# Biology 2022
---
## BIO 001: General Biology
### QUESTION 1
**(a)** Define the following: [5 marks]
**(i) Genes:**
Genes are the basic physical and functional units of heredity, composed of specific sequences of DNA located at fixed positions (loci) on chromosomes. Each gene encodes information for the synthesis of a particular protein or functional RNA molecule, thereby determining one or more heritable characteristics of an organism.
**(ii) Alleles:**
Alleles are alternative forms of the same gene that occupy the same locus on homologous chromosomes. They arise by mutation and may produce different versions of the same trait. An organism inherits one allele from each parent.
**(iii) Homozygous organism:**
A homozygous organism is one that carries two identical alleles for a particular gene at the corresponding loci on its homologous chromosomes (e.g., TT or tt). It breeds true for that trait.
**(iv) Heterozygous organism:**
A heterozygous organism carries two different alleles for a particular gene at the corresponding loci on its homologous chromosomes (e.g., Tt). The dominant allele is expressed in the phenotype, while the recessive allele is masked.
**(v) Dominant allele:**
A dominant allele is one whose phenotypic effect is expressed in the organism regardless of whether it is present in the homozygous (AA) or heterozygous (Aa) state. It masks the expression of the recessive allele when both are present. Dominant alleles are conventionally represented by uppercase letters.
**(vi) Recessive allele:**
A recessive allele is one whose phenotypic effect is expressed only when it is present in the homozygous state (aa) — that is, when no dominant allele is present to mask it. In heterozygotes, the recessive allele is carried but not expressed. Recessive alleles are conventionally represented by lowercase letters.
**(vii) Test cross:**
A test cross is a cross between an individual of unknown or uncertain genotype (which expresses the dominant phenotype and may be either homozygous dominant or heterozygous) and a homozygous recessive individual. The phenotypic ratio of the offspring reveals the genotype of the unknown parent. If all offspring show the dominant phenotype, the unknown parent is homozygous dominant; if approximately half show the recessive phenotype, the unknown parent is heterozygous.
**(viii) Sex-linked genes:**
Sex-linked genes are genes located on the sex chromosomes (the X or Y chromosome) rather than on autosomes. In most organisms, the majority of sex-linked genes are carried on the X chromosome (X-linked). Because males possess only one X chromosome (XY), they express X-linked recessive traits from a single allele, making them more susceptible to X-linked conditions such as colour blindness and haemophilia.
**(ix) Rhesus (Rh) factor:**
The Rhesus factor refers to a specific protein antigen — principally the D antigen — found on the surface of red blood cells in Rhesus-positive individuals (Rh⁺). Individuals lacking this antigen are Rhesus-negative (Rh⁻). The Rh system is clinically significant in blood transfusions and in haemolytic disease of the newborn (erythroblastosis foetalis), which can occur when an Rh⁻ mother carries an Rh⁺ foetus.
**(x) Albinism:**
Albinism is an autosomal recessive genetic condition characterised by the complete or partial absence of melanin pigment in the skin, hair, and eyes. It results from a mutation in genes encoding enzymes involved in melanin biosynthesis (most commonly tyrosinase). Affected individuals (genotype aa) have very pale skin, white hair, and pink or light blue eyes, and are highly sensitive to ultraviolet radiation and associated eye problems.
---
**(b)** Data analysis of maize fruit lengths (mm): [4 marks]
**Raw data:**
100, 120, 125, 140, 140, 110, 100, 150, 140, 130, 135, 125, 140, 120, 130, 120, 130, 155, 140, 150
**Ordered data (lowest to highest):**
100, 100, 110, 120, 120, 120, 125, 125, 130, 130, 130, 135, 140, 140, 140, 140, 140, 150, 150, 155
**i. Mean:**
Sum = 100+100+110+120+120+120+125+125+130+130+130+135+140+140+140+140+140+150+150+155
= **2,610**
Mean = 2,610 / 20 = **130.5 mm**
**ii. Median:**
n = 20 (even number of values)
Median = average of 10th and 11th values
10th value = 130, 11th value = 130
Median = (130 + 130) / 2 = **130 mm**
**iii. Mode:**
The value appearing most frequently:
140 appears **5 times**
Mode = **140 mm**
**iv. Range:**
Range = Highest value − Lowest value = 155 − 100 = **55 mm**
---
**(c)** Define genetic variation. [1 mark]
Genetic variation is the differences in DNA sequences that exist between individuals within a population, or between populations of the same species. It arises from mutations, genetic recombination during meiosis (crossing over and independent assortment), and random fertilisation. Genetic variation is the raw material upon which natural selection acts, driving evolution and enabling populations to adapt to changing environments.
---
### QUESTION 2
**(a)** Pyramid of Biomass: [4 marks]
The biomass data from the ecological study:
```
┌─────────────────────┐
│ Man 600 g/m² │ ← Tertiary Consumer (Trophic Level 4)
├─────────────────────┤
│ Rats 2000 g/m² │ ← Secondary Consumer (Trophic Level 3)
├─────────────────────┤
│ Locust 3500 g/m² │ ← Primary Consumer (Trophic Level 2)
├─────────────────────┤
│ Yam 4000 g/m² │ ← Producer (Trophic Level 1)
└─────────────────────┘
PYRAMID OF BIOMASS
```
The pyramid is drawn with the widest bar at the base (producer) and progressively narrower bars at each successive trophic level, reflecting decreasing biomass at higher levels.
---
**(b)** Trophic level of each organism: [2 marks]
| Organism | Trophic Level | Role |
|---|---|---|
| Yam | Trophic Level 1 | Producer (autotroph — photosynthesises) |
| Locust | Trophic Level 2 | Primary consumer (herbivore — feeds on yam) |
| Rat | Trophic Level 3 | Secondary consumer (feeds on locust) |
| Man | Trophic Level 4 | Tertiary consumer (feeds on rat) |
---
**(c)** Pyramid of Energy: [4 marks]
Using the 10% energy transfer rule (only 10% of energy at each trophic level is passed to the next):
- Grass (Producers): **6,000 kg**
- Grasshopper (Primary Consumer): 6,000 × 10% = **600 kg**
- Lizard (Secondary Consumer): 600 × 10% = **60 kg**
- Bird (Tertiary Consumer): 60 × 10% = **6 kg**
- Man (Quaternary Consumer): 6 × 10% = **0.6 kg**
```
┌──────────────────────────┐
│ Man 0.6 kg │ ← Trophic Level 5
├──────────────────────────┤
│ Bird 6 kg │ ← Trophic Level 4
├──────────────────────────┤
│ Lizard 60 kg │ ← Trophic Level 3
├──────────────────────────┤
│ Grasshopper 600 kg │ ← Trophic Level 2
├──────────────────────────┤
│ Grass 6,000 kg │ ← Trophic Level 1
└──────────────────────────┘
PYRAMID OF ENERGY
```
The pyramid illustrates that approximately 90% of energy is lost at each trophic level through respiration, heat, excretion, and decomposition, so energy decreases dramatically with each successive level.
---
## BIO 002: Microbiology
### QUESTION 3
**(a)** Distinguish between Natural Active Immunity and Artificial Active Immunity. [2 marks]
**Natural Active Immunity:**
Immunity that develops when an individual is naturally exposed to a pathogen through infection. The immune system recognises the pathogen's antigens and mounts a primary immune response, producing specific antibodies and memory lymphocytes (B and T cells). If the same pathogen is encountered again, the memory cells mount a rapid, stronger secondary response, preventing or minimising disease. The individual actively produces their own antibodies. *Example:* A person who recovers from chickenpox becomes immune to future infections.
**Artificial Active Immunity:**
Immunity that is deliberately induced by administering a vaccine containing weakened (attenuated), killed, or subunit antigens of a pathogen. The immune system responds to the harmless antigenic material by producing antibodies and memory cells without the individual suffering the actual disease. A booster dose may be required to maintain adequate immunity. *Example:* Measles, mumps, and rubella (MMR) vaccination.
**Key distinction:** The stimulus is natural infection in natural active immunity versus deliberate vaccination in artificial active immunity; in both cases the individual's own immune system actively generates the protective response.
---
**(b)** Describe the process of binary fission in prokaryotic cells. [2 marks]
Binary fission is the primary mode of asexual reproduction in prokaryotes (bacteria and archaea):
1. **DNA replication:** The single, circular chromosome replicates, beginning at the origin of replication (oriC). The two daughter chromosomes are attached to different regions of the plasma membrane and are pulled apart as the cell elongates.
2. **Cell elongation:** The cell increases in length, and new cell wall and membrane material are synthesised. The two chromosomes are physically separated toward opposite poles of the elongating cell.
3. **Septum formation (cytokinesis):** A ring of FtsZ protein (the bacterial tubulin homologue) assembles at the mid-cell and constricts inward, directing the formation of a transverse septum (cross-wall) of cell wall and membrane material that divides the cytoplasm equally.
4. **Cell division:** The septum completes, and the two daughter cells separate. Each daughter cell is genetically identical to the parent (barring mutation), and each contains one complete chromosome, ribosomes, plasmids, and sufficient cytoplasm for independent life.
Under optimal conditions (e.g., *E. coli* at 37°C with abundant nutrients), binary fission can occur approximately every 20 minutes, leading to rapid exponential population growth.
---
**(c)** Define and provide examples of pandemic and epidemic diseases. [3 marks]
**Epidemic:**
An epidemic is the occurrence of a disease in a community or region at a rate clearly in excess of what is normally expected for that disease in that area during a specific time period. It is localised to a particular geographical region or population.
*Examples:*
- Ebola virus disease outbreaks in West Africa (2014–2016) — primarily confined to Guinea, Sierra Leone, and Liberia.
- Cholera epidemics in regions with contaminated water supplies.
**Pandemic:**
A pandemic is an epidemic that has spread across multiple countries, continents, or the entire world, affecting a very large number of people simultaneously. It implies international or global spread of a disease.
*Examples:*
- COVID-19 pandemic (2019–2023): caused by SARS-CoV-2, spread to virtually every country worldwide.
- Influenza pandemic (1918–1919): "Spanish flu" killed an estimated 50 million people globally.
- HIV/AIDS: declared a global pandemic affecting all continents.
**Key distinction:** Scale — an epidemic is geographically localised while a pandemic crosses international boundaries and affects large populations worldwide.
---
**(d)** Outline the steps of Koch's postulates and state how they can be applied in medical microbiology. [3 marks]
**Koch's Postulates (four steps):**
1. **Association:** The suspected causative microorganism must be present in all cases of the disease and must be found in the diseased tissues or body fluids of every affected individual. It must be absent from healthy individuals.
2. **Isolation:** The microorganism must be isolated from the diseased host and grown in pure culture on artificial media in the laboratory, completely free from other organisms.
3. **Inoculation (reproduction of disease):** The pure cultured microorganism must produce the same disease when inoculated into a healthy, susceptible experimental host. The inoculated host must develop the identical signs and symptoms of the original disease.
4. **Re-isolation:** The microorganism must be re-isolated from the experimentally infected host, grown again in pure culture, and shown to be identical to the original isolated organism.
**Application in medical microbiology:**
Koch's postulates provide a rigorous framework for establishing causality between a specific microorganism and a specific disease — moving from mere association to proof of causation. They are applied when investigating newly emerging infectious diseases, verifying the aetiology of known diseases, evaluating potential pathogens isolated from patients, and guiding the development of targeted treatments and vaccines. Modern molecular Koch's postulates (proposed by Falkow) extend the original principles to viruses and organisms that cannot be cultured in vitro, using molecular and genetic evidence of pathogenicity.
---
### QUESTION 4
**(a)** Three differences between primary and secondary immune responses: [3 marks]
| Feature | Primary Immune Response | Secondary Immune Response |
|---|---|---|
| Timing | Slow — takes 7–14 days to reach peak antibody levels after first exposure | Rapid — reaches peak antibody levels within 2–3 days of re-exposure |
| Antibody titre | Low peak concentration of antibodies produced | Much higher peak antibody concentration (10–100 times greater) |
| Antibody type | IgM predominates initially, followed by some IgG | IgG predominates (class switching); higher affinity antibodies due to affinity maturation |
| Duration | Short-lived response; antibody levels decline relatively quickly | Longer-lasting; sustained antibody levels due to larger memory cell pool |
| Memory cells | Small number of memory B and T cells generated | Large pool of memory cells from primary response mounts rapid response |
---
**(b)** Four differences between bacteriophage and bacteria: [4 marks]
| Feature | Bacteriophage | Bacteria |
|---|---|---|
| Cellular organisation | Non-cellular; obligate intracellular parasite | Prokaryotic cell with cell membrane, cytoplasm, and ribosomes |
| Genetic material | DNA or RNA (never both); enclosed in a protein capsid | Always double-stranded DNA; may also carry plasmids |
| Reproduction | Cannot reproduce independently; requires a bacterial host cell for replication | Reproduces independently by binary fission |
| Metabolism | Has no metabolic activity outside a host; cannot synthesise proteins or generate ATP independently | Has complete metabolic machinery; carries out all metabolic processes independently |
| Size | Much smaller (20–200 nm); visible only by electron microscopy | Larger (1–10 μm); visible by light microscopy |
| Cell wall | Absent (no cell wall; has a protein capsid instead) | Present — typically composed of peptidoglycan |
---
**(c)** Nutritional types table: [3 marks]
| Nutritional Type | Energy Source | Electron Source | Carbon Source |
|---|---|---|---|
| Photolithoautotrophs | Light (sunlight) | Inorganic compounds (e.g., H₂O, H₂S) | CO₂ (inorganic) |
| Chemoorganoheterotrophs | Organic chemicals (oxidation of organic molecules) | Organic compounds | Organic carbon (pre-formed organic molecules) |
*Notes:*
- **Photolithoautotrophs** include cyanobacteria (use H₂O as electron donor, releasing O₂) and purple/green sulphur bacteria (use H₂S, releasing S). They are the primary producers of most ecosystems.
- **Chemoorganoheterotrophs** include most bacteria, all fungi, all animals, and protozoa. They obtain energy, electrons, and carbon from the oxidation of organic compounds such as glucose.
---
## BIO 003: Botany
### QUESTION 5
**(a)** Plant hormones: [4 marks]
**(i) Gibberellins:**
- Stimulate internode elongation in stems by promoting cell elongation and division, dramatically increasing plant height (classically demonstrated by treating dwarf plant varieties).
- Promote seed germination by stimulating the synthesis of hydrolytic enzymes (particularly α-amylase) in the aleurone layer of seeds, which break down stored endosperm reserves to provide energy for the germinating embryo.
**(ii) Auxin (Indole-3-acetic acid, IAA):**
- Promotes cell elongation by increasing cell wall plasticity (cell wall loosening), enabling turgor-driven expansion; responsible for phototropism (unequal distribution causes bending toward light) and gravitropism.
- Inhibits the growth of lateral (axillary) buds in the presence of an intact apical bud — a phenomenon called apical dominance — because high auxin concentrations from the apex suppress lateral bud outgrowth.
**(iii) Cytokinin:**
- Promotes cell division (cytokinesis) throughout the plant, particularly in the presence of auxin; high cytokinin-to-auxin ratios promote shoot formation in tissue culture.
- Delays senescence (ageing) of leaves and other plant organs by inhibiting protein and chlorophyll degradation, maintaining the metabolic activity of cells.
**(iv) Ethylene:**
- A gaseous hormone that promotes the ripening of climacteric fruits by triggering a cascade of biochemical changes — softening of cell walls, conversion of starches to sugars, and development of colour and aroma.
- Promotes leaf, flower, and fruit abscission (shedding) by stimulating the formation of the abscission zone at the base of the petiole.
---
**(b)** Steps involved in the development of pollen grains in angiosperms: [4 marks]
Pollen grains develop within the **anthers** (microsporangia) of the stamen through a process called **microsporogenesis**, followed by **microgametogenesis**:
1. **Anther development and formation of microsporocytes:**
The anther develops four microsporangia (pollen sacs). Within each microsporangium, diploid cells called **microsporocytes** (microspore mother cells, 2n) differentiate from the sporogenous tissue, surrounded by a nutritive tapetum layer that supplies materials for pollen development.
2. **Meiosis — microsporogenesis:**
Each diploid microsporocyte undergoes **meiosis I and meiosis II**, producing a tetrad of four haploid **microspores** (n), still enclosed within a common wall (callose). Genetic recombination occurs during meiosis I.
3. **Separation of microspores:**
The callose wall surrounding the tetrad is digested by enzymes (callase) secreted by the tapetum, releasing the four individual haploid microspores into the locule of the microsporangium.
4. **Microgametogenesis — pollen grain maturation:**
Each haploid microspore undergoes an asymmetric **mitotic division** (pollen mitosis I) to produce two cells within the developing pollen wall:
- A large **vegetative cell** (tube cell) — provides nutrients and will grow the pollen tube during germination.
- A smaller **generative cell** — will later divide (pollen mitosis II) to produce two **sperm cells** (either within the pollen grain before dispersal, or within the pollen tube after germination, depending on species).
5. **Pollen wall formation:**
The outer wall of the pollen grain (exine) develops from materials partly contributed by the tapetum. The exine is composed of highly resistant sporopollenin and often bears species-specific sculpturing patterns. The inner wall (intine) is primarily cellulose and pectin. The mature pollen grain is released from the anther upon dehiscence.
---
**(c)** Functions of plant tissues: [2 marks]
**Xylem:**
Conducts water and dissolved mineral salts (inorganic ions) from the roots upward through the stem to the leaves and other aerial organs via the transpiration stream. Also provides mechanical support to the plant through lignified cell walls of tracheids and vessel elements.
**Phloem:**
Conducts photosynthetically produced organic solutes — principally sucrose — and other assimilates (amino acids, hormones, signalling molecules) from source tissues (mature leaves) to sink tissues (roots, growing shoots, fruits, seeds) — a process called **translocation**.
**Sclerenchyma:**
Provides mechanical support and structural rigidity to the plant body. Sclerenchyma cells (fibres and sclereids) have heavily lignified, thickened secondary cell walls and are dead at functional maturity. They resist tensile and compressive forces, enabling plants to withstand gravity and wind.
**Chlorenchyma:**
Specialised parenchyma cells that contain numerous chloroplasts and are the primary sites of **photosynthesis** in the plant. They form the mesophyll tissue of leaves (palisade and spongy mesophyll) and carry out the light-dependent and light-independent reactions of photosynthesis.
---
### QUESTION 6
**(a)** Define fertilisation. [1 mark]
Fertilisation is the fusion of a haploid male gamete (sperm cell or spermatozoon) with a haploid female gamete (egg cell or ovum) to form a diploid zygote, restoring the full chromosome complement of the species and initiating the development of a new individual.
---
**(b)** Differentiate between seeds and fruits in tabular form: [4 marks]
| Feature | Seed | Fruit |
|---|---|---|
| Origin | Develops from the fertilised ovule | Develops from the mature ovary wall (pericarp) following fertilisation |
| Structure | Consists of embryo, seed coat (testa), and endosperm (food reserve) | Consists of the pericarp (epicarp, mesocarp, endocarp) enclosing one or more seeds |
| Function | Primary unit of reproduction; contains the embryo for propagation | Protects developing seeds; aids in seed dispersal by wind, animals, or water |
| Presence of embryo | Always contains the embryo of the next generation | Does not itself contain the embryo (the embryo is within the enclosed seed) |
| Formation | Derived from the ovule after double fertilisation | Derived from the ovary wall (and sometimes accessory tissues in false fruits) |
| Example | Groundnut seed, bean seed, maize grain | Mango, tomato, bean pod, orange |
---
**(c)** Describe the process of fertilisation in plants (angiosperms). [5 marks]
Fertilisation in flowering plants (angiosperms) is a unique process called **double fertilisation**, which is exclusive to this group:
**1. Pollination:**
Pollen grains are transferred from the anther to the stigma of the same or a different flower (self- or cross-pollination) by wind, insects, birds, water, or other agents.
**2. Pollen germination and pollen tube growth:**
Upon landing on a compatible stigma, the pollen grain absorbs water and germinates. The vegetative (tube) cell extends as a **pollen tube** that grows through the style tissue, guided by chemical signals (chemotropism — typically a calcium gradient) toward the ovule in the ovary. The generative cell divides (if not already done) by mitosis to produce **two haploid sperm cells** that travel down the pollen tube.
**3. Entry into the ovule:**
The pollen tube enters the ovule through the micropyle (a small pore in the integuments) and penetrates the embryo sac (female gametophyte). The tip of the pollen tube ruptures, releasing the two sperm cells into the embryo sac.
**4. Double fertilisation:**
Two simultaneous fertilisation events occur:
- **First fertilisation:** One sperm cell (n) fuses with the **egg cell** (n) to form the **diploid zygote** (2n), which will develop into the embryo.
- **Second fertilisation:** The second sperm cell (n) fuses with the **two polar nuclei** (n + n) in the central cell of the embryo sac to form the **triploid primary endosperm nucleus** (3n), which will develop into the **endosperm** (nutritive tissue that nourishes the developing embryo and seedling).
**5. Post-fertilisation development:**
- The zygote develops by repeated mitosis into the **embryo**.
- The primary endosperm nucleus develops into the **endosperm**.
- The ovule matures into the **seed**.
- The ovary wall matures into the **fruit** (pericarp).
- Unfertilised ovules and floral parts typically wither and are shed.
---
## BIO 004: Introductory Zoology
### QUESTION 7
**(a)** Six characteristics of the sub-kingdom Protozoa: [3 marks]
1. **Unicellular eukaryotes:** Each protozoan consists of a single cell that performs all life functions — nutrition, respiration, excretion, reproduction, and movement — within that one cell.
2. **Heterotrophic nutrition:** Protozoa obtain nutrients by ingesting other organisms or organic matter (holozoic), by absorbing dissolved organic substances (saprotrophic/osmotrophic), or by parasitism.
3. **Diverse locomotion:** Movement is achieved by pseudopodia (Sarcodina), flagella (Mastigophora), cilia (Ciliophora), or gliding mechanisms (Apicomplexa), depending on the group.
4. **No cell wall:** Unlike plant and fungal cells, protozoan cells lack a rigid cell wall; they are bounded only by a flexible plasma membrane or a specialised pellicle.
5. **Reproduction:** Reproduce asexually by binary fission, multiple fission (schizogony), or budding; sexual reproduction (by conjugation or syngamy) also occurs in many groups.
6. **Habitat:** Found in a wide range of habitats — freshwater, marine environments, moist soil, and as parasites within the bodies of animals and humans.
---
**(b)** Protozoa classification table: [4 marks]
| Group | Free-living Example | Parasitic Form Example |
|---|---|---|
| Sarcodina | *Amoeba proteus* | *Entamoeba histolytica* (causes amoebic dysentery) |
| Mastigophora (Flagellates) | *Euglena viridis* | *Trypanosoma brucei* (causes sleeping sickness) |
| Ciliophora (Ciliates) | *Paramecium caudatum* | *Balantidium coli* (causes balantidiasis in humans) |
| Apicomplexa (Sporozoans) | None (all members are obligate parasites) | *Plasmodium falciparum* (causes malaria) |
---
**(c)** Differentiate between *Paramecium* and *Amoeba*: [3 marks]
| Feature | *Paramecium* | *Amoeba* |
|---|---|---|
| Shape | Fixed, slipper-shaped (oval); shape maintained by a firm pellicle | Irregular, constantly changing shape; no fixed form |
| Locomotion | Moves by beating of numerous cilia covering the entire cell surface | Moves by extending temporary cytoplasmic projections called pseudopodia |
| Feeding | Cilia sweep food particles (bacteria) into an oral groove → cytostome (cell mouth) → food vacuole | Engulfs food by surrounding it with pseudopodia in a process called phagocytosis (amoeboid feeding) |
| Osmoregulation | Two contractile vacuoles with radiating canals for expelling excess water | One or more simple contractile vacuoles |
| Reproduction | Asexual by transverse binary fission; sexual by conjugation (exchange of micronuclei) | Asexual by binary fission; can form resistant cysts under adverse conditions |
| Nucleus | Two types: macronucleus (metabolic functions) and micronucleus (genetic/reproductive functions) | Single nucleus of one type |
---
### QUESTION 8
**(a)** Four reasons why transport is necessary in animals: [2 marks]
1. **Delivery of nutrients and oxygen:** Digested food molecules (glucose, amino acids, fatty acids) absorbed from the gut, and oxygen absorbed from the respiratory surfaces, must be transported to all body cells for metabolic processes and energy production.
2. **Removal of metabolic waste products:** Carbon dioxide produced by cellular respiration, urea from protein catabolism, and other metabolic wastes must be transported from body cells to excretory organs (lungs, kidneys, skin) for elimination.
3. **Distribution of hormones:** Chemical messengers (hormones) produced by endocrine glands must be transported in the blood to their target organs to coordinate physiological responses.
4. **Thermoregulation:** The transport system distributes heat generated by metabolic activity throughout the body, helping to maintain a stable core temperature in homeothermic (warm-blooded) animals.
---
**(b)** Six functions of blood: [3 marks]
1. **Transport of oxygen:** Haemoglobin in red blood cells (erythrocytes) binds oxygen in the lungs and releases it to metabolically active tissues throughout the body.
2. **Transport of nutrients:** Dissolved glucose, amino acids, fatty acids, vitamins, and minerals absorbed from the digestive tract are carried in the plasma to all body cells.
3. **Transport of waste products:** Carbon dioxide (transported as bicarbonate ions HCO₃⁻ in plasma and as carbaminohaemoglobin) is carried from tissues to the lungs; urea is transported from the liver to the kidneys for excretion.
4. **Defence against infection:** White blood cells (leucocytes — neutrophils, lymphocytes, monocytes) perform phagocytosis of pathogens; lymphocytes produce antibodies; plasma proteins complement the immune response.
5. **Blood clotting (haemostasis):** Platelets (thrombocytes) and clotting factors (fibrinogen, prothrombin) in plasma initiate and complete the coagulation cascade, forming a fibrin clot to seal wounds and prevent excessive blood loss.
6. **Thermoregulation and pH maintenance:** Blood distributes metabolic heat and buffers pH changes through plasma proteins and bicarbonate systems, maintaining homeostasis.
---
**(c)** Differentiate between arteries and veins: [3 marks]
| Feature | Arteries | Veins |
|---|---|---|
| Direction of blood flow | Carry blood **away** from the heart to tissues | Carry blood **toward** the heart from tissues |
| Blood pressure | High pressure — blood is pumped directly from the heart | Low pressure — blood has passed through capillary beds |
| Wall thickness | Thick walls with abundant smooth muscle and elastic fibres to withstand high pressure | Thinner walls with less muscle and elastic tissue |
| Lumen | Relatively narrow lumen | Wider lumen relative to wall thickness |
| Valves | Generally absent (except semilunar valves at heart exit — aortic and pulmonary) | Possess numerous valves throughout to prevent backflow of blood |
| Blood oxygen content | Carry oxygenated blood (except pulmonary arteries, which carry deoxygenated blood to lungs) | Carry deoxygenated blood (except pulmonary veins, which carry oxygenated blood from lungs) |
---
**(d)** Four functions of the skeleton: [2 marks]
1. **Support and posture:** The skeleton provides a rigid internal framework that supports the body's soft tissues, maintains body shape, and allows the organism to maintain an upright posture against gravity.
2. **Protection of vital organs:** Bones encase and shield delicate internal organs from mechanical damage — the cranium protects the brain, the vertebral column protects the spinal cord, and the rib cage protects the heart and lungs.
3. **Locomotion and movement:** Bones act as rigid levers to which muscles are attached via tendons. Muscle contraction moves bones at joints, producing coordinated movement of limbs and body parts.
4. **Haemopoiesis (blood cell production):** Red bone marrow within certain bones (sternum, vertebrae, pelvis, proximal femur) is the site of haematopoiesis — the continuous production of red blood cells, white blood cells, and platelets throughout life.