Samacheer Class 6 Science - The Cell

The correct order from smallest to largest is: Bacteria, Mango, Rose plant, Cow, Elephant. Bacteria are single-celled prokaryotic organisms and are microscopic in size. Mango and rose plants are multicellular organisms, with mango trees being smaller than rose plants in general. Cow and elephant are both large multicellular animals, with the elephant being significantly larger than the cow.

The correct order from smallest to largest is: Insect egg, Hen egg, Ostrich egg. Insect eggs are typically microscopic or very small in size. Hen eggs are medium-sized eggs that we commonly use in our daily lives. Ostrich eggs are the largest eggs among birds and are significantly bigger than hen eggs.

The English scientist Robert Hooke discovered the cell in 1665 while examining thin slices of cork tissue under a microscope. He observed small, box-like structures that reminded him of the cells in a monastery, so he named them cells. This discovery was groundbreaking because it was the first time the basic unit of life had been identified and described.

We have a Eukaryotic type of cells.

A typical cell consists of three major parts. The first is the cell membrane, which is an outer protective layer that controls the movement of substances in and out of the cell. The second is the cytoplasm, which is a liquid substance inside the cell that contains various organelles and where most cellular activities occur. The third is the nucleus, which is a membrane-bound structure that contains the cell's genetic material in the form of DNA and controls the cell's activities and reproduction.

Cell wall
Chloroplast

Three examples of eukaryotic cells are plant cells, animal cells, and cells found in fungi and algae. Plant cells contain a nucleus, cell wall, and chloroplasts. Animal cells contain a nucleus and various organelles but lack a cell wall and chloroplasts. Fungi and algae are also eukaryotic organisms whose cells contain a nucleus and membrane-bound organelles, though they differ in structure from typical plant and animal cells.

The cytoplasm is a watery, gel-like material found inside the cell in which various cell parts and organelles are suspended and can move freely. Because the cytoplasm provides the medium in which cellular components move and interact with each other, it is known as the 'Area of movement'. This fluid environment allows organelles like the nucleus, mitochondria, and other structures to move and function properly within the cell.

Prokaryotic cells lack a true nucleus and membrane-bound organelles and are generally smaller and simpler (as in bacteria), whereas eukaryotic cells have a membrane-bound nucleus and organelles, are larger and more complex, and undergo mitosis for cell division.

When observing plant and animal cells under a microscope, several key structural differences are visible. Plant cells contain a cell wall and chloroplasts, which are absent in animal cells. The cell wall provides rigidity and support to plant cells, while chloroplasts are responsible for photosynthesis and give plants their green color. Animal cells lack these structures but contain centrioles, which are absent in plant cells. Centrioles play a role in cell division in animal cells. Both cell types contain a nucleus, cytoplasm, and other common organelles like mitochondria and ribosomes. The sketches would show plant cells as rectangular or fixed in shape due to the cell wall, while animal cells appear more rounded or irregular in shape.

Nucleus — controls cell activities and stores genetic material; Mitochondria — produce energy by respiration (ATP synthesis); Chloroplast — conduct photosynthesis and contain chlorophyll; Endoplasmic reticulum — synthesizes and transports proteins and lipids; Golgi apparatus — modifies, packages and secretes substances.