Cell Structure and Micro-organisms - Standard 7 - General Science - Balbharati
Cell Structure and Micro-organisms
Exercise
Q. 1 Answer the following questions.
(a) What is a "cell"?
Ans. Cell is structural and functional unit of living organisms.
(b) Name the different organelles in a cell?
Ans. 1. Nucleus
2. Mitochondria
3. Endoplasmic Reticulum (ER)
4. Golgi Apparatus
5. Ribosomes
6. Lysosomes
7. Vacuoles
8. Cell Membrane
9. Cytoplasm
(c) What are micro-organisms?
Ans. The organisms which can not be seen with our eyes but only can be seen under compound microscope are called micro-organisms.
(d) Which are the different types of micro-organisms?
Ans. According to shape, and life- processes, types of micro-organisms are algae, fungi, protozoa, bacteria and viruses.
Q. 2 Fill in the blanks with the proper word.
(a) The organelle called the present in plant cells only is
Ans. Plastid.
(b) Garbage is converted into by micro-organisms.
Ans. Compost.
(c) In the cell, photosynthesis is carried out with the help of
Ans. Chloroplast.
(d) An electron microscope is necessary for the study of
Ans. Micro-organisms.
Q. 3 What is difference between us?
(a) Plant cell and animal cell.
| Plant Cell | Animal Cell |
|---|---|
| Plant cells have a cell wall, providing structural support and a definite shape. | Animal cells lack a cell wall, allowing for more flexibility in shape. |
| Lysosomes, the organelles containing digestive enzymes, are generally absent in plant cells. | Animal cells contain lysosomes, helping in cellular digestion and waste removal. |
| Chloroplasts, responsible for photosynthesis, are found in plant cells but not in animal cells. | Animal cells lack chloroplasts and depend on other organelles for energy production. |
| Plant cells typically have one larger central vacuole, which helps in storage and maintaining turgor pressure. | Animal cells have smaller vacuoles that play a role in storage and transportation of substances. |
| Plant cells contain plastids involved in various cellular processes, including photosynthesis. | Animal cells contain centrioles, helping in cell division and organization of the cytoskeleton. |
(b) Prokaryotic cell and eukaryotic cell.
| Prokaryotic Cell | Eukaryotic Cell |
|---|---|
| Prokaryotic cells lack a true nucleus, and their genetic material is present in the nucleoid region. | Eukaryotic cells have a defined nucleus enclosed in a membrane, housing the genetic material. |
| They lack membrane-bound organelles, including the endoplasmic reticulum and Golgi apparatus. | Eukaryotic cells contain membrane-bound organelles, facilitating specialized cellular functions. |
| Prokaryotic cells are generally smaller in size and simpler in structure. | Eukaryotic cells are larger and exhibit greater complexity in both structure and organization. |
| Ribosomes in prokaryotic cells are smaller and structurally different from those in eukaryotic cells. | Eukaryotic cells have larger and more complex ribosomes. |
| Ex. Cells of Bacteria and Archaea. | Ex. Cells of plants, animals, fungi, and protists. |
4. Sketch and describe in your own words, the plant cell and animal cell.
Ans.
Plant Cell:
Plant cells are eukaryotic cells, with various cell parts surrounded by a cell wall, giving them a specific shape. Plant cells have one large vacuole for storage.
These cells have four main parts: the cell wall (only in plant cells), plasma membrane (outer layer in animal cells), cytoplasm, and different cell organelles. The cell wall supports plant cells. The cytoplasm holds dispersed organelles.
Animal Cell:
Animal cells, also eukaryotic, differ from plant cells as they lack a rigid cell wall, allowing for flexibility. Instead of one large vacuole, animal cells have several smaller ones for various functions.
An animal cell includes the plasma membrane, cytoplasm, nucleus, and cell organelles. The plasma membrane protects animal cells, and the cytoplasm houses the organelles. Animal cell organelles, such as the nucleus and mitochondria, play essential roles in cellular functions.
Q. 5 Explain the uses and the harmful effects of micro-organisms.
Ans. Uses of Microorganisms:
1. Microbes are used in the production of various common foodstuffs by breaking down substances in batter, dough, and fruit juices.
2. Antibiotics, such as penicillin, are produced with the help of specific microbes and are used to destroy pathogens, control diseases like tuberculosis, typhoid, and cholera, and protect domestic animals from illnesses.
3. Vaccines are produced with the help of microbes, providing immunity against specific diseases.
4. Microbes are used in biogas plants to convert farm waste, human urine, and faeces into biogas and fertilizer.
5. Microbes are used to clear oil spills in season, oceans or lakes.
6. Microbes are involved in processes like tanning of skin and the production of ropes and strings from agave.
Harmful Effects of Microorganisms:
1. Some microbes release toxins into food, causing spoilage. Consuming spoiled food can lead to illnesses which have symptoms like loose motions and vomiting.
2. Pathogens in water contaminated with sewage or unhygienic food left uncovered can cause diseases of the alimentary canal, such as amoebiasis, typhoid, cholera, hepatitis, and gastro.
3. Respiratory pathogens released into the air through sneezing or coughing can infect healthy people. They causes diseases like the common cold, cough, diphtheria, pneumonia, tuberculosis, etc.
4. Mosquitoes, breeding in places like garbage heaps and stagnant water, transmit diseases like malaria, dengue, elephantiasis, yellow fever, chikungunya, and Zika fever through bites.
Q. 6 Give reasons.
(a) Diseases spread on a large scale during periods of heavy rainfall and floods.
Ans. Because; Stagnant water provides breeding grounds for mosquitoes, which transmit diseases like malaria and dengue. Contaminated water sources during floods can lead to the spread of waterborne diseases such as cholera and gastroenteritis.
(b) There is a possibility of food poisoning if we eat stale food.
Ans. Because; stale food encourages the growth of harmful bacteria, leading to the production of toxins. Toxins produced by these bacteria can cause foodborne illnesses with symptoms like nausea, vomiting, and diarrhea.
(c) Soil is turned over during tilling.
Ans. Because; tilling helps to aerate the soil, allowing better reaching of air, water, and nutrients to the roots of plants. It disrupts the growth of weeds and mixes organic matter, enhancing soil fertility.
(d) Fungus grows quickly in moist or humid conditions.
Ans. Because; moisture creates an ideal environment for fungal spores to germinate and grow. Fungi grows faster in humid conditions due to increased availability of water for metabolic processes.
(e) A refrigerator is used in almost every home.
Ans. Because; refrigeration slows down the growth of bacteria and molds in perishable food items, extending their shelf life. Cold temperatures help prevent the spoilage of food and maintain its freshness.
(f) Bread 'rises' during baking.
Ans. Because; the yeast in the bread dough undergoes fermentation, producing carbon dioxide gas. The trapped gas causes the dough to rise, creating a light and fluffy texture in the baked bread.
(g) Fodder is soaked in water before offering to cattle.
Ans. Because; soaking makes the fodder more palatable and digestible for the cattle. It increases the moisture content, making it easier for the animals to chew and swallow.
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