Cell Structure and Micro-organisms | Class 7 | Science | Chapter 11 | Maharashtra State Board
In this channel, we will delve into the structure and function of cells, discovering the various components that make up a cell, including the cell wall, cell membrane, cytoplasm, and cell organelles. We'll learn about the differences between plant and animal cells, and how they adapt to their environments.
We'll also venture into the realm of microorganisms, exploring the diverse ways in which they occur and interact with their surroundings. From observing and measuring microbes to understanding their growth and behavior, we'll uncover the intricacies of microbial life.
But microorganisms aren't just interesting to study; they also play a crucial role in our daily lives. We'll look at useful microorganisms like those involved in fermentation, which bring us tasty foods and drinks. And we'll examine the role of harmful microorganisms, such as pathogens, which can cause disease and illness.
Our channel won't just stop at theory; we'll also showcase practical applications of microbiology in action. We'll discuss initiatives like Swachha Bharat Abhiyan, which aim to promote cleanliness and hygiene in our communities, and highlight the importance of microbiology in maintaining public health.
So join us on this exciting journey as we explore the mysteries of cells and microorganisms! Whether you're a student, educator, or simply someone curious about the natural world, there's something here for everyone. Subscribe now and let's dive in together!
Questions & Answers
1. Answer the following questions.
(a) What is a cell? Ans. The cell is the fundamental, structural and functional unit of living organism.
(b) Name the different organelles in a cell. Ans. The nucleus, Endoplasmic reticulum, Golgi body, Lysosomes, Mitochondrion, Vacuoles, Chloroplasts, Cytoplasm, Cell membrane, Lysosome, Free ribosomes are the different organelles in a cell.
(c) What are micro-organisms? Ans. The organisms which cannot be seen with our eyes but can only be observed under a microscope are called micro-organisms.
(d) Which are the different types of micro-organisms? Ans. 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.
(a) The organelle called the chloroplasts is present in the plant cells only.
(b) Garbage is converted into fertilizer by microorganisms.
(c) In the cell, photosynthesis is carried out with the help of chloroplast .
(d) An electron microscope is necessary for the study of micro-organism .
(e) The process of preparing their own food in presence of sunlight and chloroplast by plants cells is known as photosynthesis.
3. What is the difference between us?
(a) Plant cell and animal cell.
Ans.
| Plant cell | Animal cell |
1. | Plant cell has cell wall. | Cell wall is absent in animal cell. |
2. | Plant cell has definite shape due to presence of cell wall. | Animal cell do not have definite shape. |
3. | Plant cell has one big vacuole. | Animal cells have many small vacuoles. |
4. | Plant cell has chloroplast so they produce their own food. | Animal cells do not have chloroplast, so they cannot produce their own food. |
5. | Plant cell has plastids. | Plastids are absent in animal cell. |
6. | Centrosomes are absent in plant cell. | Centrosomes are present near the nucleus. |
7. | Lysosomes are absent in plant cell. | Lysosomes are present in animal cell. |
(b) Prokaryotic cell and eukaryotic cell.
Ans.
| Prokaryotic cells | Eukaryotic cells |
1. | This cells are always unicellular. | Eukaryotic cells are present as either unicellular or multicellular. |
2. | The size of cell is generally range from 0.2 micrometers to 2.0 micrometers in diameter. | Eukaryotic cells range from 10 to 100 micrometers in diameter. |
3. | In prokaryotic cells, the cell wall is present and it is very complex in nature. | Eukaryotic cells have cell walls very rarely, if present they have simple chemical nature. |
4. | In this cells true nucleus absent, instead nucleotide is present | True nucleus is present. |
5. | DNA is arranged in circular shape | DNA is linear in shape |
6. | In prokaryotic cells, cytoplasm is present, but it is lacking in most cell organelles. | In eukaryotic cells, it consists of both cytoplasm and organelles, both are present. |
7. | Mitochondria is absent | Mitochondria is present and it is a powerhouse of cells. |
8. | Ribosomes are present, and they are small in size and shape is spherical | Ribosomes are present but they are comparatively large and linear in shape. |
9. | Endoplasmic reticulum and lysosomes and centromere’s all are absent | Endoplasmic reticulum and lysosomes and centromere’s all are present. |
10. | Plasmids are commonly found in prokaryotes. | Plasmids are very rarely found in eukaryotes |
11. | Cell division occur through binary fission | Cell division occur through mitosis |
12. | Flagella is small in size | Flagella are large in size. |
13. | In this cells only a sexual reproduction occurs. | Both sexual and asexual reproduction occurs. |
14. | Bacteria and Archaea are examples. | Plant and animal cells are examples. |
4. Sketch and describe in your on words, the plant cell and animal cell.
Ans.
Plant Cell:
Structure: Has a rigid cell wall made of cellulose.
Energy Factory: Contains chloroplasts for photosynthesis.
Storage: Large central vacuole for storing water and nutrients.
Animal Cell:
Structure: No cell wall, just a flexible cell membrane.
Energy Factory: Lacks chloroplasts; gets energy from food.
Storage: Small vacuoles, if any, for storage.
In essence, plant cells are like little solar-powered storage units with strong walls, while animal cells are more flexible and rely on external food sources for energy. Both have their unique features that suit their lifestyles!
5. Explain the uses and the harmful effects of micro-organisms.
Ans. Uses of microorganisms
Food production and processing: Microorganisms are used in the production of many foods, including bread, cheese, yogurt, beer, and wine. They are also used in food processing to ferment foods, extend their shelf life, and improve their flavour and texture.
Agriculture: Microorganisms are used to improve soil fertility, fix nitrogen, and control pests and diseases. They are also used to produce biofuels and other renewable energy sources.
Medicine: Microorganisms are used to produce antibiotics, vaccines, and other medicines. They are also used in medical research to develop new treatments for diseases.
Biotechnology: Microorganisms are used to produce a wide range of products, including enzymes, hormones, and industrial chemicals. They are also used in bioremediation to clean up pollution.
Harmful effects of microorganisms
Disease: Some microorganisms are pathogens, meaning that they can cause diseases in humans and other animals. Examples of pathogenic microorganisms include bacteria, viruses, fungi, and protozoa.
Food spoilage: Microorganisms can spoil food by causing it to rot, ferment, or become toxic. This can lead to foodborne illness, which can cause vomiting, diarrhea, and other symptoms.
Environmental damage: Microorganisms can cause environmental damage by breaking down organic matter, which can lead to water pollution and other problems.
In essence, microorganisms are like double-edged swords—they have incredible uses in various industries, but if not managed properly, they can also cause harm.
6. Give reasons.
(a) Diseases spread on a large scale during periods of heavy rainfall and floods. Ans. Heavy rainfall and floods lead to water contamination, vector breeding, sanitation disruption, population displacement, and damaged healthcare infrastructure, creating ideal conditions for the rapid spread of waterborne, vector-borne, and other infectious diseases.
(b) There is a possibility of food poisoning if we eat stale food. Ans. Eating stale food can lead to food poisoning because as food ages, harmful bacteria multiply, producing toxins that can make you sick when ingested. Stale food provides a breeding ground for these bacteria, increasing the risk of foodborne illnesses.
(c) Soil is turned over during tilling. Ans. Tilling, or turning over the soil, is done to break up compacted soil, incorporate organic matter, and create a loose, aerated environment. This enhances water infiltration, root penetration, and nutrient availability, promoting optimal conditions for plant growth. Tilling also helps control weeds and pests by disrupting their habitats.
(d) Fungus grows quickly in moist or humid condition. Ans. Fungi thrive in moist or humid conditions because water is essential for their survival and growth. Water serves as a solvent for the nutrients that fungi absorb from their surroundings, and it also helps to keep their cells hydrated and prevent them from drying out. Additionally, moist conditions create a favourable environment for fungal spores to germinate and spread.
(e) A refrigerator is used in almost every home. Ans. Refrigerators are used in almost every home because they prevent food spoilage. By keeping food at low temperatures, refrigerators slow down the growth of bacteria and fungi that cause food to spoil. This allows us to store food safely for longer periods of time, reducing food waste and saving money.
(f) Bread rises during baking. Ans. Bread rises during baking because of a tiny living organism called yeast. Yeast is added to the dough, where it eats the sugars in the flour and produces carbon dioxide gas as a by-product. This gas gets trapped in the dough’s stretchy gluten structure, causing it to puff up and rise.
(g) Fodder is soaked in water before offering to cattle. Ans. Cattle farmers often soak fodder in water before offering it to their livestock for several reasons. Soaking softens the fodder, making it easier for the cattle to chew and digest. This can improve the overall digestibility of the fodder, leading to better nutrient absorption and animal health. Additionally, soaking can help to remove dust, dirt, and other impurities from the fodder, making it cleaner and more palatable for the cattle.
7. When will you use a simple microscope and when a compound microscope?
Ans. You might use a simple microscope when you want to magnify an object moderately, like examining small insects or observing details on a coin. It's straightforward and useful for less complex tasks.
On the other hand, you'd choose a compound microscope for more detailed and higher magnification work, such as studying cells or bacteria. It uses multiple lenses for increased magnification and is suitable for more advanced scientific observations.
E X T R A
1. Fill in the blanks
1. Cell is the fundamental, structural and functional unit of living organism.
2. The four main parts of the plant cell are cell wall, cell membrane, cytoplasm and cell organelles.
3. Plant cell contains chloroplast which carry out the process of photosynthesis.
4. Mitochondria are called the power houses of the cell.
5. The outermost covering of plant cell is cell wall .
6. The outermost covering of animal cell is plasma membrane.
7. The nucleus is the most important organelle of the cell.
8. Swachha Bharat Abhiyan is a national movement started several years ago to increase awareness about public hygiene and personal hygiene.
9. The body temperature of a healthy human being is about 37°C .
10. Micro-organisms use food stuffs for their own nutrition and release toxic materials called enterotoxins .
2. Name the following:
1. An instrument used to observe cells. Ans. Microscope
2. I control the function of a cell. Ans. Nucleus
3. Outermost layer of the plant cell. Ans. Cell wall
4. Outermost layer of the animal cell. Ans. Cell membrane
5. I am the jelly like substance containing all the organelles. Ans. Cytoplasm
6. I contain thread like structures called chromosome. Ans. Nucleus
7. Which part of the cell contain organelles. Ans. Cytoplasm
8. The unit of measurement used for expressing dimension, size of the cell. Ans. Nanometer, micrometer
9. The power house of the cell. Ans. Mitochondria
10. Largest organelle in the plant cell. Ans. Vacuole
11. It is necessary for photosynthesis. Ans. Chlorophyll
12. The living substance in the cell. Ans. Cytoplasm
13. A group of cells. Ans. Tissue
14. Empty structures in cytoplasm. Ans. Vacuole
3. State whether the following statements are True or False. Correct and rewrite the false statement:
1. Cells can be easily seen with naked eyes. Ans. False. We can’t see cells with naked eyes, can be seen under microscope.
2. A single cell can perform all the functions in a unicellular organism. Ans. True.
3. Cell wall is present in both plant cells and animal cells. Ans. False. Cell wall is present only in plant cells.
4. Vacuoles are not found in plant cell. Ans. False. Large vacuole is found in plant cell.
5. Tissue is a group of dissimilar cells. Ans. False. Tissue is a group of similar cells.
6. Unicellular organisms have one celled body. Ans. True.
7. The basic living unit of an organism is an organ. Ans. False. The basic living unit of an organism is the cell.
8. The unit of measurement used for expressing dimension size of the cell is centimetre. Ans. False. The unit of measurement used for expressing dimension size of the cell is nanometer.
9. Micro-organism cannot grow in extreme adverse conditions. Ans. False. Some micro-organisms can survive in extreme adverse conditions e. g. ocean floor, ice polar region, hot water spring.
10. Some micro-organisms can grow without oxygen. Ans. True.
11. Amoeba has irregular shape. Ans. True.
12. The process of fermentation is used for making yogurt from milk. Ans. True.
13. Micro-organisms need an optimum temperature of 55°C to 70°C to grow. Ans. False. They need temperatures between 15°C to 35°C to grow well.
14. Cells with membrane bound organelles inside them are called prokaryotic cells. Ans. False. Cells with membrane bound organelles inside them are called eukaryotic cells.
15. Golgi bodies are the power houses of the cells. Ans. False. Mitochondria are the power houses of the cell.
4. Choose the correct word.
1. Which one of the following terms is not a part of the nucleus? (a) ribosome (b) DNA (c) chromosome (d) gene Ans. ribosome
2. A suitable term for the various components of cell is. (a) tissue (b) cell organelle (c) chromosome (d) gene Ans. cell organelle
3. The liquid part present in the cells is called. (a) protoplasm (b) chromosome (c) chloroplast (d) cytoplasm Ans. cytoplasm
4. The units of measurement used for expressing dimension size of the cell are, (a) centimetre (b) micrometre (c) nanometre (d) metre Ans. nanometre, micrometre.
6. The barrier between protoplasm and other environment in animal cell (a) plasma membrane (b) cell wall (c) nucleus membrane Ans. plasma membrane
7. The term cell wall is given by (a) Leeuwenhoek (b) Robert Hooke (c) Fleming Ans. Robert Hooke
8. The cell theory was proposed by (a) Watsonar Cricks (b) Schleiden (c) Schwann (d) Mengal Morgan Ans. Schleiden, Schwann.
9. Which of the following features will help you in distinguishing a plant cell from an animal cell. (a) cell wall (b) cell membrane (c) mitochondria (d) nucleus Ans. cell wall
10. The gas released during the preparation of bread, (a) O2 (b) CO2 (c) nitrogen (d) sulphur oxide Ans. CO2
11. The structural-functional unit of life is called (a) cell (b) tissue (c) organ (d) organism Ans. cell
12. Which organelle is called power house of the cell? (a) centrosome (b) lysosome (c) plastid (d) mitochondria Ans. mitochondria
13. Living substance of cell is called. (а) cytoplasm (b) protoplasm (c) nucleus (d) chromosome Ans. protoplasm
5. Give scientific reasons:
1. Mitochondria are called the power houses of the cell. Ans. Mitochondria are called the "powerhouses of the cell" because they produce energy. They take in nutrients and convert them into a usable form of energy, which the cell uses to power its various activities and functions.
2. A compound microscope is used for observing cells. Ans. A compound microscope is used for observing cells because it has multiple lenses that magnify the image of tiny objects like cells. This allows scientists and researchers to see cells in greater detail and study their structure and functions.
3. Cells are the basic structural units of living organism. Ans. Cells are the basic structural units of living organisms because they are the smallest entities that can perform all the functions necessary for life, such as growth, reproduction, and responding to the environment. Essentially, cells are the building blocks of living organisms, and all living things are made up of one or more cells.
6. Answer the following in short:
1. What is a vaccine? Ans. A vaccine is a substance that stimulates the immune system to recognize and defend against specific pathogens, such as viruses or bacteria, helping the body develop immunity without causing the disease itself.
2. What are the similarities between the Plant cell and Animal cell? Ans. Both plant and animal cells are eukaryotic cells, meaning they have a true nucleus and other membrane-bound organelles. They also have many similar organelles, such as:
• Mitochondria (produce energy)
• Endoplasmic reticulum (helps make proteins)
• Golgi apparatus (modifies proteins)
• Lysosomes (break down waste)
• Ribosomes (make proteins)
Both types of cells also have a cell membrane and cytoplasm.
3. What do micro-organisms need for growth? Ans. Microorganisms, like bacteria, need four things to grow:
1. Food - they need a source of nutrients to feed on
2. Water - they need moisture to survive
3. Warmth - they need a temperature range 15 to 35°C to thrive
4. Oxygen - some microorganisms need oxygen to breathe, while others don't need it at all.
7. Answer in details:
1. Explain the functions of organelles in a cell. Ans. the functions of some common organelles in a cell:
Nucleus: The nucleus is the control center of the cell. It contains the cell’s genetic material, or DNA, and helps to control the cell’s activities.
Cytoplasm: The cytoplasm is the jelly-like substance inside the cell where many metabolic reactions take place. It’s where proteins are made and where waste products are broken down.
Mitochondria: Mitochondria are often called the “powerhouses” of the cell because they produce energy for the cell through a process called cellular respiration.
Endoplasmic Reticulum (ER): The ER is a network of tubules and sacs that help to transport materials within the cell. It’s also where proteins are made and modified.
Golgi Apparatus: The Golgi apparatus is a series of flattened sacs that help to modify, sort, and package proteins and lipids for transport out of the cell.
Lysosomes: Lysosomes are membrane-bound sacs that contain digestive enzymes. They help to break down and recycle cellular waste and foreign substances.
Ribosomes: Ribosomes are tiny organelles found throughout the cytoplasm that help to make proteins.
Plastids: Plastids are organelles found in plant cells that help to make food through photosynthesis. Chloroplasts, which contain chlorophyll, are the most well-known type of plastid.
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