Human nails, one of the products of assimilation. Image credit

Human nails, one of the products of assimilation. Image credit

ZIMSEC O Level Combined Science Notes:Products of digestion and the Absorption and Assimilation processes

  • After food has been digested in can now be used.
  • The end products ( which would now be in the form of small soluble molecules) pass through the small intestine into the blood.
Image credit

Image credit

  • The walls of the small intestine are specially adapted so that as many food molecules as possible can be absorbed.
  • The walls of small intestine is lined by thousands of microscopic folds and projections known as villi.
  • Villi-this are long and thin finger-like projections that increase the surface area over which soluble food can be absorbed.
  • As the soluble food moves past the villi, the molecules are absorbed.
  • There are two ways in which this happens:
  • Diffusion-Some molecules pass from the intestines into the villi and then into the transport system.
  • This happens because there is a higher concentration of food molecules in the intestine than in the transport system.
  • Active uptake-some molecules pass in the same direction by active uptake.
  • This means that energy is needed to absorb the molecules.
  • Molecules move into blood where their concentration are low.
  • Both processes ( active uptake and diffusion) ensure that large numbers of food molecules enter the transport system.
  • Often times these molecules are more than what the body needs.
  • The blood carries the food to the liver using the hepatic portal vein.
  • Hepatic portal vein-is the blood vessel that carries absorbed food from the small intestines to the liver.
  • In the liver the food is regulated/controlled.
  • If there is too much food it is changed into something else and stored.
  • Excess glucose can be changed into an insoluble compound called glycogen
  • and stored into the liver until it is needed.
  • Or it can be changed to fat and stored under the skin.
  • The rest of the glucose is transported to all parts of the body.
  • It is used up during the process of respiration.
  • Respiration produces energy.
  • Amino Acids are used to make new tissue during growth and to repair old or damaged tissues and to make structures such as hair and nails.
  • If there are too many amino acids from protein digestion they must be processed.
  • Amino acids and proteins cannot be stored in the body.
  • They are converted into a wast substance called urea.
  • Urea is later removed from the body by the kidneys and passed out as urine.
  • The liver also processes poisonous substances which are circulating in the blood.
  • Alcohol is a poison and need to be removed quickly.
  • As the blood passes through the liver, the alcohol is broken down and the end products are removed by the kidneys.
  • People who drink too much alcohol suffer from a disease called liver cirrhosis.
  • The soluble foods flowing around the body in the bloodstream pass into the cells by diffusion.
  • Once in the cells the molecules can be assimilated.
  • Assimilation-is the absorption of nutrients into the body after digestion in the intestine and its transformation in biological tissues and fluids. Assimilation is occurring in every cell of the body to help develop new cells.
  • The amino acids are re-arranged to make new molecules because the protein molecules of a mammal’s tissues and cells re different from the molecules consumed in the food.
  • The fatty acid molecules and the glucose are also used up in cells.
  • Parts of the molecules are joined up with other molecules to make new molecules.
  • Some are used up to release energy during respiration.
  • Fatty molecules are used for cell membranes and for protection around organs like the heart and kidneys.

To access more topics go to the Combined Science Notes page.