KNEC KCSE BIOLOGY TOPICAL QUESTIONS

How is a mammalian heart structurally adapted to its function?

29/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2015PP2QN08

How is a mammalian heart structurally adapted to its function?

ANSWERS

Has cardiac muscles; which contract and relax continuously/without fatigue;
Cardiac muscles are interconnected/form a network of fibres; to rapidly and uniformly spread the contractions;
Divided into four chambers; for the atria to receive blood and ventrical to pump blood out of the heart.
Divided into two sides by a longitudinal septum; to prevent mixing of oxygenated and deoxygenated blood;
Ventricles have thicker walls; to generate high pressure to pump blood;
Wall of left ventricle are thicker than those of right ventricle; to pump blood over a longer distance;
Has valves; to prevent back flow of blood for double circulation;
Cuspid valves have strands of connective tissues/cordaetandinae/tendinous; to prevent the valves from turning inside out during systole when ventricles contract;
Has coronary artery to nourish/supply oxygen/nutrients the heart muscles;
Has coronary vein; to remove metabolic wastes;
Enclosed by a pericardium; to keep it in position/prevent overdilation;
Pericardium is externally surrounded with a layer of fats; to cushion the heart against mechanical damage;
Pericardium secretes pericardial fluid; to reduce friction/absorb shock;
Has Sino Atrio Node (SAN); which acts as a pace maker;
Has Atrio Ventricular Node (AVN); which relays contraction waves from Sino Atrio Node to the purkinje tissue;
Has purkinje tissue/bundle of RS; to relay waves from Atrio Ventricular Node; to the ventricular myocardium;
Cardiac muscles have numerous mitochondria; to generate energy for the muscular contractions;
Vena cava and pulmonary vein; supply blood to the heart;
Aorta and pulmonary artery; transport blood away from the heart.

Comments

K.C.S.E Biology Q & A - MODEL 2015PP1QN03

29/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2015PP1QN03

.An individual is of blood group B positive.
(a) Name the antigens in the individual’s blood.
(b) Give the reason why the individual cannot receive blood from a blood group A donor.

answers

(a) (Antigen) B; Rhesus (antigen)/Rhesus factor/Antigen D
(b) Has antibody a in the blood plasma of the recipient and will correspond with antigen A in the donor’s blood, hence there will be antigen antibody reaction/agglutination.

Comments

K.C.S.E Biology Q & A - MODEL 2014PP2QN02

28/6/2020

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K.C.S.E Biology Q & A - MODEL 2014PP2QN02

The diagram below illustrates the role played by red blood cells in the transportation of carbon (1V) oxide.

(a) Other than the carbon (IV) oxide transportation in the red blood cells, name the other form of carbon (1V) oxide transportation in humans.
(b) (i) Name substance F
(ii) Name the enzyme marked C and state its role in the reaction.
Enzyme
Role
(c) Explain why transportation of carbon (1V) oxide in red blood cells is advantageous.
(d) Explain the role of calcium ions in blood clotting.

ANSWERS

(a) Carbonic acid/carbaminohaemoglobin/hydrogen carbonate;
(b) (i) Water;
(ii) Carbonic acid;
Role: catalyses reaction between carbon IV oxide and water to form (weak) carbonic acid;
(c) Prevents accumulation of acidity/maintains pH of blood since hydrogen ions combine with haemoglobin to form Haemoglobin acids;
Faster; due to the catalytic effect of carbonic anhydrase;
(d) Activates thromboplastin; thrombokinase to neutralize heparin/convert prothrombin to thrombin;

Comments

K.C.S.E Biology Q & A - MODEL 2014PP1QN24

28/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2014PP1QN24

The table provided shows the transportation of substances in the human body.

Name the substances represented by
M
N
P

ANSWERS

M - lungs;
N - Urea, ammonia. ;
P - Digested food. water; mineral ions;

Comments

Describe the process of blood clotting in human beings.

28/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2013PP2QN07

Describe the process of blood clotting in human beings.

ANSWERS

When a blood vessel is cut/injured platelets/thrombocytes/damaged tissue/wound is exposed to the air: they release thrombokinase/thromboplastin ; an enzyme that activates the conversion of prothrombin: to thrombin: in the presence of calcium ions: vitamin K/ phylloquinone ; is needed for the formation of prothrombin; Thrombin converts (soluble blood protein) fibrinogen ; into (the fibrous form) fibrin; which forms a mesh / network across the wound: The clot so formed prevents excessive bleeding: and entry of disease agents/pathogens/micro-organisms/microbes;

Comments

Explain three protective functions of mammalian blood.

26/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2013PP1QN24

Explain three protective functions of mammalian blood.

answers

Contains antibodies that defend the body from foreign antigens;
Has white blood cells that produce antibodies/while blood cells engulf antigens;
Has platelets that initiate blood clotting to prevent excessive bleeding at an open wound prevent entry of pathogens;

Comments

State the advantage of possessing blood group AB.

26/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2013PP1QN11

State the advantage of possessing blood group AB.

answers

Can receive blood from any donor universal recepient;

Comments

State two differences between open and closed circulatory systems.

26/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2012PP1QN28

State two differences between open and closed circulatory systems.

answers

Open Closed
Blood flows in haemocoel Blood confined in vessels;
sinuses/body cavity directly
in contact with cells
Blood flows at low pressure Blood flows at high pressure;
Blood lack pigments Blood has pigments for oxygen and
Carbon (IV) Oxide transportation

Comments

K.C.S.E Biology Q & A - MODEL 2012PP1QN23

26/6/2020

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K.C.S.E Biology Q & A - MODEL 2012PP1QN23

Name the strengthening materials found in the following support tissues:
(a) collenchyrna;
(b)Xylem

answers

(a) Cellulose;
(b) Lignin;

Comments

State two ways in which heart muscles are special.

26/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2012PP1QN11

State two ways in which heart muscles are special.

answers

Can contract continuously without fatigue;
Their contraction is started by the muscles themselves/myogenic;

Comments

Explain how structural features in terrestrial plants affect their rate of transpiration.

25/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2011PP2QN07

Explain how structural features in terrestrial plants affect their rate of transpiration.

answers

Plants in arid, semi-arid and desert habitats have leaves covered with thick/waxy cuticles; that are waterproof/impermeable to water; allowing for reduced rate of transpiration; Sunken stomata; in some desert/semi arid areas plants have water vapour accumulating in the pits; reducing rate of transpiration (as the moisture in the pit is carried away by wind.) Most plants have few or no stomata on the upper surface of leaf; the fewer the stomata the less the water lost from the plant. Some plants have small stomata/stomatal size decrease when guard cells are flaccid; thus reducing transpiration rate. Plants with small/folding leaves; expose less surface area; hence reduce the rate of transpiration. Leaves with shinny surfaces; reflect light resulting
reduced leaf temperatures; thus reducing the rate of transpiration. Some plants have leaves covered with hairs/scales; which trap a layer of moisture; the leaf surface reducing rate of transpiration. Mesophyte have a thin layer of cuticle; to facilitate high transpiration rate; brad lenses exposing large area to transpiration; Many stomata on both leaf surfaces provide many apartunes to enhance transpiration.

Comments

Describe how oxygen in the alveolus reaches the red blood cells.

25/6/2020

Comments

K.C.S.E Biology Q & A - MODEL 2011PP2QN03

Describe how oxygen in the alveolus reaches the red blood cells.

answers

Inhaled oxygen dissolves in moisture in the alveolus; since the oxygen concentration
in blood is lower; than in the alveolus, oxygen diffuses; through the alveolus
epithelium, the capillary wall into the plasma; and finally into the red blood cells.