Questions - Answers
Very Short Answer type Questions:
1. Mention a single membrane bound organelle which is rich in hydrolytic enzymes.
A: Lysosomes.
2. What is the function of polysome?
A: Polysome or polyribosome help in translation of mRNA into proteins.
3. What is referred to as satellite chromosome?
A: The chromosome with a non staining secondary constriction is called a satellite chromosome. This chromosome shows a small rounded structure at the end due to secondary constriction which is called a satellite.
4. What is middle lamella made of ?
A: Middle lamella is made up of calcium pectate.
5. What is osmosis?
A: Movement of water by diffusion across selectively permeable membrane is called “Osmosis”.
6. Which of the following is not correct?
a) Robert Brown discovered the cell.
b) Schleiden and Schwann formulated the cell theory.
c) Virchow explained that cells are formed from pre-existing cells.
d) A unicellular organism carries out its life activities within a single cell.
A: a. (Robert Brown discovered the cell is not correct.)
(It is Robert Hooke who discovered the cell and Robert Brown discovered nucleus)
7. New cells generate from
a) Bacterial fermentation
b) Regeneration of old cells
c) Pre-existing cells
d) Abiotic materials
A: c. (Pre existing cells.)
8. Match the following
a. Cristae i. Flat membranous sacs in stroma
b. Cisternae ii. Infoldings in mitochondria
c. Thylakoids iii. Disc-shaped sacs in Golgi apparatus
A: Cristae - infolding in mitochondria
Cisternae - disc shaped sacs in Golgi apparatus
Thylakoids - Flat membranous sacs in stroma
9. Which of the following is correct:
a) Cells of all living organisms have nucleus.
b) Both animal and plant cells have a well defined cell wall.
c) In prokaryotes, there are no membrane bound organelles.
d) Cells are formed de novo from abiotic materials.
A: c. (In prokaryotes, there are no membrane bound organelles.)
Short Answer type Questions:
1. Discuss briefly the role of nucleolus in the cells actively involved in protein synthesis.
A: * The nucleolus is a spherical structure present in the nucleoplasm.
* It is the site for active ribosomal RNA (rRNA) synthesis.
* rRNA is a main component of ribosomes which are the seat of protein synthesis.
* Hence larger and more number of nucleoli are present in cells actively carrying out protein synthesis.
2. Briefly describe the cell theory.
A: * M. Schleiden, a botanist and T.Schwann, a zoologist together proposed the cell theory.
* According to this theory all plants and animals are composed of different kinds of cells which form tissues.
* Schwann also proposed that the bodies of all plants and animals are composed of cells and
products of cells.
* The animal cells are bounded by a plasma membrane, where as the plant cells have a cell wall surrounding the plasma membrane.
* These observations gave way to formulate the cell theory as:
* All living organisms are composed of cells and products of cells.
* Thus cell is the structural and functional unit of life.
* Later the cell theory was modified by Virchow as:
* All living organisms are composed of cells and products of cells.
* Thus cell is the structural and functional unit of life.
* “All cells arise from pre-existing cells”.
3. Differentiate between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).
A:
4. What are plasmids? Describe their role in bacteria.
A: * Plasmids are the small circular DNAs found in bacterial cells in addition to genomic DNA.
* The plasmids confer certain phenotypic characters to bacteria.
* For example resistance to antibiotics is a character conferred by plasmids to bacteria.
* Plasmids are also used for reproduction during bacterial transformation.
* They are the main tools which are used as vectors during genetic engineering experiments.
5. Distinguish between active transport and passive transport.
A:
6. What are the characteristics of a prokaryotic cell ?
A: * Cells that lack a membrane bound nucleus are called prokaryotic cells.
* Prokaryotic cells are found in bacteria, blue-green algae and mycoplasmas.
* They are usually smaller in size and multiply more rapidly than eukaryotic cells.
* The prokaryotic cell shows a cell wall surrounding a cell membrane.
* Cell membrane shows Infoldings called mesosomes.
* The cytoplasm contains genetic material in the form of a naked genomic DNA.
* In addition to genomic DNA circular DNA called plasmids are found in the cytoplasm.
* All cell organelles except ribosomes are absent in a prokaryotic cell.
* 70s ribosomes are present.
7. Cell is the basic unit of life. Discuss in brief.
A: * All organisms are composed of cells.
* Some are made up of a single cell (unicellular) while others are composed of many cells (multicellular).
* In unicellular organisms the whole organism is a single cell and all essential functions are carried out by the single cell.
* In multicellular organisms also the whole structure is made up of different types of cells that perform different functions characteristic to that organism.
* Hence cell makes up the structure of an organism and performs all functions.
* Thus “Cell is the basic structural and functional unit of life in all living organisms”.
8. Is extra genomic DNA present in prokaryotes and eukaryotes? If yes, indicate their location in both types of organisms.
A: * Yes, extra genomic DNA is present in both prokaryotes and eukaryotes.
* In prokaryotes it is present as circular DNA in the cytoplasm which confers certain phenotypic characters like antibiotic resistance to the bacterial cell.
* In eukaryotes it is present in cell organelles like mitochondria and chloroplasts and help in protein synthesis in these organelles.
9. Structure and function are co-relatable in living organisms. Can you justify this by taking plasma membrane as an example?
A: * The cell membrane or plasma membrane is composed of lipids and proteins hence called lipoproteinaceous membrane.
* The lipids are present in such a way that the hydrophilic polar head is present towards outside and hydrophobic non polar tail towards inside. Hence the non polar tail is protected from water.
* This justifies that structure and function are co-relatable.
* According to another theory “fluid mosaic model” the semi fluid nature of lipid enables lateral movement of proteins within the layer.
* Thus movement of ions and molecules across the membrane through protein carriers is possible.
* The fluid nature of cell membrane is also responsible for functions like cell growth, formation of intercellular junctions, secretion, endocytosis, cell division etc.
Long Answer type Questions: (8marks)
1. Write the functions of the following
a. Centromere
b. Cell wall
c. Smooth ER
d. Golgi Apparatus
e. Centrioles
Ans: a. Centromere:
¤ Centromere is the primary constriction of chromosome which has disc shaped structures called kinetochores.
¤ During cell division the spindle fibers get attached to the kinetochore of the centromere during metaphase of mitosis.
¤ It is due to splitting of centromere the chromatids move to opposite poles during meiosis.
b. Cell wall:
¤ Cell wall gives shape to the cell.
¤ It protects the cell from mechanical damage and infection.
¤ It also helps in cell to cell interaction and acts as a barrier to undesirable molecules.
c. Smooth Endoplasmic Reticulum (SER):
¤ It is the major site for lipid synthesis.
¤ In animal cells steroidal hormones are synthesized in SER.
d. Golgi apparatus:
¤ It helps in packaging materials to be transported inside the cell or to outside.
¤ The proteins synthesized by ribosomes are modified by the cisternae of Golgi apparatus.
¤ It is the important site for formation of glycoproteins and glycolipids.
¤ In plants the GC involves in the synthesis of cell wall materials and also plays a role in the
formation of cell plate during cell division.
e. Centrioles:
¤ Centrioles form the basal body of cilia or flagella.
¤ They also form spindle fibres that give rise to spindle apparatus during cell division in animal cells.
