CELL BIOLOGY AND HISTOLOGY - Home of Knowledge

CELL BIOLOGY AND HISTOLOGY

CELLS AND TISSUES OR CELL BIOLOGY AND HISTOLOGY

 

Question#1) Define Microscopy? What are different types of Microscope?

 

Answer:- Microscope; An optical instrument used for viewing very small objects, such as mineral samples or animal or plant cells, typically magnified several hundred times.

 

Microscopy:- Microscopy is the use of microscope to observe minute living organisms.

 

Invention of microscope:- The first compound microscope was developed by Zacharias Jansen and his son Hans in 1595 in Holland. It was simply a tube with lenses at each end and its magnification ranged from 3x to 9x.

 

Types of Microscope;- there are two main types of microscope.

Light Microscope:– A Microscope that works on the principle of light is called light microscope. A light microscope works by passing visible light through a specimen.

Types of light microscope;- there are 2 types of light microscope.

a)magnifying glass

a lens that produces an enlarged image, typically set in a frame with a handle and used to examine small or finely detailed things.

b)compound microscope:- an optical instrument for forming magnified images of small objects, consisting of an objective lens with a very short focal length and an eyepiece with a longer focal length

2)Electron Microscope:-Type of microscopes that use electrons rather than visible light to produce magnified images is called electron microscope. an electron microscope works on the principle of light. There are two types of electron microscope.

  1. A) Scanning electron microscope:-an electron microscope in which the surface of a specimen is scanned by a beam of electrons that are reflected to form an image.
  2. B) Transmission electron microscope;-

a form of electron microscope in which an image is derived from electrons which have passed through the specimen, in particular one in which the whole image is formed at once rather than by scanning.

 

Terms used in Microscopy: Two important terms are used in microscopy.

 

Magnification:- Magnification is the increase in apparent size of an object. It is an important factor in microscopy. It is denoted by X. A light microscope can magnify objects objects only about 1500 times. Electron microscope magnification power is 100000 to 2,50,000x.

Resolution;- Resolution or resolving power is the measure of the clarity of an image.

Resolution of human eye is 0.1mm. Human eye can differentiate between 2 points which are at least 0.1mm apart.

Resolution power of a compound microscope is 0.2µm. Resolution power of an electron microscope is 0.2nm.

 

 

Question#2) Write a note on history of formulation of cell theory?

Answer:- Cell:- Cell is the basic structural and functional unit of life (living organisms)

Ancient Greeks for the first time organized biological data about cells.

ARISTOTLE;- He state that plant and animals are somewhat related in their structures.

ROBERT HOOK:- He discovered cell in 1665.

ANTONIE VON LEEUENHOEK:- He observed microscopic or small creatures in pond and called them an animolecules (bacteria), this was the first observation of a living cell.

JEAN BAPTIST DE-La-mark (1809):- he proposed that “no body can have life if its parts are not cellular tissues”.

Mathias schleiden and Theodor Schwann:- cell theory was basically formulated by thes two biologists. Schlieden was a German botanist who stated that all plants are aggregation of individual cells which are fully independent.in 1839 Theodor schwann also stated that all animals are aggregation of individual cells which are fully independent. Thus Sclieden and Schwann proposed cell theory in its initial form and all credit goes to these two great scientists.

In 1885 Rudolf Virchow a German physician proposed that all cells arise from pre-existing cells. In 1862 Louis Pasteur provided experimental proof of this idea.

 

Basic Points of cell theory:- cell theory in its modern form include following principles;

All organisms are composed of one or more cells.

Cells are the smallest living things, the basic unit of organization of living organisms.

Cells arise by the divisions of pre-existing cells.

 

Question#3) Define A-cellular bodies?

Answer:- special bodies that shows characters of both living and non living are called a-cellular or sub cellular bodies or particles. Examples; virus, viroids and prions.

 

Question#4) write a note on cell wall? Describe structure and function of cell wall?

Answer:- CELL WALL;- The outer rigid protective layer of plants , bacteria and fungal cells is called cell wall.

Occurrence:_ present in plants , bacteria and fungi.

Chemical composition:- it composed of cellulose in plants. In bacteria it composed of murein (peptidoglycan), while in fungi it is composed of chitin.

Structure:Cell walls consist of 3 types of layers

Middle lamella: This is the first layer formed during cell division. It makes up the outer wall of the cell and is shared by adjacent cells. It is composed of pectic compounds and protein.

Primary wall: This is formed after the middle lamella and consists of a rigid skeleton of cellulose microfibrils embedded in a gel-like matrix composed of pectic compounds, hemicellulose, and glycoproteins.

Secondary wall: formed after cell enlargement is completed. The secondary wall is extremely rigid and provides compression strength. It is made of cellulose, hemicellulose and lignin. The secondary wall is often layered.

 

Functions;- *Thick walled cells provide mechanical support

  • Tubes for long-distance transport
  • Cutinized walls prevent water loss
  • Provide mechanical protection from insects & pathogens
  • Give specific shape to cell.

 

Question#5 ) Write a note on plasma membrane? What are its basic functions?

Answer:- Cell membrane or plasma membrane:- A thin membrane covering cytoplasm of a cell is called plasma membrane.

Occurrence:- occur in all living cells.

Composition and structure;-It is a double layered membrane composed of lipids, proteins and very less amount of carbohydrates. Fluid mosaic model shows that there is a lipid bi-layer in which proteins molecules are embedded. Carbohydrates are bound to proteins.

Functions;- 1)controlling exchange of materials between the cell and environment. 2) control ion flow. 3) give shape to cell.

Question#6) Define Cytoplasm?

Answer:- Cytoplasm:- The semi transparent and semi viscous substance present between cell membrane and nucleus is called cytoplasm.

Chemical composition:- it contain water , organic compounds (carbohydrates, proteins, lipids), enzymes and inorganic salts.

Functions:- it provide space for proper functioning of organelles and also acts as the site for various biochemical reactions. For example, Glycolysis (breakdown of glucose during cellular respiration) occurs in cytoplasm.

Question#7:- Write a short note on cytoskeleton?

Answer:- cytoskeleton:-

The cytoskeleton is a series of intercellular proteins that help a cell with shape, support, and movement. Cytoskeleton has three main structural components: Micro-filaments, intermediate filaments, and micro tubules. Micro tubules are composed of tubulin proteins and are used by cells to hold their shape . They are also major component of cilia and flagella.  Micro-filaments are thinner and are made of actin proteins.they help cells to change their shapes.

 

 Question#8) Write a comprehensive note on different types of organelles?

Answer:- Organelle:- Organelles are small structures within cells that perform dedicated functions

       Following are important organelles in a typical cell.

 Nucleus

 Ribosome

Mitochondria

*Plastids

Endoplasmic reticulum.

Golgi apparatus

 Lysosome

*Centrioles

Vacuoles.

 

Question#9) Define nucleus ? Describe the structure and function of nucleus?

 

Answer: NUCLEUS:- (Nucleus or kernal means central thing) It is the main organ in a eukaryotic cell that controls functions of all other organelles.

Location :- In animals cells it is present in the center, while in plant cells it is present at a side due to large vacuole.

Occurrence:-   a prominent nucleus present in eukaryotic cells.in prokaryotes nucleus is not present. Only nuclear materials DNA or Chromosomes are present.

Shape:- nucleus may be round, oval, crescent or of other shaped.

Structure:- Nucleus is bounded by double membrane called nuclear envelope or nuclear membrane. Nuclear membrane contain small pores called nuclear pores that make it semi permeable. Inside nuclear envelope a fluid called nucleoplasm is present. The nucleoplasm contain one or more nucleoli (singular is nucleolus). It is a dense spot where ribosomal RNA is formed and assembled to Ribosome. Chromosomes are visible in nucleus during interphase of cell division. In prokaryotes chromosome is only condensed form of DNA, while in eukaryotes chromosome is the combination of DNA and histone proteins. Each organism has a fixed number of chromosomes.

Functions :- It controls functions of all other organelles. It means it is control center for all activities of the cell.

Question#10) write a note on protein synthesizing factory of the cell?

Answer: Ribosomes (The protein synthesizing factory) :- (ribo from ribose or ribonucleic acid and soma means body) : Ribonucleic acids are small granular bodies involved in protein synthesis.

Structure and composition;- Ribosome composed of equal amount of ribonucleic acid and proteins. It is non membrane bounded organelle. It is composed of two units , one is small sub unit and the other is large sub unit.

Occurrence:- occurs both in prokaryotes and eukaryotes.

Function :- it is involved in protein synthesis, so called protein synthesizing factory.

 

Question#11) write a note on power house of the cell Mitochondrion?

Answer: Mitochondria or chondriosome (singular mitochondrion ,. Mitos means thread and chondrion means granules).an organelle found in large numbers in most cells, in which the biochemical processes of respiration and energy production occur.

Numbers:- ranges from one to thousands.

 

Occurrence:- found only in eukaryotes.

Structure

Mitochondria are shaped perfectly to maximize their productivity. They are made of two membranes. The outer membrane covers the organelle and contains it like a skin. The inner membrane folds over many times and creates layered structures called cristae. The fluid contained in the mitochondria is called the matrix.mitochondria have their own DNA and ribosome.

Function :- It is involved in respiration and thus produce energy for cell functions, that’s why mitochondrion is also called power house of cell.

 

Question#12) Define plastids? What are different types of plastids?

 

Answer: Plastids:-  (Plastos means molded) Plastids are membrane bounded organelles found in plants and photosynthetic protists( algae)

 

Types of Plastids:- there are three main types of plastids.

 

Chloroplasts :-(chloro means chlorophyll , plastos means molded) : Type of plastid that contain green pigment or chlorophyll is called chloroplast.

Chloroplasts are the food producers of the cell. The organelles are only found in plant cells and some protists such as algae. Animal cells do not have chloroplasts. Chloroplasts work to convert light energy of the Sun into sugars that can be used by cells. The entire process is called photosynthesis and it all depends on the little green chlorophyll molecules in each chloroplast.

 

STRUCTURE OF CHLOROPLAST:- Chloroplast containtwo membranes that protect the inner parts of the chloroplast. They are appropriately named the outer and inner membranes. The inner membrane surrounds the stroma and the grana (stacks ofthylakoids). One thylakoid stack is called a granum. Granum is the site for light reaction of photosynthesis while stroma is the site for dark reaction.

 

 

Leucoplasts (Leukos means white and plastos means molded“ ) are a category of plastid and as such are organelles found in plant cells. They are non-pigmented, in contrast to other plastids such as the chloroplast.Lacking photosynthetic pigments, leucoplasts are not green and are located in non-photosynthetic tissues of plants, such as roots, bulbs and seeds. They may be specialized for bulk storage of starch, lipid or protein.

 

Chromoplasts :-  (chroma means colour and plastos means molded) Chromoplasts are plastids that produce and store pigments.these are mostly present in flower petals and fruits. It gives colour to these and attract insects for pollination , thus helps in sexual reproduction.

 

Question#13) Describe the structure and function of endoplasmic reticulum?

Endoplsmic Reticulum (E.R)(endo means inner, plasma means fluid and reticulum means network of channels) :- Endoplsmic Reticulum is a network of interconnected channels that extends from cell membrane to nuclear envelope.

Types:- there are two types of endoplasmic reticulum.

 

 

 

Rough Endoplasmic Reticulum (R.E.R):- RER is so named because of its rough appearance due to numerous ribosomes that are attached to it. Due to presence of ribosomes , RER serves a function in protein synthesis.

 

Smooth Endoplsmic reticulum (S.E.R):- These are smooth in appearance so named SER. These are involved in lipid metabolism and in the transport of materials from one part of cell to another. It also detoxifies harmful chemicals that have entered cell.

 

Difference between rough and smooth endoplasmic reticulum;-

Rough Endoplsmic Reticulum

Smooth Endoplasmic Reticulum

1) This is granular

Non granular

2) RER contain Ribosome

SER contain no Ribosome

3) involved in protein synthesis

Involved in lipid formation

4) Extends from nucleus to plasma membrane.

Present inner to plasma membrane.

 

Question#14) Describe the structure and functions of Golgi apparatus?

 

Answer: GOLGI APPARATUS OR GOLGI BODIES OR GOLGI COMPLEX OR DICTYOSOMES:- A Set of flattened sacs stacked over each other in eukaryotic cell is called golgi body.golgi apparatus is named according to disscoverer name.

 The Golgi apparatus is also known as the Golgi complex or Golgi body. Along with the endoplasmic reticulum and lysosomes they form the endomembrane system. Found within the cytoplasm of both plant and animal cells, the Golgi is composed of stacks of membrane-bound structures known as cisternae. Although collectively they do not have any special name in plant cell rather the individual stake is called the dictyosomes. . Golgi apparatus are only present in eukaryotic cells.  Golgi apparatus modifies molecules coming from rough endoplasmic reticulum and packs them into small membranes bounded sacs called golgi vesicles these vesicles can be transported to various locations in cells or to its exterior in the forms of secretions.

 

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Question#15) Describe the formation and functions of lysosomes?

Answer: LYSOSOMES:-  (LYSO means Splitting, Break down or dissolution and Soma means Body) These are single membrane bounded organelles involved in the break down of materials.

Occurence:- present in all animal cells except mammalian RBC. In Plants its presence is in doubt. In prokaryotes these are absent.

Structure:- these are single membrane bounded organelles. Lysosome contain strong digestive enzymes and work in the breakdown of food and waste materials.

Function:- A lysosome during its function, fuses with the vacuole that contains the targeted material and its enzymes break down the material.In particular,

 

FORMATION:- lysosomes are formed by the fusion of transport vesicles budded from the trans Golgi network with endosomes, which contain molecules taken up by endocytosis at the plasma membrane.

 

Question#16) write a short note on centrioles?

Answer: Centrioles:-  A centriole is a small set of microtubules arranged in a specific way.   “Or”    Centrioles are hollow cylindrical organelles found in the cells of animals and many unicellular organisms.

Numbers:- each cell contain 2 centrioles. Both are collectively called as centrosome.

Location:- The centrioles are present near the exterior surface of the nucleus.

Structure:- each centriole are usually composed of nine triplets of microtubules (protein of the cytoskeleton)

Function of centrioles:
**Cell division
**Cellular organization.

 

QUESTION#17) Discuss the types of vacuoles keeping in view there major functions?

Answer: Vacuoles:- Vacuoles are fluid filled single membrane bounded organelles.

Numbers:- cells have many small vacuoles in their cytoplasm, however when a plant cell matures its small vacuoles fuses to form a large single vacuole in center.

Types of vacuoles:- The following are main types of vacuoles.

Central Vacuole:- This type of vacuole is present in plant cell and is responsible mostly for storage of water.

Contractile Vacuole;- This type of vacuoles are moveable and are present in unicellular organisms. Contractile vacuole eliminate waste from the cell.

Food vacuoles:- Food vacuole take in materials in the form of food from outside and also store them.

 

Question#18)) Compare animal cell and plant cell?

Answer: Comparison between plant and animal cell:

Differences — Similarities —

 

Animal Cell

Plant Cell

Cell wall

Absent

Present (formed of cellulose)

Shape

Round (irregular shape)

Rectangular (fixed shape)

Vacuole

One or more small vacuoles (much smaller than plant cells).

One, large central vacuole taking up 90% of cell volume.

Centrioles

Present in all animal cells

Only present in lower plant forms.

Chloroplast

Animal cells don’t have chloroplasts.

Plant cells have chloroplasts because they make their own food.

Cytoplasm

Present

Present

Endoplasmic Reticulum (Smooth and Rough)

Present

Present

Ribosomes

Present

Present

Mitochondria

Present

Present

Plastids

Absent

Present

Golgi Apparatus

Present

Present

Plasma Membrane

Only cell membrane

Cell wall and a cell membrane

Microtubules/ Microfilaments

Present

Present

Flagella

May be found in some cells

May be found in some cells

Lysosomes

Lysosomes occur in cytoplasm.

Lysosomes usually not evident.

Nucleus

Present

Present

Cilia

Present

Most plant cells do not containcilia.

 

Question#19) Compare prokaryotic and eukaryotic cells?

Answer: The distinction between prokaryotes and eukaryotes is considered to be the most important distinction among groups of organisms. Eukaryotic cells contain membrane-bound organelles, such as the nucleus, while prokaryotic cells do not. Differences in cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomalDNA.

Prokaryotes were the only form of life on Earth for millions of years until more complicated eukaryotic cells came into being through the process of evolution.

Comparison chart

Differences — Similarities —

 

Eukaryotic Cell

Prokaryotic Cell

Nucleus

Present

Absent

Number of chromosomes

More than one

One–but not true chromosome: Plasmids

Cell Type

Usually multicellular

Usually unicellular (some cyanobacteria may be multicellular)

True Membrane bound Nucleus

Present

Absent

Example

Animals and Plants

Bacteria and Archaea

Genetic Recombination

Meiosis and fusion of gametes

Partial, undirectional transfersDNA

Lysosomes and peroxisomes

Present

Absent

Microtubules

Present

Absent or rare

Endoplasmic reticulum

Present

Absent

Mitochondria

Present

Absent

Cytoskeleton

Present

May be absent

DNA wrapping on proteins.

Eukaryotes wrap their DNA around proteins called histones.

Multiple proteins act together to fold and condense prokaryotic DNA. Folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.

Ribosomes

larger

smaller

Vesicles

Present

Present

Golgi apparatus

Present

Absent

Chloroplasts

Present (in plants)

Absent; chlorophyll scattered in the cytoplasm

Flagella

Microscopic in size; membrane bound; usually arranged as nine doublets surrounding two singlets

Submicroscopic in size, composed of only one fiber

Permeability of Nuclear Membrane

Selective

not present

Plasma membrane with steroid

Yes

Usually no

Cell wall

Only in plant cells and fungi (chemically simpler)

Usually chemically complexed

Vacuoles

Present

Present

Cell size

10-100um

1-10um

 

 

 

Question#20) What are the basic relationships between cell structure and cell function?

Answer :- Cell structure and Function:- Bodies of all living organisms are composed of one or more cells. Each cell perform a specific function. It means cells are specialized in their function. It depends upon the structure of cell.

 

Difference between cells in their structure and function;- Cells of one type may differ from those of other types in the following respects.

Size and shape of cells:- A)Red blood cells are round to accommodate globular hemoglobin. B) Nerve cells are long for the transmission of nerve impulse. C) Xylem cells are tube like and have thick walls for conduction of water and support.

Surface area to volume ratio:- Root hair cells have large surface area for maximum absorption of water and salts.

Presence or absence of organelles:- a)Cells involved in making secretions have more complex endoplasmic reticulum and golgi apparatus. b) cells involve in photosynthesis contain chloroplast.

   Individual cells contribute in the functioning of the whole body. It can be explained by the following examples of the cells of human body:

  • Nerve cells conduct nerve impulse and thus contribute in coordination in body.
  • Muscle cells undergo contraction and share their role in movements in body.
  • Red blood cells carry oxygen and white blood cells kill foreign agents and so contribute in the roles of blood in transportation and defence.
  • Some skin cells act as physical barriers against foreign materials and some as receptors for temperature, touch, pain etc.
  • The cells of bone deposit calcium in their extra-cellular spaces to make the bone tough and thus contribute to the supporting role of bones.

 Question#21) EXPLAIN THAT CELL WORK AS AN OPEN SYSTEM?

ANSWER:-  Cell as an Open System

A cell works as an open system i.e. it takes in substances needed for its metabolic activities through its cell membrane. Then it performs the metabolic processes assigned to it. Products and by-products are formed in metabolism. Cell either utilizes the products or transports them to other cells. The by-products are either stored or are excreted out of cell.

 

Question#22) Write a detailed note on cell size and surface area to volume ratio?

Answer: CELL SIZE AND SURFACE AREA TO VOLUME RATIO

Cells vary greatly in size. The smallest cells are bacteria called mycoplasmas, with diameter between 0.1 ?m to 1.0 ?m. The bulkiest cells are bird eggs, and the longest cells are some muscle cells and nerve cells. Most cells lie between these extremes.Cell size and shape are related to cell function. Bird eggs are bulky because they contain a large amount of nutrient for the developing young. Long muscle cells are efficient in pulling different body parts together. Lengthy nerve cells can transmit messages between different parts of body. On the other hand, small cell size also has many benefits. For example human red blood cells are only 8 ?m in diameter and therefore can move through our tiniest blood vessels i.e. capillaries.

Most cells are small in size. In relation of their volumes, large cells have less surface area as compared to small cells. Figure shows this relationship using cube-shaped cells. The figure shows 1 large cell and 27 small cells. In both cases, the total volume is same:

Volume = 30 ?m X 30 ?m X 30 ?m = 27,000 ?m3

In contrast to the total volume, the total surface areas are very different. Because a cubical shape has 6 sides, its surface area is 6 times the area of 1 side. The surface areas of cubes are as follows:

  • Surface area of 1 large cube = 6 X (30 ?m X 30 ?m) = 5400 ?m2
  • Surface area of 1 small cube = 6 X (10 ?m X 10 ?m) = 600 ?m2 and
  • Surface area of 27 small cubes = 27 X 600 ?m2 = 16, 200 ?m.

 

 

 

 

 

Question#23) How passage of molecules occurs into and out of cells?

Answer:- Passage of molecules into and out of cells:- Cell membrane is a semi permeable membrane act as a barrier to most molecules. Cell membrane do it through the following phenomena:

 

Diffusion.

Facilitated diffusion.

Osmosis.

Filtration.

Active transport.

Endocytosis.

Exocytosis.

Question#24) Differentiate between Diffusion and Facilitated Diffusion?

Answer: 1) Diffusion:Diffusion is the movement of molecules from an area of higher concentration to the area of lower concentration i.e. along concentration gradient.

 Diffusion is a type of passive transport.passive transport is movement of molecules from a region of its higher concentration to a region of its lower concentration without expenditure of energy.

Through diffusion carbon dioxide, oxygen, glucose transported through diffusion.

 

2) Facilitated diffusion:- The movement of molecules from a region of higher of higher to a region of lower concentration with the help of transport proteins is called Facilitated diffusion.

 

The rate of facilitated diffusion is higher than simple diffusion. Many molecules do not diffuse freely across cell membranes because of their size or charge. Such molecules are taken into or out of the cells with the help of transport proteins present in cell membranes.

 

 

Question#25) Describe the rule of Osmosis in transport of materials?

Answer: OSMOSIS:

Osmosis is the movement of water across a semi-permeable membrane from a solution of lesser solute concentration to a solution of higher solute concentration.

The rules of osmosis can be best understood through the concept of tonicity of solutions. The term tonicity refers to the relative concentration of solutes in the solutions being.

The rules of osmosis can be best understood through the concept of tonicity of solutions. The term tonicity refers to the relative concentration of solutes in the solutions being compared.

  • A Hypotonicsolution has relatively less solute.
  • Isotonicsolutions have equal concentrations of solutes.
  • A Hypertonicsolution has relatively more solute.

 

Water balance problems or effect of different solutions on plant cell and animal cell:- In a solution with higher water potential than the plant cell (hypotonic solution) water enter the cell by osmosis and the cell become turgid but the animal cell bursts.in a solution of equal water potential (isotonic solution) the cell remains normal. In a solution with lower water potential (hypertonic solution) , water leaves the cell by osmosis and the living part of the cell, protoplast, shrinks.

 

Question#26)Describe how turgor pressure develops in plant cells?

Answer: Turgor Pressure:-Pressure exerted by fluid in a cell that presses the cell membrane against the cell wall. Turgor is what makes living plant tissue rigid. Loss of turgor, resulting from the loss of water from plant cells, causes flowers and leaves to wilt. Turgor plays a key role in the opening and closing of stomata. This pressure, turgidity, is caused by the osmotic flow of water from an area of low solute concentration outside of the cell into the cell’s vacuole, which has a higher solute concentration. Healthy plant cells are turgid and plants rely on turgidity to maintain rigidity. In contrast, this phenomenon is not observed in animal cells which have no cell walls to prevent them from being burst by the flow of water into the cell and must either continually pump out water, with a contractile vacuole, or live inan isotonic solution where there is no osmotic pressure

Importance of turgor:-1) maintain shape of plant cell. 2) Helps in opening and closing of stomata. 3) Opening and closing of flowers and leaves.

 

Question#27)Describe plasmolysis and deplasmolysis?

Answer: Plasmolysis: The loss of water by osmosis from a plant cell to the extent that the cytoplasm shrinks away from the cell wall. This happens when the cell is placed in a solution that has a higher solute concentration than that of the cell sap, i.e. it has a lower (more negative) water potential, since water always moves from an area of high water potential to an area of low water potential.

Deplasmolysis (Flaccidity):The entrance of water into a plasmolysed  plant cell, causing the cell membrane to return to the cell wall.

 

Question#28) What is the relationship among Osmosis and Guard cells?

Answer: Osmosis and Guard cells:

Stomata (openings) in leaf epidermis are surrounded by guard cells. During daytime guards cells are making glucose and so are hypertonic (have higher concentration of glucose) than their nearby epidermis cells. Water enters them from other cells and they swell. In this form, they assume a rigid bowed shape and a pore is created between them. At night when there is low solute concentration in guard cells, water leaves them and they become flaccid. In this form, both guard cells rest against one another and the opening is closed.

Question#29) what is the importance of semipermeable membrane for human life?

Answer: Application of knowledge about semi-permeable membranes:

The knowledge about semi-permeable membranes is applied for various purposes. We know that semi-permeable membrane is capable of separating substances. Artificially synthesized semi-permeable membranes are used for the separation of bacteria from viruses, because bacteria cannot cross a semi-permeable membrane. In advanced water-treatment technologies, membrane-based filtration systems are used. In this process, semi-permeable membranes separate salts from water (reverse osmosis).

Question#30) Define filtration?

Answer: FILTRATION

Filtration is a process by which small molecules are forced to move across semipermeable membrane with the aid of hydrostatic (water) pressure or blood pressure. In animals molecules are transported by blood and in plants by water. In this process only small molecules transported.

 

Question#31) Describe Active transport, Exocytosis and Endocytosis?

Answer: Active transport:-Active transport is the movement of molecules from an area of lower concentration to the area of higher concentration. This movement against the concentration gradient requires energy in the form of ATP.

In this process, carrier proteins of cell membrane use energy to move the molecules against the concentration gradient. For example, the membranes of nerve cells have carrier proteins in the form of “sodium-potassium pump”. In a resting (not conducting nerve impulse) nerve cell, this pump spends energy (ATP) to maintain higher concentrations of K+ and lower concentrations of Na+ inside the cell. For this purpose, the pump actively moves Na+ to the outside of the cell where they are already in higher concentration. Similarly this pumps moves K+ from outside to inside the cell where they are in higher concentration

 

ENDOCYTOSIS

It is the process of cellular ingestion of bulky materials by the infolding of cell membrane (see the steps of endocytosis in Figure 4.26).

The two forms of endocytosis are phagocytosis (cellular eating) and pinocytosis (cellular drinking). In phagocytosis cell takes in solid material while in pinocytosis cell takes in liquid in the form of droplets.

 

EXOCYTOSIS

It is the process through which bulky material is exported .. This process adds new membrane which replaces the part of cell membrane lost during endocytosis.

 

Question#32) What is tissue? Write a note on animal tissues?

Answer:- Tissue:- A group of cells that perform a specific function is called tissue.

       Animal tissues:- Tissues found in animals are called animal tissues. Important type of animal tissues are  epithelial tissue, connective tissue, muscle tissue, and nervous tissue..

 

1)  EPITHELIAL TISSUE

Epithelial tissue covers the outside of body and lines organs and cavities. The cells in this tissue are very closely packed together. This tissue has many types on the basis of the shape of cells as well as the number of cell layers. Some types include:

Squamous epithelium consists of a single layer of flat cells. It is found in lungs, heart and blood vessels. Here, it allows the movement of materials across it.

Cuboidal epithelium consists of a single layer of cube-shaped cells. It is found in kidney tubes, small glands etc. where it makes secretions.

Columnar epithelium has elongated cells. It is found in alimentary canal, gall bladder etc. where it makes secretions.

Ciliated columnar epithelium has elongated cells with cilia. It is present in trachea and bronchi and propels mucous.

Stratified squamous epithelium has many layers of flat cells. It is present in the lining of oesophagus and mouth and also over the skin. It protects the inner parts.

connective tissue:- These serves as connecting function. These are major supportive tissues. There is two types of connective tissues,. A) soft connective tissues like fatty tissues. B) Hard connective tissues like bones and cartilages. Blood is also connective tissue. The adipose tissue (found around kidneys, under skin, in abdomen etc.) is also a type of connective tissue. It provides energy and support organs.

3)MUSCLE TISSUE:

Muscle tissue consists of bundles of long cells called muscle fibers. It is the most abundant tissue in an animal. The cells of this tissue have ability to contract. There are three kinds of muscle tissue.

Skeletal muscles or striated muscles are attached to bones. Their cells are striated (striped) and contain many nuclei. They are responsible for the movements of bones.

Smooth muscles are found in the walls of alimentary canal, urinary bladder, blood vessels etc. They contain smooth (non-straited) cells, each with a single nucleus. They are responsible for the movement of substances.

Cardiac muscles are present in the wall of heart. Their cells are also striated but there is a single nucleus in each cell. They produce heartbeat.

Skeletal muscles are voluntary in action i.e. their contraction is under the control of our will. Smooth and cardiac muscles are involuntary in action i.e. their contraction is not under the control of our will.

 

4) NERVOUS TISSUE:- Nervous tissue is specialized to react to stimuli and to conduct impulses to various organs in the body which bring about a response to the stimulus. It forms communication system. These are mainly composed of neurons and found in brain spinal cord and nerves.

 

Q#33) write a detailed note on plant tissues?

 

Answer:  PLANT TISSUES

As in animals, the cells of plants are grouped into tissues with characteristic functions such as photosynthesis, transport etc. There are two major categories of tissues in plants i.e. simple tissues and compound (complex) tissues.

 

SIMPLE TISSUES

The tissues which are made of single type of cells, are called simple tissues. They are of two types i.e. meristematic tissues and permanent tissues.

 

A- MERISTEMATIC TISSUES

These tissues are composed of cells, which have the ability to divide. The cells are thin walled, have large nucleus and small or no vacuoles. They do not have inter-cellular spaces among them. Two main types of meristematic tissues are recognized in plants.

  1. Apical meristems are located at the apices (tips) of roots and shoot. When they divide they cause increase in the length of plant. Such growth is called primary growth.
  2. Lateral meristemsare located on the lateral sides of roots and shoot. By dividing, they are responsible for increase in growth of plant parts. This growth is called secondary growth. They are further of two types i.e. vascular cambium(located between xylem and phloem) and cork cambium (in the outer lateral sides of plant).

 

B- PERMANENT TISSUES

Permanent tissues originate from meristematic tissue. The cells of these tissues do not have the ability to divide. They are further classified into following types:

 

  1. Epidermal Tissues

Epidermal tissues are composed of a single layer of cells and they cover plant body. They act as a barrier between environment and internal plant tissues. In roots, they are also responsible for the absorption of water and minerals. On stem and leaves they secrete cutin (the coating of cutin is called cuticle) which prevents evaporation.

Epidermal tissues also have some specialized structure that perform specific functions; for example root hairs andstomata.

 

  1. Ground Tissues

Ground tissues are simple tissues made up of parenchyma cells. Parenchyma cells are the most abundant cells in plants. Overall they are spherical but flat at point of contact. They have thin primary cell walls and have large vacuoles for storage of food. In leaves, they are called mesophyll and are the sites of photosynthesis. In other parts, they are the sites of respiration and protein synthesis.

 

  1. Support Tissues

These tissues provide strength and flexibility to plants. They are further of two types.

 

 

  1. Collenchyma Tissue

They are found in cortex (beneath epidermis) of young stems and in the midribs of leaves and in petals of flowers. They are made of elongated cells with unevenly thickened primary cell walls. They are flexible and function to support the organs in which they are found.

 

 

COMPOUND (COMPLEX) TISSUES

A plant tissue composed of more than one type of cell is called a compound or complex tissue. Xylem and phloem tissues, found only in vascular plants, are examples of compound tissues.

 

  1. Xylem Tissue

Xylem tissue is responsible for the transport of water and dissolved substances from roots to the aerial parts. Due to the presence of lignin, the secondary walls of its cells are thick and rigid. That is why xylem tissue also provides support to plant body. Two types of cell are found in xylem tissue i.e. vessel elements and tracheids. Vessel elements or cells have thick secondary cell walls. They lack end walls and join together to form long tubes. Tracheids are slender cells with overlapping ends.

  1. Phloem Tissue

Phloem tissue is responsible for the conduction of dissolved organic matter (food) between different parts of plant body. Phloem tissue contains sieve tube cells and companion cells.Sieve tube cells are long and their end walls have small pores. Many sieve tube cells join to form long sieve tubes.Companion cells make proteins for sieve tube cells.

 

 

 

Question#34) Explain what would happen when a plant and an animal cell is placed in hypertonic solution?

Answer: In a solution with lower water potential (hypertonic solution) , water leaves the cell by osmosis and the living part of the cell, protoplast, shrinks.

 

Question#35) Describe the internal structure of chloroplast and compare it with that of mitochondrion.

Answer: STRUCTURE OF CHLOROPLAST:- Two membranes contain and protect the inner parts of the chloroplast. They are appropriately named the outer and inner membranes. The inner membrane surrounds the stroma and the grana (stacks ofthylakoids). One thylakoid stack is called a granum. Granum is the site for light reaction of photosynthesis while stroma is the site for dark reaction.

Comparison between chlorolplast and mitochondrion:

 

Similarities between chloroplast and mitochondrion: 1) Both are involved in the production of energy. 2) both are membrane bounded organelles. 3) both have their own DNA’s.

 

Differences between chloroplast and mitochondrion:

            CHLOROPLAST

       MITOCHONDRIA

1) Chloroplast is involved in photosynthesis.

1) Mitochondrion is involved in respiration.

2) chloroplast is a complex structure.

2) Mitochondrion is a simple structure.

3) Chloroplast is present only in plants and some bacteria and protists.

3) Mitochondrion is present in all living cell.

 

 

Question#36) Explain how surface area to volume ratio limits cell size?

Answer: Cell is the basic structural and functional unit of life. It means that cell controls all functions including all metabolic reactions (activities). The number of reactions increases as the volume of metabolic area increases. All the materials necessary for metabolism enter the cell through cell membrane by diffusion and osmosis. The larger the volume of the cell, larger the amount of materials that can enter into the cell. Each unit of volume requires a specific amount of surface area to supply its metabolism with raw materials. The amount of surface area available to each unit of volume varies with the size of cell. As cell grows its surface area to volume ratio decreases. At some point in its growth its surface area to volume ratio becomes so small that supply of raw materials decreases to a very large extent. At this point the cell cannot get larger. When a cell has much greater volume than surface area, then diffusion process is defficult in this case. And thus diffusion process is unsufficient for providing required amount of materials to the cell. The cell become unable to function properly and effectively in larger cells as compared to smaller cells and places a limit on cell size.

 

Question#37). Differentiate between diffusion and facilitated diffusion?

Answer: Both Simple diffusion and facilitated diffusion moves molecules from a region of  higher concentration to lower concentration . The basic difference is that simple diffusion donot involve carrier proteins  while facilitated diffusion involved carrier proteins embeded in the membrane for movement of molecules.

 

Question#38) Define the following?

 

Answer:1) Passive transport: The transport of materials from a region its higher to a region of  lower concentration without the expenditure of energy is called passive transport.

 

Phagocytosis: The process through which cell takes in large solid materials is known as phagocytosis.

 

Pinocytosis: The process through which cell takes in liquid materials is known as pinocytosis.

 

 

Selectively permeable membrane: Membrane that pass some of the materials while stop others is called selectively permeable membrane. Example: plasma membrane, nuclear membrane, etc.

 

Permeable membrane: Membrane that pass most of the materials through it is called permeable membrane. E.g, cloth.

Non-Permeable membrane: The membrane that do not allow materials to pass through it is called non permeable membrane. Example: polythene bag.

 

Isotonic solutions: Solutions containing equal amount of solutes are called isotonic solutions.

 

Solved Exercise

Understanding the Concept

 

Question#1. Explain the functions of cell membrane?

Answer: Please see answer of question number 5.

Question#2. Describe the structure of cell wall.

Answer: Please see answer of question number 4.

Question#3. Discuss nucleus structure and function.

Answer: Please see answer of question number 9.

Question#4. Describe the structure and function of endoplasmic reticulum and Golgi apparatus.

Answer: Please see answer of question number 13 and 14.

Question#5. Describe the formation and function of lysosomes.

Answer: Please see answer of question number 15.

Question#6. Explain what would happen when a plant and an animal cell is placed in a hypertonic solution.

Answer: Please see answer of question number 34.

Question#7. Describe the internal structure of chloroplast and compare it with that of mitochondrion.

Answer: Please see answer of question number 35.

Question#8. Explain the phenomena involved in the passage of matter across cell membrane.

Answer: Please see answer of question number 23, 24, 25, 30 and 31.

Question#9. Describe how turgor pressure develops in a plant cell.

Answer: Please see answer of question number 26.

Question#10. State the relationship between cell function and cell structure.

Answer: Please see answer of question number 20.

Question#11. Describe the differences in prokaryotic and eukaryotic cells.

Answer: Please see answer of question number 19.

Question#12. Explain how surface area to volume ratio limits cell size.

Answer: Please see answer of question number 36.

Question#13. Describe the major animal tissues in terms of their cell specificities, locations and functions.

Answer: Please see answer of question number 32.

Question#14. Describe the major plant tissues in terms of their cell specificities, locations and functions.

Answer: Please see answer of question number 33.

 

SHORT QUESTIONS

  1. State the cell theory.

Answer: Cell Theory: A theory in biology that includes one or both of the statements that the cell is the fundamental structural and functional unit of living matter and that the organism is composed of autonomous cells with its properties being the sum of those of its cells.

  1. What are the functions of leucoplasts and chromoplasts?

Answer: Please see answer of question number 12.

  1. Differentiate between diffusion and facilitated diffusion?

Answer: Please see answer of question number 37.

  1. What is meant by hypertonic and hypotonic solutions?

Answer:• A solution containing relatively less solute is called hypotonic solution.

A solution containing relatively more solute is called hypertonic solution

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