Questions
1. (a) Explain the following:
i) Chloroplasts
ii) Economic importance of honeybees
iii) The Heimlich manoeuvre (choking first aid)
iv) Feeding in Hydra
(b) Assuming smooth coat (S) is dominant over rough coat (s) in guinea pigs, and black colour (B) is dominant over brown colour (b). When a cross is made between a pure breed (homozygous) smooth, black guinea pig (SSBB) with a rough, brown guinea pig (ssbb):
i) Use a Punnett diagram to show the result of the F₁ generation.
ii) What will be the phenotype of the offspring in the F₁ generation?
iii) Show the types and ratio of offspring possible when two of the F₁ generation are mated.
iv) Name all the new combinations that have arisen from the cross above (1b iii).
(c) Fill in the blank spaces.
i) ______ is the connective tissue that forms the framework of the ear and nose.
ii) The organelle responsible for packaging and secreting proteins is the ______.
iii) The type of respiration in which oxygen is not required is called ______ respiration.
iv) A nucleotide is composed of a sugar, a phosphate group, and a ______.
v) ______ is the process by which nitrogenous waste is removed from the body.
vi) ______ is the gland that produces adrenaline in response to stress.
vii) The ______ and ______ are the two main excretory organs in mammals.
viii) ______ is the soft, living tissue found in the centre of a tooth, containing nerves and blood vessels.
ix) ______ produces digestive enzymes and also functions as an endocrine gland.
2. (a) Explain the process of osmoregulation in freshwater bony fish.
(b) Outline five (5) economic importance of Mollusca.
3. (a) Explain the theory of natural selection as it relates to inheritance.
(b) Briefly explain the blood circulation system in reptiles.
4. (a) Draw and label the structure of a nephron with arrows to show the direction of blood and filtrate flow.
(b) Give one function of each labelled part of the nephron drawn.
5. (a) Explain the mechanism of hearing (sound perception) in man.
(b) Mention five (5) adaptations of a bird to flight.
6. (a) Explain the adaptations of the placenta in mammals.
(b) Outline five (5) characteristics of the tadpole (larva) of a frog.
Answers
1. (a) i) Chloroplasts
Chloroplasts are double-membrane-bound organelles found in the cells of green plants and algae, containing the green pigment chlorophyll. They are the site of photosynthesis, where light energy is captured and used to convert carbon dioxide and water into glucose and oxygen, and they contain internal membrane stacks called grana, embedded in a fluid matrix called the stroma.
ii) Economic importance of honeybees
Honeybees produce honey and beeswax, which have commercial value as food and in cosmetic and industrial products. More importantly, they act as pollinators, transferring pollen between flowers as they forage, which significantly increases the yield and quality of many food crops and fruit trees, making them essential to agricultural productivity.
iii) The Heimlich manoeuvre (choking first aid)
The Heimlich manoeuvre is an emergency first-aid technique used to clear an obstructed airway in a choking victim. The rescuer stands behind the victim, wraps their arms around the victim's waist, makes a fist placed just above the navel, and delivers sharp upward and inward abdominal thrusts. This raises pressure in the abdomen and chest, forcing trapped air out of the lungs to expel the obstructing object from the airway.
iv) Feeding in Hydra
Hydra is a carnivorous cnidarian that feeds using tentacles surrounding its mouth, armed with stinging cells called cnidocytes (nematocysts). When prey, such as small aquatic organisms, contacts the tentacles, the nematocysts discharge, paralyzing the prey, which is then drawn into the mouth and passed into the gastrovascular cavity. Digestive enzymes are secreted to break down the food, and digestion is completed intracellularly by cells lining the cavity, with nutrients distributed throughout the body.
(b)
Cross: SSBB (smooth, black) × ssbb (rough, brown)
i) Punnett square (F₁ generation)
Gametes from SSBB parent: SB
Gametes from ssbb parent: sb
| × | sb |
|---|---|
| SB | SsBb |
All F₁ offspring genotype: SsBb
ii) Phenotype of F₁ offspring
All F₁ guinea pigs are smooth-coated and black (SsBb), since both smooth coat (S) and black colour (B) are dominant.
iii) F₁ × F₁ cross (SsBb × SsBb) — types and ratio of offspring
Gametes from each parent: SB, Sb, sB, sb
| × | SB | Sb | sB | sb |
|---|---|---|---|---|
| SB | SSBB | SSBb | SsBB | SsBb |
| Sb | SSBb | SSbb | SsBb | Ssbb |
| sB | SsBB | SsBb | ssBB | ssBb |
| sb | SsBb | Ssbb | ssBb | ssbb |
Phenotypic ratio:
- Smooth, black (S_B_) = 9
- Smooth, brown (S_bb) = 3
- Rough, black (ssB_) = 3
- Rough, brown (ssbb) = 1
Ratio = 9 : 3 : 3 : 1
iv) New combinations arising from the cross
The new combinations (recombinants) not present in either original parent are:
- Smooth, brown (S_bb)
- Rough, black (ssB_)
(c) Fill in the blanks
i) Cartilage
ii) Golgi apparatus (Golgi body)
iii) Anaerobic respiration
iv) Nitrogenous (organic) base
v) Excretion
vi) Adrenal gland
vii) Kidneys, and skin
viii) Pulp
ix) Pancreas
Question 2
(a) Osmoregulation in freshwater bony fish
Freshwater fish live in a hypotonic environment, meaning water constantly tends to enter their bodies by osmosis while salts tend to diffuse out. To counter this:
- The gills actively absorb salts (chloride ions) from the surrounding water against the concentration gradient, using specialized chloride cells, to replace salts lost by diffusion.
- The kidneys produce large volumes of dilute urine, filtering out the excess water that continually enters the body, while reabsorbing valuable salts back into the blood.
- The body surface is covered in relatively impermeable scales and mucus, which reduce (but do not eliminate) the inward movement of water.
- This combination of gill salt uptake and copious dilute urine production maintains a stable internal salt-water balance despite the constant osmotic influx of water.
(b) Five economic importance of Mollusca
- Oysters, mussels, and clams (bivalves) are farmed and harvested as important sources of food and income.
- Some oysters produce pearls, which are highly valued in the jewellery industry.
- Snail shells and certain mollusc shells are used to make ornaments, buttons, and lime for construction.
- Edible land snails (e.g., giant African land snails) are farmed as a protein source in some regions.
- Certain molluscs (e.g., slugs and snails) are agricultural pests, destroying crops and garden plants, causing economic losses.
Question 3
(a) Theory of natural selection as it relates to inheritance
The theory of natural selection, proposed by Charles Darwin, states that within a population, individuals show variation in inheritable traits, and those with traits better suited to their environment are more likely to survive and reproduce, passing these favourable traits to their offspring. Over successive generations, the frequency of advantageous alleles increases in the population, while less favourable alleles decrease, gradually leading to a change in the genetic composition of the population (evolution). This theory rests on the principles that variation exists among individuals, more offspring are produced than can survive, resources are limited leading to competition, and heritable traits that confer a survival or reproductive advantage are selected for and passed on through inheritance.
(b) Blood circulation system in reptiles
Reptiles possess a double circulatory system with a heart that is typically four-chambered but with an incompletely divided ventricle (except in crocodilians, which have a fully divided four-chambered heart). Deoxygenated blood from the body enters the right atrium and passes to the ventricle, while oxygenated blood from the lungs enters the left atrium and also passes to the ventricle; a partial septum reduces (but does not fully prevent) mixing of the two blood streams within the ventricle. Blood is then pumped out through separate vessels to the lungs (pulmonary circuit) and to the rest of the body (systemic circuit). This double circulation, though still somewhat incomplete due to partial ventricular mixing, is more efficient than the amphibian system, allowing higher blood pressure and more effective oxygen delivery to tissues.
Question 4
(a) Structure of a nephron
[Diagram to be hand-drawn, showing: Bowman's capsule, glomerulus, afferent arteriole, efferent arteriole, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct. Arrows should indicate: blood entering via the afferent arteriole → glomerulus (filtration into Bowman's capsule) → blood leaving via the efferent arteriole; filtrate flowing from Bowman's capsule → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting duct.]
(b) Function of each labelled part
- Bowman's capsule: Collects the filtrate (glomerular filtrate) forced out of the glomerular blood under pressure.
- Glomerulus: A knot of capillaries where blood is filtered under high pressure, removing water, salts, glucose, and urea from the blood.
- Proximal convoluted tubule: Reabsorbs useful substances such as glucose, amino acids, salts, and much of the water back into the blood.
- Loop of Henle: Creates a concentration gradient in the medulla that enables further reabsorption of water, concentrating the urine.
- Distal convoluted tubule: Fine-tunes reabsorption of ions and water, and allows selective secretion of substances into the filtrate.
- Collecting duct: Carries the final urine, with further water reabsorption regulated by ADH, to the renal pelvis.
Question 5
(a) Mechanism of hearing (sound perception) in man
Sound waves entering the outer ear are funnelled by the pinna into the ear canal and strike the eardrum (tympanic membrane), causing it to vibrate. These vibrations are transmitted and amplified by three small bones (ossicles) in the middle ear — the malleus, incus, and stapes — which pass the vibrations to the oval window of the cochlea in the inner ear. This sets up pressure waves in the fluid (perilymph and endolymph) within the cochlea, causing the basilar membrane to vibrate and stimulating hair cells in the organ of Corti. These hair cells convert the mechanical vibrations into nerve impulses, which travel along the auditory nerve to the auditory centre in the temporal lobe of the cerebral cortex, where they are interpreted as sound.
(b) Five adaptations of a bird to flight
- Hollow (pneumatic), light bones that reduce overall body weight while maintaining strength.
- Feathers, particularly the flight feathers on the wings, that provide lift and control during flight.
- A streamlined, spindle-shaped body that reduces air resistance in flight.
- Well-developed pectoral (breast) muscles anchored to a keeled sternum, providing the power needed for wing movement.
- Air sacs connected to the lungs, allowing efficient, continuous, one-way airflow through the lungs, supplying the high oxygen demand of flight.
- Absence of a urinary bladder and reduction of some organs, reducing body weight for flight.
(Any five of the above.)
Question 6
(a) Adaptations of the placenta in mammals
- The placenta has a large surface area, formed by numerous finger-like projections called villi, which increases the area available for exchange between maternal and fetal blood.
- It is highly vascularized, with an extensive network of fetal capillaries close to maternal blood spaces, facilitating efficient diffusion of substances.
- It allows the exchange of oxygen and nutrients from mother to fetus, and carbon dioxide and metabolic waste from fetus to mother, while keeping the two blood supplies separate (no direct mixing).
- It produces hormones, such as progesterone and oestrogen, which maintain pregnancy and prevent premature contraction of the uterus.
- It acts as a selective barrier, allowing beneficial substances (and some antibodies, providing passive immunity) to pass to the fetus while restricting the passage of many harmful substances.
(b) Five characteristics of the tadpole (larva) of a frog
- Aquatic, living entirely in water and adapted for a swimming mode of life.
- Possesses a long, laterally flattened tail used for propulsion through water.
- Breathes using external gills initially, later replaced by internal gills, before developing lungs at metamorphosis.
- Lacks limbs at hatching; hind limbs develop first, followed later by forelimbs, during metamorphosis.
- Possesses a two-chambered heart and a single circulatory system, similar to that of fish, before metamorphosis.
- Feeds mainly on algae and plant matter using horny jaws and a suctorial mouth, before switching to a carnivorous diet as an adult.