Kingdom Prokaryotae (Monera)

 Biology XI Notes

Kingdom Prokaryotae (Monera) - Short Questions Answers

Chapter # 06
Biology - XI
Section III - Biodiversity

Kingdom Prokaryotae (Monera)

Q.1: What are Bacteria? What are the types of Bacteria?

Ans: Bacteria:
Bacteria are the simplest and smallest living organisms which possess cellular structure. They are microscopic. They were discovered by a Dutch scientist Anton Von Leeuwenhoek in 1676, then he gave them the name bacteria in 1683.

Some microbiologists have placed bacteria in two groups:

• Eubacteria:
  It is a large division. These bacteria are the true bacteria.
• Archaebacteria:
  It is a smaller division. These are ancient bacteria.

![Types of Bacteria]
(Illustration showing different types of bacteria: Coccus, Bacillus, and Spiral)

The size of bacteria is very small, ranging from 0.5 microns to 2 microns. They are found everywhere, in soil, water, and air. They do not have chlorophyll, so they live as parasites in plants and animals or saprophytes on dead organic substances.

Q.2: Describe the structure of Ulva?

Ans: Ulva belongs to the green algae. It grows in marine water and is considered a primitive plant in the group. It is also known as sea-lettuce. Its body is called thallus, which consists of erect broad sheet-like branches, or blades. From the base of the plant, thread-like colorless structures are given out which help in the attachment of the plant to any rock or stone and thus act like a hold-fast. The hold-fast does not absorb water.

The body of Ulva is composed of two layers of cells. The outer layer has contact with water, while the inner layer is prevented from the water contact. The cells are elongated. Each cell contains cytoplasm, a nucleus, and a single cup-shaped chloroplast.

Q.3: Describe the life cycle of Ulva with alternation of generations?

Ans: Life-Cycle of Ulva:
The life cycle of Ulva is completed in two stages. The first stage is gametophyte, in which the male and female gametes are produced by separate plants. These gametes unite together to form a zygote. The zygote develops into a sporophyte, which is the second stage of the life cycle. The sporophyte forms spores which produce gametophyte again. This whole process of the life cycle is called alternation of generations. In Ulva, gametophyte and sporophyte plants are similar in structure, so this process is termed as isomorphic alternation of generations. The life cycle is described as follows:

Gametophytic Stage:
In this stage, sexual reproduction takes place, and two types of male and female gametes are formed. The male and female plants are separate but similar in structure. The male plant produces male gametes, and the female plant produces female gametes. These male and female gametes are externally similar and...

(The diagram illustrates the life cycle of Ulva, including stages such as gametophyte, fertilization, diploid zygote, diploid sporophyte, meiosis, and zoospores.)

Internally different, they are called isogametes. They come in water and fuse together to form zygote. The zygote is diploid and it contains 26 chromosomes. It germinates into sporophyte which is also diploid in nature.

Sporophytic Stage:
It is the second stage of the life cycle of Ulva. It is developed by the germination of zygote. The sporophyte resembles the gametophyte in structure. The sporophyte produces zoospores by asexual reproduction. In the formation of zoospores, meiosis takes place due to which they become haploid and contain 13 chromosomes. The zoospores become free after maturation. Half of the zoospores form male and half produce female gametophyte of Ulva plant. In this way, its life cycle is completed.

Q.4: Describe the structure of Euglena?

Ans: Euglena is a microscopic unicellular living organism. It is found in fresh water. It is considered as an animal and as well as a plant because it has the properties of both. It is plant-like because it has chlorophyll. It is animal-like because it has no cell wall and is motile.

Shape and Structure:
Euglena is microscopic in nature. It has an elongated body. Its upper end is blunt and lower end is pointed. Around the body, a covering is present, called pellicle. Inside the body, cytoplasm is present which consists of two parts, outer ectoplasm and inner endoplasm. Ectoplasm is more viscous than endoplasm.
In the cytoplasm, many plate-like bodies are found, called chloroplasts. They contain green color and perform the function of manufacturing the food material, so Euglena can manufacture its own food material like plants with the help of chlorophyll. In the center of the body, the nucleus is present which contains a small nucleolus. The nucleus controls all the functions of the body.

Mouth:
At the upper end of the body, a funnel-shaped depression is present, called mouth or cytostome. The mouth opens into the gullet which leads into another structure, called reservoir. Near to the reservoir, one or few contractile vacuoles are present which help in the excretion of harmful substances and water. The contractile vacuoles open into the reservoir. The mouth and gullet are not used for feeding but they are used only for excretion. Water and other waste materials are removed from the body in this process.

Movement:
In Euglena, movement takes place by a long thread-like body, called flagellum. It arises from the upper part of the reservoir. Near the reservoir, a reddish body is also found, called eyespot. It is very sensitive to light. The animal moves to a place with the help of flagellum where suitable light is present.

Taxonomic Position of Euglena:
Euglena is an example of Eukaryotes. It contains certain characters of plants as well as animals.

Q.5: Describe the structure of Slime Mold?

Ans: Slime molds are fungi-like protists. They form a special group of organisms, which are animal-like in their body structure and plant-like in their reproduction.

Slime molds are creeping multinucleate masses of cytoplasm, looking like egg white. They grow rapidly up to one foot in damp and shady places, crawl over grasses, decaying leaves, old and rotten logs of wood. They may be colorless and sometimes contain different colors like orange, red, brown, or violet. They do not contain chlorophyll and live as saprophytes.

Structure:
The body of slime mold consists of an irregularly shaped mass of protoplasm, which is naked, i.e., has no proper body wall. The naked protoplasm is bounded by a non-cellular, thin, flexible slimy layer. Due to the presence of this slime layer, it is called a slime mold. Within the slime layer, protoplasm also contains a plasma membrane. Slime mold has no proper shape and size. The protoplasm consists of outer ectoplasm and inner endoplasm. The protoplasm contains many diploid nuclei. This body of slime mold is called plasmodium. It produces pseudopodia and shows amoeboid movement, so it seems to be like a giant amoeba. By the help of pseudopodia, it engulfs and digests bacteria and food particles, so it also contains food vacuoles and undigested food particles in the cytoplasm.

Q.6: Describe the life cycle of Slime Mold?

Ans: Life Cycle of Slime Mold (Plasmodium):
In the life cycle of slime mold, there are two types of reproduction:

• Asexual reproduction
• Sexual reproduction

Asexual Reproduction:
In slime mold (Plasmodium), asexual reproduction takes place by sporangia or fruiting bodies. These are produced in dry and warm weather. At the time of reproduction, the slime mold comes out of darkness and moves to exposed places which are dry.

The sporangia are developed on small stalks. These sporangia are small and golf-ball-like structures. The sporangia are of different colors. In the sporangium, many rounded spores are produced. Each spore is uninucleate and covered by a thick spiny wall. In the formation of spores, meiosis occurs, so haploid spores are formed. The spores are liberated out, and spores are dispersed by wind or rain to other places.

Germination of Spore:
The spore germinates on moist dead leaves, logs, or soil. From the spore, a tiny spindle-shaped structure comes out, called swarm spore or swarm cell.

(Illustration labeled as Fig. 7-6: "Slime molds. Pictorial life cycle of Physarum polycephalum" showing the stages of spore germination, meiosis, myxamoebae formation, plasmogamy, karyogamy, zygote formation, and development into young plasmodium and sporangium.)

From each spore, one to four swarm cells may be produced. The swarm spores are naked and biflagellate; one flagellum is long and one is short. The swarm spores are uninucleate and amoeboid.

• Myxamoeba:
  Sometimes instead of swarm cells, one to four amoeboid cells are produced from the spores, called myxamoebae. These are formed in dry conditions. These myxamoebae divide and form many myxamoebae.

Sexual Reproduction:
In slime mold, both swarm cells and myxamoebae may behave as gametes. They take part in sexual reproduction.

The swarm cells are fused together by their posterior ends. By their fusion, a zygote is formed, which is binucleate and flagellate. By the help of flagella, it swims for a short time, then it loses its flagella. The two nuclei of it fuse together to form a diploid nucleus.

The myxamoebae which come out of spores may also fuse together to form a zygote.

The diploid nucleus of the zygote, produced by swarm cells or myxamoebae, divides by mitosis and forms many nuclei; then, by gradual process, it grows into a new plasmodium.

Q.7: Describe the structure of Phytophthora and symptoms of the disease late blight of Potato?

Ans: Phytophthora (Late Blight of Potato)
Phytophthora infests and causes a disease in potato and tomato, called late blight.

Structure:
The body of Phytophthora is known as mycelium. It is branched and composed of many thread-like structures, called hyphae. The mycelium is unseptate. In the mycelium, cytoplasm is present, which has many nuclei. Due to the unseptate and multinucleate condition, it is called coenocytic mycelium. The mycelium is intercellular or intracellular and absorbs food material from host cells by haustoria.

Symptoms:
This disease is visible after flower formation. Due to the disease, many black or bluish-brown spots are produced on the leaves, which increase their size and ultimately cover the whole leaf. Later on, the tubers are affected. Their skin turns brown, and tissues become very soft.

Q.8: Describe the Asexual Reproduction of Phytophthora?

Ans: Asexual Reproduction:
In this reproduction, zoospores are produced in reproductive organs, called sporangia. At the time of reproduction, many erect branches arise from mycelium, called sporangiophores; they come out of the stomata of lower epidermis of host leaves. They produce more branches, at the tips of which oval or lemon-shaped sporangia are formed.

(Fig. 7-7(B): Asexual Reproduction in Phytophthora)

Each sporangium produces eight biflagellate zoospores. After maturation, it ruptures and all the spores become free. During favorable conditions, each zoospore forms a germ tube. It enters the host leaf through stomata or cuticle and produces new mycelium of Phytophthora.

Q.9: Describe the Sexual Reproduction of Phytophthora?

Ans: Sexual Reproduction:
In Phytophthora, sexual reproduction is of oogamous type. In this method, two entirely different types of male and female reproductive organs are produced; males are antheridia and females are the oogonia.

• Fertilization:
  At the time of fertilization, the male nucleus migrates into the oogonium; the male and female nuclei are fused together to form an oospore.

• Germination of Oospore:
  At the time of germination, the oospore forms a germ-tube. At the tip of the germ tube, a sporangium is formed, which produces many spores. When the spores are mature, the wall of the sporangium ruptures and the spores are released.

• (Fig. 7.8: Sexual Reproduction in Phytophthora)

  The sporangium ruptures and all the spores come out. During favorable conditions, they germinate into new mycelium of Phytophthora.

Q.10: Distinguish between the following?

Ans: Sexual Ulva and Asexual Ulva:

Sexual Ulva	Asexual Ulva
Sexual Ulva is gametophyte.	Asexual Ulva is sporophyte.
It is haploid, contains 13 chromosomes.	It is diploid, contains 26 chromosomes.
It produces male and female gametes by mitosis. Male and female Ulva are separate	It produces spores by meiosis.
Fertilization takes place in the reproductive stage of sexual Ulva. Q.11: Describe the Important Characters of Phylum Protozoa? Ans: Important Characters of Phylum Protozoa: They are microscopic; their body consists of only one cell. They live singly or in groups. They are rounded, oval, elongated, or irregular in shape. The protoplasm consists of outer ectoplasm and inner endoplasm. A definite nucleus is present in the body. Respiration takes place through the external surface or by diffusion. The movement occurs by pseudopodia, cilia, or flagella. Reproduction is by simple cell-division or by sexual method. During unfavorable conditions, some protozoans form non-motile spores or cysts, covered by a thick layer. When favorable conditions return, the spores are liberated out and develop into new animals. Some protozoans live as parasites in the bodies of animals and plants. Q.12: Write down the names of Classes of Phylum Protozoa? Ans: The Phylum Protozoa is divided into the following classes: Class — Mastigophora or Flagellata Class — Rhizopoda or Sarcodina Class — Ciliata Class — Suctoria Class — Sporozoa Q.13: What are the characters of Class Mastigophora (Flagellata)? Ans: Class - Mastigophora or Flagellata: The shape of the body does not change. It remains constant. They live singly or in colonies. The body is covered by an outer covering, called Pellicle. It is elastic. Sometimes a shell is also present around the body, which is made up of cytoplasm, chitin, or cilia. Ectoplasm and endoplasm cannot be clearly separated from each other. A nucleus is present. From the outer surface of the body, one or more thread-like bodies are developed, called flagella. They help in locomotion. Reproduction takes place by asexual or sexual methods. In class Flagellata, there are two types of animals. (Fig. 7-9: Euglena illustration showing flagellum, mouth, pharynx, eyespot, reservoir, contractile vacuole, chloroplast, nucleus, nucleolus, and other parts.) With Chlorophyll: They live in fresh as well as in marine water. They have chlorophyll and manufacture their food like plants. e.g. Euglena - It lives single. Volvox - It lives in the form of a colony. Noctiluca - It lives in the sea. It emits light. Without Chlorophyll: They do not have chlorophyll. They are usually parasites. e.g. Trypanosoma and Leishmania. They live as parasites in the body of vertebrates. (Fig. 7-10: Volvox; Fig. 7-11: Trypanosoma) Q.14: What are the characters of Rhizopoda? (Sarcodina) Ans: Class Rhizopoda or Sarcodina: They have a very soft body wall, which can change the shape of the body. In some animals, the body is covered by a shell. e.g. Globigerina. From their outer surface, pseudopodia are produced, which help in locomotion and to capture the food. The protoplasm is divided into ectoplasm and endoplasm. Nucleus is one or more. Excretion takes place by contractile vacuole. In marine animals, contractile vacuole is absent. e.g. Amoeba, Heliozoans, Foraminiferans, Globigerina. (Fig. 7-12: Amoeba) Q.15: What are the characters of Class Suctoria of Phylum Protozoa? Ans: Class - Suctoria: These animals have a close relationship with ciliate animals, and they seem to have evolved from them. Their characters are as follows: They have cilia which help in swimming, but the adult animals are without cilia. They are attached to any solid object by the help of a long rod-like structure. They contain two types of nuclei, micronucleus (smaller) and mega nucleus (large). From their body, certain thin structures are developed, called tentacles. (Fig. 7-13: Acineta (Suctoria)) Q.16: What are the characters of Class Ciliata of Phylum Protozoa? Ans: Class - Ciliata: Their body is provided with cilia, which help in locomotion and to get food into the body. They have a mouth, through which the food enters the body. The food may also be taken through the general surface. They contain two nuclei, micronucleus and macronucleus. Body is covered by pellicle. Excretion takes place by contractile vacuole. e.g., Paramecium, Stentor, Vorticella. (Fig. 7-14: Paramecium) Q.17: What are the characters of Class Sporozoa of Phylum Protozoa? Ans: Class - Sporozoa: The animals of this class are usually parasites. They do not produce special organs for locomotion. They perform very slow movement, called amoeboid movement. They contain cytoplasm and nucleus. Reproduction takes place by asexual and sexual methods. They cause some dangerous diseases in man and other vertebrates, such as malaria by Plasmodium. Their life cycle is completed in the body of two hosts: one is the body of a vertebrate, and the other is the body of an invertebrate. The plasmodium is transferred into the body of man from the body of a female Anopheles mosquito. Q.18: Describe the Life Cycle of Plasmodium in the body of man? Ans: Life Cycle of Plasmodium in the Body of Man: (Asexual Cycle - Schizogony) When a female Anopheles mosquito bites a healthy person, it transfers its sporozoites into the blood of man. The sporozoites are very small spindle or sickle-shaped bodies. They contain cytoplasm and nucleus. In man, the life cycle of Plasmodium consists of four phases. Pre-erythrocytic Stage: After some time, these sporozoites are transferred from the blood to the liver cells. Each sporozoite enters a liver cell and lives as a parasite. It becomes rounded in shape and is called a cryptozoite. The cryptozoite uses liver cell as its food material. Schizogony in Liver Cells: In liver cells, each cryptozoite starts multiplication. It divides by a simple process called schizogony. By this process, it produces many small bodies called merozoites. These merozoites become free by rupturing the liver cell. Each merozoite enters a new liver cell and behaves as a cryptozoite; it starts the same process again. In this way, two or three times schizogony process is completed in liver cells. Erythrocytic Stage (Trophozoite Stage): After some time, some of the merozoites or cryptozoites are transferred into the bloodstream. Each body enters a Red Blood Corpuscle (RBC). In RBC, the cryptozoite or merozoite is now known as trophozoite. In RBC, the trophozoite shows certain changes which are as follows: Ring Like Stage: In trophozoite, a vacuole appears and its nucleus transfers to the margin, so it becomes ring-shaped; this stage is called Ring Stage. Amoeboid Stage: After some time, the vacuole disappears, the nucleus comes back in the center, and from the outer surface of trophozoite, finger-like pseudopodia are produced. It becomes amoeba-shaped; this stage is called Amoeboid Stage. Schizont Stage: After some time, pseudopodia of trophozoite disappear, and it is converted into a rounded structure. Now it is ready to multiply by schizogony process; it is called Schizont. The schizont divides into many bodies known as Merozoites. The merozoites become free by rupturing the outer layer. These merozoites enter new RBCs; now each merozoite acts as a trophozoite and repeats the schizogony process once again. In this way, two or three times this process is repeated in RBCs of man. Post-Erythrocytic Stage: From the RBCs, some merozoites are again transferred into the liver cells and start schizonic reproduction; it is called post erythrocytic stage. Gametogony (Formation of Gametocytes): When schizogony is completed many times in the blood of man, then instead of forming merozoites, another type of bodies are produced, known as Gametocytes. Now it is necessary that these bodies should be transferred into the body of a female Anopheles mosquito. In the body of man, the life cycle of Plasmodium is completed. Q.19: Describe the stages of Life Cycle of Plasmodium in Mosquito? Ans: Stage of Life Cycle of Plasmodium in the Body of Female Anopheles Mosquito: (Sexual Cycle in Mosquito) The sexual cycle of Plasmodium is completed in the stomach of female Anopheles mosquito. In this cycle, the following stages are present. Gametogony (Formation of gametes) Syngamy (Fusion of gametes) Sporogony (Formation of sporozoites) When a female Anopheles mosquito bites a malaria patient and sucks his blood, along with blood gametocytes, schizonts, merozoites are transferred into the body of mosquito. In the body of mosquito only gametocytes remain alive and active, while other bodies are destroyed by the action of enzymes of stomach. (Fig. 7-15: Lifecycle of Plasmodium (Malaria Parasite) - Illustration showing various stages including Infection of Corpuscle, Ring Stage, Amoeboid Stage, Trophozoite, Schizogony, Gametocyte formation, Ookinete, Oocyst formation, and Sporozoite development in the mosquito's body) The gametocytes are of the types: Micro-gametocytes Macro-gametocytes Gametogony (Formation of Male and Female Gametes): Microgametocytes are smaller in size. Each micro-gametocyte produces many male gametes from its outer surface. These male gametes are thread-like structures; after maturation, these are separated from micro-gametocyte and move towards female gamete to take part in fertilization. Macro-gametocytes are larger in size. Each macro-gametocyte develops into a single female gamete, called oocyte. It has a small part at one side, known as the reception cone. Syngamy (Fertilization): The fusion of two male and female gametes is called syngamy. At the time of fertilization, many male gametes move towards the female gamete, but only one male gamete is attached with the reception cone, its nucleus is transferred into the female gamete, and by the fusion of two nuclei, a zygote is formed. Sporogony (Germination of Zygote and Formation of Sporozoites): After some time, the zygote starts germination. It develops into a worm-like structure called ookinete. The ookinete then changes into a rounded structure, known as oocyst. It is also covered by a protective covering. In the oocyst, many bodies are produced by the process of division. These are called sporoblasts. Each sporoblast produces many thread-like structures from its outer surface, called sporozoites. These sporozoites become free after some time, and then they are stored in the salivary glands of the mosquito. When this female Anopheles mosquito bites a healthy person, the sporozoites are transferred into his body, and hence malaria can be started once again. Q.20: What are the symptoms and precautions/treatment of Malaria? Ans: Symptoms of Malaria: The symptoms of malaria appear after many days of infection. The period of the parasite in the body before symptoms is called the incubation period. The symptoms of malaria are fever with shivering, vomiting or feeling of vomiting, loss of appetite, constipation, then headache, pain in the muscles and joints. In malaria, the fever may be up to 106°F, there are shaking chills and seating. Precautions and Treatment: Mosquitoes should be killed, which are the cause of malaria. There should not be stagnant water places anywhere because the mosquitoes lay their eggs in stagnant water. In case of malaria, anti-malarial drugs should be used. Q.21: Distinguish between the following? Ans: Flagellata and Sarcodina: Flagellata Sarcodina It is the class of Phylum Protozoa, the animals of this class contain one or two flagella, which help in locomotion. The animals of this class do not contain flagella. Their locomotory organs are called pseudopodia. Their body has a particular shape; it is not changed. They have an irregular shape of body. It can be changed regularly. They have fast locomotion, called Flagellary locomotion. They have slow locomotion, called amoeboid locomotion. Some members contain chlorophyll, i.e., they are autotrophs, and some are parasites. e.g., Euglena, Trypanosoma They do not contain chlorophyll. e.g., Amoeba

KINGDOM PROKARYOTAE (MONERA)

Biology XI Notes
Kingdom Prokaryotae (Monera) - Short Questions Answers

Chapter # 06
Biology - XI
Section III - Biodiversity

KINGDOM PROKARYOTAE (MONERA)

Q.1: What are Bacteria? What are the types of Bacteria?

Ans: BACTERIA:

Bacteria are the simplest and smallest living organisms which possess cellular structure. They are microscopic. They were discovered by a Dutch scientist Anton Von Leeuwenhoek in 1676, then he gave them the name bacteria in 1683.

Some microbiologists have placed bacteria in two groups:
Eubacteria:
It is a large division. These bacteria are the true bacteria.

Archaeabacteria:
It is a smaller division. These are ancient bacteria.

(Diagram: Types of Bacteria)

• Coccus

  • Micrococcus
  • Diplococci
  • Streptococci
  • Staphylococci

• Bacillus

  • Microbacillus
  • Diplobacilli
  • Streptobacilli
  • Staphylobacilli

• Spiral

  • Spiral
  • Vibrio

The size of bacteria is very small, ranges from 0.5 microns to 2 microns. They are found everywhere, in soil, water and air. They do not have chlorophyll, so they live as parasites in plants and animals or saprophytes on dead organic substances

TYPES OF BACTERIA:

There are four types of bacteria.
Cocci:
They are spherical in shape. According to the arrangement, they are of following types.

• Micrococcus:
  They are single, not arranged in groups.
• Diplococci:
  They are found in groups of two.
• Streptococci:
  They are arranged in chain-like manner.
• Sarcina:
  Group of eight bacteria, also called octant.
• Staphylococci:
  They are present in bundles or groups.
• Tetrad:
  Group of four bacteria.

Bacilli:
They are rod-shaped bacteria. They may also be found (i) Singly, called microbacillus, (ii) in group of two, called diplobacilli, (iii) arranged in a chain, streptobacilli, (iv) In groups of many known as staphylobacilli.

Spirilli:
These are spiral or corkscrew-shaped bacteria. They are never found in groups, e.g., Spirocheta.

Vibrio:
They are comma-shaped. They are also not found in groups.

Q.2: Describe the structure of Bacterial cell?

Ans: STRUCTURE OF BACTERIA:
Bacteria are simplest and smallest living organisms. The size of bacterial cell is 0.2 micron (µ) to 2µ in breadth and 2 to 10µ in length.

Bacteria are unicellular but may form groups or colonies.
A bacterial cell consists of following parts:

• Flagella
• Pilli
• Capsule
• Cell wall
• Cell membrane
• Cytoplasm
• Mesosomes
• Nucleoid (Nuclear material)
• Plasmi
• Flagella:
• Flagella are thin hair-like structures arise from basal body, a structure present beneath the cell membrane. Flagella are locomotory organs of bacteria i.e., help in the movement of the body.

• Pilli:
  These are fine, hollow, filament-like structures. These are not used in locomotion, but help in conjugation process of reproduction.

  Capsule:
  It is an additional protective layer around the cell wall and found in some bacteria, it is composed of polysaccharides and proteins. In some bacteria slime-capsule is present, which is used for the protection of bacterial cell against phagocytosis and increases the activity of bacterial cell.

  Cell wall:
  It is present around the bacterial cell. It is composed of amino acids, sugars and chitin. Cellulose is not present in bacterial cell. In some bacteria capsule is also present around the cell wall. In the cell wall of bacteria a compound is present, called peptidoglycan. It helps to maintain the cell shape and provides strength. It surrounds the cell wall like a network.

  Cell Membrane:
  Internal to the cell wall cell membrane or plasma membrane is present. The protoplasm of bacterial cell is bounded by cell membrane. It is composed of lipids and proteins. Cell membrane is semi-permeable and responsible for the osmotic behavior of the cell. Cell membrane also acts as respiratory structure due to the absence of mitochondria.

  Cytoplasm:
  The cytoplasm is a fluid material. It is dense and contains granules of glycogen, proteins and fat. Mitochondria and endoplasmic reticulum are absent. In the cytoplasm ribosomes are present. They are small minute granules composed of protein and R.N.A. and help in protein formation.

  Mesosomes:
  The plasma membrane of bacterial cell is folded inward to form a special structure, called mesosomes. The mesosomes take part in cell division, DNA-replication, secretion of certain enzymes, respiration and active transport of enzymes.

• Nucleoid:
  In bacteria there is no complete nucleus, but it contains nuclear material called Nucleoid. It is an irregular-shaped dense structure called chromatin body or bacterial chromosome. It does not contain nuclear membrane, nucleoplasm and nucleolus. Due to the absence of a complete nucleus the bacterial cell is called prokaryotic cell.

  Plasmid:
  It is a small fragment of extra genetic material double stranded DNA. It replicates itself. It does not take part in growth and metabolism. It is used as vector in genetic engineering.

• Q.3: Describe the diversity of bacteria?

  Ans: DIVERSITY OF BACTERIA:

  Types On The Base Of Flagella:
  On the basis of flagella the bacteria are classified into different groups:

  • Atrichous:
    These bacteria are without flagella.
  • Monotrichous:
    These bacteria contain one polar flagellum.
  • Lophotrichous:
    These bacteria contain a tuft of flagella only at one pole.
  • Amphitrichous:
    These bacteria contain tuft of flagella at two poles of the body.
  • Peritrichous:
    These bacteria contain flagella around the whole cell.

  Gram-Positive And Gram-Negative:
  A Danish Microbiologist Hans Christian Gram discovered a violet dye for the identification of unknown bacteria. On the basis of this dye (color) bacteria are classified into two groups:

  • Gram-Positive Bacteria:
    These bacteria are stained with violet dye.
  • Gram-Negative Bacteria:
    These bacteria are not stained with violet dye.

  Some microbiologists have placed bacteria in two groups:

• Eubacteria:
  It is a large division. These bacteria are the true bacteria.
• Archaeabacteria:
  It is a smaller division. These are ancient bacteria.

Q.4: Describe the nutrition in bacteria?

Ans: There are different types of bacteria according to their nutrition.

• Autotrophic bacteria
• Heterotrophic bacteria
• Symbiotic bacteria

Autotrophic Bacteria:
The bacteria which utilize $\text{CO}_2$ and get energy from sunlight or from some chemical reactions are called autotrophic bacteria. They can synthesize organic compounds. They may be further divided into two groups.

• Photosynthetic Autotrophs:
  These bacteria have chlorophyll dispersed in the cytoplasm. They utilize the atmospheric $\text{CO}_2$ and get energy from sunlight and perform the process of photosynthesis, but they use hydrogen sulphide ($\text{H}_2\text{S}$) instead of water to get hydrogen, thus they release sulphur instead of oxygen.

  $$\text{CO}_2 + 2\text{H}_2\text{S} \xrightarrow{\text{Light, Chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 2\text{S}$$

• Chemo-Autotrophs or Chemosynthetic Bacteria:
  These bacteria get energy by the oxidation and reduction process of various inorganic compounds, such as nitrates, ammonia, sulphur, ferrous ions, etc., so they are known as chemosynthetic bacteria.

Heterotrophic Bacteria:
These bacteria take their food from other living or non-living substances. These are of two types:

• Parasites:
  These bacteria obtain their food from the body of living organisms. They live in another organism and are fully dependent on the host. These bacteria cause diseases in the host and sometimes death occurs.

• Saprophytes:
  They obtain their food from dead organic substances. The soil humans are formed from the decay of plants and animals and it contains organic compounds. The bacteria change these compounds into simpler ones and get energy by this process.

Symbiotic Bacteria:
Some bacteria form an association with other organisms and both get benefits from each other; such bacteria are called symbiotic bacteria. For example, Rhizobium radicicola bacteria live in the roots of leguminous plants (e.g., Pea plant). These bacteria convert nitrogen into its compounds, Nitrites and Nitrates. This process is called nitrogen fixation. As a result of this process, bacteria get food material from plants. Such bacteria are called symbiotic bacteria.

Q.5: Describe the respiration in bacteria?

Ans: According to the respiration, there are two types of bacteria.

• Aerobes:
  These bacteria need oxygen for respiration. Aerobes bacteria are of two types:

  • Obligate Aerobes:
    These bacteria require $\text{O}_2$ and die in its absence.
  • Facultative Aerobes:
    These bacteria use $\text{O}_2$, but can also survive in its absence.

  The bacteria which require a little amount of $\text{O}_2$ are called Microaerophilic bacteria.

• Anaerobes:
  These bacteria do not need $\text{O}_2$ for respiration. Anaerobe bacteria are of different types:

• Obligate Anaerobes:
  Some bacteria are killed in the presence of $\text{O}_2$. These are called obligate anaerobes.
• Facultative Anaerobes:
  The bacteria which use $\text{O}_2$ but also can respire without it, they are called facultative anaerobes.

Q.6: Describe the locomotion in bacteria?

Ans: From the body of many bacteria whip-like bodies are produced, called flagella. They help in locomotion. They differ in number and distribution. In some bacteria, only one flagellum is present at the terminal side, while in others, the body is completely covered by flagella. Mostly bacilli and spirilli bacteria are motile, and cocci are non-motile.

According to the movement, the bacteria are of different types, such as:

• Phototactic Bacteria:
  These bacteria move towards or away from light.
• Chemotactic Bacteria:
  These bacteria move towards or away due to the presence of chemicals.
• Magnetotactic:
  These bacteria are able to detect magnetic fields of the earth.

Q.7: Describe the growth in bacteria?

Ans: Growth is an increase in the number of cells and size of cells. Bacteria take their food from the environment by diffusion or active transport process. Oxygen is required for aerobic bacteria, and it is not needed for anaerobic bacteria. The factors which affect the growth are:

• Temperature
• Available nutrients
• pH
• Ionic concentration

Stages or Phases of Growth:
In bacteria, there are four phases of growth:

• Lag Phase:
  This is the inactive phase of bacteria. In this stage, bacteria prepare themselves for growth. The cells accumulate essential substances such as water and proteins.

• Log Phase:
  The logarithmic phase (Log phase) is the period in which bacteria grow very rapidly. Their metabolic activities are maximum. Their rate of reproduction is more, and the rate of death is very slow, so they increase their number rapidly.

• Stationary Phase:
  After an active growth phase, bacteria face a shortage of food, pH changes, and energy loss, so they try to maintain themselves. They also start dying as a result of which their multiplication is equal to their death rate. The number of cells is almost unchanged, so it is called the stationary phase.

• Death Phase:
  When conditions are totally unfavorable, death occurs rapidly among growing cells. When the death rate is faster than the multiplication rate, it is called the death phase.

Q.8: Describe the process of binary fission in bacteria?

Ans: In this process, the parental cell divides into two daughter cells. First, the nucleus (nuclear material) divides into two nuclei, and bacterial cell elongates, and a constriction develops in the middle. One nucleus migrates into each separate area of the cell. The plasma membrane grows inwards, and the cell also divides into two daughter cells. The two daughter cells have the same properties as the parent cell.

Q.9: Describe genetic recombination in bacteria?

Ans: Genetic Recombination: (Sexual Reproduction)
There is no sexual reproduction in bacteria in a true or definite form, but a combination of two genetic materials takes place by certain methods. These are considered as sexual reproduction. These methods are of three types:

• Conjugation:
  When two changed forms of the same bacteria are kept together, the genetic material of one bacterial cell is transferred into another bacterial cell through a tube; the conjugating.

The process is known as conjugation. Conjugation method was reported by two scientists Joshua Lederberg and Edward Tatum in 1946. They got Nobel prize for their work. Joshua Lederberg and Edward Tatum observed conjugation between two strains of the common intestinal bacterium Escherichia coli.

Transduction:
In this process, the genetic material of one bacterial cell is transferred into another cell through bacteriophage virus. This process was reported by Lederberg and Zinder in 1952.

Transformation:
When the genetic information of one bacterium is transmitted into another bacteria and due to this information bacterium undergoes changes i.e., its nature is transformed, the process is called transformation.

This process was reported by an English scientist Fred Griffith in Pneumococcus bacteria.

Q.10: Describe the endospore formation in bacteria?

Ans: Some bacteria, especially the rod-shaped ones, have the ability to form endospores during unfavorable conditions. In this process, the protoplasm shrinks and forms a rounded mass. It is covered by a thick wall. It is known as an endospore.
The endospore is extremely resistant to heat, chemicals, freezing, and dryness. It may remain for a long time. Under favorable conditions, the endospore germinates into a single bacterial cell.

Q.11: Describe the importance of bacteria?

Ans: Bacteria have both positive and negative importance. They play a very important role in the life of human beings.

Positive Importance:

• Decaying of Dead Bodies (Decomposers):
  Bacteria decompose the dead remains of plants, animals, and human beings into simpler compounds. In this way, they help to clean the world.

• Bacteria in Industries:

• Bacteria are used in the dairy industry. They change milk into curd.
• They are used in the formation of butter and cheese from milk.
• They are used in the ripening of tobacco leaves.
• Bacteria are used in the preparation of alcohol and vinegar.
• Bacteria are also used in the leather industry.

• Digestion in Alimentary Canal:
  Certain bacteria are present in the intestine of man and help in the digestion of cellulose by an enzyme called cellulase.

• Fertility of Soil:
  Bacteria increase the fertility of soil by adding organic substances due to the decomposition of dead bodies.

• Genetic Engineering (Bio-Technology):
  Bacteria are used in genetic engineering. Escherichia coli bacteria are used to produce growth hormones and the production of insulin.

• Medical Bacteria:
  From bacteria, many important antibiotics have been obtained, such as Terramycin, Streptomycin, Neomycin, Thyrothrycin, Subtilin, Riboflavin, which is a vitamin produced by Clostridium bacteria.

• Nitrogen Fixation:
  Bacteria change nitrogen into its compounds like $\text{NO}_2$ and $\text{NO}_3$; this process is called nitrogen fixation.

Negative Importance:

• Spoilage of Food:
  Bacteria spoil our food stuff in large amounts by chemical processes. It is a great loss.

• Diseases in Man:
  Bacteria are responsible for causing various diseases in man and other animals, such as tuberculosis (T.B.), pneumonia, cholera, typhoid, tetanus, syphilis, diphtheria, etc.

• Diseases in Plants:
  Bacteria also cause diseases in various plants, such as citrus canker, fire blight of apple, ring disease of potato, wilt of solanaceae plants, etc.

Q.12: Write a note on control of bacteria?

Ans: Control of Bacteria:
When the infection of pathogenic organisms is brought to the minimum limit in a population, it is called control of these pathogenic organisms. It is necessary for the control of diseases, protection of food from spoilage, and also to prevent the damage of industrial products.

The different methods to control the infectious microorganisms are as follows:

• Infected persons should be properly treated by effective medicines.
• Persons in a population should be treated by immunization and vaccination.
• In epidemic conditions, the infected persons should be kept in quarantine to avoid the spread of infection to healthy persons.
• At different possible stages, the life cycle of pathogens should be disrupted, so it cannot cause further infection.
• The host bodies of pathogens should be identified and treated well to control the disease.
• By different ways, knowledge and awareness about diseases and infections of pathogens should be provided to the public.
• Many methods should be used to kill or inhibit the infection of pathogens, such as:
• High-temperature treatment
• By ultraviolet rays
• By the use of antiseptics
• By the use of antibiotics
• By chemotherapy

Q.13: What are immunization and vaccination?

Ans: Immunization and Vaccination:
The resistance against infection by pathogenic organisms is called immunity. It can be developed in the body by different ways. One method to develop immunity is vaccination or active immunization. Vaccination is used to control many diseases. A vaccine is either used orally, e.g., Polio vaccine, or taken into the body by syringe, e.g., Tetanus vaccine.

The procedure of vaccination is very effective and beneficial for human beings because it helps to control many dangerous diseases such as measles, diphtheria. When a large proportion of the population is immune, then the disease spreads poorly throughout the population.

Q.14: What are the uses and misuses of antibiotics?

Ans: Use and Misuse of Antibiotics:
Antibiotics are the chemical substances which are used to kill microorganisms that cause infectious diseases. These are produced by certain microorganisms and prevent the activity of other microorganisms.

The first antibiotic is Penicillin, which was isolated from Penicillium fungus in 1940. After that, a great work has been done in this field, and many antibiotics have been isolated or synthesized for the treatment of infectious diseases.

Use of Antibiotics:

• Antibiotics have their effect against the bacteria and kill them and control their infection.
• The antibiotics are used as vaccination to develop resistance in the body. They maintain the immune system.
• Antibiotics are also used in agriculture to kill different organisms. These are also used in animal feeds to provide growth-promoting substances.

Misuse of Antibiotics:

• By the extensive use of antibiotics, more resistance is developed in pathogenic microorganisms; after that, they cause more serious infection in the body.
• Antibiotics have many side effects. Other organs of the body may be damaged, such as liver cells and kidney cells.
• Antibiotics may react with human metabolism, and in severe cases, death of a person may occur.
• Some antibiotics cause allergy in the body, such as Penicillin.

Q.15: Write a note on Cyanobacteria? (Blue-green algae)

Ans: Cyanobacteria (Blue-Green Algae):
Important Characters:

• They are water-living simple organisms.
• They are prokaryotes, i.e., they do not have a true nucleus, like bacteria, so-called cyanobacteria.
• They contain blue-green pigments, chlorophyll a (green) and phycocyanin (blue), so they are also called blue-green algae.
• They are unicellular or may be found in groups or colonies.
• They have a double-layered cell wall.
• Their cytoplasm is differentiated into two parts:
  • Outer colored part, Chromoplasm with green and blue pigments.
  • Inner color part, Centroplasm.
• Asexual reproduction takes place by hormogonia, fragmentation, akinetes, or zoospores.
• Sexual reproduction is absent.

Q.16: Describe the structure and reproduction of Nostoc?

Ans: Nostoc belongs to the group Cyanophyta of Kingdom Monera. It is found in freshwater ponds, streams, lakes, etc.

Structure:

• The body of Nostoc is called Thallus. It is very simple in structure. The thallus consists of many thread-like bodies, known as filaments. Each filament is unbranched and composed of many spherical cells, which are arranged in beaded form. All the cells are similar in structure. The whole filament is covered by a gelatinous sheath, which protects the filament. The gelatinous mass is in colony form, called coenobium.
• In the filament of Nostoc, some larger, light-yellowish and thick-walled cells are also present, called heterocysts. The heterocysts take part in reproduction and nitrogen fixation. They convert nitrogen into its simpler form, which is easily utilized by the plant.

Structure of a Cell:

• Each cell of Nostoc is spherical in shape. It is covered by a double-layered wall. The outer layer of the cell wall is thick, composed of cellulose and pectic compounds. The inner layer is thin, composed of purely cellulose.

The protoplasm of the cell consists of two parts:

• Chromoplasm:
  It is the outer colored part. It contains color pigments, chlorophyll a, phycocyanin, xanthophyll, and carotene. These pigments are not found in plastids, but around this region, a plasma membrane is present.

• Centroplasm or Central Body:
  It is the inner part of protoplasm. It is colorless but stores food material in the form of cyanophycean starch. In Nostoc, endoplasmic reticulum, mitochondria, Golgi bodies, and vacuoles are absent, but ribosomes and pseudovacuoles are present.

  In the cell of Nostoc, a true nucleus is absent, but the central body acts like a nucleus and controls all the functions. It is an incomplete nucleus because it does not have a nuclear membrane and nucleolus, so it is also called an incipient nucleus. Due to the presence of an incomplete nucleus, the cell of Nostoc is considered a prokaryotic cell.

Nutrition:
Nostoc contains chlorophyll, so it can manufacture its own food material, i.e., it is autotrophic. It also takes part in nitrogen fixation, i.e., it converts nitrogen into nitrates by heterocyst.

Reproduction:
In Nostoc, the reproduction takes place by the following methods:

• By Hormogonia:
  The filament of Nostoc breaks up into many pieces, called hormogonia. Each hormogonium grows into a new filament.

• By Arthrospores or Akinetes:
  During unfavorable conditions, some cells of Nostoc filament become enlarged, and they are covered by a thick wall. They are called akinetes or arthrospores or resting spores. They also store food material. They take rest and germinate during favorable conditions into new filaments.

• By Heterocyst:
  The heterocysts also take part in reproduction. They are separated from the filament and change themselves into reproductive cells. (Each heterocyst develops into a new filament by cell division.)

• Q.17: What is the importance of Cyanobacteria?

• Ans: Importance of Cyanobacteria:

• These organisms take part in nitrogen fixation. Nostoc and Anabaena are used as nitrogen fertilizers in agriculture to improve soil fertility.
• During photosynthesis, they use $\text{CO}_2$ and $\text{H}_2\text{O}$. They release oxygen as a byproduct. In this way, they take part in changing and flourishing the environment.
• Many organisms of cyanobacteria are found in the form of phytoplankton. They are used as food by many aquatic animals.
• They also produce an unpleasant smell in water and make it unsuitable for drinking.

Q.18: Distinguish between the following?

Ans: Flagella and Pili:

Flagella	Pili
These are extremely thin appendages in bacterial cells.	These are hollow filamentous appendages in bacterial cells.
These are larger in size.	These are smaller than flagella.
They originate from a basal body, a structure in the cytoplasm beneath the cell membrane.	They do not originate from a basal body .
They help in locomotion. Photosynthetic Bacteria and Chemosynthetic Bacteria: Photosynthetic Bacteria Chemosynthetic Bacteria These bacteria contain chlorophyll. These bacteria do not contain chlorophyll. They use sunlight during photosynthesis. They do not use sunlight. They manufacture their food by the use of $\text{CO}_2$ and $\text{H}_2\text{S}$. They do not manufacture their food, but they use chemical substances, taking part in their oxidation and reduction to get energy. They use sulfur, called green sulfur bacteria. They use different inorganic chemical substances.	They help in conjugation, which is a process of reproduction

VARIETY OF LIFE

 Biology XI Notes

Variety of Life - Short Questions Answers
Biology - XI
Section III - Biodiversity

VARIETY OF LIFE

 Q.1: What is classification? Describe the different characters of classification?

Ans: There are different kinds of living organisms in the world. These organisms differ from each other in size, shape, and color. They are classified into different groups and sub-groups on the basis of their characters. This system of classification is known as Taxonomy.

THE CELL

 Biology XI Notes

The Cell – Short Questions Answers
Chapter # 04
Short Questions Answers
Section II – Unity Of Life

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THE CELL

Q.1: What is a cell?

Ans:
The cell is the smallest fundamental, structural and functional unit of living organisms OR cell is the basic unit of life.

The discovery and study of cells became possible after the invention of microscope. The microscope was invented by an Italian scientist Galilio in 1610.

The word cell was first used by a scientist Robert Hooke in 1665. He observed a piece of cork under microscope and found many small chambers in it. He named each chamber as a cell. Another scientist Robert Brown discovered a rounded body in the cells of Orchids in 1831. This body was named as nucleus.

Q.2: Write a short note on Cell Theory?

Ans:
Cell Theory: This theory was proposed by two German scientists, Schleiden (1838), Schwann (1839) and Virchow. It is a fundamental theory. The main points of this theory are as follows:

• All organisms are composed of one or more cells.
• The cell is the structural and functional unit of life. Schleiden and Schwann described the cell a de novo structure i.e. it could arise from non-cellular material, but a German scientist Rudolf Virchow in 1855 added a third very important point to the cell theory.
• A new cell is always produced only by the division of pre-existing cell. It is not a de novo structure.

Importance Of Cell Theory:
It brought a great revolution in the field of biology and proved that the body of living organisms performs all activities and functions by the interaction of cell units.

Q.3: Write a note on Microscope?

Ans:
MICROSCOPE:
Microscopes are the instruments which are used to observe microorganisms or small organisms.

Kinds Of Microscopes:
There are different kinds of microscopes. These kinds are as follows:

• Light microscope
• X-ray microscope
• Electron microscope

Light Microscope:
In this microscope, visible light is used as a source of illumination.

• Simple Microscope (Dissecting Microscope):
  In this microscope, a single lens is used to study the object.

• Compound Microscope:
  In this microscope, more than one lens is used.

X-Ray Microscope:
In this microscope, short-wave length X-rays are used as a source of light. This microscope is very efficient to observe the three-dimensional structure of cell parts.

Electron Microscope:
In this microscope, an electron beam is used for illumination. In this type of microscope, an electron beam is emitted from the source (cathode or metal filament). This beam passes through the specimen, and the image is seen on a photographic film or on a screen.

Q.4: What is the technique to isolate the components of the cell?

Ans: COMPONENTS OF THE CELL

• To determine the chemical composition of various parts of a cell, its components are isolated; this process is known as fractionation.

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In fractionation:

• Many similar types of cells are placed in a cold environment in a homogenizer, and then a spinning action is applied, called Centrifugation.
• At low speed, larger particles like cell nuclei are separated, and these are settled down at the bottom, in the sediments.
• Smaller particles remain in the fluid, which are transferred into another test tube. These particles are centrifuged at high speed, which helps to separate these particles in various fractions. After their separation, they can be studied easily.

Q.5: What are the types of cell?

Ans:
According to the structure, the cells are classified into two groups:

• Prokaryotes
• Eukaryotes

Prokaryotic Cell:
These cells are found in simple living organisms like blue-green algae, bacteria. These cells do not contain a complete and true nucleus. Nuclear membrane and nucleolus are absent, so instead of a true nucleus, the genetic material is found in the cytoplasm. They contain mesosomes. Their genetic material does not contain Histone protein, so true chromosome is absent. Their nuclear material is usually coiled and present in a region, called nucleoid. These cells also do not have those organelles which are covered by membrane such as mitochondria, golgi bodies, lysosomes, and chloroplasts.

Eukaryotes:
These organisms contain a true nucleus in their cells. They contain all necessary membrane-bound organelles, such as mitochondria, golgi bodies, plastids, lysosomes, etc., which provide particular structural and functional organization to the cells.

Eukaryotes also contain chromosomes with DNA and Histone protein. Eukaryotes are either Unicellular or Multi-cellular.

Q.6: Name the different parts of a cell?

Ans:
A typical eukaryotic cell consists of the following parts:

• Plasma membrane
• Nucleus
• Cytoplasm and cytoplasmic organelles
• Cell wall: It is found in plant cell, bacterial cell, fungal cell, but absent in animal cell.

Q.7: Describe the structure and functions of Plasma Membrane?

Ans: FLUID MOSAIC BILAYERED MODEL OF CELL MEMBRANE
On the inner side of cell wall around the protoplasm, a thin, delicate and elastic membrane is found, called plasma membrane. It is also called plasma-lemma. It consists of proteins and phospholipids. Many other types of lipids are also present, such as cholesterol. It controls the process of osmosis.

The structure of plasma membrane was proposed by two scientists, Singer and Nicholson. This structure is called Fluid mosaic model. The cell membrane consists of a double layer of phospholipids; along these lipids proteins are also present. This is a bilayered structure of plasma membrane.

Each layer of phospholipids has two ends:

• Hydrophobic End:
  It is non-polar end i.e. the inner part.

• Hydrophilic End:
  It is polar end i.e. the outer part.

The inner, non-polar hydrophobic ends are present opposite to each other. In these layers, proteins are present in different manner. There are two types of proteins:

• Extrinsic proteins
• Intrinsic proteins

Extrinsic Proteins (Peripheral Proteins):
These proteins are present along the surface of lipids. These are also called peripheral proteins. They have loose attachment with membrane surface.

Intrinsic Proteins (Integral Proteins):
These proteins are found deeply in the lipid layers. They help in the movement of water-soluble ions outside or inside the cell.

Functions Of Cell Membrane:

• It protects the cytoplasm of a cell.
• It maintains the cell shape.
• It is semi-permeable membrane. It helps in permeability i.e. allows to pass different solutions of molecules in and out of the cell.

Q.8: Describe the permeability of Plasma Membrane (Cell membrane)?

Ans:
The process of flow of solutions and important materials in and out of a cell known as selected or differential permeability. This permeability is of two types:

• Passive transport
• Active transport

Passive Transport:
It is of two types:

• Diffusion Or Passive Permeability:
  When two solutions or substances of different concentration are mixed, it is called diffusion. In this process, the movement of molecules is from high to low concentration without membrane. It helps in the diffusion of many substances like gases, O₂ and CO₂.

• Osmosis:
  When a solvent moves from the region of higher concentration to the region of lower concentration in the presence of a semi-permeable membrane, it is called osmosis. It helps to maintain osmoregulation i.e., keeps the balance between the osmotic pressure inside and outside the cell.

Active Transport:
It is opposite to diffusion. In this process, the molecules move from lower to the higher concentration. In this type of transport, energy is required. Active transport is of two types:

• Endocytosis:
  When the cell membrane takes in certain materials by infolding in the form of vacuole, it is called endocytosis. It is of two types:

  • Phagocytosis
  • Pinocytosis

  Phagocytosis:
  In this process, the plasma membrane absorbs solid particles; for example, the white blood cells absorb unnecessary harmful particles from the blood. It is also called cell-eating process.

  Pinocytosis:
  It is a process of taking fluid in large amount. When the living cells take up fluid vesicles, it is called pinocytosis. It is also called cell drinking process.

• Exocytosis:
  When the cell membrane allows the movement of certain materials out of the cell, it is called exocytosis. It is the process of membrane fusion after the movement of materials.

Q.9: Write a note on Cell Wall?

Ans:
The cell wall is present in plant cells on the outer side of the plasma membrane. It is composed of cellulose, but it also contains lignin and pectin which make it stronger. In a young cell, the cell wall is thin and delicate, but in a large cell it becomes thick and strong. The cell wall consists of three layers:

• Primary wall
• Secondary wall
• Middle Lamella

Primary Wall:
It is found around a young plant cell on the outer side of the plasma membrane. It is thin and elastic. It contains hemicellulose (50%), cellulose (25%), and a small amount of pectic substance.

Secondary Wall:
It is formed on the inner side of the primary wall in an old and large cell. After its formation, the cell wall becomes thick and non-elastic. It contains cellulose with lignin and other substances.

Middle Lamella:
It is the layer between two cells. It helps to attach the cells. It is made up of calcium and magnesium pectates.

Functions Of Cell Wall:

• It gives a definite shape and structural framework to the cell.
• It protects the inner contents of the cell.
• It provides mechanical support to the cell.
• It is a permeable membrane for diffusion and helps in the absorption of minerals and solutes along with water in the cells of root hairs.

Q.10: What are Plasmodesmata?

Ans:
The cell wall separates the protoplasm of one cell from the adjacent cell, but in many cases this separation is not in a proper way. In such cases, minute pores are present in the cell wall. Through these pores, the protoplasts of the adjacent cells communicate with each other by certain protoplasmic strands, called plasmodesmata. The plasmodesmata take part in the translocation of nutritive materials and transmission of stimuli from cell to cell.

Q.11: Describe the structure and functions of Nucleus?

Ans:
The nucleus was discovered by a scientist Robert Brown in 1831. It is spherical or oval in shape and is located in the centre in a young cell, while in a mature cell, it comes to lie on one side.

STRUCTURE OF NUCLEUS:

• Nuclear-Membrane:
  The nucleus is surrounded by a thin, transparent membrane known as the nuclear membrane. It separates the cytoplasm from the nucleus. The nuclear membrane has numerous large pores which help in direct communication between cytoplasm and the nucleoplasm.

• Nucleoplasm Or Karyolymph:
  In the nucleus, there is a dense but clear mass of protoplasm, called nuclear-sap or nucleoplasm. It contains enzymes and other complex substances which take part in the formation of DNA and RNA.

• Chromatin Network:
  In the nucleoplasm, a network of fine loosely connected threads is present, called the chromatin network. The chromatin is the hereditary material. In division of the nucleus, the chromatin forms a definite number of thread-like structures, called chromosomes, which contain hereditary units on their surface, called genes. Chemically, chromatin consists of Ribonucleic acid (RNA) and Deoxyribonucleic acid (DNA).

• Nucleolus:
  In each nucleus, one or more globular bodies are present, called nucleolus. They consist of proteins and RNA. The nucleolus produces ribosomes, which take part in protein synthesis.

FUNCTIONS OF NUCLEUS:

• The nucleus controls all the vital activities of a cell, so it is considered as the brain of the cell.
• It produces chromosomes during cell division. The chromosomes transfer hereditary characters from parent cell to daughter cell.
• It directly takes part in cell division and reproduction.
• It produces DNA and RNA. DNA is a genetic material, and RNA takes part in protein synthesis.
• In the nucleolus of the nucleus, ribosomes are produced, which help in protein synthesis.

Q.12: Describe the structure and types of Chromosomes?

Ans: STRUCTURE OF CHROMOSOMES:
Structurally, the chromosomes are composed of proteins and DNA. Their number in a living body is constant, and it remains unchanged from generation to generation.

A visible and prominent chromosome can be studied very easily during cell division. Each chromosome consists of two thread-like structures, called chromatids. These chromatids are attached to each other by a small body, known as centromere. The part of chromatid from centromere to end is called arm.

Types of chromosomes according to the position of centromere:

• Telocentric:
  These are rod-shaped chromosomes. These have centromere at their proximal end.

• Acrocentric:
  These are also rod-shaped chromosomes, but the centromere is between two chromatids in such a manner that one arm is short and another is long.

• Sub-Metacentric:
  These are J or L-shaped chromosomes. In these chromosomes, the centromere is present in the centre in such a manner that two unequal arms are formed.

• Metacentric:
  These are V-shaped chromosomes. In these chromosomes, the centromere is present almost in the centre and two equal arms are formed.

Q.13: Describe the structure and functions of Endoplasmic Reticulum?

Ans:
It is a network of fine tube-like structures, which extend from cell membrane to the nuclear membrane. It is of two types. It consists of Lipoproteins.

• Agranulated or smooth endoplasmic reticulum (SER).
• Granulated or rough endoplasmic reticulum (RER).

Smooth endoplasmic reticulum does not contain ribosomes on their surface. It is found in steroid-producing cells, like fat cells, liver, and muscles.

In skin, the smooth endoplasmic reticulum converts cholesterol into vitamin D (a lipid compound). This vitamin helps to make bones strong and healthy.

Rough endoplasmic reticulum contains ribosomes on their outer surface. This reticulum is found in the cells which take part in protein synthesis, such as pancreas and salivary glands of mammals.

Functions:

• It helps in the exchange of important materials between cytoplasm and nucleus.
• It is involved in protein synthesis due to the presence of ribosomes.
• It is the passage for RNA to transfer from nucleus to the cytoplasm.
• It takes part to neutralize the harmful effect of drugs.
• It helps in detoxification of chemicals.
• In skin, smooth endoplasmic reticulum converts cholesterol into a lipid compound, called Vitamin-D in the presence of sunlight. This vitamin makes the bones healthy and strong.

Q.14: Write a note on Mitochondria (Chondriosomes)?

Ans: MITOCHONDRIA OR CHONDRIOSOMES:
They are small spherical or plate-like bodies present in the cytoplasm. Mitochondria are transferred from mother to the new generation. These are present in eggs and not in sperms, so mother transfers them into the new generation. Mitochondria have their own DNA, so they take part in the production of their component protein. (Mitochondria consist of 3 parts.)

• An Outer Membrane:
  It is smooth and consists of proteins and lipids.

• Inner Membrane:
  It forms numerous folds; these cristae enzymes and co-enzymes are present which help in the oxidation of starch, fatty acids, and amino acid. These compounds are converted into CO₂ and water. In this process, energy is released in the form of ATP. This energy is stored in the mitochondria.

• Matrix:
  It is the central granular part. It contains many organic compounds. Mitochondria are the main centers of the intercellular energy production; they are called the powerhouse of the cell. Almost all the respiratory activities take place in mitochondria, and they contain a number of enzymes.

Q.15: Write a note on Golgi apparatus (Dictyosomes)?

Ans: GOLGI APPARATUS: (DICTYOSOMES)
The Golgi bodies are found only in certain types of cells. In plant cells, they are present throughout the cell, while in animal cells, a single Golgi complex is present. Golgi bodies were discovered by a scientist Golgi.

Golgi bodies are found in plant and animal cells. In animal cells, a single Golgi apparatus is present, but in plant cells, they are more. The Golgi complex of plants and lower invertebrates is called dictyosomes.

The Enzymes – Short Questions Answers

 Biology XI Notes

Chapter # 03
Short Questions Answers
Section II – Unity Of Life

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THE ENZYMES

Q.1: What are enzymes and what are the characters of enzymes?

Ans: ENZYMES:
Enzymes are the organic proteinaceous substances which catalyze chemical reactions in the living organisms. These are considered as bio-catalysts. They increase the rate of chemical reaction but are not consumed in the process:

The term enzyme was used by a scientist, Friedrich Wilhelm Kuhn in 1878.

Characteristics Of Enzymes:

• Enzymes are made up of proteins. They are big molecules with higher molecular weight.
• They can react with both acidic and alkaline substances due to the presence of proteins.
• In a biochemical reaction, only a small amount of enzyme is required as compared to the substrate.
• Enzymes are not consumed during the reaction. They remain unaffected and can be used again and again.
• The enzymes catalyze only specific reactions, that is, each individual enzyme is restricted in its catalytic activity to one particular reaction or one group of related chemical reactions.
• Their activities can be accelerated by certain ions or salts, called activators, such as Ni, Mn, Mg, Cl, etc.
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• They do not initiate the reaction, but only increase its rate by lowering the energy of activation.
• Some enzymes contain a non-proteinaceous part, called Prosthetic group.
• When many different enzymes catalyze the same chemical reaction, they are known as isoenzymes.
• The enzymes have a specific active centre which is attached to the substrate. If this active centre is bonded with another substrate, then the enzyme loses its activity.
• Enzymes are sensitive to change in temperature and pH. Heat, alcohol and concentrated solution of inorganic acids stop the activity of enzymes.

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Q.2: What are the types of enzymes?
OR
Describe the structure and composition of Enzymes?

Ans: STRUCTURE AND COMPOSITION OF ENZYMES: (TYPES OF ENZYMES)
The enzymes are basically proteinaceous in nature. They have relatively high molecular weight of 40,000 and Catalase has a molecular weight of 250,000.

Certain enzymes consist only of protein; they are called simple protein enzymes. Many enzymes have an attached non-protein group; they are known as conjugated protein enzymes or holoenzymes. It was proposed by Euler in 1932. The holoenzyme consists of two parts:

• The protein part, called apoenzyme.
• The non-protein part, called prosthetic group.

On the basis of prosthetic group, the holoenzymes are of two types:

• With inorganic ions: When the prosthetic group is an inorganic ion, it is called co-factor, such as Mg, Ca, K, Mn, etc. e.g. Phosphatase, carboxylase, Peptidase, Amidase, etc.
• With organic compound: When the prosthetic group is an organic compound, this organic compound is called co-enzyme. It has only 1% part of whole enzyme.
  e.g.
• NAD (Nicotine amide adenine dinucleotide)
• NADP (Nicotine amide adenine dinucleotide phosphate)
• ATP (Adenosine triphosphate)

Q.3: Describe the function or mode of action of enzymes?

Ans: MODE OF ACTION:
The action of enzyme depends upon the structure of enzyme. It has three-dimensional structure. It has an active site, which is of a particular size and shape. This active site is attached with substrate.

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Fischer (1898) proposed a theory about the action of enzyme, called key-lock theory. This theory was improved by Paul Filder and D.D. Woods. According to the theory, each enzyme can react with a specific substrate in the manner of a lock and key, just like a lock can be unlocked by a particular key.

The site of enzyme which is active and attached with substrate is called active site. This site helps in the catalytic action. Sometimes other molecules are connected with active site, but there is no bond formation and no chemical reaction.

Koshland in 1959 proposed another theory about the action of enzymes, called Induce Fit Model Theory. According to this theory, when enzyme combines with a substrate, some changes occur in the structure of enzyme, due to this change the enzyme performs its catalytic function in more effective manner.

Q.4: Describe the different factors of enzymes?

Ans: FACTORS AFFECTING ENZYME ACTIVITIES:
Following factors affect the enzyme activity.

• Temperature
• Substrate concentration
• pH
• Co-enzyme, activators, and inhibitors
• Water
• Radiation

Temperature:
Enzymes are sensitive to heat. They lose their activity at high temperature. The enzymes are denatured by heat, i.e., they are destroyed. The optimum temperature for most of the enzymes is 30°C to 37°C. At freezing point, they become inactive but are not destroyed; at 100°C, the enzymes are completely destroyed.

Substrate Concentration:
With the increase of substrate concentration, the rate of reaction is also increased. The enzyme molecule is much larger than its substrate. When concentration of substrate is low, the active sites on the enzyme molecule may not be occupied; thus, the enzyme does not work. When enzyme is saturated with substrate concentration, then the rate of reaction becomes independent of concentration, and further increase in substrate has no effect.

pH:
Each enzyme has an optimum pH at which the enzyme shows maximum activity. Change in pH can cause loss of its activity. It can be destroyed. When pH scale is shifted to the alkaline or acidic side, its activity is dropped. The optimum pH of pepsin is 1.6 (acidic), while pH of trypsin is 8.2 (alkaline).

Co-Enzymes, Activators, And Inhibitors:
Other groups, such as co-enzymes and co-factors, increase or decrease the enzyme action. These groups are of three types:

• Co-Enzymes:
  The organic molecule of enzyme is called co-enzyme. Its presence increases the activity of certain enzymes. Without these co-enzymes, their activity is stopped. e.g., COA, NAD, FAD, etc.

• Activators:
  Activators are the inorganic substances which increase the activity of enzyme; for example, Phosphatase enzyme has Mg⁺² as an activator, and Zn⁺² is the activator of enzyme carbonic anhydrase.

• Inhibitors:
  Inhibitors are the substances which decrease the activity of enzyme. These inhibitors either attach directly with enzyme or its activator, then the activity of enzyme is stopped. The inhibitors are of two types:

  • Competitive inhibitors
  • Non-competitive inhibitors

  Competitive inhibitors:
  These inhibitors resemble the normal substrate, these are attached with the active site of enzyme, so take part to reduce the function of enzyme. If the reaction is reversible, it can be controlled by increasing the concentration of substrate; in this way the substrate gets site of enzyme for attachment and reaction is proceeded.

  Non-Competitive Inhibitors:
  When certain substances are attached to a part of enzyme, away from active site, its activity is affected; such inhibitors are called non-competitive inhibitors. By the attachment of these substances, the enzyme becomes less active. The binding site other than active site is called Allosteric site.

• Water:
  Water also plays an important role to affect the activity of enzymes. In germinating seeds, water enters the body and helps to produce enzymes. The enzymes become active during germination.

• Radiation:
  Ultraviolet rays, n-rays, γ-rays, and x-rays destroy the activity of enzymes. 

Q.5: Write a note on Feedback inhibition?

Ans: FEEDBACK INHIBITION:
When product is formed in a chemical reaction, it binds with its enzyme; it is called feedback inhibition. It regulates the activity of enzymes. When the product is in more amount, it is attached competitively with enzyme's active site. The product is used, then inhibition is reduced, as a result of which more product is formed.

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In some enzymatic reactions, the end product binds non-competitively at allosteric site on the first enzyme of the reaction. This binding stops the reaction and no more product is formed.