The Cell Online Test 6th Science Lesson 11 Questions in English

Like a brick wall, your body is composed of basic building blocks, and are named as “Cells”. The cell is the basic structural and functional unit of every living organism. The cell is self-sufficient to carry out all the fundamental and essential functions of an organism.

The Englishman Robert Hooke was a scientist, mathematician, and inventor. He improved microscope which was used in those days, and built a compound microscope.

Robert Hooke placed water-lens beside the microscope to focus the light from an oil-lamp on specimens to illuminate them brightly. So that he able to see the minute parts of the objects clearly.

Based on the observations made by him Hooke published a book named Micrographia in the year 1665, where he first used the term Cell. He described the structure of tissue using the term cell.

In Latin the word ‘cellua’ means a small chamber. The branch of science that deals with the study of cells is called ‘Cell Biology’.

A typical cell consists of three major parts:
1. An outer cell membrane.
2. A liquid cytoplasm.
3. A nucleus.

The size of cells may vary from a Micro-meter (a million of a metre) to a few Centi-meters. Most cells are microscopic and cannot be seen with the naked eye. They can be observed only through the Microscope.

Smallest size of the cell is present in Bacteria. The size of the bacterial cell ranges from 0.01 micro meter to 0.5 micro meter.

On the other-hand the largest cell is the egg of an ostrich with 170 milli meter width. We can see this with the naked eye.

In Human body the nerve cells are believed to be the longest cells. They can be observed only through the Microscope.

Cell size has no relation to the size of an organism. It is not necessary that the cells of, say an elephant be much larger than those of a mouse.

Organisms may be either unicellular (single cell) or multicellular. Organisms such as Bacteria, Amoeba, Chlamydomonas, and Yeast are unicellular.

Organisms such as Spirogyra, Mango, and Human beings are multicellular. (i.e) made up of a few hundreds to million cells.

The number of cells present in different organisms may vary. Approximate number of cells in the human body is 3.7 X10^13 or 37,000,000,000,000.

Generally, cells are classified into two types. First one is Prokaryotic cell. It has No true nucleus consisting of no nuclear membrane. Another one is Eukaryotic cell. It has True nucleus consisting of nuclear membrane.

The unicellular organisms like Bacteria has Prokaryotic cells. It has No true nucleus. This type of nucleus is called as nucleoid. No nuclear membrane is around this nucleoid.

Bacterial cells were the first form of life on earth. It is ranging from 0.003 to 2.0 micro meter in diameter. Eg. Eschericia coil bacteria.

Cells which has true nucleus is called as eukaryotic cell. It is bigger than prokaryotic cells. It’s organelles bounded by membrane. Ex. Plants, animals, most of the fungi and algae.

Both plant and animals are made up of cells. Both cells are eukaryotic in nature, having a well defined membrane – bound nucleus.

Plant cell
* It is usually larger in size. It is hard in nature. * Plant cell have a cell wall in addition to their cell membrane. * Plant cell have chloroplast which contain chlorophyll * Plant cells have large vacuoles. Centrioles are absent.

Animal cell * Animal cells are generally smaller than plant cells. It is not so hard as plant cell. * A cell wall is absent. * Chloroplast is usually absent. * An animal cell may have many small vacuoles. * Centrioles are found in animal cells.

Cell wall Surrounds and protects the cell, Make the cell stiff and strong. It has the special name as Supporter and protector.

Cell membrane Holds and protects the cell, Controls the movement of materials in and out of the cell. It has a special name as Gate of the cell.

Cytoplasm is a watery, gel-like material in which cell parts move. It is also called as Area of movement.

Mitochondria Produce and supply most of the energy for the cell. It is called as Power house of the cell.

Chloroplasts Contain green pigment chlorophyll and Capture the energy of sunlight and use it to produce food for the cell by photosynthesis. It is called as Food producers for the cell (Plant cell).

Vacuoles Store food, water, and chemicals. It has a special name called as Storage tanks. IT is scattered over the cytoplasm.

Nucleus acts as ‘brain’ of the cell. It Regulates and controls all the cell activities. It is also called as Control centre.

Nucleus membrane Surrounds and protects the nucleus control the movement of materials in and out of the nucleus. It is the Gate of the nucleus.