Science Textbook Solutions for Class 8 Science Chapter 10 - Cell and Cell Organelles

Important points to remember :

  1. cell is the structural and functional unit of living organisms. 
  2. According to the functions, cells of different  sizes and structures are found in different  organs. 
  3. Endocytosis  -  To gulp/engulf  food and other substanes from outer environment. 
  4. Exocytosis  -  To  excrete  waste materials out of cell. 
  5. Isotonic  solution -  Medium  outside  and  inside  the  cell  has same  proportion  of  water,  water doesn’t go in or out.
  6. Hypotonic  solution -  The  cell  has less water  than  outside  medium,  so water  enters  the  cell. This is called  endomosis. Eg. If raisins are kept in water, after sometime  they swell and become turgid. 
  7. Hypertonic solution The cell has more water than the outside medium so water comes out of the cell. Eg. If fruit  pieces  are kept in thick  saturated  sugar solution,  the  water from fruit  pieces  enter the  sugar solution. 
  8. Camilio  Golgi described the Golgi complex  for the  first  time. He developed the staining technique  called  'Black reaction' and with the help of it, he studied nervous system. 
  9. Mitochondria  are absent in RBCs. Due to this, the oxygen which is carried by them is not used for themselves. 

Question 1: Who am I ?
A. I am ATP producing factory ?
Answer : Mitochondria

B. I am single layered. but maintain cellular osmotic pressure.
Answer : cell wall

C. I support the cell, but I am not cell wall. I have a body resembling net.
Answer : cell membrane

D. I am chemical factory of the cell.
Answer : Mitochondria

E. Leaves are green because of me.
Answer : chlorophyll

Question 2: What would have happend ? If.........
A. RBCs had mitochondria.
Answer : RBC's are a type of cells which are found in blood. Their function is to carry oxygen to different cells and tissues of the body. They do not contain mitochondria for two purposes:
firstly, it saves the space in the red blood cells and so more of oxygen can bind to it
secondly, it prevents the use of oxygen which is bounded to RBC's.

If mitochondria would have been present in RBC's, the oxygen which is carried by them will be used up by the RBC's. Thus, there will be less or no oxygen left which can be transported to the cells and tissues.

B. There had been no differences between mitochondria and plastids.
Answer : Mitochondria and plastids are two different structures and they have specific functions. Mitochondria are found in both plants and animals whereas plastids are found only in plants. The main role of mitochnodria is to provide energy to the cells for carrying out their various functions. If, there would have been no difference between mitochondria and plastids, there would have been no structure which would provide energy and thus all the processes which take place in the cell would cease.

C. Genes are absent on chromosome
Answer : Genes are hereditary structures which contain the information which is passed on from one generation to another. They are required for the transmission of information from one generation to another. They are responsible for the characteristics of all the living organisms. They store the information for the various processes which occur in all the living organisms.

D. Plasma membrane had not been selectively permeable.
Answer : Plasma membrane is selectively permeable which means it allows the entry or exit of selective materials inside and outside the cell. In its absence, the regulated movement of substances in  and out of the cell will be affected.

E. Plants lacked anthocyanin.
Answer : Anthocyanin is a pigment which is present in plants and imparts them purplish colour. In the absence of this pigment, the structures which usually have purple colour due to its presence would appear colourless.

Question 3: Who is odd man among us ? Give reason.

a. Nucleolus, mitochondria, plastids, endoplasmic reticulum
Answer : Plastids are the odd one out because they are organelles which are found only in plant cells. Rest all the organelles are found in both plants and animals.

b. DNA. Ribosomes, Chlorophyll
Answer : Chlorophyll is the odd one out beacuse it is a type of pigment which is found in plants only. DNA and ribosomes are found in both plants and animals.

Question 4: Give functions.
a. Functions of the plasma membrane
Answer : It gives shape and support to the cell. It acts as a mechanical barrier to protect the internal contents of the cell. It separates the contents of the cell from its surrounding medium. It performs physical activities such as diffusion and osmosis.

b. Functions of cytoplasm
Answer : It is the medium for all cellular chemical reactions. It is a medium in which the organelles remain suspended. It helps in the movement of the different cellular elements.

c. Functions of lysosomes
Answer : Lysosomes destroy foreign materials that enter the cell. Dead and worn-out organelles are removed by lysosomes. Cells are autolysed by lysosomes, and their contents are released within the cell.

d. Functions of vacuoles
Answer : The main function of vacuoles is to store food in a cell. They also help in storing and expelling wastes and toxic by products of metabolic reactions. They help in maintaining the turgidity and rigidity of a cell.

e. Functions of nucleus
Answer : It is the control centre of a cell as it controls all the activities of the cell. It also contains gene-containing chromosomes which are the units of inheritance in an organism.

Question 5: Who gives me the colour? (Select the correct option)
 a. Red tomato     1.Chlorophyll
b. Green leaf.       2. Carotene
c. Carrot                3. Anthocyanin
d. Violet                4. Lycopene
Answer :
 a. Red tomato 4. Lycopene
b. Green leaf 1.Chlorophyll
c. Carrot 2. Carotene
d. Violet 3. Anthocyanin

# Can you Tell 
1. How many types of cells are found in living organisms ? 
Answer : Your body has many different kinds of cells. Though they might look different under a microscope, most cells have chemical and structural features in common. In humans, there are about 200 different types of cells, and within these cells there are about 20 different types of structures or organelles.

2. Which instrument had you used to observe cells ? 
Answer : Microscope is used.

3. What  happens to  the  agricultural  waste after  a few days when it is dumped in a compost pit ?
Answer : When agricultural waste put in compost pit, after a few days it becomes organic matter which is called compost. Compost is decomposed organic material. Composting is a natural process in which Bacteria, fungi and other microorganisms help the organic matters to break down into simpler substances.

4. Which  type  of  energy  is  required  to  run    the  fans, computers and electric bulbs ? Where is this energy produced ? 
Answer : Electric energy is required to run fan, bulb and computers. Electric energy is produced in power plants.

5. What  is  the  benefit  of  foldings  of  inner  membrane  in mitochondria ? 
Answer : The folding of the inner membrane increases the surface area inside the organelle. The advantages of folding the inner membrane of mitochondria are as belows : The folding of inner membrane increases the surface area inside the organelle . Matrix is the fluid which is in mitochondria.

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