Essay Questions 6, 7, 8 And 9

Essay Questions 6, 7, 8 and 9.

6 (a) Trypsin is an enzyme and peptide is a substrate. Peptide attached to the active site of trypsin. Enzyme – substrate is formed//Trypsin – peptide is formed. Trypsin(enzyme) speeds up the hydrolysis/breakdown of peptide. Amino acid is formed. Trypsin is unchange//Trypsin can be used again.

6 (b) Pepsin reaction pH 2 is the optimum pH for pepsin reaction. Pepsin is active in an acidic medium. The hydrochloric acid in the stomach prepares the medium for the reaction. The reaction is nil at pH more than 4//The reaction occurs in the range of pH 0 to 4. Pepsin is denatured/inactive in an alkaline medium.

Salivary amylase reaction pH 7 is the optimum pH for amylase reaction. Salivary amylase is active in the neutral medium. The medium is prepared by the saliva in the mouth. The reaction of amylase is nil at pH more than 9 and less than 5//The reaction occurs at pH 5 to 9. Amylase is denatured/inactive in an acidic and alkaline medium.

6 (c) The formation of urine Ultrafi ltrati on – Blo od are brought into the gl om erulus through the renal a rtery . The high pressure in the glomerulus forces water, ur ea, gluc ose, am ino ac ids, mine ral salt s and ot he r sma ll m olec ule s (glomerular filtrate) except red bl oo d cells and pl as ma pr ot eins into the caps ular spac e.

Reab so rpt io n Reabsorption occurs along the renal tubule (PCT, LOH,DCT) and the colle cting duc t. At the PC T, glucose, amino acids, Na+, Cl- are reabsorbed into blood capillaries through active transport. Water is reabsorbed through osmosis. At the LOH , water is also reabsorbed through osmosis. Na+ and Cl- are reabsorbed through active transport. At the DC T, more water, Na+ and Cl- are reabsorbed.

When the filtrate reaches the CD, very little salt (Na+ and Cl-) is left and 99% of water has been reabsorbed. Only little water will be reabsorbed here.

Secretio n Secretion occurs along the renal tubules and the collecting duct (activ ely a t the DC T). It occurs through PT and AT. The substances secreted include H+, K+, NH3, urea, creatinine, toxins and certain drugs. Secretion helps eliminate and increase waste removal. Urine mainly consists of water, nitrogenous wastes (urea, uric acid), salts (H+, K+, HCO3-), drugs or toxins.

7 (a) (i) The spoilage microbes are responsible for spoiling the quality of food. They cause the food to change colour/produce unpleasant odours/alter physically. The pathogenic microbes cause diseases. They attack/infect the human cells//produce toxic products which cause harmful effects.

7. (a)(ii) The disease can spread through food and water tr ans mis sio n, dr opl ets and airbo rne, di rec t cont ac t or thr oug h vector s. When a person consumes food or water which are contaminated with harmful/pathogenic microbes, he will be infected. Typhoid and cholera are such examples. Droplets containing viruses and bacteria from sneezes and cough of an infected person can cause illnesses such as colds. They can be transmitted through airborne.

Some pathogens are transmitted by vectors carrying diseases such as mosquitoes, flies and cockroaches. Malaria is caused by Plasmodium sp. transmitted by the mosquito Anopheles sp. Houseflies spread cholera and food poisoning.

Direct contact with an infected person or using his personal items such as towels and clothes can cause disease such as tinea and ringworm (skin disease) caused by fungus. Having sexual intercourse with them can also be infected with AIDS, syphilis or gonorrhoea. The pathogens can be found in their semen or vaginal fluid.

7.(b)(i) Immunity is the body resistance to the pathogens which cause a disease by identifying and destroying them.

7.(b)(ii) students must show relationship between A & B

7.(b)(ii)

8.(a) Paramecium aurelia and Paremecium caudatum shows an int ersp ecific comp etitio n. Both compete for the same resources. For example for food, space, oxygen and others. The rate of reproduction in Paramecium aurelia is higher than Paremecium caudatum. Paramecium aurelia is stronger and have better adaptations than Paramecium caudatum.

8.(b) The mass of harvested mustard in farm B is higher than the mass of harvested mustard in farm A. The competition in farm A is higher because the seedlings are too near to each other compared to farm B. The mustard seedlings co mp et e for the sam e reso urces such as water, nutrients, sunlight, oxygen and carbon dioxide. The mustard seedlings in farm B get more water, nutrients and other resources compared to farm A, therefore their growth rate is higher. In the end, the size of mustard planted in farm B is bi gg er and tal ler than farm A. The mustard shows an in tras pe cific compe ti tio n.

8.(c) Adv ant ag es Ecot ouris m can be developed in Kampung P. Artificial ecosystem can be planned well. The economic status of the villagers will increase.

Dis adv anta ges There will be disruption to the habitat. The mangrove swamp will be extinct. The area is exposed to wind and wave actions. It can also cause bad erosion. The animals will be extinct. The biodiversity will be affected. The food web/food chain will be also be disturbed. The natural cycle (eg. carbon cycle, nitrogen cycle, phosphates cycle) will be destroyed. We can say that the project will give mo re di sa dv antage s to the ecosystem.

9.(a) Form at ion of zy go te The sperm will fertilise the ovum to form a zygote.

Develo pment o f zy got e The zy go te will undergo mitosis to form an embr yo. The embryo divides repeatedly by mitosis to form a solid mass of cells called the morul a. The morula continues dividing by mitosis to form a hollow ball filled with fluid cavity called the bl as toc ys t. The blastocyst will implant itself to the endometrium during imp lant ati on.

9.(b)The mat erna l b lood and the foe tal bl oo d do not mix. Exchange of materials such as nutrients, respiratory gases and waste products occurs in the placenta. Anyway some substances like drugs, alcohol, carffeine, nicotine, HIV and rubella virus can peneterate. The mother’s blood group may be different from the foetus because of the influence from the father’s genotype. If the blood mix, it will clot and can cause blockage and this can lead to death. The placenta, therefore prevents the mixing of the blood groups from the mother and the foetus. The mother’s blood pressure is higher than the foetus. The placenta also protects the foetus from the high pressure because the vessels of the foetus will burst due to the high pressure of blood .

9.(c) The father is het erozy go us ( I A I o ). During meiosis he produces sperms that will inherit gene I A or I o . The mother is also het erozy go us ( I B I o ). During meiosis she produces an ovum that inherits gene I B or I o. After fertilisation, the zygote is produced. It then develops into a foetus.

The genotype of the foetus will either be I A I B , I A I o , I B I o or I o I o . Therefore the child will inherit either blo od gr oup AB, A, B or O. The chances of the child inherits blood group O will be 25 %. The child will have hom ozygous I o I o .