Chapter 11 Cell Structure and Micro-organisms Solutions

Maharashtra State Board Class 7 Science Solutions Chapter 11 Cell Structure and Micro-organisms

Class 7 Science Chapter 11 Cell Structure and Micro-organisms Textbook Questions and Answers

1. Answer the following questions.

Question a.
What is a cell?
Answer:
The cell is the fundamental, structural and functional unit of living organism.

Question b.
Name the different organelles in a cell.
Answer:
The nucleus, endoplasmic reticulum, Golgi bodies, lysosomes, mitochondria, vacuoles, plastids, chloroplasts are the different organelles in a cell.

Question c.
What are micro-organisms?
Answer:
The organisms which cannot be seen with our eyes but can only be observed under a microscope are called micro-organisms.

Question d.
Which are the different types of micro-organisms?
Answer:
Algae, fungi, bacteria, protozoa and viruses are various types of micro-organism. Some are unicellular and others are multicellular. Some of them are useful and some are harmful.

2. Fill in the blanks with the proper word.

Question a.
The organelle called the ……………. is present in the plant cells only.
Answer:
chloroplasts

Question b.
Garbage is converted into ……….. by microorganisms.
Answer:
fertilizer

Question c.
In the cell, photosynthesis is carried out with the help of …………….
Answer:
chloroplast

Question d.
An electron microscope is necessary for the study of ……………….
Answer:
micro-organism

Question e.
The process of preparing their own food in presence of sunlight and chloroplast by plants cells is known as ………...
Answer:
photosynthesis.

3. What is the difference between us?

Question a.
Plant cell and animal cell.
Answer:

Question b.
Prokaryotic cell and Eukaryotic cell
Answer:

4. Sketch and describe in your on words, the plant cell and animal cell.

Question a.
Sketch and describe ¡n your on words, the plant cell and animal cell.
Answer:
There are two types of cell-animal cells and plant cells. These cells contain various types of membrane beyond cell-organelles. Plant cells have a definite shape due to the presence of cell wall. Besides, unlike animal cells, plant cells contain single large vacuole. All these cells are known as eukaryotic cells. It cell has four main parts: the cell wall, cell membrane, cytoplasm and cell organelles.
1. Cell wall: The cell wall is the outermost covering of a cell. It is present only in plant cells.

2. Plasma membrane: The plasma membrane, also called the cell membrane, is a kind of thin covering, (a) It is extremely delicate and flexible, (b) It is the outermost covering of animal cells.

3. Cytoplasm: The liquid part in the cell, present around the nucleus is called cytoplasm, (a) It occupies the space between the plasma membrane and nucleus, (b) Cell organelles are scattered in the cytoplasm.

4. Cell organelles: These mainly include the nucleus, endoplasmic reticulum, Golgi bodies, lysosomes, mitochondria, vacuoles, plastids etc.

Plant cells contain chloroplasts.
(a) The nucleus is the most important organelle of the cell, (b) There is a porous double membrane around it. (c) The nucleus controls all functions of the cell, (d) The endoplasmic reticulum is a sprawling net-like organelle. Its function is to make necessary changes in the proteins produced by ribosomes and send them to the Golgi bodies, (e) Golgi bodies are made up of several flat sacs. Their function is the proper distribution of proteins.

(f) Mitochondria and plastids are organelles with double outer coverings, (g) As mitochondria produce energy, they are called the powerhouses of the cell, (h) The chloroplasts in plant cells carry out the function of photosynthesis, (i) Vacuoles help to throw out waste products of the cell, (j) Vacuoles in animal cells are small whereas there is only one large vacuole in a plant cell.

5. Explain the uses and the harmful effects of micro-organisms.

Question a.
Explain the uses and the harmful effects of, micro-organisms.
Answer:
Micro-organisms which are helpful are called useful micro-organisms.
Uses:
1. Micro-organisms present in nodules of leguminous plants, convert atmospheric nitrogen into its compounds and these compounds help to increase the soil fertility and protein content in the soil.

2. Some micro-organisms are useful in process of fermentation, making the food easily digestible and more nutritious. For producing milk products like butter, buttermilk, cheese, paneer, etc.

3. Microbes present in soil, dung etc. decompose garbage and convert into manure of best quality and surrounding is kept clean.

4. Microbes are also useful for sewage disposal. They help in decomposition of organic compounds in it.
5. Microbes are used in production of vaccines.

6. Microbes are also used in processes like tanning of skin, production of ropes and strings, from agave.
7. Some microbes use oil for their growth. Such microbes are used to clear a layer of oil floating on the surface of an ocean or lake formed due to leak or spill.

8. Farm waste, human urine and faeces, wet garbage etc. is collected and used in a biogas plant to produce biogas and fertilizer.

Harmful effects:
1. Disease producing micro-organisms are called pathogens, they are harmful micro-organisms.

2. Fungus grows on moist food, and microbes release enterotoxins into the food. Such toxins spoil the foods. Eating such spoiled food causes food poisoning i.e. loose motions and vomiting.

3. Pathogens may be present in water bodies contaminated with sewage, and dirt from surroundings, in food with flies sitting on it. If such contaminated food or water is consumed, we may fall ill with diseases like amoebiasis, typhoid, cholera, hepatitis, gastro, etc.

4. Pathogens are released in the air by a person having infection of the respiratory, sneezes or coughs. A healthy person may get infected by pathogens on breathing in the same air and contract diseases like common cold, cough, diphtheria, pneumonia, tuberculosis, etc.

5. Microbes that cause diseases like malaria, dengue, elephantiasis, yellow fever, chikunguniya, zike
fever etc. gain entry into the human body through the bite of a female mosquito.

6. Give reasons.

Question a.
Diseases spread on a large scale during periods of heavy rainfall and floods.
Answer:

Question b.
There is a possibility of food poisoning if we eat stale food.
Answer:

Question c.
Soil is turned over during tilling.
Answer:

Question d.
Fungus grows quickly in moist or humid condition.
Answer:

Question e.
A refrigerator is used in almost every home.
Answer:

Question f.
Bread rises during baking.
Answer:

Question g.
Fodder is soaked in water before offering to cattle.
Answer:

7. When will you use a simple microscope and when a compound microscope?

Question a.
When will you use a simple microscope and when a compound microscope?
Answer:

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