Science 8 First Term Comprehensive Review

The small intestine is the primary site for nutrient absorption in the digestive system. After food is partially digested in the stomach, it moves into the small intestine, where enzymes and bile further break it down. The walls of the small intestine are lined with tiny villi and microvilli that increase the surface area, allowing for efficient absorption of nutrients like carbohydrates, proteins, fats, vitamins, and minerals directly into the bloodstream. This process is crucial for providing the body with the necessary nutrients for energy and overall health.

Roots are specialized plant organs that anchor the plant in the soil while also serving the crucial function of absorbing water and essential nutrients. They have a large surface area and are equipped with root hairs that enhance their ability to take up moisture and dissolved minerals. This process is vital for plant growth and overall health, as it provides the necessary resources for photosynthesis and metabolic functions. Unlike stems, leaves, or flowers, roots are specifically adapted for this absorption role, making them essential for the plant's survival.

Chloroplasts are specialized organelles found in plant cells that contain chlorophyll, the pigment responsible for capturing sunlight. This process of photosynthesis converts light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water. Mitochondria are involved in cellular respiration, the nucleus houses genetic material, and ribosomes are responsible for protein synthesis. Therefore, chloroplasts are uniquely suited to perform photosynthesis, making them the primary site for this essential process in plants.

When two heterozygous parents (Aa) are crossed, their possible gametes are A and a. The Punnett square shows the combinations of these gametes: AA, Aa, Aa, and aa. Out of the four possible genotypes, only one is homozygous recessive (aa). Thus, the probability of producing an aa offspring is 1 out of 4, or 25%.

Ernest Rutherford conducted the gold foil experiment in 1909, where he directed alpha particles at a thin sheet of gold. Most particles passed through, but some were deflected at large angles, suggesting that an atom is mostly empty space with a dense, positively charged nucleus. This experiment led to the understanding that the nucleus contains protons, fundamentally changing the model of the atom and laying the groundwork for modern atomic theory.

An atom is electrically neutral when the positive charge from protons in the nucleus is balanced by the negative charge from electrons surrounding the nucleus. Protons carry a positive charge, while electrons carry an equal but opposite negative charge. When the number of protons equals the number of electrons, their charges cancel each other out, resulting in an overall neutral charge for the atom. If there is an imbalance, the atom becomes an ion, carrying a net positive or negative charge.

The statement incorrectly defines genotype and phenotype. The genotype is the genetic makeup of an organism, encompassing the specific alleles it carries. In contrast, the phenotype is the observable physical characteristics or traits that result from the interaction between the genotype and the environment. Therefore, the two terms are reversed in the statement, making it false.