The most likely explanation for the variation is the offspring were produced from different combination of genes. A single pair of gold fish mentioned in the question means a male and a female gold fish. The two of them mated and contributed different genes to the fertilized fish eggs, this results in production of various body shape and colouration which is known as variation.
We first have to understand what a vascular system is. A vascular system consists of the water-carrying tube(xylem) and food-carrying tube(phloem). These 2 tubes are very essential for plants to survive. The xylem transports water to the leaves thru the stem to nourish the leaves so as to make food. The word equation is : Water + Carbon dioxide ----> Glucose + Oxygen. The phloem on the other hand transports the food from the leaves that creates them amd sent them to all parts of the plant. It is often a misconception that food is only sent to the fruits. The plant receives nutrition from the food that is made by the leaves. Overall the vascular system plays a very importamt roles in the survival of the plant.
To put it simple, think of the vascular system of a plant like the circulatory system of a human. Without the circulatory system, the human is unable to receive oxygen for breathing and remove carbon dioxide which is acidic in nature and pose a threat to the human body.
Assuming a 10% trophic efficiency, the herbivore (primary consumer) will get 10% of the producer energy. Then, the second consumer that eat the herbivore will get 10% of the primary consumer energy, so it is 10%*10%= 1% of the primary producers.
Then, the t<span>ertiary consumer should get 0.1% of the primary producers' energy.</span>
Yes there is, there is the cycle which trees and plant organisms produce oxygen, and homes animal organisms which can be beneficial to decomposition and other things.
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