Analyzing Statements on Environmental Science and Ecology Concepts

The question asks us to identify the correct statement(s) among the given options related to biological oxygen demand (BOD), organisms in sewage water, ecology, and parasites.

Statement Analysis:

Statement (A): The BOD (Biological Oxygen Demand) of sewage water is very high

Biological Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a specific temperature and time. Sewage water contains a large amount of organic pollutants. Microorganisms, primarily bacteria, decompose this organic matter. This decomposition process requires oxygen. A high concentration of organic matter means that a large amount of oxygen will be consumed by these decomposers, resulting in a high BOD value. Therefore, the BOD of sewage water is typically very high, indicating significant organic pollution.

This statement is correct.

Statement (B): The aerobic organisms rapidly increase in sewage water due to low content of dissolved oxygen

Aerobic organisms require dissolved oxygen to survive and carry out their metabolic processes, including the decomposition of organic matter. As discussed in statement (A), the high BOD of sewage water leads to a rapid consumption of dissolved oxygen by decomposer microbes. This often results in a significantly low content of dissolved oxygen in sewage water. In conditions of low dissolved oxygen, aerobic organisms cannot thrive and their numbers would decrease, while anaerobic or facultative anaerobic organisms might increase. Therefore, aerobic organisms do not rapidly increase due to low dissolved oxygen; rather, low dissolved oxygen is detrimental to them.

This statement is incorrect.

Statement (C): Ecology is the study of interrelationship between the organisms and their physical environment

Ecology is a branch of biology that studies the interactions among organisms and their biophysical environment, which includes both biotic (living) and abiotic (non-living or physical) components. The physical environment includes factors like temperature, light, water, soil, and nutrients. Studying how organisms interact with each other and with these physical factors is the core focus of ecology.

This statement is correct.

Statement (D): Parasites are those organisms, which do not depend on other living organisms for their food

A parasite is an organism that lives on or inside another organism, called a host, and benefits from the host by getting nutrients at the host's expense. Parasites are fundamentally dependent on their hosts (other living organisms) for food and shelter. They exploit the host for resources, often causing harm. Organisms that do not depend on other living organisms for food might be producers (like plants, which make their own food) or decomposers (like bacteria or fungi, which break down dead organic matter).

This statement is incorrect.

Conclusion:

Based on the analysis:

• Statement (A) is correct.
• Statement (B) is incorrect.
• Statement (C) is correct.
• Statement (D) is incorrect.

Therefore, the correct statements are (A) and (C).

Revision Table: Key Concepts

Additional Information on Environmental & Ecological Terms

Understanding these terms is crucial for environmental science and biology.

• BOD and Water Quality: A higher BOD value indicates a higher level of organic pollution in water bodies. Clean water sources typically have low BOD (around 1-2 mg/L), while heavily polluted water like raw sewage can have BOD values ranging from 200 to 600 mg/L or even higher.
• Dissolved Oxygen (DO): DO is essential for aquatic life, particularly fish and aerobic invertebrates. When BOD is high, the DO levels drop significantly due to microbial respiration, which can lead to the death of aerobic aquatic organisms.
• Types of Organisms based on Oxygen Need:
  • Aerobic: Require oxygen.
  • Anaerobic: Do not require oxygen and can even be harmed by it.
  • Facultative Anaerobic: Can survive with or without oxygen.
• Branches of Ecology: Ecology can be studied at various levels, including organismal ecology, population ecology, community ecology, ecosystem ecology, and landscape ecology. It also includes sub-disciplines like environmental ecology and behavioural ecology.
• Types of Interactions: Organisms interact in various ways, including mutualism (both benefit), commensalism (one benefits, the other is unaffected), parasitism (one benefits, the other is harmed), predation (one hunts and kills another), and competition (both are negatively affected).