(i) Ostrich (Struthio cametus), its egg size is about 15 em x 13 cm weighing about 3 pounds.
(ii) An egg provides sufficient proteins, fats, vitamin A and vitamin D.
(iii) Eggs contains lot of cholestrol that may cause heart diseases. We should not eat many eggs in a day for long period.
(iv) Our duty is that we should make our friends, relatives and community to know about useful and harmful effects of eating eggs.

Mitochondria are known as 'Power House' of the cell. They are said so because the energy required for various life activities is released by mitochondria in the form of ATP molecules. The body uses energy stored in ATP for synthesis of new compounds and for mechanical work. As ATP instantly provide energy, the are called energy currency of the cell?

Difference between unicellular and multicellular organisms are as given below:

Multicellularity provides division of labour. This helps the organisms to perform various life processes in a better way.

(a) Plant cells have big vacuoles full of cell sap that provide them turgidity and rigidity. Plant vacuoles store amino acids, sugars, various organic acids and some proteins.
(b) In unicellular organisms, they may serve the following purposes:
(i) Forming Food Vacuoles: In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has ingested. The food items are digested by the enzymes later on.
(ii) Removal of excess water and wastes: In some unicellular organisms, specialised vacuoles play important roles in expelling excess water and some wastes from the cell.

(i) Lysosomes contain powerful digestive enzymes capable of breaking down all organic material.
(ii) Lysosomes help to keep the cell clean by digesting worn out cell organelles and foreign material such as bacteria or food.
(iii) RER (Rough Endoplasmic Reticulum) makes the digestive enzymes present in the lysosomes.

Functions of Golgi apparatus:
(i) Golgi apparatus is the secretory organelle of the cell. It packages and dispatches the material synthesised in the cell to intracellular (plasma membrane and lysosomes) and extracellular targets.
(ii) Golgi complex is also involved in the formation of Lysosomes.
(iii) Golgi apparatus is also involved in the synthesis of many substances such as polysaccharides, glycoproteins etc.

Golgi apparatus is connected to ER. It collects simpler molecules from ER and convert them into more complex molecules. These are then packaged in small vesicles and are stored or transported inside or outside the cell. If Golgi apparatus is not present in the cell, all the above processes of modification, storage and transportation will not be possible.

Cell Theory: Schleiden and Schwann proposed that:
(i) all the plants and animals are composed of cells and that
(ii) the cell is the basic unit of life. Later on Virchow added that
(iii) all cells arise from pre-existing cells.

Prokaryotic Cell:
Nuclear region is poorly defined due to absence of a nuclear membrane and is known as nucleoid.
Eukaryotic Cell:
Membrane-bound cell organelles are present.

1. When concentration of CO₂ is more inside the cell than outside, CO₂ diffuses from the cell to outside of cell. If CO₂ concentration inside the cell is less, CO₂ moves inside the cell from outside.
2. The water move in and out of the cell by the process of osmosis. Osmosis is the passage of water from a region of high water concentration through semi-permeable membrane (cell membrane) to a region of low concentration of water.

Difference

Example of osmosis:
(i) Absorption of water by plant roots.
(ii) Absorption of water by freshwater unicellular organisms such as Amoeba.

(i) The egg loses water and shrinks.
Reason. The egg membrane acts as semipermeable membrane. The concentrated salt solution present outside the egg is hypertonic so the egg loses water by osmosis. 
(ii) The egg gains water and swells.
Reason. The pure water is hypotonic (dilute) then egg cells, so water from the outside moves into the egg cells by osmosis. Gain of water results in swelling of egg