w
e help of suitable diagram explain why the sun is visible to us two
sunrise and two minutes after the actual sunset.
a)
Define reflex action State its significance
How do plants respond to external stimuli?
What is chemical reaction 7 Explain ) Saponification b) Esterification
d) Neutralization reaction
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Answers
Answer:
) Reflex action : It is defined as an unconscious, automatic and involuntary response of effectors, i.e. muscles and glands, to a stimulus, which is monitored through the spinal cord.
Significance : The deep tendon reflexes provide information on the integrity of the central and peripheral nervous system. Generally, decreased reflexes indicate a peripheral problem, and lively or exaggerated reflexes a central one.
(b) Plants produce hormones and respond to external stimuli, growing towards sources of water and light, which they need to survive. A tropism is a growth in response to a stimulus and an auxin is a plant hormone produced in the stem tips and roots, which controls the direction of growth.
2. The Sun is visible to people on Earth about 2 minutes before the Sun rises above the horizon. Also we are able to see the Sun for about 2 minutes after the Sun goes below the horizon. ... At Sunrise and Sunset the main effect is due to temperature. Hot air is less dense and has a smaller refractive index.
Explanation:
Saponification is an organic chemical reaction that utilizes an alkali to cleave an ester into a carboxylic acid and alcohol. As we will see shortly, the primary use for this reaction is during the production of soap products. The terms ester, carboxylic acid, and alcohol are functional groups. A functional group is simply a group of molecules or atoms that we can easily identify in a compound.
Functional Groups
Unfortunately, our friend alkali does not belong to this club. Rather, an alkali is a fancy term for a base that dissolves in solution, producing hydroxide (OH) ions. Given what we know about the background of saponification, let's discuss the reaction and mechanism in greater detail.
Mechanics: Reaction and Mechanism
The general saponification reaction is shown on screen here. As you can see, saponification involves two major players: ester and alkali. Note that one of the products is a carboxylate ion. This is simply a carboxylic acid that carries a negative charge once its proton is removed. Use this ion as an ID marker to help you decide whether or not you are dealing with a saponification reaction.
General Equation for Saponification
If we look at the mechanism, or instruction guide for this reaction, we will see there is a series of steps that must be followed. Those steps, provided with illustrations, are shown here:
Step 1: The hydroxide ion from the alkali molecule swoops in and performs a nucleophilic attack on the ester or fatty molecule. Don't be alarmed by the word nucleophile. It simply refers to a molecule that will form a chemical bond due to its attraction to electrons in a different atom or molecule.
Step 1 of the Saponification Reaction
Step 2: The OR group becomes a leaving group, following Step 1. OR refers to the oxygen atom bonded to R, which is simply a placeholder for any molecule or atom. Desperately wanting to leave, the OR group departs, causing a double bond to form. This creates a carbonyl group. This new product may look familiar, as it is a carboxylic acid functional group.
Step 2 of the Saponification Reaction