Biology Case study (4 Marks)

Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Describe briefly the four major groups of Protozoa.

In addition to proteins, viruses also contain genetic material, that could be either RNA or DNA. No virus contains both RNA and DNA. A virus is a nucleoprotein and the genetic material is infectious. In general, viruses that infect plants have single stranded RNA and viruses that infect animals have either single or double stranded RNA or double stranded DNA. Bacterial viruses or bacteriophages (viruses that infect the bacteria) are usually double stranded DNA viruses. The protein coat called capsid made of small subunits called capsomeres, protects the nucleic acid. These capsomeres are arranged in helical or polyhedral geometric forms. Viruses cause diseases like mumps, small pox, herpes and influenza. AIDS in humans is also caused by a virus. In plants, the symptoms can be mosaic formation, leaf rolling and curling, yellowing and vein clearing, dwarfing and stunted growth.

(1) Viruses are made up of:
(a) Proteins & DNA
(b) Proteins only
(c) Proteins & RNA
(d) Proteins & DNA / RNA

(2) Bacteriophages are usually :
(a) Single stranded DNA viruses
(b) Double stranded RNA viruses
(c) Double stranded DNA viruses
(d) Single stranded RNA viruses

(3) Which is not a viral disease of humans:
(a) Pneumonia (b) Herpes (c) Mumps (d) Smallpox

(4) Select the incorrect statement regarding Capsomeres:
(a) Capsomeres are sub-units of Capsid
(b) Capsomeres are made of peptidoglycans
(c) Capsomeres may be arranged in helix or polyhedron
(d) Capsomeres are made of proteins

(5) Which of these is not a symptom of viral infection in crops:
(a) Leaf rolling (b) Curling of leaf (c) Decay of roots (d) Vein clearing

There are thousands of different eubacteria or 'true bacteria'. They are characterized by the presence of a rigid cell wall, and if motile, a flagellum. The cyanobacteria (also referred to as blue-green algae) have chlorophyll a similar to green plants and are photosynthetic autotrophs. The cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies are generally surrounded by gelatinous sheath. They often form blooms in polluted water bodies. Some of these organisms can fix atmospheric nitrogen in specialized cells called heterocysts, e.g., Nostoc and Anabaena. Chemosynthetic autotrophic bacteria oxidise various inorganic substances such as nitrates, nitrites and ammonia and use the released energy for their ATP production. They play a great role in recycling nutrients like nitrogen, phosphorous. iron and Sulphur.

(1) Which of the following can be termed as 'Photosynthetic Autotrophs'
(a) All monerans (b) Chemosynthetic Bacteria (c) Cyanobacteria (d) All Eubacteria

(2) Blue green algae are characterized by :
(a) They often form blooms in polluted water bodies.
(b) Some of these organisms can fix atmospheric nitrogen
(c) Their colonies are generally surrounded by gelatinous sheath.
(d) All of these

(3) Which is incorrect about Heterocysts:
(a) These are specialized cells
(b) These are present in all Cyanobacteria.
(c) Nostoc and Anabaena have Heterocysts.
(d) Organisms having these cells can fix atmospheric nitrogen

(4) Green plants are similar to Blue green algae in having:
(a) chlorophyll a (b) Heterocysts (c) chlorophyll b (d) None of these

(5) Which of these can be described as ‘true Bacteria’.
(a) Cyanobacteria only
(b) Only Chemosynthetic autotrophic bacteria
(c) Bacteria without cell wall.
(d) Eubacteria