Bio Notes

It works in five main processes:

1. Ingestion

2. Digestion

3. Absorption

4. Assimilation

5. Egestion

1⃣ Ingestion

✅ Meaning:

Ingestion is the process of taking food into the body.

🦷 What happens:

• Food enters through the mouth

• Teeth chew the food (mechanical digestion / mastication)

• Tongue mixes food with saliva

• Saliva contains amylase enzyme, which starts digestion of starch

📍 Organ involved: Mouth

2⃣ Digestion

✅ Meaning:

Digestion is the process of breaking large, complex food molecules into simple, soluble substances.

🔬 Types of digestion:

(a) Mechanical digestion

• Chewing by teeth

• Churning of food in the stomach

(b) Chemical digestion

• Enzymes break food chemically

🧪 Examples:

• Amylase → starch → sugar

• Pepsin → proteins → peptides

• Lipase → fats → fatty acids + glycerol

📍 Organs involved:

• Mouth

• Stomach

• Small intestine

3⃣ Absorption

✅ Meaning:

Absorption is the process by which digested food passes into the blood.

🩸 Where it occurs:

• Small intestine

🔍 How:

• The inner wall has tiny finger-like structures called villi

• Villi increase surface area

• Nutrients enter:

  • Blood capillaries (glucose, amino acids)

  • Lacteals (fatty acids and glycerol)

📍 Result:

• Nutrients are now in the bloodstream

4⃣ Assimilation

✅ Meaning:

Assimilation is the process of using absorbed nutrients by body cells.

🧠 What happens:

• Glucose → used for energy (respiration)

• Amino acids → build muscles and tissues

• Excess glucose → stored as glycogen in liver

• Fats → stored under the skin

📍 Occurs in:

• All body cells

• Mainly regulated by the liver

5⃣ Egestion

✅ Meaning:

Egestion is the removal of undigested and unabsorbed food from the body.

🚫 Important:

• Egestion ≠ excretion

• Egestion removes solid waste

• Excretion removes metabolic waste (urine, sweat)

🧻 Process:

• Undigested food enters large intestine

• Water is absorbed

• Waste is stored in rectum

• Removed through anus as faeces

📍 Organs involved:

• Large intestine

• Rectum

• Anus

Respiratory system ——> (1) = Nasal cavity -    Air rich in oxygen enters the mouth through the nasal cavity.

2 - Pharynx —- Contains lining of mucus which traps dirt/ dust particles inside it and pushes it back to the mouth to be swallowed or thrown out.

3 - Larynx - Contains Goblet cells which contains a thin lining in the eosophagus and protects it.

4 - Trachea - It carries air from the nose and mouth to the bronchi.

• It is kept open by C-shaped rings of cartilage so it doesn’t collapse.

• It helps filter air using mucus and tiny hairs (cilia) that trap dust and germs.

5 - Bronchi — They carry air from the trachea (windpipe) into the lungs.

• Inside the lungs, the bronchi branch into smaller tubes called bronchioles.

• They help distribute air evenly throughout both lungs.

6 - Bronchioles — They branch off from the bronchi.

• They carry air deeper into the lungs.

• They control airflow by expanding and contracting (using smooth muscles).

• They lead air to the alveoli, where gas exchange happens.

7. Alveoli —- They are the site of gas exchange.

8. Oxygen passes from the alveoli into the blood.

9. Carbon dioxide passes from the blood into the alveoli to be breathed out.

10. They have very thin walls and many capillaries, which makes gas exchange fast and efficient.

Capillaries ———> They surround the alveoli in the lungs.

• They allow exchange of gases:

  • Oxygen from the alveoli passes into the blood.

  • Carbon dioxide from the blood passes into the alveoli to be exhaled.

• Their walls are very thin (just one cell thick) to make this exchange easy.

Glucose (from food) + Oxygen (from breathing) → Energy (ATP) + Carbon dioxide + Water.

• The chemical equation: C6​H12​O6​+6O2​→6CO2​+6H2​O+energy(ATP)

• It happens in the mitochondria of cells (often called the “powerhouse” of the cell).

• The energy (ATP) produced is used for all activities of the cell, like movement, growth, and repair.

DIGESTIVE SYSTEM – DETAILED NOTES

1. Mouth (Buccal Cavity)

Ingestion

• Digestion begins in the mouth.

• Food is taken in and prepared for swallowing.

Chewing (Mastication) – Physical Digestion

• Teeth cut, tear, and grind food into smaller pieces.

• This is physical digestion because:

  • The food’s size changes

  • Its chemical nature stays the same

• Chewing increases the surface area of food, making digestion easier later.

Role of Saliva – Chemical Digestion

Saliva is released by salivary glands.

Saliva contains:

• Salivary amylase (enzyme)
  → Breaks starch into maltose (simple sugar)

• Water
  → Softens food

• Mucus
  → Makes food slippery and easy to swallow

✔ This is chemical digestion because enzymes change food chemically.

Bolus Formation

• Chewed food mixed with saliva forms a soft ball called a bolus.

• The bolus is swallowed into the oesophagus.

2. Oesophagus (Food Pipe)

• The oesophagus connects the mouth to the stomach.

• Food moves by peristalsis:

  • Wave-like muscle contractions

  • Push food downward

• No digestion occurs here.

3. Epiglottis – Preventing Food from Entering the Windpipe

• The epiglottis is a flap-like structure.

• It is located at the entrance of the trachea (windpipe).

What happens during swallowing?

• When you swallow:

  • The epiglottis closes over the trachea

  • This prevents food from entering the windpipe

• Food is safely directed into the oesophagus.

✔ If food enters the windpipe, it causes choking.

4. Stomach

The stomach is a muscular sac that stores and digests food.

Churning – Physical Digestion

• Strong muscles contract and relax

• Food is mixed and crushed

• Food becomes a semi-liquid called chyme

• This is physical digestion.

Chemical Digestion in the Stomach

The stomach releases gastric juice, which contains:

1. Hydrochloric acid (HCl)

   • Kills harmful bacteria

   • Provides acidic medium for enzymes

2. Pepsin (enzyme)

   • Breaks proteins into smaller peptides

✔ Proteins are mainly digested here.

5. Small Intestine

The small intestine is the main site of digestion and absorption.
It has three parts:

A. Duodenum

• First and shortest part

• Receives:

  • Bile from liver

  • Pancreatic juice from pancreas

Functions:

• Bile emulsifies fats (breaks large fat droplets into smaller ones)

• Pancreatic enzymes digest:

  • Carbohydrates

  • Proteins

  • Fats

✔ Major chemical digestion happens here.

B. Jejunum

• Middle part of small intestine

• Digestion continues here

• Nutrients are broken into simple soluble forms

Examples:

• Glucose

• Amino acids

• Fatty acids and glycerol

C. Ileum

• Last and longest part

• Absorption of nutrients happens here

• Inner lining has villi:

  • Finger-like projections

  • Increase surface area

Villi absorb:

• Glucose → into blood

• Amino acids → into blood

• Fatty acids → into lymph

6. Summary Table

Key Exam Words to Use

• Mastication

• Peristalsis

• Chyme

• Enzymes

• Emulsification

• Villi

• Absorption

trachea is covered in c - shaped Cartilaginous rings that protect the trachea lining.

the capillaries contain Deoxygenated blood/ impure blood until the alveoli gives air rich in oxygento the blood cells in the capillaries.

The amount of breathes a person does in a minute is called breathing rate.

A person breathes 12–20 times per minute

Oxygen debt is the extra oxygen needed after exercise to remove lactic acid.

circulatory system — Circulatory system is a body system that allows transportation/transfers nutrients such as oxygen and other important substances such as amino acids (protien) glucose (starch) through the blood. The main parts of the circulatory system is - 1= The heart

2 = The blood and blood vessels.

there are 2 parts of the part——> the left and right side.