BIO BOTANY [5 Mark each]

The Beneficial Aspects of Lichens:

1. Lichens secrete organic acids like oxalic acids which corrodes the rock surface and helps in weathering of rocks, thus acting as pioneers in Xerosere.
2. Usnic acid produced from lichens show antibiotic properties.
3. Lichens are sensitive to air pollutants especially to sulphur-di-oxide. Therefore, they are considered as pollution indicators.
4. The dye present in litmus paper used as acid base indicator in the laboratories is obtained from Roccella montagnei.
5. Cladonia rangiferina (Reindeer moss) is used as food for animals living in Tundra regions.

The characters of different types of Mycorrhiza:

Mycorrhiza
Ectomycorrhiza	Endomycorrhiza	Ectendomycorrhiza
The fungal mycelium forms a dense sheath around the root called mantle. The hyphal network penetrate the intercellular spaces of the epidermis and cortex to form Hartignet. e.g.Pisolithus tinctorius.	The hyphae grows mainly inside the roots, penetrate the outer cortical cells of the plant root. A small portion of the mycelium is found outside the root. This form is also called Vesicular Arbuscular Mycorrhizal fungi (VAM fungi) due to the presence of vesicle or arbuscle like haustoria. 1. Arbuscular mycorrhiza (VAM) e.g. Gigaspora 2. Ericoid mycorrhiza- e.g., Oidiodendron 3. Orchid mycorrhiza -e.g. Rhizoctonia	The fungi form both mantle and also penetrates the cortical cells.

Features of Basidiomycetes:

1. Basidiomycetes include puffballs, toad stools, Bird nest’s fungi, Bracket fungi, stink horns, rusts and smuts.
2. The members are terrestrial and lead a saprophytic and parasitic mode of life.
3. The mycelium is well developed, septate with dolipore septum (bracket like). Three types of mycelium namely primary (Monokaryotic), secondary (Dikaryotic) and tertiary are found.
4. Clamp connections are formed to maintain dikaryotic condition.
5. Asexual reproduction is by means of conidia, oidia or budding.
6. Sexual reproduction is present but sex organs are absent. Somatogamy or spermatisation results in plasmogamy. Karyogamy is delayed and dikaryotic phase is prolonged. Karyogamy takes place in basidium and it is immediately followed by meiotic division.
7. The four nuclei thus formed are transformed into basidiospores which are borne on sterigmata outside the basidium (Exogenous). The basidium is club shaped with four basidiospores, thus this group of fungi is popularly called “Club fungi”. The fruit body formed is called Basidiocarp.

Features of Ascomycetes:

1. Ascomycetes include a wide range of fungi such as yeasts, powdery mildews, cup fungi, morels and so on.
2. Although majority of the species live in terrestrial environment, some live in aquatic environments both fresh water and marine.
3. The mycelium is well developed, branched with simple septum.
4. Majority of them are saprophytes but few parasites are also known. (Powdery mildew – Erysiphe).
5. Asexual reproduction takes place by fission, budding, oidia, conidia and chlamydospore.
6. Sexual reproduction takes place by the fusion of two compatible nuclei.
7. Plasmogamy is not immediately followed by karyogamy, instead a dikaryotic condition is prolonged for several generations.
8. A special hyphae called ascogenous hyphae is formed.
9. A crozier is formed when the tip of the ascogenous hyphae recurves forming a hooked cell. The two nuclei in the penultimate cell of the hypha fuse to form a diploid nucleus. This cell form young ascus.
10. The diploid nucleus undergo meiotic division to produce four haploid nuclei, which further divide mitotically to form eight nuclei. The nucleus gets organised into 8 ascospores.
11. The ascospores are found inside a bag-like structure called ascus. Due to the presence of ascus, this group is popularly called “Sac fungi”.
12. Asci gets surrounded by sterile hyphae forming fruit body called ascocarp.
13. There are 4 types of ascocarps namely Cleistothecium (Completely closed), Perithecium (Flask shaped with ostiole), Apothecium (Cup shaped and open type) and Pseudothecium.

The salient features of zygomycetes:

1. Most of the species are saprophytic and live on decaying plant and animal matter in the soil. Some lead parasitic life (Example: Entomophthora on housefly)
2. Bread mold fungi (Example: Mucor and Rhizopus) and Coprophilous fungi (Fungi growing on dung Example: Pilobolus) belong to this group.
3. The mycelium is branched and coenocytic.
4. Asexual reproduction by means of spores produced in sporangia.
5. Sexual reproduction is by the fusion of the gametangia which results in thick walled zygospore. It remains dormant for long periods. The zygospore undergoes meiosis and produce spores.

The Various Types Of Sexual Reproduction In Fungi:

1. Planogametic copulation: Fusion of motile gamete is called planogametic copulation.
   • Isogamy – Fusion of morphologically and physiologically similar gametes. (Example: Synchytrium).
   • Anisogamy – Fusion of morphologically or physiologically dissimilar gametes (Example: Allomyces).
   • Oogamy – Fusion of both morphologically and physiologically dissimilar gametes. (Example: Monoblepharis).
2. Gametangial contact: During sexual reproduction a contact is established between antheridium and oogonium (Example: Albugo).
3. Gametangial copulation: Fusion of gametangia to form zygospore. (Example: Mucor and Rhizopus).
4. Spermatization: Auninucleate pycniospore/microconidium is transferred to receptive hyphal cell (Example: Puccinia / Neurospora)
5. Somatogamy: Fusion of two somatic cells of the hyphae (Example: Agaricus).

The Various Types Of Asexual Reproduction In Fungi:

1. Zoospores: They are flagellate structures produced in zoosporangia (Example: Chytrids)
2. Conidia: The spores produced on condiophores (Example: Aspergillus)
3. Oidia / Thallospores / Arthrospores: The hypha divide and develop into spores called oidia (Example: Erysiphe).
4. Fission: The vegetative cell divide into 2 daughter cells. (Example: Schizosaccharomyces – yeast).
5. Budding: A small outgrowth is developed on parent cell, which gets detached and become independent. (Example: Saccharomyces-yeast).
6. Chlamydospore: Thick walled resting spores are called chlamydospores. (Example: Fusarium).

The Salient Features Of Cyanobacteria:

• The members of this group are prokaryotes and lack motile reproductive structures.
• The thallus is unicellular in Chroococcus, colonial in Gloeocapsa and filamentous trichome in Nostoc.
• Gliding movement is noticed in some species (Oscillatoria).
• The protoplasm is differentiated into central region called centroplasm and peripheral region bearing chromatophore called chromoplasm.
• The photosynthetic pigments include c-phyocyanin and c-phycoerythrin along with myxoxanthin and myxoxanthophyll.
• The reserve food material is cyanophycean starch.
• In some forms a large colourless cell is found in the terminal or intercalary position called heterocysts. They are involved in nitrogen fixation.
• They reproduce only through vegetative methods and produce akinetes (thick wall dormant cell formed from vegetative cell), hormogonia (a portion of filament get detached and reproduce by cell division), fission and endospores.
• The presence of mucilage around the thallus is characteristic feature of this group. Therefore, this group is also called Myxophyceae.
• Sexual reproduction is absent.
• Microcystis aeruginosa and Anabaena flos-aquae cause water blooms and release toxins and affect the aquatic organism. Most of them fix atmospheric nitrogen and are used as biofertilizers (Example: Nostoc and Anabaena). Spirulina is rich in protein hence it is used as single cell protein.

The role of bacteria in soil fertility:

Economic importance of bacteria
S.No.	Beneficial aspects	Bacteria	Role
Soil fertility
1.	Ammonification	1. Bacillus ramosus 2. Bacillus mycoides	Convert complex proteins in the dead bodies of plants and animals into ammonia which is later converted into ammonium salt
2.	Nitrification	1. Nitrobacter 2. Nitrosomonas	Convert ammonium salts into nitrites and nitrates
3.	Nitrogen fixation	1. Azotobacter 2. Clostridium 3. Rhizobium	(i) Converting atmospheric nitrogen into organic nitrogen (ii) The nitrogenous compounds are also oxidized to nitrogen (iii) All these activities of bacteria increase soil fertility

The role of bacteria in antibiotic production and medicines:

Economic importance of bacteria
Antibiotics
1.	Streptomycin	Streptomyces griseus	It's cures urinary infections, tuberculosis, meningitis and pneumonia
2.	Aureomycin	Streptomyces aureofaciens	It's used as a medicine to treat whooping cough and eye infections
3.	Chloromycetin	Streptomyces venezuelae	It cures typhoid fever
4.	Bacitracin	Bacillus licheniformis	It is used to treat syphilis
5.	Polymyxin	Bacillus polymyxa	It cures some bacterial diseases

The uses of bacteria in industries:

Zinder and Lederhcrg (1952) discovered transduction in Salmonella typhimurum. Phage mediated DNA transfer is called transduction.

Transduction is of two types:

1. Generalized transduction and
2. Specialized or restricted transduction.

1. Generalized transduction: The ability of a bacteriophage to carryr genetic material of any region of bacterial DNA is called generalised transduction.

2. Specialized or restricted transduction: The ability of the bacteriophage to carry only a specific region of the bacterial DNA is called specialized or restricted transduction. 

J. Lederberg and Edward L Tatum demonstrated conjugation in E. coil in the year 1946. In this method of gene transfer the donor cell gets attached to the recipient cell with the help of pili.
The pilus grows in size and forms the conjugation tube. The plasmid of donor cell which has the F+ (fertility factor) undergoes replication. Only one strand of DNA is transferred to the recipient cell through conjugation tube. The recipient completes the structure of double stranded DNA by synthesizing the strand that complements the strand acquired from the donor.

The process of transformation:

Transfer of DNA from one bacterium to another is called transformation. In 1928, the bacteriologist Fredrick Griffith demonstrated transformation in mice using Diplococcus pneumoniae. Two strains of this bacterium are present. One strain produces smooth colonies and are virulent in nature (S type), in addition another strain produced rough colonies and are avirulent (R type). When S-type of cells were injected into the mouse, the mouse died. When R-type of cells were injected, the mouse survived. He injected heat killed S-type cells into the mouse the mouse did not die.

When the mixture of heat killed S-type cells and R-type cells were injected into the mouse. The mouse died. The avirulent rough strain of Diplococcus had been transformed into S-type cells. The hereditary material of heat killed S-type cells had transformed R-type cell into virulent smooth strains. Thus the phenomenon of changing the character of one strain by transferring the DNA of another strain into the former is called transformation.

Most of the gram positive cell wall contain considerable amount of teichoic acid and teichuronic acid. In addition, they may contain polysaccharide molecules. The gram negative cell wall contains three components that lie outside the peptidoglycan layer:

1. Lipoprotein
2. Outer membrane and
3. Lipopolysaccharide.

Thus the different results in the gram stain are due to differences in the structure and composition of the cell wall.

Plasmids are extrachromosomal double stranded, circular, self – replicating, autonomous elements. They contain genes for fertility, antibiotic resistant and heavy metals. It also help 1 in the production of bacteriocins and toxins which are not found in bacterial chromosome.

The size of a plasmid varies from 1 to 500 kb usually plasmids contribute to about 0.5 to 5% of the total DNA of bacteria. The number of plasmids per cell varies. Plasmids are classified into different types based on the function. Some of them are F (Fertility) factor, R (Resistance) plasmids, Col (Colicin) plasmids, Ri (Root inducing) plasmids and Ti (Tumour inducing) plasmids.

The ultra structure of a bacterium:

The General Characters of Bacteria:

1. They are prokaryotic organisms and lack nuclear membrane and membrane bound organelles.
2. The genetic material is called nucleoid or genophore or incipient nucleus.
3. The cell wall is made up of polysaccharides and proteins.
4. Most of them lack chlorophyll, hence they are heterotrophic (Vibrio cholerae) but some are autotrophic and possess Bacteriochlorophyll (Chromatium).
5. They reproduce vegetatively by binary fission and endospore formation.
6. They exhibit variations which are due to genetic recombination and is achieved through conjugation, transformation and transduction.

In the lysogenic cycle the phage DNA gets integrated into host DNA and gets multiplied along with nucleic acid of the host. No independent viral particle is formed.

As soon as the phage injects its linear DNA into the host cell, it becomes circular and integrates into the bacterial chromosome by recombination. The integrated phage DNA is now called prophage. The activity of the prophage gene is repressed by two repressor proteins which are synthesized by phage genes. This checks the synthesis of new phages within the host cell. However, each time the bacterial cell divides, the prophage multiplies along with the bacterial chromosome. On exposure to UV radiation and chemicals the excision of phage DNA may occur and results in lytic cycle.

Each virus possesses only one type of nucleic acid either DNA or RNA. The nucleic acid may be in a linear or circular form. Generally nucleic acid is present as a single unit but in wound tumour virus and in influenza virus it is found in segments. The viruses possessing DNA are called ‘Deoxyviruses’ whereas those possessing RNA are called ‘Riboviruses’.

Majority of animal and bacterial viruses are DNA viruses (HIV is the animal virus which possess RNA). Plant viruses generally contain RNA (Cauliflower Mosaic virus possess DNA). The nucleic acids may be single stranded or double stranded. On the basis of nature of nucleic acid viruses are classified into four categories. They are viruses with ssDNA (Parvo viruses), dsDNA (Bacteriophages), ssRNA (TMV) and dsRNA (wound tumour virus).

David Baltimore (1971) classification is based on mechanism of RNA production, the nature of the genome (single stranded -ss or double stranded – ds ), RNA or DNA, the use of reverse transcriptase (RT), ss RNA may be (+) sense or (-) antisense. Viruses are classified into seven classes.

Table 1.2: Different Classes of viruses
Class	Example
Class 1 - Viruses with dsDNA Class 2 -Viruses with (+) sense ssDNA Class 3-Viruses with dsRNA Class 4 -Viruses with (+) sense ssRNA Class 5 - Viruses with (-) antisense ssRNA Class 6 - Viruses with (+) sense ss RNA -RT that replicate with DNA intermediate in life cycle Class 7 - Viruses with ds DNA - RT that replicate with RNA intermediate in life cycle	Adenoviruses Parvo viruses Reo viruses Toga viruses Rhabdo viruses Retro viruses Hepadna viruses

Living characters:

1. Presence of nucleic acid and protein.
2. Capable of mutation.
3. Ability to multiply within living cells.
4. Able to infect and cause diseases in living beings.
5. Show irritability.
6. Host – specific.

Non – living characters:

1. Can be crystallized.
2. Absence of metabolism.
3. Inactive outside the host.
4. Do not show functional autonomy,
5. Energy producing enzyme system is absent.

A flow chart representing the various levels of organisation and integration in living organisms: