4.1A: Cells as the Basic Unit of Life - Biology

4.1A: Cells as the Basic Unit of Life - Biology

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A cell is the smallest unit of a living thing and is the basic building block of all organisms.

Learning Objectives

  • State the general characteristics of a cell

Key Points

  • A living thing can be composed of either one cell or many cells.
  • There are two broad categories of cells: prokaryotic and eukaryotic cells.
  • Cells can be highly specialized with specific functions and characteristics.

Key Terms

  • prokaryotic: Small cells in the domains Bacteria and Archaea that do not contain a membrane-bound nucleus or other membrane-bound organelles.
  • eukaryotic: Having complex cells in which the genetic material is contained within membrane-bound nuclei.
  • cell: The basic unit of a living organism, consisting of a quantity of protoplasm surrounded by a cell membrane, which is able to synthesize proteins and replicate itself.

Close your eyes and picture a brick wall. What is the basic building block of that wall? A single brick, of course. Like a brick wall, your body is composed of basic building blocks, and the building blocks of your body are cells.

Cells as Building Blocks

A cell is the smallest unit of a living thing. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Thus, cells are the basic building blocks of all organisms. Several cells of one kind that interconnect with each other and perform a shared function form tissues; several tissues combine to form an organ (your stomach, heart, or brain); and several organs make up an organ system (such as the digestive system, circulatory system, or nervous system). Several systems that function together form an organism (like a human being). There are many types of cells all grouped into one of two broad categories: prokaryotic and eukaryotic. For example, both animal and plant cells are classified as eukaryotic cells, whereas bacterial cells are classified as prokaryotic.

Types of Specialized Cells

Your body has many kinds of cells, each specialized for a specific purpose. Just as a home is made from a variety of building materials, the human body is constructed from many cell types. For example, epithelial cells protect the surface of the body and cover the organs and body cavities within. Bone cells help to support and protect the body. Cells of the immune system fight invading bacteria. Additionally, blood and blood cells carry nutrients and oxygen throughout the body while removing carbon dioxide. Each of these cell types plays a vital role during the growth, development, and day-to-day maintenance of the body. In spite of their enormous variety, however, cells from all organisms—even ones as diverse as bacteria, onion, and human—share certain fundamental characteristics.


Remember the first subject we reviwed together. I told you
Living things are made of cells and that t hese cells were the basic building blocks of life .

But how small really are they? how much a micrsocpe is enhancing their size? Remember I told you to think of a sandcastle. If you see it from the distance it will look like a smooth building. But as you get closer you begin to see is made of millions of tiny sand grains.

Let´s see how small cells really are:

Light microscopes magnify 1500 times an object. Nowadays we have electron micorscopes which may magnify 500,000 times the actuak size if an object.

Nucleus : The nucleus controls the cell activity.

Now watch this video on cell structure to understand the different functions of each oragnelle.

cell structure

Comparition bwteween Animal and Plant Cells

  • Once you had learned that the cell is the smallest unit of life
  • let´s focus on multicellular organisms.

  • Organisms are like machines, some have just one part like bacterias and others have many parts, like us: we have got trillions of cells
  • Lager size
  • Long life: life span is not limited to a single cell
  • Specialization: each type of cell has a particular job.

1 comentario:

The Cell – The Basic Unit of Life Questions and Answers

Q4. Cells were observed prior to Robert Hooke by

Q5. Who initiated cell concept

Q6. Cell was discovered by

Q7.Cell was discovered in

  1. 18 th Century
  2. 19 th Century
  3. First half of 17 th Century
  4. Second haif of 17 th Century

Q8. Cell, as basic unit of plants, was discovered by

Q9. Cell theory states that

  1. All cells are living
  2. All cells have nucleus
  3. Cells are fundamental structural units of living organisms
  4. Cells reproduce by mitosis and meiosis

Q10. Robert Brown Is known for his discovery of

Q11. Who applied cell theory to plants

Q12. The living substance of cell was named sarcode by

Q13. The modern cell theory is called

Q14. Which ones do not have cellular structure

Q15. Robert Hooke discovered cell in

Q16. ‘Micrographia’ was written by

Q17. Cell theory was modified by

Q18. Omnis cellula e cellula is generalization given by

Q19.Cells of Robert Hooke were actually

Q20. Cell principle is not applicable to

Q21. Distinction of individual cells is absent in coenocytic organism

Q22.Who believied in the individuality of cells?

Q23. Who saw the living matter for the first time?

Q24. A nucleus is absent in the mature

Q25. A tissue having more nonliving material than the living matter is

Q26. Who proposed protoplasmic theory as opposed to cell theory?

Q27. The theory proposing that body an organism consists of incompletely divided cells is

  1. Organismal theory
  2. Protoplasmic theory
  3. Cell theory
  4. Theory of cell Lineage

Q28. Organismal theory was proposed by

Q29. Cells are autonomous because

  1. They systhesise components of living protoplasm from nonliving materials
  2. They are able to grow and divide
  3. Each cell has its own life span
  4. All the above

Q30. “Each cell leads a double Life” was first proposed by

Q31. Ageing is slow or absent in

Q32. Which are less efficient?

  1. Multicellular animals
  2. Multicellular plants
  3. Colonial organisms
  4. Unicellular organisms

Q33. A multicellular organism possesses

  1. Differentiated cells
  2. Undifferentiared cells
  3. Dedifferentiated cells
  4. All the above.

Q34. Numbrer of type of cells found in human body is

Q35. Cells which lose their nucleus during differentiation are

Q36.A nucleated differentiated cell that has lost the power to dedifferentiate is

Q37.First successful culture was obtained by

Q38. Callus was grown successfully for the first time by

Q39. Morphogenesis in tissue culture was discovered by

Q40. Who proposed for the first time that cells are totipotent

Q41. Steward et al performed experiment to prove cellular totipotency on

Q42.Explant is

  1. Propagule
  2. Callus used for subculturing
  3. Part of plant used in tissue culture
  4. Part of tissue culture used for planting

Q43. What was done by Steward et al in order to separate individual cells of carrot root?

  1. Shaking in liquid medium
  2. Homogenisation
  3. Pressure sieving
  4. Microsurgery

Q44.Single cells in Steward’s culture formed

Q45. Embryoids are

  1. Sonamatic embryo-like structures
  2. Small embryos through fertilization in culture
  3. Early embryo stages used for propagation in tissue culture
  4. All the above

Q46. In animals, cellular totipotency has been restricted only to

  1. Germinal cells
  2. Epithelial cells
  3. Zygote
  4. Zygote and early blastomeres

Q47. Animal cloning is carried out by

  1. Artificial fertilization of ovum
  2. Direct growth of ovum
  3. Ovum with somatic nucleus
  4. All the above

Q48. The first successful animal cloning, Dolly, was accomplished by

Q49. Cells capable of division are

Q50. Differentiated cells are

  1. Premitotic specialized
  2. Post-mitotic specialized
  3. Premeiotic specialized
  4. Post-meiotic specialized

Q51.RBCs are

  1. Differentiated cells
  2. Undifferentiated cells
  3. Dedifferentiated cells
  4. Dead cells

Q52. During differentiation, RBCs lose

Q53. Dedifferentiated cells are formed in the region of

Q54. Functionally important dead cells are

Q55. Rapidly dividing unorganized mass of cellsin tissue culture is

Q56. First successful tissue culture was that of

Q57. Tissue used by Steward et al (1957) to prove cellular totipotency was

Q58. White performed successful tissue culture in

Q59. The smallest animal egg is that of

Q60.Largest animal cell is that of

Q61. Human egg is larger than human sperm because it has

Watch the video: Lecture A (September 2022).


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