When the temperature reaches 0˚C (32˚F), the top layer of the lake freezes and turns into ice. In solid form, water molecules are less dense and thus ice floats on the top of the lake.
This solid barrier prevents any wind-induced mixing as well as protects the relatively warm water underneath. Furthermore, light is also blocked so that photosynthesis is inhibited during this period. As the lake water is separated from the atmosphere, no direct oxygen diffusion occurs.
All these factors together causes a more even distribution of nutrients and gases in a lake in winter.
A very useful term to describe Bacteria that can't synthesize their own food energy is called a Heterotroph. A Heterotroph relies on other organisms for nutrition, whether plant or animals. There are two types of Heterotrophs: <em><u>Photoheterotroph</u> and <u>Chemoheterotroph.</u></em><em><u /></em><u /> Photoheterotrophs use light for energy,but can't use carbon dioxide as their carbon source. They get their carbon from compounds such as carbohydrates, fatty acids, and alcohol. Chemoheterotrophs get thteir energy by oxidation of preformed organic compounds such as animals, fungi, bacteria and almost all pathogens.
They re called granum singular and grana plural
The Arenal Volcano in Costa Rica
