NUTRITION IN PLANTS AND ANIMALS
The diagram below shows chemical reactions I, and II which are controlled by enzymes respectively.
1. 1989 Q1 P1
Name reaction II and enzyme B
K.C.S.E Biology Q & A - MODEL 2019PP2QN06
The table below shows the rate of product formation for two enzymes, H and J over a range of pH values
(a) On the same axis, plot graphs of the rate of product formation against pH.
GRAPH PAPER (b) Account for the rate of product formation for enzyme H between: (i) pH 1.0 and 3.0 (ii) pH 3.0 and 7.0. (c) From the graph, determine: . (i) the pH value at which the rate of product formation of the two enzymes was the same (ii) the value of the rate of product formation for enzymes H and J at the pH value stated in (c)(i) above (iii) the optimum pH value for enzyme J (d) State one variable that may lead to the change in the optimum rate of product-formation of the two enzymes. (e) Suggest with a reason, the likely part of the human alimentary canal where enzyme H would be found.
answers
​(b) (i) Rate of product formation increases with the increase in pH to the optimum then decreases;
pH 5 is the optimum pH value for activity of enzyme H; between pH 1 and 2 enzyme H/enzyme molecules are activated; Between pH 2 and 3 enzyme H (enzyme molecules) are denatured/destroyed; (. Enzyme is inactivated/ less active for denatured (ii) Rate of product formation (sharply) decreases with increase in pH; Enzyme H is (not formed by increase in pH hence is denatured); No product forms above pH 4.0 to 7.0; because all enzymes (enzyme molecules) are denatured; (c) (i) 4.0 (ii) 15.0 mg/hr (iii) 7.0 (d) -Temperature -Substrate concentration; -Enzyme concentration; -Cofactors -Co-enzymes -(Enzyme) inhibitors (e) Stomach; Acidic medium/Low pH K.C.S.E Biology Q & A - MODEL 2019PP1QN19
Below is a diagram of the human digestive system.
​(a) Label with Y on the diagram where enzyme amylase is produced.
(b) Besides the digestive role, explain one other function of the part labelled H.
answers
(b) Endocrine function/secrets (insulin/ glucagon) hormones; responsible for blood sugar regulation;
K.C.S.E Biology Q & A - MODEL 2019PP1QN18
Name the type of tooth in carnivores mainly used for piercing and killing of preys.
answers
K.C.S.E Biology Q & A - MODEL 2019PP1QN07
Distinguish between chemical and mechanical digestion.
answers
K.C.S.E Biology Q & A - MODEL 2018PP2QN08
Describe what happens to a meal rich in proteins along the alimentary canal from ingestion to egestion.
answers
​The meal is ingested through the mouth; (In the mouth), it is chewed/masticated (by teeth); to reduce/break it into smaller particles; mixed with saliva (from salivary gland);
The food is then rolled (by the tongue) into boluses; and pushed down into the oesophaghus/swallowed; The boluses move by peristalsis (into the stomach); Constant contractions/relaxations of the stomach walls mix the food, (giving rise to chime); Presence of food in the stomach further stimulates production of gastric juice; which contains pepsinogen; and rennin/chymosin; Pepsinogen is activated to pepsin; by hydrochloric acid; (contained in the gastric juice). Pepsin breaks down proteins to peptides; Rennin converts/coagulates the protein, caseinogen; in milk to casein; (which is abundant in young children). It is then pushed into the duodenum (through the pyloric sphincter); Pancreatic juice in the duodenum contains trypsin; which digests proteins into peptides; (secreted in an inactive form, trypsinogen) In the ileum, intestinal juice/Succus enfericus is secreted; It contains peptidase enzymes; which breaks down polypeptides into amino acids; It also contains polypeptidase enzyme; which breaks down peptides to amino acids,completing the process of digestion of the proteins; The amino acids are absorbed into the bloodstream/pass through the epithelia of the villi, and the capillary walls into the blood-stream; by active transport; The undigested/indigestible proteins/food substances pass through to the colon/large intestines; where water is absorbed; leaving a semi-solid waste material being passed on to the rectum; then out through the anus (as faeces);
K.C.S.E Biology Q & A - MODEL 2018PP1QN03
Which sets of teeth would be used in chewing sugarcane for maximum extraction of sap?
answers
K.C.S.E Biology Q & A - MODEL 2017PP1QN17
How is the surface area increased in the mammalian small intestines?
answers
K.C.S.E Biology Q & A - MODEL 2017PP1QN06
Name two enzymes in the human digestive system which are secreted in an inactive form.
answers
K.C.S.E Biology Q & A - MODEL 2017PP1QN03
During a practical investigation on food tests, students were provided with the following reagents.
Benedict’s solution Sodium hydrogen carbonate Dilute hydrochloric acid.
​(a)Identify the food substance the students were to test.
(b) State the role of dilute hydrochloric acid and sodium hydrogen carbonate during the experiment. (i) Dilute hydrochloric acid (ii) Sodium hydrogen carbonate
answers
​a) Non reducing sugar;
b) (i) Hydrolyze/break down sucrose! non reducing sugars to reducing sugars/glucose/fructose; (ii) neutralize the acid;
K.C.S.E Biology Q & A - MODEL 2016PP1QN24
How does nutrition as a characteristic of living organisms differ in plants and animals?
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN23
​
State two functions of saliva.,
answers
K.C.S.E Biology Q & A - MODEL 2016PP1QN13
State two factors that affect enzymatic activities
(b)Explain how one of the factors stated in (a) above affects enzymatic activities.
answers
K.C.S.E Biology Q & A - MODEL 2015PP1QN17
How is a human stomach adapted to
(i) protein digestion? (ii) churning?
answers
​ (i) Has gastric glands; that secrete gastric juice;
(ii) Thick muscular wall; that contract and relax;
K.C.S.E Biology Q & A - MODEL 2014PP2QN07
Describe the process of carbohydrate digestion in human beings.
answers
​In the mouth;
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