The primary cell wall of plants consists of cellulose microfibrils embedded in a matrix of hemicellulose, pectin, and proteins. Secondary walls contain lignin. Chitin is in fungi and arthropods, peptidoglycan in bacteria. Cellulose is a polymer of β-glucose units and provides structural support.
Explanation:
The sinoatrial (SA) node, located in the right atrium, generates electrical impulses spontaneously and initiates each heartbeat, setting the rhythm. It is called the natural pacemaker. The atrioventricular (AV) node delays the impulse before it travels to the ventricles. The bundle of His and Purkinje fibers conduct the impulse through the ventricles.
Explanation:
The spinal cord is a long tubular bundle of nervous tissue extending from the medulla oblongata to the level of the first/second lumbar vertebra (L1-L2), where it tapers into the conus medullaris. Below this, nerves form the cauda equina. It transmits impulses between the brain and body and coordinates reflexes.
No comments yet. Be the first to start the discussion!