(a) Blue-green algae are also considered as bacteria. Discuss their major similarities with bacteria. (10 marks) (b) What do you…

(a) Similarities of blue-green algae with bacteria (10 marks)

Blue-green algae (cyanobacteria) share these major features with bacteria:

• Prokaryotic organisation: no true nucleus or nuclear membrane; a nucleoid of naked, circular DNA without histones.
• No membrane-bound organelles (no mitochondria, endoplasmic reticulum, Golgi or chloroplasts); the photosynthetic thylakoids lie free in the cytoplasm.
• 70S ribosomes.
• A cell wall of peptidoglycan (murein), of the Gram-negative type with an outer membrane and lipopolysaccharide, so they are sensitive to lysozyme and penicillin.
• Reproduction by binary fission, fragmentation and spores; no true sexual reproduction, though gene transfer occurs by conjugation, transformation and transduction (cyanophages).
• Presence of plasmids, and nitrogen fixation by nitrogenase, as in Azotobacter.
• Absence of flagella (cyanobacteria glide) and a mucilage sheath around the cell.

They differ from most bacteria in having chlorophyll a and oxygenic photosynthesis, which is why they were once classed with algae.

(b) Virus of bacteria and its application in medical sciences (10 marks)

Virus of bacteria (2 marks). A bacteriophage is a virus that infects bacteria: an obligate parasite made of a nucleic acid core inside a protein coat (capsid), as in the T4 phage with head, tail and tail fibres, which multiplies by the lytic or lysogenic cycle.

Medical applications (8 marks):

• Phage therapy: phages, or their lysins, against antibiotic-resistant infections (Pseudomonas, Staphylococcus, Klebsiella); used in Georgia and Poland and in trials elsewhere.
• Phage typing to identify strains of bacteria such as Salmonella Typhi and Staphylococcus in epidemiology.
• Rapid detection of bacteria, such as the luciferase reporter phage for Mycobacterium tuberculosis.
• Phage display to obtain antibodies, peptides and vaccine candidates.
• Vectors (lambda, M13) for cloning, and transduction in genetic studies.
• Disinfection of hospital surfaces and food.
• Study of phage defences led to CRISPR-Cas gene-editing tools.

(c) Mineralization and nitrogen fixation, and their help in improving soil quality (10 marks)

Description (6 marks):

• Mineralization: heterotrophic microbes break organic nitrogen (proteins, humus) into ammonium (ammonification), which Nitrosomonas and Nitrobacter oxidise to nitrite and nitrate (nitrification). Net release occurs when the C:N ratio of the residue is below about 25:1.
• Symbiotic fixation: Rhizobium in the root nodules of legumes (with leghaemoglobin protecting nitrogenase) reduces N₂ to NH₃; also Frankia in Alnus and Casuarina and Anabaena in Azolla.
• Non-symbiotic fixation: free-living Azotobacter and Beijerinckia (aerobic), Clostridium (anaerobic) and cyanobacteria (Nostoc, Anabaena); Azospirillum is associative.

Soil quality (4 marks):

• They add plant-available nitrogen at low cost, reducing the need for chemical fertiliser and its pollution.
• Mineralization releases nitrogen, phosphorus and sulphur from residues and builds humus, improving structure and water retention.
• Legume rotations, green manures, Azolla in rice and biofertilisers raise fertility and organic matter and sustain soil biodiversity.

(d) Fossilization and the major types of fossils (10 marks)

Fossilization (2 marks) is the process by which the remains, impressions or traces of ancient organisms are buried and preserved in sedimentary rocks over long periods.

Major types (8 marks):

• Petrifaction (permineralization): the cell spaces are filled with silica or calcium carbonate, preserving internal structure, as in petrified wood and the Deccan intertrappean plants.
• Compression: the plant is flattened under sediment to a carbon film, as in leaves on shale.
• Impression: an imprint of the surface with no organic matter left.
• Mould and cast: the mould is the cavity left after decay, and the cast is the mineral infilling of it.
• Incrustation: mineral, often lime, deposits around the plant.
• Coal balls and coal: partly carbonised plant matter.
• Amber (resin) with trapped insects and plant parts, and coprolites.
• Microfossils (pollen, spores) in sediments; an Indian example is Williamsonia from the Rajmahal Hills.

(e) Chemotaxonomy and its contribution to solving taxonomic problems (10 marks)

Chemotaxonomy (chemosystematics) (2 marks) is the use of chemical characters, such as secondary metabolites, proteins and other macromolecules, to classify plants and clarify their relationships.

Contribution (8 marks):

• Betalains occur in most families of the order Caryophyllales and never together with anthocyanins, which supports placing Cactaceae there; Caryophyllaceae and Molluginaceae, which have anthocyanins instead, are exceptions that mark them as distinct lineages.
• Glucosinolates link Brassicaceae with Capparaceae and Resedaceae, in Brassicales.
• Flavonoid profiles identify hybrids and their parents, for example in Baptisia.
• Alkaloids, terpenoids and iridoids support relationships among genera, and chemotypes separate races in Mentha and Thymus.
• Seed proteins and serology settle uncertain placements.
• Chemical convergence limits their use, so they must be combined with morphological and molecular evidence.