NABTEB 2021 BIOLOGY ANSWERS

1-10 ADBCBDCAAB

11-20 BBABCCDCDD

21-30 DDACDBCDDC

31-40 CCCDAABDBD

41-50 BDCDDBDACD

 

NABTEB 2021 BIOLOGY SOLUTIONS

 

(1ai)

Plasmolysis: Filament of Spirogyra in pond of water was placed on a glass slide. It was observed under low power of the microscope and the cells were found to be turgid. The pond water was absorbed using a filter paper. A drop of strong salt solution was added and was left for a few minutes. It was observed that the cell wall was leaving a gap between the cell wall and the plasma membrane, showing that exosmosis has occurred or the cells have been plasmolysed.

 

(1aii)

Osmosis using living materials:

 

Method:

(i) Obtain three cassava or yam tubers

(ii) Peel off the tubers with a knife

(iii) Scoop out a portion of the tubers with a knife

(iv) Prepare a concentrated solution of sugar solution

(v) Pour some amount of the sugar solution into the scooped parts of the tubers and note the levels of the solution in the tubers

(vi) Put one tuber in boiling water for about five minutes to kill the cells

(vii) Put the base of each tuber in petri dishes containing some amounts of water

(viii) Sugar solution is put in fresh cube A, one fresh cube B is filled with water and the boil cube C.

 

Observations:

(i) Level of sugar solution in A has risen

(ii) Levels of solutions in B and C remained the same

 

Conclusion:

(i) Water has been drawn by osmosis through the yam tissues in A into the sugar solution (higher concentration of solute, but lower concentration of water).

(ii) There is no rise in B because the concentration of the water in yam is the same as the concentration of the water in the petri dish.

(iii) Osmosis does not occur in dead tissues as observed in C.

 

(1b) Role of diffusion in the activities of organisms:

(i) Gaseous exchange in the gills e.g. fish

(ii) For movement of oxygen from the maternal blood into the placenta

(iii) Movement of carbon dioxide out of the foetus into the placenta

(iv) Movement of oxygen out of the leaf through the stomata during the day

(v) Absorption of end products of digestion by the villi of the ileum into the blood.

*PART II*

_(Answer only ONE Question from this section)_

(2a)

Characteristics of wind pollinated flower (Birch tree flowers)

(i)They have no petals.

(ii) Stigma feathery to catch pollen from wind

(iii) Stamens and stigmas exposed to air currents.

(iv) Pollen are smooth, light, easily airborne.

(v) Large amount of pollen.

 

(2b)

(i) Berry: tomato, orange

(ii) Drupe: coconut, mango

(iii) Caryopsis: rice,wheat

(iv) Cypsela: tridax fruit, sunflower

 

(2c)

Aim: To prove that oxygen is necessary for germination.

Apparatus: Two conical flask marked A and B, seeds of pea, water, cotton wool, pyrogallic acid, test tubes.

Procedure: Take two conical flask with a cork and mark them A and B respectively. Place a wet cotton wool in each flask with some soaked Pea seeds. Pyrogallic acid absorbs oxygen so a test tube of in flask B in such a way that the chemical does not drop in the flask. In flask A hang a test tube of plain water.

Observation: The seeds in flask A germinate because of presence of oxygen and seeds in flask B do not germinate because pyrogallic acid absorbs oxygen.

Result: Oxygen is necessary for germination

 

=====================================================

 

 

(3a)

(i) Nitrogen – Leaves turns pale green or yellow

(ii) Magnesium – yellowing of leaves(Chlorosis)

(iii) Potassium – Plants generally turn dark green (both leaves and stems) and appear stunted

 

(3bi)

(i) Parenchyma

(ii) Collenchyma

(iii) Sclerenchyma (fibre)

 

(3bii)

(i) Xylem

(ii) Phloem

 

(3c)

Obtain a healthy young well watered potted plant. Remove the bark of a stem with its associated phloem in a form of a ring ring and the control, the bark is removed but the phloem is left intact. Leave the ringed plant for a week. It will be observed that the section above the ring is found to be swollen.

 

It is also observed that the sugar level at the swollen section is greater than the region below the ring.

In the control experiment, there were no swollen at the section above the ring. Since the ringed involved the removal of the phloem tissue, the sugar could not be translocated across the ringed section. It implies that the phloem is the pathway for the transport of organic materials in plants.

====================================================

*PART III*

_(Answer only ONE Question from this section)_

(4a)

Sensory cell is a cell that receives a particular stimulus (such as sounds, light, touch, smell, taste, and temperature) and converts it to impulse to be transmitted to the brain or nervous system

(4b)

(i) Tongue – for taste

(ii) Ear – for hearing and balance

(iii) Eyes – for sight

(iv) Nose – for smelling

(v) The skin – for touch, temperature and pain

(4c)

8 – 10CM DIAGRAM OF VERTICAL SECTION OF A MAMMALIAN SKIN

[https://i.imgur.com/evFLd5Q.jpg]

=====================================================

(5)

=====================================================

*PART IV*

(6ai)

Chromosome: This is thread-like structure of nucleic acids and proteins, found in the nucleus of living cells, carrying genetic information or genes.

(6aii)

Phenotype: It is the physical expression or observable characteristics of an individual’s genetic make-up.

(6aiii)

Genotype: It is the genetic make-up of an organism in terms of a particular set of alleles it possesses.

(6aiv)

Sex linked genes: This refers to a single gene on a sex chromosome which control certain characters and are inherited together with the sex.

(6av)

Heterozygote: This is a cell or organism that contain two different alleles of a particular gene or genes.

(6b)

(i)COMPARATIVE ANATOMY:

Is the structural similarity in features That exist or abound in many groups of organisms; Which show them to have a basic body plan;

Which points to a common ancestor or origin

(ii) COMPARATIVE EMBRYOLOGY:

Embryology is the study of stages in the development of embryo in various organisms. A study of comparative embryology provides further evidence for evolution. A very young human embryo looks very similar to very young embryos of other mammals, birds, reptiles, fish and amphibians. The structure and mode of formation of the embryonic membrane: chorion, amnion, and allantois are all similar. All these features are related to the fish (which lives in water) indicating that terrestrial vertebrates descended from common ancestors who lived in water.

(6ci)

(i) It leads to competition.

(ii) Decline in the rate of reproduction

(6cii)

(i) Bush burning

(ii) Overgrazing

(iii) Fertilizer application

(iv) Deforestation