Summary Notes designed for the International Baccalaureate Diploma Programme. These notes are detailed yet concise, with all the information to achieve a 7 in IB Biology HL or SL. These notes were made using information from the IB syllabus, Oxford IB Diploma HL Biology Textbook, Bioninja and the B...
Unit 6.1
• In the mouth, mechanical digestion is used to increase the surface area. Saliva contains salivary
amylase.
• HCl in the stomach lowers the pH to 2 which
kills bacteria and pepsin breaks down
proteins.
• The walls of the stomach are adapted to
expand when food enters.
• The duodenum is the first section of the
small intestine.
• Bile from the gall bladder is secreted into the
duodenum to emulsify fats.
• Amylase, lipase and endopeptidase are also
secreted by the pancreas.
• The contraction of circular and longitudinal muscle helps move the bolus in the small intestine
and the oesophagus, known as peristalsis.
• Enzymes digest most macromolecules in food into monomers in the small intestine:
• Starch→Maltose →Glucose using amylase and maltase
• Lipids →Fatty Acids+Glycerol using lipase
• Proteins→Peptides →Amino Acids using protease and pepsin
• Nucleic Acids→Nucleotides using nucleases
• All of these reactions are catabolic and require water.
• Most enzymes work at pH 7, with pepsin being an exception.
• The small intestine is made up of 4 tissue layers:
• Serosa • Submucosa
• Muscle Layer • Mucosa
• Absorption is the uptake of digested molecules into the blood.
• The inner epithelial lining of the small intestine is folded into finger-like projections called villi and
microvilli.
• The villi are highly adapted to absorption:
• Microvilli further increase surface area
• Rich blood supply created by network of
capillaries
• Short diffusion pathway (one cell thick
epithelium)
• Lacteals absorb lipids into the lymphatic system
• Intestinal crypts release digestive juices
• Membrane proteins facilitate transport of
digested materials into epithelial cells
• Membrane transport in the epithelial cells:
• Lipids are non polar and pass via simple diffusion
• Water soluble molecules such as fructose and vitamins pass via facilitated diffusion
• Amino acids and charged ions pass via active transport using ATP
• Glucose passes by actively transporting Na+ to create a concentration gradient (cotransport)
, Unit 6.2
• The blood consists of the plasma, buffy coat and erythrocytes.
• Red blood cells have many adaptations, including a biconcave shape,
no nucleus and haemoglobin.
• haemoglobin + oxygen ⇌ oxyhaemoglobin
• Platelets help the clotting of blood, which helps:
• Stop pathogens from entering the body
• Stop you from losing too much blood
• A pathogen is defined as a disease-causing
organism.
• Plasma acts as a solvent and dissolves or
carriers other components if the blood, such as
hormones, waste, iron, minerals, amino acids,
glucose, salts etc.
• Coronary arteries supply the cardiac muscles
with blood.
• Cardiac muscle cells are myogenic, meaning
they can beat independently.
• The heart is double circulatory which helps
contain pressure:
• Pulmonary circulation: blood moves from the
heart to lungs to heart.
• Systemic circulation: blood moves from the heart to body to heart.
• Arterioles and venules are used to join capillaries from the arteries and veins.
• There are three main blood vessels, the veins, arteries and capillaries.
• The arteries bring oxygenated blood away from the heart under high pressure (excluding
pulmonary artery):
• The inner layer (endothelium) is smooth to prevent clotting.
• The middle layer contains elastic fibres and muscle to maintain high pressures.
• The outer layer is made out of collagen/elastic fibres for protection.
• The veins bring deoxygenated blood to the heart under low pressure (excluding pulmonary
vein):
• The inner layer consists of endothelium cells.
• The middle layer has few elastic fibres and muscle as it operates under low pressure.
• The outer layer is the thickest and is made out of collagen/elastic fibres for protection.
• Veins have valves to prevent back flow, and a larger lumen.
• Capillaries surround tissue and organs to allow the exchange of substances:
• Only consist of endothelium cells, and are one cell thick for fast diffusion.
• They are very small to create a steeper concentration gradient and operate under low
pressure.
• The basement membrane is permeable to many substances.
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