Biology Quiz 2 PDF

## GEN. BIO. 2- Lesson 3: ORGANISIMAL BIOLOGY: Plant vs Animal Digestive System **Digestion** is the process of breaking down food into components that can be absorbed by the body. - **Mechanical digestion:** smashes food into smaller fragments - **Chemical digestion:** breaks down large molecule...

## GEN. BIO. 2- Lesson 3: ORGANISIMAL BIOLOGY: Plant vs Animal Digestive System **Digestion** is the process of breaking down food into components that can be absorbed by the body. - **Mechanical digestion:** smashes food into smaller fragments - **Chemical digestion:** breaks down large molecules in food into their component subunits. Digestion contributes to **homeostasis** by providing the body with the nutrients to sustain life of cells. ### Digestive System A digestive system includes all of the organs, tissues, and cells involved in: - ingesting food - breaking it into small molecules that can cross the plasma membrane - absorbing the nutrient molecules - eliminating undigested particles. ### DIGESTIVE SYSTEM OF HYDRA In some invertebrates, digestion occurs in a sadlike **gastrovascular cavity**, as seen in the figure above. This is an example of an **incomplete digestive tract** in Hydra. Hydra has: - a single opening, the mouth, which serves as entry for food and exit of wastes. ### DIGESTIVE SYSTEM OF EARTHWORM Other vertebrates and all vertebrates have a more efficient **complete digestive tract**, which is a tube that has specialized regions along its length as in earthworm: - **Mouth:** where food enters - **Anus:** for exit of food Earthworms feed on decayed organic matter found in the soil. - The muscular pharynx draws in a large amount of soil with a sucking suction. - The soil enters the **esophagus** to the **crop**, a storage area with thin expansive walls. - From the crop, it goes to the **gizzard**, where thick muscular walls crush the food and ingested sand grinds it. - Digestion is extracellular within the **intestine**. - The intestine is where most of the enzymatic digestion and absorption of nutrients occur. - Digestion is considered extracellular within the intestine in earthworms because the breakdown of food occurs outside the cells, within the lumen of the digestive tract. #### Process in the Intestine: - Food is first mechanically processed in the gizzard. - When it reaches the intestine, digestive enzymes (secreted by the intestinal cells) act on the food in the lumen of the intestine. - The enzymes break down complex organic matter like carbohydrates, proteins, and fats into smaller molecules (e.g., glucose, amino acids, fatty acids) that can be absorbed by the intestinal walls. ### Extracellular Nature Since the breakdown of food occurs in the lumen of the intestine, which is external to the cells lining the intestine, this digestion is categorized as **extracellular**. ### HUMAN DIGESTIVE SYSTEM The human digestive system is a complex system that processes food, extracts nutrients, and eliminates waste. It is composed of the **alimentary canal** and **accessory organs.** #### Alimentary Canal 1. **Mouth:** The entry point for food. - Teeth break food into smaller pieces (mechanical digestion) - Saliva (containing amylase) begins the breakdown of carbohydrates (chemical digestion). - Salivary glands secrete saliva which moisten the food and forms it into a mixture called bolus in preparation for swallowing. - Saliva contains the enzyme, ptyalin or salivary amylase, that converts starch to sugar. 2. **Pharynx:** A muscular tube that connects the mouth to the esophagus and helps in swallowing food. 3. **Esophagus:** A muscular tube that moves food from the pharynx to the stomach using rhythmic contractions called peristalsis. Peristalsis serves to move the food along the various tubular organs, from the esophagus to the rectum. 4. **Stomach:** J-shaped organ: - Stores food and mixes it with gastric juices, which contain hydrochloric acid and enzymes like pepsin to digest proteins. - The stomach churns food into a semi-liquid form called chyme. 5. **Small Intestine:** Divided into three parts: duodenum, jejunum, and ileum. - **Duodenum:** Digestion of proteins, carbohydrates, and fats using enzymes from the pancreas and bile from the liver. - **Jejunum & Ileum:** Absorb nutrients into the bloodstream via villi and microvilli. - The walls of the intestine contain fingerlike projections called villi, where nutrients are absorbed and carried to all the cells of the body by the bloodstream. - Digestion in the small intestine is aided by the pancreatic juice secreted by the pancreas. Pancreatic juice is made up of trypsin that breaks down the protein, amylase, that changes starch to sugar and lipase that breaks down fats. Undigested food goes to the large intestine. 6. **Large Intestine (Colon):** - Absorbs water and electrolytes from undigested food. It compacts waste into feces for elimination. - Contains large populations of bacteria, including Escherichia coli which provides Vitamin K which is necessary for blood clotting. - Escherichia coli (E. coli) is a type of bacteria naturally found in the human gastrointestinal tract. One of its beneficial roles in the body is the production of Vitamin K, particularly Vitamin K2 (menaquinone), which is essential for blood clotting and bone health. - The undigested food is already a semi-solid material known as feces which are discharged through the anus. 7. **Rectum and Anus:** Function: The rectum stores feces, and the anus controls the release of waste through defecation. #### Accessory Organs 1. **Salivary Glands:** Produce saliva, which contains enzymes like amylase to begin carbohydrate digestion. 2. **Liver:** - Largest gland - Produces bile, which emulsifies fats to aid in digestion. 3. **Gallbladder:** Stores and releases bile into the small intestine. 4. **Pancreas:** Produces digestive enzymes (amylase, lipase, proteases) and bicarbonate to neutralize stomach acid in the duodenum. #### Summary of Functions 1. **Ingestion:** Mouth takes in food. 2. **Digestion:** Breakdown of food into smaller components (mechanical and chemical). 3. **Absorption:** Nutrients absorbed primarily in the small intestine. 4. **Elimination:** Waste compacted in the large intestine and expelled via the rectum and anus. This system ensures the body gets energy and essential nutrients for growth, repair, and maintenance.