed germination, the only variable should be: air A and C have this condition, but the result is: after a period of time, most of the seeds in cup A germinate, and the seeds in cup C do not germinate, indicating that the germination of soybean seeds requires air

3) It is not difficult to see from the experimental step 2 and the diagram that it is not clear whether the seeds are alive or not The number of seeds in the three glasses is not the same

Therefore, the answers are: (2) a and b; c

1）a、b；The germination of soybean seeds is not related to light; (or germination is not related to light);

2) a, c3) soybeans should be evenly distributed or soybeans should have germination ability (vigorous vitality) (answer one point to score).