ORGANISMS EXCHANGE SUBSTANCES WITH THEIR ENVIRONMENT

Question 1

What happens during digestion?

Answer 1

Large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes

Question 2

How do mammals digest carbohydrates?

Answer 2

• In the mouth, teeth chew the food which increases the surface area. Your salivary glands release amylase which hydrolyses the 1-4 glycosidic bonds in starch into smaller chains and maltose
• Aesophaegus squeezes the food to the stomach- peristalsis
• the food is then transported to the Geodenum, where pancreatic amylase hydrolyse starch into maltoses
• In the ileum maltose hydrolyse the maltose into a glucose, where it is absorbed into the blood stream

Question 3

How do mammals digest lipids?

Answer 3

• In the geodenum fat digestion occurs, resulting in fatty acids and monoglycerides, these are emulsified by bile salts
• lipase hydrolysis then forms micelles, which are absorbed by the epithelial cells (endocytosis)
• The soft ER reconstructs the micelles into lipids, the bile salts are sent to the liver
• the Golgi apparatus combines the fatty globules with proteins to form CHYLOMICRONS (more soluble)
• they fuse with the basil membrane and are exocytosis into the lacteal or bloodstream

Question 4

How are proteins digested in mammals?

Answer 4

• pancreas releases endopeptidases and exopeptidase to the stomach
  -The stomach releases peptic juice which contains hydrochloric acid to maintain pH two and kill pathogens, and endopeptidases
• in the stomach endopeptidases hydrolysed bonds within the polypeptide chains , the exopeptidases then hydrolyse the bonds at the terminal end of the chain
• In the ileum dipeptidases hydrolyse dipeptides into amino acids

Question 5

What is the co-transport mechanism for the absorption of amino acids and disaccharides?

Answer 5

• sodium potassium pump actively transport, sodium ions out of the cell and potassium ions into the cell
• This maintains a diffusion gradient for sodium into the cell
• sodium can only use facilitated diffusion through a carrier protein which requires sodium to cotransport with amino acids or monosaccharides in order to be transported into the cell
• The high concentration of monosaccharides in the cell means that facilitated diffusion into the bloodstream occurs readily

Question 6

What is the basic structure and function of the villi?

Answer 6

• they have a large capillary network which increases the surface area for absorption, a capillary is one Celtic and therefore have a short diffusion pathway, blood is continually flowing through capillaries maintaining the concentration gradient
  -the Villi is surrounded by epithelial cells, they have microvilli, this increases the surface area, embedded enzymes e.g. dipeptidases, sucrases, this insures that the enzymes don’t get lost in the bloodstream, they also contain many mitochondria for active transport
• goblet cells are also present around the epithelial cells to produce mucus
• The lacteal transport lipids
• blood flows from capillary to liver to be stored, the vein is called hepatic portal

Question 7

True or false? Bigger organisms have a smaller SA:V ration than smaller organisms

Answer 7

TRUE

Question 8

Why is a large SA:V ratio important in organisms?

Answer 8

• Increases metabolic rate

Question 9

How do organisms with smaller SA:V ratios adapt to facilitate exchange?

Answer 9

• Short diffusion pathways - capillary walls only one cell thick
• Folds in the membranes of cells eg. villi and microvilli
• Maintained concentration gradient - heart pumps blood around the body so that blood in the lungs have a low concentration of oxygen, encouraging diffusion
• Proteins - protein channel and carriers facilitate diffusion and active transport