13. What is the function of red blood cells, white blood cells and platelets? 14. How does digestion begin? Digestion stantsinu the wouth with Cheariug and Saliva breakind down food 15. What is a reflex and what system is responsible forlreflexes?

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Certainly! Here are the answers to your questions numbered 13 through 15:

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**13. What is the function of red blood cells, white blood cells, and platelets?**

- **Red Blood Cells (Erythrocytes):**
  - **Primary Function:** Transport oxygen from the lungs to the body's tissues and carry carbon dioxide from the tissues back to the lungs for exhalation.
  - **Key Feature:** Contain hemoglobin, a protein that binds oxygen and gives red blood cells their characteristic color.

- **White Blood Cells (Leukocytes):**
  - **Primary Function:** Defend the body against infections, foreign invaders, and disease.
  - **Types and Roles:**
    - **Neutrophils:** Engulf and destroy bacteria and fungi.
    - **Lymphocytes (B cells and T cells):** Coordinate the immune response and remember specific pathogens for faster response upon future exposures.
    - **Monocytes:** Differentiate into macrophages to engulf pathogens and dead cells.
    - **Eosinophils and Basophils:** Involved in combating multicellular parasites and allergic reactions.

- **Platelets (Thrombocytes):**
  - **Primary Function:** Aid in blood clotting to prevent excessive bleeding when blood vessels are injured.
  - **Mechanism:** Aggregates at the site of injury, forming a plug and releasing chemicals that facilitate the clotting process.

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**14. How does digestion begin?**

Digestion **begins in the mouth** through a combination of mechanical and chemical processes:

- **Mechanical Breakdown (Chewing):**
  - **Action:** Teeth grind and break down food into smaller pieces, increasing the surface area for enzymes to act upon.
  
- **Chemical Breakdown (Saliva):**
  - **Produced By:** Salivary glands.
  - **Contains Enzymes:** Such as **amylase**, which begins the digestion of carbohydrates by breaking down starches into simpler sugars.
  - **Lubrication:** Saliva moistens food, forming a manageable mass called a bolus that can be easily swallowed.

This initial phase of digestion facilitates the subsequent enzymatic breakdown and nutrient absorption further along the digestive tract.

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**15. What is a reflex and what system is responsible for reflexes?**

- **Reflex:**
  - **Definition:** An involuntary and automatic response to a specific stimulus that does not require conscious thought.
  - **Example:** Pulling your hand back quickly after touching a hot surface.

- **Responsible System: The Nervous System**
  - **Components Involved:**
    - **Peripheral Nervous System (PNS):** Detects the stimulus through sensory neurons.
    - **Central Nervous System (CNS):** Processes the information, typically via the spinal cord, and sends signals back through motor neurons to execute the response.
  - **Reflex Arc:** The neural pathway that mediates the reflex, typically involving:
    1. **Sensory Receptor:** Detects the stimulus.
    2. **Sensory Neuron:** Transmits the signal to the CNS.
    3. **Integration Center:** Processes the signal (often within the spinal cord).
    4. **Motor Neuron:** Carries the response signal to the effector.
    5. **Effector:** Executes the response (e.g., muscle contraction).

Reflexes are crucial for protecting the body from harm and enabling quick reactions without the delay of routing signals through the brain.

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I hope these explanations help clarify your questions!
**13. Functions of Blood Cells and Platelets:** - **Red Blood Cells:** Carry oxygen to tissues and remove carbon dioxide. - **White Blood Cells:** Fight infections and protect against diseases. - **Platelets:** Help in blood clotting to prevent excessive bleeding. **14. How Digestion Begins:** Digestion starts in the mouth where food is broken down by chewing and saliva, which contains enzymes that begin to break down carbohydrates. **15. Reflexes and the Nervous System:** - **Reflex:** An automatic, involuntary response to a stimulus. - **Responsible System:** The nervous system, which includes the brain and spinal cord, processes the stimulus and sends signals to respond. I hope these simplified answers help!

13. What is the function of red blood cells, white blood cells and platelets? 14. How does digestion begin? Digestion stantsinu the wouth with Cheariug and Saliva breakind down food 15. What is a reflex and what system is responsible forlreflexes?

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