CSEC Biology Paper 2 January 2019 - Free CXC Past Paper with Answers

Name TWO biotic factors and ONE abiotic factor that may account for the extinction of a species.

Biotic factors Abiotic factor

State TWO activities of humans which may have a negative impact on species diversity and TWO measures that may be taken to reduce the impact of these activities.

Activities Measures

The graph in Figure 1 shows the growth of two populations of spider mites: one which feeds on plants and one which is carnivorous and preys on the plant-eating spider mites.

Figure 1. Fluctuations in predator and prey populations

Label on the graph the curve which represents the predator, using the letter A.

Use the number of organisms and the shape of the curves to state TWO reasons for your answer in (b) (i).

Assuming that the population of the predator drops to zero, extend the curve of the prey population on the graph. (Assume that no other changes have occurred in this community.)

Assuming that the population of the prey drops to zero, extend the curve of the predator population on the graph. (Assume that no other changes have occurred in this community.)

A farmer planted 50 seeds of corn on a plot of land and 100 seeds from the same batch on a neighbouring plot of the same size, hoping to reap twice the yield of corn. He gave both plots the same amount of fertilizer and water. However, the yield of corn obtained from the plot with 100 seeds was much less than that of the plot with only 50 seeds. Suggest THREE possible reasons for the lower yield obtained in the plot with the larger number of seeds.

What is the effect on the expression of phenotype for continuous and discontinuous variation?

Continuous variation Discontinuous variation

State how the data for continuous variation should be presented graphically.

State ONE characteristic of human beings that shows (i) continuous variation (ii) discontinuous variation

State TWO cellular components of blood.

A couple with blood groups A and B has a son with blood group O. Complete the genetic diagram below to show how this is possible.

(i) Parents' phenotypes: Blood group A $\times$ Blood group B

Parents' genotypes: Parents' gametes: Fertilization cross

What is the genotype of the child with blood group O?

Two sisters, ages 15 and 16, have the same biological parents and were brought up under the same conditions in the same home. The 15-year-old is much taller than the 16-year-old. Suggest THREE events which take place during sexual reproduction which may have led to the variation in the height of the two sisters.

SECTION B Answer ALL questions.

(a) (i) With the aid of a labelled diagram, describe how the mammalian heart pumps deoxygenated blood from the cells in the body to the lungs to become oxygenated.

Pumping of deoxygenated blood from the body to the lungs Description

The structure of arteries and veins differ from each other. Explain how TWO of these differences allow these blood vessels to carry out their functions.

Green plants also have specialized vessels such as xylem to transport water to their various tissues and organs.

(i) State ONE similarity and ONE difference between the structure of a blood capillary and the structure of a xylem vessel found in the stem of a green plant. Similarity Difference

Suggest TWO reasons why green plants do not need to depend on xylem for transporting oxygen to their cells.

Diseases may be categorized as pathogenic (P) when they are caused by a pathogen and hereditary (H) when they are caused by faulty genes. Classify the following diseases by inserting either 'P' for pathogenic or 'H' for hereditary in EACH bracket:

Yellow fever ( ) Sickle-cell anaemia ( ) Measles ( ) Haemophilia ( )

John and his friend were bitten by Aedes aegypti mosquitoes while visiting an area in which many individuals had tested positive for dengue fever. John did not contract the disease but his friend did.

Describe how the mode of transmission of dengue fever differs from that of the human immunodeficiency virus (HIV).

Use this difference and your knowledge of the immune system to suggest TWO reasons why John did not contract dengue fever.

Compare the treatment method normally used for a viral disease with the treatment method normally used for diabetes and compare ONE preventative measure normally used for a viral disease with ONE preventative measure normally used for diabetes.

Outline TWO methods used to control the mosquito vector and for EACH method state the stage in the life cycle that is targeted.

Outline ONE major function of EACH of the following parts of the human brain:

Cerebrum Cerebellum Medulla

A motorcyclist crashed into a wall on his way home from a party at which he drank five beers. After determining that he was alive, the paramedic at the scene of the collision checked the motorcyclist's pupil reflex. Complete the flow diagram in the following box to show the sequence of events involved in the pupil reflex.

Pupil reflex impluse pathway Light stimulus $\rightarrow$ receptor cells in retina $\rightarrow$ $\rightarrow$ motor neurons in $\rightarrow$ nerve $\rightarrow$ muscles contract $\rightarrow$ pupil

Suggest THREE conclusions that the paramedic may make if the accident victim is alive but shows no response to the pupil reflex test.

Explain THREE physiological reasons why the consumption of excess alcohol could have caused the motorcyclist to crash.