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Detailed topic 1 notes

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These comprehensive A-Level Biology SNAB Topic 1 notes provide clear and detailed coverage of all essential concepts, including cell structure, biological molecules, membranes, and genetic inheritance. Designed specifically for the Edexcel Salters-Nuffield specification, the notes feature concise explanations, helpful diagrams, and key exam tips to support effective revision. Ideal for students aiming to deepen their understanding and improve exam performance, this well-organized document saves time and enhances learning by presenting complex topics in an accessible and engaging way.

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, 11. 9. 23
L1 - 1.1 - Transport in substance - ms Boyle

SA to volume ratio - Why do we need an Exchan'ge system?
• Human or mammals have a large size, increase in size of organism : surface area to
volume ratio decreases - the diffusion distance increasing hence metabolic rate
increase.
• Diffusion become insufficient. As result large organism have mass transport -
consisting of heart and circulation - move substance around the body and allows
gas change.
3 cubes X 3 cubes
2 cubesacubes
SA =
6 x 32 = 54
SA =
6x 28 = 24
r
V =
33 =
27
V = 23 =
8
SA: V =
SAIV =
54 : 27 =
54/27 2
=



SA : V =
SAIV =
24:8 = 2418:3


a cubes x4 cubes

SA = 6x42 =
96
V = 43 =
64
SA V
. -

SAIV =
96 64
. =
96/64 =
1 5
.




The bigger the Sa to volume ratio the faster the rate of diffusion

Human Earthworm m = am-

surface = 180 dm2 Surface = 0.36 dm2
volume = 68 dm2 M Volume = 0.0048 dm2·
180/68= 2.5
15 don't 0.36/0.0048 = 75 dm-

The earthworm has a higher SA to volume ratio which suggest that it has a smaller
diffusion distance and doesn’t need mass transport .

-we Have a specialized organs for gas ' exchange.
-Earthworm is moist better diffusion.
·

, L1 - 1.1 - The heart - ms Boyle 11. 9. 23


• four chambers - RL atrium and ventricle
• four main blood vessels -vena cave, aorta,
plumery vine plumery artery
• Atrioventricular valve - Tricuspid bicuspid -
separate atria from ventricle
• Semilunar valve - separate atria from ventricle
• Tendinous chords - prevent atrioventricular
from turning in and out due to pressure
• Septum - prevent oxygenated and deoxygenated
blood from mixing
• Cardiac muscle - thicker on LHS - pumps blood septumY
at high pressure. cardiac
muscle


Double circularly system - Passes through the heart twice
Why - respiration release energy - want to get blood around - get energy.


• The deoxygenated blood from the body Enters the vena cava and then travels to
Right atrium then into through the t-valveInto the right ventricle and pumps out
of the Pulmonary artery (way from the heart)
• The oxygenated blood from the lungs enter the Pulmonary vein (towards the
heart)into the left atrium and Through the b-valve it enters the left ventricle And
blood pump to the rest of the body throughAorta. N


Irregular beating of the heart is called - arrhythmia

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