<h2>Answer:</h2>
Following are the four combinations of active or inactive regulatory proteins that could be present anytime in the cell:
- Active repressor , Active activator
- Active repressor, Inactive activator
- Inactive repressor, Active activator
- Inactive repressor, Inactive activator
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.
The greenhouse effect is the trapping of a stars warmth in the lower atmosphere of a planet by gasses in the air trapping the energy. This is similar to what actual greenhouses do, where they trap the warmth and humidity of the air inside it so plants can flourish. Farm animals produce a huge amount of the greenhouse gasses required for our planet to trap the suns warmth.
