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1. Acid Reaction with Metals – Hydrogen Gas
When an acid reacts with a metal, hydrogen gas is usually released. This is a common chemical reaction studied in science.
General Reaction
Metal + Acid → Salt + Hydrogen Gas
How the Reaction Happens
Acids contain hydrogen ions. When a metal reacts with these ions, the metal replaces hydrogen from the acid and forms a salt. During this process, hydrogen gas is released.
Important Observations
- Bubbles of gas are formed
- The reaction may produce heat
- A new substance called salt is produced
Examples
- Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
- Magnesium + Sulphuric acid → Magnesium sulphate + Hydrogen
Identification of Hydrogen Gas
Hydrogen gas burns with a “pop” sound when a burning splint is brought near it.
Importance
This reaction is useful in laboratories for preparing hydrogen gas and understanding chemical reactions.
2. Precipitation Reaction (Formation of Solid Product)
A precipitation reaction is a chemical reaction in which an insoluble solid substance is formed from two liquids.
What is a Precipitate?
The solid substance formed during the reaction is called a precipitate.
How it Happens
When two aqueous solutions are mixed, their ions combine to form a solid that does not dissolve in water.
Important Features
- Formation of solid particles
- Colour change may occur
- The reaction usually takes place in liquids
Example
Silver nitrate solution + Sodium chloride solution → White precipitate of silver chloride
Uses of Precipitation Reactions
- Water purification
- Chemical analysis
- Preparation of compounds in laboratories
Importance
These reactions help scientists identify substances and remove impurities from solutions.
3. Phloem Tissue (Transport of Food in Plants)
Phloem is a special plant tissue responsible for transporting food from leaves to all parts of the plant.
Main Function
Leaves prepare food through photosynthesis. Phloem carries this food to roots, stems, fruits, and flowers.
What Phloem Transports
- Glucose
- Sugars
- Nutrients
Direction of Transport
Unlike xylem, phloem can transport food both upward and downward.
Difference Between Xylem and Phloem
- Xylem → transports water and minerals
- Phloem → transports food
Importance of Phloem
- Supplies energy to plant cells
- Helps in growth and storage of food
- Maintains healthy functioning of the plant
Example
Food made in leaves reaches roots through phloem tissue.
4. Breakdown of Glucose into Pyruvate (Cytoplasm)
The breakdown of glucose into pyruvate is the first step of respiration and occurs in the cytoplasm of the cell.
What is Cytoplasm?
Cytoplasm is the jelly-like substance present inside the cell where many chemical activities take place.
Process Name
This process is called glycolysis.
What Happens During Glycolysis
- One glucose molecule breaks into smaller molecules called pyruvate
- A small amount of energy is released
- The process does not require oxygen in the beginning
Further Breakdown
After glycolysis:
- In presence of oxygen → complete respiration occurs in mitochondria
- In absence of oxygen → anaerobic respiration takes place
Importance
This process provides energy needed for body functions and cell activities.
Example
Human cells continuously break down glucose to release energy for movement and growth.
5. Testosterone (Male Sex Hormone)
Testosterone is the main male sex hormone responsible for the development of male characteristics.
Produced By
It is mainly produced in the testes.
Functions of Testosterone
- Development of male reproductive organs
- Growth of facial hair and body hair
- Deepening of voice during puberty
- Muscle and bone development
Role During Puberty
Testosterone becomes more active during adolescence and causes physical changes in boys.
Comparison with Other Hormones
- Estrogen → female hormone
- Progesterone → female reproductive hormone
- Insulin → controls blood sugar
Importance
This hormone is essential for normal growth, reproduction, and overall male health.
Example
Increase in height and voice changes during teenage years are influenced by testosterone.