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Q1. Medulla controls involuntary actions
Description
The correct answer is Medulla. The medulla is a very important part of the brain that controls many involuntary activities of the body. Involuntary actions are those actions that happen automatically without our thinking. Examples include breathing, heartbeat, blood pressure control, swallowing, coughing, sneezing, and vomiting. These activities continue even when a person is sleeping.
The medulla is located in the lower part of the brain and is connected to the spinal cord. It acts like a control center for automatic body functions. If the medulla stops working properly, many important body systems can fail because the body cannot control breathing and heartbeat normally.
Easy Explanation
When we breathe, we do not think every second about taking air in and out. The medulla automatically controls this process. In the same way, when blood pressure changes, the medulla helps maintain balance in the body.
Step-by-Step Understanding
Step 1: The body performs many automatic activities.
Step 2: These activities are called involuntary actions.
Step 3: The medulla controls these automatic functions.
Step 4: It sends signals to organs like the heart and lungs.
Step 5: Therefore, medulla is responsible for involuntary actions.
Examples
- Breathing while sleeping.
- Vomiting when harmful food enters the stomach.
Key Points
- Medulla is part of the hindbrain.
- It controls involuntary activities.
- It is connected to the spinal cord.
- It controls heartbeat and breathing.
- It is essential for survival.
Q2. Least distance of distinct vision is 25 cm
Description
The correct answer is 25 cm. The least distance of distinct vision is the minimum distance at which a normal human eye can see an object clearly without strain. For a healthy young adult, this distance is approximately 25 centimeters.
If an object is brought closer than 25 cm, the eye muscles have to work very hard to focus, and the image becomes blurry. This is why books are usually kept at a comfortable reading distance.
Easy Explanation
Our eyes contain a lens that changes shape to focus light properly on the retina. When an object is too close, the lens cannot adjust enough to focus clearly. Therefore, 25 cm is considered the normal minimum distance for clear vision.
Step-by-Step Understanding
Step 1: Light from an object enters the eye.
Step 2: The eye lens focuses the light on the retina.
Step 3: For nearby objects, the lens becomes thicker.
Step 4: There is a limit to this adjustment.
Step 5: At about 25 cm, objects are seen most clearly.
Formula Related Concept
Power of lens depends on focal length.
Formula:
Power (P) = 1 / Focal Length (f in meters)
Although this formula is not directly used here, understanding focusing helps explain why eyes need proper distance for clear vision.
Examples
- Reading a book comfortably at about 25 cm distance.
- Mobile phones are usually held around this distance for clear viewing.
Key Points
- Least distance of distinct vision = 25 cm.
- It is also called the near point of the eye.
- Normal eyes can focus clearly at this distance.
- Closer objects may appear blurry.
- Reading too close can strain the eyes.
Q3. Chemical name of Slaked Lime is Calcium Hydroxide
Description
The correct answer is Calcium Hydroxide [Ca(OH)₂]. Slaked lime is formed when quick lime reacts with water. It is commonly used in whitewashing, water treatment, and construction work.
Chemical Reaction
Calcium Oxide + Water → Calcium Hydroxide
CaO + H₂O → Ca(OH)₂
This reaction releases heat, so it is called an exothermic reaction.
Easy Explanation
Quick lime absorbs water and changes into slaked lime. The new substance formed is soft and white in color. It is widely used for coating walls because it gives a smooth finish.
Step-by-Step Understanding
Step 1: Quick lime is calcium oxide (CaO).
Step 2: Water is added to quick lime.
Step 3: A chemical reaction occurs.
Step 4: Heat is released during the reaction.
Step 5: Calcium hydroxide is formed.
Why the Formula is Ca(OH)₂
- Calcium has valency 2.
- Hydroxide group (OH) has valency 1.
- Two hydroxide ions combine with one calcium ion.
- Therefore formula becomes Ca(OH)₂.
Examples
- Whitewashing walls in homes.
- Treating acidic soil in farming.
Key Points
- Slaked lime = Calcium Hydroxide.
- Formula is Ca(OH)₂.
- Formed by adding water to quick lime.
- Used in whitewashing and construction.
- Reaction releases heat.
Q4. Displacement reaction example
Description
The correct answer is:
Fe + CuSO₄ → FeSO₄ + Cu
This is called a displacement reaction because iron replaces copper from copper sulphate solution. A more reactive metal displaces a less reactive metal from its compound.
Easy Explanation
Iron is more reactive than copper. When iron is placed in copper sulphate solution, iron takes the place of copper. Copper comes out as a separate metal.
Step-by-Step Understanding
Step 1: Copper sulphate contains copper ions.
Step 2: Iron is added to the solution.
Step 3: Iron is more reactive than copper.
Step 4: Iron replaces copper from the compound.
Step 5: Iron sulphate and copper are formed.
Understanding the Formula
Fe + CuSO₄ → FeSO₄ + Cu
- Fe = Iron
- CuSO₄ = Copper sulphate
- FeSO₄ = Iron sulphate
- Cu = Copper metal
Observations During Reaction
- Blue color of copper sulphate fades.
- Brown copper metal gets deposited.
- Solution changes color due to iron sulphate formation.
Examples
- Iron nail dipped in copper sulphate solution.
- Zinc replacing copper from copper sulphate.
Key Points
- More reactive metal replaces less reactive metal.
- Iron is more reactive than copper.
- This reaction is called displacement reaction.
- New substances are formed.
- Color change is observed.
Q5. Gap between two neurons is Synapse
Description
The correct answer is Synapse. A synapse is the tiny gap between two neurons where nerve impulses pass from one neuron to another. It plays a major role in communication inside the nervous system.
Neurons do not touch each other directly. Signals move chemically across the synapse with the help of neurotransmitters.
Easy Explanation
When one neuron wants to send a message to another neuron, the signal jumps across a small gap called a synapse. This allows messages to travel throughout the body very quickly.
Step-by-Step Understanding
Step 1: A nerve impulse travels through a neuron.
Step 2: The impulse reaches the end of the neuron.
Step 3: Chemicals called neurotransmitters are released.
Step 4: These chemicals cross the synapse.
Step 5: The next neuron receives the signal.
Functions of Synapse
- Helps communication between neurons.
- Transfers nerve impulses quickly.
- Helps control body activities.
- Important for reflex actions and brain functioning.
Examples
- Pulling your hand away from a hot object.
- Brain sending signals to muscles during movement.
Key Points
- Synapse is the gap between neurons.
- Signals pass through neurotransmitters.
- It helps rapid communication.
- Essential for nervous system functioning.
- Important in reflex actions and thinking.
Extra Quick Revision Points
Brain and Nervous System
- Medulla controls involuntary actions.
- Synapse connects neurons indirectly.
- Neurons carry nerve impulses.
Vision
- Least distance of distinct vision = 25 cm.
- Healthy eyes focus clearly at this distance.
Chemistry
- Slaked lime = Calcium Hydroxide.
- Displacement reaction occurs when reactive metals replace less reactive metals.
Important Formulas
- Power of Lens
P = 1/f - Displacement Reaction Example
Fe + CuSO₄ → FeSO₄ + Cu - Slaked Lime Formation
CaO + H₂O → Ca(OH)₂