The valve that prevents backflow from the right ventricle into the right atrium is the: MCQ with Answer and Explanation

Explanation:
Plant cells possess a rigid cell wall of cellulose, chloroplasts for photosynthesis, and a large central vacuole. Animal cells lack cell wall and chloroplasts, and have small temporary vacuoles if present. Centrioles are present in animal cells (centrosome) but absent in higher plant cells. Both have plasma membrane. The cell wall provides shape and protection. These differences are fundamental in cell biology.

Explanation:
The Reticular Activating System (RAS), or Ascending Reticular Activating System (ARAS), is a complex network of neurons located in the core of the brainstem (spanning the medulla, pons, and midbrain). It projects diffusely to the thalamus and cerebral cortex. Its primary function is to regulate the overall level of arousal, consciousness, and wakefulness of the brain. It filters incoming sensory information, allowing important stimuli to reach conscious awareness, and plays a crucial role in the sleep-wake cycle and transitions between sleep stages.

Explanation:
Genes are specific sequences of DNA that code for proteins or RNA, and they are arranged linearly on chromosomes within the nucleus. DNA replication is semi-conservative, meaning each newly synthesized DNA molecule consists of one original parental strand and one newly synthesized strand, as proven by the Meselson-Stahl experiment. RNA is typically single-stranded, allowing it to fold into complex shapes and perform various functions, unlike the double-stranded DNA helix. Thus, statements 1 and 2 are correct.