What is best for students to observe, and it is best to have changes to improve students' observation ability.

The color change of animals is not only beneficial to escape the attack of natural enemies, but also to catch food. This is a special ability gradually formed by animals in the long evolution process.

frogs also have this wonderful characteristic. It is green in green grass, often brown in paddy fields and brown in rock streams.

rain frog and tree frog are "chameleons" among frogs. Once the environment changes, the color of its skin also changes with < P >. During the day or on light objects, its skin color is light; And in the dark

corner, its skin color will suddenly darken; If it is in a dry environment, its skin color will become pale.

Let's do a simple experiment to observe this "magic" of the rain frog.

prepare five cans (cans or jars with colorless glass), and line the inside with colored paper.

The colors of colored paper are black, brown, white, yellow and pink (even the bottom of the bottle is attached).

Then, put the five rain frogs into bottles with colored paper. Cover it with cardboard (the side of cardboard facing down

should also be pasted with colored paper and a few small holes should be dug to make the air circulate). After that, every 2 minutes,

you observe and record the change of frog color, and the results are shown in the table on the next page:

As can be seen from the table, in dark environment (such as black and brown), frog color changes rapidly with the change of ring

; In light-colored environments (such as white and yellow), the color of frogs hardly changes.

If you paint the rain frog's eyes with black paint, or cover them with black cloth, so that it can't see the outside color

, what will happen if you look at the frog's body color again? Time 2 minutes 4 minutes 1 hour 1 hour 2 hours

Color paper 2 minutes 4 minutes

Black green turns light gray to produce black to black

mottled color

Brown green turns light gray without change without change with light black

mottled

White flowers without change. Change

Yellow does not change

Pink light pink is further added and deepened, which is close to the color pink

Deep paper

The color change of the rain frog is due to the pigment particles contained in skin cells. When the pigment particles are concentrated in one

point of the cell, the skin color becomes lighter; When the pigment particles are scattered, the skin color becomes darker. The change of pigment particle < P > is related to the sensitivity of eyes. When the eyes feel the change of the external environment, it immediately spreads to the frog's brain. By the simultaneous regulation of hormones in the brain and the body, the frog's skin changes accordingly.

A long time ago, Darwin observed and studied the color change of animals. He caught a black moth near Manchester, an industrial city in Britain. However, most of the similar moths caught in non-industrial areas were white. Darwin found that black moths (called geometrid) were all white. However, in the industrial zone with many chimneys, there is a lot of soot, and the houses and villages are all black < P >. If the black moth lands on these objects, it is less likely to be found by foreign natural enemies such as birds than the white moth, and the black moth has more chances to survive. On the contrary, in non-industrial areas, the moth can't be easily found, so it survives.

As a result of long-term natural elimination, the white moth was eliminated and the black moth was retained in the industrial area.

non-industrial areas are the opposite. Darwin called this phenomenon "natural selection". Darwin believed that this was the result of the evolution of living things, which was very slow.

Later, it was found that many animals changed color. Evasion is a reptile, which can quickly change its body color with different environments. If it stands on a taupe stone, its body

color is taupe, and if it stays on a green tree, its body color will turn green immediately.

Octopus, known as the chameleon in the water, is also a famous expert in chameleon.

Octopus is a mollusk. It can magically change its body color with the color of its surroundings. Its milky white body can become dark red, brown, blue gray, purple brown and so on. In this way,

is flickering and unpredictable in the sea, which makes the other party dazzled and unpredictable. Darwin once saw a small octopus in the shallow sea. After seeing people, he stayed still. Then it seems to be grinding to find a safe place, secretly climbed a few centimeters forward and stopped. Every time it occupies a new terrain, it changes its body color with the color of the surrounding environment.

The behavior of animals changing color inspires people. Since the 193s, people have systematically studied the phenomenon of color change in alkali metal halides and alkaline earth metal compounds. At present, there are

hundreds of substances with the property of light and color alternation in the world. Militarily, people think that in the event of a modern war,

we should first protect our eyes. In order to prevent the eyes from being damaged by nuclear flash and laser, a protective device containing color-changing substance < P > should be developed, which can reduce the light transmittance from 8% to .4% in a few thousandths of a second.

2. Where is the tadpole's tail?

Frogs have metamorphosis during their growth and development. The eggs laid by the female frog hatch a small tadpole with a long tail < P >, but when it reaches a certain stage, the small tadpole grows four calves, while the tail gradually shrinks and disappears < P >. Where is this long tail? You might as well raise some tadpoles yourself and observe them carefully.

every spring, frog eggs are most easily found in rice fields or ponds. Pay attention to distinguish frog eggs < P > from toad eggs when collecting. Frog's eggs are wrapped by the egg film, forming a single small ball, and each egg < P > ball is then aggregated into a ball, which is called an egg block. The egg film on the outside of toad eggs forms a long band, and the eggs line up in it, just like a string of black balls wrapped in a long capsule.

Divide the collected egg pieces into small pieces, put them into jars (or old washbasins, waste cans, etc.), and raise them at room temperature

. The water depth in the bottle is preferably four or five centimeters, not more than ten centimeters, otherwise it is easy to lack oxygen. Change the water every three or four days, and after about a week, the eggs hatch into tadpoles.

two or three days after the tadpoles come out together, change the water for the second time, the water depth is 1 cm, and put some aquatic plants. It is best to use fresh natural water, such as well water, stream water and pond water. If tap water is used, it needs to be exposed to the sun for one day in advance to remove chlorine. The optimum water temperature for raising tadpoles is < P > between 12 and 22 degrees Celsius. When the water temperature is higher than 25 degrees Celsius, it doesn't like to eat, which will affect its growth.

At the beginning, tadpoles were only fed with some egg yolk powder. After three days, it is necessary to put some soil in the bottom of the water (the best

is to borrow soil from the pool where frog eggs are collected). There are many tiny creatures in the soil for tadpoles to eat. Also

some live fish and worms, small fish and shrimp, steamed bread residue, etc. should be supplied, but the dosage should be small to keep the water clean.

If it is found that most tadpoles squeeze into the water to breathe, and rarely go to the bottom to feed, it means that there is insufficient oxygen in the water, so change the water quickly. It is best to change the water once a day, at least every other day.

the soil in the water can be changed once a week.

After one month's rearing, some tadpoles begin to metamorphose. At first, I saw two small protrusions on both sides of the tadpole's tail. These two protrusions are getting bigger and bigger, and they are transparent, so I can see the structure inside. Do you notice that the protrusions on both sides of it are born at the same time? Later, these two protrusions gradually became < P > two hind legs. Then, the front legs began to grow on both sides of the body. Please note, how many days after their hind legs grow, do they

start to grow their front legs? After all four legs grow out,

does the tail still exist? How did the tail disappear? Through breeding and observation, you will find out that the tail loss and the growth of four legs are carried out at the same time. One side of the leg is long and the tail is gradually shrinking.

After tadpoles grow limbs, their body gradually becomes flat from round, their mouths become wider, and stripes appear on their backs. However,

growing front legs is the decisive moment of metamorphosis. At this time, tadpoles took off their lips and teeth, grew big mouths, and began to breathe with their lungs. They changed from eating omnivorous food to eating animal food on land. As its body structure < P > and living habits have changed, its feeding methods should be changed accordingly.

You can put some small pieces of wood on the water, so that the young frog can climb up to rest and breathe, otherwise the young frog will drown

.

when the young frog can jump, you can fish it out and put it in a wooden basin or an old washbasin to raise it.

spread turf on the bottom of the basin (shovel some turf with soil by the pool or pond). The basin can be covered with an old

screen to prevent it from jumping out. You often spend your spare time catching some small insects in the grass and putting them on the grass in the pot. Put a plate of water on the corner of the turf. At this time, you can focus on observing which insects the little frog likes to eat most. So think about it: Why are frogs friends of human beings?

Professor Tong Dizhou, a famous late scientist in China, had a strong interest in frog metamorphosis when he was a child. He made a lot of observations and studies. At the age of 28, he went to Belgium to study.

Once, his teacher, Professor Blasche, wanted to do an operation to peel frog egg membranes. This kind of operation is very difficult to do.

Blasche failed for several years, but Tong Dizhou, who likes raising tadpoles since childhood, quietly

did it. At that time, Blasche said happily: "Tong, a little man, is really good!"

This incident gave Tong Dizhou great encouragement. From then on, he was convinced that "China people are not stupid". After returning home,

during the Anti-Japanese War, the working conditions were extremely difficult. He didn't even have glassware for cultivating frog eggs, so

he used coarse ceramic bowls and wine glasses instead. He traveled all over the field and collected many frog eggs. He and his colleagues did < P > many experiments on frog embryos and observed the changes of tadpole tails. The final result is the same as your experimental observation < P >.

3, merits and demerits of fungi

Fungi include yeast, mold and mushrooms. It has a very close relationship with people. As mentioned earlier, our people have long known that yeast and mold are used to make wine, sauce, bean curd, vinegar and so on.

Yeast can also be used to make bread and steamed bread. Edible mushrooms among mushrooms, such as mushrooms, Lentinus edodes, auricularia auricula, Hericium erinaceus, Ganoderma lucidum, Poria, etc., are not only rich in nutrition, but also can be used as medicines. In recent years, it has been found that many kinds of fungi contain anticancer substances, which has attracted more and more attention. In addition, fungi

have also played a significant role in textile, paper making, leather making and other industries, so I won't elaborate here.

don't think that fungi are good for people, but they also have a bad side. For example, a few yeasts can < P > spoil stored food, while others can make people and animals sick. The harm of mold to people is even greater: after grain < P > or feed is infected with mold, grain will deteriorate; Toxins produced by some molds can cause cancer, < P > or cause human and animal deaths. Some of the mushrooms are poisonous, and people and animals will be poisoned if they eat white poisonous umbrella, fine mesh beef liver and < P > toad fungus by mistake.

You may want to do an experiment yourself to evaluate the merits and demerits of fungi! Then, first

do a small experiment on leavening and see the contribution of yeast.

weigh out 1 grams of flour, put it in a small bowl, add some water and make dough. Divide the dough into two parts

. Mix in a proper amount of fresh yeast (flour fertilizer can also be used, which contains yeast) Then, divide the

two dough into two parts, and finally make four doughs (two with yeast and two without yeast).

Find four test tubes, and knead all four pieces of dough into strips thinner than the test tubes and almost equal in length. Put

four strips into the test tube respectively, push them to the bottom of the tube with a glass rod, and then press the upper ends of the strips flat. Finally, wrap the test tube mouth with

four layers of gauze.

Mark the outer wall of the test tube with a colored pen, mark the length of the dough, then measure the length of the dough with a ruler

and write it down.

put a test tube with yeast and a test tube without yeast in a cold place, and write down the temperature

here. The remaining two are placed at 25-3 degrees Celsius, and the temperature is also recorded.

after p>15 minutes, you can see that

the dough in the test tube with yeast added, which is placed in a hot place, begins to stretch. Observe and measure every 15 minutes. However, the dough in the test tube without yeast did not change < P >.

why does the dough stretch? This is because the yeast has been fully nourished in it, and it can reproduce and grow rapidly under the appropriate temperature and humidity. In the process of growth and reproduction, the mother bacteria will produce a large amount of carbon dioxide gas, which makes the dough volume increase, but the thickness of the test tube is fixed, so the dough has to be stretched upward. The length of elongation can indirectly indicate the growth and reproduction speed of mother bacteria.

So, why didn't the dough without yeast change? What about the two

test tubes in the cold? Can you explain it clearly?

After you have mastered the method of measuring yeast growth and reproduction with dough, you can do another interesting experiment

.

In p>1928, Russian scientist Tolkien discovered that onions secrete a substance that can kill yeast, called

phytoncide. Now, we can use experiments similar to the above to verify Tolkien's findings.

As in the previous experiment, put two pieces of dough mixed with yeast in a test tube, and add one gram of chopped onion paste (chop and mash the onion) into one test tube. The other test tube did not put onions for comparison.

then, mark the mark, measure the length and write it down.

Put both test tubes at 25-3 degrees Celsius. After 15 minutes, 3 minutes, 45 minutes and 6 minutes, < P > measure the length of the dough respectively. It was found that the dough without chopped onion paste was elongated, while the dough with chopped onion paste remained unchanged. It is proved that onion has the efficacy of killing yeast. If you replace onions with garlic, mustard, peppers, fennel, potatoes, tomato leaves and so on. What will be the result

? You can also choose other plants to do a series of experiments, and then you can know which ones have bactericidal effect and which ones have no bactericidal effect.

Let's do another small experiment to see the mistakes of mold.

You cut off a small piece of bread (steamed bread or rice will do), dip it in water and put it on a plate

. After an hour or two, some water will evaporate. Then, button it with a teacup or a small bowl, and then

put the plate in a warm place (about 3 degrees Celsius). In a couple of days, when you open the teacup, you will see

filamentous things like cotton or cobwebs grow on the bread. You fasten the teacup again. After

two or three days, you can see that there are different colors of powder on these filamentous things.