Cell Structure

• When a very thin slice of a plant stem is looked at under a microscope, it looks like it’s made up of many small box-like parts — these are cells.

• The slice in the picture is magnified 60 times. So if a cell looks 2 mm long in the image, in real life it’s only 0.03 mm long.

• Such thin slices are called sections.

Types of Sections

1. Longitudinal Section – Cut along the length of the stem (you see the inside part stretched out).

Scalar Quantities

A scalar quantity does not tell us the direction. You can describe it with just a number and a unit.

Examples:

• Mass – 5 kg

• Time – 10 second

• Temperature – 25°C

Acids are substances that release hydrogen ions (H⁺) in water, making the solution acidic. They have a pH less than 7. Examples include lemon juice and vinegar. Alkalis are substances that release hydroxide ions (OH⁻) in water, making the solution alkaline. They have a pH greater than 7. Examples include baking soda and soap. The pH scale measures how acidic or alkaline a solution is, ranging from 0 to 14. When acids and alkalis mix, they react in a neutralization process. This reaction produces salt and water. Neutral solutions have a pH of exactly 7. Indicators like litmus paper change color to show if a solution is acid or alkali. This helps us test and understand different substances.

1. Acids are substances that release hydrogen ions (H⁺) in water and have a pH less than 7.

2. Alkalis are bases that dissolve in water and release hydroxide ions (OH⁻), with a pH…

Microorganisms are tiny creatures you cannot see.Some help make food like bread and yogurt grow free.Yeast helps dough rise and makes bread soft and light.Good bacteria turn milk into cheese just right.Microbes help vegetables ferment and taste yummy.But some germs in food can make your tummy feel crummy.They spoil food, so we keep it cold or sealed tight.Washing hands and cooking well keeps food safe and bright.Microbes work hard in soil, helping plants grow.They can be friends in food and nature, this you should know.

1. Microorganisms are tiny living things that we can see only with a microscope.

2. Some microorganisms help make food like curd, cheese, and bread through a process called fermentation.

3. Good bacteria in yogurt help our stomach digest food better.

4. Yeast, a type of fungus, helps bread dough rise and become soft.

5. Some microorganisms can spoil food by making it rot or smell bad.

Some chemical reactions take heat from their surroundings and store it as chemical energy.

Those are are called endothermic reactions.

When endothermic reaction takes place temperature decreases.

The word equation between sodium hydrogencarbonate and citric acid

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Sodium hydrogencarbonate + citric acid -> Sodium citric + water + carbon dioxide

Investigating Variation 

Variation means differences among living things of the same species.For example, all humans are the same species, but we don’t all look the same — we have different heights, hair colors, and eye colors.

Investigation of Variation

To investigate variation, scientists or students can collect data and compare characteristics.

Example investigation: Investigating height in your class

1. Measure the height of all students in the class.

The turning effect of a force is the effect that makes an object rotate or turn around a fixed point when a force is applied.

why?

Because when a force is applied away from a fixed point, it doesn’t just push the object—it also makes it rotate around that point.

Here’s why:

• The part of the object closer to the fixed point (pivot) stays almost still.

• The part where the force is applied tries to move.

• energy resources are things that give us energy

• everything needs energy

• solar energy comes from the sun

• wind energy comes from moving air

• hydro energy comes from flowing water

• biomass energy comes from plants wood and animal waste

Law of Demand & Price Elasticity of Demand (PED)

• The Law of Demand says that when the price increases, people usually buy less of that product.

• But how much less they buy depends on how sensitive or responsive they are to price changes.

Price Elasticity of Demand (PED)

PED shows how much demand changes when the price changes.

• Price Inelastic Demand → Demand changes a little when price changes.Example: Rice, petrol, toothpaste – people still need them even if prices rise.