8.1 - Transport systems in multicellular organisms Flashcards
Why do multicellular organisms need transport systems?
To supply oxygen and nutrients to cells, remove waste products, and transport substances efficiently across large distances within the body.
How do single-celled organisms transport substances (5)? Why are these transport methods sufficient?
Through diffusion, osmosis, active transport, endocytosis, and exocytosis, which are sufficient due to their small size and high surface area to volume ratio.
Why is diffusion alone insufficient for transport in multicellular organisms?
Because diffusion over long distances is too slow to meet the high metabolic demands of the organism.
How does surface area to volume ratio affect the need for a transport system?
As organisms grow larger, their surface area to volume ratio decreases, reducing the efficiency of diffusion for substance exchange.
What are the 6 key reasons multicellular organisms need specialised transport systems?
- High metabolic demands require rapid supply of oxygen and nutrients.
- Increased diffusion distance as organism size increases.
- Smaller surface area to volume ratio reduces efficiency of diffusion.
- Hormones and enzymes need to be transported to target sites.
- Digested food must be distributed to all cells.
- Waste products must be transported to excretory organs.
Why do metabolic demands increase the need for a transport system?
Multicellular organisms require large amounts of oxygen and nutrients and produce significant waste, which cannot be efficiently exchanged through diffusion alone.
How does digestion create the need for a transport system?
Food is digested in one organ system but must be transported to all cells for respiration and metabolism.
Why do waste products require a transport system?
Waste products of metabolism must be transported away from cells to excretory organs to prevent toxicity and maintain homeostasis.
Give an example of a molecule that must be transported within the body and explain why.
Hormones, such as insulin, are produced in one part of the body (e.g., pancreas) but needed elsewhere to regulate metabolic processes.
What is the role of circulatory systems in large multicellular animals?
They transport gases (oxygen and carbon dioxide), nutrients, waste products, and hormones around the body.
What are the three key features of most circulatory systems?
- A liquid transport medium (blood).
- Vessels to carry the transport medium.
- A pumping mechanism to move the fluid around the system.
What is a mass transport system?
A system where substances are transported in a mass of fluid, with a mechanism to move the fluid around the body.
What are the two main types of circulatory systems found in large multicellular animals?
Open circulatory systems and closed circulatory systems.
What is an open circulatory system?
A system where the transport medium is not fully contained within vessels and is pumped directly into the body cavity (haemocoel).
How does an open circulatory system function?
The transport medium flows into the haemocoel, where it directly bathes tissues, allowing exchange. It then returns to the heart via an open-ended vessel.
What is the haemocoel?
The open body cavity in animals with an open circulatory system where the transport medium flows under low pressure and contacts tissues.
What happens in the haemocoel, during the open circulatory system?
Exchange of substances occurs between the transport medium and tissues, supplying nutrients and removing waste.
Why is an open circulatory system considered less efficient than a closed system?
- Low pressure means slower circulation, reducing transport efficiency.
- Steep diffusion gradients cannot be maintained, limiting the rate of exchange.
- Blood flow cannot be directed to specific tissues to meet changing demands (e.g., during activity).
In which types of animals is an open circulatory system found?
Open circulatory systems are found in invertebrates, including:
1. Most insects (e.g., grasshoppers, bees, ants).
2. Some molluscs (e.g., snails, clams).
What is insect blood called?
Insect blood is called haemolymph.
What is the difference between insect blood and vertebrate blood?
Unlike vertebrate blood, it does not carry oxygen or carbon dioxide.
What does haemolymph transport?
Insect blood is called haemolymph. Unlike vertebrate blood, it does not carry oxygen or carbon dioxide. Instead, it transports:
1. Nutrients (e.g., sugars, amino acids).
2. Nitrogenous waste products (e.g., uric acid).
3. Immune cells involved in defense against pathogens.
Why doesn’t haemolymph carry oxygen or carbon dioxide in insects?
Insects have a separate gas exchange system called the tracheal system, which delivers oxygen directly to tissues via a network of air-filled tubes (tracheae). This removes the need for haemolymph to transport respiratory gases.
What is the tracheal system?
A network of air-filled tubes (tracheae) that transports oxygen directly to cells.
How is the insect body cavity structured in relation to circulation?
The insect body cavity is divided by a membrane, and the heart extends along the thorax and abdomen. The heart pumps haemolymph forwards towards the head, allowing it to flow freely over tissues before returning to the heart.
What are the key disadvantages of an open circulatory system in insects?
- No precise control over blood distribution – haemolymph cannot be directed to areas with higher demand.
- Low pressure leads to slow circulation, reducing efficiency in nutrient and waste transport.
- Lack of steep diffusion gradients, making diffusion of substances slower and less efficient.
What is a closed circulatory system?
A circulatory system where blood is fully enclosed within blood vessels and does not come into direct contact with body cells.
How does blood circulate in a closed circulatory system?
The heart pumps blood under high pressure, allowing it to move rapidly through the vessels and return directly to the heart in a continuous loop.
How do substances enter and leave the blood in a closed circulatory system?
Substances such as oxygen, nutrients, and waste products move in and out of the blood by diffusion through the thin walls of capillaries.
How can blood flow to different tissues be controlled in a closed circulatory system?
Blood flow is regulated by vasodilation (widening of blood vessels) to increase flow and vasoconstriction (narrowing of blood vessels) to reduce flow, depending on tissue demand.
What role do blood pigments play in a closed circulatory system?
Most closed circulatory systems contain blood pigments like haemoglobin, which bind to oxygen and transport it efficiently to body tissues.
Why is a closed circulatory system more efficient than an open circulatory system?
- Higher pressure ensures blood moves faster and reaches tissues quickly.
- Better control of blood distribution to meet varying oxygen and nutrient demands.
- Efficient exchange of substances due to continuous blood circulation.
Which 4 animal groups have a closed circulatory system?
- Echinoderms (e.g., sea urchins, starfish).
- Cephalopod molluscs (e.g., octopuses, squid).
- Annelid worms (e.g., earthworms).
- All vertebrates, including fish, amphibians, reptiles, birds, and mammals.
Give 2 examples of Echinoderms.
- Sea urchins
- Starfish
Give 2 examples of Cephalopod molluscs.
- Octopuses
- Squid
Give 1 example of Annelid worms
Earthworms
What is a single closed circulatory system?
A circulatory system where blood passes through the heart only once per full circulation of the body.
Which animals have a single closed circulatory system?
It is found in fish and annelid worms (e.g., earthworms).
How does blood circulate in a single closed system?
Blood is pumped from the heart, travels around the body, and returns to the heart in one loop without passing through the heart a second time.
What happens to blood as it passes through capillaries in a single closed system?
It passes through two sets of capillaries:
- First capillary bed – for gas exchange (oxygen and carbon dioxide exchange in gills or lungs).
- Second capillary bed – for substance exchange (nutrients and waste exchange in organs and tissues).
How does passing through two sets of capillaries affect blood pressure?
Blood loses pressure significantly after passing through the capillaries, causing it to return to the heart slowly.
How does low blood pressure affect animals with single closed circulation?
Slower blood flow limits the efficiency of oxygen and nutrient delivery, resulting in lower activity levels in most animals with this system.
Why are fish an exception to the limitations of a single closed circulatory system?
Fish have a highly efficient system that allows them to be very active despite low blood pressure.
How do fish compensate for the inefficiency of a single closed circulatory system?
- Counter-current gaseous exchange in gills extracts more oxygen from water.
- Their body weight is supported by water, reducing energy needed for movement.
- They are ectothermic (cold-blooded), so they don’t use energy to regulate body temperature.
What is a double closed circulatory system?
A system where blood passes through the heart twice per full circulation of the body, ensuring higher pressure and efficiency.
Why do mammals need a double circulatory system?
Most mammals are active land animals that maintain their own body temperature, requiring an efficient transport system for oxygen and nutrients.
What are the two separate circulations in a double closed circulatory system?
- Pulmonary circulation – blood is pumped from the heart to the lungs for gas exchange.
- Systemic circulation – oxygenated blood is pumped from the heart to the rest of the body before returning.
How does blood flow in a double closed circulatory system?
- Blood is pumped from the heart to the lungs to pick up oxygen and remove carbon dioxide.
- It returns to the heart before being pumped again to the rest of the body.
Why is a double circulatory system more efficient than a single circulatory system?
Blood only passes through one capillary network per circuit, maintaining higher pressure and allowing for faster blood flow.
How does maintaining high blood pressure benefit mammals?
It ensures rapid delivery of oxygen and nutrients to tissues, supporting high activity levels and thermoregulation (heat control).
