CBSE Class 10 Science Chapter 8: How Do Organisms Reproduce? NCERT Solutions

Solution: DNA (Deoxyribonucleic acid) is the molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known organisms. In reproduction, DNA copying is of paramount importance because it ensures the faithful transmission of genetic information from the parent organism to the offspring. This process allows offspring to inherit traits and characteristics from their parents, leading to the continuity of the species. Each DNA molecule contains the blueprint for building specific proteins, which in turn determine the body design and functions of an individual. Therefore, accurate DNA replication before cell division is essential for maintaining the species' identity and ensuring that the new generation resembles the parent generation.

Solution: Variations are changes in the genetic material that can arise during reproduction. These variations are highly beneficial for the survival of a species as a whole, rather than for any single individual. If the environment undergoes drastic changes (like extreme temperature fluctuations, new diseases, or scarcity of food), the existing population might not be able to survive. However, if there are variations within the population, some individuals might possess traits that make them better adapted to the new conditions. For example, a few bacteria might be naturally resistant to a rise in temperature. These resistant individuals can survive and reproduce, ensuring the continuation of the species even if the majority die. While these variations are crucial for species' long-term survival and evolution, they may not always be advantageous for the individual organism experiencing them. Some variations might even be neutral or detrimental to the individual's immediate survival.

Solution: Binary fission and multiple fission are both modes of asexual reproduction where a single parent cell divides to produce offspring. The key difference lies in the number of daughter cells produced and the conditions under which they occur:

Binary Fission: In this process, a parent cell divides into two approximately equal-sized daughter cells. The nucleus divides first, followed by the cytoplasm. This is a common method of reproduction in unicellular organisms like Amoeba and bacteria, typically occurring under favorable environmental conditions when resources are abundant.

Multiple Fission: In multiple fission, a single parent cell divides to produce many daughter cells simultaneously. This process often occurs when the organism is under unfavorable conditions, such as lack of food or extreme temperatures. The nucleus divides repeatedly to form many nuclei, and then the cytoplasm surrounds these nuclei, eventually leading to the formation of numerous small daughter cells. Organisms like Amoeba (under unfavorable conditions) and Plasmodium reproduce through multiple fission.

Solution: Reproduction through spores offers several significant advantages to an organism, enhancing its survival and dispersal capabilities:

1. Widespread Dispersal: Spores are typically very small and lightweight, allowing them to be easily carried by wind, water, or animals to new and distant locations. This wide dispersal helps the organism colonize new habitats and reduces competition for resources in the original location.
2. Survival Under Unfavorable Conditions: Spores are often surrounded by a thick, protective wall. This wall acts as a barrier, preventing dehydration and protecting the spore from extreme temperatures, mechanical damage, and other harsh environmental conditions. This allows the organism to survive periods of scarcity or unfavorable climate until conditions improve for germination.
3. Production in Large Numbers: A single sporangium can produce a vast number of spores, increasing the probability that at least some of them will land in a suitable environment to germinate and grow into new individuals.