KNEC KCSE BIOLOGY TOPICAL QUESTIONS AND ANSWERS

How is the human eye adapted to its function?

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN19

How is the human eye adapted to its function?

answers

Adaptations of the eye.

The presence of:-

The sclerotic layer which contains tough connective tissue fibres which helps it to support and protect the other parts of the eye ball.
The choroids which contain many blood capillaries which supply oxygen and nutrients of the retina and removes metabolic wastes from eye.
Its highly pigmented, to prevent reflection of light within the posterior chamber of the eye ball.
The retina which contains photoreceptor cells called cones and rods. It is said to be the light sensitive part of the eye. Cones are adapted for light and colour vision while rods are adapted for dim light vision.
The vitreous humour-Which is under pressure. It helps to maintain the shape of the posterior chamber of the eye ball. It also plays an important part in the refraction of light rays enabling them to be focused on the retina.
The cornea, transparent and curved which helps to play an important role in focusing of the image on the retina. It accounts for the largest refraction of light rays.
The aqueous humour –Contains oxygen and nutrients, which nourish the cornea and the lens. It is under pressure thus helping to maintain the shape of the anterior chambers of the eye. It also plays a part in the refraction of light rays enabling them to be focused on the retina.
The Iris is heavily is heavily pigment, to prevent entry of light into the eye except through its central aperture called the pupil. It contains circular and radial muscles which constrict or dilate the pupil depending on the intensity of light.
The Iens is elastic, therefore allows changes in its shape depending on the tension exerted through the suspensory ligaments. This enables it to bring light rays causing from either near or far objects into sharp focus on the forea.
The ciliary’s body Contains the ciliary muscles whose contraction and relaxation alters the tension exerted on the suspensory ligaments.
This in turn alters the shape of the lens enabling it to focus for both near and distant objects.
The eyelids which are movable and opaque structures can be closed through a reflex action to protect the eye from too much light or from foreign objects.
The eye muscles help to move the eye ball within the orbit. The lateral rectus muscles move the eye up and down whole the oblique muscles the eyeball in its up and down movement.
The lachrymal gland which continuously secretes a watery, saline and antiseptic fluid called tears. The tears moisten the cornea and wash foreign particles out of the eye.
The eyelashes, which are many hairs, protect the eye from the entry of small foreign particles.
The eyebrows raised portion of the skin above the eye, thickly covered with hair, whose functions are to prevent sweat and dust from entering the eye.

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Describe how gaseous exchange takes place in terrestrial Plants.

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN18

Describe how gaseous exchange takes place in terrestrial Plants.

answers

Gaseous exchange in terrestrial plants.
Gaseous exchange in plants involves two main respiratory gases: carbon IV oxide and oxygen.
During daytime green plants take in carbon IV oxide for photosynthesis and oxygen for respiration. During photosynthesis oxygen is given out as a by product and released to the atmosphere. In plants such as the flowering plants stomata in the leaves and lenticels in the woody stems and pneumatophores/breathing roots in aquatic woody plants provide the surface for gaseous exchange. Gaseous exchange taken place by diffusion across the respiratory surface.
Stomata
These are located mainly in the leaves and in younger parts of the stem. The opening and closing of stomata is controlled. Mainly by the intensity of light. They are normally open during the day and closed during the night. Several theories explaining the mechanism of stomata opening and closing have been put forward.
1. Photosynthetic theory
Guard cells have chloroplasts. During daylight, they carry out photosynthesis producing surges. The surges increase the osmotic pressure of the cell sap. This causes water to more into guard cells from the neighboring epidermal cells by osmosis.
The results is an expansion and increase in turgidity of the guard cells causing the stomata to open.
In darkness photosynthesis stops. The sugar in the guard cells is converted to starch. This lowers the osmotic pressure of guard cells causing the to lose water to neighboring cells by osmosis.
The guard cells become flaccid and the stomata close.
The guard cells become flaccid and the stomata close.
2. Starch – sugar interconversion:
The enzymatic conversion of starch to sugar proceeds more readily in an alkaline environment(high PH).The conversion of sugar to starch occurs more readily in an acidic environment (low Ph).During the night, when photosynthesis is not taking place, carbon dioxide accumulates in leaf cells it combines with water to form carbonic acid. This lower the PH in the guard cells leading to conversion of sugar to starch this decreases the osmotic pressure in the guard cells causing them to lose water to the neighboring epidermal cells. The guard cells become flaccid and the stomata close.
During daylight, when photosynthesis is taking places, the concentration of carbon dioxide in the leaf cells, raising their PH, and favouring the conversion of starch to sugar. This increases the osmotic pressure in the guard cells causing them to take in is an expansion and increase in turgidity of the guard cells causing the stomata to open.
3. Potassium Ion (K+) mechanism
When guard cells are exposed to light, their chloroplasts manufacture ATP. The ATP drives at K+ pump in the cell membrane of the guard cells. This causes an active uptake of K+ into the guard cells from surrounding epidermal cells.
Accumulation of K+ in guard cells increases the osmotic pressure of their cell sap. This causes water to move into the guard cells from neighbouring epidermal cells by osmosis. The result is an expansion and increase in turgidity of the guard cells causing the stomata to open.
-At the onset of darkness, chloroplast stop making ATP and its concentration in guard cells falls rapidly stopping K+ pump, K+ migrate from the guard cells
Causing them to lose water to the neighbouring cells by osmosis. The guard cells become flaccid and the stomata close.
-Water molecules are pumped into the guard cells from adjacent epidermis cells.
-A small extent of gaseous exchange takes place in the stem through structures called lenticels.
These are small gaps in the bark usually circular or oval & slightly raked on the bark surface.
The cells in these area are thin walled and loosely packed leaving air space which communicates with air spaces in the cortex. Hence 02 for respiration is taken up & C02 is given out.

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K.C.S.E Biology Q & A - MODEL 2005PP1QN17

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN17

After an ecological study of feeding relationships students Constructed the food web below.

a) Name the process through which energy from the sun is incorporated into the food web.
b) State the mode of feeding of the birds in the food web
c) Name two ecosystems in which the organisms in the food web live
d) From the information in the food web, construct a food chain with the large bird as a quarternary consumer.
e) What would happen to the organisms in the food web if bird N migrated?
f) Not all the energy from one trophic level is available to the next level. Explain
g) (i) Two organisms which play a role in the ecosystems are not included in the food web. Name them.
(ii) State the role played by the organisms named in g(i) above.
h) i) State three human activities that would affect the ecosystems.
ii) Explain how the activities stated in h(i) above would affect the ecosystems.

answers

a)Photosynthesis
b)Heterotrophic – holozoic
c) Small fish pond / dam, rain forests.
d) Algae Zoo plankton small fish bird large bird.
e)-Snails would increase in number
-Bird M would increase in number.
-Green plants would decrease in number
f) The energy to be passed on from one trophic level to the next is contained in food materials. Most of the food taken in by consumers passed on from one trophic level to the next is consumers passes through the digestive track as undigested matter that is removed as faeces. The digested materials are absorbed in to the bloodstream and conveyed to various tissues of the body. Most of the absorbed food materials are used in respiration, to Produce is lost as heat during sweating, evaporation and transpiration in plants.
g)i) Scavengers e.g. vultures
Decomposers e.g. bacteria
ii) Scavengers feed on dead bodies of herbivores and carnivore / the consumers.
-Decomposers act upon the remains of the producers, consumers, & Scavengers causing decay, to release inorganic materials, which are later re-used by producers to make new organic compounds.
h) i) -Deforestation
-Overgrazing
-Soil erosion
-Hunting, poaching
-Over fishing
-Poor waste disposal // Environmental pollution
ii) Deforestation
Lack of trees leads to reduced number producers in an ecosystem.
Overgrazing
Many animals eat away and trample the vegetation hence reducing / depleting the number of producers.
-Lead to gully erosion hence carrying away some of the underground and crawling animals (Consumers)

Comments

Name two modern methods of food preservation and for each state the biologic principle behind it.

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN16

Name two modern methods of food preservation and for each state the biologic principle behind it.

answers

b) Refrigeration
It inactivates disease causing organisms/micro-organisms.
Irridation –The radiation kills/destroys the micro-organism.
Pasteurization (for milk only)
Canning-Kills the micro – organisms.

Comments

Name two organisms that cause food spoilage

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN16

Name two organisms that cause food spoilage

answers

a) - Fungus
-Bacteria

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K.C.S.E Biology Q & A - MODEL 2005PP1QN15

18/6/2020

In a garden with plants of same species, 705 plants had red flowers while 224 had white flowers.
a) Work out the ratio of red to white flowered plants
b) (i) Using letter R to represent the dominant gene, work out a cross between F1 offspring and a white flowered plant.
(ii) What is the genotypic ratio from the cross in b(i) above?
c) What is meant by the term allele?

answers

a) 3:1

c)Apart of Genes with contrasting characteristics

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K.C.S.E Biology Q & A - MODEL 2005PP1QN11

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2005PP1QN11

The diagram below represents a part of the rib cage.

a) Name the parts labeled W, Y and Z.
W ……………………………………………………
Y …………………………………………………….
Z ……………………………………………………..
b) How does the part labeled Z facilitates breathing in?

answer

Lactic acid

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How is the human eye adapted to its function?

How is the human eye adapted to its function?

Describe how gaseous exchange takes place in terrestrial Plants.

Describe how gaseous exchange takes place in terrestrial Plants.

K.C.S.E Biology Q & A - MODEL 2005PP1QN17

K.C.S.E Biology Q & A - MODEL 2005PP1QN17

Name two modern methods of food preservation and for each state the biologic principle behind it.

Name two modern methods of food preservation and for each state the biologic principle behind it.

Name two organisms that cause food spoilage

Name two organisms that cause food spoilage

K.C.S.E Biology Q & A - MODEL 2005PP1QN15

K.C.S.E Biology Q & A - MODEL 2005PP1QN15

K.C.S.E Biology Q & A - MODEL 2005PP1QN14

K.C.S.E Biology Q & A - MODEL 2005PP1QN14

K.C.S.E Biology Q & A - MODEL 2005PP1QN13

K.C.S.E Biology Q & A - MODEL 2005PP1QN13

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K.C.S.E Biology Q & A - MODEL 2005PP1QN11

K.C.S.E Biology Q & A - MODEL 2005PP1QN11

Name the organism that causes amoebic dysentery.

Name the organism that causes amoebic dysentery.

Why would carboxyhaemoglobin lead to death?

Why would carboxyhaemoglobin lead to death?

Name three factors in seeds that cause dormancy.

Name three factors in seeds that cause dormancy.

State the importance of osmosis in plants.

State the importance of osmosis in plants.

Name the substance which accumulates in muscles when respiration occurs with insufficient oxygen.

Name the substance which accumulates in muscles when respiration occurs with insufficient oxygen.

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