Class 8 Basic Science - Chapter 01 Life's Mysteries in Little Chambers - Questions and Answers
SCERT Solutions for Class 8 Basic Science Chapterwise
Chapter: 01 - Life's Mysteries in Little Chambers
* The body of all organisms is made up of cells.
ഈ ബ്ലോഗിലെ എല്ലാ പോസ്റ്റുകളും ഒരുമിച്ച് കാണാനും ആവശ്യമുള്ളവ എളുപ്പത്തിൽ തിരഞ്ഞെടുക്കാനും ഇവിടെ ക്ലിക്കുക.
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* Microscope is used to observe the cells.
* Microscopes in which more than one lens is used are called compound microscopes.
A compound microscope magnifies an object only 2000 times (maximum) its size. While electron microscopes, which utilize electrons instead of a light source, can magnify objects million times clearly.
* Eyepiece and Objective lenses are the two types of lenses seen in a compound microscope.
* The lens in the condenser focuses light on the material to be observed.
The diaphragm of the condenser helps to regulate the intensity of light.
* Mirror is with a plane mirror on one side and a concave mirror on the other side.
* Stages for the preparation of the observation material (for instance, a cross-section of plantain root)
1. Put the material in water (to prevent dehydration)
2. Take thin sections of the material and keep it in a watch glass containing water.
3. Put the thinnest complete sections to a watch glass containing stain.
(to get colour to cells)
4. Add one or two drops of glycerin to the slide. (to prevent the drying up)
5. Wash one of the stained sections and place it in the glycerin on the slide.
6. By using a needle, place a cover glass over it without forming air bubbles.
7. By using tissue paper, wipe out the excess glycerin.
8. Place the slide and observe it through the microscope.
* Milestones in the history of Cell Biology) :
* The cell theory:- (formulated by M.J Schleiden and Theodor Schwann )
1. The body of all organisms is made up of cells.
2. Cells are the structural and functional units of organisms.
* Functions performed by the cells:-
- Resist foreign particles,
- Release energy from nutrients,
- Synthesise biomolecules.
* The covering of a cell?
Cell membrane (plasma membrane)
* Why plasma membrane is called a selectively permeable membrane?
As they allow only the essential materials to pass.
* Protoplasm?
All substances inside the cell membrane (Cytoplasm + Nucleus = protoplasm )
* The controlling centre of a cell?
Nucleus.
* Prokaryotes are organisms without a nucleus in their cell.
(eg:- Bacteria, Cyanobacteria, Mycoplasma)
Eukaryotes are organisms with well-defined nucleus in their cell.
(eg:- Amoeba, Animals, Plants)
* Parts of a nucleus :
* Cell organelles?
Specific parts are seen in the cytoplasm.
Cell organelles are seen in both the plant and animal cells:- Mitochondrion, Endoplasmic reticulum, Ribosome and Golgi complex.
Cell organelles are seen only in plant cells:- Vacuole and Plastids.
Cell organelles are seen only in animal cells:- Centrosome and Lysosome.
* Different types of cell organelles and their functions:-
* Examples for pigments presented in different chromoplasts:-
- Xanthophyll (yellow),
- Carotene (yellowish orange),
- Anthocyanin (red, purple).
* Pigment seen in the chloroplast?
- Chlorophyll (green).
* The secret behind the change in the colour and taste of fruits?
As fruits ripen, chloroplasts change to chromoplasts, to change its green colour. Starch in the fruits is converted to sugar, to change its taste.
PRACTICE QUESTIONS & ANSWERS
1. Sketch the picture of a compound microscope and label its parts.
2. what is a microscope?
Answer: Microscope is a device used to magnify an object.
3. The microscopes in which more than one lens is used are called ....................
Answer: compound microscopes
4. what are the main parts of a microscope?
Answer: The main parts of a microscope are Eyepiece, Knobs, Objective Lens, Stage and clip, condenser, Diaphragm, and Mirror
*Eyepiece - Eyepiece in a compound microscope is used to see objects.
*Knobs - Knobs are used to adjust the position.
*Objective lens - Objective lens is used to magnify the object.
*Stage and clip - Stage and clip is used to hold and fix the glass slide.
*Condenser - Condenser lens focuses light on the material to be observed.
*Diaphragm - Diaphragm, a part of the condenser, helps to regulate the intensity of light.
*Mirror - Plane mirror is used to reflect sunlight.
Concave mirror is used to reflect artificial light.
5. Why do we use a slide made of glass to place the material to be observed?
Answer: In a microscope glass slide is used to place the material, because the glass slide is transparent. So it allows light rays to pass through it.
6. Preparation of Observation Material steps
1. Put the material to be observed in a Petri dish containing water to prevent dehydration.
2 . Take thin cross-sections of the material
3. Put the sections into a watch glass containing water.
4. Put the thinnest and complete sections to a watch glass containing stain.
5. Add one or two drops of glycerin to the slide to avoid drying up of the material.
6. Wash the stained section with clean water and place it in the glycerine on the slide.
7. Put a cover glass over the material.
8. Wipe out the excess glycerin using tissue paper.
7. Who discovered the cell first?
Answer: Robert Hooke.
8. Define cell theory. Who put forward this theory?
Answer: The cell theory was formulated by M.J Schleiden and Theodor Schwann. It states that
a) The body of all organisms is made up of cells.
b) Cells are the structural and functional units of organisms.
9. What are the main functions performed by cells?
Answer:
* Resist foreign particles.
* Release energy from nutrients.
* Synthesize biomolecules .
10. What is the difference between protoplasm and cytoplasm?
Answer: All substances inside the cell membrane constitute the protoplasm. The cytoplasm is the part of the protoplasm excluding the nucleus.
11. Define cell organelles .Give some examples.
Answer: Cell organelles are the specific parts in the cytoplasm to perform physiological functions.
Eg:– Mitochondrion, Ribosome, Endoplasmic reticulum...etc
12. Mitochondrion is called ‘power house’ of the cell. Why?
Answer: Because it is the part where production and storage of energy take place.
13. Why is the endoplasmic reticulum known as the cytoskeleton?
Answer: Because it provides firmness and shape to the cell.
14. Nucleus is the regulatory centre of the cell. Justify.
Answer: Nucleus controls all the cellular activities due to the presence of genes.
15. What are the differences between a compound microscope and an electron microscope?
Answer:
* Compound microscope magnifies an object up to 2000 times. But an electron microscope can magnify millions of times.
* In a compound microscope light is the source of magnification, but in an electron microscope electrons are used as the source of magnification.
* Compound microscope is easy to handle, but electron microscope is
difficult to handle.
16. Write short notes on various cell organelles.
Answer:
a) Mitochondrion - They are the powerhouse of the cell. Mitochondrion helps in the production and storage of energy. They are abundantly seen in the cells of the brain, liver and muscles where energy requirement is high.
b) Endoplasmic reticulum - They are the passage in the cells. Conduction of materials inside the cells takes place through this organelle. It is also known as the cytoskeleton as it provides firmness and shape to the cell.
c) Ribosome - It is the centre of protein synthesis in the cell. It is seen either attached to the endoplasmic reticulum or free in the cytoplasm.
d) Vacuole - It is covered by a membrane called a tonoplast. It stores water, salts and excretory materials.
e) Golgi complex - It collects cell secretions like enzymes, hormones mucous etc in small vesicles. Abundantly seen in glandular cells.
17. Illustrate the structure of a nucleus and write short notes on each part.
Answer:
I) Nuclear membrane -
It is a double-layered membrane that covers the nucleus.
ii) Nucleoplasm -
It is the fluid part of the nucleus. Nucleolus and chromatin reticulum are seen here.
iii) Chromatin reticulum-
They are seen as a network in the nucleoplasm. They carry genes
iv) Nucleolus -
They are spherical bodies, that play a major role in the synthesis of ribosomes.
v) Nuclear pore -
Nuclear pores are the pores in the nuclear membrane. They help in the conduction of materials to and from the nucleus.
18. Define prokaryotes and eukaryotes with examples.
Answer: In some organisms, the cells do not contain a nucleus. Such organisms
are called prokaryotes.
Eg:– Bacteria, cyanobacteria, mycoplasma etc...
In some organisms, a well-defined nucleus covered by a membrane is seen. These organisms are called eukaryotes.
Eg - Amoeba, plants and animals.
19. What are plastids ? Name different types of plastids.
Answer: Plastids are cell organelles that are exclusively found in plant cells. They are of three kinds namely chloroplast, chromoplast and leucoplast.
20. What are the functions of chromoplast, chloroplast and leucoplast?
Answer:
Chromoplast imparts colour to flowers and fruits.
Chloroplast helps in photosynthesis.
Leucoplast is plastids having no specific colour. They are abundantly seen in the cells where food materials are stored.
21. Name the pigments in plastids.
Answer:
Xanthophyll – yellow-coloured pigment.
Carotene - Yellowish orange.
Anthocyanin - Red /purple coloured pigment.
22. The colour and taste of fruits change when they ripen. Why?
Answer: Because as fruits ripen, chloroplast changes to chromoplast and starch
converted into sugar.
23. Name the cell organelles found only in animal cells. Write their function.
Answer:
a) Centrosome - It helps in cell division.
b) Lysosome - It helps to destroy foreign particles entering the cell.
24. Tabulate the differences between plant cells and animal cells.
Answer:
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