WAEC 2020 - BIOLOGY ANSWER

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BIOLOGY OBJ
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31-40: CABCCBDDCB
41-50: DCBBCBBAAA

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ANSWERS:


(1ai)
When the head moves or changes position,the endolymph fluid in the semi-cricular canals moves and stimulates the nerve endings. The nerve endings then transmit the impulses through vestibular to the cerebellum of the brain where the new position at the head is interpreted and the appropriate responses sent to the muscular system to maintain body balance

(1aii)
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(1aiii)
The cavity of the middle ear is a narrow air-filled space. A slight constriction divides it into an upper and a lower chamber, the tympanum (tympanic cavity) proper below and the epitympanum above. These chambers are also referred to as the atrium and the attic, respectively. The middle-ear space roughly resembles a rectangular room with four walls, a floor, and a ceiling. The outer (lateral) wall of the middle-ear space is formed by the tympanic membrane.
The middle ear in human can be split into three parts; external, middle and inner. The middle ear lies within the tempor

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(2ai)
A deficiency disease is a disease caused by a lack of essential dietary elements and especially a vitamin or mineral. It distorts the normal functioning of the human body thereby giving rise to diseases. These diseases affect the organ, tissue and vital system of the human body.

(2aii)
-Nutrient Deficiency Disease
(i) Night blindness.
(ii) Pellagra(a skin and digestive problem)
(iii) Beri-Beri(wasting of muscles, paralysis, stunted growth.
(iv) Anaemia
(v) Scurry

-Remedy
(i) Eating meal rich in vitamin A(retinol) eg Liver, egg, fish, milk, fresh vegetables.
(ii) Foods rich in yeast, liver, milk, eggs and whole grain.
(iii) Eating meal rich in liver, groundnuts, yeast and rice.
(iv) Eating meal rich in folic acid eg leafy vegetables, liver.
(v) Eating of fresh citrus fruits.

(2bi)
Starch in a tuber of yam is carried out as thus:
-By adding few drops of dilute iodine solution on a raw piece of yam.
-After this, it would be observed that the colour will change blue-black confirming the presence of starch.

(2bii)
Glucose in orange fruit requires:
-Putting a small quantity of glucose solution in a test tube, with few drops of Benedict solution (about 2%).
-The mixture is boiled for 4-6minutes.
-After this, a brick-red or orange precipitate is seen confirming the presence of glucose.

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BONUS
(4ai)
Independent assortment of genes states that a pair of alleles/genes of contrasting character segregates independently and combines randomly/distribute itself with either of another pair of alleles/ genes.Hence, during the formation of gamete, the distribution of one pair of allele does not affect the distribution of other allelic pair.

(4aii)
Blood group O can only exist in homozygous form because it has no antigen on its red blood cell while blood group A can exist both in homozygous and heterozygous form because of the presence of antigen on their blood cell. Therefore they exhibit co-dominance.

(4b)
TABULATE:
Class of vertebrate| Example
Pisces | cat fish
Amphibians | toad
Reptiles | lizard
Aves | bird
Mammals | man

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(6ai)
External Fertilization: This type of fertilization occurs when the sperm from the male animal meets the egg/ovum from the female animal, outside the body of the animal. It is common in pisces and amphibians.

(6aii)
Internal fertilization: a type of fertilization by which the sperm from the male meets the egg/ovum inside the body of the animal. It is common in mammals and birds.

(6bi)
(i) Pisces e.g: Tilapia, Croaker, Titus
(ii) Amphibians e.g.: Frogs, Toads, Newts

(6bii)
Internal fertilization:
(i) Mammals e.g. Man, Rat, Monkeys
(ii) Aves e.g. Parrots,Hawks, Eagles

(6ci)
(i) Malnourished and underdeveloped foetus
(ii) Low supply of oxygen to the foetus due to reduced diffusion
(iii) Leads to the death of foetus and miscarriage of pregnancy

(6cii)
(i) Amnion
(ii) Amniotic fluid
(iii) Umbilical cord

(6d)
Competition in feeding among organisms for scarce resources leads to the death of weaker members of the species and the reproduction of the stronger members, leading to a dynamic equilibrium that balances the rate of death to the rate of birth.

(6e)
(i) Problem of Wave
(ii) Effects of temperature
(iii) Salinity of the Marine
(iv) Humidity

(6fi)
Moisture helps in the germination of seeds by helping to activate the metabolic activities needed for germination, dissolved oxygen content in moisture acts is very beneficial to the biochemical process involved in germination.

(6fii)
Viable seeds are healthy and contain the organic requirements for a healthy germination, and is most times resistant to harsh weather conditions, and lack of nutrients.

(6g)
Light energy is considered a limiting factor in production of food by autotrophs because, photosynthesis which is the main process by which autotrophs produce food cannot take place in the absence of light. The energy from light is solely responsible for the process of photosynthesis.

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