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WASSCE Gambia - independent subject foundations study materials
WASSCE Gambia - independent subject foundations study resources

WASSCE Gambia - independent subject foundations practice questions

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Question 1Upper-secondary functions, calculus, geometry and probability

Convert the binary number 11011_2 into its decimal (base 10) equivalent:

  1. 23
  2. 25
  3. 27 Correct answer.
  4. 29

Explanation

Expand in powers of 2: 1 × 2^4 + 1 × 2^3 + 0 × 2^2 + 1 × 2^1 + 1 × 2^0 = 16 + 8 + 0 + 2 + 1 = 27.

Question 2Upper-secondary functions, calculus, geometry and probability

Evaluate 28 in modular arithmetic modulo 5 (i.e., 28 mod 5):

  1. 1
  2. 2
  3. 3 Correct answer.
  4. 4

Explanation

Divide 28 by 5: 28 = 5 × 5 + 3. The remainder is 3, so 28 ≡ 3 (mod 5).

Question 3Upper-secondary functions, calculus, geometry and probability

Evaluate the logarithmic expression without using mathematical tables: log_10(500) + log_10(2).

  1. 2
  2. 3 Correct answer.
  3. 5
  4. 10

Explanation

Apply the product rule of logarithms: log_a(x) + log_a(y) = log_a(xy). Thus, log_10(500) + log_10(2) = log_10(500 × 2) = log_10(1,000) = log_10(10^3) = 3.

Question 4Upper-secondary functions, calculus, geometry and probability

An arithmetic progression (AP) has a first term of 4 and a common difference of 3. What is the 15th term of the sequence?

  1. 42
  2. 45
  3. 46 Correct answer.
  4. 49

Explanation

The n-th term of an AP is given by T_n = a + (n - 1)d. For the 15th term: T_15 = 4 + (15 - 1) × 3 = 4 + 14 × 3 = 4 + 42 = 46.

Question 5Upper-secondary functions, calculus, geometry and probability

Find the sum of the first 6 terms of the geometric progression (GP): 5, 10, 20, 40, ...

  1. 155
  2. 315 Correct answer.
  3. 320
  4. 635

Explanation

Here, first term a = 5 and common ratio r = 10 / 5 = 2. Since r > 1, the sum formula is S_n = a(r^n - 1) / (r - 1). For n = 6: S_6 = 5(2^6 - 1) / (2 - 1) = 5(64 - 1) / 1 = 5 × 63 = 315.

Question 6Upper-secondary functions, calculus, geometry and probability

In a senior secondary class of 40 students, 25 study Biology, 20 study Chemistry, and 8 study neither subject. How many students study both Biology and Chemistry?

  1. 5
  2. 13 Correct answer.
  3. 15
  4. 18

Explanation

Total students studying at least one subject = 40 - 8 = 32. Using the inclusion-exclusion principle: n(B ∪ C) = n(B) + n(C) - n(B ∩ C) => 32 = 25 + 20 - n(B ∩ C) => 32 = 45 - n(B ∩ C) => n(B ∩ C) = 45 - 32 = 13.

Question 7Upper-secondary functions, calculus, geometry and probability

Find the roots of the quadratic equation: 2x^2 - 5x - 3 = 0.

  1. x = 3 or x = -1/2 Correct answer.
  2. x = -3 or x = 1/2
  3. x = 1 or x = -3/2
  4. x = -1 or x = 3/2

Explanation

Factorise the quadratic: 2x^2 - 6x + x - 3 = 2x(x - 3) + 1(x - 3) = (2x + 1)(x - 3) = 0. Setting each factor to zero gives 2x + 1 = 0 => x = -1/2; x - 3 = 0 => x = 3.

Question 8Upper-secondary functions, calculus, geometry and probability

Calculate the gradient (slope) of the straight line passing through the Cartesian coordinates P(2, -3) and Q(6, 5):

  1. 1/2
  2. 2 Correct answer.
  3. -2
  4. 4

Explanation

Gradient m = (y_2 - y_1) / (x_2 - x_1) = (5 - (-3)) / (6 - 2) = (5 + 3) / 4 = 8 / 4 = 2.

Question 9Upper-secondary functions, calculus, geometry and probability

If θ is an acute angle in a right-angled triangle such that tan θ = 3/4, calculate the value of sin θ + cos θ.

  1. 7/10
  2. 1
  3. 7/5 Correct answer.
  4. 12/25

Explanation

In a right triangle where opposite = 3 and adjacent = 4, the hypotenuse = √(3^2 + 4^2) = √(9 + 16) = √25 = 5. Therefore, sin θ = 3/5 and cos θ = 4/5. Their sum is 3/5 + 4/5 = 7/5 (or 1.4).

Question 10Upper-secondary functions, calculus, geometry and probability

From the top of a vertical observation cliff 30 metres above water level, the angle of depression of a canoe on the River Gambia is 45°. How far is the canoe from the base of the cliff?

  1. 15 m
  2. 30 m Correct answer.
  3. 30√3 m
  4. 60 m

Explanation

By alternate angles, the angle of elevation from the boat to the cliff top is also 45°. Using trigonometry: tan 45° = Opposite / Adjacent = 30 / d. Since tan 45° = 1, d = 30 / 1 = 30 metres.

Question 11Upper-secondary functions, calculus, geometry and probability

A chord subtends an angle of 110° at the centre of a circle. What is the measure of the angle subtended by the same chord at any point on the major arc of the circumference?

  1. 45°
  2. 55° Correct answer.
  3. 70°
  4. 110°

Explanation

By circle theorem, the angle subtended by an arc or chord at the centre of a circle is twice the angle subtended by it at any point on the remaining circumference: Angle at circumference = 110° / 2 = 55°.

Question 12Upper-secondary functions, calculus, geometry and probability

In a cyclic quadrilateral PQRS, angle P measures 78°. What is the measure of the opposite interior angle R?

  1. 78°
  2. 90°
  3. 102° Correct answer.
  4. 112°

Explanation

A fundamental circle theorem states that opposite angles of a cyclic quadrilateral (a four-sided polygon inscribed in a circle) are supplementary (sum to 180°). Angle R = 180° - 78° = 102°.

Question 13Upper-secondary functions, calculus, geometry and probability

Calculate the curved surface area of a cone having a base radius of 7 cm and a slant height of 25 cm (Take π = 22/7).

  1. 350 cm^2
  2. 550 cm^2 Correct answer.
  3. 704 cm^2
  4. 1,100 cm^2

Explanation

Curved surface area of a cone A = πrl = (22/7) × 7 × 25 = 22 × 25 = 550 cm^2.

Question 14Upper-secondary functions, calculus, geometry and probability

Calculate the total surface area of a solid sphere with a radius of 7 cm (Take π = 22/7).

  1. 154 cm^2
  2. 308 cm^2
  3. 616 cm^2 Correct answer.
  4. 1,437.3 cm^2

Explanation

Surface area of a sphere A = 4πr^2 = 4 × (22/7) × 7^2 = 4 × (22/7) × 49 = 4 × 22 × 7 = 616 cm^2.

Question 15Upper-secondary functions, calculus, geometry and probability

Find the variance of the numbers: 2, 4, 6, 8, 10.

  1. 4
  2. 8 Correct answer.
  3. 10
  4. 16

Explanation

Mean x̄ = (2 + 4 + 6 + 8 + 10) / 5 = 30 / 5 = 6. Deviations (x - x̄): -4, -2, 0, 2, 4. Squared deviations: 16, 4, 0, 4, 16. Sum of squared deviations = 40. Variance = Σ(x - x̄)^2 / N = 40 / 5 = 8.

Question 16Upper-secondary functions, calculus, geometry and probability

Two unbiased fair dice are rolled simultaneously. What is the probability of obtaining a sum of 8 on the two upward faces?

  1. 1/12
  2. 5/36 Correct answer.
  3. 1/6
  4. 7/36

Explanation

Total possible outcomes when rolling two dice = 6 × 6 = 36. Outcomes with sum 8: (2,6), (3,5), (4,4), (5,3), (6,2) - exactly 5 favourable outcomes. Probability = 5/36.

Question 17Upper-secondary functions, calculus, geometry and probability

Solve the exponential equation for x: 2^(2x - 3) = 32.

  1. x = 2
  2. x = 4 Correct answer.
  3. x = 5
  4. x = 8

Explanation

Write both sides to the same base: 32 = 2^5, so 2^(2x - 3) = 2^5. Equate the exponents: 2x - 3 = 5, which gives 2x = 8 and x = 4.

Question 18Upper-secondary functions, calculus, geometry and probability

A trader invested D20,000 at compound interest of 10% per annum compounded annually. What is the total compound amount accumulated after 2 years?

  1. D22,000
  2. D24,000
  3. D24,200 Correct answer.
  4. D26,000

Explanation

Using the compound interest formula: A = P(1 + r/100)^n = 20,000(1 + 0.10)^2 = 20,000 × 1.21 = D24,200.

Question 19Upper-secondary functions, calculus, geometry and probability

If matrix A = [[2, 3], [1, 4]], what is the determinant of matrix A?

  1. 5 Correct answer.
  2. 8
  3. 10
  4. 11

Explanation

The determinant of a 2×2 matrix [[a, b], [c, d]] is given by ad - bc. For matrix A: det(A) = (2 × 4) - (3 × 1) = 8 - 3 = 5.

Question 20Upper-secondary functions, calculus, geometry and probability

The bearing of town Y from town X is 060°. What is the back bearing of town X from town Y?

  1. 120°
  2. 150°
  3. 240° Correct answer.
  4. 300°

Explanation

If the forward bearing θ is less than 180°, the back bearing is θ + 180°. Here, 060° + 180° = 240°.

Question 21English grammar, contextual language and reading evidence

Choose the option that correctly completes the sentence: 'The number of candidates who registered for this year's examination _____ higher than last year's figure.'

  1. were
  2. have been
  3. are
  4. is Correct answer.

Explanation

The head of the subject is the singular noun 'number', not the plural 'candidates' inside the following modifying phrase. 'The number of ...' therefore takes a singular verb, while the contrasting expression 'A number of ...' takes a plural one ('A number of candidates are ...').

Question 22English grammar, contextual language and reading evidence

Select the option that correctly uses the subjunctive mood to complete the sentence: 'The school board insisted that every candidate _____ present at the examination hall thirty minutes before the scheduled start.'

  1. is
  2. are
  3. was
  4. be Correct answer.

Explanation

Verbs expressing demands, insistence, recommendations, or mandates (such as 'insist', 'demand', 'recommend') take a subjunctive 'that'-clause using the base form of the verb ('be') regardless of the subject's number.

Question 23English grammar, contextual language and reading evidence

Choose the option that correctly completes the inverted conditional sentence: '_____ he known about the change in the WASSCE timetable, he would not have missed the practical paper.'

  1. If
  2. Should
  3. Had Correct answer.
  4. Were

Explanation

In an inverted third conditional sentence, 'if' is omitted and the auxiliary 'had' is fronted before the subject: 'Had he known...' is equivalent to 'If he had known...'.

Question 24English grammar, contextual language and reading evidence

Choose the phrasal verb that best completes the sentence: 'The municipal council decided to _____ the planned construction of the market stalls due to budgetary constraints.'

  1. call off Correct answer.
  2. call on
  3. call out
  4. call up

Explanation

'Call off' means to cancel an event, plan, or project that had previously been arranged.

Question 25English grammar, contextual language and reading evidence

Identify the option that correctly completes the sentence: 'Hardly had the chief examiner entered the auditorium _____ the students stood up in silence.'

  1. when Correct answer.
  2. than
  3. then
  4. that

Explanation

Correlative negative adverbs 'hardly' and 'scarcely' pair exclusively with 'when' (or 'before') to introduce the subsequent clause. 'Than' pairs with 'no sooner'.

Question 26English grammar, contextual language and reading evidence

Select the correct option to complete the sentence: 'The auditor's findings were completely at variance _____ the figures presented by the board.'

  1. to
  2. from
  3. with Correct answer.
  4. against

Explanation

'At variance' is a fixed prepositional phrase that always takes 'with'. It means to be in conflict or disagreement with something, so the auditor's findings are 'at variance with' the board's figures.

Question 27English grammar, contextual language and reading evidence

Choose the word nearest in meaning (synonym) to the underlined word: 'The senior magistrate praised the witness for her METICULOUS account of the traffic collision.'

  1. careless
  2. hesitant
  3. vague
  4. painstaking Correct answer.

Explanation

'Meticulous' means showing great attention to detail, very careful, and precise. 'Painstaking' is its exact synonym.

Question 28English grammar, contextual language and reading evidence

Choose the word most nearly opposite in meaning (antonym) to the underlined word: 'The minister presented a COMPREHENSIVE blueprint for agricultural mechanization.'

  1. limited Correct answer.
  2. exhaustive
  3. detailed
  4. inclusive

Explanation

'Comprehensive' means complete, broad, and including all or nearly all elements. Its antonym is 'limited' (or partial/incomplete).

Question 29English grammar, contextual language and reading evidence

Select the option that best completes the sentence in formal academic register: 'The statistical correlation was deemed _____ because it was based on an unrepresentative sample.'

  1. spurious Correct answer.
  2. authentic
  3. tangible
  4. profound

Explanation

'Spurious' means false, illegitimate, or not what it purports to be (e.g., a spurious statistical correlation that does not reflect a true causal relationship).

Question 30English grammar, contextual language and reading evidence

What is the meaning of the underlined idiom in the sentence: 'The young entrepreneur decided to THROW IN THE TOWEL after months of mounting debts.'?

  1. Launder soiled clothing items
  2. Borrow capital from commercial banks
  3. Seek advice from veteran businessmen
  4. Admit defeat and abandon a struggle Correct answer.

Explanation

'To throw in the towel' originated in boxing (where a fighter's corner throws a towel into the ring) and idiomatically means to surrender, admit defeat, or quit an endeavor.

Question 31English grammar, contextual language and reading evidence

Identify the figure of speech used in the sentence: 'All hands were on deck to save the cargo boat from sinking in the stormy river.'

  1. Synecdoche Correct answer.
  2. Metonymy
  3. Hyperbole
  4. Euphemism

Explanation

Synecdoche is a figure of speech in which a part of something is used to represent the whole (or vice versa). 'Hands' is a part of the human body used here to represent the whole crew or workers.

Question 32English grammar, contextual language and reading evidence

Identify the figure of speech exemplified in the sentence: 'The State House announced new economic measures yesterday.'

  1. Metonymy Correct answer.
  2. Simile
  3. Oxymoron
  4. Personification

Explanation

Metonymy uses an associated entity or attribute to refer to the concept itself. 'The State House' (the physical presidential residence) is used metonymically to refer to the President and the executive branch.

Question 33English grammar, contextual language and reading evidence

Which of the following phrases contains an oxymoron?

  1. A deafening silence enveloped the courtroom. Correct answer.
  2. The wind howled through the tall palm trees.
  3. He ran as fast as a frightened gazelle.
  4. The car cost an arm and a leg.

Explanation

An oxymoron juxtaposes two contradictory or opposite terms side by side. 'Deafening' (extremely loud) and 'silence' (complete absence of sound) are direct semantic opposites.

Question 34English grammar, contextual language and reading evidence

Choose the word that has the same vowel sound as the underlined letters in 'firm'.

  1. term Correct answer.
  2. fear
  3. farm
  4. foam

Explanation

'Firm' contains the long central vowel /ɜː/. The word 'term' contains this exact same vowel phoneme /ɜː/. 'Fear' contains /ɪə/, 'farm' contains /ɑː/, and 'foam' contains /əʊ/.

Question 35English grammar, contextual language and reading evidence

Which of the following words contains the consonant sound /θ/ as in 'think' rather than /ð/ as in 'this'?

  1. breathe
  2. clothe
  3. thigh Correct answer.
  4. though

Explanation

'Thigh' begins with the voiceless dental fricative /θ/ (as in 'think', 'thin', 'theft'). The words 'breathe', 'clothe', and 'though' contain the voiced dental fricative /ð/.

Question 36English grammar, contextual language and reading evidence

Which syllable receives the primary stress in the four-syllable noun 'pho-tog-ra-phy'?

  1. First (PHO-tog-ra-phy)
  2. Second (pho-TOG-ra-phy) Correct answer.
  3. Third (pho-tog-RA-phy)
  4. Fourth (pho-tog-ra-PHY)

Explanation

In words ending with the suffix '-graphy', primary stress falls on the antepenultimate (third from last) syllable, which is the second syllable: pho-TOG-ra-phy (/fəˈtɒɡrəfi/).

Question 37English grammar, contextual language and reading evidence

In the sentence: 'FATOU bought a new bicycle yesterday', where the word in capital letters receives emphatic stress, which question does the sentence answer?

  1. Did Fatou borrow a new bicycle yesterday?
  2. Did Fatou buy an old bicycle yesterday?
  3. Did Mariama buy a new bicycle yesterday? Correct answer.
  4. Did Fatou buy a new motorcar yesterday?

Explanation

Emphatic stress on 'FATOU' contrasts the subject with other possible persons, contradicting the proposition that someone else (such as Mariama) performed the action.

Question 38English grammar, contextual language and reading evidence

Choose the option that correctly identifies the grammatical name and function of the underlined clause: 'The student WHO SCORED THE HIGHEST MARK IN MATHEMATICS was awarded a prize.'

  1. Noun clause, subject of the sentence
  2. Prepositional phrase, modifying 'prize'
  3. Adverbial clause of condition, modifying 'was awarded'
  4. Adjectival (relative) clause, qualifying the noun 'student' Correct answer.

Explanation

The clause 'who scored the highest mark in Mathematics' is introduced by the relative pronoun 'who' and modifies/qualifies the antecedent noun 'student'. Hence, it is an adjectival (relative) clause.

Question 39English grammar, contextual language and reading evidence

Select the sentence that demonstrates correct punctuation and comma usage with a non-restrictive relative clause:

  1. The River Gambia, which flows into the Atlantic Ocean, is vital for inland trade. Correct answer.
  2. The River Gambia which flows into the Atlantic Ocean is vital for inland trade.
  3. The River Gambia, which flows into the Atlantic Ocean is vital for inland trade.
  4. The River Gambia which flows into the Atlantic Ocean, is vital for inland trade.

Explanation

Because 'The River Gambia' is a unique proper noun, the relative clause adds non-essential extra information (non-restrictive) and must be set off by a pair of parenthetical commas.

Question 40English grammar, contextual language and reading evidence

What is the primary rhetorical purpose of a thesis statement in a persuasive or argumentative essay?

  1. To provide anecdotal humor to entertain the reader
  2. To describe the physical setting where the author wrote the piece
  3. To summarize all bibliographical sources in alphabetical order
  4. To state clearly the writer's central argument or position to be defended Correct answer.

Explanation

A thesis statement explicitly states the central claim, proposition, or argument that the essay will develop and substantiate with evidence throughout the body paragraphs.

Question 41Biological organization, inheritance, regulation and ecosystems

What biological phenomenon occurs when a plant cell is placed in a hypertonic solution, causing water to leave the vacuole by osmosis and the cytoplasm to shrink away from the cell wall?

  1. Turgidity
  2. De-plasmolysis
  3. Hemolysis
  4. Plasmolysis Correct answer.

Explanation

Plasmolysis is the shrinking of the plant protoplasm away from the rigid cellulose cell wall caused by the osmotic ex-osmosis of water when exposed to a hypertonic (higher solute concentration) external medium.

Question 42Biological organization, inheritance, regulation and ecosystems

During the light-dependent stage of photosynthesis in the thylakoid membranes of chloroplasts, what is the role of the photolysis of water?

  1. Fixing atmospheric carbon dioxide directly into triose phosphates
  2. Absorbing green wavelengths of the visible spectrum
  3. Synthesizing starch granules for seasonal storage in roots
  4. Providing electrons and protons (H+) while releasing oxygen gas Correct answer.

Explanation

Photolysis splits water molecules (2H2O → 4H+ + 4e- + O2) using light energy absorbed by Photosystem II, supplying electrons to replace those excited in chlorophyll, protons for NADP+ reduction, and evolving oxygen gas.

Question 43Biological organization, inheritance, regulation and ecosystems

Which specialized heart valves prevent the backflow of blood from the ventricles into the atria during ventricular systole?

  1. Semilunar valves (aortic and pulmonary)
  2. Eustachian valves
  3. Atrioventricular valves (bicuspid/mitral and tricuspid) Correct answer.
  4. Precapillary sphincters

Explanation

The atrioventricular (AV) valves-the tricuspid on the right and bicuspid (mitral) on the left-close firmly at the onset of ventricular systole to prevent regurgitation of blood into the atria.

Question 44Biological organization, inheritance, regulation and ecosystems

What is the primary role of bile salts secreted by the liver and stored in the gall bladder during digestion in the duodenum?

  1. Hydrolyzing polypeptides into free amino acids
  2. Synthesizing intrinsic factor for vitamin B12 absorption
  3. Neutralizing salivary amylase to stop carbohydrate digestion
  4. Emulsifying large fat globules into microscopic droplets to increase lipase surface area Correct answer.

Explanation

Bile salts (such as sodium glycocholate) lower surface tension and emulsify large dietary lipids into a fine emulsion of microscopic droplets, dramatically increasing the surface area for pancreatic lipase to digest fats.

Question 45Biological organization, inheritance, regulation and ecosystems

In which segment of the human nephron does the greatest percentage of water, glucose, and sodium reabsorption take place under normal physiological conditions?

  1. Proximal convoluted tubule Correct answer.
  2. Descending limb of the Loop of Henle
  3. Distal convoluted tubule
  4. Collecting duct

Explanation

The proximal convoluted tubule (PCT) has extensive microvilli and abundant mitochondria, reabsorbing approximately 65–70% of filtered water and sodium, and 100% of filtered glucose and amino acids by active transport and osmosis.

Question 46Biological organization, inheritance, regulation and ecosystems

Which hormone, secreted by the posterior pituitary gland in response to elevated blood plasma osmolarity, increases the water permeability of the kidney collecting ducts?

  1. Aldosterone
  2. Glucagon
  3. Insulin
  4. Antidiuretic hormone (Vasopressin) Correct answer.

Explanation

Antidiuretic hormone (ADH or vasopressin) stimulates the insertion of aquaporin water channels into the apical membranes of collecting duct epithelial cells, promoting water reabsorption into the blood and producing concentrated urine.

Question 47Biological organization, inheritance, regulation and ecosystems

What is the correct sequence of neurons involved in transmitting an impulse along a simple spinal reflex arc?

  1. Effector → Motor neuron → Sensory neuron → Receptor
  2. Effector → Relay neuron → Motor neuron → Receptor
  3. Receptor → Motor neuron → Brain → Sensory neuron → Effector
  4. Receptor → Sensory neuron → Relay (interneuron) → Motor neuron → Effector Correct answer.

Explanation

A stimulus is detected by a receptor, generates an action potential along an afferent sensory neuron into the spinal cord, passes via synapses through a relay interneuron, exits via an efferent motor neuron, and activates the effector (muscle or gland).

Question 48Biological organization, inheritance, regulation and ecosystems

In a monohybrid cross between two heterozygous tall pea plants (Tt × Tt), where tall (T) is completely dominant over dwarf (t), what is the expected phenotypic ratio among the offspring?

  1. 1 tall : 1 dwarf
  2. 2 tall : 2 dwarf
  3. 3 tall : 1 dwarf Correct answer.
  4. 4 tall : 0 dwarf

Explanation

The Punnett square produces genotypes 1 TT, 2 Tt, and 1 tt. Because T is dominant, both TT and Tt individuals are tall (3/4), while tt individuals are dwarf (1/4), yielding the classical Mendelian 3 : 1 phenotypic ratio.

Question 49Biological organization, inheritance, regulation and ecosystems

Why are X-linked recessive genetic disorders, such as hemophilia and red-green color blindness, expressed much more frequently in human males than in females?

  1. Males carry two defective X chromosomes while females carry only one
  2. Females lack X chromosomes entirely in somatic cells
  3. The Y chromosome carries suppressor genes that promote X-linked disorders
  4. Males have only one X chromosome (hemizygous) and will express any mutant allele present on it Correct answer.

Explanation

Human males have an XY sex chromosome pair. Because they have only one X chromosome (hemizygosity), a single recessive mutant allele on the X chromosome has no homologous counterpart on the Y to mask it, resulting in phenotypic expression.

Question 50Biological organization, inheritance, regulation and ecosystems

What mutualistic symbiotic association occurs between Rhizobium bacteria and the root nodules of leguminous plants such as groundnuts?

  1. The plant provides carbohydrates while the bacteria convert atmospheric nitrogen gas into usable ammonium compounds Correct answer.
  2. The bacteria secrete toxic pesticides while the plant produces glucose
  3. The bacteria digest cellulose cell walls to release sugars for the host plant
  4. The plant supplies carbon dioxide while the bacteria perform oxygenic photosynthesis

Explanation

Rhizobium bacteria within root nodules fix inert atmospheric dinitrogen (N2) into organic nitrogen compounds using nitrogenase enzymes, in exchange for photosynthesized organic carbon and a protected microaerobic niche from the host legume.