KNEC KCSE BIOLOGY TOPICAL QUESTIONS AND ANSWERS

Explain structure and functions of the human eye.

4/11/2021

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Explain structure and functions of the human eye. (20mks)

Conjuctiva - Protects eyeball from mechanical injury.
Cornea - Allows light to pass through
Iris - Controls amount of light passing through
Forea - Where image is formed
Sctera - Protect the eye ball; give it shape
Choroid - Absorbs stray lights
Provide nourishment to the eye.
Aqueous/vitreous humour - refract light into the eye towards retina maintain shape of eye ball.
Ciliary body - Controls curvature of the lens.
Rods - Perceive light of low intensity
Cones - Perceives light of high intensity.

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Describe the mechanism of inhalation in man

4/11/2021

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(a) Describe the mechanism of inhalation in man. (10mks)

External intercostals muscles contract; internal intercostals muscle relax, Rib cage move outwards; and upwards; Diaphragm muscles contract, Diaphragm flatten; volume in thoraci cavity increases; pressure reduces.
Atmospheric air enters the lungs; inflate (correct sequence to be followed)

(b) Using photosynthesis theory explain the mechanics of opening of stomata. (10mks)

Guard cells have chloroplast which photosynthesis in the presence of light, to form sugar, the osmotic pressure of guard cell increases; water move from neighbouring cells into guard cells being thicker than outer walls. Causes the outer wall to stretch more resulting guard cells budging outwards.

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A group of students carried out a study of the population growth of flour weevils.

4/11/2021

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A group of students carried out a study of the population growth of flour weevils. They put 16 grams of maize flour into two equal boxes K and L respective . They then introduced equal numbers of weevils into the boxes. The boxes were kept under similar environmental conditions. The weevils were counted at intervals and the results recorded in the table below.

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table.
Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks)
Number in K: ..
Number in L:......

K - 555
L - 1020

(c) (i) On what day was the population of weevils in K 580. (1mk)

86th Day

(ii) Between which days was the population difference greatest . (1mk)

100 - 120

(d) Account for the shape of graph L between day 5 and day 100. (4 mks)

Increase in population; because there is adequate food; the number of reproducing individuals is increasing; wastes products have not accumulated to toxic levels.

(e) State factors that would make the human species assume the graph curve above in K. (4mks)

Diseases
Lack of food
Death rate equal to birth rate.

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Name the end products of the light stage in photosynthesis.

19/6/2020

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K.C.S.E Biology Q & A - MODEL 2006PP1QN27

Name the end products of the light stage in photosynthesis.

answers

Hydrogen; Oxygen

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

19/6/2020

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

The chart below represents a simplified nitrogen cycle.

What is represented by X,Y, and Z?

answers

X- Denitrifying bacteria/ denitrification
Y- Animals/ Herbivores; accept primary consumers
Z- Nitrogen fixing bacteria ( in soil) accept Azotobacter.

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

19/6/2020

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K.C.S.E Biology Q & A - MODEL 2006PP1QN25

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

answer

A mouse has a larger surface area to volume ratio than a dog, hence losses more energy per unit body weight/ mouse losses heat faster than a dog.

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

19/6/2020

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K.C.S.E Biology Q & A - MODEL 2006PP1QN24

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

answers

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)

Comments

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.

Comments

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

18/6/2020

Comments

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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​Explain structure and functions of the human eye. (20mks)

​(a) Describe the mechanism of inhalation in man. (10mks)

​(b) Using photosynthesis theory explain the mechanics of opening of stomata. (10mks)

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table. Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks) Number in K: .. Number in L:......

​(c) (i) On what day was the population of weevils in K 580. (1mk)

​(ii) Between which days was the population difference greatest . (1mk)

​(d) Account for the shape of graph L between day 5 and day 100. (4 mks)

(e) State factors that would make the human species assume the graph curve above in K. (4mks)

Name the end products of the light stage in photosynthesis.

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.

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

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

How is the human eye adapted to its function?

Describe how gaseous exchange takes place in terrestrial Plants.

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

Explain how a biotic factors affect plants

How is the mammalian skin adapted to its functions?

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

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

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Explain structure and functions of the human eye. (20mks)

(a) Describe the mechanism of inhalation in man. (10mks)

(b) Using photosynthesis theory explain the mechanics of opening of stomata. (10mks)

(a) Using a suitable scale ,draw two graphs on the same axes from the results in the table.
Plot approximate number of weevils present on the Y – axis( Use graph paper provided) (8mks)

(b) What were the approximate number of weevils present in the two boxes on the 70th day. (2mks)
Number in K: ..
Number in L:......

(c) (i) On what day was the population of weevils in K 580. (1mk)

(ii) Between which days was the population difference greatest . (1mk)

(d) Account for the shape of graph L between day 5 and day 100. (4 mks)