The Structure of a Cell and Micro-organisms – Maharashtra Board Class 8 Solutions for General Science (English Medium)
Characteristics of the cell membrane:
- It is the outermost covering of the cell.
- It is very thin and flexible.
- It protects the inner parts of the cell.
- It regulates the flow of substances which enter and leave the cell.
- It maintains the shape of the cell.
Functions of the nucleus:
- It controls and regulates all the functions of the cell.
- It takes active part in the process of cell division.
- The genes located on the chromosomes in the nucleus help to transmit the inherited characteristics from the parental generation to the next generation.
Functions of vacuoles:
- They store the products of excretion.
- They also store secretions of the cell temporarily.
Ribosomes, mitochondria and nucleus are present in both plant and animal cells.
Chromosomes contain DNA which carries genetic information.
The plant cell contains chloroplasts which assist in photosynthesis.
- Mitochondria are primarily tubular in shape.
- They are double-walled membranous structures with folds on the inner membrane.
- They produce energy from the food material present in the cell.
- This energy is supplied whenever required by the cell.
- Mitochondria are therefore called the powerhouses of the cell.
- Antibiotics are substances produced from microorganisms which kill other microorganisms.
- In 1929, Alexander Fleming discovered the antibiotic penicillin during the growth of the fungus Penicillium.
- Only certain bacteria are able to produce certain antibiotics.
- An antibiotic can kill only specific microorganisms.
- For example, the antibiotic penicillin kills diphtheria and pneumonia germs, chloromycetin kills typhoid germs and streptomycin kills tuberculosis germs.
Bacteria which produce harmful effects on human beings are called harmful bacteria.
- Staphylococcus bacteria produce a poisonous substance called enterotoxin as it grows on foodstuffs. After entering the body, this substance causes vomiting and diarrhoea.
- Clostridium bacteria produce toxic substances in expired canned food. Such foodstuffs cause vomiting and diarrhoea if consumed.
- Diseases such as typhoid, tuberculosis, diphtheria and pneumonia are also caused by bacterial infection.
Bacteria which are beneficial to human beings are called useful bacteria.
- The Rhizobium bacteria found in the root nodules of leguminous plants are used as nitrogen-fixing agents. They convert the nitrogen in the air into nitrogenous compounds. These nitrogenous compounds enter the soil and make it fertile.
- The bacterium Azotobacter lives independently and fixes atmospheric nitrogen into nitrogenous compounds.
- Soil contains several bacteria which decompose the dead and decaying matter of several plants and animals and produce humus. This increases the fertility of the soil.
- The name ‘cell’ was first used by the scientist Robert Hooke.
- The cell wall of the plant cell consists of the substance cellulose.
- The cell wall is found only in the plant cell.
- Mitochondria is the powerhouse of the cell.
- The cell membrane is the outer covering of the cell.
Differences between plant cells and animal cells:
|S.No.||Plant cells||Animal cells|
|1.||The cell wall is the outermost covering of the plant cell.||The cell membrane is the outermost covering of the animal cell.|
|2.||Cell wall is present.||Cell wall is absent.|
|3.||Vacuoles are larger and more in number.||Vacuoles are smaller and fewer.|
|4.||Chlorophyll is present.||Chlorophyll is absent.|
Differences between cell membrane and cytoplasm:
|1.||The cell membrane is the outer covering of the cell.||The cytoplasm is a substance inside the cell.|
|2.||It protects the inner parts of the cell.||It has cell organelles embedded in it.|
|3.||It is a thin, flexible membrane.||It is a semi-fluid substance.|
|4.||It is made of lipids and proteins.||It is made of organic and inorganic substances.|
|5.||It regulates the flow of substances in and out of the cell.||The cell organelles embedded in the cytoplasm carry out various life processes of the cell.|