KNEC KCSE BIOLOGY TOPICAL QUESTIONS

Thin walls/ thin epithelium for faster diffusion of gases/ to reduce distance for faster diffusion.
Moist for dissolving gasses
Large surface area for maximum diffusion/ gaseous exchange
highly vascularized to facilitate diffusion/ to enhance gradient.
Speed up diffusion

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K.C.S.E Biology Q & A - MODEL 2006PP1QN23

19/6/2020

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K.C.S.E Biology Q & A - MODEL 2006PP1QN23

State the function of each of the following parts of human ear.
a) Ear ossicles
b) Cochlea
c) Semi circular canals
d) Eustachian tube.

answers

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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)

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Explain how a biotic factors affect plants

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2004PP1QN19

Explain how a biotic factors affect plants

answers

Wind.
In windy conditions the rate of transpiration increases; wind disperses fruits/ seeds; is an agent of pollination; acc. Spores for seed.
Temperature
Changes in temperatures affects the rate of photosynthesis and other biochemical reactions/ metabolic reactions/ enzymatic reactions/ enzymatic reactions, temperature increases rate of transpiration;
Lights
Plants need light for photosynthesis, some plants need light for flowering/ photoperiodism/ seeds like lettuce require light for germination.
Humidity
When humidity is low, the rate of transpiration increases;
PH
Each plant requires a specific pH to grow well/ acidic/ alkalinity/ neutral;
Salinity
Plants with salt tolerant tissues grow in saline area, plants in estuaries adjust to salt fluctuations;
Topography
North facing slopes in temperature lands have more plants than south facing slope
Plants on windward side have stunted/ distorted growth;
Comparisons of mountains and valleys
Description of other areas with other topographies e.g. River valley rainfall/ water
- Fewer plants in areas/ semi arid and
- Water is needed for germination/ is a raw material for photosynthesis/ dissolves/ minerals salts/ provides turgidity for support/ fruits/ seeds
Pressure;
Variation in atmospheric pressure affect availability of CO+2+ which affects photosynthesis and low pressure increase rate of transpiration; and affect amount of oxygen; for respiration
Mineral salts/ trace elements
- Affects distribution of plants in the soils
- Plants thrive well where there are mineral salts in the soil
Plants living in the soil deficient in particular mineral element have special methods obtaining it; for example legumes obtaining from nitrogen by fixation or carnivorous.

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How is the mammalian skin adapted to its functions?

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2004PP1QN18

How is the mammalian skin adapted to its functions?

answers

The skin is made of epidermis and dermis. The epidermis is made up of three layers. The outermost layer is known as cornified layer; made up of dead cells that protect against mechanical damage/ desiccation/ microbes; the granular layer; is made up of living cells that give rise to the cornified layer, the malpighian layer; contain actively dividing cells that rise to new epidermal cells, that contain melanin that protects the skin against ultra violet rays.
The dermis has several components has sweat glands’ sudondic glands that produce sweat; sweat evaporates carrying it with latent of vaporization) thus reducing the body temperature; under cold conditions little/ no.
Sweat is produced thus heat is conserved; the sweat contains water/ sodium chloride/ uric acid/ urea; the skin is excretory organ.
Has hair, the hair stands erect to trap air when temperature is low to reduce heat loss/ lies flat to allow heat loss when the temperature is high.
Has nerve endings, which are sensitive to stimuli/ such as heat/ cold/ pain/ pressure/ touch
Has subcutaneous fats/ adipose tissue, that insulate the body against heat loss.
Has arteriole; that vasodilate when temperature are high to lose heat by radiation/ convection ( see converse)
Has sebaceous gland; which secrete sebum, an antiseptic/ water repellant/ that prevent drying/ cracking of skin/ skin supple
acc blood vessels/ capillaries for arterioles to supply food/ nutrients/ oxygen/ remove excretory products.

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Describe how fruits and seeds are suited to their modes of dispersal.

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2003PP1QN19

Describe how fruits and seeds are suited to their modes of dispersal.

answers

Water dispersed fruit / seeds

Mesocarp / seed has air spaces thus light / buoyant to float.
Therefore carried away by water.
The fruit / seeds are protected from soaking by water proud pericarp.

Animal dispersed fruits / seeds

Presence of hooks for attachment to animals; thus carried to other placed
Fruits are brightly coloured; succulent; aromatic attract animals, which feed on them.
The seed coats are registrant to digestive enzymes; thus carried to other places on them.
The seeds are dropped always from parent plant in faeces/ droppings.

Self dispersed fruits / seeds / explosive mechanisms

The dry pods / fruit split (along lines of weakness / satures)
Scattering seeds away from parent plant

Wind dispersed fruits / seeds

Censer mechanism
Perforated capsule is usually loosely attached to stalk / the long stalk is swayed by wind scattering seeds.
Presence of hairs / wing – like structure, floss / extensions which increase surface area / for buoyancy making is easy for fruits / seeds to be blown away
Fruits / seeds are light due to small size; therefore easily carried a ways by wind.

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Describe the functions of the various parts of the human eye.

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2003PP1QN18

Describe the functions of the various parts of the human eye.

answers

Sclerotic layer – (made up of collagen fibres thus) protects the eye maintains shape of eyeball.
Cornea

Allows light to enter the eye
Refracts light towards retina

Conjunctive - Protects cornea
Eyelids

Protects cornea from mechanical & chemical damage / protects eye form entry of foreign particles.
protects retina from bright light (by reflex action)

Choroids

(Contains black pigment which)prevents reflection of light within the eye / absorbed light.
Nourishes the eye / retina / supply oxygen / remove CO2

Ciliary muscles

Alter shape of lens during accommodation
Ciliary body produces aqueous humour.

Suspensory ligaments – adjusts shape of lens during accommodation
Lens – Refracts light rays / focuses light on retina
Vitrerous aqueous humour once.
Aqueous Humour – Nourishes cornea / lens Refracts light
Irus – ( pigmented thus) – gives the eye its colour / absorbs light controls amount of light entering the eye / adjusts size of pupil impulses.
Pupil – light enters the eyes through pupil.
Retina – has photoreceptor cells / rods / cones / image formation ;l generates impulses.
Fever / yellow spot – visual acuity / most sensitive part of retina with only cones.
Blind spot – point where nerve fibre emerges from the optic nerve / where the optic nerve leaves the eye / point where blood vessels & nerve fibres enter the eye.
Optic nerve – transmit impulses to brain.

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K.C.S.E Biology Q & A - MODEL 2003PP1QN17

18/6/2020

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K.C.S.E Biology Q & A - MODEL 2003PP1QN17

Some students used a model to demonstrate the effect of sweating on human body temperature. Two boiling tubes A and B were filled with hot water. The temperature of water in the tubes was taken at the start of the experiment and then at 5 minutes interval. The surface of tube A was continuously wiped with a piece of cotton wool soaked in methylated spirit. The results obtained are shown in the table below.

a) On the same axes, plot graphs of temperature of water in the tubes against time.
b) At what rate was the water – cooling in tube A?
c) Why was tube B included in the set up?
d) Account for the rate of cooling in tube A.
e) State two processes of heat loss in tube b.
f) What would be the expected results if tube A was insulated?
g) What would the insulation be comparable to in:
i) Bird
ii) Mammals?
h) Name the structures in the human body that detect:
i) External temperature changes
ii) Internal temperature changes

answers

b)     80 – 18 = 62; 2.48C /Min
            2.5            25

    c)     Control
    d)     Rate was faster in tube A; because the film of methylated sprit evaporated; removing heat from the tube;
    e)     Convection ; radiation
    f)     Lower rate of heat loss;
    g)     i) birds
               Feather
            ii) Mammals?
                Fur
    h)     i) external temperature changes
                Temperature
            ii) Internal temperature changes
                 Hypothalamus

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Describe how the cervical, lumbar and sacral vertebrae are suited to their functions.

17/6/2020

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K.C.S.E Biology Q & A - MODEL 2002PP1QN20b

Describe how the cervical, lumbar and sacral vertebrae are suited to their functions.

answers

 Cervical vertabrae

Vertebraterial canals for passage of ( vertebral) artery; atlas has ( broad) surfaces for articulation with condylyses of skulls to permit nodding
Axis has adenoid process/ protein Centrum to permit rotary/ turning act as a pivot for atlas/ skull/ movement of atlas/ Branched / forked/ short/ broad transverse processes, for attachment of ( neck) muscles; ace zygopophysis, for articulation between vertebrae ( acc. Vertebraterical canals and zygopophogen if shown on a diagram of the vertebrae
Has a short reduce neural spine, for attachment of ( neck) muscles, has wide / larger neural canal; for passage of spinal cord/ alternatively has wide neural for protection of spinal cord.

Lumbar

Broad/ long/ neural spine for attachment of ( powerful back) muscles long/ large/ well development/ transport processes for attachment of muscles ( that maintain posture and flex the muscles)
Has metamorphosis and hypothesis for muscle attachment large/ thick centrums for support
Prezygapophysis/ post/ zygapophysis for articulation between vertebrae ( acc. Anapophysis for hypopyses)

Sacral Vertebrae

Anterior vertebrae has a well developed transverse process, which are fused to the pelvis girdle/ articulate with pelvic girdle
Vertebrae fused, for strength transmit weight of the stationary animal to the rest of the body.
Sacrum has a broad base/ short neural spine; for attachment of (back)

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Name three types of skeletons found in multicellular animals

17/6/2020

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K.C.S.E Biology Q & A - MODEL 2002PP1QN20

Name three types of skeletons found in multicellular animals

answers

Hydrostatic
Exoskeleton
Endoskeleton

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<<Previous

Name the end products of the light stage in photosynthesis.

Name the end products of the light stage in photosynthesis.

K.C.S.E Biology Q & A - MODEL 2006PP1QN26

K.C.S.E Biology Q & A - MODEL 2006PP1QN26

A dog weighing 15.2kg requires 216kj while a mouse weighing 50g requires 2736kj per day. Explain.

A dog weighing 15.2kg requires 216kj while a mouse weighing 50g requires 2736kj per day. Explain.

State four ways in which respiratory surfaces are suited to their function.

State four ways in which respiratory surfaces are suited to their function.

K.C.S.E Biology Q & A - MODEL 2006PP1QN23

K.C.S.E Biology Q & A - MODEL 2006PP1QN23

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

Explain how a biotic factors affect plants

Explain how a biotic factors affect plants

How is the mammalian skin adapted to its functions?

How is the mammalian skin adapted to its functions?

Describe how fruits and seeds are suited to their modes of dispersal.

Describe how fruits and seeds are suited to their modes of dispersal.

Describe the functions of the various parts of the human eye.

Describe the functions of the various parts of the human eye.

K.C.S.E Biology Q & A - MODEL 2003PP1QN17

K.C.S.E Biology Q & A - MODEL 2003PP1QN17

Describe how the cervical, lumbar and sacral vertebrae are suited to their functions.

Describe how the cervical, lumbar and sacral vertebrae are suited to their functions.

Name three types of skeletons found in multicellular animals

Name three types of skeletons found in multicellular animals

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