Digestive System Overview

Digestive System

• The mouth mechanically breaks down food through chewing (chewing) and chemically through saliva containing amylase.
• The stomach produces gastric juices, containing acids and enzymes, like pepsin. It churns food into chyme.
• The small intestine is the primary site for digestion and absorption.
• Enzymes (amylase, protease, lipase) break down carbohydrates, proteins, and lipids respectively.
• Nutrients absorb into bloodstream through villi.
• The large intestine absorbs water and electrolytes from the remaining food and forms feces.
• The pancreas produces digestive enzymes (amylase, lipase, protease) and bicarbonate to neutralize stomach acid.
• The liver produces bile that emulsifies fats aiding digestion in the small intestine.
• The gallbladder stores bile.
• The rectum and anus store and expel waste.

Enzymes Involved in Digestion

• Amylase breaks down starch into sugars (in mouth and small intestine).
• Protease (e.g., pepsin) breaks down proteins to amino acids (active in stomach).
• Lipase breaks down lipids (fats) to fatty acids and glycerol (in small intestine).
• Lactase breaks down lactose into glucose and galactose (in small intestine).
• Nuclease breaks down nucleic acids to nucleotides.

Digestion of Different Molecules

• Carbohydrates are broken down into monosaccharides (e.g. glucose) by amylase (mouth) and other enzymes (small intestine).
• Cellulose/fiber is not digested by human enzymes, increasing stool bulk and facilitating peristalsis.
• Proteins are broken down into amino acids by proteases (stomach - pepsin, small intestine - trypsin and chymotrypsin).
• Lipids are broken down into fatty acids and glycerol by lipase (small intestine).

Body Position and Pill Intake

• Body position affects pill absorption. Swallowing upright ensures efficient passage through the esophagus and stomach.

Proteases in Digestion (Lab Review)

• Proteases are protein-digesting enzymes.
• Stomach samples are likely to contain proteases.
• Protease activity can be measured by protein breakdown indicators (like biuret solution).

Photosynthesis

Leaf Structure and Function

• Cuticle reduces water loss.
• Epidermis is a protective outer layer.
• Stomata are pores for gas exchange.
• Mesophyll contains chloroplasts for photosynthesis.
• Xylem and phloem transport water/nutrients and sugars respectively.

Stomata Adaptations

• Dry environments have fewer/smaller stomata to reduce water loss.
• Wet environments have more stomata for better gas exchange.

Light Absorption

• Plants primarily absorb blue (430-450nm) and red light (640-680nm).
• Green light is reflected making plants appear green.

Photosynthesis Equation

• 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂

Light-Dependent and Light-Independent Reactions

• Light-dependent reactions occur in thylakoid membranes using light energy to convert water to oxygen, ATP, and NADPH
• Light-independent reactions (Calvin Cycle) occur in the stroma. Using ATP and NADPH from light-dependent reactions to convert CO₂ into glucose.

Chloroplast Structure

• Outer membrane encloses the chloroplast.
• Inner membrane surrounds the stroma.
• Thylakoids are sacs where light-dependent reactions happen.
• Stroma is the fluid where the Calvin cycle occurs.