the heart and circulation

what is the one primary purpose of the heart and circulation?

to move substances around the body

how do substances move in very small organisms?

by diffusion

how do substances move in most complex multicellular organisms?

by a mass transport system to move substances efficiently over long distance by mass flow

what is mass transport?

the bulk movement of gases or liquids in one direction, usually through a system of vessels and tubes

what do larger organisms require a mass transport system

they have a smaller surface area to volume ratio and a higher metabolic rate, and diffusion alone is insufficient to supply cells with all substances they need

what is an open circulatory system?

blood circulates in large open spaces in insects
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 from the cavity back into the heart through small, valved openings

what is a closed circulatory system?

the blood is enclosed within blood vessels in vertebrates which generates higher blood pressure so blood travels faster and the process is more efficient

what is the process of blood in a closed circulatory system?

the blood leaves the heart under pressure and flows along arteries and then arterioles to capillaries
the blood then returns to the heart by venules and then veins

what do single circulatory systems in fish do?

the heart pumps deoxygenated blood to the gills
gaseous exchange takes place in the gills
blood leaving the gills then flows round the rest of the body before returning to the heart

what do double circulatory systems do?

the right ventricle of the heart pumps deoxygenated blood to the lungs where it receives oxygen
the oxygenated blood returns to the heart to be pumped a second time out to the rest of the body

why are double circulatory systems efficient?

blood flows through the heart twice for each complete circuit
the heart gives the blood returning from the lungs a boost which reduces the time it takes for the blood to circulate round the body
allows for high metabolic rate

What is mass flow?

a liquid and all the particles it contains are transported in one direction due to a difference in pressure

what is the transport medium in animals?

blood 

what are the components in blood and their percentages?

plasma - 55% of total volume of blood, which has 91% of liquid water, 7% of soluble proteins, and 2% of hormones, electrolytes and nutrients

cellular component - 45% of total volume of blood (WBCs, platelets, red blood cells)

why is water important in the human body?

it is the medium in which all metabolic reactions take place in cells and all substances are transported around the body 

what type of molecule is water?

it is a dipole, polar molecule as it has unevenly distributed electrical charge - the hydrogen end is slightly positive and the oxygen end is slightly negative

why is water a liquid at room temperature?

hydrogen bonds form between the positive and negatively charged regions 
these hydrogen bonds are stronger than intermolecular forces between gases
so it takes more energy to break hydrogen bonds

what are the two properties of water?

solvent properties - many chemicals dissolve easily in water

thermal properties - has a high specific capacity

why is water a good solvent?

ionic substances can dissolve, polar molecules can dissolve (but non-polar cannot) 

why can ionic substances dissolve in water?

the negative ions are attracted to the positive ends of the water molecules whilst the positive ions are attracted to the negative ends

the ions become hydrated in aqueous solution as they become surrounded by water molecules

why can polar molecules dissolve easily in water?

the polar groups (-OH group in sugars and -NH2 group in amino acids) become surrounded by water and go into solution 

they are hydrophilic 

why can’t non-polar molecules dissolve in water?

they lack the partial charges needed to form hydrogen bonds with water

to enable transport, lipids combine with proteins to form lipoproteins

what are the three behaviours of water?

cohesion, adhesion, surface tension

what is cohesion?

cohesion is the attraction of water molecules to each other

hydrogen bonds between water molecules allow for strong cohesion between them

what is adhesion? 

adhesion is where water is able to hydrogen bond to other molecules 

how do cohesion and adhesion work together?

they both allow for water to flow easily 

water molecules pull other water molecules along due to cohesion 

water adheres to the sides of a vessel due to adhesion 
 

what is surface tension?

surface tension is the cohesive force of water molecules due to hydrogen bonds, creating a "skin" on the surface that is hard to break

the molecules are pulled more strongly by the cohesive forces from the molecules below and to the sides, creating an inward net force

it allows for insects like the pond skater to move on the water’s surface
and keeps the column of water in the xylem from breaking