Nutrients enter a cell DOWN the concentration gradient by the process of DIFFUSION.
This process of absorption of digested nutrients mainly uses diffusion (only some times active transport), which is a kind of method of material transportation where the net movement is fluid will flow from a region of higher concentration to the region of lower concentration, due to its original random movement.
Therefore, this net movement can be described as down the concentration gradient, and this process is diffusion.
Answer:
You could line up 109 Earths across the face of the sun.
Answer:
At the base of Actinopterygii
*This is a unique characteristic of this group.
Explanation:
A peculiar characteristic organ observed in ray-finned fish (as well as in Sarcopterygii, or lobe-finned fish) but not in cartilaginous fish like shark is the swim bladder.
This organ is often described to be a sac containing gas. It helps these set of fish adjust its buoyancy and its position in the water by regulating the concentration of gas present in it.
The swim bladder is formed as a pouch coming off the embryonic digestive tract, and in chondrosteans and holosteans, with a set of teleosts e.g. the eels, it maintains an open pathway to the esophagus. In majority of the bony fish, the swim bladder is totally sealed off, as gas levels in their swim bladder are regulated by producing gas into the bladder via a network of capillaries, the rete mirabile (Latin word for "marvelous net").
The swim bladder is homologous to the lungs of tetrapods. Since they are formed in the same vein. Few fishes that have an open swim bladder employs it as a breathing organ.
Indirect methods like mark and recapture become a strong tool to estimate population size or density in species on which it is impossible to apply a direct methods. <em>Because of their biological and ecological characteristics, the Gypsy moth and the Green lizard populations are good examples for which mark and recapture would work well.</em>
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There are different methods to study population density. There are direct methods and indirect methods. Among these last ones, we might find the Mark-Recapture technique.
The Mark-Recapture technique assumes that
- <em>the population is closed during the sampling season, there is no mortality nor natality, </em>
- <em>marks in the individual last the whole sampling season, and they do not affect the marked individual or their behavior. </em>
- <em>marked individuals are randomly distributed in the population, and </em>
- <em>all the individuals have the same probability of being sampled.</em>
The method consists of capturing a sample of individuals belonging to the population under study. After capturing the individuals, the researcher marks and releases them again. The third step is to sample again: The researcher captures new individuals and counts how many of them are marked. These marked individuals belong to the first sample.
Indirect methods like this become a strong tool to estimate population size or density in species on which it is impossible to apply a direct method such as <em>counting individuals</em>.
For instance, if we need to estimate insects population density (<u><em>Gypsy moth population</em></u>) or reptiles population density (<u><em>Green lizard population</em></u>) because of their biological and ecological characteristics, the best way of doing it is by applying indirect methods. <em>These species characterize as small-sized, fast to escape, they can hide in small inaccessible places, they have nocturnal habits, their reproductive rate is too high, and their distribution rate is wide. </em>Among many other characteristics, their population density can not be estimated by direct methods. Mark-Recapture technique is the most suitable one.
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