Dr PS Verma Dr. VK Aggarwal Solution Class 9 Biology 2nd Chapter – “The Fundamental Unit of Life: Cell” in here.
Short answer Type Questions (Carrying 2 marks each): Page No. 118
(1) The difference between prokaryotic and eukaryotic cell are given below:-
(i) Prokaryotic cell is generally small (1 to 10 mm) whereas eukaryotic cell is generally large (5 – 100 mm).
(ii) In Prokaryotic cell nucleus is absent whereas In eukaryotic cell nucleas is present.
(iii) Prokaryotic cell contains single chromosome whereas eukaryotic cell contains more than one chromosome.
(2) The difference between organ and organelle are following:
(i) Organs are found in multicellular organisms whereas Organelles are found in all eukaryotic cells.
(ii) Organs are large sized or macroscopic whereas Organelles are very small sized, either microscopic or submicroscopic.
(iii) Organs may be external or internal to the body of an organisms whereas Organelles are mostly internal.
(3) The difference between nucleus and nucleoid are following:
(i) Nucleus is larger in size whereas Nucleoid is comparatively smaller in size.
(ii) Nucleus has a covering of double membrane envelope whereas in Nucleoid, coverig membrane is absent, it lies free in the cytoplasm.
(iii) Nucleolus is present in Nucleus whereas Nucleolus is absent in Nucleoid.
(4) The difference between light and electron microscopic are following:-
(i) Light microscopic uses glass lenses whereas Electron microscope uses electromagnets.
(ii) Light microscope uses a beam of light to illuminate the object whereas Electron microscope uses a beam of electrons instead of light.
(iii) Internal vacuum is not required in Light microscope whereas Internal vacuum is essential in ELECTRON microscope.
(5) While studying a thin slice of cork, Robert Hooke saw that the work resembled the structure of ho0neycomb which are consisting of many little compartments. Cork is a substance which obtained from bark of one of tree. This was in the year 1665 when Hooke made this chance discovery through a self designed microscope. Robert Hooke called this boxes cells.
(6) There are two types of protein molecules: Intrinsic proteins, and extrinsic proteins.
Intrinsic proteins completely covers the lipid bilayer. And second one occur either on the outer surface or on the inner surface of the lipid membrane.
(7) Plasma membrane performs certain physical activities such as diffusion and osmosis for the intake of some substances. Also certain biological or physiological activities such as active transport and endocytosis are performed by the plasma membrane.
(8) An example of diffusion across plasma membrane: In amoeba, oxygen enters the cell by the process of diffusion when the level or concentration of Oxygen inside the cell decreases.
(9) Two some raisins in a bowl full of water.. After some hours you will observe that the raising are swelled up..Now,Put those swelled up raisins in a bowl full of water.. And some salt in it..Here, you will observe the raisins will shrink.
(10) The difference between Diffusion and Osmosis are following:
(i) Diffusion can occur in any medium whereas Osmosis occurs only in liquid medium.
(ii) The diffusing molecules may be solids, liquids or gases whereas Osmosis involves movement of solvent molecules only7.
(iii) Semi permeable membrane is not required in Diffusion whereas, Semipermeable membrane is required.
(11) Endocytosis is the ingestion of material by the cells through the plasma membrane. It is a collective term that describes three similar processes : phagocytosis, photocytosis and receptor mediated endocytosis. These processes are pathways to specifically internalize solid particles, small particles and ion, and macromolecules, respectively. All of them require energy that’s why may be regarded as different forms of active transport.
(12) When eukaryotic cells are placed in hypotonic solution, more water will enter the cell than leave. The overall result is that water enters the cell. In such a situation cell is likely to swell up.
When eukaryotic cells are placed in hypertonic solution, in this case too water crosses the plasma membrane i both directions, but this time more water leaves the cell than enters it. Therefore, the cell will shrink.
When the eukaryotic cell is placed in isotonic solution, in this case water crosses the plasma membrane in both directions, but the amount going in is the same as the amount going out, so there is no overall movement of water. In such a situation cell will maintain the same size.
(13) (a) Smallest cell organelle is – Ribosome.
(ii) Largest cell organelle- Plastid in plants and Mitochondria in animals.
(iii) ER studded with ribosomes – Rough endoplasmic reticulum.
(iv) Functional segments of the DNA molecule- Genes.
(14) (i) The difference between Chromoplast and Chloroplast are following:-
(1) Chromoplast are non green coloured plastids whereas Chloroplast are green plastids.
(2) In Chromoplasts Chlorophylls are absent. Only carotenoids are present whereas In Chloplasts, they contain chlorophyll and carotenoids.
(ii) The difference between Ribosomes and Centrosome are following:
Ribosomes are dense, spherical and grannular particles which occur freely in the matrix or remain attatched to the endoplasmic reticulum. Whereas, Centrosome is not bounded by any membrane but consists of two granule like centriols.
Ribosomes play an important part in the synthesis of proteins whereas Centrosomes helps in cell division in animal cells.
(15) The main difference between plant cell and animal cell are following:-
(i) Plant cell are larger than anim,al cell whereas animal cell are generally small in size.
(ii) The plasma membrane of plant cells is surrounded by a rigid cell wall of cellulose. Whereas Cell wall is absent.
(iii) In Plant cell, Plastids are present whereas In animal cell, except the protozoan Euglena. No animal cell possesses plastids.
(16) If nucleus is removed from a cell, the protoplasm will ultimately dry up and the cell will die
This is due to the nucleus controls all the metabolic activities of a cell.
(17) Spinach looks green due to the presence of chloroplasts,
Papaya is yellow and edible part of watermelon is red due to the presence chromoplasts.
Page No. 119
(18) (a) Two main function of Endoplasmic reticulum:-
(i) Smooth ER of liver of vertebrates helps in detoxification. It metabolises various toxic or poisonous substance such as drugs, aspirin, insecticides, petroleum products and pollutants. These toxic substances make their entry in animal’s body through food, air or water.
(ii) Smooth ER plays an important role in the biosynthesis of glycolipids, phospholipids and cholesterol. These lipids are used in the formation of plasma or cell membrane and various steroid hormones.
(ii) The two main function of Lysosome:-
(i) Lysosomes serve as intracellular digestive system, hence called digestive bags.
(ii) Lysosomes also remove the worn out and poorly working cellular organells by digesting them to make way for their new replacement.
(19) (a) The cell organelle which synthesizes protein. called Ribosome.
(b) The type of plastid which stores food called Leucoplasts.
(20) Lysosomes are also known as suicide bags due to during breakdown of cell structure, when the cell gets damaged, lysosomes may burst and the enzymes eat up their own cells.
(21) (a) Cell inclusions are non living material present in cytoplasm. Cell inclusions are another name of cell organelled. Cell inclusions are combined name for cell wall and plasma membrane.
(b) Cytosol:- It is the soluble part of cytoplasm. It forms the ground surface or background material of the cytoplasm and is located between the cell organelles.
(c) Protoplasm:- The contents of a living cell, contained within the plasma membrane, from protoplasm. Protoplasm is usually differentiated into the nucleus and cytoplasm.
(d) Nucleoplasm:- Nucleoplasm is the liquid ground substance present in the nucleus.
(22) In the nucleolus Ribosomes get synthesized.
(23) (a) Mitochondria:- The mitochondria are tiny bodies of var5ying shapes and size, distributed in the cytoplasm. Each Mitochondrion is bounded by a double membrane envelope. Outer membrane is porous. The inner membrane is thrown into folds and therefore have an area several times the surface of area of the outer membrane.
(b) Plastids:- Plastids occur in most plant and are absent in animal cell. Like the mitochondria, the plastids also have their own genome and ribosome. They are self replicanting organelles like the mitochondria.
(24) The names of cell organells are followed:
(25) The main functional regions of the cell are:-
(i) Plasma membrane,
(26) (a) Chromatin- Nucleus
(b) Chromosome- Nucleus
(c) Tonoplast- Vacuoles
(d) Nucleolus- Nucleus
(27) Gene:- It is a distinct unit of hereditary information. Gene is inherited from one generation to next and determines an observable characteristic or trait of an organism. Gene have to carry coded information of parents to their children or progeny, so that children exactly remains their parents.
These are located on chromosomes.
(28) This is because, Lysosomes serve as intracellular digestive system.
(29) Mitochondria is called the power plant of eukaryotic cell.
Mitochondria are sites of cellular respiration. They use molecular oxygen from air to oxidise the carbohydrates and fats.
(30) Centrioles are hollow and cylindrical structures which are made up of microtubules.
The function of Centrioles:
(i) It migrates to the poles of animal cells and is involved in the formation of the spindle.
(ii) In plant cells, cell division involves polar caps for the spindle formation.
(31) Lipids gets synthesised in the smooth endoplasmic reticulum
Proteins gets synthesised in the ribosomes and rough endoplasmic reticulum.
(33) Plasmolysed means water crosses the plasma membrane in both directions, but this time more water leaves the cell than enters it. Therefore the cell will shrink.
Long Answer Type Questions Answers (Carrying 5 marks each) Page No. 119
(1) Diagram Figure 2.14 Page No. 78
Description: The proteins are present not to give strength to the membrane but to serve as (i) enzymes (ii) transport proteins (iii) pumps(iv) receptor proteins. Presence of lipids and proteins provides flexibility to the plasma membrane. This property of flexibility of the plasma membrane helps in endocytosis.
(2) Figure 2.12
Functions of the main cell organells are followed:-
Endoplasmic Reticulum – It forms the supporting skeletal framework of the cell.
Ribosomes – It synthesises proteins.
Golgi Apparatus – It produces vacuoles which contain cellular secretion.
Plastids – These are present only in plants and trap solar energy to manufacture food for plants.
Vacuoles – They help to maintain the osmotic pressure in a cell.
Peroxisomes – They carry out some oxidative reactions.
Centrosome – It helps in cell division in the animal cell.
Lysosomes – It serves as intracellular digestive system as it digest the foreign materials which enter the cell.
Mitochondria – These are the sites of cellular respirations.
(3) The nucleus is a large centrally located spherical cellular component. It is bounded by 2 nuclear membranes both are forming a nuclear envelope.
Nuclear envelope encloses a space between 2 nuclear membranes and is connected to a system of membranes namely Endoplasmic Reticulum (shortly ER).
The nuclear envelope separates the nucleus from the cytoplasm. The nuclear envelope contains many pores and encloses the liquid ground substance, The nucleoplasm. Nucleopores allows transfer of materials between the nucleoplasm and the cytoplasm.
(4) (i) Golgi Apparatus: Golgi Apparatus consists of a set of membrane bounded, fluid filled vesicles, vacuoles and flattened cisternae. Cisternae are usually stacked together in parallel rows.
Golgi apparatus exists as an extensive network near the nucleus in the animal cells. However, the plant cells contain many freely distributed subunits of Golgi apparatus, called dictyosomes.
The main function of Golgi apparatus is secretory. It produces vacuoles or secretary visicles which contain cellular secretions ex. Emzymes, proteins, cellulose, melanin pigment etc.
(ii) Mitochondria: The mitochondria are tiny bodies of var5ying shapes and size, distributed in the cytoplasm. Each Mitochondrion is bounded by a double membrane envelope. Outer membrane is porous. The inner membrane is thrown into folds and therefore have an area several times the surface of area of the outer membrane.
Mitochondria are sites of cellular respiration. They use molecular oxygen from air to oxidise the carbohydrates and fats.
Mitochondria are able to make some of their own proteins, so they are regarded as semiautonomous organelles.