SPEC POINT 1.1 Flashcards
SPEC POINT 1.1
Comparing single -celled organisms to multicellular organisms:
Explain why many multicellular organisms need a transport system:
- The cells of all organisms need the supply of oxygen and glucose, and removal of carbon dioxide and urea
- Single celled organisms, such as bacteria and amoeba, have a high surface area to volume ratio, meaning they can meet these requirements by diffusion alone. Due to Ficks Law, high surface area means high rate of diffusion.
- However, multi cellular organisms have a low surface area to volume ratio, meaning they have an inadequate rate of diffusion. This means respiration cannot occur and cells stop functioning (lack of ATP)
What happens if diffusion is inadequate?
- Diffusion is only effective over short distances
- If it is inadequate, then there will be a high concentration of carbon dioxide outside some cells and low concentration of oxygen outside some cells
- This results in a lack of concentration gradient for diffusion and the cells dont get enough oxygen and nutrients to continue functioning
- Lack of respiration increases the pH, causing the cells to die
What does a circulatory system contain?
- A heart (pump) - contracts to put pressure on the transport medium. The pressure generates movement of the fluid and transport by mass flow
- A transport medium (blood) - transports substances by dissolving them and moving them by mass flow
- Blood vessels - These keep the fluid at high pressure, so it can move greater distances (more important in larger organisms)
Explain how circulatory systems improve the rate of supply and removal of substances within organisms:
- It has a transport medium (blood) which acts as a solvent (solvents absorb solutes) for biologically important molecules, such as oxygen, glucose, carbon dioxide, amino acids, urea, so it can transport them.
- The heart contracts to put pressure on the transport medium and the transport medium moves from high pressure to low pressure
- Dissolved substances get transported by mass flow
- Blood vessels maintain pressure on transport medium, so it can move greater distances
- This maintains high concentration gradients near cells
- So high rate of diffusion is maintained for all substances and all cells
What is an open circulatory system?
One where the transport medium (blood) is not contained in closed blood vessels.
An open circulatory system consists of a heart that pumps a fluid called HAEMOLYMPH through short vessels and into a large cavity called the HAEMOCOEL
Describe how an open circulatory system works:
- The heart contracts, increasing the pressure on the haemolymph
- The haemolymph moves through the vessels towards the haemocoel
- This maintains the concentration gradient near cells
- Substances are exchanged across the cells by diffusion
- The haemolymph returns to the heart (when the heart relaxes)
- Because the vessels are open ended, the haemolymph isnt under high pressure
- Small organisms such as insects have an open circulatory system
What is a closed circulatory system?
One where the transport medium is enclosed within blood vessels at all times
Describe how an closed circulatory system works:
- The heart contracts to put pressure on the transport medium
2.The transport medium can be put under higher pressure so it can be moved over greater distances (this is when organisms are larger and more metabolically active) - The transport medium doesn’t make direct contact with cells and tissues and it is responsible for transporting gases such as oxygen and carbon dioxide
What is mass transport?
What does it help to do?
The bulk movement of liquids/gases in one direction
1. maintain diffusion gradients
2. ensure effective cell activity
3. bring substances quickly
What is mass flow?
The movement of fluid down a pressure gradient
What is a single circulatory system?
A simple loop in which blood flows
What is a double circulatory system?
Where the blood passes through the heart twice for each complete circuit of the body
Describe how an double circulatory system works:
- Blood moves through the heart twice in each circuit of the body
- The heart contracts to put pressure on the blood
- The blood moves to the gas exchange organs and becomes oxygenated (pulmonary circuit)
- It then returns to the heart, and is then pumped again to the rest of the body (systemic circuit)
- While moving through the systemic circuit, the blood is deoxygenated
Describe the advantages of double circulatory systems:
- The pulmonary and systemic circuits are separate
- Deoxygenated blood can be pumped at a lower pressure to the gas exchange organs (lungs), so they aren’t damaged
- Oxygenated blood can be pumped at a higher pressure in the systemic circuit so the gas exchange is more efficient than a single circulatory system
- its better for organisms that are larger and more metabolically active
