Class8.L-6. Cell: structure and function

EXERCISE:

A.Choose the correct option for each of the following.

1)Which of the following is a selectively permeable membrane ?- b)Plasma membrane

2)The function of chloroplasts is to – b)prepare food

3)These are called the powerhouse of the cell-a)Mitochondria

4)Identify the organelle that is found in a plant cell but not in animal cell.

-d)Chloroplast

5)Who first observed cork cells under a crude microscope?-c) Hooke

B.State whether the following statements are True (T) or Flase (F).

1.Nuclear membrane is absent in plant cells .(F)

2)Leucoplast is a type of plastid .(T)

3)Vacuoles are prominent in plant cells .(T)

4)Size of the cells depends upon the size of the organism.(T)

5)All cells have a clear and definite nucleus .(F)

C.Fill in the blanks with the correct words .

1)In animals tissue ,one cell is separated from another by a – Plasma membrane.

2)Cells without a well-developed nuclear membrane are called-Prokaryotes.

3)The structures that help in the transfer of characters from parent to the

offspring are- Genes.

4)The jelly-like substance that is present in between the nuclear membrane and cell membrane is – Cytoplasm.

5)The term ‘cell’ was first coined by –Robert Hooke .

D.For the following analogies, compare a plant cell to that of a factory.

1)The structure acts as a checkpoint for the entry and exit of the materials.-Cell or plasma membrane

2)this structure is the office or the control centre of entire factory .-Nucleus

3)This is the space or the site where all the other components are situated .

- Cytoplasm

4)This structure gives extra support to the plant cell .- Cell wall

E.Answer the following questions briefly.

1)What is the function of lysosomes in animal cell ?

ANS:-Lysosomes contain chemical substances called enzymes that can digest cells , and a variety of intracellular and extracellular materials.

2)Differentiate between a unicellular and multicellular organism with an example each .

ANS:-

Unicellular	Multicellular
1)This type of organism made up of only a single cell. 2)Example: Amoeba, Yeast,Bacteria	1)This type of organism made up of many cells. 2)Example: Plants,Animals

3)Define cell. Explain the variation in size that a cell undergoes .

ANS:-The smallest structural and functional unit of an organism is called cell.

The size of cells may be as small as a micrometer or as large as a few centimeters. Bacteria is the smallest living organism with size 0.1 to 0.5 micrometre. Human nerve cells are said to be longest cells.

4)How are daughter cell form ?

ANS:-Once a cell is formed, it starts ingesting and digesting food, and grows in size. After reaching a certain size, it divides to form two daughter cells. They are the exact copies of parent cell.

5)Define prokaryotic and eukaryotic cells with two example each .

ANS:-Prokaryotic :Cells that do not have a well-defined membrane-bound nucleus are called prokaryotic cells. Examples: Bacteria ,Nostoc .

Eukaryotic cells: Cells that have a well-defined membrane-bound nucleus are called eukaryotic cell. Example: Cheek cells , Onion cells .

F.Answer the following questions in detail.

1.Differentiate between the organelles present in a plant cell and animal cell in the form the given table.

ANS:-

Organelles	Plant cell	Animal cell
Cell wall	Present	Absent
Cell membrane	Present; lies inside the cell wall; enclose the cytoplasm	Present; Enclose the cytoplasm
Nucleus	Present; has nuclear membrane, Nuclelus, Nucleoplasm, Chromosomes.	Present; has nuclear membrane, Nuclelus, Nucleoplasm, Chromosomes.
Vacuole	Several in number ; large in prominent	If present ,small in size and few in numbers
Chloroplast	Present	Absent

2.Draw a neat and well-labelled diagram of generalized cell.Also explain the components in the nucleus of the cell.

ANS:-

Nucleus is considered as Brain of a cell. It is surrounded by a membrane called the nuclear membrane. It has a semi-solid substance called nucleoplasm which contains thread like substances called chromosomes. Chromosomes carry the hereditary material called genes from parent to the offspring. A non-membrane bound spherical structure called nucleolus also present inside the nucleus.

3.Write a brief history on the discovery of cells .

ANS:- In 1665, an English scientist named Robert Hooke observed a thin slice of cork under his basic microscope. He noticed tiny empty spaces enclosed by walls which are looked like compartments and named them cells.

In 1670, a Dutchman named Antonie Van Leeuwenhoek observed and described the cells in a drop of pond water using a microscope.

In 1838, a German botanist, Matthias Jakob Schleiden, declared that 'the cell is the basic building block of all plant material!

Theodor Schwann, a German biologist, declared that animal tissues are made up of 'cells' and finally concluded that 'cell is the basic unit of life.

4.Give the steps involved in the preparation of slide to view cells under a microscope using wet mount method .

ANS:-To view a cell under the microscope, the sample is first placed on a glass slide; this step is called mounting. Mounting are two types : dry mounting and wet mounting. Dry mounting does not require water, whereas wet mounting requires water.Specimens to be viewed under a microscope are often colored using dyes like methylene blue, safranin or crystal violet. This colors are absorbed by the tissues and organelles present in the cell, which brightens and differentiates them, making it easier for us to view the detailed structure.

5.Explain how cells very in shape , size and number .

ANS:-Cells become specialized to perform specific functions and exist in different shapes. For example:

a)Nerve cells are elongated as they need to carry messages .

b)Muscle cells are cylindrical and branched to help in movement by contracting and relaxing.

c)Skin cells are flat in shape to produce a large surface area for covering the body.

d)White blood cells (WBC) can change their shape to help in destroying the germs in the body.

e)Sperm cells need to swim long distances, so they have a wiggly tail .

f)Cells in plants may be hexagonal, rectangular or spherical, depending on their functions.

The size of cells may be as small as a micrometer ( 01 to 0.5 for bacteria) or as large as a few centimetres. Depending on the number of cells there are two types of organism: Unicellular and Multicellular. Unicellular organism are made of only one single cell (Amoeba, Bacteria) on the other hand multicellular organism are made up of many cells(Plant ,Animals).

6. How do cell division and cell growth play a role in the life of a cell?

ANS:-Once a cell is formed, it starts ingesting and digesting food, and grows in size. After reaching a certain size, it divides to form two daughter cells. These new cells are exact copies of the parent cell. New cells are needed not only for the growth of an organism, but also to replace dying, damaged or worn-out cells in the body. When a tissue is damaged, the surrounding cells begin to divide to replace the damaged cells. However, in the brain, the spinal cord and nerves, the damage is permanent because these cells cannot undergo division to replace the damaged cells.