• By which process does blood travel in one direction across the circulatory system?
MASS FLOW/MASS TRANSPORT - (which is due to a difference in pressure) (to overcome the limitations of diffusion)
→ Components of blood:
1. Plasma
2. Platelets
3. White blood cells
4. Red blood cells
→ Roles of blood:
1. To carry out the transport of dissolved substances
2. Regulation of body temperature
3. Transferring energy around the body
1.2. WATER AS A SOLVENT
Dipolar molecules
→ Water is a dipolar molecule (which means it has unevenly distributed electrical charge)
the hydrogen end of the molecule is slightly positive (+) and the oxygen end is slightly negative (-)
WHY?
• Electrons are shared by covalent bonding
• Electrons from the hydrogen atoms are pulled towards the oxygen, making each hydrogen atom in
water slightly positive
• Pull of electrons closer to oxygen atoms give it a slightly negative charge
Cohesion
→ H bond= hydrogen bonds (weak bonds)
• Cohesion: is a property of water due to the partly positive and partly negative molecules
: allows water droplets to form
How does it work?
1. The negative charge in oxygen atoms attract hydrogen atoms from nearby molecules
2. These forces are hydrogen bonds, and this holds molecules together
3. Water is cohesive (molecules stick together easily to hold the shape)
4. Water forms droplets due to the force of cohesion holding the water molecules together
Adhesion
• Adhesion: (water to non-water attraction)
→ How does water being dipolar help it be a solvent?
- the dipole nature of water molecules mean water is a good solvent for ionic (charged) or polar
(partially charged) substances
-the ions within water are held in in place by attractive electrostatic forces
➢ Anions (-) are attracted to hydrogen atoms when dissolved in water
➢ Cations (+) are attracted to oxygen atoms when dissolved in water
2
, LUCIA ROMERO
The importance of water
→ 80% of a cells’ content is water
WHY IS WATER IMPORTANT?
1. Most chemical reactions within organisms take place in water
: (e.g., hydrolysis reactions in water require water as a reactant)
2. Water transports dissolved materials (ionic and polar substances)
: materials need to be transported to where they are needed in any organism
(Single celled organisms transport substances by diffusion but when the size of an organism increases it’s volume increases more than
its surface area)
→ Larger organisms cannot rely on diffusion for transport (The organism cannot carry out diffusion fast enough to move the materials it
needs)
- Raw materials become limited and waste products build up inside the organism
1.3. BLOOD VESSELS
Transport systems (in general)
1. Insects don’t have a circulatory system, they don’t have
blood vessels
: they have a pump and blood
: they have an open circulation
2. Fish have a close single circulation system (blood is
pumped to the gills and then it moves to the body without
returning to the heart
3. Mammals have closed, double circulatory system (blood
passes through the heart twice in one circuit)
Features of mass transport systems in organisms
1. A branching system to supply materials to many areas simultaneously
2. A way of ensuring that materials travel quickly and in the right direction in the circulatory system this is done by the heart (a pump) and
blood vessels
3. A suitable transport medium (e.g., water) is needed to carry materials
Types of blood vessels
Arteries
- Arteries carry blood away from the heart → they get smaller and branch into arterioles,
which then turn to capillaries
Characteristics:
1. Have thick muscular walls containing elastic fibres to withstand high pressure of
blood and maintain the blood pressure as it recoils after the blood has passed through
2. Have a narrow lumen to maintain high pressure
3. Have collagen (to prevent bursting)
4. Smooth endothelium (layer of cells inside) layer: so that the blood travels faster without friction to reduce it
3
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