Biological Systems: Nutrition, Circulation, and Ingestion
Biological Systems and Nutrition
The digestive tract converts food into nutrients, which pass into the bloodstream. The respiratory system absorbs oxygen into the blood and is responsible for expelling carbon dioxide from cellular respiration. The circulatory system transports nutrients to cells and waste substances to the excretory and respiratory systems. Once nutrients reach the cells, they are used to synthesize complex molecules or are degraded to release stored energy. Following cellular respiration, carbon dioxide enters the circulatory system to be transported to the lungs for expulsion. Waste substances are carried by the circulatory system to the excretory system, where they are eliminated from the body.
Heartbeat Propagation
- The heartbeat begins in the sinoatrial node.
- The atria contract and the pulse is transmitted to the atrioventricular node.
- The atria relax, and the bundle of His transmits the impulse to the ventricles.
- The ventricles contract.
Passive Ingestion Systems
Passive systems utilize specialized structures for feeding:
- Ciliary Structures: Cilia and flagella facilitate food intake. Sponges possess flagellated cells called choanocytes, which use their flagella to group food particles before ingestion. Some bivalves have their entire outer surface coated with ciliated gills.
- Filters: Many aquatic animals feed on microbial pathogens or small organic particles using filters through which water circulates, retaining food particles.
Active Ingestion Systems
This system involves animals with specialized organs adapted for the capture and restraint of food.
Adaptations for Feeding
- Radula: Mollusks possess a radula, an organ composed of numerous sharp, small teeth.
- Tentacles: Some animals use tentacles to capture prey. Cephalopod mollusks have muscular tentacles, while cnidarians possess stinging cells known as cnidoblasts.
- Jaws: Arthropods have jaw structures with varying morphologies adapted to their specific diet.
- Teeth: Vertebrates possess teeth for cutting and crushing food. The shape, number, and development of teeth vary by species and have evolved based on dietary requirements.
- Beaks: Birds lack teeth but possess a horny beak, which varies in shape and size depending on their feeding habits.