WAEC Biology 2011 past questions and answers

Taxonomy is the science of classifying and naming organisms; nomenclature is only the naming part.

A tissue is a group of cells working together; blood is a tissue, while the other options are single cells.

Cells at the root tip (the meristem) keep dividing and have not yet taken on a particular job, so they are unspecialised. Sperm and muscle cells are specialised, and somatic cells just means body cells in general.

Sperm and ovum are both gametes; their shared function is sexual reproduction.

In a salt solution less water enters Amoeba by osmosis, so there is less water to pump out and the vacuole fills and empties less often.

Paramecium lives naturally in fresh water rich in decaying matter such as ponds, lakes and puddles; a clean aquarium is not its natural habitat.

Water crosses the endodermis by osmosis through the cells (vacuolar pathway), helped by active pumping of salts; simple diffusion is not the mechanism here.

Mitochondria release energy by respiration, so very active cells contain many of them.

The cell is in anaphase of mitosis; II points to one of the chromatids being pulled to the poles.

The lines running from pole to pole in a dividing cell are the spindle fibres, which pull the chromatids apart.

Secondary thickening comes from two meristems: the vascular cambium (new xylem and phloem) and the phellogen or cork cambium (new bark).

A monocot root has many vascular bundles in a ring around a large central pith; a dicot root has little or no pith.

Haemoglobin is the red, iron-containing pigment inside red blood cells that carries oxygen.

The nasal cavity has a moist lining and a rich blood supply that warm and moisten air on its way in.

Lung books (spiders), mouth and trachea are breathing structures; the stomach is for digestion.

Ultrafiltration lets small molecules through the glomerulus; vitamins are small, so they pass into the filtrate.

Exercise increases respiration, which releases heat; the body sweats more so evaporation can cool it.

Sensory and motor neurons carry impulses over long distances and are myelinated. Relay (intermediate) neurons are short and lie inside the central nervous system, and many have no myelin sheath.

Effectors are muscles and glands that respond to impulses; glands are effectors, while tongue and skin act here as sense organs.

One nucleus divides into 2, then 4, then 8: three divisions (2³ = 8).

Sperm production needs a temperature a little below normal body temperature; the scrotum keeps the testes cooler.

Animals like frogs lay eggs without shells that would dry out on land; their eggs and young need the conditions found in water to develop.

Cassava is planted from pieces of the stem (stem cuttings).

Endosperm cells have three sets of chromosomes: 3n = 36, so n = 12. A hybrid plant body is diploid, 2n = 24.

The Krebs cycle takes place in the matrix of the mitochondria; glycolysis happens in the cytoplasm.

In cyclic photophosphorylation the excited electrons travel a loop and come back to the same chlorophyll, making ATP on the way.

Photosynthesis makes new organic matter, so active photosynthesis increases dry weight.

The enzyme moves one phosphate from ATP onto glucose, giving glucose phosphate and ADP.

Without phloem, food made in the leaves cannot reach the roots; the roots starve and die, and then the whole plant dies.

Glucose is soluble and would draw water into the cells; starch is insoluble, so storing it as starch avoids osmotic problems.

This is the biuret test; a purple (violet) colour shows protein.

Producers make food by photosynthesis; a mushroom is a fungus with no chlorophyll, so it is a decomposer.

The tail bone (coccyx) is a reduced remnant of a tail that has no real function in humans: a vestigial structure.

In DNA a purine (adenine) always pairs with a pyrimidine (thymine), which keeps the width of the double helix constant.

(a)(i) Roots grow towards gravity (positively geotropic); shoots grow away from it (negatively geotropic).
(ii) Pin three germinating bean seedlings on moist cotton wool/blotting paper: one with the radicle horizontal, one pointing up, one pointing down (control); keep moist and dark; after 2–3 days the horizontal and upward radicles have curved downwards; this shows positive geotropism. (Or: use a clinostat — on a rotating clinostat a horizontal radicle grows straight, on a stationary one it bends down.)
(b) A bitter substance dissolves in saliva; it stimulates taste buds for bitterness, found mainly at the back of the tongue; sensory cells send impulses along the sensory nerve to the brain; the brain interprets the taste as bitter.
(c) 1. Thyroid — thyroxine — controls metabolic rate, growth and development.
2. Pancreas (islets of Langerhans) — insulin — lowers blood sugar by converting glucose to glycogen.
3. Ovary — oestrogen — development of female secondary sexual characters. (Spellings must be correct.)

In (a)(ii) always include a control seedling.

(a) Diagram of correct size, with title, showing oesophagus leading into the stomach; liver above/right of the stomach with the gall bladder beneath it; bile duct joining the duodenum; duodenum as the U-shaped loop after the stomach; pancreas lying in the loop of the duodenum with the pancreatic duct; all organs labelled.
(b)(i) Any two: hepatitis; cirrhosis; liver cancer; jaundice; liver fluke infection.
(ii) Any five: jaundice (yellow skin and eyes); weakness and tiredness; loss of appetite and weight; poor fat digestion (less bile); swelling of the abdomen (fluid build-up); poor blood clotting/bleeding; build-up of poisons in the blood; possible death.
(c)(i) Vitamin A: night blindness, dry skin, xerophthalmia (dry eyes).
(ii) Vitamin C: scurvy — bleeding/swollen gums, slow healing of wounds.
(iii) Vitamin K: slow or failed blood clotting, excessive bleeding.

Draw organs in their true positions; labels must be ruled and not cross.

(a)(i) Whenever energy is changed from one form to another, some of it is lost (degraded) as heat, so no transfer is 100% efficient.
(ii) Producers trap light energy and store part of it as chemical energy; when a herbivore eats the plant only part of that energy is passed on, the rest being lost as heat in respiration, movement and waste; the same happens at each higher level; so energy decreases along the chain (about 10% passes on), energy flow is one-way, and food chains are short.
(b)(i) Any three: food shortage/famine; disease; shortage of water; lack of space/housing; war; natural disasters.
(ii) e.g. Food shortage — mechanised farming, use of fertilisers and improved varieties, irrigation, food storage. Disease — vaccination, good hygiene and sanitation, better health care. Space — building high-rise houses, planning towns, family planning. Water — boreholes, dams and water treatment.

Link the law directly to heat loss at each trophic level.

(a)(i) Genotype is the genetic make-up (the alleles) of an individual; phenotype is its observable characteristics.
(ii) Genotype: the genes/alleles inherited from the parents; mutation; (crossing over/independent assortment). Phenotype: the genotype; the environment (e.g. nutrition, climate); interaction of dominant and recessive alleles.
(b) Parents BB × bb → gametes B and b → F₁ all Bb (black).
F₁ cross Bb × Bb → gametes B, b × B, b → F₂: BB, Bb, Bb, bb → 3 black : 1 white.
(i) White = ¼ × 240 = 60 puppies.
(ii) Black = ¾ × 240 = 180 puppies.

The F₂ of a monohybrid cross gives a 3 : 1 ratio.

(a)(i) Putrefaction: breakdown of dead organisms and wastes by bacteria and fungi, releasing ammonia/ammonium compounds.
(ii) Nitrogen fixation: conversion of free atmospheric nitrogen into nitrogen compounds (ammonia, nitrates) by bacteria such as Rhizobium, Azotobacter, or by lightning.
(iii) Nitrification: oxidation of ammonium compounds to nitrites (Nitrosomonas) and then to nitrates (Nitrobacter).
(iv) Denitrification: conversion of nitrates back to free nitrogen gas by denitrifying bacteria (e.g. Pseudomonas).
(b) Fixation adds nitrogen compounds to the soil / denitrification removes them; fixation turns N₂ into compounds / denitrification turns nitrates into N₂; fixation is done by nitrogen-fixing bacteria (and lightning) / denitrification by denitrifying bacteria; fixation favoured by aerated soil / denitrification by waterlogged, poorly aerated soil; fixation increases soil fertility / denitrification reduces it.
(c) Urea in urine is broken down by bacteria into ammonia/ammonium compounds; nitrifying bacteria convert ammonium to nitrites then nitrates; nitrates dissolve in soil water; roots absorb them by active transport.

Name the bacteria involved at each step.

(a)(i) Immunity is the ability of the body to resist infection by a disease-causing organism, through antibodies and white blood cells.
(ii) Natural (active) immunity: surviving an attack of yellow fever, the body makes antibodies and memory cells. Artificial (active) immunity: vaccination with yellow fever vaccine (weakened virus) makes the body produce antibodies. (Also passive: antibodies passed from mother to baby.)
(iii) Any four: tuberculosis (BCG); polio; measles; diphtheria; whooping cough (pertussis); tetanus; hepatitis B; yellow fever.
(b) Translocation is the movement of manufactured food (sugars, amino acids) through the phloem from the leaves to other parts of the plant.
(c)(i) Differences: mammals have a heart/pump, plants have none; mammals have blood in vessels (arteries, veins, capillaries), plants have xylem and phloem; mammals have a circulatory (closed loop) system, plants do not circulate; mammal blood carries respiratory gases, plants exchange gases by diffusion; plants carry water in dead xylem, mammals' vessels are living.
(ii) Similarities: both use tubes/vessels; both carry dissolved food; both carry water and mineral salts; both transport hormones; both carry waste products; both use a liquid medium.

Give differences as matching pairs (plant vs mammal).