Z-SCHEME OR LIGHT REACTION:

"The reaction which depends upon light are called light reactions or Z-Scheme."

It is also called an "ENERGY CONVERSION PHASE".

That phase is completed by following the steps.

(1) Photosystems:

Photosynthetic pigments are organized into clusters called photosystems in the thylakoid membrane. The photosystems absorb and utilize solar energy.

There are the following parts of photosystems.

(a) Antenna Complex:

In the photosystem, the part which absorbs light energy is called the antenna complex.

The antenna complex contains carotenoid chlorophyll b and chlorophyll a.

(b) Reaction Centre:

The area which takes electrons (energy)k from the antenna complex and starts the light reaction is called the reaction center. The reaction center contains.

(i) One or more molecules of chlorophyll a.

(ii) Primary electron acceptor.

(iii) Electron-associated protein.

(c) Electron Transport Chain :

Photosystems contain a series of electron transport systems and chains such systems contain PQ, cytochrome, and PC.

There are two photo systems:

• Photosystem I

• Photosystem II

Reaction in Photosystem II:

PS II absorbs light of 680 nm wavelength it contains chlorophyll which is the best light absorber of 680 nm. PS II chlorophyll antenna complex transfer this energy to the reaction center and then from the reaction center to the primary electron acceptor.

This acceptor traps the high-energy electrons and then pushes these electrons to the series of electron carriers' electron transport chains.

During this flow of electrons following reactions take place.

Non-Cycle Phosphorylation:

That process is completed by following the steps.

(i) PS II absorbs light and an electron is excited.

(ii) P680 As Oxidizing Agent:

The excited electron is shifted to the reaction center and then to electron (primary) acceptors of PS II.

That chlorophyll is oxidizing and acts as a strong oxidizing agent. It has an electron "hole" that must be filled.

(iii) Photolysis:

The breakage of water during this light reaction is called photolysis.

This reaction breaks water into two Hᐩ, 2eー, and one oxygen atom. Oxygen atoms combine with another atom to form oxygen molecules O2  ─ to remove in the air.

(iv) Electron Transport Chain: (First):

Photoexcited electrons are shifted from PS II to PS I by the electron transport chain. This chain consists of :

(a) PQ          Plastoquinone

(b) Cyt         Cytochromes - two complex.

(c) PC           Plastocyanin - Copper-containing protein.

(v) Photophosphorylation:

The formation of ATP in the presence of light is called photophosphorylation.

Energy flow provides energy for the synthesis of ATP-ATP formation during non-cyclic electron flow is called non-cyclic photophosphorylation.

This ATP provides chemical energy for dark reactions as the electrons move down the chain their energy is decreased.

(vi) Reactions in Photosystem I:

The electrons reach the bottom of the electron transport chain and fill the electron hole in PS I.

PS I has chlorophyll a and absorb light of 700 nm. It is also called P700.

When PS I absorb light and its electrons move towards the primary acceptor of PS I. So the hole is produced which is filled by the electron of PS II.

(vii) Second Electron Transport Chain:

From the primary acceptor of PS I the electrons are shifted to a second electron transport chain. This chain consist of

(a) Fd - ferredoxin - ion-containing protein.

(b) NADP - nicotinamide adenine dinucleotide phosphate.

The electrons are from the primary acceptor to Fd and from Fd to NADP. In the presence of NADP reductase enzyme, the NADP changes into NADPH.

NADPH molecule provides reducing power for the formation of sugar during Calvin Cycle.

(viii) Cyclic Phosphorylation:

The process in PS-I is in which electrons are shifted from Fd to cytochrome, then to PC, and again to PS I. During this reaction, no NADPH and oxygen is produced. It does not take place by PS-II. It takes place by PS II. It takes place in PS I when the chloroplast produces low ATP for the Calvin Cycle. When more NADPH is collected in the chloroplast and the demand for ATP is fully supplied that cyclic phosphorylation is down.

The cyclic flow is a short circuit it is started due to the rise of NADPH. It is a temporary shifting of electrons from non-cyclic to cyclic electron flow.

Discuss the role of antibiosis and immunization in controlling bacterial disease?

CHEMICAL METHODS:

Chemical methods for control of bacterial include antiseptics, disinfectants and chemotherapeutic agents controlling bacterial diseases.

(1) Antiseptics:

These are chemical substances used on living tissues to kill and inhibit the growth of microorganisms.

(2) Disinfectants:

These chemical agents are used to inhibit the growth of vegetative cells on the non-living materials.

These include oxidizing and reducing agents. For example halogens, phenols, hydrogen peroxide, Potassium permagnate, alcohol and formaldehyde etc.

(3) Chemotherapeutic:

Chemotherapeutic agents and antibiotics work with natural defense and stop the growth of bacteria and other microbes. They destroy or inhibit the growth of microorganisms in living tissues.

These are Sulfonamides, tetracycline, penicilin, etc.

Some other processes that kill/inhibit the microbial population are:

(i) Microbicidal Effect:

Microbicidal effect is one that kills the microbes immediately.

(ii) Microbistatic:

Microbistatic inhibits the reproductive capacities of the cells and maintain the microbial population at constant size.

Mode of Action:

Mode of action, of different physical and chemical agents, of control vary.

Damage can result malfunctions in cell wall, cell membranes, cytoplasm, enzymes, or nuclei acid.

IMMUNIZATION AND VACCINATION:

To control and prevent microbial diseases following methods are used:

(i) Immunization (e.g. vaccination)

(ii) Antisepsis (used to eliminate or reduce infection)

(iii) Chemotherapy and

(iv) Public health measures (e.g. water purification, sewage disposal and food preservation)

Pasteur made many discoveries about the cause and prevention of infectious diseases. His work is very important in developing immunity by vaccines.

Pasteur's Work on Chicken Cholera:

In 1880's he isolated the bacterium that caused chicken cholera. He grew it in a pure culture.

To isolate the bacterium of this disease, Pasteur used the techniques of Koch. He also demonstrated this publically.

Experiment:
He inoculated healthy chicken with this pure cultures.

He waited for many days but chicken cholera did not develop in the chicken.

Error in his experiment:

Pasteur found that he had used the cultures several weeks old instead of fresh one.

Discovery:

He discovered that somehow bacteria had lost their ability to produce the disease (virulence) after standing and growing old.

These less virulent bacteria, could still stimulate the host (in this case the chicken) to produce antibodies.

Antibodies are substances that protect the host against infection from virulent organism.

(i) Pasteur's Work on Anthrax:

Pasteur applied the above mentioned principle for the prevention of anthrax.

This culture of the less virulent germs was called vaccine (in Latin vacca means cow).

Similarly immunization with less virulent germs was called vaccination.

(ii) Pasteur's Work on Rabies:

Then Pasteur also developed a vaccine for hydrophobia, or rabies.

It is a disease transmitted to people by bites from rabid dogs, cats, and other animals.

(iii) Pasteur Honouring Edward Jenner:

Pasteur honoured Edward Jenner (1749 - 1823).

Jenner successfully vaccinated a boy against small pox in 1796.

He observed that milkmaids who contracted cowpox from the cows, never developed small pox.

He tested his hypothesis by inoculating a bot (James Phipps) first with cowpox causing material and later with small pox causing material. The boy did not get small pox.

Explain the Two to Five kingdom classification.

MODIFICATION OF OLD CLASSIFICATION:

Two to Five Kingdom Classification Systems:

Different classification systems recognize Two to five kingdoms

For centuries, the living organisms have been classified into Two kingdoms, plants and animals.

(1) Kingdom (Plante):

Plant can prepare their own food from simple inorganic material and store energy (autotroph), while.

(2) Kingdom (Animalia):

Animals cannot synthesize their own food from simple inorganic material and depend for their food either on autotrophs or on decaying organic matter (heterotrophs).

Objection in Old Classification:

Bacteria were included in plants.

Many biologist found this system satisfactory, while other found it unworkable for many unicellular organisms like.

Euglena that have both plant like (presence of chlorophyll) and animal like (lack of cell wall) characters and also because it.

Ignores the differences between Prokaryotic and Eukaryotic cells.

(3) Kingdom (Protista):

In 1866, Ernst Hackel proposed a third kingdom PROTISTA to accommodate Euglena like organisms and bacterial.

In 1937, E-Chatton suggested differentiating terms:

Procariotique (from Greek pro, meaning before, and karyon, meaning nucleus) used to describe bacterial and blue-green algae, and Eu-caritique (from Greek eu, mean true) to describe animal and plant cells.

(4) Kingdom (Fungi):

Write structure and life cycle of Bacteriophage?

STRUCTURE OF T4:

The structure under an electron microscope looks like a tadpole and consists of a head and tail.

(1) Head:

(i) The head is elongated having:

      (a) Pyramidal (having two triangular structures with a common base).

      (b) Hexagonal or

      (c) Prism-shaped structure.

(ii) To it straight tail is attached.

(iii) Head contains double-stranded DNA.

(2) Tail:

The structure of the tail is more complex than the head.

(i) Tail has a core of protein which is surrounded by a sheath of another protein.

(ii) On one side of the sheath is the collar and on the other side is the end plate (Base plate).

(iii) Six tail fibers are attached to the end plate. These fibers are for attachment.

Volume of Phage:

It is about 1/1000 of the host.

Life Cycle of Bacteriophages:

The bacteriophage replicates only inside the bacterial cell. There are many steps in replication.

(1) Attachment (Adsorption) of Phage to the Host Cell:

(i) First of all the bacteriophage attaches to the bacterial cell at the receptor site. The receptor sites are present on the cell wall of the bacterium.

(ii) During attachment, weak chemical union occurs between virion and receptor site.

(2) Penetration:

In this step, the tail releases the enzyme lysozyme. This enzyme dissolves a portion of the bacterial cell wall.

The tail sheath contracts and the tail core is forced into the cell through the cell wall and cell membrane.

The virus injects its DNA into the cell (just as the syringe is used to inject the vaccine).

The protein coat, consisting of head and tail, remains outside the cell.

Many animal viruses enter the host cell as a whole.

A Phage Injecting its DNA in to host

After penetration one of the following cycles take place:

(1) Lytic cycle.

(2) Lysogenic cycle.

(1) Lytic Cycle:

During the lytic cycle following steps occur.

(i) Multiplication:

Soon after entering the bacterium, the viral DNA takes the control of the biosynthetic machinery of the host.

The host is forced to synthesize viral DNA and proteins. As a result, viruses begin to multiply.

Within 25 minutes about 200 new Bacteriophages are formed.

(ii) Lysis

After the formation of bacteriophages, the bacterial cell bursts (lysis occurs).

Newly formed bacteriophages are released to infect other bacteria. A new lytic cycle may start.

The phage that causes the lysis of the host cell is called lytic or virulent phage.

(2) Lysogenic Cycle:

In some cases instead of the lytic cycle, the lysogenic cycle takes place. It occurs as follows:

(i) Formation of Prophage:

The viral DNA does not take over the control of the host's machinery.

The DNA is incorporated into the bacterial chromosome. Phage at this stage is called prophage and this process is known as lysogeny.

The phage which causes lysogeny is called temperate (lysogenic) phage. 

Lysogenic bacteria are resistant to infection by the same or related phages.

(ii) Replication:

During lysogeny, the bacterium lives and reproduces normally.

Viral DNA is the part of a bacterial chromosome and passes to each daughter cell generation after generation.

(iii) Induction:

Some times the viral DNA detaches from the chromosomes of the host and the lytic cycle starts. This process is called induction is spontaneous or environmentally induced excision of the prophage from the bacterial chromosome.