3.2 - Transport In Animals

Question 1

Why do multicellular animals require transport systems?

Answer 1

• the metabolic demands of most multicellular organisms are high, so diffusion alone would be too slow to provide respiring cells with enough oxygen+ glucose and to remove waste
• the SA:V ratio gets smaller as organisms get bigger, so diffusion distances gets too far and the exchange surface to absorb/remove substances gets relatively smaller
• molecules like hormones and enzymes are made in special cells in limited locations around the body, but may be needed in another place
• food will be digested in one organ system, but must be transported to be used in respiration/ cell metabolism
• waste products are made by every metabolically active cell and must be removed from the cells and transported to excretory organs

Question 2

What is mass flow?

Answer 2

The bulk movement of materials.

It is directed movement, so involves some kind of force

Question 3

What are the advantages of a mass flow transport system?

Answer 3

• brings substances quickly from one exchange site to another
• maintain the diffusion gradients at exchange sites and between cells+their fluid surroundings
• ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range

Question 4

What is an open circulatory system?

Answer 4

• blood held in very few vessels
• haemolymph (insect blood) bathes tissues and cells
• in small animals eg insects

Question 5

How does blood travel around the body in an open circulatory system?

Answer 5

• haemolymph (insect blood) is pumped directly from the heart into the body cavity (haemocoel).
• it travels through the body at low pressure, and comes in direct contact with the tissues and cells. This is where exchange takes place between the transport medium and cells
• transport medium then renters the heart through an open-ended vessel

Question 6

What is a closed circulatory system?

Answer 6

• blood contained entirely within vessels
• tissue fluid bathes cells and tissues
• larger organisms
• eg vertebrates

Question 7

What are single and double circulatory systems?

Answer 7

SINGLE:
Blood flows through the heart once in each complete circulation of the body
Eg fish

DOUBLE:
Blood flows through the heart twice during one complete circulation of the body

Question 8

Describe how blood flows through the body of an organism with a single closed circulatory system

Answer 8

• blood flows through 2 sets of capillaries before it returns to the heart
• first, it exchanges oxygen and carbon dioxide (eg at gills of fish)
• in the second set of capillaries, in the different organ systems, substances are exchanged between the blood and the cells
• blood is pumped around the body at low pressure to avoid damage to the capillaries
• as a result, rate of blood flow is slow, so there is a slow delivery of oxygen and glucose to respiring cells
• this means that the efficiency of the exchange processes and activity levels of organisms with a single circulatory system tend to be low.

Question 9

How can fish be so active with a single circulatory system?

Answer 9

• they have a relatively efficient single circulatory system - the counter current gaseous gas exchange mechanism in gills allows them to take a lot of oxygen from the water
• body weight is supported by the water + don’t maintain their own body temperature, greatly reducing metabolic demands

Question 10

what is a double closed circulatory system?

Answer 10

Most efficient system for transporting substances around the body

2 separate circulations:
• blood pumped from the heart to the lungs to pick up oxygen and unload CO2, then returns to heart

• blood flows through heart and is pumped to the rest of the body before returning to heart again

Question 11

how is efficiency maintained in a double circulatory system?

Answer 11

• blood travels through the heart twice per full circuit
• each circuit (to lungs + to body) only passes through one capillary network, which means relatively high pressure and fast flow of blood can be maintained

Question 12

What is collagen?

Answer 12

Provides structural support to maintain the shape and volume of the blood vessel

Question 13

What is smooth muscle?

Answer 13

contracts or relaxes, which changes the size of the lumen

Question 14

What are elastic fibres?

Answer 14

composed of elastin and can stretch and recoil, providing vessel walls with flexibility

Question 15

what is the endothelium?

Answer 15

lines the inside of the blood vessel

smooth, so blood can flow easily

Question 16

Describe how blood flows through the body of an organism with a double closed circulatory system.

Answer 16

Deoxygenated blood flows into the right atrium via the vena cava, then flows into the right ventricle through an atrioventricular valve

Blood flows from the RV to the pulmonary artery, where blood is taken to the lungs and oxygenated.

Oxygenated blood returns to the heart and enters the left atrium via the pulmonary vein. It is then pumped into the left ventricle, passing through an atrioventricular valve.

From the left ventricle, the blood is pumped into the aorta and then around the body at high pressure, depositing oxygen at respiring cells.

Deoxygenated blood returns to the right atrium

Question 17

What are arteries?

Answer 17

Transport blood away from the heart (usually at high pressure) to tissues

Question 18

What are arterioles?

Answer 18

Narrow blood vessels that branch off of arteries. Transport blood into capillaries

Question 19

What are veins

Answer 19

Transport blood towards the heart (usually at low pressure)

Question 20

What are venules?

Answer 20

Narrow blood vessels that transport blood from capillaries to the veins

Question 21

What is the endothelium?

Answer 21

• one cell thick
• lines the lumen
• smooth so reduces friction for free blood flow

Question 22

What are elastic fibres?

Answer 22

• allow the walls of the blood vessels to stretch, enabling them to withstand the force of flood pumped out of the heart
• recoil in between contractions of the heart, helping to even out surges of blood

Question 23

What is smooth muscle?

Answer 23

Can contract/relax to change the volume of blood vessels (changing volume of the lumen and local blood pressure

Question 24

What is collagen?

Answer 24

Tough, strong protein that protects blood vessels from damage by over-stretching

Question 25

What is vasoconstriction?

Answer 25

When smooth muscle in a blood vessel contracts, narrowing the lumen

Question 26

What is vasodilation?

Answer 26

When smooth muscle in blood vessels relax, increasing the diameter of the lumen

Question 27

What is the structure of an artery?

Answer 27

• narrow lumen
• endothelium
• thick elastic layer
• smooth muscle
• collagen

Question 28

What is the structure of an arteriole?

Answer 28

• lumen
• endothelium
• lower proportion of elastic fibres than an artery
• more smooth muscle than an artery
• collagen

This allows them to contract and control the amount of blood flow

Question 29

What are capillaries?

Answer 29

Microscopic blood vessels that link arterioles and venules

Form an extensive network through the tissues of the body

Substances are exchanged through the capillary walls between the tissue cells and the blood