Biology Chapter 6.1 Test Revision (+chapter 2.3)   

Monosaccharides are single sugar units Disaccharides consist of 2 monosaccharides linked together. (e.g. maltose is made by linking 2 glucose molecules togethere.g.2 sucrose is made by linking a glucose and a fructose) Polysaccharides consist of many monosaccharides linked together (e.g. starch, glycogen and cellulose- all made by linking together glucose molecules

 Lipids and carbohydrates are both used for energy storage in humans  Lipids usually used for long term energy storage  Lipids that are used as fats are stored in specialised groups of cells called adipose tissue (located beneath the skin and also around some organs e.g. the kidneys)    

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Amount of energy released in cell respiration per gram of lipids is double the amount released from a gram of carbohydrate Stored lipids have some secondary roles that could not be performed as well by carbohydrates Because lipids are poor conductors of heat- can be used as heat insulators Fat is liquid at room temperature- can also act as a shock absorber- reason for adipose tissue around the kidneys and some other organs Glycogen is the carbohydrate that is used for energy storage- in liver + some other muscles Glycogen is used for short term storage Because glycogen can be broken down to glucose rapidly and then transported easily by the blood to where it is needed. Glucose can be used in either anaerobic or aerobic respiration Whereas fats and fatty acids can only be used in aerobic respiration

 Health risks of fats  Positive correlation between saturated fatty acids intake and rates of CHD (coronary heart disease)  However, finding a correlation doesn’t prove that saturated fats cause the disease  Populations that don’t fit the correlation

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Kenya has a diet that is rich in meat, fat, blood & milk Therefore high consumption in of saturated fats yet CHD is almost unknown among the Maasai High fats leads to obesity

Mouth

Chewing- saliva moistens food to make a bolus for swallowing salivary amylase begins chemical digestion for starch

Salivary glands

Secrete saliva, includes amylase to being digestion of starch

Oesophagus

A wave of muscle contractions pushes the bolus into the stomach

Stomach

Muscular contractions continue mechanical digestion- acid kills bacteria-pepsin begins digestion of protein

Liver

Secretion of surfactants in bile to break up liquid droplets

Gall bladder Pancreas

Storage and regulated release of bile Secretion (taking from outside to inside) of lipase, amylase and protease Bile from the liver and gall bladder neutralises acid and emulsifies fatspancreatic amylase and lipase digest carbohydrates and fats- trypsin digests polypeptides to amino acids

Small intestine (duodenum)

Small intestine (ileum)

Lower half of small intestine absorbs nutrients into the blood via the villi

Large intestine

Water is reclaimed and returned to the blood leaving semi-solid faecesstored in rectum

Rectum Anus

Stores faeces temporarily Faeces- containing undigested food, dead cells + other waste- is forced out of anus

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Need for digestion of large food molecules- to break down the diverse mixture of large carbon compounds in food to yield ions and smaller compounds that can be absorbed Need for enzymes in digestion- digestion requires surfactants to break up lipid droplets and enzymes to catalyse reactions

 The contraction of circular and longitudinal muscle of the small intestine mixes the food with enzymes and moves it along the gut  Food is moved by peristalsis (wave of contractions moving food along the digestive system, especially the intestine)  Smooth- not striated muscle-short cells. It exerts force most of the time-moderate force mostly-occasionally high level of force when required to move food-it is divided into longitudinal and circular muscles.  In small intestine to churnin (movement here is very slow) allowing digestion to take place- best by mixing substrate and enzyme Amylase  digest starch Lipases  to digest triglycerides and phospholipids Proteases  to digest proteins and peptide  Digestion in the small intestine  Enzymes digest most macromolecules in food into monomers in the small intestine  Enzymes secreted by the pancreas into the lumen of the small intestine carry out these hydrolysis reactions -Starch is digested to maltose by amylase -Triglycerides are digested to fatty acids and glycerol or fatty acids and monoglycerides by lipase -Phospholipids are digested to fatty acids, glycerol and phosphate by phospholipase

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-Proteins and polypeptides are digested to shorter peptides by protease Because of the great length of the small intestine, food takes hours to pass through, allowing time for digestion of most macromolecules to be completed Some substances remain largely undigested- because humans cant synthesise the necessary enzymes Cellulose for example is not digested and passes on to the large intestine as one of the main components of dietary fibre The process of taking substances into cells and the blood is called absorption In the human digestive system nutrients are absorbed principally in the small intestine The rate of absorption depends on the surface area of the epithelium that carries out the process The small intestine in adults is approx 7m long and 25-30mm wide and has lots of folds on its inner surface giving a large surface area Villi and micro-villi increase the surface area Villi are small projections of the mucosa on the inside of the intestine wall A villus is between 0.5mm and 1.5mm long and there can be as many as 40 of them per square mm of small intestine wall. They increase the surface area by a factor of about 10 Glucose cant pass through the plasma membrane by simple diffusion because its polar and therefore hydrophilic Sodium-potassium pumps in the inwards-facing part of the plasma membrane pump sodium ions by active transport from the cytoplasm to the interstitial spaces inside the villus and potassium ions in the opposite direction To have balance concentration This creates a low concentration of sodium ions inside the villus epithelium cells Sodium-glucose co-transporter proteins in the microvilli transfer a sodium ion and a glucose molecule together from the intestinal lumen to the cytoplasm of the epithelium cells This type of facilitated diffusion is passive but it depends on the concentration gradient of sodium ions created by active transport Glucose channels allow the glucose to move by facilitated diffusion from the cytoplasm to the interstitial

spaces inside the villus and on into blood capillaries in the villus   

Villi  finger like extensions that increase the surface area of the ileum Lacteal  used to transport and absorbs dietary fats in the villi-it is part of the lymph system that eventually joins up to the capillaries Circular muscle to longitudinal muscle