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BIOLOGY
PAPER 2
JULY/August 2014
Marking scheme:
1.
a)i)
(2mks)
ii) Auxins/ produced by shoot and root tip accumulate on lower side of shoot and root due to gravity;
higher concentration of auxins on lower side of shoot causes rapid growth; than upper side of the shoot. Therefore, the shoot
bends upwards;
higher concentration of auxins on lower side of the root inhibits rapid growth therefore the root bends downwards;
(4mks)
b) Use of a klinostat;
(1mk)
c) Phototropism that exposed leaves to maximum light for photosynthesis;
Geotropism enables roots to extend deeply in the soil for anchorage;
(any one 1mk)
2 a)
i) Optimum temperature for maximum enzyme activity;
Temperature below optimum level inactivate the enzymes/ temperature above optimum level denatures enzymes;
ii) Optimum PH for maximum enzyme activity; enzymes are denatured by pH below optimum/ strong acid or alkalis;
(2mks)
b) When blood sugar level rises above normal. Insulin hormone is produced;
insulin stimulate liver cells to convert glucose into glycogen. Also stimulate liver cells to convert glycogen into fats/
stimulates liver cells to increase oxidation of glucose;
when blood sugar level falls below normal level, glucagon hormone is produced; glucagou stimulate the liver cells to convert
glycogen to glucose;
(4mks)
3 a) – Increase the number of aquatic animal;
- Reduce the number of water weeds;
- Cover the jar with alluminium foil to block light from reacting the water weeds;
(any two 2mks) b) i)
Carbon IV oxide was absorbed from water; and used for photosynthesis; without replacement. The PH of water rises;
(3mks)
ii) Carbon iv oxide was produced; by animals during respiration; this reduced the ph of water;
(3mks)
4 a) Gene for red fur/colour and gene for white fur or colour are co-dominance;
Acc: partial dominance /incomplete dominance
(1mk)
b) Parental genotype
RW
Parental Gamete
X
RR
;
x
F. Genotype
F.
phonotype
Red
Red
Roan
Roan
Phenotypic Ratio Red
Red : Roan
1 : 1
(4mks)
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c) Plant breeding / Animal breeding
Improvement of yields;
(any 1)
d)
– Mutation;
- Crossing over;
- Fertilization;
- Independent assortment of genes;
Any two 2mk)
5 a)
S-Pancrease;
U- Duodenum;
b) Emulsification of fats; to increase the surface area for reaction of lipase; provide alkaline PH; for action for pancreatic amylase;
lipase; Trypsin; / Neutralize acidic chyme from stomach; to provide alkaline medium for efficient enzymatic activity;
(Any four)
(4mks)
c) i)
Pancreatic trypsin;
pancreatic amylase;
pancreatic lipase;
(Any two)
(2mks)
ii)
- Trypsin converts proteins to peptides;
- Pancreatic amylase converts starch to maltose;
- Pancreatic lipase converts lipids to fatty;
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Acids and glycerol;
(any two)
(2mks)
6a) A-Intermittent /Discountinous growth;
B- Continous growth;
b) Rigid/hard exoskeleton; prevents growth; the exoskeleton is shed during moulting; this allows rapid growth ;to occur
before the new exoskeleton hardens up;
(4mks)
c) Ecdysone/ moulting hormone;
(1mk)
(d) i) P&Q
Slow rate of growth, due to small number of cells dividing; the young organism is still adapting to new environment;
iii) Q & R
- Rapid/ fast rate of growth; due to large number of dividing cells;
- The organisms has adapted to the environment;
(4mks)
- No limiting factors like space, wastes e.t.c.;
e) i) Internal fertilization;
ii) Provide protection to the developing embryo from harsh environment;
- Less number of gametes are involved./ No waste of gametes;
- Developing embryo experiences little environmental changes;
(Any two)
f) i) Meiosis;
ii) Crossing over;
Synapsis/ formation of bivalents;
(2mks)
(1mk)
(2mks)
7. A balanced diet refers to a meal (food) that contains all the nutrients (carbohydrates, proteins, lipids, vitamins, mineral salts and
water) in their right proportion;
A balanced diet is important to children because it contains:(i) Proteins that play the following roles in children:- Forms body structures;
- Used in formation of enzymes;
- Forms haemoglobin found in red blood cells;
- Forms hormones used to regulate life processes;
- Forms antibodies that provides immunity against diseases;
- Is oxidized during starvation to release energy,
ii) Carbohydrates that plays the following roles in children:- Provide energy required by children during oxidation;
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iii) Roughage that plays the following roles:-Makes food to be bulk hence a child gets satisfied easily;
- It promotes peristalysis which prevents constipation in children;
iv) Lipids
- are oxidized to release energy;
- Forms part of the structure of the cell membrane;
- Used as an insulator against excess heat loss in children/
- Used to form layers around organs which protect them from mechanical injury;
- Act as a source of metabolic water
- Stores various types of vitamins ie. Fat soluble
v) Water
- used to dissolve food;
- It cools the body;
- Provides a media for transport;
Facilitates hydrolysis process;
Maintains the shape of the cells;
vi) Mineral salts includes:- Calcium for teeth and bone formation to prevent rockets
- Phophorus for teeth and bone formation
- Iodine used in formation of thyroid hormone which prevents goitre;
- Iron used for haemoglobin formation that prevent anaemia;
vii) Vitamins that play at the following roles:- Vitamins A prevent poor night vision in children;
- Vitamin B1 prevents beriberi
- Vitamin B2 prevents pellegra
- Vitamin B12 used in formation of blood cells to prevent pernacious anaemia;
- Vitamin C protects against infection that prevent scurvy
- Vitamin D prevents rickets;
- Vitamin E prevents sterelity;
- Vitamin K prevents excessive bleedings;
(Any 20)
8 The gaseous system in mammals includes the nostrils, trachea, bronchus, bronchioles, the lungs, the rib cage, the intercostals
muscles, the diaphragm, the vertebral column;
The Nostrils:
Is lined with hairs that trap foregn particles in the hair; is lined with goblet cells that secret mucus which trap solid particles and
pathogens;
Tranchea / wind pipe
- Made up of incomplete rings of cartilage a long its length which resist collapse when pressure is low in chest cavity;
- The incomplete cartilage rings have gaps on the side facing the oesophagus which allow smooth swallowing;
- It is lined with goblet cells that secrete mucus that trap foreign particles and pathogens;
- It is lined with cilia which move mucus upwards into the pharynx;
- Has epiglottis that prevents food entering into it during swallowing;
Lungs
- They are covered with pleural membrane;
- The pleural membrane secrets pleural fluid that lubricates the lungs (reduce friction) during movement;
- The lungs are elastic hence expand and contract to hold and expel large volume of air;
- The lungs are made up of very many alveoli that gives a large surface area for gaseous exchange (70m2)
- The alveoli are:- Moist which dissolve the diffusing gases;
- Covered by a thin layer of wall for easy diffusion of gases a cross it;
- Highly vascularised which enhances faster transportation of gases;
Diaphragm
- a muscular layer that contract and relax to facilitate inhalation and exhalation respectively;
The ribcage
-they protect the lungs from mechanical damage;
Provide surface for the attachment of the intercostals muscles;
The ricage and intercostals muscles forms an air-tight thoracic cavity that maintains constant air pressure;
Intercostals muscles
They contract and relax which changes the thoracic volume to enhance inhalation and exhalation in mammals;
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