The single-celled organisms are called unicellular and if the organisms are made up of more than one cell are called multicellular.

The simple microscope was developed by Antony Von Leeuwenhoek.

The compound microscope was developed by Robert Hooke.

The branch of biology which deals with the study of cells is called cytology.

The living substance of the cell is called protoplasm.

Examples of

(a) unicellular organisms:

bacteria

amoeba

yeast

chlamydomonas ETC.

(b) multicelluar organisms: PLANTS like rose, neem, animals like man, hydra etc.

Examples of different cellular shapes.

irregular — amoeba

oval — chlamydomonas (slipper organism)

oblong — paramecium

elongated — striated muscle cells

very long or thread like — nerve fibre cells

cubical or rectangular — plant cell

The smallest cell — Bacterial cell

The longest cell — Nerve cells

The largest cell — Ostrich egg

Cell theory explains

Every living organism is made up of one or many cells.

The structural unit of all the living organisms is the cell.

The functional unit of all the living organisms is the cell.

All cells arise from the pre-existing cells.

The three scientists who contributed in the cell theory are:

M.J. Schleiden

Theodor Schwann

Rudolph Virchow

Animal cells have no cell walls.

The cell wall is made up of cellulose which is rigid and gives shape to the cell.

The cell wall is freely permeable while the cell membrane is semi-permeable.

The supportive framework which helps in the distribution of various product across the cell is endoplasmic reticulum.

Power house of the cell — Mitochondria

Synthesise proteins — Ribosomes.

The organelle found only in the animal cell which initiate and regulate cell division is Centrosome.

The organelle found only in the plant cell is plastid.

Green plastids are chloroplasts

Other plastids are amyloplasts.

Cell organelles are concerned with specific functions.

The IMPORTANCE of cell division is.

Production of NEW cells.

For growth and repair.

Replacement of the dead and worn out cells. –

For reproduction.

The process of fusion of sperm and an egg is called fertilisation.

The result of fertilisation is Zygote.

Hope it helps U! :)