BECE Past Questions & Answers – 1995 (SCIENCE)

SCIENCESectionB

SOLUTIONS

ESSAY

1. (a) (i) Diffusion
The random movement of atoms, molecules, orions from one sitein a mediumto
another, resultingin completemixing
Or:
Themovement of particles of asubstance fromaregion ofhigher concentration to a
region of lower concentration

(ii)
SurfaceTension
A condition existingat thesurfaceofaliquid, resemblingastretched elasticskin
Or:
Thepropertyof aliquid that makes its surfacebehavelikeastretched elasticskin

(iii)
Capillarity
The rising and fallingofaliquid’s surfacewhereit is in contact with asolid

(b) Why waterwets glass
The adhesiveforceof attraction between the water molecules and the molecules ofglass is greater than the cohesiveforces of attraction amongthe watermolecules, hencewater tends to clingto theglass orwet theglass.

(c) (i) The compositionof blood
• The red blood cells or corpuscles
• Thewhite blood cells orcorpuscles
• Blood platelets
• Plasma (containing water; dissolved food substances likeglucose, amino acids and fattyacids;hormones, enzymes, metabolic waste substances such as carbon dioxide, salts andurea)

(ii) Functionsof blood

 Transports oxygen to thecells of thebody
 Transports metabolic waste materials awayfrom the cells of thebody
 Transports digested foodnutrients to parts ofthe body
 Helps to maintain auniform bodytemperature
 Prevents excessiveblood loss byclotting.
 Helps to protect thebodyagainstinfections and diseases

(d)
(i)
howions areformed fromatoms
Atoms become chargedwhen theylose orgain electrons in order to bemorestable or
attain a completelyfilledoutershell. When atoms gainelectrons, theybecome negatively
charged ions, knownas anions;when theyloseelectrons, theybecomepositivelycharged
ions, known as cations

(ii)
Difference

(iii) CHEMICALSYMBOL
(α) an atomofLithium Li
(β) (γ) amolecule ofchlorine an atomof oxygen Cl2
O

2. (a) Makea labeled diagramofthehumaneye

(b) (i) Two defects ofthe eye
Longsightedness, short sightedness,
(ii) Longsightedness: Iscorrected usingaconvex(converging) lens

Shortsightedness: Iscorrected usingaconcave (diverging) lens

(c) (i) A satellite
A heavenlybodythat moves round (orbits) alarger heavenlybody

(ii)

Natural Satellite Artificial Satellite
Created byGod(ornature) Manufactured byman

Has no mechanical orelectrical devices Has man-mademechanical or electrical
devices
[anyone]

(iii) Us
 es ofartificial satellites
Weatherstudies and forecasting
 Telecommunication
 SendingandreceivingTV signals
 Takingphotographs fromspace for various purposes
 Internet networking
 Global PositioningSystem (GPS)-aworldwide navigation system

(d) SUBSTANCE FORMED on reaction with diluteHCl
(i) (ii) (iii) Ammonia (NH3)
Sodiumhydroxide (NaOH) Calcium carbonate (CaCO3) Ammonium chloride (NH4Cl)
Sodiumchloride (NaCl)and water(H2O)
Calcium chloride (CaCl2), Carbondioxide (CO2)
and water(H2O)

3. (a) Typeofchangeandexplanation
(i) An egg is boiledforfive minutes
Chemical change, sincethereis a new substanceformed; and the changeisnot reversible

(ii) A pieceof breadis chewedinthemouth for two minutes
Chemical change, sincethereis a new substanceformed; and the changeisnot reversible

(iii) A pieceofmeatis chewedinthemouth for two minutes
Physical change, sinceno new substanceis formed.

(iv) A pieceofwoodisburnt to ashes
Chemical change, sinceanew substanceis formedand the changeisnot reversible

(b) Definitions
(i) Amachine
A mechanical devicethat makes work easierand / or faster

(ii) Mechanical advantageofa machine
The ratio of theload to the effort
Or: = Load / effort

(iii) Velocity ratio ofa machine
The ratio of theeffortdistanceto theload distance
= (effort distance) / (loaddistance)

(c) Mechanical Advantage = Load / Effort
= 3000 N / 150 N
= 20
(NB: themechanical advantagehas no units, sinceitis a ratio)

(d) (i) General causes ofdiseases
 Dirtyenvironments
 Lack of personal hygiene
 Lack of proper nutrition (ordeficiencyof certain food nutrients)
 Contact with or sharingitems with person infectedwith communicable diseases.
 Lack of regularmedicalcheckups

(ii) Ways ofpreventing diseases
 Cleaningourenvironments regularly
 Keepingour bodiesandpersonal items cleanalways
 Eatingbalanced diets
 Avoidingcontact with orsharingitems with persons infected with communicable diseases
 Goingfor medicalcheckups regularly

4. (a)

SEXUAL REPRODUCTION ASEXUAL REPRODUCTION
Occurs bythefusion of two separate sex
cells – male and female
Occurs bythe meiosis of onlyonecell
Results in offspringwithdifferent traits
from parents Results in offspringwithsame traits as
parents
Twoparents of oppositesexareinvolved Onlyoneparent is involved

(b) PLANT VEGETATIVEPART

(i) cassava stem cutting
(ii) onion bulb
(iii) banana sucker
(iv) yam stem tuber
(v) ginger rhizome
(vi) pineapple sucker / crown

(c) (i) Density ofa substance
Themass per unit volume ofthe substance
Or: Density = mass / volume

(ii) Determinationof density ofsoil
– Themass, M, of agivenquantityof thesoil is determined using abeam balanceor chemical balanceor electronicscale
– A measuringcylinder is filled with waterto a suitable volume, V1and the readingis recorded.
– Thesoil is gentlypouredinto the measuring cylinder and the new (higher)volume, V2is read and recorded
– Thevolumeof thesoil is calculatedas V2– V1

– Thedensityof thesoil is calculatedas =

(d)

(i) SUBSTANCE Commonsalt SOLVENT
water
(ii) Paint water (ifemulsion), turpentine (if oil paint)
(iii) Coal tar petrol / kerosene
(iv) Sucrose water
(v) Chlorophyll alcohol