Punjab State Board PSEB 11th Class Biology Important Questions Chapter 8 Cell: The Unit of Life Important Questions and Answers.
PSEB 11th Class Biology Important Questions Chapter 8 Cell: The Unit of Life
Very short answer type questions
Question 1.
Give one difference between the characteristic feature of Gram positive and Gram negative bacteria.
Answer:
Gram positive bacteria retain crystal violet dye and stain blue in colour, while Gram negative bacteria loose dye colour on washing.
Question 2.
What is the name given to the infoldings of plasmalemma in fungal cell below the wall?
Answer:
Mesosomes.
Question 3.
What does ‘S’ refers in a 70S and 80S ribosome? [NCERT Exemplar]
Answer:
The ‘S’ refers to Svedberg units of sedimentation coefficient. The sedimentation coefficient is a measure of the speed of the sedimentation for a particular cell organelle in ultracentrifuge.
Question 4.
What are inclusion bodies?
Answer:
Reserve material in prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies.
Question 5.
In which organelle the proteins required for functioning of nucleus are formed?
Answer:
Proteins required are formed in cytoplasm.
Question 6.
Which is considered to be the main arena of cellular activities in plant and animal cells?
Answer:
Cytoplasm is considered to be the main arena of cellular activities.
Question 7.
Mention a single membrane bound organelle, which is rich in hydrolytic enzymes. [NCERT Exemplar]
Answer:
Lysosome.
Question 8.
What is the significance of vacuole in a plant cell? [NCERT Exemplar]
Answer:
The vacuole in a plant cell helps to maintain osmotic pressure for turgidity and osmosis. It also stores useful as well as waste substances.
Question 9.
Why are the mitochondria and plastids called semi-autonomous particles?
Answer:
These are called so, because they are not dependent upon nuclear DNA and cytoplasmic ribosomes for the synthesis of proteins, while other organelles are dependent.
Question 10.
What is referred to as satellite chromosome? [NCERT Exemplar]
Answer:
Sometimes, few chromosomes have non-staining secondary constrictions at a constant location. This gives appearance of a small fragment called satellite. The chromosome having satellite are known as satellite chromosomes.
Question 11.
What do you meant by 9+2 pattern of organisation?
Answer:
It means that 9 microtubule doublets surround two single microtubules.
Question 12.
Define the microbodies.
Answer:
Membrane bound minute vesicles that contain various enzymes are called microbodies. These are present in both plant and animal cells.
Short answer type questions
Question 1.
Differentiate between prokaryotic and eukaryotic cells.
| Prokaryotic Cell | Eukaryotic Cell |
| •» Nuclear membrane absent | Nuclear membrane present |
| •» Cell organelles absent (except ribosome) | Cell organelles present |
| •» Endomembrane system absent | Endomembrane system present |
| •» Example: bacteria | Example: RBC, neuron |
Question 2.
Describe passive transport, osmosis and active transport in plasma membrane.
Answer:
Passive Transport: The plasma membrane is selectively permeable to some molecules present on either side of it. Many molecules can move briefly across the membrane without any requirement of energy and this is called the passive transport.
Osmosis: Neutral solutes may move across the membrane by the process of simple diffusion along the concentration gradient, i.e., from higher concentration to the lower. Water may also move across this membrane from higher to lower concentration. Movement of water by diffusion is called osmosis.
Active Transport: As the polar molecules cannot pass through the nonpolar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across the membrane. A few ions or molecules are transported across the membrane against their concentration gradient, i.e., from lower to the higher concentration. Such a transport is an energy dependent process, in which ATP is utilised and is called active transport, e.g., Na+/K+ Pump.
Question 3.
What is endomembrane system in a cell?
Answer:
Certain cell organelles function in coordinated manner. Their v coordination makes the endomembrane system of cell. Following structures comprise the endomembrane system:
- Endoplasmic Reticulum
- Golgi Complex
- Lysosome, and
- Vacuoles.
Question 4.
Cells in the epithelial tissue are held together with very little intercellular material (matrix). Specialised junctions provide both structural and functional links between individual cells. Three types of cell junctions have been recognised.
(a) Name the three types of cell junctions and write their functions.
(b) What value is shown by such an arrangement?
Answer:
(a) The three types of cell junctions are:
- Tight junctions,
- Gap junctions and
- Adhering junctions
Functions of cell junctions are ‘
- Tight junctions prevent the leaking of substances across a tissue.
- Gap junctions facilitate the cells to communicate with each other by connecting their cytoplasm.
- Adhering junctions perform cementing of the adjacent cells to keep them together.
(b) No individual can function alone in a society. We need some form of interaction and help from others; so lend a helping hand to the needy.
Question 5.
Give a brief description of ribosomes.
Answer:
Ribosomes are the granular structures first observed under the electron microscope as dense particles by George Palade (1953). They are composed of ribonucleic acid (RNA) and proteins and are not surrounded by any membrane. The eukaryotic ribosomes are 80S while the prokaryotic ribosomes are 70S. Here ‘S’ stands for the sedimentation coefficient; it indirectly is a measure of density and size. Both 70S and 80S ribosomes are composed of two subunits.
Question 6.
Write a short note on-
(i) Cytoskeleton,
(ii) Cilia & Flagella
Answer:
(i) Cytoskeleton: An elaborate network of filamentous proteinaceous structures present in the cytoplasm is collectively referred to as the cytoskeleton. The cytoskeleton in a cell are involved in many functions such as mechanical support, motility, maintenance of the shape of the cell.
(ii) Cilia and Flagella: Cilia (sing.: cilium) and flagella (sing.: flagellum) are hair-like outgrowths of the cell membrane. Cilia are small structures which work like oars, causing the movement of either the cell or the surrounding fluid. Flagella are comparatively longer and responsible for cell movement. The prokaryotic bacteria also possess flagella but these are structurally different from that of the eukaryotic flagella.
Long answer type questions
Question 1.
Write the functions of the following: [NCERT Exemplar]
(i) Centromere
(ii) Cell wall
(iii) Smooth ER
(iv) Golgi apparatus
(v) Centrioles
Answer:
(i) Functions of Centromere
(a) It is a narrow non-stainable area which join chromatids together to form a chromosome.
(b) The centromere thus, keep the two chromatids of a chromosome in an intact stage.
(c) This is an essential step for chromosomes of a cell during cell division whether it may be mitosis or meiosis.
(ii) Functions of Cell Wall
(a) It helps in providing a definite shape to the cell and also protects protoplasm against any mechanical injury, i.e., damage and infection.
(b) It also helps in cell-to-cell interaction.
(c) It provides barrier to undesirable macromolecules and attack of pathogens.
(iii) Functions of Smooth Endoplasmic Reticulum
(a) It provides mechanical support to colloidal complex of cytoplasmic matrix.
(b) It holds various cell organelles in position.
(c) It conducts information from outside to inside of cell.
(iv) Functions of Golgi Apparatus
(a) It performs the function of packaging material.
(b) It acts as an important site for the formation of glycoproteins and glycolipids.
(c) It helps in the production of complex carbohydrates other than glycogen and starch.
(d) It helps in the formation of cell wall.
(v) Functions of Centrioles
(a) Formation of new centrioles from pre-existing one’s during cell division.
(b) They form basal bodies, which in turn form cilia and flagella.
(c) They form spindle fibres that give rise to spindle apparatus during cell division .in animal cells.
Question 2.
Is there a species or region specific type of plastids? How does one distinguish one from the other? [NCERT Exemplar]
Answer:
Plastids are both region or species specific. These are as follows :
(i) Proplastids: These are colourless, rounded but amoeboid plastid precursors, found in meristematic and newly formed cells of plants. It has a double membrane envelope that surrounds a colourless matrix, containing DNA, ribosomes and reserve food. A few vesicles and lamellae also occur in the matrix.
(ii) Leucoplasts: These are colourless plastids that occur in non-green plant cells commonly near the nucleus. They are as follows:
(a) Amyloplasts: These leucoplasts store starch, e.g., tuber of potato, grain of rice and wheat.
(b) Elaioplasts: These store fats, e.g., Rose.
(c) Aleuroplasts: They are protein storing plastids, e.g., Castor endosperm.
(iii) Chromoplasts: These are non-photosynthetic coloured plastids which synthesise and store carotenoid pigments. They appear, orange, red or yellow in colour. These mostly occur in ripe fruits (tomato and chillies) carrot roots, etc.
(iv) Chloroplasts: These are photosynthetic plastids, which are green in colour and found in the leaves of all green plants. They have lamellae organised in the form of grana.