KNEC KCSE BIOLOGY TOPICAL QUESTIONS - ATIKA SCHOOL

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K.C.S.E Biology Q & A - MODEL 2019PP2QN06

2/7/2020

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

2/7/2020

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;

Name the type of tooth in carnivores mainly used for piercing and killing of preys.

2/7/2020

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

canine acc. canines

Distinguish between chemical and mechanical digestion.

1/7/2020

K.C.S.E Biology Q & A - MODEL 2019PP1QN07

Distinguish between chemical and mechanical digestion.

answers

chemical digestion entails the action on / broken down of ingested food materials (in the alimentary canal) by the action of digestive enzymes (and converted into form that can be easily absorbed or assimilated in to the body system)while mechanical digestion refers to physical break down of(large) food molecules (into smaller form or pieces )which can subsequently be acted upon by digestive enzymes

Describe what happens to a meal rich in proteins along the alimentary canal from ingestion to egestion.

1/7/2020

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);

Which sets of teeth would be used in chewing sugarcane for maximum extraction of sap?

1/7/2020

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

Premolars; molars;

How is the surface area increased in the mammalian small intestines?

30/6/2020

K.C.S.E Biology Q & A - MODEL 2017PP1QN17

How is the surface area increased in the mammalian small intestines?

answers

Presence of numerous villi/microvilli;
Being long;
Being highly coiled;

Name two enzymes in the human digestive system which are secreted in an inactive form.

30/6/2020

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

Pepsin (secreted as pepsinogen);
Trypsin (secreted as trypsinogen);
Rennin/chymosin (Secreted as Prorennin/Prochymosin;

K.C.S.E Biology Q & A - MODEL 2017PP1QN03

30/6/2020

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;

How does nutrition as a characteristic of living organisms differ in plants and animals?

30/6/2020

K.C.S.E Biology Q & A - MODEL 2016PP1QN24

How does nutrition as a characteristic of living organisms differ in plants and animals?

answers

Plants make their own food from carbon (IV) oxide and water in the presence of light /photosynthesize/ autotrophic; while animals eat readymade food (some plants and animals heterotrophic;
If photosynthesis described all raw materials must be mentioned;
Carbon (IV) oxide the (IV) must be bracketed.
If sources of food for animals are mentioned then both plants and animals must appear.

State two functions of saliva.

30/6/2020

K.C.S.E Biology Q & A - MODEL 2016PP1QN23

State two functions of saliva.,

answers

Lubricating food;
Digestion of starch;
Moistens food; Provides alkaline medium;
Softens food/ Dissolves food.

State two factors that affect enzymatic activities

30/6/2020

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

Temperature PH co- factors, co- enzymes; enzyme product concentration; substance concentration/ metabolic poison

(b)

Temperature- increase in temperature increases rate of enzymatic activity upto an optimum
Low temperature decreases enzymatic activity/ too high temp above optimum point denatures enzymes.
Ph- Enzymes work best at optimum ph/extreme ph denatures enzymes.
Enzyme conc – Increase in conc. increase enzymatic activity.
Co- enzymes – complements enzymes increasing rate of activity
Substrate concentration increase enzymatic activity up to certain level.

K.C.S.E Biology Q & A - MODEL 2015PP1QN17

29/6/2020

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;

Describe the process of carbohydrate digestion in human beings.

28/6/2020

K.C.S.E Biology Q & A - MODEL 2014PP2QN07

Describe the process of carbohydrate digestion in human beings.

answers

In the mouth;

Food is chewed; to increase surface area for enzyme activity/saliva contains salivary amylase;
Saliva mixes with food and provides an alkaline medium; for amylase enzymes;
Salivary amylase acts on starch and converts them to maltose;

In duodenum;

Food is mixed with bile; and pancreatic juice;
Bile provides alkaline medium; for activity of duodenal enzymes; and neutralizes acidic
chyme from the stomach;
Pancreatic juice contains pancreatic amylase; which converts starch to maltose;

In the Ileum;

Epithelial cells in Ileum secrete succus entericus; which contains enzymes;
sucrase; which acts on sucrose and converts it to fructose and glucose;
Lactase; which acts on lactose and converts it to galactose and glucose;
Maltase; acts on maltose and converts it to glucose;

K.C.S.E Biology Q & A - MODEL 2014PP1QN26

28/6/2020

K.C.S.E Biology Q & A - MODEL 2014PP1QN26

The table provided shows the concentration of sodium and iodine in sea water and cell sap of a plant.

(a) (i) Name the process through which the plant cells take up sodium ions.
(ii) Give a reason for your answer in (a) (i) above.
(b) If the plant was sprayed with a chemical that inhibits respiration:
(i) which of the two ions uptake will be affected’?
(ii) give a reason for your answer in (b) (i) above.

ANSWERS

(a) (i) Diffusion;
(ii) Sea water contains a higher concentration of sodium ions than the cell sap;
(b) (i) Iodide ions;
(ii) Sea water has a lower concentration of iodide ions than the cell.
The plant requires energy to take up the iodide ions (by active transport);

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