There was no life on Earth for the first billion years because the atmosphere was not suitable for life. Earth's first atmosphere had lots of water vapor but had almost no oxygen. Later, frequent volcanic eruptions put several different gases into the air.
Answer:
The correct answer would be a. Fragments of DNA that have desired genes are isolated to form recombination DNA for use in a host. Genetic engineering refers to the direct manipulation or modification of the desired gene in a cell in order to produce novel or improved organism.
Explanation:
Answer:
B. decreases salivation and increases blood pressure
Explanation:
The sympathetic nervous system is part of the autonomous nervous system which controls involuntary responses of the body such as salivation and blood pressure.
The sympathetic nervous system is majorly responsible for body actions that are produced when threat is perceived. It generates responses referred to as the “fight or flight” response. Examples of such responses include, increased breathing, increased high blood pressure, dilation, decreased salivation, etc.
Activation of the sympathetic nervous system would result in rise in the blood pressure as can be witnessed by someone whose body has perceived a threat or reacting to a stressful situation.
The control of salivary production by the sympathetic nervous system leads to the release of noradrenaline which acts on certain receptors that results in decrease in the production of saliva. This is evident in a person that is facing a threat also.
He discovered that cells come from cells that already exist
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