AP Inter 1st Year Botany Study Material Chapter 9 Cell: The Unit of Life

Andhra Pradesh BIEAP AP Inter 1st Year Botany Study Material 9th Lesson Cell: The Unit of Life Textbook Questions and Answers.

AP Inter 1st Year Botany Study Material 9th Lesson Cell: The Unit of Life

Very Short Answer Questions

Question 1.
What is the significance of vacuole in a plant cell?
Answer:
In plnats, vacuole contains sap mainly composed of water, metabolic byproducts, excretions and other waste materials. They also play an important role in osmoregulation.

Question 2.
What does ‘s’ refer to a 70s and 80s ribosome?
Answer:
In both 70 ‘s’ ribosomes, and 80 ‘S’ ribosomes, ‘s’ stands for the sedimentation coefficient, [expressed in Svedberg unit]. It is indirectly a measure of density and size.

Question 3.
Mention a single membrane bound organelle which is rich in hydrolytic enzymes.
Answer:
Lysosome.

Question 4.
What are gas vacuoles 7 State their functions.
Answer:
Gas vacuoles are the aggregates of a number of small hollow cylindrical vesicles present in the cytoplasm of the floating purple and green photosynthetic bacteria. They are peroneable to atmospheric gases and help the bacteria to help floating on the surface of water.

Question 5.
What is the function of a polysome?
Answer:
Several ribosomes may attach to a single m-RNA and form a chain called polyribosomes or polysome. The ribosomes of a polysome translate the m-RNA into proteins.

Question 6.
What is the feature of a metacentric chromosome?
Answer:
The metacentric chromosome has middle centromere forming two equal arms of the chromosome.

Question 7.
What is refered to as satellite chromosome?
Answer:
A few chromosomes have non-staining secondary constrictions at a constant location, which gives the appearence of a small fragment called satellite. The chromosome with satellite is called satellite chromosome.

Question 8.
What are microbodies? What do they contain?
Answer:
Peroxysomes and glyoxisomes are called Microbodies. Peroxysomes are involved in the convertion of fatty acids into carbohydrates and in photorespiration. Glyoxysomes contain the enzymes of glyoxylatic cycle which convert stored lipids to carbohydrates.

Question 9.
What is middle lamella made of? What is its functional significance?
Answer:
Middle lamella is mainly composed of calcium pectate and holds or glues the different . neighbouring cells together.

Question 10.
What is osmosis?
Answer:
Movement of molecules or ions or water from low concentrated place to high concentrated place through semi permeable membrane is called osmosis.

Question 11.
Which part of the Bacterial cell is targeted in gram staining?
Answer:
Chemical composition of the cell envelope.

Question 12.
Which of the following is not correct? a) Robert Brown discovered the Cell. b) Schleden and Schwann formulated the cell theory c) Virchow explained that cells ae formed from pre existing cells d) Aunicellular organism carries out its lofe activities with in a single cell.
Answer:
a) is not correct. The cell was discovered by “Robert Hooke”.
b) is correct.
c) is correct.
d) is correct.

Question 13.
New cells generate from a) Bacterical Fermentation b) regeneration of old cells c) Pre existing cells d) Abiotic materials.
Answer:
Pre existing cells.

Question 14.
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.

Answer:

a) Cristae	ii) Infoldings in Mitochondria
b) Cisternae	iii) Disc shaped sacs in Golgi apparatus
c) Thylakoids	i) Flat membranous sacs in stroma

Question 15.
Which of the following is correct : a) Cells of all living organisms have a nucleus b) Both animals and plant cells have a well defined cell wall, c) In Prokaryotes, there are no membrane bound organcells. d) Cells are formed de novo from abiotic materials.
Answer:
“C” is correct. In Prokaryotes, there are no membrane bound organelles like chloroplast. Mitochondria, ER of Golgi complex.

Short Answer Type Questions

Question 1.
Describe the cell organelle which contains chlorophyll Pitments.
Answer:
The chlorophyll containing cell organelle is chloroplast. They are found in mesophyll cells of the leaves. They are lens shaped, oval, spherical or discoid or ribbon shaped, having 5 – 10 pm length and 2 – 4 pm width. They varies in number from one (chlamydomonus) to 20 – 40 per cell in the masophyll.

Each chloroplast is a double membrane bound structure with periplastidial space in between them. Inner to Inner membrane fluid filled space is present called the stroma. A number of organised flattened membranous sacs called the thylakoids are present in the stroma, which are arranged like a pile of coins called grana. The grana are inter connected by flat membranous tubules called stroma lamellae.

The stroma of the chlorplast contains enzymes required for the synthe is of carbohydrates proteins, small circular double stranded DNA molecules and 70s Ribosomes, photosynthetic pigments are present in thylakoids, involve in high reaction of photosynthesis.

Question 2.
Describe the structure and function of celi organelle that can be considered as power house of the cell.
Answer:
Mitochondria is considered as power house of the cell.

Each mitochondria is sausage shaped or cylindrical having a diameter of 0.2 to 1.0 µm and length of 1.0 to 4.1 µm. Mitochondria is a double membrane bound cell organelle of which outer membrane is smooth and inner membrane forms a number of infoldings towards inside called the cristae.

The space inner to inner membrane is fluid filled called matrix. The cristae contains several stalked particles called oxysomes or elementary particles. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP hence they are called power house of the cell. The matrix also contains single circular DNA molecule, 80s RNA molecules and 70s Ribosomes.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 1

Question 3.
Describe the structure of nucleus.
Answer:
The cell organelle that controls all the metabolic activities of the cell is called nucleus. It was first described by Robert Brown in 1831. Each nucleus is a spherical ball like structure, consists of 4 parts. They are A) Nuclear membrane, B) Nucleoplasm, C) Chromatin material and D) Nucleolus.

A) Nuclear membrane :
Nucleus is covered by double layered lipoprotenous membrane with perinuclear space in between them. At certain places, Nuclear pores are present which acts as passages between nucleoplasm and the cyloplasm in both directions.

B) Nucleoplasm :
Inner to nuclear membrane, nucleoplasm in present. It consists of chromatin material, nucleolus and RNA molecules nucleoplasm is also called karyoplasm.

C) Chromation material:
Inter phase nucleus has a loose and indistinct network of nucleoprotein fibres called chromatin. It contains DNA and some basic proteins called histones some on histone proteins and also RNA. The chromation is furthur classified into Heterochromatin and Euchromatin of these, Euchromatin is delicate, less condensed and active.

D) Nucleolus :
It is a dense, spherical shaped structure present inside the nucleus. It plays an indirect role in protein synthesis by producing rib somes.

Functions :

It controls the heriditary characterestics of an organism.
It is responsible for the protein synthesis, cell division, growth and differentiation.
It controls all the metabolic activities of the cell.

AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 2

Question 4.
Comment on the cartwheel Structure of centriole.
Answer:
Centrosome is an organelle usually containing two cylindrical structure called centrioles. They are surrounded by amorphous pericentriolar materials. Both the centrioles in a centrosome lie perpendicular to each other in which each has an organisation like “cartwheel”. They are made up of nine evenly spaced peripheral fibrils of tubulin. Each of the peripheral fibril is a triplet. The adjacent triplets are also linked.

The central part of the centriole is also proteinaceous and called the ‘Hub’, which is connected with tubules of the peripheral triplets by radial spokes made of protein. The centrioles form the basal body of cilia and flagella and spindle fifres that give rise to spindle apparatus during cell division in animal cells.

Question 5.
Briefly describe the cell theory.
Answer:
Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells. Schleiden, examined a large number of plants and observed that all plants are composed of different kinds of cells which form the tissues of the plant. Schleiden and Schwann together formulated cell theory. But this theory did not explain as to how new cells were formed. Rudolf virchow first explained that cells divided and new cells are formed from pre-existing cells. He modified the hypothesis of Schleiden and Schwann and give a definite shape to cell theofy- Which states that,

all living organisms are composed of cells and products of cells
all cells arise from the pre-existing cells.

Question 6.
Differentiate between Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).
Answer:

Rough ER	Smooth ER
i. Rough ER is studded with ribosomes.	i. Smooth ER is not associated with ribosomes.
ii. These are mainly composed of cisternae	ii. These ae mainly composed of tubules
iii. Generally associated with nuclear membrane.	iii. Generally associated with plasma membrane.
iv. Main function is protein synthesis.	iv. Main function is lipid synthesis.

Question 7.
Give the biochemical composition of plasma membrane. How are lipid molecules arranged in the membrane?
Answer:
Plasma membrane is made up of lipids that are arranged in fila. Later biochemical investigations clearly revealed that the cell membrane also posses protein and Carbohydrate. The lipids are arranged with in the membrane, with the polar (hydrophilic) head towards the outer sides and the tail (hydrophobic)towards the inner part. With in the lipids, proteins are classified into integral or peripheral proteins.

An improved model Nicholson (1972) widely accepted as “Fluid Mosaic Model”, According to this, the quasi fluid nature of lipid enables lateral movement of proteins within the overall bilayer.

Question 8.
What are plasmids? Describe their role in Bacteria.
Answer:
Plasmids are small circular DNA molecules outside the genomic DNA. The plasmid DNA conferms certain unique phenotypic characters to Bacteria i.e„ resistance to antibiotics, the plasmid DNA is used to monitor bacterial transformation with foreign DNA.

Question 9.
What are histones? What are their functions?
Answer:
Histones are the proteins closely associated with DNA molecules. They are responsible for structure of chromatin and play an important role in the regulation of gene expression. Five types of histone have been identified H1, H2A, H2B, H3and H4. The other 4 types of histones associate with DNA to form Nucleosomes. They plan an instrumental role in the regulation of many important biological process involving DNA such as transcription, DNA repair & cell cycle.

Question 10.
What is cytoskeleton? What functions is it involved in?
Answer:
An elaborate network of filamentous proteinaceous structures present in the cytoplasm is called cytoskeleton. Eukaryotic cells contain three major components of cytoskeleton, microfilaments, intermediate filaments and microtubules. Cytoskeleton is involved in mechanical support, maintanance of cell shape, cell motility, intracellular transport, signaling across the cell and Karyokinesis.

Question 11.
What is endomembrane system? What cell organelles are not included in it? Why?
Answer:
A group of cell organelles with coordinate functions is called endomembrane system. Mitochondria, chloroplast and peroxisomes are not associated with endomembrane system. Because their functions are not coordinated with the ER, Golgicomplx, lysosomes and vacuoles.

Question 12.
Distinguish between Active transport and Passive transport?
Answer:

Active transport	Passive transport
1. Movement of molecules or ions across the plasma membrane by utilising ATP is called Active transport.	1. Movement of molecules across the plasma membrane without utilising metabotic energy is called passive transport.
2. It is carried out against the concentration gradient. Ex : uptake of salt by cells through solution pump.	2. It is carried out along the concentration gradient. Ex: If the concentration of water is more outside the cell than inside, water will flow into the cell, called diffusion.

Question 13.
What are mesosomes? What do they help in?
Answer:
Extensions of the plasma membrane into the cell are called mesosomes. These extensions are in the form of vesicles, tubules and cisternae. They help in cell wall formation, DNA replication and its distribution to daughter cells, help in respiration, secretion processes to increase the surface area of the plasma membrane to absorb nutrients and enzymetic content.

Question 14.
What are nucleosomes? What are they made of?
Answer:
Under electron Microscope, chromation appears as “beads on string”. These beads are known as Nucleosomes. Atypical nucleosome contains 20,0 bp of DNA double helix wrapped around a core of histone octamer having two copies of each of four types of histone proteins viz H2A, H2B, H3 and H4. HI Histone lies outside the nucleosome core and seals the two turns of DNA by binding at the point where DNA enters and leaves the core. The DNA continues between two nucleosomes is called linker DNA.

Question 15.
How do neutral solutes move across the Plasma membrane? Can the polar molecules also move a cross it in the same way? If not then how are these transported across the membrane.
Answer:
Neutral solutes move a cross the plasma membrane by the process of simple diffusion along the concentration gradient i.e., from higher concentration to the lower concentration. Polar molecules can not pass through the non polar lipid bilayer. Beacuse they require a carriers protein of the membrane to facilitate their transport across the membrane.

Question 16.
Name two cell organelles that are double membrane bound. What are the .characteristics of these two organelles. State their functions and draw labelled diagrams of both.
Answer:
Mitochondria and chloroplasts are double membrane found cell organelles. Mitochondria is a rod shaped cell organelle or sausage shaped or cylindrical having a diameter of 0.2 to 1.0 mµ and length of 1.0 to 4 mµ. They are the sites of aerobic respiration and produce cellular energy in the form of ATP hence they are called “Power houses of the cell”.

Chloroplasts are lens shaped, oval, spherical or ribbon like bodies having 5-10 mp length and 2.4 mµ width. They contain enzymes required for the synthesis of carbohydrates and proteins.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 1

Question 17.
What are the characteristics of a prokaryotic cell?
Answer:

Nuclear envelope is absent. Cell shows a single circular, supercoiled naked DNA called nucleoid.
Nucleous is absent.
Endomembrane system is absent.
Mitochondria, plastids, lysosomes, peroxisomes and cytoskeleton are absent.
Respiratory enzymes are located in cell membrane.
70 s type of ribosomes are present.
Cell is surrounded by a cell wall, made up of polysaccharides, lipids and proteins.
Cells divide amitotically.

Question 18.
Cell is the basic unit of life. Discuss in brief.
Answer:
Schleiden explained a large number of plants and observed that all plants are composed Of different kinds of cells which form the tissues of the plant. All living organisms are composed of cells and products of cells. All cells arise from pre-existing cells. A cell is the basic unit of life. It is the smallest unit (or building block) of a living organism that is capable of life. Within cells, there are structures that work togehter to allow the cell to live. Some structures transport materials throughout the cell other structures make food and others release energy for the cell to use.

When you look at a green plant, there is a green chemical called chlorophyll. This chemical enables’ plants to use the sun’s energy to make food for themselves. This is found in the cell part called the chloroplast. The nucleus of plant cells is the control centre of the cells. It directs everything a cell’does. The cytoplasm’ is a fluid inside the cell and the cell parts float in it.

Question 19.
Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Give a critical comment.
Answer:
Lysosomes are the membrane found vesicular structures, filled with hydrolytic enzymes capable of digesting proteins, lipids and nucleic acids. These enzymes are optimally active at the acidic pH. Under starvation, lysosomes digest cellular contents by releasing hydrylyzing enzymes and cause death of cells called acetolysis.

Vacuole is the membrane found space present in the cytoplasm, contains mainly water, metabolic bye products, excretions and other waste materials. In some plant cells, vacuolar sap contains some pigments like anthocyanin which impart colour to the plant part; The vacuole is covered by single membrane called Tonoplast. The tonoplast facilitates the transport of number of ions and other materials against concentration gradients, into the vacuole. Vacuoles play an important role in osmoregulation.

Question 20.
Briefly give the contributions of the following scientists in formulating the cell theory, a) Rudolf Virchow b) Schleiden and Schwann.
Answer:
a) Rudolf Virchow :
He first explained that cells divided and new cells are formed from pre existing cells (Orhnis cellula – e cellula). He modified the hypothesis of Schleiden and Schwann to give the cell theory a final shape cell theory states that all living organisms are composed of cells and porducts of cells. All cells arise from pre-existing cells.

b) Schleiden and Schwann :
In 1838, Mathias Schleiden, examined a large number of plants and observed that cell plants are composed of different kinds of cells which form the tissues of the plant. Theodoe Schwann (1839), a British Zoologist, studied different types of animal cells and reported that cells had a thin outer layer which is called plasma membrane. He also concluded, based on his studies ‘ on plant tissues, the presence of cell wall is a unique character of the plant cells. Based on this, Schwann proposed the hypothesis that the bodies of animals and plants are composed of cells and products of cells.

Question 21.
Is extra genomic DNA present in prokaryotes and eukaryotes? If yes, indicate their location in both the types of organisms.
Answer:
Yes, Extra genome DNA is present in prokaryotes and Eukaryotes. In Prokaryotes, extra genome DNA (plasmid) is present along with Nucleoid and floats freely with in the cytoplasm. In Eukaryotes well defined nucleus is present with specific number of chromosomes. But a extra genome DNA is present in cell organelles like Mitochondria and chloroplast. These two organelles are believed to have originally been independent prokaryotes.

Question 22.
Structure and function are correlatabie in living organisms. Can you justify this by taking plasma membrane as an example?
Answer:
Plasma membrane is made up of bilayered lipids. Later biochemical investigations clearly revealed that the plasma membrane also possess protein and carbohydrate. The lipid component of the membrane is phosphoglycerides. The proteins present in the membrane are integral or peripheral type. Integral proteins are burried in the membrane. Peripheral proteins are on the surface of the membrane. Plasma membrane play an important role in transport of the molecules into and out of cells. This membrane is selectively permeable to some molecules present on either side of it. Many molecules can move freely across the membrane without utilising energy is called passive transport of ions.

As the polar molecules cannot pass through non-polar lipid bilayer, they require carrier protein of the membrane to facilitate their transport across the membrane against concentration gradient i.e, from lower to higher concentration. Such a transport by utilising energy is called active transport of ions.
Ex : Na⁺/K⁺ Pump.

Question 23.
Discuss briefly the role of nucleolus in the cells actively involved in protein synthesis.
Answer:
The nucleoplasm contains nucleous and chromatin material. The nucledi are spherical structures, involved in the synthesis of ribosomal RNA. Longer and more numerous nucledi are present in cells actively carrying out protein synthesis. The nucleous develops from the secondary constriction of a specialized chromosome known as the “nucleolar organiser”. The nucleolus consists of RNA, protein and small amount of DNA. It disappears during the end of prophase and reappears at the end of Telophase. It is also called Plasmosome or ‘Ribosomal factory1. –

Question 24.
Explain the association of Carbohydrate to the plasma membrane and its significance.
Answer:
Plasma membrane is made up of lipids and proteins. Later, biochemicals investigations clearly revealed that the cell membrance also possess protein and carbohydrate. They are present s short, unfranched or branched chains of sugars (oligosaccharides) attached either to exterior ectoproteins or the polar ends of phospholipids at the external surface of the plasma membrane. All types of oligosaccharides of the plasma membrane are formed by various combinations of six principle sugars like D-galactose, D-mannose, L-fructose, N-acetyl neuramic acid (sialic acid), N-acetyl D-glucosamine and N-acetyl – D – gaiactosamine.

Significance :

Glycophorins are found to contain certain antigenic determinants for the ABO Blood groups and MN flood groups.
Sialic acid contents a high negative change to the cell surface of erythrocyte.

Question 25.
Multicellular organisms have division of labour. Explain.
Answer:
Multicellular organisms are made up of millions and trillions of cells. All these cells perform specific functions. All the cells specialised for performing similar functions are grouped together as tissues in the body. Hence a particular function is carried out by a group of cells at a definite plae in the body. Similarly different functions are carried out by different groups of cells in an organism. By dividing labour, multicelled organisms are able to complete more complex tasks.

Question 26.
What are nuclear pores? State their function.
Answer:
The nuclear membrane is interupted by a minute pores. Which are formed by the fusion of its two membranes. These pores are called Nuclear pores. These regulate the transportation of molecular, between the nucleus and cytoplasm. In eukaryotic cells, the nucleus is separated from the cytoplasm by nuclear envelope. The envelope safeguards the DNA contained in the nucleus. Inspite of this barrier, there is still communication between the nucleus and cytoplasm by nuclear pores.

Each nuclear pore is a large complex of proteins that allows small molecules and ions to freely pass of diffuse into or out of the nucleus. Nuclear pores also allow necessary proteins to enter the nucleus from the cytoplasm ; if the proteins have special sequences that indicate, they belong to the nucleus. These sequences tags are known as nuclear localization signals. Similarly RNA transcribed in the nucleus and proteins are destined to enter the cytoplasm have nuclear export sequences that tag them for release through the nuclear pores.

Long Answer Type Questions

Question 1.
What structural and functional attributes must a cell have to be called a living cell?
Answer:
All living organisms are made up of cells and product of cells. Cell is the basic structural and functional unit of living organism. Each cell have different organelles and perform different functions.

Cells obey laws of energetics i.e., they transform energy.
Cells highly structured with emergent properties.
Cells have an evolutionary origin.
Cells metabolize means possess metabolic pathways, process nutrients, self adjust to environment.
Cells self replicate – nucleic acids, ribosomes.
Cells osmoregulate – vacuoles, vesicles.
Cells communicate – Glycoproteins.
Cells shows animation Cyclosis.
Cell grow, divide and differentiate.
Cells die.

Question 2.
Eukaryotic cells have organelles which may
a) Not be bound by a membrane
b) Bound by a single membrane
c) Bound by a double membrane.
Give the various sub-cellular organelles into these three categories.
Answer:
a) Not be bound by a membrane : Nucleolus
b) Bound by a single membrane : Lysosomes, vacuoles.
c) Bound by a double membrane : Mitochondria, chloroplast, nucleus..

Question 3.
The genomic content of the nucleus is constant for a given species where as the extra chromosomal DNA is found to be variable among the members of a population. Explain.
Answer:
In Prokaryotes (Bacteria) in addition to the genomic DNA, small circular DNA molecules are present in the cytoplasm. These small DNA molecules are called plasmids. They confers unique phenotypic character to such bacteria (i.e.,) resistance to antibiotics. It is also used to monitor bacterial transformation with foreign DNA.

In Eukaryotes, extra DNA molecules are present both in chloroplast (stroma) and mitochondria (matrix). Because of the presence of this DNA molecules, they are treated as self – autonomous cell organelles.

Question 4.
Justify the statement. “Mitochondria are power houses of the cell.
Answer:
Mitochondria is sausage – shaped or cylindrical structure having a diameter of 0.2 to 1.0 µm and length 1.0 to 4.1 µm. Each mitochondrion is a double membrane bound structure with outer membrane and inner membrane dividing its lumen distinctly into two aqueous compartments. The inner compartment is called the matrix. The outer membrane forms the continuous limiting boundary of the organelle. The inner membrane forms a number of infoldings called the cristae towards the matrix.

The cristae increase the surface area. The mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called “power houses” of the cell. The matrix also possesses a single circular DNA molecule, a few RNA molecules, ribosomes (70s) and the compartments required for the synthesis of proteins.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 3

Question 5.
Is there a species specific or region specific type of plastids? How does on distinguish one from the other?
Answer:
Plastids are species specific and are found in all plant cells and in euglenoides. They bear some specific pigments thus imparting specific colours to the part of the plant which posseses them. Based on the type of pigments, plastids are classified into three types. They are Leucoplasts, Chromoplasts, Chloroplasts.

Leucoplasts :
They are the colourless plastids which store food materials. Based on the storage product, they are of 3 types namely Amyloplasts (store starch), elaioplasts (store oils) and aleuroplasts (store proteins).

Chromoplasts :
They are coloured pigments which were in yellow, orange or red in colour. In these plastids, fat soluble carotenoids like carotene and xanthophylls are present which imparts orange, red or yellow colour.

Chlorplasts :
These are green coloured plastids which help in synthesis of food materials by photosynthesis. They contain chlorophyll and carotenoid pigments which trap light energy. Each chloroplast is a oval or spherical, double membrane bound cell organelle. The space present inner to inner membrane is called stroma. A number of organised flattened membranas sacs called thyloukoids are present in the stroma.

Thylakoids are arranged in stacks like the piles of coins called grana. The thylakoids of the different grana are connected by membranous tubules called the stroma lamellae. The stroma of the chloroplast contains enzymes required for the syntheis of carbohydrates and proteins.

Question 6.
Write the functions of the following.
a) Centromere b) Cell wall c) Smooth ER d) Golgi complex e) Centrioles
Answer:
a) Centromere :
It is required for proper chromosome seggregation. The centromere keeps the two sister chromatids together. It is also where the chromosomes attaches to the spindle apparatus during Mitosis and Meiosis.

b) Cell wall:
It gives a definite shape to the cell and protects the cell from mechanical damage and infection. It also helps in cell-to-cell interaction and acts as a barrier to undesirable macromolecules.

c) Smooth ER :
It helps in synthesis of lipids, metabolism of carbohydrates and calcium concentration, drug detoxification and attachment of receptors on cell membrane proteins. The smooth ER also contains the enzyme Glucose – 6 – Phosphatase which converts Glucose – 6 – Phosphate to Glucose.

d) Golgi complex :
It is the important site for the formation of glycoproteins and glycolipids. It is also involved in the synthesis of cell wall materials and also plays a main role in the formation of cell plate during cell division.

e) Centrioles :
They form the basal body of cilia and flagella and spindle fibres that give rise to spindle apparatus during cell division in animal cells.

Question 7.
Are the different types of plastids interchangeable? If yes, give examples where they are getting converted from one type to another.
Answer:
Yes. Plastids are inter changeable in form. Generally three types of plastids are present in plant cells namely, leucoplasts (storage), chromoplasts (coloured, attraction) and chloroplasts (synthesis of food). Chromoplasts are coloured plastids (orange, yellow or red), occurs in the cells of petals, fruits etc.

They contain less chlorophylls.and more carotenes (orange) or (red) and xanthophylls (yellow). The red colour of tomato is due to the presence of lycopene in the chromoplasts. The chromoplasts of red algae contain phycocyanin and phycoerythrin. The chromoplasts of Brown algae contain fucoxanthin.

Depending upon circumstances, one type of plastid may be converted into another type.
For Ex :

The leucoplasts in stem tubers of potato, on exposure to sunlight transofrm into chloroplasts.
In capsicum, the cells of ovary consists of leucoplasts. When ovary changes into fruit, leucoplasts are transformed into chloroplasts. When the fruit ripens chloroplasts are changed into chromoplasts.

Question 8.
Describe the structure of the following with the help of labelled diagrams.
i) Nucleus ii) Centrosome.
Answer:
i) Nucleus :
It was first discovered by Robert Brown. Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming. The interphase nucleus has highly extended and elaborate nucleoprotein fibres called chromatin, nuclear matrix and one or two nucleoli. Electron micrsocopy has revealed that the nucleus is covered by double layered nuclear envelope, with a space between called perinuclear space, forms a barrier between materials present inside the nucleus and the cytoplasm.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 2

The outer nuclear envelope remains continuous with the endoplasmic reticulum and also bears ribosomes. At a number of places, the nuclear envelope is interrupted by nuclear pores, which allows the passage of RNA and protein molecules in both directions between the nucleus and cytoplasm. The nucleoplasm contains nucleolus and chromatin. The nucleoli and spherical structures, involved in active ribosomal RNA synthesis. The chromatin, in different stages of cell division, become chromosomes. They contain DNA and some basic proteins called histones and also RNA. Nucleus plays an important role in biogensis of ribosomes. It plays a significant role in mitosis.

ii) Centrosome :
Centrosome is an organelle usually containing two cylindrical structures called centrioles. They are surrounded by amorphous pericentriolar materials. Both the centrioles in a centrosome lie perpendicular to each other in which each has an organisation like cartwheel. They are made up of nine evenly spaced peripheral fibrils of tubulin. Each of the peripheral fibril is a triplet. The adjacent triplets are also linked. The central part of the centriol is also proteinaceous and called the ‘hub’, which is connected with tubules of the peripheral triplets by radial spokes made of protein. The centrioles form the basal body of cilia and flagella and spindle fibres that give rise to spindle apparatus during cell divirsion in animal cells.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 4

Question 9.
What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.
Answer:
Centromere is the region of chromosome that becomes attached to spindle fibres. Special proteins surrounded the centromere. They form a disc shaped structures called kinetochores.

Each chromosome shows centromere at a specific position. Basing on the position of centromere, four types of chromosomes are recognised. They are :
1) Metacentric :
“If the centromere is situated at mid point of a choromosome”. It is “V” shaped and consists of two equal arms.

2) Sub-metacentric :
“If the centromere is situated slightly away from mid point of a chromosome”. It is ‘L’ shaped. It consists of two unequal arms.

C) Acrocentric :
If the centromere is situated at the sub terminal position of a chromosome. It is rod shaped or “J” shaped. It consists of very long arm and a very small arm.

D) Telocentric :
“If the centromere is situated at the terminal position of a chromosome”. It is “i” shaped and has only one arm.
AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 5

Intext Questions

Question 1.
What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
Answer:
Extensions of plasma membrane into the cell in the form of vesicles, tubules and lamellae are called mesosomes. They help in cell wall formation, DNA Replication and its distribution to daughter cells, in respiration, secretion and to increase the surface area of plasma membrane (absorption of nutrients) and enzymatic content.

Question 2.
How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Answer:
Neutral solutes move across the plasma membrane by the process of simple diffusion along the concentration gradient. Polar molecules cannot pass through the non polar lipid bilayer, they require a carrier protein of the membrane to facilitate their transport across the membrane.

Question 3.
Name the two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
Answer:
Chloroplast and Mitochondria.

Chlorplast is a lens shaped, oval or spherical or even ribbon like organelle, involves in photosynthesis.
Mitochondria is a sausage shaped or cylindrical cell organelle, involved in Respiration.

AP Inter 1st Year Botany Study Material Chapter 9 Cell The Unit of Life 1

Question 4.
What are the characteristics of prokaryotic cells.
Answer:
i) Nuclear envelope is absent. Cell shows a single circular, supercoiled naked DNA called nucleoid.
ii) Nucleous is absent.
iii) Endomembrane system is absent.
iv) Mitochondria, plastids, lysosomes, peroxisomes and cytoskeleton are absent.
v) Respiratory enzymes are located in cell membrane.
vi) 70 s type of ribosomes are present.
vii) Cell is surrounded by a cell wall, made up of polysaccharides, lipids and proteins.
viii) Cells divide amitotically.

Question 5.
Multicellular organisms have division of labour. Explain.
Answer:
Multicellular organisms are made up of millions and trillions of cells. All these cells perform specific functions. All the cells specialised for performing similar functions are grouped together as tissues in the body. Hence a particular function is carried out by a group of cells at a definite plae in the body. Similarly different functions are carried out by different groups of cells in an organism. By dividing labour, multicelled organisms are able to complete more complex tasks.

Question 6.
Cell is the basic unit of life. Discuss in brief.
Answer:
Schleiden explained a large number of plants and observed that all plants are composed Of different kinds of cells which form the tissues of the plant. All living organisms are composed of cells and products of cells. All cells arise from pre-existing cells. A cell is the basic unit of life. It is the smallest unit (or building block) of a living organism that is capable of life. Within cells, there are structures that work togehter to allow the cell to live. Some structures transport materials throughout the cell other structures make food and others release energy for the cell to use.

Question 7.
What are nuclear pores ? State their function.
Answer:
The nuclear membrane is interupted by a minute pores. Which are formed by the fusion of its two membranes. These pores are called Nuclear pores. These regulate the transportation of molecular, between the nucleus and cytoplasm. In eukaryotic cells, the nucleus is separated from the cytoplasm by nuclear envelope. The envelope safeguards the DNA contained in the nucleus. Inspite of this barrier, there is still communication between the nucleus and cytoplasm by nuclear pores.

Question 8.
Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
Answer:
Lysosomes are the membrane found vesicular structures, filled with hydrolytic enzymes capable of digesting proteins, lipids and nucleic acids. These enzymes are optimally active at the acidic pH. Under starvation, lysosomes digest cellular contents by releasing hydrylyzing enzymes and cause death of cells called acetolysis.

Question 9.
Describe the structure of the following with the help of labelled diagrams.
(i) Nucleus (ii) Centrosome
Answer:
i) Nucleus :
It was first discovered by Robert Brown. Later the material of the nucleus stained by the basic dyes was given the name chromatin by Flemming. The interphase nucleus has highly extended and elaborate nucleoprotein fibres called chromatin, nuclear matrix and one or two nucleoli. Electron micrsocopy has revealed that the nucleus is covered by double layered nuclear envelope, with a space between called perinuclear space, forms a barrier between materials present inside the nucleus and the cytoplasm.

Question 10.
What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.
Answer:
Centromere is the region of chromosome that becomes attached to spindle fibres. Special proteins surrounded the centromere. They form a disc shaped structures called kinetochores.

2) Sub-metacentric :
“If the centromere is situated slightly away from mid point of a chromosome”. It is ‘L’ shaped. It consists of two unequal arms.

C) Acrocentric :
If the centromere is situated at the sub terminal position of a chromosome. It is rod shaped or “J” shaped. It consists of very long arm and a very small arm.

D) Telocentric :
“If the centromere is situated at the terminal position of a chromosome”. It is “i” shaped and has only one arm.