NABTEB GCE 2021 BIOLOGY (O’LEVEL)

BIOLOGY OBJ
1-10: CBABACBBDC
11-20: CBCBCBBADD
21-30: DDBACBBCAD
31-40: ACAADBBBDA
41-50: DCADDACADC

BIOLOGY THEORY SOLUTIONS

ANSWER FOUR QUESTIONS IN ALL. ANSWER AT LEAST ONE(1) QUESTION FROM EACH SECTION

PART I:

(1a)
Diagram [https://i.imgur.com/hG7l0Tb.jpg]

(1b)
(i) Colonial organisms appear as a sphere while Filamentous organisms appear as a thread
(ii) Colonial organisms are generally sessile while Filamentous organisms are either sessile or floating

(1c)
(i) Colonial organisms: Volvox, Pandorina, Eudorina

(ii) Filamentous organisms: Chladophora, spirogyra, Zygnema

PART II:

(2a)
(i) Crop rotation
(ii) Cover crops
(iii) Conservation tillage
(iv) Contour farming
(v) Mulching

(2bi)
Reproduction is the process of producing offsprings that are biologically or genetically similar to the parent organism.

(2bii)
(a) budding
(b) fragmentation
(c) vegetative propagation
(d) spore formation

(2c)
(i) It is the number one source of oxygen in the atmosphere.
(ii) It contributes to the carbon cycle between the earth, the oceans, plants and animals.
(iii) It contributes to the symbiotic relationship between plants, humans and animals.

(iv) It serves as the primary energy process for most trees and plants.

(3ai)
(i) Help aeration of the soil.
(ii) Composting process which forms manure.
(iii) Enriches the soil with nitrates and other nutrients.

(3aii)
(i) Minerals
(ii) Organic matter
(iii) Water
(iv) Air

(3bi)
Stem:
When unilateral light falls on the stem, the auxin/growth hormone/IAA is displaced from the lighted to the dark side. The increase in auxin concentration on the dark side increases growth on that side causing the stem to bend towards the light/positive phototropism.

Roots:
The auxin is displaced from the lighted side to the dark side. The increase in auxin concentration retards growth on the dark side causing the root to bend away from the light/negative phototropism.

(3bii)
TABULATE:
=Tropic Movement:
(i) Response to unilateral stimulus
(ii) Not reversible

=Nastic Movement:
(i) Response to diffuse stimulus

(ii) Reversible

PART III:

(4ai)
Enzymes can be defined as biological polymers that catalyze biochemical reactions.

(4aii)
(i) They are affected by pH and temperature
(ii) They can be allosterically regulated by a several means
(iii) Are not destroyed or altered by the reactions which they catalyse

(4b)
(i) Transports hormones and nutrients throughout the body
(ii) Transports oxygen to cells and removes carbon dioxide

(4c)
(i) Fertilization is the process of reproduction in which fusion of male gamete with the female gamete takes place and results in formation if zygote cell.

(ii) Gestation is the The period of time during which an infant animal or human physically develops inside the mothers body until it is born.

(iii) Lactation is the process of milk secretion from the mammary glands of a mother soon after childbirth.

(iv) Hormones are chemicals synthesized and produced by the specialized glands to control and regulate the activity of certain cells and organs.

(5a)
TABULATE:
(i)
– Vector: Tse-tse fly
– Causative organism: Trypanosoma brucei
– Diseases transmitted: Sleeping sickness

(ii)
– Vector: Anopheles mosquito
– Causative organism: Plasmodium
– Diseases transmitted: Malaria

(iii)
– Vector: Black fly
– Causative organism: Onchocerca volvulus
– Diseases transmitted: River blindness

(5bi)
Voluntary action: Involves the response to a stimulus that is controlled at will by the brain. in this action, an impulse is carried from a sensory neurone via the spinal cord to the brain which interprets and sends the message back through the motor neurone to effector organ. The action is not automatic. e.g. running, writing, jumping, laughing, reading, smiling.

(5bii)
Involuntary action or reflex action: It is a rapid or automatic response to a stimulus. It does not involve the brain for initiation. Therefore, the action is not under the control of the will, e.g. sneezing, coughing, knee jerk, salivation, secretion of grand, blinking

(5c)
(i) Malnutrition
(ii) Decrease in population size

(iii) Natural disasters

PART IV:

(6ai)
Succession is defined as the orderly changes that occur in plant and animal community of a given area over a period of time until a stable community is formed

(6aii)
(a) Nudation
(b) Invasion
(c) Competition and reaction
(d) Stabilization or climax

(6b)
(i) Bush burning: It destroys timber, young trees, seeds and the humus rich soil. The natural habitats of animals especially mammals and birds are destroyed.

(ii) Pesticides: It can contaminate soil, water, turf, and other vegetation. In addition to killing insects or weeds, pesticides can be toxic to a host of other organisms including birds, fish, beneficial insects, and non-target plants.

(iii) Fertilizers: Fertilizers release nutrients as they enter surface water. These nutrients stimulate microorganism growth and reproduction, reducing the dissolved oxygen found in marine ecosystems. Fish and other aquatic species suffocate when their habitat doesn’t have enough dissolved oxygen in surface water.

(6c)
(i) Used for cross breeding
(ii) To study about the hereditary nature of plants

(iii) Used for artificially selecting the type of crop

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Source: Expo