1. Revision for Mid year Examination
Science (Biology)
Revision for Mid year Examination

2. Topics Biological Molecules (Nutrients) Enzymes Nutrition in Man
Nutrition in Plants

3. Biological Molecules (Nutrients)
What are the components of the nutrients we need?
Carbohydrate
Fats
Protein

4. Biological Molecules (Nutrients)
What are the function of these nutrients?

5. Biological Molecules (Nutrients)
How do we test for the nutrients?
Food Test
Benedict’s Test
Starch Test
Emulsion Test
Biuret’s Test

6. 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.

7. 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.

8. Enzymes Enzymes work best at their optimum temperature
Beyond their optimum temperature, enzymes are denatured.
Thus, enzyme action decreases.

9. Enzymes Describe the effects of pH on enzyme action.
Enzymes work best at their optimum pH.
At extreme changes in pH, enzymes are denatured.

10. 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

11. 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.

12. 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.

13. 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.

14. 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.

15. Enzymes
Enzymes remain chemically unchanged at the end of the reaction.
- Enzymes can then be reused.

16. 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

17. 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

18. Nutrition in Man 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

19. 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

20. 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

21. 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

22. 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
no fat digestion occurs in the mouth due to absence of lipase

23. 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

24. Nutrition in Man 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

25. 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

26. 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

27. 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