8.1 - Transport systems in multicellular organisms

Question 1

Why do multicellular organisms need transport systems?

Answer 1

To supply oxygen and nutrients to cells, remove waste products, and transport substances efficiently across large distances within the body.

Question 2

How do single-celled organisms transport substances (5)? Why are these transport methods sufficient?

Answer 2

Through diffusion, osmosis, active transport, endocytosis, and exocytosis, which are sufficient due to their small size and high surface area to volume ratio.

Question 3

Why is diffusion alone insufficient for transport in multicellular organisms?

Answer 3

Because diffusion over long distances is too slow to meet the high metabolic demands of the organism.

Question 4

How does surface area to volume ratio affect the need for a transport system?

Answer 4

As organisms grow larger, their surface area to volume ratio decreases, reducing the efficiency of diffusion for substance exchange.

Question 5

What are the 6 key reasons multicellular organisms need specialised transport systems?

Answer 5

1. High metabolic demands require rapid supply of oxygen and nutrients.
2. Increased diffusion distance as organism size increases.
3. Smaller surface area to volume ratio reduces efficiency of diffusion.
4. Hormones and enzymes need to be transported to target sites.
5. Digested food must be distributed to all cells.
6. Waste products must be transported to excretory organs.

Question 6

Why do metabolic demands increase the need for a transport system?

Answer 6

Multicellular organisms require large amounts of oxygen and nutrients and produce significant waste, which cannot be efficiently exchanged through diffusion alone.

Question 7

How does digestion create the need for a transport system?

Answer 7

Food is digested in one organ system but must be transported to all cells for respiration and metabolism.

Question 8

Why do waste products require a transport system?

Answer 8

Waste products of metabolism must be transported away from cells to excretory organs to prevent toxicity and maintain homeostasis.

Question 9

Give an example of a molecule that must be transported within the body and explain why.

Answer 9

Hormones, such as insulin, are produced in one part of the body (e.g., pancreas) but needed elsewhere to regulate metabolic processes.

Question 10

What is the role of circulatory systems in large multicellular animals?

Answer 10

They transport gases (oxygen and carbon dioxide), nutrients, waste products, and hormones around the body.

Question 11

What are the three key features of most circulatory systems?

Answer 11

1. A liquid transport medium (blood).
2. Vessels to carry the transport medium.
3. A pumping mechanism to move the fluid around the system.

Question 12

What is a mass transport system?

Answer 12

A system where substances are transported in a mass of fluid, with a mechanism to move the fluid around the body.

Question 13

What are the two main types of circulatory systems found in large multicellular animals?

Answer 13

Open circulatory systems and closed circulatory systems.

Question 14

What is an open circulatory system?

Answer 14

A system where the transport medium is not fully contained within vessels and is pumped directly into the body cavity (haemocoel).

Question 15

How does an open circulatory system function?

Answer 15

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.

Question 16

What is the haemocoel?

Answer 16

The open body cavity in animals with an open circulatory system where the transport medium flows under low pressure and contacts tissues.

Question 17

What happens in the haemocoel, during the open circulatory system?

Answer 17

Exchange of substances occurs between the transport medium and tissues, supplying nutrients and removing waste.

Question 18

Why is an open circulatory system considered less efficient than a closed system?

Answer 18

1. Low pressure means slower circulation, reducing transport efficiency.
2. Steep diffusion gradients cannot be maintained, limiting the rate of exchange.
3. Blood flow cannot be directed to specific tissues to meet changing demands (e.g., during activity).

Question 19

In which types of animals is an open circulatory system found?

Answer 19

Open circulatory systems are found in invertebrates, including:
1. Most insects (e.g., grasshoppers, bees, ants).
2. Some molluscs (e.g., snails, clams).

Question 20

What is insect blood called?

Answer 20

Insect blood is called haemolymph.

Question 21

What is the difference between insect blood and vertebrate blood?

Answer 21

Unlike vertebrate blood, it does not carry oxygen or carbon dioxide.

Question 22

What does haemolymph transport?

Answer 22

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.

Question 23

Why doesn’t haemolymph carry oxygen or carbon dioxide in insects?

Answer 23

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.

Question 24

What is the tracheal system?

Answer 24

A network of air-filled tubes (tracheae) that transports oxygen directly to cells.

Question 25

How is the insect body cavity structured in relation to circulation?

Answer 25

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.

Question 26

What are the key disadvantages of an open circulatory system in insects?

Answer 26

1. No precise control over blood distribution – haemolymph cannot be directed to areas with higher demand. 2. Low pressure leads to slow circulation, reducing efficiency in nutrient and waste transport. 3. Lack of steep diffusion gradients, making diffusion of substances slower and less efficient.

Question 27

What is a closed circulatory system?

Answer 27

A circulatory system where blood is fully enclosed within blood vessels and does not come into direct contact with body cells.

Question 28

How does blood circulate in a closed circulatory system?

Answer 28

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.

Question 29

How do substances enter and leave the blood in a closed circulatory system?

Answer 29

Substances such as oxygen, nutrients, and waste products move in and out of the blood by diffusion through the thin walls of capillaries.

Question 30

How can blood flow to different tissues be controlled in a closed circulatory system?

Answer 30

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.

Question 31

What role do blood pigments play in a closed circulatory system?

Answer 31

Most closed circulatory systems contain blood pigments like haemoglobin, which bind to oxygen and transport it efficiently to body tissues.

Question 32

Why is a closed circulatory system more efficient than an open circulatory system?

Answer 32

1. Higher pressure ensures blood moves faster and reaches tissues quickly. 2. Better control of blood distribution to meet varying oxygen and nutrient demands. 3. Efficient exchange of substances due to continuous blood circulation.

Question 33

Which 4 animal groups have a closed circulatory system?

Answer 33

1. Echinoderms (e.g., sea urchins, starfish). 2. Cephalopod molluscs (e.g., octopuses, squid). 3. Annelid worms (e.g., earthworms). 4. All vertebrates, including fish, amphibians, reptiles, birds, and mammals.

Question 34

Give 2 examples of Echinoderms.

Answer 34

1. Sea urchins 2. Starfish

Question 35

Give 2 examples of Cephalopod molluscs.

Answer 35

1. Octopuses 2. Squid

Question 36

Give 1 example of Annelid worms

Answer 36

Earthworms

Question 37

What is a single closed circulatory system?

Answer 37

A circulatory system where blood passes through the heart only once per full circulation of the body.

Question 38

Which animals have a single closed circulatory system?

Answer 38

It is found in fish and annelid worms (e.g., earthworms).

Question 39

How does blood circulate in a single closed system?

Answer 39

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.

Question 40

What happens to blood as it passes through capillaries in a single closed system?

Answer 40

It passes through two sets of capillaries: 1. First capillary bed – for gas exchange (oxygen and carbon dioxide exchange in gills or lungs). 2. Second capillary bed – for substance exchange (nutrients and waste exchange in organs and tissues).

Question 41

How does passing through two sets of capillaries affect blood pressure?

Answer 41

Blood loses pressure significantly after passing through the capillaries, causing it to return to the heart slowly.

Question 42

How does low blood pressure affect animals with single closed circulation?

Answer 42

Slower blood flow limits the efficiency of oxygen and nutrient delivery, resulting in lower activity levels in most animals with this system.

Question 43

Why are fish an exception to the limitations of a single closed circulatory system?

Answer 43

Fish have a highly efficient system that allows them to be very active despite low blood pressure.

Question 44

How do fish compensate for the inefficiency of a single closed circulatory system?

Answer 44

1. Counter-current gaseous exchange in gills extracts more oxygen from water. 2. Their body weight is supported by water, reducing energy needed for movement. 3. They are ectothermic (cold-blooded), so they don’t use energy to regulate body temperature.

Question 44

What is a double closed circulatory system?

Answer 44

A system where blood passes through the heart twice per full circulation of the body, ensuring higher pressure and efficiency.

Question 45

Why do mammals need a double circulatory system?

Answer 45

Most mammals are active land animals that maintain their own body temperature, requiring an efficient transport system for oxygen and nutrients.

Question 46

What are the two separate circulations in a double closed circulatory system?

Answer 46

1. Pulmonary circulation – blood is pumped from the heart to the lungs for gas exchange. 2. Systemic circulation – oxygenated blood is pumped from the heart to the rest of the body before returning.

Question 47

How does blood flow in a double closed circulatory system?

Answer 47

1. Blood is pumped from the heart to the lungs to pick up oxygen and remove carbon dioxide. 2. It returns to the heart before being pumped again to the rest of the body.

Question 48

Why is a double circulatory system more efficient than a single circulatory system?

Answer 48

Blood only passes through one capillary network per circuit, maintaining higher pressure and allowing for faster blood flow.

Question 49

How does maintaining high blood pressure benefit mammals?

Answer 49

It ensures rapid delivery of oxygen and nutrients to tissues, supporting high activity levels and thermoregulation (heat control).