101. In an algal sample, two fusing gametes are unequal in size, but the larger one has not been identified as a non-motile female gamete. On the available evidence, the safest classification is:
ⓐ. isogamy
ⓑ. anisogamy
ⓒ. oogamy
ⓓ. fragmentation
Correct Answer: anisogamy
Explanation: The only decisive observation supplied is that the gametes differ in size. That condition supports anisogamy. Oogamy would require further evidence showing that the larger gamete is a non-motile female gamete and that the smaller gamete is a motile male gamete. Without those sex-specific and motility details, assigning oogamy would exceed the evidence. Isogamy is excluded by the size difference, while fragmentation does not involve gametes. The wording “safest classification” calls for a conclusion limited to what has actually been observed. Taxonomic and reproductive decisions should not add an unreported feature merely to reach a more specialised category.
102. A large non-motile female gamete fuses with a smaller motile male gamete in an alga. This reproductive condition is:
ⓐ. fragmentation of the thallus
ⓑ. isogamy between equal gametes
ⓒ. anisogamy between unequal motile gametes
ⓓ. oogamy involving a non-motile egg
Correct Answer: oogamy involving a non-motile egg
Explanation: Oogamy combines inequality in gamete size with a pronounced difference in sexual role and motility. The female gamete is large, stores more cellular material and remains non-motile, while the smaller male gamete is motile and reaches it for fusion. Isogamy is incompatible with the size difference. Although oogamy belongs within the broader idea of unequal gametes, the fully differentiated gamete profile supplied is more specific than ordinary anisogamy. Fragmentation does not involve gametes at all. The four linked clues—large female, female non-motility, smaller male and male motility—converge on oogamy and distinguish it from the other algal sexual types.
103. The pair in which both algae are cited as examples of oogamy is:
ⓐ. Ulothrix and Spirogyra, both isogamous examples
ⓑ. Eudorina and Ulothrix, anisogamous and isogamous respectively
ⓒ. Volvox and Fucus, two standard oogamous examples
ⓓ. Spirogyra and Eudorina, isogamous and anisogamous respectively
Correct Answer: Volvox and Fucus, two standard oogamous examples
Explanation: Volvox and Fucus are standard examples of oogamy, where a large non-motile female gamete fuses with a smaller motile male gamete. Ulothrix may exhibit flagellated isogametes, while Spirogyra provides an example of non-motile isogametes. Eudorina is associated with anisogamy, involving gametes that differ in size. The pairing is not based on body form or algal class alone; Volvox is colonial and green, whereas Fucus is a brown marine alga. Their shared feature is the sexual relation between differentiated male and female gametes. This demonstrates that one reproductive condition may occur in algae with very different thallus organisation and classification.
104. Motility of the smaller male gamete is experimentally blocked in an oogamous alga while the large female gamete remains stationary. The reproductive step most directly impaired is:
ⓐ. male-gamete movement toward the egg
ⓑ. conversion of the female gamete into a zoospore
ⓒ. fragmentation of the parent thallus
ⓓ. formation of equal-sized isogametes
Correct Answer: male-gamete movement toward the egg
Explanation: In the oogamous condition described for algae, the female gamete is large and non-motile, while the smaller male gamete is motile. Blocking male motility directly interferes with its ability to reach the stationary female gamete, reducing the likelihood of fusion. The treatment does not transform the egg into an asexual spore, initiate vegetative fragmentation or make the gametes equal in size. The prediction follows from the functional asymmetry of the pair: one gamete remains in place and the other provides movement. The experiment illustrates how motility contributes to fertilisation in oogamy without defining the female gamete as a passive spore or altering the overall reproductive category.
105. Use the gamete descriptions below.
| Profile | Description |
|---|
| P | Similar-sized flagellated gametes |
| Q | Unequal-sized gametes without the complete egg-sperm profile |
| R | Large non-motile female gamete and smaller motile male gamete |
The correct sequence of sexual types for P, Q and R is:
ⓐ. anisogamy, isogamy, oogamy
ⓑ. oogamy, anisogamy, isogamy
ⓒ. isogamy, oogamy, anisogamy
ⓓ. isogamy, anisogamy, oogamy
Correct Answer: isogamy, anisogamy, oogamy
Explanation: Profile P has similar-sized gametes, so it represents isogamy; their flagella provide motility but do not alter the size relation. Profile Q establishes inequality without the specialised large non-motile female and smaller motile male pattern, making anisogamy the supported category. Profile R contains the complete sex-specific size and motility relation of oogamy. The progression moves from equivalent gametes to unequal gametes and then to strongly differentiated female and male gametes. Solving the table requires using all supplied characteristics rather than identifying the types from motility alone. The three profiles summarise the principal algal sexual categories through increasingly distinct gamete differentiation.
106. Algae account for at least one-half of global carbon-dioxide fixation. Which conclusion is correct?
ⓐ. Algae contribute less than \(50\%\) of carbon-dioxide fixation in freshwater habitats alone.
ⓑ. Algae contribute \(50\%\) or more of the stated global carbon-dioxide fixation.
ⓒ. Algae contribute exactly \(50\%\) under all environmental conditions.
ⓓ. Algae contribute less than \(50\%\) when marine forms are included.
Correct Answer: Algae contribute \(50\%\) or more of the stated global carbon-dioxide fixation.
Explanation: The expression “at least one-half” establishes a minimum contribution of \(50\%\), represented mathematically as \(\geq 50\%\). It does not mean that the algal contribution is exactly \(50\%\) in every season, habitat or environmental condition. The statement refers to the global contribution of algae and is not limited to freshwater or marine ecosystems separately. Through photosynthesis, algae fix carbon dioxide into organic matter and form the primary food base of many aquatic ecosystems. Their large contribution to global carbon fixation also supports oxygen production and the transfer of energy and organic carbon through aquatic food chains.
107. A severe decline in photosynthetic algae occurs in a well-lit aquatic ecosystem. The most immediate combined ecological effect is expected to be:
ⓐ. reduced local oxygen addition and a weaker primary food base
ⓑ. increased oxygen production and greater consumer biomass
ⓒ. immediate formation of vascular plants from the remaining algae
ⓓ. complete independence of aquatic animals from primary producers
Correct Answer: reduced local oxygen addition and a weaker primary food base
Explanation: Photosynthetic algae release oxygen into their surroundings and produce organic matter that supports aquatic food chains. A severe decline in their abundance would reduce both functions. Less photosynthetic activity means less local addition of dissolved oxygen under illuminated conditions, while lower primary production leaves less food and energy available to organisms feeding directly or indirectly on algae. The prediction does not imply that every oxygen molecule or food source disappears immediately, since other producers and physical oxygen exchange may remain. It identifies the direct ecological consequences of losing a major producer group. Algal decline affects aquatic animals through both the chemical environment and the reduced transfer of newly fixed carbon into the food web.
108. A graph plots dissolved oxygen concentration against time during daylight in two comparable ponds. Pond P contains abundant photosynthetic algae and shows a steady rise, whereas Pond Q has very few algae and remains nearly level. The pattern is best explained by:
ⓐ. greater fragmentation of algae in Pond Q
ⓑ. conversion of oxygen into algal hydrocolloids in Pond P
ⓒ. stronger photosynthetic oxygen addition in Pond P
ⓓ. seed production by submerged vascular plants in Pond Q
Correct Answer: stronger photosynthetic oxygen addition in Pond P
Explanation: The vertical variable is dissolved oxygen concentration, and the decisive trend is its daylight increase in the pond with abundant algae. Photosynthetic algae release oxygen, some of which enters the surrounding water and raises the dissolved concentration. Pond Q lacks a comparable algal population, so its oxygen level shows little increase under the stated conditions. The graph does not provide evidence about fragmentation, hydrocolloid manufacture or seed production. Its inference is limited to the relation between algal abundance and oxygen addition during daylight; respiration, atmospheric exchange and other producers may also influence actual pond oxygen. The contrasting slopes support a stronger net photosynthetic contribution from algae in Pond P.
109. Equal algal cultures are placed in illuminated and dark containers containing similar water. Dissolved oxygen rises in the illuminated culture but falls in the dark culture. The observation most strongly supports the conclusion that:
ⓐ. respiration in darkness raises dissolved oxygen
ⓑ. photosynthesis in light raises dissolved oxygen
ⓒ. fragmentation in light consumes dissolved oxygen
ⓓ. zoospore release in darkness raises dissolved oxygen
Correct Answer: photosynthesis in light raises dissolved oxygen
Explanation: The two cultures contain comparable algae and water, while light availability is the changed condition. The oxygen increase in the illuminated culture is consistent with photosynthetic oxygen production exceeding oxygen consumption during the observation period. In darkness, photosynthetic oxygen release stops while cellular respiration continues, allowing dissolved oxygen to decline. The experiment does not test conversion into fungi, fragmentation or a difference between zoospores and thallus cells. Its strongest justified inference concerns the effect of illumination on net oxygen change in an algal culture. The result connects algal photosynthesis with local oxygen enrichment while respecting the limit of the evidence: it measures net dissolved oxygen, not every individual process occurring in the containers.
110. Aquatic animals may depend indirectly on algae even when they do not consume algae themselves, since algae:
ⓐ. supply only minerals, not organic matter, to consumers
ⓑ. form vascular tissues eaten by higher trophic levels
ⓒ. contribute primary production to aquatic food chains
ⓓ. prevent energy transfer from producers to consumers
Correct Answer: contribute primary production to aquatic food chains
Explanation: Algae fix carbon dioxide through photosynthesis and build organic matter, making them primary producers in aquatic ecosystems. Some animals consume algae directly, while predators may feed on those algal consumers. Energy and matter originating in algal production can consequently reach animals several feeding steps away. Indirect dependence does not require the higher consumer to eat algae itself. Algae do not make animals autotrophic, form vascular roots or remove every gas from water. Their ecological role is based on producing biomass and contributing oxygen to the aquatic environment. The food-chain connection explains why a reduction in algae can influence organisms at multiple consumer levels rather than affecting only species that graze directly on the algal thallus.
111. A large-scale disturbance sharply reduces algal photosynthesis across oceans while terrestrial plant productivity initially remains unchanged. Which global effect is most directly expected?
ⓐ. reduced aquatic \(CO_2\) fixation and oxygen production
ⓑ. increased agar yield without altered primary production
ⓒ. halted terrestrial photosynthesis despite unchanged plants
ⓓ. conversion of marine algae to heterotrophic nutrition
Correct Answer: reduced aquatic \(CO_2\) fixation and oxygen production
Explanation: Algae contribute a major share of global carbon-dioxide fixation and form the primary photosynthetic base of aquatic ecosystems. A broad reduction in their photosynthetic activity would lower the conversion of \(CO_2\) into organic matter and decrease oxygen released into surrounding water. Terrestrial productivity was specified as initially unchanged, so the disturbance does not imply an immediate halt to land-plant photosynthesis. Commercial products such as agar depend on particular algae, but their production cannot compensate for loss of ecosystem-scale carbon fixation. The predicted effect follows from the central role of algal photosynthesis in aquatic primary production and oxygen balance.
112. The group containing only marine algae cited as food sources is:
ⓐ. Porphyra, Laminaria and Sargassum
ⓑ. Gelidium, Chlorella and Volvox
ⓒ. Ulothrix, Spirogyra and Eudorina
ⓓ. Marchantia, Laminaria and Fucus
Correct Answer: Porphyra, Laminaria and Sargassum
Explanation: Porphyra, Laminaria and Sargassum are named among the marine algae used as food. They represent different algal groups, showing that food use is not restricted to one class. Gelidium is better known here as an agar source, while Chlorella is a unicellular protein-rich supplement and Volvox is a colonial green alga. Ulothrix, Spirogyra and Eudorina are used chiefly as reproductive or structural examples rather than as the stated marine food trio. Marchantia is a liverwort and not an alga. The correct grouping depends on the source-use relation supplied for these organisms, not merely on recognising that each name belongs somewhere within plant diversity.
113. Which statement correctly describes the use of marine algae as food?
ⓐ. Exactly \(70\) marine algal species are consumed in every region.
ⓑ. Approximately \(70\) marine algal species are used as food, including Porphyra, Laminaria and Sargassum.
ⓒ. Porphyra, Laminaria and Sargassum are the only algae used as food.
ⓓ. All known marine algal species are regularly consumed as food.
Correct Answer: Approximately \(70\) marine algal species are used as food, including Porphyra, Laminaria and Sargassum.
Explanation: Approximately \(70\) species of marine algae are reported to be used as food. Porphyra, Laminaria and Sargassum are representative examples from this larger group and should not be treated as the only edible algae. The number is approximate, so it does not indicate that exactly \(70\) species are consumed in every geographical region. It also does not imply that all marine algae are edible or regularly consumed. The statement therefore combines an estimated number with selected examples and highlights the economic importance of marine algae as food without converting the estimate into an absolute or universal count.
114. The source-product pairing that accurately identifies the two major algal hydrocolloids is:
ⓐ. green algae—algin; brown algae—agar
ⓑ. red algae—algin; green algae—carrageen
ⓒ. brown algae—carrageen; red algae—starch
ⓓ. brown algae—algin; red algae—carrageen
Correct Answer: brown algae—algin; red algae—carrageen
Explanation: Brown algae provide algin, while red algae provide carrageen. Both substances are hydrocolloids with a strong capacity to hold water, a property that supports several commercial applications. The source relation is class-specific in the comparison and must not be reversed. Agar is also obtained from certain red algae, particularly Gelidium and Gracilaria, but it is not the brown-algal product paired with algin. Starch is a stored food in green algae rather than the red-algal hydrocolloid requested. Linking each product with its algal source is essential when several commercially useful substances occur within the same broad group.
115. Algin and carrageen are commercially useful mainly in relation to their ability to:
ⓐ. produce motile gametes in culture
ⓑ. form root-like structures in thalli
ⓒ. convert algal spores into seed-like bodies
ⓓ. retain water and form useful colloids
Correct Answer: retain water and form useful colloids
Explanation: Algin from brown algae and carrageen from red algae are hydrocolloids. Their molecules interact with water and help produce thickened, gel-like or stabilised preparations, which explains their commercial importance. This property is unrelated to gamete motility, development of true roots or conversion of spores into seeds. The products are extracted substances rather than reproductive cells or organs. Understanding the shared property also clarifies why two chemically distinct algal products can serve related industrial purposes despite coming from different classes. The biological source and the physical behaviour of the product must both be retained: brown and red algae supply different hydrocolloids, while water-holding capacity explains their broad utility.
116. Agar used in microbial culture media and in products such as ice-creams and jellies is obtained chiefly from:
ⓐ. the pair Porphyra and Sargassum
ⓑ. the pair Chlorella and Volvox
ⓒ. the pair Gelidium and Gracilaria
ⓓ. the pair Laminaria and Fucus
Correct Answer: the pair Gelidium and Gracilaria
Explanation: Gelidium and Gracilaria are red algae that serve as important sources of agar. Agar can produce a firm gel, making it valuable as a supporting medium for growing microorganisms in laboratories. The same gelling property supports its use in foods such as ice-creams and jellies. Porphyra is noted as a food alga, while Sargassum, Laminaria and Fucus are brown-algal examples with other source relations. Chlorella is a unicellular protein-rich food supplement, and Volvox is a colonial green alga. The source-use connection joins taxonomy with application: the named red algae supply a substance whose physical properties suit both culture media and food products.
117. A unicellular alga is selected as a compact protein-rich food supplement for use during space travel. The alga is:
ⓐ. Chlorella
ⓑ. Gelidium
ⓒ. Sargassum
ⓓ. Gracilaria
Correct Answer: Chlorella
Explanation: Chlorella is a unicellular alga rich in protein and is used as a food supplement, including in contexts involving space travellers. Its identity rests on the combination of cellular organisation and nutritional use. Gelidium and Gracilaria are red algae known primarily as sources of agar, while Sargassum is a marine brown alga that may be used as food but is not the unicellular protein-rich supplement described. The stated use does not imply that Chlorella supplies every nutritional requirement or that all unicellular algae have the same use. It links one named alga with a specific practical application arising from its high protein content and compact biological form.
118. Examine the source-use records below.
| Record | Algal source | Product or use |
|---|
| P | Brown algae | Algin |
| Q | Red algae | Carrageen |
| R | Gelidium and Gracilaria | Agar |
| S | Chlorella | Protein-rich supplement |
The valid records are:
ⓐ. P and R only
ⓑ. Q and S only
ⓒ. P, Q, R and S
ⓓ. P, R and S only
Correct Answer: P, Q, R and S
Explanation: Record P is valid since algin is obtained from brown algae. Record Q is also valid because carrageen is a hydrocolloid supplied by red algae. Gelidium and Gracilaria are red-algal sources of agar, supporting record R, while Chlorella is a unicellular protein-rich alga used as a food supplement, confirming record S. The table brings together products with different biological and commercial roles: algin and carrageen are water-holding hydrocolloids, agar is a gelling material used in culture media and foods, and Chlorella itself is consumed as a supplement. All four relations are independently accurate, so no row requires correction.
119. A laboratory receives four algal products with their labels accidentally exchanged. The sample that forms a firm microbial-culture gel should be relabelled as:
ⓐ. carrageen obtained only from brown algae
ⓑ. algin obtained from Chlorella
ⓒ. protein supplement obtained from Gelidium
ⓓ. agar obtained from Gelidium or Gracilaria
Correct Answer: agar obtained from Gelidium or Gracilaria
Explanation: Agar is the algal product widely used to solidify microbial culture media. Its principal named sources here are the red algae Gelidium and Gracilaria. Carrageen is also obtained from red algae rather than only from brown algae, while algin comes from brown algae and is not obtained from Chlorella. Chlorella is consumed as a protein-rich supplement, whereas Gelidium is associated with agar production. The ability to form a stable gel underlies the described laboratory use. Identifying the sample requires connecting three pieces of information: the physical function of the product, its name and its biological source.
120. An algal specimen is unicellular and protein-rich but does not supply agar. It is marketed directly as a dietary supplement. This profile most closely matches:
ⓐ. Gracilaria
ⓑ. Chlorella
ⓒ. Gelidium
ⓓ. Sargassum
Correct Answer: Chlorella
Explanation: Chlorella is identified by the combined profile of unicellular organisation, high protein content and direct use as a food supplement. The statement that it does not supply agar helps separate it from Gelidium and Gracilaria, the named red-algal sources of that hydrocolloid. Sargassum is a multicellular marine brown alga and belongs among the algal examples used as food, but it does not fit the unicellular supplement description. The classification uses both biological form and economic role. Neither feature alone is as discriminating as their combination, since many algae are edible and many algal products have commercial value, but Chlorella uniquely matches the complete supplied profile.
