Biology p3 ms
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BIOLOGY
PAPER3 (PRACTICAL)
MARKING SCHEME
1. a) (i) leaf
(ii) P – stoma; rej stomata.
Q – palisade cells/layer/mesophylls
R – Spongy layer/cell/mesophylls
S – vascular bundle/xylem/phloem
T – Intercellular/air spaces
U – Upper epidermis.
b. (i) Site for photosynthesis.
(ii) Adaptation
- Numerous chloroplasts (which contain chlorophyll) for photosynthesis.
- Closely packed/vertical arrangement for maximum absorption of light.
- Positioned on the upper surface to absorb maximum light.
c. - Light
- Temperature
d. Length = 1cm accept ± 0.1
Actual length = length of image
Magnification
= 10,000
5,000
= 2 um 2 micrometers .rej.if no units
2. a)
Food substance procedure observation conclusion
starch Put solution K in a test tube Blue black Presence of starch
add iodine solution
Put solution L in a test tube No colour change/colour of Absence of starch
add iodine solution iodine/brown
Reducing sugars Put solution K in a test tube No colour change; colour Absence of reducing sugars
and equal volume of of benedicts solution
benedicts solution; heat to remains
boil
Put solution L in a test tube Colour changes to Presence of reducing
Add benedict’s solution; green,yellow,orange sugars.
heat to boil. ,brown
12/2 = 6marks
b.i)
Test with procedure observation conclusion
Iodine solution Put contents of visking Blue black Presence of starch
tubing in a test tube add
iodine solution
Benedicts solution Put contents of visking Colour changes from blue Presence of reducing
tubing in a test tube add to green, yellow, orange sugars.
Benedict’s solution brown
heat
ii)
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Biology p3 ms
Test with procedure observation conclusion
Iodine solution Put contents of the beaker No colour change/colour of Absence of starch.
in a test tube add iodine iodine/brown.
solution
Benedicts solution Put contents of the beaker Colour changes from blue Presence of reducing
in a test tube add to green, yellow orange sugars
Benedict’s solution then brown.
Then heat
6 /2= 3 marks
N:B Mark procedure once. But must be correct at all cases.
c. Reducing sugar molecules are small in sizes; able to pass through the semi – permeable membrane intopthe
visking tubing by diffusion. (2mksl
Starch molecules are too large; to pass through the semi -permeable membrane/visking tubing into the beaker.
(2mks)
d. Cell membrane (1mk)
3. a)
Specimen steps identity
A 1b,3a; Arachnida
B 1a,2a,4a; Pisces
C 1b,2b,5b,6b; Chilopoda
D 1a,2a,4b,7b,8a Reptilia
E 1a,2a,4b,7a; Aves
F 1b,3b,5a; Insecta
b) External fertilization (1mk)
Disadvantage: - low chances of fertilization.
- Eggs and zygotes are prone to predators. (Mark any one.)
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