UrbanPro
true

Learn Class 8 with Free Lessons & Tips

Ask a Question

Post a Lesson

All

All

Lessons

Discussion

Lesson Posted on 29 Mar Learn Cell – Structure and Functions

Cell - Structure and Functions

Maan Gulati

I would like to utilize my lively and energetic attitude in teaching students with great enthusiasm....

Chapter – 8 Cell — Structure and Functions Cell: The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and... read more

                                                                     Chapter – 8
                                                   Cell — Structure and Functions

  • Cell: The smallest structural and functional unit of an organism, which is typically microscopic and consists of cytoplasm and a nucleus enclosed in a membrane.
  • All organisms are made of smaller parts called organs.
  • Organs are made of still smaller parts. The smallest living part of an organism is a ‘cell’.
  • Cells were first observed in cork by Robert Hooke in 1665.
  • Cells exhibit variety of shapes and sizes.
  • Number of cells also varies from organism to organism.
  • Some cells are big enough to be seen with the unaided eye. Hen’s egg is an example.
  • Some organisms are single-celled, while others contain large number of cells.
  • The single cell of unicellular organisms performs all the basic functions performed by a variety of cells in multi cellular organisms.
  • The cell has three main parts, (i) the cell membrane, (ii) cytoplasm which contains smaller components called organelles, and (iii) the nucleus.
     
  • Cell membrane: The basic component of a cell. The cytoplasm and nucleus are enclosed within cell membrane. There is an outer thick layer in cells of plants called cell wall.
  • Cytoplasm: The jelly-like substance present between the cell membrane and the nucleus. Various organelles present in the cytoplasm are:
    (i) Mitochondria
    (ii) Plastids (present only in plant cell)
    (iii) Endoplasmic reticulum (ER)
    (iv) Ribosome
    (v) Lysosomes
    (vi) Vacuole
    (vii) Golgi body
    (viii) Centrosome (present only in animal cell).
     
  • Nucleus: Nucleus is separated from cytoplasm by a nuclear membrane. It is generally spherical in the centre of the cell.
  • Nuclear membrane: Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane.
  • Nucleolus: Nucleus contains a still smaller round body known as nucleolus.
  • Chromosomes: Nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of character from the parents to the off springs
  • Cells without well organised nucleus, i.e. lacking nuclear membrane, are called prokaryotic cells.
  • Plant cells differ from animal cells in having an additional layer around the cell membrane termed cell wall.
  • Coloured bodies called plastids are found in the plant cells only. Green plastids containing chlorophyll are called chloroplasts.
  • Plant cell has a big central vacuole unlike a number of small vacuoles in animal cells.
  • Size of cells: The size may be as small as a millionths of a metre or may be as large as a few centimetres. Size of the cells has no relation with the size of the body of the animal or plant. It is related to its function.

 

read less
Comments
Dislike Bookmark

Asked on 10 Jan Learn Exponents and Powers

4. Evaluate [(1/2)-1 - (1/3)-1]-1.

Answer

Asked on 10 Jan Learn Comparing quantities

5. A fan is marked ar Rs 15600 and it is available for Rs 12480. Find the discount given and discount percent

Answer

Asked on 10 Jan Learn Algebraic Expressions And Identities

6. Using identities evaluate: (99)2.

Answer

Asked on 10 Jan Learn Data handling

6. Which of the following need a histogram to show the data? (i) The number of letters for different... read more
6. Which of the following need a histogram to show the data? (i) The number of letters for different areas in a postman’s bag. (ii) The height of competitors in an athletics meet. read less

Answer

Asked on 10 Jan Learn Introduction To Graphs

6.State whether True or False. Correct that is false. (i) A point whose x coordinate is zero and y-coordinate... read more
6.State whether True or False. Correct that is false. (i) A point whose x coordinate is zero and y-coordinate is non-zero will lie on the y-axis. (ii) A point whose y coordinate is zero and x-coordinate is 5 will lie on y-axis. (iii) The coordinates of the origin are (0, 0) read less

Answer

Asked on 10 Jan Learn Practical Geometry

7. Construct a quadrilateral PQRS where PQ = 4 cm, QR = 5 cm, ∠P = 50°,∠Q = 110° and ∠R= 70°.

Answer

Asked on 10 Jan Learn Visualizing Solid Shapes

7. The number of face of a pyramid is 5. Find the number of its vertices when its edges are eight.

Answer

Asked on 10 Jan Learn Playing with Numbers

8: Make a 5 digit number using each of the digits 4,5,6,7,8. Also, see that the number made shall be divisible by 132.

Answer

Asked on 10 Jan Learn Factorization

9. Divide 10(x3y2x2 + x2y3z2 + x2y2z3) by 5x2y2z2.

Answer

About UrbanPro

UrbanPro.com helps you to connect with the best in India. Post Your Requirement today and get connected.

Overview

Questions 473

Lessons 150

Total Shares  

+ Follow 166 Followers

You can also Learn

Top Contributors

Connect with Expert Tutors & Institutes for Class 8

x

Ask a Question

Please enter your Question

Please select a Tag

X

Find Tutors, Trainers & Institutes near you

Post requirement and connect with the tutors in your locality

  • Select the best Tutor
  • Book & Attend a Free Demo
  • Pay and start Learning

Want to learn something New?

Find best tutors, trainers & institutes near you on UrbanPro

Post your learning requirement

UrbanPro.com is India's largest network of most trusted tutors and institutes. Over 55 lakh students rely on UrbanPro.com, to fulfill their learning requirements across 1,000+ categories. Using UrbanPro.com, parents, and students can compare multiple Tutors and Institutes and choose the one that best suits their requirements. More than 7.5 lakh verified Tutors and Institutes are helping millions of students every day and growing their tutoring business on UrbanPro.com. Whether you are looking for a tutor to learn mathematics, a German language trainer to brush up your German language skills or an institute to upgrade your IT skills, we have got the best selection of Tutors and Training Institutes for you. Read more