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OCR Biology A 3.1.2 Transport in Animals A Level Notes
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3.1.2A - Transport systems in 3.1.2C - Blood vessels 3.1.2D - Formation of tissue fluidmulticellular organisms arteries - transport blood away from heart, high blood tissue fluid - formed from blood plasma which leaks
pressure, rapid blood flow, carries oxygenated blood from capillaries (as a result of hydrostatic pressure),
single-celled organisms - large SA:VOL = short diffusion
(except in the pulmonary artery) bathing cells + aiding exchange, lymphocytes can pass
distances = adequate to use passive/active transport =
but plasma proteins/WBC cannot
efficient exchange arterioles - distribute blood from arteries to capillaries,
smooth muscle, contract to constrict the diameter, ↑ hydrostatic pressure - pressure exerted by a fluid (blood
multicellular organisms - transport systems are needed
resistance to flow (↓ reduce flow of blood), used to divert against the vessels) as a result of the systolic pressure
as diffusion distances become too long, unable to supply
flow of blood to more active areas of the body from the heart
the metabolic needs of the organism
capillaries - link arteries and veins, site of exchange, ↓ oncotic pressure - pressure exerted by plasma proteins
size - multicellular organisms are large, cells are further
blood pressure and blood flow, mix of oxygenated and (albumin) on the blood plasma, stays constant along the
away from the surface (↑ diffusion distances) and outer
deoxygenated blood capillary as plasma proteins are too large to leave
layers of cells use up the supplies
venules - distribute blood from capillaries to venules, HP at arterial end is higher (blood has just been pumped
surface area to volume ratio (SA:VOL) - multicellular
consists of smooth muscle, collagen and elastic tissue by the heart) than the HP and OP in tissue fluid = fluid
organisms have a small SA:VOL (each gram of tissue has a
outside endothelium moves out
smaller area of body surface for exchange), so a specialised
transport system is required veins - transport blood to the heart, low blood pressure, HP at venous end is lower than the OP of the plasma
slow blood flow, carries deoxygenated blood (except in proteins in the blood = fluid moves in (only 90%)
metabolic rate - multicellular organisms have high
the pulmonary vein), include valves to prevent backflow
activity levels, thus have higher energy requirements lymph - fluid of the lymphatic system that carry excess
(aerobic respiration) and require good supplies of O2 and tissue fluid (10%), containing more WBC (produced at the
nutrients - an efficient transport system is needed lymph nodes), wanted substances drain out of lymph to
the bloodstream at the subclavian vein
3.1.2B - Circulatory systems 3.1.2D - Structure and function of blood
Blood Tissue fluid Lymph
general features - circulatory fluid to carry substances, blood - body fluid used to transport materials around the
contractile pumping device (create pressure to push fluid body - 55% plasma, 45% cells (RBC, WBC + platelets) RBC ✔ ✖ too large to ✖
around the body) and vessels to carry fluid and to pass through
exchange substances plasma - pale yellow liquid medium, 90% water
capillary wall
(controlled), 10% dissolved substances (glucose and
open circulatory system - blood flows freely through the plasma proteins (controlled) and vitamins, hormones and
body cavity (no vessels) e.g. insects (haemolymph bathes products of digestion (vary in concentration)) WBC ✔ some more than in
tissues directly) tissue fluid
red blood cells (erythrocytes) - carry O2 (no nucleus =
closed circulatory system - blood only flows in vessels carries more O2, biconcave shape = ↑ SA:VOL, Hb
through the pumping device (two types below) molecule binds to O2) Platelets ✔ some (in ✖
damaged
single circulatory system - blood passes the heart only white blood cells (leukocytes) - fight disease (large and capillaries)
once per complete circuit of the body e.g. fish spherical) e.g. phagocytes (phagocytosis = engulf
pathogens) or lymphocytes (produce antibodies)
double circulatory system - blood passes the heart twice Proteins ✔ some small ✔ antibodies
per complete circuit of the body e.g. mammals platelets - cell fragments that aid blood clotting proteins
, Larger lumen to
ease blood flow
Prevents backflow so blood is unidirectional
(also aided by muscles contracting and
squeezing blood through the vein)
Endothelium (squamous epithelium)
Elastic (part of the Tunica Intima) made out of collagen
Dominant layer, thick to
withstand high pressures Thinner tunica media
of the aorta, smaller Smooth muscle, with a thick layer of elastic fibres as veins do not need Capillary
towards arterioles to stretch and recoil
Connective tissue made out of collagen
Made out of collagen
smooth muscle - widens airways in situations where oxygen is
required, trachea, bronchi, large/small bronchioles
elastic fibres - necessary during recoil of lungs (helps
exhalation), stretch in inhalation, all components
Aid substance
movement
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