Topic – 1.3
(a) Organisms from the genus Chlorella are protoctists.
State the additional information required to name Chlorella according to the binomial system.
(b) Fig. 1.1 shows the structure of an organism from the genus Chlorella.
(i) Identify two cell structures in Fig. 1.1 that indicate that Chlorella is not a prokaryote.
(ii) Identify two cell structures in Fig. 1.1 that are found in both fungi and protoctists.
(iii) State the names of two other kingdoms, apart from fungus, prokaryote and protoctist ……………. and ……………. .
(c) Chlorella is sold as a nutritional supplement. Spirulina is another nutritional supplement.
Table 1.1 shows some nutritional information for Chlorella and Spirulina supplements and the recommended daily intake for some nutrients.
(i) One tablet contains 5 g of Chlorella supplement.
Using the information in Table 1.1, calculate the number of tablets of Chlorella supplement a person needs to take to provide the recommended daily intake of iron.
Give your answer to one decimal place.
(ii) Explain the advantages of taking Chlorella as a dietary supplement rather than Spirulina.
Use the data in Table 1.1 to justify your answer.
(iii) State the name of one food that is a principal dietary source of vitamin C.
(d) Chlorella is also a good source of protein.
(i) State the importance of proteins in active transport.
(ii) State the name of the smaller molecules that proteins are made from.
▶️ Answer/Explanation
(a) Ans: species (name)
The binomial system requires both the genus and species name. Since “Chlorella” is the genus, the species name is needed for full classification.
(b)(i) Ans: nucleus ; chloroplast
Prokaryotes lack membrane-bound organelles. The presence of a nucleus and chloroplasts confirms Chlorella is a eukaryote.
(b)(ii) Ans: any two from: cytoplasm ; cell wall ; cell membrane ; nucleus
These structures are common in both fungi and protoctists, as they are eukaryotic organisms with similar cellular organization.
(b)(iii) Ans: animal and plant
The five-kingdom classification system includes Animalia and Plantae, alongside Fungi, Prokaryotae, and Protoctista.
(c)(i) Ans: 6.5 (tablets)
From Table 1.1, Chlorella has 15.4 mg iron per 100 g. For 5 g (one tablet), iron content is \( \frac{15.4 \times 5}{100} = 0.77 \, \text{mg} \). The recommended daily intake is 5 mg, so tablets needed = \( \frac{5}{0.77} \approx 6.5 \).
(c)(ii) Ans: Chlorella contains vitamin C and more calcium than Spirulina, supporting immune function and bone health.
Vitamin C prevents scurvy, and calcium strengthens bones. Chlorella provides these nutrients, whereas Spirulina lacks vitamin C and has less calcium.
(c)(iii) Ans: citrus fruit / (named) fruit / (named) vegetable
Oranges, lemons, and bell peppers are rich in vitamin C, essential for collagen synthesis and immunity.
(d)(i) Ans: Proteins act as carriers in membranes, enabling active transport of molecules against their concentration gradient using energy (ATP).
Carrier proteins bind and transport specific molecules, ensuring selective uptake of nutrients.
(d)(ii) Ans: amino acids
Proteins are polymers of amino acids linked by peptide bonds, forming diverse structures for biological functions.
Topic – 11.1
(a) Fig. 2.1 is a diagram of the gas exchange system in humans.
(i) State the names of the parts labelled X, Y and Z in Fig. 2.1.
(ii) The wall of the trachea contains rings of tissue.
State the name of this tissue and describe its function.
(iii) State the names of two types of cells responsible for protecting the breathing system from particles.
(b) A scientist estimated the pressure and volume in the thorax during one breath.
Fig. 2.2 shows a graph of the results.
Describe and explain the changes in the thorax that occur during section A only in Fig. 2.2.
(c) Complete the sentences to describe the effect of carbon dioxide concentration on breathing.
During physical activity, the carbon dioxide concentration of the blood ……….. .
This is detected by the ……….. .
This results in an increased rate and greater ……….. of breathing.
▶️ Answer/Explanation
(a)(i)
X: External intercostal muscle (helps in rib movement during breathing).
Y: Bronchiole (smaller airway branching from bronchi).
Z: Diaphragm (contracts/flattens during inhalation).
(a)(ii)
Name: Cartilage (a strong, flexible connective tissue).
Function: Prevents tracheal collapse during pressure changes.
(a)(iii)
1: Ciliated cells (sweep mucus and trapped particles away).
2: Goblet cells (secrete mucus to trap foreign particles).
(b)
Section A represents inhalation:
– Thoracic volume increases due to diaphragm contraction and rib movement.
– Pressure decreases as air rushes into the lungs (Boyle’s Law: \( P \propto \frac{1}{V} \)).
(c)
During activity, CO2 concentration increases.
Detected by chemoreceptors in the brain.
Results in faster and deeper breathing to expel CO2.
Topic – 13.1
(a) Fig. 3.1 shows a kidney nephron and its associated blood vessels.
The compositions of fluids A, B and C were analysed.
Table 3.1 shows the results for five components of the fluids.
(i) State the names of fluid A and fluid C in Fig. 3.1.
(ii) Using the information in Fig. 3.1 and Table 3.1, describe and explain the differences in the compositions of fluids A, B and C.
(b) Outline how blood glucose concentration is controlled.
(c) A gene mutation may be involved in the development of type 1 diabetes.
(i) Describe what is meant by a gene mutation.
(ii) Outline the treatment of type 1 diabetes.
▶️ Answer/Explanation
(a) (i) A: Blood/Plasma
C: Urine
Explanation: Fluid A is blood/plasma as it enters the nephron, and fluid C is urine, the waste product excreted after filtration and reabsorption.
(a) (ii) The differences arise due to filtration (protein too large to pass), reabsorption (glucose fully reabsorbed), and selective excretion (urea and excess ions/water remain in urine).
(b) Blood glucose is regulated by insulin (lowers glucose via glycogen storage) and glucagon (raises glucose via glycogen breakdown), controlled by pancreatic feedback.
(c) (i) A gene mutation is a random change in DNA base sequence, potentially altering protein function.
(c) (ii) Type 1 diabetes is treated with insulin injections, blood glucose monitoring, diet control, and exercise.
Topic – 16.3
(a) Fig. 4.1 shows a diagram of two flowers from different plants of the same species.
(i) Describe what is meant by the term species.
(ii) Complete the diagram in Fig. 4.1 to show self‑pollination and cross‑pollination by:
- drawing one arrow to show the pathway of pollen during self‑pollination and labelling this arrow self‑pollination
- drawing one arrow to show the pathway of pollen during cross‑pollination and labelling this arrow cross‑pollination
- labelling the names of the structures involved in pollination.
(iii) State the function of the parts labelled X and Y in Fig. 4.1.
(b) Explain why self‑pollination that results in production of offspring is a form of sexual
reproduction and not asexual reproduction.
(c) State the type of environmental conditions that hydrophytes are adapted to live in.
▶️ Answer/Explanation
(a) (i) A species is a group of organisms that can interbreed to produce fertile offspring. This definition ensures genetic compatibility and reproductive success within the group.
(ii) For self-pollination, draw an arrow from the anther to the stigma of the same flower. For cross-pollination, draw an arrow from the anther of one flower to the stigma of the other. Label these structures clearly.
(iii) X (Ovary): Contains ovules (female gametes) and is the site of fertilization. Y (Sepal): Protects the flower bud during development.
(b) Self-pollination is sexual reproduction because it involves the fusion of male (pollen) and female (ovule) gametes, resulting in genetic variation. Asexual reproduction does not involve gametes or meiosis.
(c) Hydrophytes are adapted to live in aquatic (water) environments, where they have specialized structures for buoyancy and gas exchange.
Topic – 17.4
Fig. 5.1 is a pedigree diagram showing the inheritance of blood group in one family.
(a) State the number of people in Fig. 5.1 with:
XY chromosomes ………… .
only one \(I ^{A}\) allele. …………. .
(b) Explain how Fig. 5.1 shows that blood group is an example of discontinuous variation.
(c) State one example of discontinuous variation in plants.
(d) Explain why the inheritance of blood group is an example of codominance.
(e) A person with the genotype \(I ^{A}I^{o}\) has a child with a person with the genotype \(I ^{B}I^{o}\).
Complete the genetic diagram to determine the probability of the offspring having the blood group AB.
probability of the offspring having the blood group AB ………….. .
▶️ Answer/Explanation
(a) 4 (XY chromosomes); 3 (only one \(I^{A}\) allele).
In the pedigree diagram, 4 individuals are male (XY chromosomes), and 3 individuals have only one \(I^{A}\) allele (heterozygous \(I^{A}I^{o}\)).
(b) Blood group shows discontinuous variation because there are distinct phenotypes (A, B, AB, O) with no intermediates.
Discontinuous variation is characterized by clear-cut categories, unlike continuous variation (e.g., height).
(c) Example: Seed shape (round/wrinkled) or Flower color (e.g., red/white).
Discontinuous variation in plants includes traits with distinct, non-overlapping phenotypes.
(d) Blood group inheritance is codominant because \(I^{A}\) and \(I^{B}\) alleles both express fully in the phenotype (AB blood group).
Codominance occurs when neither allele is recessive, and both contribute equally to the phenotype.
(e) Probability = 25% (0.25).
Gametes: \(I^{A}\), \(I^{o}\) × \(I^{B}\), \(I^{o}\). Punnett square yields 4 combinations: \(I^{A}I^{B}\) (AB), \(I^{A}I^{o}\) (A), \(I^{B}I^{o}\) (B), \(I^{o}I^{o}\) (O). Only 1 out of 4 is AB.
Topic – 19.3
(a) The flow chart in Fig. 6.1 shows one pathway of nitrogen as it travels through the nitrogen cycle.
Complete the flow chart in Fig. 6.1.
(b) State the names of two processes that occur in both the carbon and nitrogen cycles.
(c) State the principal source of energy input to biological systems.
▶️ Answer/Explanation
(a) The nitrogen cycle involves several key steps: lightning/root nodules fix atmospheric nitrogen, converting it into nitrate. Ammonia is converted to urea, which is further processed into nitrate. Finally, denitrification returns nitrogen to the atmosphere.
(b) Both the carbon and nitrogen cycles involve decomposition (breakdown of organic matter) and feeding (transfer of nutrients through trophic levels). Another common process is excretion, which releases nutrients back into the environment.
(c) The principal source of energy for biological systems is the Sun. Solar energy drives photosynthesis, forming the basis of energy flow in ecosystems.
Final Answers:
(a) lightning / root nodules ; nitrate ; urea ; nitrate ; denitrification ;
(b) any two from: decomposition / decay ; feeding ; excretion ;
(c) (the) Sun ;