The Ell Flashcards

Question

What is endocytosis and it’s types?

Answer 1

Endocytosis is a type of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell. Endocytosis: It is the process in which the cell membrane helps to tal in material by infolding.in the form ofvacuole.Endoeytosis maybe(a) phagocutos;, in which solid particles are picked and ingested by the cell eif: W B.C picked un foreign bodies from the blood stream. In this way they destroy the harmful bacten which enter into our body. It is also called cell eating process (b) pinocytosis when liquid material in bulk, in the form of vesicles is taken in by endocytosis, the process is called pinocytosis which is also called cell drinking process.

Answer 2

Exocytosis: The process of membrane fusion and the movement of material out of a cell is called exocytosis.

Answer 3

Cell-wall is the non-living component of cell. It is secreted and maintained by living portion of cell called protoplasm. The chief structural component of plant cell wall is cellulose, a polysaccharide. In addition to cellulosé, pectin and a few other compounds may also be found in cell-wall.

Answer 4

A plant cell-wall can be differentiated into three layers, (i) middle lamella (i) primary wall (1.3 um thick and elastic) (ili) secondary wall (5-10 u m thick and rigid).

Answer 5

Middle Lamella: The first formed cell plate works as a cementing layer between two daughter cells and is called middle lamella. It is a common layer between two cells and the two cells are separated when middle lamella is dissolved. It is composed of calcium and magnesium pectates.

Answer 6

Primary wall is the first product of cell, synthesised by protoplast, deposits on either side of middle lamella. In young enlarging cells primary wall remains thin and elastic, becoming thick and rigid with the approach of cell maturity. Primary wall contains hemicellulose up to 50 percent, cellulose up to 25 percent and smaller amount of pectic substances. Femicelitiose forms matrix of the wall in which cellulose micro fibrils are embedded.

Answer 7

Secondary wall is formed by deposition of cellulose at the inside of primary wall. It mainly consists of cellulose or varying mixtures of cellulose. secondary wall may be modified through the deposition of Lignin and other substances.

Answer 8

At some places in the cell wall, the deposition of wall material does not take place, these places are known as plasmodesmata (Singular-plasmodesma), through which cellular contents of neighbouring cells remain in communication with each other.

Answer 9

In the cell wall cellulose deposits in the form of fibres. The cellulose fibres of each successive layer lie at different angles, increasing the strength of the cell-wall

Answer 10

It performs two important functions, firstly it provides a mechanical support and gives a definite shape and protection to the cell. It acts like a skeletal frame work of plants, particularly in vascular plants the cell walls provide the major supporting frame work. Secondly, being hydrophilic in nature it is capable of imbibing water and thus helps in the movement of water and solutes towards protoplasm i.e. Cell wall acts as permeable structure.

Answer 11

Nucleus was discovered by Robert Brown in 1831. It is the most important and prominent part of the cell which controls all its activities. It is commonly spherical or oval in shape, but tay be lobed or elongated and is surrounded by a membrane called nuclear membrane. It is double-¡membraned structure;, Usually cells have one, some have two or more nuclei. Some small organisms have several small nuclei per cell (coenocytic). The nuclear membrane is not a complete barrier. It is perforated by nuclear pores. Certain substances pass freely through these pores between the nucleus and the surrounding cellular substances

Answer 12

The Nucleus is filled with a protein rich substance called the Nucleoplasm or Karyolymph. In the nucleoplasm are numerous fine strands in the form of net work called chromatin net work or nuclear reticulum,

Answer 13

chromatin net work or nuclear reticulum, which is composed of nuclei acid, Deoxyribo-nucleic acid (DNA) and protein, During cell division, the chromatin changes to form chromosomes. Chromosomes contain the hereditary units called genes that carry the hereditary information from generation to generation.

Answer 14

The chromosomes vary in number from species to species, e.g. 8 in the fruitfully, 46 in humans, 20 in corn etc.

Answer 15

A typical chromosome is composed of two parts the arm and centromere. Before cell division each chromosome consists of two threads called chromatids. These two chromatids are joined by centromere. Each chromatid has one DNA molecule. The part of chromatids from centromere to end is called arm. The chromosomes are of different types, depending on the position of centromere. These types are:

Answer 16

(1) Metacentric: Chromosome with equal arms. in) Sub-metacentric: Chromosome with unequal arms. (in) Acrocentric or Subtelocentric: Rod like chromosome with one arm very small and the other very long. The centromere is subterminal. (iv) Telocentric: Location of centromere at the end of chromosome,

Answer 17

Also, within the nucleus is a spherical body called nucleolus. There may be more than one nucleoli in one nucleus. The number varies in different kinds of cells. It disappears during cell division and reappears afterwards. The nucleolus is believed to play an important role in the synthesis of ribonucleic acid and ribosome in Eukaryotic cells.

Answer 18

Amoeba, the cytoplasm has two distinct parts, an outer clear cytoplasm and an inner granular endoplasm in most cells.

Answer 19

The cytoplasm exhibits active streaming movements around the inner surface of the cell.' This movement is known as cyclosis.

Answer 20

The cytosol is a watery solution of salts, sugar, amino acids, proteins, fatty acids, nucleotides and other materials.

Answer 21

Observations under electron microscope, however, reveal that cytoplasm is nota simple colloid since it contains many different kinds of minute organelles and also a mesh of tiny filaments, the microfibrils that form a sort of skeleton, giving rigidity to cell and helping unicellular organisms in movement. Many of the orgenelles and even individual molecules of the cytoplasmare thought to be attached to the cytoskeleton.

Answer 22

The electron microscope reveals a complex network of channels, the endoplasmic reticulum (ER) which extends from plasma membrane to the nuclear membrane. It is an elaborate, tube like system of lipoprotein. There are two types of endoplasmic reticulum: (a) Agranulated or Smooth endoplasmic reticulum (SER) and (b) Rough or granulated endoplasmic reticulum (RER). Smooth endoplasmic reticulum is not associated with ribosomes. It is found in steroid producing cells like adipose cells (fat cells), interstitial cells, glycogen storing cells (liver) and the muscle cells. Rough or granular endoplasmic reticulum (RER), is heavily coated with ribosomes on its outer surface towards cytoplasmic surface. Rough ER, occurs mostly in protein synthesising cells. Such as those of the mammalian salivary glands and pancreas. Although most cells contain both rough and smooth ER but they vary from cell to cell.

Answer 23

Smooth E.R. in the skin converts cholesterol into the lipid compound called vitamin D whenever sunlight strikes the skin; this vitamin helps to maintain strong, healthy bones. North African women of Bedouin tribe, who wear dark, full length garment get very little exposure to sun light and thus the smooth E.R. in their skin cells cannot make vitamin D. As a result, these women sometimes develop soft, weak bones.

Answer 24

The endoplasmic reticulum has many important functions. Primarily, it serves as a supporting platform for the ribosomes. The ER, forms a structural framework of the cell with increased surface for various metabolic reactions, and they themselves take an active part by means of attached enzymes. ER also provide conducting pathways for import- export and intracellular circulation of various substances. ER also provides passage for Ribonucleic acid (RNA) to pass from the nucleus to various organelles in the cytoplasm, thereby, controlling chielly the synthesis of proteins. It also helps in detoxification of harmful drugs, storage and release of Ca'? ions and manufacture lipids.

Answer 25

Mitochondria or Chondriosomes are universally present in the cytoplasm of animals and plants. They appear as minute granules, vesicles, rodlets, threads or strings depending upon physiological conditions of the cells. They are seen to be in constant motion in living cells Mitochondria are the centre of aerobic respiration. Each mitochondrion is approximately about 0.2 to 1.0 nm in diameter and about 10 um long. There are two thin membranes which form the boundary of the mitochondrion. Both membranes are formed of lipids and proteins. The inner membrane forms irregular, incomplete partitions called Cristae. The interior of the mitochondrion contains fluid like organic matrix. with a number of chemical compounds in It. On the cristae are located enzymes and co-enzymes by means of which carbohydrates (starch) fatty acids (lipids) and amino acids (proteins) are metabolized to CO, and H,O. Energy in the form of ATP is released in this process which is stored within mitochondria. Adenosine triphosphate (ATP) is energy rich compound and it provides energy to the cells of organs or various activities. Hence mitochondria are known as Power House "where energy is stored and released wherever and whenever required by a living body. Mitochondria have a semi-autonomous existence in the cell; they have their own DNA that directs production of some of their component proteins and they can divide in half and thus reproduce independently of the cell's normal cell-division cycle.

Answer 26

Golgi apparatus (Dictyosome): The Golgi apparatus, like the endoplasmic reticulum, is a canalicular system with sacs, but unlike the endoplasmic reticulum it has parallel arranged, flattened, membrane bound vesicles which lack ribosomes. After the name of its discoverer Golgi, it was named as Golgi-body, The Golgi complex of the plants and lower invertebrates cells is usually referred as dictyosome. The Golgi bodies of plant cells and Golgi complex of animal cells basically have same morphology. Each of them is disc-shaped and consists of central, Nattened, plate like compartments called cisternae, peripheral network of inter connecting tubules and peripherally occuring vesicles and Golgian vacuoles. Usually in animal cells single Golgi apparatus is found in each cell, in plant cell, they may be more. Golgi apparatus are especially prominent in glandular cells The products of E.R, are modified and stored, and then sent to other destinations They perform the function of collection, packaging and distribution. In addition to its finishing work, the Golgi apparatus manufacture certain macromolecules by itself. Many polysaccharides secreted by cells, like cell-wall and cell plate material in plant cell are Golgi products.

Answer 27

spherical bodies, a few micrometer in diameter, surrounded by a single membrane, originated by Golgi apparatus and containing digestive enzymes. They occur only in the cytoplasm of animal cells, and function in the digestion of material taken into the cell by phagocytosis, as bacteria are ingested by white blood corpuscles. Normally they function as destroyers of foreign particles and worn out cellular components. When the membrane of lysosomes is ruptured, the cell undergoes chemical breakdown, or lysis. Since release of the enzymes, cause a cell to destroy itself by digesting its own proteins, lysosomes have been referred as "suicide sacs" and this process is called autophagy.

Answer 28

In 1965 W.G.Hers of Belgium explained how the absence of apparently unimportant lysosomal enzyme, oc-glucosidase, could lead to the storage of undigested glycogen accumulate in lysosome causing swelling of the organelles and irreversible damage to the cells and tissues. Diseases of this type, characterized by the deficiency of a lysosomal enzyme and the corresponding accumulation of undergraded substrate are called lysosomal storage disorder,

Answer 29

-Tay-sachs disease - Gaucher's disease - Krabbe's disease

Answer 30

Mental retardation, blindness, death by age 3.

Answer 31

Liver and spleen enlargement, erosion of long bones, mental retardation in infantile form only

Answer 32

Loss of myelin, mental retardation, death by age 2

Answer 33

They are especial protoplasmic double membrane bound organelles which function as chemical synthesizers and storage bodies. Plastids occur in greatest number in cells of plants and in the primitive single celled organisms, the Protoctists. There are three types of plastids e.g. Chloroplast, Chromoplast and Leucoplast.

Answer 34

Chloroplast (Gr: Chloro=green, Plast-living): The most common type of plastid is chloroplast containing chlorophyll which gives plant their green colour and is of great importance in the manufacture of food by the process of photosynthesis. Chloroplasts contain a substantial amount of DNA and are capable of programming synthesis of some other, new structural components. It has its own DNA and RNA.

Answer 35

Chromoplast (Gr: Chroma=colour, Plast=living): They have pigments like xanthophyll, and carotene. The chromoplasts are responsible for the various colour combinations found in flowers, fruits and other coloured parts except green.

Answer 36

Leucoplast (Gr: Leuco=white): These are colourless plastids which develop in the absence of sunlight and are thus commonly found in all under-ground parts of the plants. They store the food material as carbohydrates, lipids and proteins.

Answer 37

Proplastids are immature, colourless plastids occuring in cells of meristematic tissues. They consist of double membrane enclosing granular stroma. They multiply by division. In mature cells proplastids develop into chloroplast or chromoplast or leucoplast.

Answer 38

Energy. They have an ability to convert solar energy (light energy) into chemical/food energy by the process of photosynthesis, therefore called site of Photosynthesis.Chloroplasts belong to a groupof double-membrane bound orgenelles. They contain chlorophyll and its associated proteins. Inside the chloroplast other membranous system, arranged into Nattend.sa called thylokoids. In some regions thylokolds are stacked forming structure call grana (sing: granum). The fluid outside the thylokoid called stroma.

Answer 39

During photosynthesis chlorophyll captures the energy of sunlight and transfers it to other molecules in the thylakoid membranes. These molecules in turn transfer the energy to ATP and other energy-carrier molecules. The energy carriers diffuse into stroma, where their energy is used to derive the synthesis of sugar from carbon dioxide. Due to this movement of energy from one form to another, chloroplast is an energy converting organelle.

Answer 40

Peroxisome are single membrane bounded microbodies that contain enzymes for transferring hydrogen atom to oxygen, forming hydrogen peroxide (H,O,), a toxic molecule that is immediately broken down to water by the enzyme catalase. Peroxisome are abundant in cells that are metabolizing alcohol. Peroxisome are believed to help in detoxification of alcohol. They are found in plants and animals. Peroxisomes contain enzymes that breakdown damaging compounds e.g peroxisomes within liver and kidney cells breakdown and detoxify fully, half of the alcohol a person drink.

Answer 41

Another type of microbodies found in plants only which are also consider as specialized peroxisomes called glyoxysomes. They are found in the fat storing tissues, Each glyoxysome has a single layered bounding membrane enclosing a fine granular stroma. Glyoxysome contain enzymes that initiate the conversion of fatty acid into sugar.

Answer 42

The cytosol is organised into a three dimensional network of Abrous proteins called cytoskeleton. It plays fundamental roles in mitosis, meiosis, cytokinesis, cell-wall deposition, the maintenance of cell-shape and cell differentiation. There are three types of cytoskeleton elements found in cells. Microflaments Intermediate filaments Microtubules

Answer 43

Microflaments are solid strand of about 7 nm in diameter and several cm in length especially in muscle cells. They are consists of two actin chain that intertwine in a helical fashion, some microfilaments also contain myosin protein with actin. They perform function of muscle Contactor , changes in cell shape, including division of cytoplasmic in diving animal cells, cytoplasmic streaming movements of pseudopodia

Answer 44

Intermediate filaments are solid strands of 8 to 11 nm in diameter, 10 to 100 um in length. They are intermediate in between microtubules and microfilaments. They are made up of atleast five different types of protein, form rope like polymer of fibrous protein. Unlike the other two types of cytoskeleton elements, intermediate filaments do not assemble and disassemble. Therefore, they are Important in maintaining the shape of cell, attachment of muscle cells, support of nerve cell processes (axon).

Answer 45

Microtubules are hollow tubes with an outer diameter of 25 nm, may be more than 50 um in length. They are composed of protein, tublulin. A single micro tubule consists of hundreds of thousands of tubulin sub-units usually arranged in 13 columns called proto filaments, they are responsible for the movement of Chromosomes during cell division, movement of organelles within cytoplasm, movement of cilia and flagella.

Answer 46

'These are so named because they contain high concentration of Ribonuclei. acid (RNA). These small structures are sites of protein synthesis in all cell types prokaryotic As We l) nos eukaryotto cells., Ribosomes are found freely dispersed in fire cytoplasm in prokaryotic cells, But in eukaryolle cellS' they Are bund Tree is well as attached to endoplasmic reticulum. They are compeysed°bout-58 or more diferent pinds of proteins, There are millions of these per cell, and tney are all identical kibosomes may be regarded as "Protein factories Under the hirection of the nucleus they produce the protein needed by the cell.

Answer 47

Each ribosome consists of two unequal subúnits. The larger subunit is dome- shaped and smaller one forms a cal kn the flat surface of the bigger subunit ribosomes adhere themselves to endoplasmie reticulum by the larger subunits. Although ribosomes are among the smallest organelles, they are among the most vital cellular components. Recent investigations reveal that the ribosomes are manufactured in the nucleolus from where they are transferred to the cytoplasm through nucleopores. Ribosome may be regarded as 'protein factories' made up of two unit, large and small.

Answer 48

Microtubules radiate from a microtubkye organizaing center near the nucleus, Called centrosome (centro = nucleus, soma = body). Within the centrosome of an animal cell is a pair of centrioles, Centrioles are short; barrel - shaped structures of microtubules,lying perpendicular to one another. Each centriole is composed of nine sets of triplet microtubules arranged in a ring. When a cell divides, the centrioles replicate, move to opposite side of the cell and thread like fibres begin to radiate from centrioles in all directions called astral rays Centriole are the dark bodies appear near nucleus before cell-division in animal and low plant's cell.

Answer 49

Genrally vacuoles (except food vacuole) are nonprotoplasmic liquid filled cavities in the cytoplasm and are surrounded by a membrane called the tonoplast. The tonoplast is selectively permeable, it allows certain substances to enter in the vacuole. in animal cells they are temporarily formed at the time of their need. These are conspicuous organelles of plant cells. They are more prominent in mature cells whereas less prominent in immature cells. The vacuoles in plant cells are filled with cell sap and act as store house, which often plays role in plant defence. which is necessary for plant cell enlargement. In animal cells, lysosomes are rich in hydro lytic enzymes, including proteases, ribonucleases and glycosidases. Plant vacuoles sometimes act as lysosome as they contain hydrolytic enzymes and after death of cells tonoplast lose its differential permeability and its enzyme causes lysis of the cell.

Answer 50

They are called plus strand because they act directly as mRNA after infecting a host cell, attaching to the host's ribosomes and being translated. As indicated by their name, these viruses lack envelopes and consist only of a nucleic acid core surrounded by a protein capsid. They infect plants and bacteria, causing polio and cold in human beings.

Answer 51

The enveloped Plus Strand RNA viruses, all of which parasitize animals, are distinguished from the members of the preceding group by their lipid-rich envelopes. They infect arthropods and vertebrates, causing Leukemia and yellow fever in human beings.

Answer 52

Minus-Strand RNA viruses are distinguished from Plus-Strand RNA viruses because they carry the RNA strand complementary to the mRNA that carries the genetic information of the appropriate mRNA, which then functions in the cell. They infect plants and animals, causing flu, mumps andrabies in human beings.

Answer 53

A virus that is replicated in a host Cell via the enzyme reverse transcriptase to produce DNA from its RNA genome. They are envolped viruses. Retroviruses are either single stranded RNA (e.g. HIV) or double stranded DNA (e.g. Hepatitis B) viruses.

Answer 54

These are double-stranded, icosahederal RNA viruses, infect plants and animals, causing colorado tick fever in human beings.

Answer 55

Many DNA viruses have Small genomes; some of these viruses have Single Stranded DNA, others have Double-Stranded DNA. Among them are the parvoviruses which infect animals, they are icosahedral and about 20 nanometers in diameter, They infect animals causing viral hepatitis and wartz in human beings.

Answer 56

The herpesviruses, one of the major groups of large-genome, double stranded DNA viruses. They cause herpes shingles, cancer and poxes in human

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