One junior high school biology question, one junior high school biology question

Food is digested in the small intestine and broken down into small molecules that can be absorbed. Food stays in the small intestine for a longer period of time, generally 3-8 hours, which provides time for full absorption. The small intestine is the longest part of the digestive tube, the human small intestine is about 4m long, the small intestinal mucosa forms many annular folds and a large number of villi protrude into the intestinal lumen, the surface of each villi is a layer of columnar epithelial cells, and the cell membrane at the top of the columnar epithelial cells forms many small protrusions, called microvilli.

The presence of annular folds, villi and microvilli increases the surface area of the small intestinal mucosa by a factor of 600 to about 200 m2. This gives the small intestine a large absorption area.

Inside the villi are tissues such as capillary networks, capillary lymphatic vessels, smooth muscle fibers, and neural networks (Figures 8-8). The relaxation and contraction of smooth muscle fibers allow the villi to stretch and oscillate, and the movement of the villi accelerates the flow of blood and lymph and aids in absorption.

The human small intestine is slender, coiled in the abdominal cavity, about 5 6 meters long, the inner surface of the small intestine has many annular folds, the surface of the folds has small intestinal villi, the small intestine villi epithelial cells are towards the side of the intestinal lumen, and there are some microvilli, due to the presence of annular folds, small intestinal villi and microvilli, the inner surface area of the small intestine is nearly 600 times larger than the original. It is estimated that the inner surface area of an adult's small intestine is about 200 square meters. The greater the inner surface area, the more it absorbs.

In addition, there are capillaries in the villi of the small intestine, and the villi wall and capillary wall of the small intestine are very thin, and they are composed of only one layer of epithelial cells, which makes it easy for nutrients to be absorbed into the blood, and then transported from the blood to the whole body for various life activities.

c Definitely wrong, the larger the temperature difference between day and night, the sweeter The temperature difference is large, the photosynthesis is strong during the day, and the respiration consumption is less at night. As a result, sugar accumulates.

d Definitely false Low temperature and humidity are not conducive to the preservation of fruits.

A is also false that the offspring of lychee propagation with seeds will mutate, resulting in the separation of traits, and asexual propagation can be used to maintain a certain excellent trait.

So choose B

If the answer is wrong, don't look down My analysis A: Seeds can't, and tissue culture can be used to directly obtain the next generation with the same excellent traits.

b It is said that the removal of the apical advantage can increase the number of side branches of the tree, and thus the yield can be correspondingly increased c The temperature difference should be as large as possible in the appropriate orientation, because the temperature is moderately high during the day is conducive to photosynthesis and the synthesis of organic sugars, and the low temperature at night can inhibit the main activity of plants at night - respiration consumption.

d Low temperature is correct, but damp is wrong Fresh fruit preservation conditions should be low temperature and proper humidity and not humidity!

Choosing the D a option, the seeds cannot maintain the excellent traits due to the trait separation of the offspring, so the excellent trait cannot be passed on from generation to generation.

Option b, removing the top bud will only benefit the growth of the side buds and will have no effect on the yield.

Option c, within a certain range, the larger the temperature difference, the more conducive to the accumulation of organic matter such as glucose, so it is wrong.

Option d Low temperature inhibits respiration It is good to preserve the sugar in the lychee, and the moisture is kept moist so correct.

I think it's D thinking that when I buy lychees, the fruit shop owner will know where to put the lychees.

Seed reproduction, with a large degree of variation, and vegetative reproduction can well retain genetic characteristics, which belongs to asexual reproduction.

The temperature difference between day and night is small, and the accumulated sugar cannot stay, and the sugar content is low. Turpan, Xinjiang is because of the large temperature difference between day and night, and the fruit will be particularly sweet.

A false, lychee is asexual reproduction;

C is wrong, it stands to reason that the temperature difference should be large and the sugar content is high. This is because plants photosynthesize to produce organic matter during the day, and the stored organic matter contains a large amount of sugars. At night, photosynthesis is not possible, but it can still respire and consume organic matter.

If the temperature is low at night, the respiration will be weakened, and less organic matter will be consumed, so more organic matter will be stored, and the sugar content will be higher.

d False, the temperature should be moderate.

1. Select D. Plants respire and photosynthesize at the same time under light, and because photosynthesis is relatively strong, the carbon dioxide produced by respiration is immediately synthesized into organic matter as a raw material for photosynthesis, so it does not exhibit respiration.

2. Choose B. Deep ploughing of loosening soil can increase the concentration of oxygen in the soil and promote the respiration of plants.

3、b。The direction of free diffusion of water in living organisms is from low concentrations to high concentrations4,c. In the evening, the leaves of the tree store the products of the day's photosynthesis and contain more organic matter than in the morning.

5. Temperature, humidity, oxygen concentration.

6. Make the starch grains appear blue and easy to observe.

DBA water molecules are freely diffused, ranging from high to low concentrations.

c The starch produced by photosynthesis is stored in the leaves in the evening, which is consumed at night, so the starch content in the evening is higher than that in the morning.

Temperature, moisture, air.

Detect the presence of starch.

The pros and cons of mutation are for the organism in which the mutation occurs, regardless of other species or environmental factors.

In this question, the virus mutates, making it more difficult to kill, and the virus has a higher survival rate and better adaptability, which is powerful for the virus.

Don't listen upstairs, it's the answer that's wrong, it's definitely the wrong answer.

The benefits here are for the mutated creatures, not for us.

That is to say: for the mutation of the enterovirus, it is beneficial for the enterovirus!

The advantage is for the virus. This question is a test of your logical thinking. People think that the disease is harder**, so it's not good, but if the virus itself is more contagious, the more powerful it is, which is a good thing.

Thinking of it this way is favorable variation. Got it?