Overview: Heredity - 2 | Science for Grade 8 PDF Download

Ans. Sex determination refers to the process by which an organism's sex (male or female) is determined. In many organisms, including humans, sex determination is influenced by the presence or absence of certain sex chromosomes. In humans, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome triggers the development of male characteristics. However, in some organisms, such as birds, reptiles, and certain fish, sex determination can be influenced by factors such as temperature or social dynamics.

Ans. Evolution occurs through the process of natural selection, which is driven by several factors. The main driving forces of evolution include: - Genetic variation: Individuals within a population possess different genetic traits, which arise through mutations or genetic recombination during reproduction. - Selective pressure: Environmental factors, such as competition for resources or predation, exert selective pressure on individuals with certain traits. Those individuals with advantageous traits are more likely to survive and reproduce, passing on their traits to future generations. - Adaptation: Over time, the traits that confer a survival advantage become more common in the population, leading to the evolution of new species or the adaptation of existing ones.

Ans. There are several evidences of evolution that support the theory, including: - Fossil record: Fossils provide a record of past life forms and their characteristics, showing the progression of species over time. - Comparative anatomy: Similarities in the structure and function of different organisms' body parts suggest common ancestry. For example, the pentadactyl limb (five-digit limb) found in mammals, reptiles, and birds indicates a shared evolutionary history. - Comparative embryology: The similarities in the early stages of development among different species suggest a shared ancestry. For example, the presence of gill slits in the embryos of both fish and humans indicates a common evolutionary origin. - Molecular biology: By comparing the DNA sequences of different organisms, scientists can identify similarities and differences that indicate their evolutionary relationships. The more similar the DNA sequences, the more closely related the species. - Biogeography: The distribution of species across different geographic regions provides evidence for evolution. For example, the presence of similar species on different continents suggests that they share a common ancestor and have evolved independently.

Ans. Human evolution is the evolutionary process that led to the emergence of modern humans. It occurred through a series of gradual changes over millions of years. Some key milestones in human evolution include: - Bipedalism: The ability to walk upright on two legs is a defining characteristic of humans. This adaptation freed up the hands for tool use and allowed for efficient long-distance travel. - Increase in brain size: The human brain has undergone significant enlargement over time, resulting in increased cognitive abilities and the development of complex societies. - Use of tools: The ability to create and use tools played a crucial role in human evolution. It allowed early humans to obtain food, build shelters, and manipulate their environment. - Language development: The development of language and communication skills enabled early humans to share knowledge, cooperate, and pass on cultural information. - Cultural evolution: Humans have the unique ability to transmit knowledge and skills from one generation to the next through cultural practices. This has allowed for the accumulation of knowledge and the development of complex societies.

Ans. Classification is the process of categorizing organisms into groups based on their shared characteristics. It is closely related to evolution because classification reflects the evolutionary relationships between different species. By grouping organisms based on their similarities, scientists can infer their common ancestry and understand the patterns of evolutionary change. Classification is important in understanding the diversity of life because it allows us to organize and study the vast array of species on Earth. It helps us identify and name new species, understand their evolutionary history, and make predictions about their characteristics and behavior. Additionally, classification provides a framework for communication and collaboration among scientists, enabling the sharing of knowledge and the development of a unified understanding of the natural world.