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_Biology SNAB - Topic 1 A+ Level- Lifestyle, Health and Risk
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Biology SNAB - Topic 1 A+ Level-Lifestyle, Health and Risk
What is mass flow? - ANS-Mass flow is the bulk transport of substances from one area
to another due to pressure differences
What are mass transport systems used for? - ANS-The mass transport system are used
to carry materials from specialised exchange organs to the body cells, and to remove
metabolic waste.
Why do animals need a mass transport system? - ANS-In order to survive, animals
require essential substances to enter and leave the body in sufficient quantities and be
transported around the body, which is usually done via diffusion. However, due to the
size is organisms increasing diffusion becomes insufficient. Therefore animals have a
heart and circulatory system which moves substances around the body and allows
exchange of substance to take place.
As the size of the organism increases, the surface area..., diffusion distance...,
metabolic rate.... - ANS-SA - decreases
DD - increases
Metabolic rate (hence input and output requirements) - increases.
What are the features of a mass transport system? - ANS-A network to move through
(vessels)
A medium for movement (a fluid - blood)
Controlled direction - to move substances to/from where they are needed (eg. blood is
moved along a pressure gradient created by the heart, the direction of flow controlled by
the valves
Maintenance of speed - contraction of heart + elastic recoil of arteries helps to maintain
the pressure gradient, thus speed.
Open circulatory system - ANS-In insects and some other animal groups, blood
circulates in large open spaces.
A simple heart pumps blood out into cavities surrounding the animal's organs.
Substances can diffuse between the blood and cells. When the heart muscle relaxes,
blood is drawn in from the cavity back into the heart through small, valved openings
,along its length.
Closed circulatory system - ANS-Many animals, including all vertebrates, have a closed
circulatory system in which the blood is enclosed within blood vessels. This generates
higher blood pressure as the blood is forced along fairly narrow channels instead of
flowing into large cavities. FYI animals with this type of circulatory systems are larger in
size and more active.
What are the advantages of a closed circulatory system? - ANS-Blood flows after
because of the vessels and so the blood system is more efficient eg delivering
substances around the body.
Single circulatory system - ANS-A circulatory system where the blood flows through the
heart and is pumped out to travel all around the body before returning to the heart.
Double circulatory system - ANS-Blood passes through the heart twice in one complete
circuit of the body e.g. in a human
Why is a double circulatory system beneficial for mammals and birds? - ANS-The heart
gives the blood an extra 'boost' that reduces the time it takes for the blood to circulate
around the whole body. This allows birds and mammals to have a high metabolic rate,
as oxygen and food substances (glucose) required for metabolic processes can be
delivered more rapidly to cells and meet the needs of the organism.
Why do only small animals have an open circulatory system? - ANS-Movement of
oxygen, carbon dioxide and other products carried by blood relies on diffusion in
animals with an open circulatory system; diffusion us only fast enough for small
organisms.
Explain how a double circulatory system enables mammals to carry out effective gas
exchange (3) - ANS-One side of the heart transports blood to the lungs and the other
side of the body. So this separates the oxygenated and deoxygenated blood, which
maintains a steep conc. gradient.
What are the advantages of a double circulatory system? - ANS-Blood can pass slowly
through the region where gaseous exchange takes place; maximising the transfer of
oxygen and carbon dioxide and then be pumped vigorously around the rest of the body
enabling the organism to be very active and have a higher metabolic rate
Explain why animals need a heart and a circulatory system (4) - ANS-Heart needed to
, pump blood around the body (1)
Mass flow(1)
Low SA:V ratio (1)
Overcome limitations of diffusion (1)
High metabolic rate (1)
Compare and contrast the heart and circulatory system of a snake with that of a human
(4) - ANS-Compare:
Both have a {double/closed} circulatory system
Both have arteries, veins, and two atria
Contrast:
The blood mixes in the heart, while in a human heart the oxygenated and deoxygenated
blood is separated by the septum
Snake does not have a septum between the {ventricles} whereas the human heart
does.
Explain why a snake needs a heart (2) - ANS-To pump blood to supply {oxygen and
glucose} to body cells, because a small SA:V ratio does not allow diffusion to occur at a
sufficient rate.
What is the structure of water? - ANS-Water is a simple molecule composed of two
small, positively charged hydrogen atoms and one large negatively charged oxygen
atom.
Why is water a polar molecule? - ANS-Due to the uneven distribution of charge within
the molecule- the hydrogen atoms have a partial positive charge and the oxygen atom
has a partial negative charge due to the difference in electronegativity, causing one side
to be more positive than the other.
FYI the charged nature of the water molecule gives it stability and allows it to act as a
solvent. Also the hydrogen bonding between water molecules is also responsible for the
unique thermal properties of water.
Explain why polar molecules and ionic molecules such as sodium chloride dissociate
(separate) in water (SOLVENT PROPERTIES) - ANS-They dissociate because the
force of attraction between the negatively charged part of the water molecule and the
positively charged sodium ion is greater than the forces of attraction between the Na+
and Cl- ions. The negative part of the water molecule attracts and pulls away the
positive part of the water attracts and pulls away the negatively charge chloride ions.
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