Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs.

The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids. The green coloured pigments called chlorophyll are found in the thylakoid membranes. It is the sight for the process of light-dependent reactions of the photosynthesis process. The thylakoids are arranged in stacks known as grana and each granum contains around 10-20 thylakoids.

The light-dependent reactions use light energy to make two molecules needed for the next stage of photosynthesis: the energy storage molecule ATP and the reduced electron carrier NADPH. In plants, the light reactions take place in the thylakoid membranes of organelles called chloroplasts.

retardation means negative acceleration.

Or

Rate of Decrease in velocity

For example: Brakes applied on a moving vehicle is an example of negative acceleration.

1.A gun recoils when a bullet is fired from it: When a bullet is fired from a gun, the gun exerts a force on the bullet in the forward direction. This is the action force. The bullet also exerts an equal force on the gun in the backward direction. This is the reaction force. Due to the large mass of the gun it moves only a little distance backward by giving a jerk at the shoulder of the gunman. The backward movement of the gun is called the recoil of the gun.
2.A man walking on the ground
3.Rowing a boat 
4.A person is moving forward during swimming

5.Rocket propulsion

6. A bird while flying pushes the air downwards with the help of its wings.

7. When a person is lying on a bed, his weight is opposed by a reaction force from the bed (assuming it must be there because of Newton’s third law of Motion).

1. If you use the same force to push a truck and a car, the car will have more acceleration than the truck because the car has less mass.
2. It is easier to push an empty shopping cart than a full one, because the full shopping cart has more mass than the empty one. This means that more force is required to push the shopping cart.
3. When a person kicks a ball the person exerts force in a specific direction, that is the direction in which it will travel. In addition to this, the stronger the ball is kicked, the stronger the force we put on it and the further away it will travel.
4. Suppose two people are walking and among the two people, if one is heavier than the other, then the one weighing heavier will walk slower because the acceleration of the person weighing lighter is greater.
5. When riding a bicycle, the bicycle acts as mass and our leg muscles pushing on the pedals of the bicycle is the force.

1. Catching a cricket ball: When a fielder catches a cricket ball, he drags his hands backwards in order to increase the time taken by the ball to reduce its momentum to zero. This reduces the rate of change of momentum, thereby decreasing the force exerted on the hands by the ball.

 2. Seat belts in a car: When brakes are suddenly applied or a car crashes with an object, the seat belts increase the time taken to move forward, thereby decreasing the rate of change of momentum. Thus, the force of impact is reduced and fatal accidents can be prevented.

3. Athletes lands on sand: When an athlete lands from a height on a hard floor, he may hurt his feet because his feet comes to rest instantenously. So, a very large force is exerted by the floor on his feet. On the other hand, when he lands on sand, his feet pushes the sand for some distance, therefore the time duration in which his feet comes to rest increases. Thus, the force exerted on his feet decreases and he is saved from getting hurt.

Latent heat: The heat associated with a state change is known as latent heat.

Latent heat of fusion: The amount of heat required to change 1 kg of a solid into a liquid at the melting point is called latent heat of fusion of the substance.

Latent heat of vaporisation: The amount of heat required to change 1 kg of a liquid into a gas at the boilng point is called latent heat of vaporization of the substance.

• The mitochondria is also called powerhouse of the cell.
• It is surrounded by two membranes.
• The outer membrane is porous wherea the inner membrane has deep folds that provides a large surface to perform the chemical reactions required for the generation of ATP.
• The inner membrane is compartmentalized into various cristae.
• The ground substance or space enclosed by inner membrane is called matrix.
• Mitochondria have their own DNA and ribosomes and are hence capable to produce some of their required proteins all by themselves.

Ernest Rutherford was interested in knowing how the electrons are arranged within an atom. Rutherford designed an experiment for this. In this experiment, fast moving alpha (α)-particles were made to fall on a thin gold foil.

• He selected a gold foil because he wanted as thin a layer as possible. This gold foil was about 1000 atoms thick.
• α-particles are doubly-charged helium ions. Since they have a mass of 4µ, the fast-moving α-particles have a considerable amount of energy. 

It was expected that α-particles would be deflected by the sub-atomic particles in the gold atoms. Since the α-particles were much heavier than the protons, he did not expect to see large deflections. But, the α-particle scattering experiment gave totally unexpected results .

1. Most of the space inside the atom is empty because most of the α-particles passed through the gold foil without getting deflected.
2. Very few particles were deflected from their path, indicating that the positive charge of the atom occupies very little space.
3. A very small fraction of α-particles were deflected by very large angles, indicating that all the positive charge and mass of the gold atom were concentrated in a very small volume within the atom.

From the data he also calculated that the radius of the nucleus is about 10⁵ times less than the radius of the atom.

Cells are the basic, fundamental unit of life. So, if we were to break apart an organism to the cellular level, the smallest independent component that we would find would be the cell.

Fluidity:fluidity is a property shown by liquids and gases. It means tendency to flow. Liquid and gases can change their shapes when a force is applied externally. This is the reverse of rigidity.
Kinetic energy:kinetic energy is also called energy of motion since particles of matter always remaining motion, they have kinetic energy.
Density:density is mass per unit volume. Density means how compact a substance is. Solid, because their particles are tightly packed, occur smaller volume and have greater densities. Gases have particles which can move around freely and therefore they can occupy more volume therefore, gases have least density.
Compressibility: compressibility means reduction in the volume of a substance on applying pressure. Solids and liquid are incompressible. This is because there is very empty space between the particles of solids and liquids. For example, you cannot fill more petrol in your car petrol tank even if you apply pressure. On the other hand, gases are easily compressible on applying pressure. It is because there are large empty space between the particles of gases.

Cell membrane shows lipid bilayer and protein molecules studded in between. It provides the fluid character to the membrane. It also provides flexibility to the membrane. Flexibility is necessary for the membrane to perform endocytosis, exocytosis, etc. 

The movement of water molecules from a region of its higher concentration to a region of its lower concentration, across a semipermeable membrane is called osmosis.

For example -

• If you put a carrot in salty water, the salt water will pull out the water from inside the carrot (which is mostly made up of water). Within a few hours, the carrot will be limp, its cells shriveled.

• Humans suffering from cholera are also affected by osmosis. The bacteria that overpopulate the intestines reverse the flow of absorption and do not allow water to be absorbed by the intestines, which results in dehydration.

• When the fingers are placed in water for a longer period of time, they become pruney due to the flow of water inside the cells.

Membrane-bound organelles are cellular structures that are bound by biological membrane. The membrane may be a single layer or a double layer of lipids and typically with interspersed proteins. Membrane-bound organelles offer several advantages to eukaryotic cells. First, cells can concentrate and isolate enzymes and reactants in a smaller volume, thereby increasing the rate and efficiency of chemical reactions. The plasma membrane, or the cell membrane, provides protection for a cell. It also provides a fixed environment inside the cell. And that membrane has several different functions. One is to transport nutrients into the cell and also to transport toxic substances out of the cell.

Diffusion is the process wherein the molecules merge as a result of their kinetic energy of random motion. It occurs in liquids and gases because their molecules move randomly. The molecules move from a region of higher concentration to a region of lower concentration, down the concentration gradient, until the concentration equalizes throughout the medium.

Various components presents inside a cell are known as cell organelles. For example plasma membrane, nucleus cytoplasm all are cell organelles.

Most of the important activities of the cell occur in the cytoplasm. Cytoplasm contains molecules such as enzymes which are responsible for breaking down waste and also aid in metabolic activity.
Cytoplasm is responsible for giving a cell its shape. It helps to fill out the cell and keeps organelles in their place. Without cytoplasm, the cell would be deflated and materials would not be able to pass easily from one organelle to another.
Cytosol is the part of the cytoplasm that does not contain organelles. Instead, cytosol is confined by the boundaries of a matrix which fills the part of the cell that does not contain organelles.

Bases are also electrolytes which give ions in aqueous solutions and these ions help to conduct electricity.

Eg : NaOH(aq) → Na⁺(aq)+OH⁻(aq)

But better use Strong Base as it gives ions easily rather than weak base ; thus strong base conduct electricity easily than weaker base.

Action and reaction are of equal magnitude and opposite direction.

So, if they act on same body, they will cancel each other giving resultant zero.

As there is no force, there will be no motion.

Matter- Matter is anything which occupies space and has mass is called matter. Air and water, sugar and sand, hydrogen and oxygen etc. Matter is made up of very small tiny particles. Particles of matter have space between them they attract each other.

Classification- On the basis of physical properties, matter is classified as solids, liquids and gases. On the basis of chemical properties, matter is classified as elements, compounds and mixtures.

      •  Solids- Solids have strong molecular force and a definite shape and size solids can neither flow nor be compressed.

      •  Liquids- Liquids have weak intermolecular flow and large intermolecular spaces. Liquids do not have a definite shape but can flow.

      •  Gases- Gases have weak intermolecular flow, high compressibility, and no definite shape and volume.