NEET Biology Cell The Unit of Life Important Questions Set 01

These Class 11 NEET Biology important questions on Cell : The Unit of Life give 45 questions with step-by-step answers, arranged as very short, short and long answer types, as asked in school and board examinations. They help NEET aspirants revise the definitions, structures, differences and key terms of the chapter.

Very Short Answer Type Questions

Question 1. Who expanded the cell theory and gave the statement Omnis cellula e cellula?
Answer: Rudolf Virchow.

Question 2. Where do almost all cellular activities occur in a cell?
Answer: Cytoplasm.

Question 3. Which structure provides some extra properties to bacteria like resistance to antibiotics?
Answer: Plasmid.

Question 4. Which is the innermost component of the cell envelope of bacteria?
Answer: Plasma membrane.

Question 5. Which part of a lipid molecule is hydrophilic in nature?
Answer: Polar end.

Question 6. What is the shape of kinetochore?
Answer: Kinetochore is a disc shaped structure on centromere in chromosome.

Question 7. Which type of ER is involved in steroid and lipid synthesis?
Answer: SER.

Question 8. In which medium, the enzymes of lysosomes work?
Answer: Acidic medium.

Question 9. Which stain is used to observe mitochondria?
Answer: Janus Green

Question 10. Briefly describe hub in the structure of centriole.
Answer: The centre of the centriole possess a proteinaceous mass known as hub.

Short Answer Type Questions

Question 11. Explain the type of organisms on the basis of number of cells present in their body.
Answer: (i) Unicellular organisms – the body of these organisms is made of a single cell, e.g., Amoeba bacteria etc.
(ii) Multicellular organism – the body of these organisms is made of a many cells, e.g., plants, animals etc.

Question 12. How the study of cell and its detailed structure was made possible?
Answer: The study of a cell was made possible only with the help of microscope as a cell is too small to be seen by the naked eye. Electron microscope was later on invented to study all the structural details of the cell.

Question 13. Mention the postulates of the theory given by Schleiden and Schwann in 1839.
Answer: The postulates of the theory given by Schleiden and Schwann in 1839 are :
(i) All living organisms are composed of cells and products of cells.
(ii) All cells arise from pre-existing cells.

Question 14. Define the two types of cells on the basis of organisation of their nucleus.
Answer: On the basis of the organisation of the nucleus, the cells are of two types – Prokaryotic and eukaryotic. Cell which has a membrane-bound nucleus within it is called eukaryotic and the cell which lacks a membrane-bound nucleus is called prokaryotic.

Question 15. Are organelles without membrane present? Comment.
Answer: Yes, organelles without membrane are present such as ribosomes and centrioles. Ribosomes are found in both prokaryotic and eukaryotic cells. These are also found in two cell organelles – mitochondria and chloroplasts. Centrioles are found in animal cells.

Question 16. Cells show great variation in their shape and size. Explain.
Answer: Different cells vary considerably in their shape in different organisms and in different tissues of the same organisms. They may be either polygonal (liver cells), spherical (egg of many animals), round and oval (mesophyll cells), elliptical (fat cell). The cells may be very small (microscopic) or very large (macroscopic) in size, for example - Mycoplasma is the smallest cell of 0.3 μm in length. Bacterial cell size ranges from 3 to 5 μm.

Question 17. Write a short note on nuclear material of prokaryotes.
Answer: Due to the absence of nuclear membrane, nuclear material lies naked in the cytoplasm and the region where it is located is called nucleoid. The nuclear material is composed of the genomic DNA, which is circular in nature and equivalent to a single chromosome.

Question 18. Explain the ribosomes found in prokaryotic cells.
Answer: The non-membrane bound organelles found in prokaryotic cell are known as ribosomes. These are 70 S type and lie free in the cytoplasm or attached to the cell membrane. They are responsible for protein synthesis.

Question 19. What are inclusion bodies?
Answer: Reserve material in the prokaryotic cells are stored in the cytoplasm in the form of inclusion bodies. These bodies are not bounded by any membrane system and lie free in the cytoplasm. For example phosphate granules, cyanophyceae granules and glycogen granules.

Question 20. Explain the cell wall of bacteria.
Answer: It is rigid but elastic covering of the bacterial cell that lies between glycocalyx and plasma membrane. Cell wall provides shape and protection to the bacterial cell. It also provides a strong structural support to prevent the bacterium from bursting or collapsing when placed in a hypotonic or hypertonic solution.

Question 21. When will you suppose that the cell is dead?
Answer: Protoplasm is called physical basis of life which provides the main arena for all metabolism of life and if protoplasm is dead then cell will be supposed dead.

Question 22. Explain the different components of bacterial flagellum.
Answer: Bacterial flagellum is made of three parts – filament, hook and basal body. Basal body of the flagellum is a rod like structure. The hook is bent and thicker part of the flagellum just outside the cell wall. The filament is the longest portion that extends from cell surface to the outside.

Question 23. Explain the types of proteins found in cell membrane. Who gave fluid mosaic model of plasma membrane?
Answer: The types of proteins found in cell membrane are integral and peripheral. The integral proteins pass into the lipid bilayer to different depths. They may be partially or totally buried in the membrane. The peripheral proteins lie on the surface of the membrane. Singer and Nicolson gave the fluid mosaic model.

Question 24. Write a short note on facilitated diffusion.
Answer: Facilitated diffusion : It occurs through the agency of special membrane proteins i.e., carrier proteins. Energy is not required. The transport is along concentration gradient but carrier protein functions as facilitated pathways for the movement of substances.

Question 25. Explain the secondary cell wall.
Answer: In mature plant cell, more layers of wall material are added internal to the primary wall. These layers are called the secondary cell wall. Addition of secondary wall brings about thickening of the cell wall. Thickening of cell wall occurs particularly in cells that form the harder woody parts of plants.

Question 26. Give the differences between SER and RER.

Answer:

Differences between SER and RER

Question 27. Write a short note on lysosomes.
Answer: Lysosomes are simple tiny spherical sac-like structures evenly distributed in the cytoplasm. These are formed by budding off vesicles from Golgi apparatus. They are bound by a single membrane. They are rich in hydrolytic enzymes such as hydrolases – lipases, proteases, carbohydrases. These enzymes are capable of digesting carbohydrates, proteins, lipids and nucleic acids. These enzymes are active in acidic conditions and synthesised by RER.

Question 28. (a) What is the difference between two membranes of mitochondria?
(b) What does mitochondrial matrix contain?
Answer: The outer membrane is smooth and forms the continuous limiting boundary of the mitochondria whereas the inner membrane forms a number of infoldings called the cristae. The matrix contains single circular DNA molecule, a few RNA molecules, 70S ribosomes and the components required for the synthesis of proteins.

Question 29. Draw a well-labelled diagram of chloroplast.
Answer: A well-labelled diagram should show these parts: Outer membrane; Inner membrane; Granum; Thylakoid; Stroma lamella; Stroma.

Question 30. Explain the structure found in nucleus which is responsible for rRNA synthesis.

Answer:

Nucleolus : It is a spherical structure found in the nucleoplasm.

(i) It is not separated from rest of the nucleoplasm as it is not bound by a membrane.

(ii) It is the site for ribosomal RNA (rRNA) synthesis. Thus, nucleoli are larger and more numerous in cells that are actively involved in protein synthesis.

Long Answer Type Questions

Question 31. Write a contribution of the following scientists in the field of cytology.
(a) Anton Von Leeuwenhoek
(b) Robert Brown
(c) Camillo Golgi
(d) Rudolf Virchow
(e) Flemming

Answer:

(a) Anton Von Leeuwenhoek : He was the first person to observe and describe the living cell.

(b) Robert Brown : He discovered the nucleus of a cell.

(c) Camillo Golgi : He was the first to observe Golgi complex.

(d) Rudolf Virchow : He expanded the cell theory and gave the statement omnis cellula e cellula which means all cells arise from pre-existing cells.

(e) Flemming : He discovered the chromatin present inside the nucleus of a cell.

Question 32. What are the three basic structures of a cell? Explain.

Answer:

Plasma membrane, nucleus and cytoplasm

Plasma membrane forms the limiting boundary of the cell and separates its content from the external environment.

Nucleus, a dense membrane-bound structure present inside the cell. It contains the chromosomes that store the genetic information in the form of DNA.

Cytoplasm is the semifluid matrix occupying the maximum volume of the cell. It is the main site for all cellular activities which take place cells. Cellular activities include various chemical reactions that occur in the cytoplasm and provide a living state to the cell.

Question 33. Explain the cell wall, plasma membrane and cytoplasm of a prokaryotic cell.
Answer: (1) Cell wall and plasma membrane : Almost all prokaryotic cells are encapsulated by a cell wall surrounding a plasma membrane. A cell wall is rigid in nature which provides additional strength and structural support to the prokaryotic cell. Plasma membrane of prokaryotic cell is semi-permeable that communicates with the external environment for exchange of materials. It is similar in structure to the plasma membrane of eukaryotic cells.
(2) Cytoplasm : The fluid present in the cell is called the cytoplasm. It contains various structures present in the cell.

Question 34. Draw a well-labelled diagram of a plant cell.
Answer: A well-labelled diagram should show these parts: Rough endoplasmic reticulum; Smooth endoplasmic reticulum; Plasmodesmata; Nucleus; Nucleolus; Golgi; Microtubule apparatus; Nuclear envelope; Plasma membrane; Vacuole; Middle lamella; Cell wall; Peroxisome; Mitochondrion; Cytoplasm; Chloroplast; Ribosomes.

Question 35. Give differences between cis and trans face of Golgi Body.

Answer:

Question 36. Define the following
(a) Polyribosome
(b) Plasmids
(c) Cristae
Answer: (a) Polyribosome : Several ribosomes in bacteria may get attached to a single strand of mRNA and form a chain called polyribosome.
(b) Plasmids : The extra-chromosomal segments of circular DNA present in the cytoplasm of prokaryotic cells like bacteria are called plasmids.
(c) Cristae : The inner membrane of mitochondria forms a number of infoldings called the cristae.

Question 37. Mention five differences between plant and animal cell.

Answer:

Question 38. Explain the following '
(a) Passive transport
(b) Active transport

Answer:

(i) Passive transport : It is a mode of membrane transport where the cell does not spend any energy nor shows any special activity. Therefore, many molecules can move briefly across the membrane without any requirement of energy. In this way of transport, the cell membrane plays a passive role and the transport is according to the concentration gradient.

(ii) Active transport : It is uphill movement of materials across the membrane where the solute particles move against their concentration gradient i.e., from their lower to higher concentration. Such a transport requires energy, which is obtained from ATP, Thus, it is an energy dependent process.

For example Na⁺/K⁺ pump in animal cells etc.

Question 39. The composition of cell wall varies in different groups of living organisms. Comment.
Answer: 1. Bacterial cell wall : The bacterial cell wall consists of peptidoglycan which contains polymers of modified sugars (N-acetyl glucosamine and N-acetyl muramic acid), cross-linked by short peptides. Peptidoglycan is also called murein or mucopeptide.
2. Fungal cell wall : The fungal cell wall is generally composed of chitin, a polymer of acetylglucosamine units.
3. Algal cell wall : The algal cell wall is made up of cellulose, galactans, mannans and minerals like calcium carbonate.
4. Plant cell wall : The plant cell wall is chiefly composed of the insoluble polysaccharides, cellulose. Certain other compounds, such as hemicellulose, pectin and proteins also occur in the cell wall.

Question 40. Describe the structure of Golgi apparatus.

Answer:

Structure :

(i) It is a membranous organelle composed of flattened sac-like cisternae stacked on one another. There are usually 4–8 cisternae present in a stack. These cisternae resemble to smooth endoplasmic reticulum.
(ii) Cisternae form an extensive network and are arranged near the nucleus in a concentric pattern.

(iii) The shape, size and number of cisternae may vary in different cells but have a similar organisation in one type of cells. Their size may range from 0.5 μm to 1.0 μm in diameter.
(iv) The cisternae membranes are smooth and curved having either convex or a concave outline. The curved outlines provide a distinct property to the membranes and thus, represent two poles or faces of golgi. These two faces are cis or the forming face (convex) and trans or the maturing face (concave) that communicate with the membranes of the ER. These two faces of the golgi are entirely different, but interconnected and function as a single unit.

Question 41. Mention the functions of Golgi apparatus.
Answer: Functions :
(i) The important function of Golgi apparatus is to package the material and prepare for secretions. The packaged material is delivered either to the intracellular targets i.e. within the cell or secreted extra cellular targets i.e., outside the cell. The material to be secreted moves from ER to the Golgi apparatus in the form of vesicles. These vesicles are then fuse with the cis face and move towards the maturing face of the golgi apparatus. Therefore, golgi apparatus is closely associated with ER in structural as well as functional aspects.
(ii) A number of proteins synthesised by ribosomes on the ER are transferred to Golgi apparatus. These proteins are then modified in the cisternae of Golgi apparatus before they are released from its trans face.
(iii) Golgi apparatus is the important site of formation of glycoproteins and glycolipids.

Question 42. Explain the following vacuoles
(a) Sap vacuoles
(b) Contractile vacuoles
(c) Food vacuoles

Answer:

(a) Sap vacuoles : They store and concentrate mineral salts as well as nutrients.

(b) Contractile vacuoles : In protozoan like Amoeba, Paramecium etc. these vacuoles are found which take part in osmoregulation and excretion.
(c) Food vacuoles : In many cells, as in protists, food vacuoles are formed by engulfing the food particles. They contain digestive enzymes with the help of which nutrients are digested.

Question 43. Draw a well-labelled diagram of mitochondrion.
Answer: A well-labelled diagram should show these parts: Outer membrane; Inner membrane; Inter-membrane space; Matrix; Crista.

Question 44. Explain the structure of cilia and flagella.

Answer:

Structure :
(i) Cilia and flagella are membrane-bound extensions of the plasma membrane. They arise from the centriole- like basal bodies present at their bases that anchor and control their movements.
(ii) They are cylindrical structures and their core is called axoneme which possess a number of microtubules running parallel to the long axis. The axoneme is made up of nine microtubule doublets arranged radially along the periphery and a pair of microtubules present in the centre. Such an arrangement of microtubules is referred as (9 + 2) organisation.

(iii) The pair of tubules present in the centre are connected to each other by a bridge and enclosed in common sheath called the central sheath.

(iv) The central sheath is connected to each peripheral doublet of microtubules by a radial spoke. Thus, there are total nine radial spokes.

(v) The peripheral doublets are also connected to each other via linkers.

Question 45. Write a short note on nuclear envelope.
Answer: Nuclear envelope : It bounds the nucleus on the outside and separates it from the cytoplasm. It is made up of two membranes – outer and inner. The inner membrane is smooth whereas the outer membrane may be smooth or its cytoplasmic surface may bear ribosomes like the RER. The outer membrane is often connected to ER. These two membranes of the nuclear envelope are separated by a space known as perinuclear space. The space is 10 to 50 nm in width. Nuclear envelope contains a large number of pores which are formed by the fusion of its two membranes. The nuclear pores control the passage of substances to inside or outside of the nucleus e.g., RNA, ribosomes, proteins.