Science Chapter 6 Tissues

Difference between  the plant cell and the animal cell are:

The plasma membrane provides shape and support to the cell. It is a selectively permeable membrane and keeps a check on the movement of substances in and out of the cell by the process of diffusion or osmosis.  Thus, if the plasma membrane is ruptured it cell contents will be in direct contact with the enviroment  and movement of substances will no longer be selective. Free movement may lead to the death of the cell.

Golgi apparatus perform the function of storage, packaging and dispatch of substances synthesised by endoplasmic reticulum. It transports the material in and out of the cell. It is also reponsible for the formation of lysosomes. Therefore, if there were no golgi bodies then there would be no storage, packaging and transport of material. The formation of lysosomes will not take place in the absence of Golgi apparatus. All this will lead ultimately to the death of Golgi apparatus.  

Mitochondria are known as ‘Power House’ of the cell.They are called so because they produce energy in the form of ATP molecules. ATP is the energy currency of the cell. It is stored and used for making new compounds and mechanical work. 

The proteins are synthesised on the Rough Endoplasmic Reticulum (RER) and the ribosomes attached to it. While the lipids are synthesised on the Smooth Endoplasmic Reticulum (SER).

Osmosis is the passage of water from a region of its high concentration to the region of its lower concentration through a semipermeable membrane.

a) Water gathers in the hollowed portion of potato B and C because the plasma membrane of potato cup act as semipermeable membrane and the concentration gradient causes the water to move from the cell to the hllowed portion by the process of osmosis.

(b) Potato cup A is necessary as it acts as a control. This shows that osmosis occurs only when there is concentration gradient and a living semi permeable membrane. 

(c) (i) In the potato cup A, there is no concentration gradiesnt for osmosis to occur.

(ii) In the potato cup D, the semi permeability of potato membrane is lost due to boiling. So, no water movement occurs.

Compound microscope.

No, all organisms have basic building units called cells. Cells are the basic structural and functional unit of any living cell.

To the specific function they perform.

Cell organelles.

Plasmodium (Malaria parasite) and Yeast are unicellular organisms.

Amoeba, Paramoecium, Euglena are single celled organisms.

Compound microscope

The three features found in almost every cell are plasma membrane, nucleus and cytoplasm.

Plasma membrane.

Cell wall.

Cell wall provides shape and protection to plant cell.
Cell membrane provides protection, shape and flexibility to the cell. It acts as a selectively permeabl Allows only selected materials to move in and out of the cell through the process of diffusion or osmosis.

The memberane bound little structures found within the cell are called as cell organelles. They are the functional units of a cell.

An ostrich egg.

Mycoplasma.

The nerve cell.

Dead.

Living.

Diffusion is the spontaneous movement of a substance from a region of its high concentration to the region where its concentration is low. For example the movement of CO₂ or O₂ across the cell membrane.

Diffusion.

Plasma membrane regulates the entry and exit of materials in a cell. It allows the movement of only certain substances  while prevents the others from doing so. Thus, it is called selectively permeable membrane.

Osmosis.

The movement of water from its region of higher concentration to the region of its lower concentration through a semipermeable membrane is called osmosis.

Endocytosis is the process of engulfing food and other materials by a cell from the external environment. The flexibility of the cell membrane helps in the process For example - Amoeba engulf food through this process.

Depending on the concentration difference between the cell and the solution the following three things could happen:

(i) If the solution surrounding the cell is less concentrated (hypotonic) than the cytoplasm, the water will move into the cell, i.e., the cell will gain water and swell.

(ii) If the solution has the same concentration as that of cytoplasm of cell, there will be no net movement of water across the cell membrane, i.e., no gain or loss of water from the cell.

(iii) If the solution is highly concentrated (hypertonic) as compared to the  cytoplasm, i.e., the solution is concentrated, the cell will lose water by osmosis.

The following results are observed

(i) When an egg without shell is placed in concentrated salt solution for 5 minutes - The egg shrinks due to loss of water by the process of osmosis. 

Reason. The egg membrane acts as semipermeable membrane. The water concentration inside the cell is more therefore water moves out of the cell.

(ii) When an egg without shell placed in concentrated salt solution for 5 minutes. - The egg gain water and swells.

Reason. The concentration of water is much more on the outside thus water moves into the egg cells through egg cell membrane by osmosis.

Chromatin material is the entagled mass of thread like structures which are organised to formchromosomes during the time of cell division. 

Genes are the functional segments of DNA present linearly on chromosomes. 

Cytoplasm is the fluid content present inside the cell. It houses all the cell organelles.  

Robert Hooke 

Cell wall is a rigid structure found outside the plasma membrane of the plant cells. It is composed of cellulose - a fibrous polysaccharide. 

Cell wall performs the following functions in the plant cell:

(i) It gives a definite shape to the cell.

(ii) It provides rigidity and strength to the cell.

(iii) It protects the cell.

(iv) It also withstands the osmotic pressure which is developed by cell contents and protects the cell from bursting.

Nucleus. It is the control centre of the cell. It is covered by an double layered envelope called the nuclear membrane . There are numerous pores in the nuclear membrane for the transfer of materials. It consists of a dense region called nucleolus. The nucleus has chromatin which forms the chromosomes during cell division. Chromosomes consists of DNA and protein. The genes are functional unit of DNA which are responsible for the hereditary characters of an organism. 

Genes are the functional segments of  DNA (deoxyribonucleic acid) molecule. Genes are arranged in a single linear order along the chromosome. They are formed due to condensation of chromatin material at the time of cell division. It is the unit of heredity which is transferred from a parent to offspring. Genes are found inside the nucleus. 

When we observe the cheek cells under microscope we observe that the cells are flat and polygonal in shape with irregular boundaries. They are arranged edge to edge forming a delicate sheet of cells. There is a darkly stained dot like structure which represents the nucleus. 

Chromosomes are rod shaped structures found in the nucleus of the  dividing cell. Chromosome  is composed of DNA and protein. It contains information for inheritance of features from parents to next generation.

Onion peel cell is an eukaryotic cell.

Reason. Onion peel cell contains a well defined nucleus enclosed within a nuclear membrane.

A eukaryotic cell has a definite nucleus that is a  nuclear membrane bound nucleus. It also contains membrane bound organelles in its cytoplasm.

Nucleoid is the undefined nuclear region containing only nucleic acids, in the prokaryotic cells. It is not bounded by a nuclear membrane and lies in direct contact with the cytoplasm.

Bacteria and Cyanobacteria (earlier called blue green algae) are prokaryotic unicellular organisms.

A cell which does not have a definite nucleus that is the nucleus is not bounded by a nuclear membrane is called as a prokaryotic cell. It has an undefined nuclear region called nucleoid. 

Cell theory was proposed by  Schleidn and Schwann and Rudolf virchow. It states that:

(i) the cell is the basic unit of life. 

(ii) all the plants and animals are composed of cells and that

(iii) all cells arise from pre-existing cells.

Functions of Cell:

(i) It acts as the funtional and structural unit.

(ii)  Synthesis and transport of substances.

(iii) Energy Production.

(iv) Cellular replication.

Nucleus

Ribosomes are the sites for protein synthesis.

Chloroplast.

Endoplasmic reticulum forms a network system and helps in the transport of substances in and out of the cell. It also provides the attachment sites for ribosomes which are the site for protein synthesis. The endoplasmic reticulum helps in the synthesis of lipids and fats. 

Viruses lack any membranes. Hence, they do not show characteristics of life until they enter a living cell and use its cell machinery to multiply.

Mitochondria.

Lysosome.

Ribosomes.

(i) Rough endoplasmic reticulum (RER) has ribosomes on its surface and therefore helps in the  synthesizing proteins.

(ii) Smooth endoplasmic reticulum (SER) helps in the manufacture of fat molecules or lipids.

Centrioles are found an animal cells.

Centrosome helps in cell division in animal cells. 

Endoplasmic Reticulum  is a membranous network, enclosing a fluid-filled lumen. Its main functions are:

(i) Synthesis of proteins (Rough ER)

(ii) Synthesis of lipids and their secretion (SER).

(iii) Secretion of enzymes and hormones inside the cell or when secreted out of the cell.

(iv) ER also produces substance for new cellular parts (especially cell membrane).

(v) ER provides internal support (mechanical support) to the cell.

Golgi apparatus consists of flattened membranous sac like structures called Cisternae. These are placed one above the other (stacked) in parallel rows. These membranes are often in connections with membranes of ER.

These are functions of Golgi apparatus:

(i) Golgi apparatus is the secretory organelle of the cell. It packages and dispatches the material synthesized in the cell to intracellular (plasma membrane and lysosomes) and extracellular targets.

(ii) Golgi complex is also involved in the formation of lysosomes and peroxisomes.

(iii) Golgi apparatus is also involved in the synthesis of complex substances such as polysaccharides, glycoproteins etc from simple substances.

(iv) It helps in storage, modification and packaging of synthesised substances in the vesicles.

Lysosomes are membrane bound vesicles act as waste disposal system of the cell. Lysosymes have digestive enzymes which help in digesting foreign material as well as worn-out cell organelles. The enzymes breakdown the organic substances. Lysosymes are called the suicide bags of the cell as they help in the digestion of damaged, worn out parts of its own cell. 

Functions of Lysosomes:

(i) Extracellular digestion. Sometimes lysosome enzymes are released outside the cell to break down extracellular material. 

(ii) Digestion of foreign material. Lysosomes also destroy any foreign material such as bacteria.

(iii) Cellular digestion. Lysosomes help in the breakdown and digestion of various substances inside the cell

(iv) Waste disposal - Lysomes acts as suicidal bags and digest any damaged or worn out cells of the cell they are present in. 

Mitochondria are rod-shaped cell organelle found in the cytoplasm. Each mitochondrion  is a double membrane bounded structure. The outer membrane of mitochondrion is smooth. But the inner membrane of the mitochondrion is folded inwardly into the matrix of mitochondrion forming finger-like projections called Cristae. Cristae greatly increase the surface area of the inner membrane. Mitochondria also has its own DNA. It helps in the synthesis of ATP which is the energy currency of the cell. 

Functions of Mitochondria are:

(i) They help in cellular respiration.

(ii) The stepwise released energy by the oxidation of food (usually glucose) is converted into chemical energy in the form of ATP (adenosine triphosphate) molecules.

(iii) They have their own DNA and proteins hence they prepare their own proteins. 

ATP stands for Adenosine triphosphate.

ATP is the energy currency of the cell. The stored ATP is used for the synthesis of new chemical compounds and mechanical works. 

Plastids are found in plant cells only. Plastids are double membrane bounded structures.  It has an extensive and numerous membrane layers embedded in a material calle stroma. They also have their own DNA and ribosomes. . TThey are of two types of plastids - chromoplasts and leucoplasts.

Leucoplasts are colourless or white plastids and do not contain any pigment. Function. Leucoplasts are involved in formation and storage of starch and oil drops. For example, Amyloplasts found in potato tuber store starch.

Chromoplasts are coloured plastids i.e., They may contain pigment of different colours. For example, Blue green chromoplasts found in blue green algae.

The most important chromoplasts are chloroplasts which contain green pigment, known as chlorophyll. Chloroplasts are the kitchen of the cell and are very important because they trap solar energy and prepare food for all non-green organisms, directly or indirectly. The process of preparing food by green plants is known as Photosynthesis. 

Other non-green chromoplasts are responsible for characteristic colour of flowers and fruits.

The shrinkage or contraction of the protoplasm away from the cell wall when kept in an hypertonic solution is called plamolysis. 

Vacuoles are are single membraned storage sacs for solid or liquid content. The membrane covering the vacuoles is called tonoplast. The fluid in the vacuoles is called cell sap. In most plant cells, vacuole is big and centrally placed. The liquid cell sap of vacuole provide turgidity and rigidity to plant cells. In animal cells either they are absent or are small. 

In an unicellular organism have a single cell and  all functions are performed by the same cell. Multicellular organisms have more than one cells. The cells are present in colonies or are differentiated and specialsed into groups that carry out specific functions. Multicellularity provides division of labour. This helps the organisms to perform various life processes in a better way.

 Internal structure of Plant and Animal cell. 

Lysosomes contain digestive or hydrolytic enzymes. When a cell gets damaged or worn out the lysomes burst releasing the enzyme that digest their own cell. Thus they are called as ‘suicide bags’.

(i) Structure found only in animal cells:centrosomes, golgi apparatus.

(ii) Structures found only in plant cells : cell wall, plastids, polar caps, dictyosomes and big vacuoles.

Cell is the fundamental unit of a living organism.

The cell is enclosed by an outer Plasma membrane which is selectively permeable. Plant cells have an additional cell wall located outside the plasma membrane. The cell is filled with a translucent viscous substance  called the cytoplasm in which are embedded the organelles. The control centre of the cell is the nucleus, it contains all the information necessary for the cell to function and to reproduce further cells of the next generation.

Surrounding the nucleus is the Endoplasmic reticulum (ER) which may have the ribosomes which are the site of protein synthesis. Ribosomes, a granular structures, also found in cytoplasm.
The power house of the cell is the mitochondria which helps in releasing energy by the oxidation of food in cell.
There are flat membranous secretory structures in the cell the Golgi bodies. In plant cells there is an additional structure the chloroplast which is the site for photosynthesis.
Cells also contain lysosomes which are also called suicide bags. They digest and remove the unwanted debris of the cell. Centriole helps in cell division. Cytoplasm also contains vacuoles filled with cell sap.
In plant cells vacuole are present which act as storage sacs. Vacuoles are large in plant cells nd small or non existeant in animal cells.

The main regions of all cells are:

(i) The plasma membrane

(ii) The nucleus and

(iii) The cytoplasm.

The two cell organelles that contain their own genetic material are:
(i) Mitochondria and (ii) Chloroplast.

Each cell has got cell organelles and each cell organelle performs a special function, e.g., making of new material, removal waste from the cell, release of energy etc. If the organization of a cell is destroyed, the functioning of the cell organelle will be disturbed, and cell will not be able to perform the basic functions. Thus, cell will ultimately die.

Nucleolus.

Tissue is the group of cells similar in structure that work together to achieve a particular function. For example - blood, bone , xylem and phloem etc

Xylem formed of four types of elements. They are (i) tracheids (ii) vessels (iii) xylem parenchyma (iv) xylem phloem.

Simple tissues are made of one type of cells which coordinate to perform a common function. For example parenchyma, epidermis etc

Complex tissues are made of more than one type of cells. All these coordinate to perform a common function. For example Vascular tissues. 

Functions of stomata:

(i) Exchange of gases, particularly C0₂ and 0₂, with atmosphere.

(ii) Loss of water in the form of vapour during transpiration.

The specific function of cardiac muscle is to contract and relax rhythmically throughout life.

(a) Squamous epithelium

(b) Tendon

(c) Phloem

(d) Adipose tissue

(e) Blood

(f) Nervous tissue.

(i) Skin — Epithelial tissue

(ii) Bark of tree — Epidermal tissue

(iii) Bone — Connective tissue

(iv) Lining of kidney tubule — Cuboidal epithelium

(v) Vascular bundle — Complex permanent tissue

Parenchyma is found in cortex and pith of root and stem. When it contains chlorophyll, it is called chlorenchyma, found in green leaves. 

Cells of epidermis form a continuous layer without intercellular spaces. It protects all the parts of the plant. It performs the function of absorption in the roots. It may have a waxy covering called cutin which prevents loss of water in desert plants.

Cork act as a protective tissue in the following ways:

(i) Its cells are dead and compactly arranged without intercellular spaces thus it provides mechanical strength and protection to the cell.

(ii) They also have deposition of suberin on the walls that makes them impervious to gases and water. Thus, cork protects the underlying tissues from excessive loss of water, adverse external environment and mechanical injuries.

This diagram is of xylem complex tissue.

Location. It is found in vascular bundle.

During development, from zygote (formed by the union of egg and sperm) a large number of cells are formed. These cells undergo differentiation and division of labour to produce various specialised cells to perform different functions in the living body. These cells group together to form tissues. 

Plants are stationary or fixed, they do not need in a plant are supportive, which provide them with structural strength. Most of these tissues are dead as dead tissue provide more strength. The growth in plant tissues is limited to certain regions only. 

A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue. For example phloem, blood etc.

Multi-cellular organisms show division of labour because a particular function is carried out by a cluster of cells (tissue) at a definite place in the body. The tissue is arranged and designed so as to give the highest possible efficiency of function.

The two main group of plant tissue are
(i) meristematic tissues and (ii) permanent tissues.

Meristematic divide frequently to give rise new cell. So, they need dense cytoplasm and soft cell wall. Vacuoles are full of cell sap and provide turgidity and rigidity to the cell. Presence of vacuoles may cause hindrance in cell division. Thus meristematics cells lack vacuoles. 

The meristematic tissues are present only at the growing regions such as shoot tip, root tip and cambium parts of the plant.

The characteristics of meritematic cells are:

(i) thin cell walls.

(ii) abundant or dense cytoplasm and single large nucleus.

(iii) spherical, oval, polygonal or rectangular shape.

(iv) no intercellular spaces between them.

(v) either no vacuoles at all or a few vacuoles.

(vi) highly dividing. 

The main function of meristematic tissue is to produce new cells continuously for increasing cell number,and growth of the plant.

On the basis of location The meristem can be classified into three types:

(i) Apical meristem is present at the tip of stem, root and their branches.

(ii) Intercalary meristem is found at the leaf base,  above or  below the nodes.

(iii) Lateral meristem is found in vascular bundles and known as cambium. The meristematic tissue, which may appear in most of dicot plants, is known as cork cambium.

Plant permanent tissues are group of cells which have  lost the ability to divide. They are produced by meristematic tissue but lose the ability to divid and are differentiated to perform particular function/functions. 

Simple permanent tissues consists of one type of cells only. The cells are similar in origin, structure and functions. For example parenchyma, collenchyma etc. 

These are Simple permanent plant tissues:
(i) Parenchyma
(ii) Collenchyma 
(iii) Sclerenchyma.

Parenchyma. It is the basic or fundamental tissue found in plants. Parenchyma acts as a packing tissue and therefore, it is found in between other tissues. Parenchyma tissue cells store starch, proteins, minerals etc.
i. These are thin walled, circular or polygonal and isodiametric, i.e., having similar sides. 
ii. They are living and consists of cytoplasm and a nucleus.
iii. There are many small or a single big central vacuole.
iv. They may not have intercellular space or may have intercellular spaces. 
Some parenchymatous cells have pigmented chromoplats. The most important are the cells which contain a number of chloroplasts and the tissue is green, it is known as chlorenchyma.
Some non-green chromoplasts provide different colours to flowers and fruits.
Sometimes the cells contain big air spaces in between them. Such tissue is known as aerenchyma. On the other hand some tissues are green, containing many air spaces then it is called spongy tissue.

The arenchyma performs the following functions.

(i) They store and assimilate food.

(ii) They provide mechanical support as they maintain the turgidity of cells.

(iii) Store waste products such as tannin, gum, crystals of chemicals etc.

(iv) Chlorenchyma containing chloroplasts prepare food through photosynthesis.

v) Parenchymatous cells containing non-green chromoplasts contain pigment that give characteristic colour to flowers (e.g., petals) and fruits.

Collenchyma ia a type of simple permanent tissue The cells in this type of tissue are living, elongated having irregularly thickened corners. The thickening of the walls are due to cellulose and pectin. They have very little intercellular spaces. These tissues provide flexibility and mechanical support to the plant. 

The main functions of chollenchyma are to provide mechanical support, tensile strength and elasticity flexibility to the organ in which they are present. 

Sclerenchyma. Sclerenchyma (scleras-hard) is the chief mechanical tissue of plants. It is a permanent tissue.
Structure : The cells are made up of sclerenchymatous tissue. The cells are usually long, narrow, pointed at both ends and uniformly thickened by the deposition of lignin without any space in between the cells. The walls are often very highly thickened so that the lumen or cell cavity is nearly obliterated. They are usually provided with simple pits which may be oblique or straight.

Characteristics : The cells of the sclerenchyma are dead. The tissue makes the plant hard and stiff. The sclerenchyma cells are also known as fibres or sclerenchyma fibres, since they are elongated thread-like. 
Location : The tissue is present in stems and vascular bundles, in veins of leaves and in the hard covering of seeds and nuts.

Function : Sclerenchyma fibres give necessary strength, rigidity and flexibility to the plant body. Fibres are thick walled and excellent textile fibres of commercial importance such as jute, sunn hemp.

The outermost layer of cells i.e., usually the epidermis is not continuous at some places e.g., on the surface of leaves or green herbaceous stems.

The epidermis of the young shoot and leaves contains numerous minute pores called stomata. Each stomatal opening is surrounded by two semilunar cells known as the guard cells.

The term ‘stoma’ (plural-stomata) is applied to the stomatal opening plus the guard cells. The guard cells are living and contain chloroplasts. Their inner walls (wall towards opening) are thicker and outer walls thinner. The guard cells regulate the opening and closing of the stomatal pore.

Major Functions of Stomata are:

(i) Stomata are essential for exchange of gases between the plant and the atmosphere.

(ii) Normally, plants eleminate excessive water in the form of vapour through stomatal openings. The process is called Transpiration.

(iii) When there is shortage of water, stomatal openings get closed to reduce water loss. Stomatal openings also close down during night. Thus, stomata regulate water loss from plants i.e., they regulate transpiration.

(1) Difference between Meristematic cells and Permanent cells.

(2) Difference between Parenchyma and Collenchyma.

These are difference between collenchyma and sclerenchyma.

Difference between sclerenchyma fibres and sclereiods.

A complex tissue is made up of more than one type of cells which work together in coordination as a unit. For example - xylem and phloem .

Vascular tissues in plants perform the function of transport. The xylem tissue transports—(i) water and dissolved minerals from roots to various parts plant body. While the phloem transports prepared food material from leaves to different plant parts.

The conducting tissue like xylem and phloem together form the vascular bundles. 

Xylem is a complex plant tissue or vascular tissue. Xylem consists of four elements that are-:

(i) Tracheids. A tracheid is an elogated hollow cell with its both ends tapering. The walls of these cells are thick by the deposition of lignin. At certain spots lignin is not present.These spots are termed as pits. These cells are arranged in such a fashion so as to form a system of long tubes and channels in which water can move readily. The tracheids are dead cells. The walls show various kinds of thickenings.

(ii) Vessels are tube like structures formed by a number of cells placed end to end with their transverse walls dissolved or absorbed. The side walls of these tubes also have deposition of lignin. The thickening of the walls show various kinds of patterns. They are also dead cells.

(iii) Wood (xylem) Parenchyma. These are parenchymatous, thin walled living cells. They help in short term conduction of materials. They also store starch and fatty materials.

(iv) Wood Fibres. Xylem sclerenchyma consists of lignified dead fibres. They provide mechanical support.

The most important element of xylem is vessel because they conduct most part of water and mineral salts upward from roots to different parts of shoots.

Fig. 6.10. Tracheids of xylem.

Phloem consists of the following four elements:

(i) Sieve tubes (ii) Companion cells

(iii) Phloem parenchyma (iv) Phloem sclerenchyma.

The most important element of phloem is sieve-tubes because they translocate food materials from leaves to other parts of plant.

Structure of Phloem. Phloem is a complex permanent tissue of the plant. The phloem consists of four types of elements: sieve tubes, companion cells, phloem fibres and the phloem parenchyma
The main conducting part of the phloem is sieve tube which is formed of elongated cylindrical cells arranged in vertical rows. The terminal walls of each sieve tube member has many minute pores through which food material passes very easily. The entire porous plate is termed as sieve plate. Each sieve tube member is supported by a long parenchymatous cell called the companion cell which helps the sieve tubes in the conduction of food material.
Phloem parenchyma formed of parenchymatous cells. They store the food material. Phloem also contains phloem fibres, also known as Bast Fibres.
 A longitudinal section of phloem.

(i) Xylem and Phloem.

(ii) Vessel and Sieve Tube.

(iii) Vessel and Tracheid.