Learn Unit II: World of Living with Free Lessons & Tips

• Inhalation in humans occurs through a process called negative pressure breathing. When the diaphragm and intercostal muscles contract, the volume of the thoracic cavity increases, causing a decrease in intra-thoracic pressure. As a result, air moves from an area of higher pressure (outside the body) to an area of lower pressure (inside the lungs), filling the lungs with fresh air.

• Herbivores have longer small intestines than carnivores because plant matter is more difficult to digest and requires more time for processing. The longer length of the small intestine provides a larger surface area for absorption of nutrients, especially since plant material contains complex carbohydrates and cellulose that require extensive enzymatic breakdown and microbial fermentation for digestion. Additionally, herbivores often have symbiotic relationships with gut microbes that aid in the digestion of plant material, necessitating a longer digestive tract.

Reflex action is an involuntary and rapid response to a stimulus that bypasses conscious thought. It involves a simple neural pathway called a reflex arc, which includes a sensory neuron, interneuron, and motor neuron. Walking, on the other hand, is a voluntary and coordinated movement involving various muscle groups controlled by the brain's motor cortex and cerebellum. Unlike reflex actions, walking requires conscious intention and coordination between different parts of the brain and muscles.

To demonstrate hydrotropism, one could set up an experiment using a potted plant placed horizontally with its roots positioned at one end of a transparent container filled with moist soil. By observing the direction of root growth over time, one can demonstrate how the roots grow towards the moist soil, indicating the plant's response to the water gradient. Alternatively, one could use a gel medium with a water gradient to more precisely control the water distribution and observe root growth towards the water source.

• Green seeds are the recessive trait, so they will only appear in the F2 generation if both parents carry the recessive allele. In the F1 generation, which results from crossing two purebred parents (one dominant and one recessive), all offspring will exhibit the dominant trait (red seeds).

• The closer relation between species can be determined by the number of shared characteristics. If species A shares ten characteristics with species B and species C shares fifteen characteristics with species D, the pair of species C and D share a closer relation because they share a greater number of characteristics.

• Mendel referred to genes as "factors" in his experiments on pea plants. He hypothesized the existence of discrete hereditary units that determine specific traits. Genes are located on chromosomes, which are thread-like structures found in the nucleus of cells.

• DNA copying errors, known as mutations, can introduce variations in the genetic code. While some mutations may have no noticeable effect, others can result in changes to an organism's characteristics or traits, which can impact the reproductive process by altering the genetic information passed on to offspring. Mutations can contribute to genetic diversity within populations, which is important for adaptation and evolution.