Biology Test 299

Metabolism is indeed a defining characteristic of all living organisms, encompassing the entire range of biochemical processes that occur within a living organism to maintain life. These processes include anabolism (the synthesis of complex molecules from simpler ones) and catabolism (the breakdown of complex molecules into simpler ones), both of which are essential for growth, energy production, and cellular repair. This metabolic complexity is absent in non-living entities, making metabolism a key feature distinguishing the living from the non-living. An interesting additional fact is that the study of metabolism has led to the development of various fields, including biochemistry, molecular biology, and metabolic engineering.

• Anaerobic bacteria prefer and some require an environment without oxygen. Many pathogenic bacteria prefer anaerobic soil conditions and are known to outcompete or kill off aerobic bacteria in the soil.
• The heterocyst of nostoc works on nitrogen fixation with the help of nitrogenase enzymes.
• Hence, statement 2 is incorrect.

• The statement is true. Growth in living organisms is an internal process that results from cell division and enlargement, a fundamental aspect of biological life that is controlled by the organism's genetic material.
• This type of growth is dynamic and regulated, differing significantly from the accretion seen in non-living objects, where material accumulates externally without any underlying biological processes.
• This distinction highlights the complexity and regulated nature of growth in living systems, which is essential for development, repair, and reproduction.
• An interesting fact is that growth patterns can vary widely among living organisms, with some showing determinate growth (stopping after reaching maturity) and others showing indeterminate growth (continuing throughout life).

Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall.

The endosymbiotic theory suggests that cyanobacteria, through a symbiotic relationship with early eukaryotic cells, gave rise to the chloroplasts found in modern plants. The presence of chlorophyll a in both cyanobacteria and chloroplasts supports this theory, making the reason a correct explanation of the assertion.

• Nostoc, oscillatoria do not possess flagella but are motile by a swaying motion.
• Anabena is motile through a gliding type movement. This movement is caused by waves of propulsion across the entire trichome.
• Hence, all of the above cells lack flagella.

Archaebacteria and eubacteria are indeed placed in separate domains (Archaea and Bacteria, respectively) due to significant differences in their genetic makeup and the unique composition of their membrane lipids. This classification reflects their evolutionary divergence, making Option A correct.

Nostoc is photoautotroph and oxygenic, chlorobium is photoautotroph and anoxygenic and nitrosomonas is chemoautotrophic.

The defining characteristic of gymnosperms is that their seeds are not enclosed by an ovary, which is why they are referred to as having "naked seeds." This contrasts with angiosperms, where the seeds are enclosed within a fruit. The lack of an ovary in gymnosperms means that the ovules and subsequently the seeds are exposed, directly on the surface of reproductive structures like cones. This trait is a key evolutionary adaptation of gymnosperms, making the reason a correct explanation for the assertion.

The assertion is correct as the presence of a notochord at some stage in life is a defining characteristic of all chordates. The reason correctly explains the function of the notochord, which is to provide a scaffold for the developing nervous system and to act as a primary axial support structure in the embryonic stages of all chordates. This support is crucial for the body structure before the development of the vertebral column in vertebrates.