8. Cell - Structure and functions Science class 8 exercise Additional Questions With Solutions
8. Cell - Structure and functions Science class 8 exercise Additional Questions With Solutions ncert book solution in english-medium
NCERT Books Subjects for class 8th Hindi Medium
Chapter Review
Chapter Review:
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The structural and functional unit of the living organism is called cell.
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Cells were first observed in cork by Robert Hooke in 1665.
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The smallest living part of an organism is a ‘cell’.
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Cells exhibit variety of shapes and sizes.
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The organism which is made of only one cell that is called unicellular organism. Ex : amoeba and paramecium.
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The organism which is made of more than one cell are called multi cellular organism. Ex : human and tree.
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A tissue is a group of similar cells having a specific function
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The nucleus contains thread-like structures called chromosomes.
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Genes control the transfer of hereditary characteristic from parent to offspring; it is carried by the chromosomes.
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Green colour plastid is called chloroplast.
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The nerve cell receives and transfers messages, thereby helping to
control and coordinate the working of different parts of the body. -
The smallest cell is 0.1 to 0.5 micrometre in bacteria. The largest
cell measuring 170 mm ×130 mm, is the egg of an ostrich. -
Gene is a unit of inheritance in living organisms. It controls the transfer of a hereditary characteristic from parents to offspring.
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Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane.
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The cells having nuclear material without nuclear membrane are termed prokaryotic cells.Examples are bacteria and blue green algae.
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The cells, like onion cells and cheek cells having well organised nucleus with a nuclear membrane are designated as eukaryotic cells.
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They are scattered in the cytoplasm of the leaf cells. These are called plastids.
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Coloured bodies called plastids are found in the plant cells only.
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Green plastids containing chlorophyll are called chloroplasts.
Text Book Exercise
Exercise
Q1. Indicate whether the following statements are True (T) or False (F).
(a) Unicellular organisms have one-celled body. (T/F)
(b) Muscle cells are branched. (T/F)
(c) The basic living unit of an organism is an organ. (T/F)
(d) Amoeba has irregular shape. (T/F)
Answer : (a) (T), (b) (F), (c) (F), (d) (T).
Q2. Make a sketch of the human nerve cell. What function do nerve cells perform?.
Answer : The nerve cell receives and transfers messages, therby helping to control and coordinate the working of different parts of the body.
Q3. Write short notes on the following:
(a) Cytoplasm (b) Nucleus of a cell
Answer : (i) Cytoplasm : it is the jelly-like substance fou nd in between the nucleus and the cell membrane. It contains nucleus and many small structures called organelles. Cytoplasm, along with nucleoplasm, forms the living substance of the cell, called the protoplasm.
(ii) Nucleus : It is an important components of the living cell. It is generally spherical and located in the centre of the cell. It can be stained and seen easily with the help of a microscope. Nucleus is separted form the cytoplasm by a membrane called the nuclesr membrane. the liquid substance of the nucleus is termed as nucleoplasm.
Q4. Which part of the cell contains organelles?
Answer : Cytoplas m contains organelles of the cell.
Q5. Make sketches of animal and plant cells. State three differences between them.
Answer : Fig. 8.2. (a) Animal cell, (b) Plant cell.
Q6. State the difference between eukaryotes and prokaryotes.
Answer : Eukaryotes have well-organised nucleus with nuclear membrane while prokaryotes do not have this.
Q7. Where are chromosomes found in a cell? State their function.
Answer : Chromosomes are found in nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to te offspring.
Q8. ‘Cells are the basic structural units of living organisms’. Explain.
Answer : Cells many Cells in the body acumulate to build tissue. Tissues form body organs and body organs form body system. All systems forms a body. As cells give shape to the body. This may be compared to bricks. Brickes are assembled to make a building. So, cell is called the basic structural unit of loiving organisms.
Q9. Explain why chloroplasts are found only in plant cells?
Answer : Chloroplast contain chlorophyll which synthesise food in plant by the process of photosynthesis. No photosynthesis occurs in animals. So, they do not contion chloroplasts.
Q10. Complete the crossword puzzle with the help of cules given below.
Across
1. This is necessary for photo - synthesis.
3. term for component presesnt in the cytoplasm.
6. The living substance in the cell.
8. Unit of inheritance present on the chromosomes.
Down
1. Green plastids.
2. Formed by collection of tissues.
4. It separates contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.
Answer:
Text Book Exercise
Text Book Exercise:
Q4. Which part of the cell contains organelles?
Answer : Cytoplas m contains organelles of the cell.
Q5. Make sketches of animal and plant cells. State three differences between them.
Answer : Fig. 8.2. (a) Animal cell, (b) Plant cell.
Q6. State the difference between eukaryotes and prokaryotes.
Answer : Eukaryotes have well-organised nucleus with nuclear membrane while prokaryotes do not have this.
Q7. Where are chromosomes found in a cell? State their function.
Answer : Chromosomes are found in nucleus of the cell. They carry genes and help in inheritance i.e., transfer of characters from the parents to te offspring.
Q8. ‘Cells are the basic structural units of living organisms’. Explain.
Answer : Cells many Cells in the body acumulate to build tissue. Tissues form body organs and body organs form body system. All systems forms a body. As cells give shape to the body. This may be compared to bricks. Brickes are assembled to make a building. So, cell is called the basic structural unit of loiving organisms.
Q9. Explain why chloroplasts are found only in plant cells?
Answer : Chloroplast contain chlorophyll which synthesise food in plant by the process of photosynthesis. No photosynthesis occurs in animals. So, they do not contion chloroplasts.
Additional Questions With Solutions
CELL, STRUCTURE AND FUNCTION:
Ques: What is cell?
Ans: The structural and functional unit of the living organism is called cell.
Ques: Name the instrument by which cell can be seen.
Ans: Microscope.
Ques: What is unicellular organism?
Ans: The organism which is made of only one cell that is called unicellular organism. Ex – amoeba and paramecium.
Ques: What are multi cellular organisms?
Ans: The organism which is made of more than one cell are called multi cellular organism. Ex – human and tree.
Ques:Which part of the cell contains organelles?
Ans: Cytoplasm.
Ques:Distinguish between plant cell and animal cell.
Ans:
Plant cell |
Animal cell |
|
|
Ques: Name the projection in amoeba by which it take food.
Ans: Pseudopodia.
Ques:What is tissue?
Ans: A tissue is a group of similar cells having a specific function.
Ques:What are the basic components of a cell?
Ans: The basic components of a cell are cell membrane, cytoplasm and nucleus.
Ques:Name the components of cell which are enclosed within the cell membrane.
Ans: Cytoplasm and nucleus.
Ques:State the difference between eukaryotes and prokaryotes.
Ans: The difference between eukaryotes and prokaryotes:
Eukaryotes |
Prokaryotes |
|
|
Additional Questions With Solutions
Additional Question With Solutions
Ques: What are chromosomes?
Ans: The nucleus contains thread-like structures called chromosomes.
Ques:What are genes?
Ans: Genes control the transfer of hereditary characteristic from parent to offspring; it is carried by the chromosomes.
Ques:What is protoplasm?
Ans: The all entire contents of a living cell is known as protoplasm.
Ques:When can the chromosomes be seen?
Ans: Chromosomes can be seen only when the cell divides.
Ques:Which component of a cell is called the living substances of the cell?
Ans: Protoplasm.
Ques:What is chloroplast? Write its functions.
Ans: Green colour plastid is called chloroplast.
Functions of chloroplast:
(i) It provides green colour to the leaves.
(ii) It is essential for photosynthesis.
Ques: Name the components or organelles of cytoplasm in an animal cell.
Ans: The components or organelles of cytoplasm in an animal cell.
(i) Mitochondria
(ii) Golgi body
(iii) Vacuole
(iv) Ribosome
(v) Lisosome
Ques: Explain why chloroplasts are found only in plant cell?
Ans: The plants make their food themselves by the process of photosynthesis. Photosynthesis needs chlorophyll, which is called chloroplast. It also provides the green pigment to the plants’ leaves. So it is very important for the plants.
Ques:Cells are the basic structural units of living organism; explain.
Ans: Bricks are assembled to make a building. Similarly, cells are assembled to make the body of every organism. The brick is unit part of the building. Thus, cells make tissue; tissues make organs; and various organs make together the body. So we can say cells are the basic structural units of living organism
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Science Chapter List
1. Crop Production And Management
2. Microorganisms : Friend And Foe
3. Synthetic Fibres And Plastics
4. Materials : Metals And Non-Metals
5. Coal And Petroleum
6. Combustion And Flame
7. Conservation of Plants And Animals
8. Cell - Structure and functions
9. Reproduction in animals
10. Reaching the age of adolescence
11. Force And Pressure
12. Friction
13. Sound
14. Chemical Effects of Electric Current
15. Some Natural Phenomena
16. Light
17. Stars And The Solar System
18. Pollution of Air and Water
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