The seasons are caused as the Earth, tilted on its axis, travels in a loop around the Sun each year. Summer happens in the hemisphere tilted towards the Sun, and winter happens in the hemisphere tilted away from the Sun. As the Earth travels around the Sun, the hemisphere that is tilted towards or away from the Sun changes.
Answer:
Multicellular eukaryotes evolved from unicellular prokaryotes by the process of endosymbiosis
Explanation:
All living beings have evolved from three groups of animals closely related with each other.Domains: Archaea,bacteria and eukarya.the archaea and bacteria are unicellular organism surrounded by single cell water and and coiled stand of DNA. Eukaryotic cells are more complex and with a linear strand of DNA which is in the nucleus. Actually mitochondria which had evolved from a free living bacterium which was swallowed by another cell. The host cell benefited from the chemical energy that mitochondria produced and mitochondria in turn is benefited to be inside the protected environment. Mitochondria is the main organelle which the multicellular eukaryotes with unicellular prokaryotes.
Answer:
The correct answer is: (A).
Explanation:
- In the question, it is mentioned that the algae can grow under the conditions of "enough sunlight" and "enough nutrients".
- Sunlight reaches the algae, by first falling on the surface made up of ice and snow and then refracting from there into the top layer of the ice where the algae grows.
- However, the capability of both snow and ice to reflect sunlight is far more than that of refracting sunlight.
- Therefore, the amount of light received by the algae is similar in absence or presence of the layer of snow on the top layer of ice.
- However, on deposition of snow on the layer of the ice, the weight of the ice increases and it sinks below into sea water.
- This allows more nutrient rich sea water to percolate into the ice and reach the algae.
- The algae receive more nutrients from the sea water and hence is capable undergoing better metabolism and growth.
- Hence, more algae are produced under such a situation.
Answer:
Mitosis occurs in somatic cells; this means that it takes place in all types of cells that are not involved in the production of gametes. Prior to each mitotic division, a copy of every chromosome is created; thus, following division, a complete set of chromosomes is found in the nucleus of each new cell. Indeed, apart from random mutations, each successive duplicate cell will have the same genetic composition as its parent, due to the inheritance of the same chromosome set and similar biological environment. This works well for replacing damaged tissue or for growth and expansion from an embryonic state. Because the genes contained in the duplicate chromosomes are transferred to each successive cellular generation, all mitotic progeny are genetically similar. However, there are exceptions. For example, there are genetic variations that arise in clonal species, such as bacteria, due to spontaneous mutations during mitotic division. Furthermore, chromosomes are sometimes replicated multiple times without any accompanying cell division. This occurs in the cells of Drosophila larvae salivary glands, for example, where there is a high metabolic demand. The chromosomes there are called polytene chromosomes, and they are extremely large compared to chromosomes in other Drosophila cells. These chromosomes replicate by undergoing the initial phases of mitosis without any cytokinesis (Figure 2). Therefore, the same cell contains thick arrangements of duplicate chromosomes side by side, which look like strands of very thick rope. Scientists believe that these chromosomes are hyper-replicated to allow for the rapid and copious production of certain proteins that help larval growth and metamorphosis
Explanation:
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