Biology_2019_STPM term 3_Objectives

Which group of invertebrate taxa is sessile and processes double layered body wall with numerous pores?

• Arthropoda

• Cnidaria

• Mollusca

• Porifera

Answer explanation

Porifera are sessile multicellular organisms that have porous bodies where water moves in and out of them. Their body wall is divided into two layers with a central mesophyll. Porifera are sponges with unspecialised cells.

In Malaysia, poaching of tigers has reduced their population significantly. This causes negative impacts on the interactions between populations of different species such as mousedeer and wild boar.

Based on the statement above, which level of biodiversity is affected?

• Ecosystem diversity

• Genetic diversity

• Population diversity

• Species diversity

Answer explanation

Species diversity is the number of different species in a community. It refers to the number of each species and its abundance in a population. This diversity affects their relationship with one another.

• Ⅰ and Ⅲ

• Ⅰ and Ⅳ

• Ⅱ and Ⅲ

• Ⅱ and Ⅳ

Answer explanation

In the phosphorus cycle, phosphorus is found in rocks as inorganic phosphate. Water erodes the rock surface and carries inorganic phosphate into the soil. Decomposition release dissolved phosphate into water.

In an experiment, a student rears some guppy fish in a small natural pond. The student gives the fish sufficient food and maintains good water quality. After a period of time, the population of fish stops increasing.

The population of guppy fish does not increase due to

• sexual selecction

• space limitation

• intra-specific competition

• toxic waste products accumulation

Answer explanation

Intraspecific competition is an interaction of competition in between individuals of the same species. The individuals of the same species occupy the same niche and compete for exactly the same resources.

Results of a field study on the density of Mimosa sp. using 50 cm × 50 cm quadrats are given in the table.

What is the density of Mimosa sp. per m²?

• 4

• 16

• 40

• 160

Which population will show a J-shaped growth curve?

Ⅰ. A squirrel population in a stable tropical rainforest.

Ⅱ. A small herd of elephants relocated into a protected national park.

Ⅲ. Replants mangroves trees in Matang Mangroves Forest Reserve, Perak.

Ⅳ. A seal population rebounds after large numbers were killed by a disease.

• Ⅰ and Ⅲ

• Ⅰ and Ⅳ

• Ⅱ and Ⅲ

• Ⅱ and Ⅳ

Answer explanation

J-shaped growth curve is where the population density of an organism in an environment increases rapidly in an exponential form. The population stops abruptly due to environmental resistance and population size drops suddenly.

In a small community, marriage never occurs with members outside their own immediate community. As a result, they are genetically unique and their gene frequencies are different from other populations.

Which are true about the genetic uniqueness of the population?

Ⅰ. Bottleneck effect

Ⅱ. Founder effect

Ⅲ. Genetic drift

Ⅳ. Sexual selection

• Ⅰ and Ⅱ

• Ⅰ and Ⅳ

• Ⅱ and Ⅲ

• Ⅲ and Ⅳ

Answer explanation

Sexual selection is a mode of natural selection in which members of one sex choose mates of the other sex to mate. This reduces the gene frequency of the population. As a consequence, sexual selection can lead to the evolution of traits as only the fittest alleles are selected for. The bottleneck effect is a type of drift which greatly reduces genetic diversity. It happens when the size of a population is severely reduced. The allele frequency in the remaining population that increases in size through sexual selection will be different from the original population.

Which statement is true about hybrid breakdown?

• The hybrids produced diet at an early age.

• This is a prezygotic isolating mechanism.

• The hybrid fail to produce functional gametes.

• The F₁ hybrids are fertile but the F₂ are infertile.

Answer explanation

Hybrid breakdown is where some hybrids in the first generation are viable and fertile but when they mate with one another or with either parent's species, the offspring produced is sterile or weak.

Genes Q and R are linked and the distance between the genes is 20 map units. In the cross between Qr/qr?

• 10%

• 20%

• 30%

• 40%

Answer explanation

The proportion of recombinants resulting from a dihybrid test cross is used to calculate the crossover value. Crossover values can be used to locate the relative positions of genes on chromosomes. 1% of crossover value = 1 map unit.

The ability to taste phenylthiocarbamide (PTC) is a dominant trait. In a population, 49% of the individuals are unable to taste PTC. What is the frequency of the dominant allele in that population?

• 0.70

• 0.51

• 0.49

• 0.30