Question

Heterotrophic bacteria helps in (a) Curding of milk (b) Production of antibiotic (c) Nitrogen fixation in leguminous plant (d) All of these

Short answer

(a) Curding of milk and (b) Production of antibiotic

Step-by-step solution

Understand Heterotrophic Bacteria

Heterotrophic bacteria are those bacteria that cannot synthesize their own food and depend on other organisms for their food. They use organic materials as source of carbon and energy, which can lead them to play various roles in nature.

Evaluate Option (a)

Let's examine the role of bacteria in curding of milk. The curding of milk is a process where milk solidifies, and it is caused by the fermentation of lactose (milk sugar) by bacteria, most commonly lactic acid bacteria like Lactobacillus. This Lactobacillus bacteria is a type of heterotrophic bacteria. So, heterotrophic bacteria do help in curding of milk.

Evaluate Option (b)

In the case of antibiotic production, there are many antibiotics that are produced by fermentative bacteria. These bacteria are often heterotrophic, since they use organic compounds from other organisms as a source of nutrients. So, heterotrophic bacteria do help in the production of antibiotics.

Evaluate Option (c)

For nitrogen fixation, certain bacteria play a key role by converting atmospheric nitrogen into nitrates that can be used by plants. However, the key bacteria responsible for nitrogen fixation in leguminous plants is Rhizobium, which is not a heterotrophic bacteria, but a kind of symbiotic bacteria. Therefore, heterotrophic bacteria do not have significant role in nitrogen fixation in leguminous plant.

Conclude the Solution

From the analysis of the options, we can conclude that heterotrophic bacteria help in curding milk and the production of antibiotics, but not in nitrogen fixation in leguminous plants.

Key concepts

Curding of Milk

The transformation of milk into curd is a testament to the importance of heterotrophic bacteria in our daily lives. Lactobacillus, a typical representative of this group, initiates the curding process by breaking down lactose, the sugar found in milk, into lactic acid. This acidification causes the milk proteins, primarily casein, to coagulate, leading to the thickened texture of curd.

The science behind this transformation is both intriguing and practical. It's not just about altering the texture — the production of lactic acid also preserves the curd by creating an environment unfriendly to harmful microbes. This traditional method of extending milk's shelf life has been used for centuries, illustrating a natural way to benefit from microbial activity.

Adding a small amount of existing curd to milk can initiate this process, since the curd acts as an inoculation source, providing the required bacteria to start the fermentation. Thus, through the actions of heterotrophic bacteria, milk is converted into a nutritious and longer-lasting food product.

Antibiotic Production

The search for new antibiotics often leads us to the microscopic world, where heterotrophic bacteria play a crucial role in antibiotic production. These bacteria seek organic compounds to survive, and in doing so, some produce substances that are lethal to other microorganisms. These substances are what we know as antibiotics.

Penicillin, discovered by Alexander Fleming, is a classic example of an antibiotic that originates from a heterotrophic fungus, Penicillium. Similarly, bacteria like Streptomyces, which live in the soil and are heterotrophic as well, are prolific producers of antibiotics. These organisms engage in a microbial 'arms race', constantly evolving to outcompete their neighbors. In this process, they create powerful compounds that can be harnessed as antibiotics.

The production of these life-saving drugs on a commercial scale generally involves fermentative processes. Heterotrophic bacteria consume the provided organic material and produce antibiotics as secondary metabolites. This biotechnological exploitation of microbial warfare has had an immense impact on modern medicine, offering us a spectrum of antibiotics to overcome various infections.

Nitrogen Fixation

Nitrogen fixation is a phenomenal process that converts inert atmospheric nitrogen (\( N_2 \) into reactive nitrates usable by plants. This conversion is crucial, considering that nitrogen is a vital component of DNA, proteins, and other cellular constituents. However, it is important to clarify the misconception related to heterotrophic bacteria and their role in nitrogen fixation.

While heterotrophic bacteria contribute significantly to various biological processes, nitrogen fixation in leguminous plants is predominantly performed by symbiotic bacteria like Rhizobium. These bacteria form nodules on the roots of legumes and fix nitrogen directly from the air. This symbiosis benefits the plants as they get a direct supply of essential nutrients, and the bacteria, in return, receive carbohydrates and a protective environment from their plant hosts.

Other non-symbiotic bacteria, such as Azotobacter and Clostridium, can also fix nitrogen independently, but their contribution to soil nitrogen levels is generally less significant compared to symbiotic bacteria. It's essential to understand the specific roles different bacteria play in the nitrogen cycle to appreciate their contributions to ecosystem productivity and agricultural success.