Revision for Mid year Examination
Topics

1)
2)
3)
4)
Biological Molecules (Nutrients)
Enzymes
Nutrition in Man
Nutrition in Plants
Biological Molecules
(Nutrients)

What are the components of the
nutrients we need?
Carbohydrate
Fats
Protein
Biological Molecules
(Nutrients)

What are the function of these
nutrients?
Biological Molecules
(Nutrients)

 How do we test for the nutrients?
Food Test
 Benedict’s Test
 Starch Test
 Emulsion Test
 Biuret’s Test
Enzymes

What are enzymes?
Enzymes are biological catalysts that speed up the rate
of reaction without themselves being chemically
changed at the end of the reaction.
Enzymes

Describe the effects of temperature on enzyme action.
 At low temperature, enzymes are inactive.
 Thus, little enzyme action.
 As temperature increases, enzyme action also
increases.
Enzymes

 Enzymes work best at their optimum
temperature
 Beyond their optimum temperature, enzymes are
denatured.
 Thus, enzyme action decreases.
Enzymes

Describe the effects of pH on enzyme action.
 Enzymes work best at their optimum pH.
 At extreme changes in pH, enzymes are denatured.
Enzymes

Explain the effects of temperature on enzyme action.
 At low temperature, enzymes have very little kinetic
energy and are inactive.
 They move slowly and collide less frequently with
the substrate molecules.
 Substrate molecules bind to enzymes’ active site less
frequently  little enzyme action
Enzymes

 As temperature increases, enzymes gain more kinetic
energy and moves around faster.
 Thus, enzymes collide with the substrate molecules
more frequently .
 Substrate molecules bind to enzymes’ active site
more frequently  enzyme action increases.
Enzymes

 Enzymes work best at their optimum temperature.
 Beyond their optimum temperature, active sites of
the enzymes are physically altered.
 Enzymes lose its specificity and can no longer bind
the substrate.
 Enzymes are denatured  enzyme action decreases.
Enzymes

Describe / Explain how enzymes work.
- Enzymes work based on the lock and key
hypothesis.
- Enzymes are like the lock and substrates are the
keys.
- Enzymes have active sites which have a specific
shape complementary to its substrate.
Enzymes

- Enzymes and substrate will collide.
- Substrate will bind to the enzymes at the active site.
- Products are then formed and released from the
enzymes’ active site.
Enzymes

- Enzymes remain chemically unchanged at the end of
the reaction.
- Enzymes can then be reused.
Nutrition in Man

Describe / Explain the role of bile in digestion
 bile is produced in the liver and secreted into the
duodenum
 bile emulsifies fats by breaking up fat droplets into
smaller droplets
 this increases the fats surface area for lipase to digest
into fatty acids and glycerol
Nutrition in Man
 Describe the parts played
in the digestion of food by
(i) the pancreas
(ii) the liver
The pancreas:
 pancreas secretes pancreatic juice into the duodenum
 pancreatic juice contains amylase, trysin and lipase for
digestion
 pancreatic amylase will digest starch to maltose
 trypsin digests proteins to polypeptides
 pancreatic lipase digests fats into fatty acids and glycerol
Nutrition in Man

(ii) the liver
 the liver produces bile which aids in the digestion of
fats
 bile helps to emulsify the fats by breaking it up into
smaller fat droplets
 this increases the surface area for lipase to digest
Nutrition in Man

 thus, lipase can digest fats faster
 liver plays a part in assimilation of glucose and
amino acids
 excess glucose is converted into glycogen by the
hormone insulin
Nutrition in Man

 glycogen is stored in the liver
 excess amino acids is deaminated whereby the
amino group is removed
 the remains of the amino acid is converted to glucose
and excess glucose is converted to glycogen
Nutrition in Man

 normal amounts of glucose and amino acids will
leave the liver via the hepatic vein
 the glucose is used for respiration to produce energy
 the amino acids is used for growth, repair of worn
out tissues and synthesis of protoplasm
Nutrition in Man

Describe what happens to fats as they pass through the
following regions of the alimentary canal:
 the mouth cavity
 the duodenum
 the rest of the small intestine
the mouth cavity
no fat digestion occurs in the mouth due to absence of lipase
Nutrition in Man

(ii)
the duodenum
 bile produced in the liver is secreted into the
duodenum
 bile emulsifies fats by breaking it up into smaller fat
droplets
 this increases the surface area for lipase to digest into
fatty acids and glycerol
Nutrition in Man

(ii) the rest of the small intestine
 in the ileum, the fatty acids and glycerol would be
absorbed into the lacteals in the villi
 villi are minute finger-like projections of the walls of the
small intestine in the lacteal, fatty acids and glycerol
recombines to form fats
 fats will then be carried away by the lymphatic vessels
Describe / Explain how the small intestine is adapted to carry
out absorption of nutrients

The small intestine is adapted for absorption in three ways:
 firstly, its inner walls are extensively folded to increase
surface area for absorption
 secondly, its wall bears numerous villi
villi are minute finger-like projections that increases the surface
area for absorption
 thirdly, the small intestine is long and coiled to provide
sufficient time for absorption
Describe / Explain how the villi is adapted to carry out its
function/s

 Main function of villi is absorption of digested food
substances
 Villi is richly supplied with blood capillaries and lacteals
 Glucose and amino acids are absorbed into the blood
capillaries
 fats are absorbed into the lacteal
 blood capillaries and lacteals carry away the absorbed
food substances quickly

 this maintains the concentration gradient for diffusion to
occur
 wall of the villi is also only one-cell thick
 this provides a short diffusion distance for diffusion to
occur faster