The food chain of an ecosystem can be complex, but not too long, due to which of the following:

Ecosystem. The food chain can be complex, but not too long, because animals (such as frogs) may change their food at different stages of ontogeny, and the food chain linked to predation will change with it. The food chain may change in different seasons due to the different main foods and the composition of the predator's main food.

Producer photosynthesis.

Strength does not change the food chain. The food chain is also known as the "nutrient chain". In order to maintain their own life activities, various organisms in the ecosystem must feed on other organisms.

Relationship. This feeding relationship is actually the relationship between solar energy from one organism to another, that is, the flow and conversion of material energy through the food chain. A food chain generally consists of 3-5 links

The number of organisms at different points in the food chain is relatively constant in order to maintain a natural balance. There are many kinds of organisms in the ecosystem, and they play different roles in the ecosystem, and according to the role they play in the movement of energy and matter, they can be classified into three categories: producers, consumers and decomposers.

The most common relationship between organisms is predation

After all, only the producer doesn't have to prey on other creatures

The longest food chain is generally not more than one trophic level, has this teacher talked about it?

Matter and energy decrease step by step along the food chain to 5 There is very little energy in matter

a. The flow of energy is gradual, disproportionate, and thus the food chain.

The trophic level is generally not more than 4-5, a wrong;

b. Multiple food chains to the top level make the number of organisms at the highest trophic level stable, only the species of animals and plants, the more complex the nutritional structure, the higher the stability of resistance, b error;

c. There are many kinds of organisms at the same trophic level, i.e., biodiversity.

The higher the degree, the more conditions and opportunities can be provided for the survival of all kinds of organisms, c correct;

That is, if a certain species dies for some reason, other species will also occupy the ecological position, thus avoiding the imbalance in the structure and function of the system, d correct

Selection: CD

Answer] a. Analysis] can be enriched through the food chain is harmful substances, and the order of the food chain and celery is higher and more stupid. The higher the content of hazardous substances, b, c, and d are not hazardous substances, so the answer to this question is A.

In the ecosystem, such as the food chain: grass rabbit eagle, rabbit eats grass, grass photosynthesis is used to photosynthesize and the stored matter and energy enters the body of the rabbit, the eagle eats the rabbit, and the matter and energy stored in the rabbit's body goes to the eagle's body, so the material and energy in the ecosystem flows along the food chain and the food web

So the answer is: matter; Energy.

For example, in the food chain of "grass rats, snakes, and owls", if the number of snakes decreases significantly, the number of owls will decrease and the number of rats will increase for a period of time; Then, the decrease of owls and the increase of rats will gradually increase the number of snakes, so that the whole ecosystem is in a dynamic equilibrium state, which shows that the ecosystem has a certain ability to self-regulate, but there is a certain limit to this ability to regulate

Therefore, d

Generally speaking, the more types of organisms in the ecosystem, the more complex the food chain and food web, the stronger the regulating ability of the ecosystem If the number of organisms in the "natural enemy" position in a food chain decreases, then the number of eaters will increase rapidly as a result But this increase is not unlimited, with the increase in number, the population density increases, the intraspecific struggle is bound to intensify, coupled with the absence of the "pressure" of natural enemies, the quality of the eater itself (such as running speed, vigilance and sensitivity, etc.) must decline, It leads to the spread of epidemics, the increase of the old, weak, sick and disabled, and finally causes its density to decrease until it is relatively stable That is, the number of natural enemies decreases, causing the number of eaters to increase first and then decrease, and finally tends to stabilize From the figure, it can be seen that the species of b, c, and d are out of balance, and the strongest regulation ability is a

Therefore, a