Question

a) Briefly describe why the discovery of endospores was important to microbiology.

b) Describe the molecular adaptations in the cytoplasmic membrane of psychrophiles and non-psychrophiles in cold and hot environments.

c) (i) Briefly describe the differences between algae and cyanobacteria.

(ii) Define dimorphic fungi.

(iii) Describe FOUR unique characteriestics of parasitic helminthes such as round worms that enable them to survive in human.

d) (i) A person may get the influenza virus more than once even though antibodies are produced. Briefly explain this. (1 mark)

(ii) Describe FOUR characteristics of viruses.

e) (i) Differentiate FOUR characteristics between Gram-positive and Gram-negative bacteria.

(ii) State TWO functions of bacterial slime layers involved in the formation of biofilms.

Answer 1

a. Endospores were discovered by John Tyndall. He discovered endospores as the heat resistant spores of bacteria which survived even after 100 degree celsius.Discovery of endospores have provided a simplified model for cellulat differentiation especially in the model organism Bacillus subtiles which have lead to deeper insights of understanding of gene expression, transcription factors and the sigma factor sub units of RNA polymerase.

b Adaptations of cytoplasmic membranes Psychrophiles: Psychrophiles have a high content of short, unsaturated fatty acids in their lipid membranes which allows for the lipid cell membrane to have a lower melting point and increases the fluidity of the membranes. In addition, carotenoids are present in the membrane, which help modulate the fluidity of it.

Ci Alage are eukaryotes while as Cyanobacteria are prokaryotes.

2. Algae have chloroplasts in their cells while as cyanobacteria lack chloroplasts.

3. The green algae contain membrane-bound organelles along with a nucleus. In contrast, cyanobacteria do not have membrane-bound organelles.

cii Dimorphic fungi are fungi that have a yeast phase and a mold (filamentous) phase. One of the characteristics common to most dimorphic fungi is the ability to convert the mold forms to the yeast forms by incubating subcultures in enriched media at 35°-37°C. In general, dimorphic fungi produce a mold form at 25-30°C and a yeast form at 35-37°C. Colonies of dimorphic molds are gray-white and have a delicate cobweb appearance on blood agar. For example Blastomyces dermatitidis

c iii Adaptations of rouns worms are:

1. Round worms have a hard and flexible yet permeable skin cuticle that enables them to maintain their internal fluids under high pressure.

2. They have a complete digestive system. It allows them to eat, digest food, and eliminate wastes all at the same time.

3. Roundworms have a tough covering of cuticle on the surface of their body. It prevents their body from expanding. This allows the buildup of fluid pressure in their partial body cavity. The fluid pressure adds stiffness to the body and thus provides a counterforce for the contraction of muscles, allowing roundworms to move easily over surfaces.

4. Roundworms obtain the oxygen their bodies need through diffusion, a process of gas exchange Diffusion allows roundworms to provide oxygen to their cells without the use of complex organs, such as lungs.

d i The influenza viruses keep on changing through antigenic drift. These are small changes (or mutations) in the genes of influenza viruses that can lead to changes in the surface proteins of the virus: HA (hemagglutinin) and NA (neuraminidase). The HA and NA surface proteins of influenza viruses are “antigens,” which means they are recognized by the immune system and are capable of triggering an immune response, including production of antibodies that can block infection. The changes associated with antigenic drift happen continually over time as the virus replicates. The small changes that occur from antigenic drift usually produce viruses that are closely related to one another. However, the small changes associated with antigenic drift can accumulate over time and result in viruses that are antigenically different. When antigenic drift occurs, the body’s immune system may not recognize and prevent sickness caused by the newer influenza viruses. As a result, a person becomes susceptible to flu infection again, as antigenic drift has changed the virus enough that a person’s existing antibodies won’t recognize and neutralize the newer influenza viruses.

d ii Four characteristics of viruses are:

1. They are non cellular sub microscopic particles consisting mainly of a nucleic acid surrounded by a protein envelope called capsid. Therefore, a unit of virus is referred to as ‘a virus particle’ rather than ‘a virus cell’.

2. They lack the complex enzymatic and biosynthetic machinery essential for independent activities of cellular life .

3. They can multiply only inside suitable living cells.

4 They do not increase in size

e i Gram positive have a thick peptidoglycan layers while as gram negative have a thin peptidoglycan layers

2. Gram positive have a smooth and single layered cell wall while as gram negative have a wavy and double layered wall.

3.Porins are absent in gram positive while present in the outer wall of Gram negative.

4. Gram positive are usaually cocci or spore forming rods while as Gram negative are non spore forming