$\text{CO}_2 + \text{H}_2\text{O}$ Much Greater Most organisms

ATP (Adenosine Triphosphate): Energy currency of cells. Formed from ADP + inorganic phosphate using energy released during respiration. Used for muscle contraction, protein synthesis, nerve impulses, etc.
Gas Exchange in Plants:
- Stomata: For $\text{CO}_2$ and $\text{O}_2$ exchange.
- Inter-cellular spaces: Ensure all cells are in contact with air.
- Diffusion: Direction depends on environmental conditions.
  - Night: $\text{CO}_2$ elimination (from respiration) is major.
  - Day: $\text{CO}_2$ used for photosynthesis; $\text{O}_2$ release is major.
Gas Exchange in Animals:
- Aquatic Organisms:
  - Use dissolved oxygen in water (low amount).
  - Faster breathing rate than terrestrial organisms.
  - Fish: Water taken through mouth, forced over gills; dissolved $\text{O}_2$ absorbed by blood.
- Terrestrial Organisms:
  - Use atmospheric oxygen.
  - Specialized organs (e.g., lungs) with large surface area, fine/delicate membranes, internal location, and passages for air movement.
- Human Respiratory System:
  - Air enters through nostrils (filtered by hairs, moistened by mucus).
  - Passes through throat and into lungs. Rings of cartilage in throat prevent collapse of air-passage.
  - Within lungs, passage divides into smaller tubes ending in alveoli (balloon-like structures).
  - Alveoli: Provide surface for gas exchange. Walls have extensive network of blood vessels.
    - Breathing in: Ribs lift, diaphragm flattens, chest cavity enlarges, air sucked into expanded alveoli.
    - $\text{CO}_2$ from blood (from body) released into alveoli.
    - $\text{O}_2$ from alveolar air taken up by blood for transport to cells.
  - Residual volume of air in lungs ensures sufficient time for gas exchange.
  - Respiratory Pigment: Haemoglobin (in red blood corpuscles) has high affinity for oxygen, transports $\text{O}_2$.
  - $\text{CO}_2$ is more soluble in water, mostly transported in dissolved form in blood.

Transportation

Movement of substances within the body.

1. Transportation in Human Beings (Circulatory System)

Components: Heart, blood, blood vessels.
Blood: Fluid connective tissue.
- Plasma: Fluid medium, transports food, $\text{CO}_2$, nitrogenous wastes, salts (dissolved form).
- Red Blood Corpuscles (RBCs): Carry oxygen (due to haemoglobin).
- Platelets: Circulate and plug leaks in vessels by clotting blood at injury sites.
Heart: Muscular pumping organ, size of a fist.
- Chambers: Four chambers (two atria, two ventricles) to prevent mixing of oxygenated and deoxygenated blood.
- Double Circulation: Blood passes through the heart twice in one complete cycle.
- Pathway:
  1. Oxygen-rich blood from lungs $\to$ Left atrium (relaxes).
  2. Left atrium contracts $\to$ Left ventricle (relaxes).<