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• Large biological molecules that are too large to cross the cell membrane, such as carbohydrates, are broken down by hydrolysis into smaller molecules which can move through the cell membrane and be easily absorbed into the blood.
• Hydrolysis breaks bonds with the use of water.
• Disaccharides are broken down into monosaccharides by membrane-bound disaccharides enzymes attached to the cell membranes of epithelial cells lining the ileum.
• Monosaccharides can be transported across the cell membrane of the ileum epithelial cells by transporter proteins.
• Glucose and fructose are converted into sucrose by sucrase.
• Glucose and galactose are converted into lactose by lactase.
• Lipids are broken down by lipase into monoglycerides and fatty acids.
• Lipase is an enzyme that catalyses the breakdown of lipids into monoglycerides and fatty acids by the hydrolysis of the ester bonds.
• Lipase is made in the pancreas but works in the small intestine.
• Bile salts are produced in the liver and emulsify lipids.
• Small droplets of lipid droplets have a larger surface area than one large droplet, increasing the surface area of lipids and increasing the amount for lipase to work on.
• Monoglycerides and fatty acids stick to bile salts to create micelles.
• Proteins are broken down by different peptidases which are enzymes that catalyse the breakdown of proteins into amino acids by the hydrolysis of peptide bonds.
• Endopeptidase hydrolyses peptide bonds within a protein Molecule.
• Exopeptidase hydrolyses peptide bonds at the ends of a protein Molecule, removing single amino acids.
• Dipeptidase and exopeptidase are located on the cell surface membrane of epithelial cells in the small intestine.
• Glucose is absorbed by active transport with sodium ions with a cotransporter protein.
• Galactose is absorbed the same way.
• Fructose is absorbed by facilitated diffussion.
• Monoglycerides and fatty acids are lipid soluble so can diffuse directly across the epithelial cell membrane.
• Amino acids are absorbed by co-transport and are actively transported out of the epithelial cells into the blood.
• Nations are actively transported out of the epithelial cells into the blood against a concentration gradient.
• Nations diffuse from the lumen into epithelial cells through sodium dependant transporter proteins while carrying amino acids with them.
• Proteinases (pepsin) from the stomach and trypsin from the pancreas hydrolyze proteins into amino acids.
• The pancreas secretes enzymes into the small intestine to break down carbohydrates, proteins, and fats.
• Carbohydrases are produced by the salivary glands and pancreas to hydrolyze starch into maltose, sucrose, and lactose.
• In single-celled organisms, substances can diffuse directly across the cell membrane due to their small size and the short distances involved.
• In multicellular animals, diffusion is slow because some cells are deep within the body and large animals have a low surface area to volume ratio, making it difficult to exchange enough substances to supply a large volume of animal.
• Body size and surface area affect heat exchange, with smaller organisms needing a relatively high metabolic rate to generate heat.
• Animals with a compact shape have a small surface area, minimising heat loss.
• Animals not with a compact shape have a large surface area, increasing heat loss.
• Small desert mammals have kidney structure adaptations to conserve water, reducing water loss.
• Small mammals in cold regions eat high energy foods to support their high metabolic rate.
• Small mammals have thick layers of fur or will hibernate.
• Osmosis is the diffusion of water molecules through a partially permeable membrane from a high water potential to an area with lower water potential
• Water potential is how likely a water molecule is to diffuse out or into a solution
• Pure water has the highest water potential
• If two solutions have the same water potential, then they are isotonic
• Factors that affect Osmosis:

  • The water potential gradient: the higher the water potential gradient, the faster the rate of osmosis
  • The thickness of the exchange surface: the thinner the surface, the faster the rate of osmosis
  • The surface area of the exchange surface: the larger the area, the faster the rate of osmosis
• Serial dilution process:

  1. Place test tubes into the rack

  2. Add 10cm of 1M sucrose solution and add 5cm of distilled water into the remaining test tubes

  3. Take a pipette to add 5cm of sucrose solution from the 1st test tube and add to the 2nd test tube - this halves the concentration to 0.5M

  4. Repeat for the remaining concentrations: 0.25M, 0.125M