Module 3.1.2 - Transport in animals

Question 1

What can single-celled organisms and multicellular organisms diffuse across?

Answer 1

single-celled - An outer membrane
multicellular - relatively big and have low SA to V ratio and a higher metabolic rate

Question 2

What does the circulatory system do?

Answer 2

Uses blood to carry glucose and oxygen around the body, also carries hormones, antibodies and waste products

Question 2

Why do multicellular organisms have a double circulatory system?

Answer 2

Very active so cells are respiring very quickly so need constant supply of glucose and oxygen, CO2 needs removing from cells quickly

Question 3

What circulatory system do fish have?

Answer 3

Single

Question 4

What circulatory system do mammals have?

Answer 4

Double

Question 5

What is a single circulatory system?

Answer 5

• blood only passes through the heart once each complete circuit of the body
• fish are less active so only have a single C.System

Question 6

What is a double circulatory system?

Answer 6

• blood passes through the heart twice for each complete circuit of the body
• mammals are more active so have a double C.System

Question 7

What is a closed circulatory system?

Answer 7

All vertebrates (fish and mammals) have a closed system as blood is enclosed inside blood vessels

Question 8

What is an open circulatory system?

Answer 8

Some invertebrates (insects) have an open circulatory system as blood isn’t enclosed in blood vessels all the time, instead it flows freely through the body cavity

Question 9

What are types of blood vessels?

Answer 9

• arteries
• arterioles
• capillaries
• venules
• veins

Question 10

What are arteries?

Answer 10

• carry blood away from the heart to rest of the body
• walls are thick and muscular, elastic tissue to stretch and recoil as heart beats to help maintain high pressure
• inner lining (endothelium) is folded, allowing artery to expand/maintain high pressure
• all arteries carry oxygenated blood except pulmonary arteries which take deoxygenated blood to lungs
• lumen is the space in the centre of the arteries

Question 11

What are arterioles?

Answer 11

• arteries branch into arterioles which are much smaller than arteries
• have a layer of smooth muscle like arteries, but have less elastic tissue
• smooth muscle allows them to expand or contract, controlling amount of blood flowing to tissue

Question 12

What are capillaries?

Answer 12

• arteries branch into capillaries, smallest of the blood vessels
• substances like glucose and oxygen, are exchanged between cells and capillaries, adapted for efficient diffusion

Question 13

What are venules?

Answer 13

• capillaries connect to venules, which have thin walls that contain some muscle cells
• venules join together to form veins

Question 14

What are veins?

Answer 14

• takes blood back to the heart under low pressure
• wider lumen than arteries have, with very little elastic or muscle tissue as less pressure
• contain valves to stop blood flowing backwards
• blood flows through the veins helped by contractions of body muscles surrounding them
• all veins carry deoxygenated blood except the pulmonary veins, which carry oxygenated blood to the heart

Question 15

What is tissue fluid?

Answer 15

• surrounds cells in tissues
• made from substances that leave the blood plasma
• cells take in oxygen and nutrients from tissue fluid and release metabolic waste into it
• capillary bed (network of capillaries in an area of tissue) has substances move out of capillaries, into tissue fluid by pressure filtration

Question 16

What is pressure filtration?

Answer 16

• hydrostatic pressure inside capillaries is greater than HP in tissue fluid at start of capillary bed, nearest arteries
• difference in HP forces fluid out capillaries and into spaces around cells, forming tissue fluid
• as fluid leaves, HP reduces in capillaries so HP is much lower at end of capillary bed that’s nearest to venules
• as water leaves capillaries, conc of plasma proteins in capillaries increases and water potential decreases
• plasma proteins in capillaries generate a form of pressure called oncotic pressure so at venule end of capillary bed, high oncotic pressure at low water potential
• because water potential in capillaries is lower than water potential in tissue fluid, some water re-enters capillaries from tissue fluid at venule end by osmosis

Question 17

What are lymph vessels?

Answer 17

• not all tissue fluid re-enters capillaries at vein end of capillary bed, some tissue fluid is left over
• this extra fluid gets returned to blood through lymphatic system
• smallest lymph vessels are lymph capillaries
• excess tissue fluid passes into lymph vessels and is called lymph once inside
• valves in lymph vessels stop lymph going backwards
• lymph gradually moves towards main lymph vessels in thorax (chest cavity)

Question 18

What is the lymphatic system?

Answer 18

Drainage system made up of lymph vessels

Question 19

What does the heart consist of?

Answer 19

2 muscular pumps, right and left

Question 20

What type of blood does each side of the heart pump?

Answer 20

Right - deoxygenated blood to the lungs
Left - oxygenated blood to the rest of the body

Question 21

What do the Atrioventricular (AV) valves link?

Answer 21

The atria to the ventricles

Question 22

What do the semi-lunar (SL) valves link?

Answer 22

The ventricles to the pulmonary artery and aorta

Question 23

What is the purpose of the atrioventricular and semi-lunar valves?

Answer 23

To stop blood flowing the wrong way

Question 24

What does the valves being open or closed depend on?

Answer 24

Relative pressure of the heart chambers as they only open one-way

Question 25

What happens if there is high pressure behind a valve?

Answer 25

The valve is forced open

Question 26

What happens if there is high pressure in front of a valve?

Answer 26

The valve is forces shut

Question 27

What type of direction does blood flow have through the valves?

Answer 27

Unidirectional - only flows in one direction

Question 28

What is the cardiac cycle?

Answer 28

• ongoing sequence of contractions and relaxations of the atria and ventricles
• volumes of atria and ventricles changes as they contract and relax, which alters the pressure
• this causes valves to open and close, which moves blood through the heart

Question 29

How many stages are in the cardiac cycle?

Answer 29

3

Question 30

What happens in stage 1 of the cardiac cycle?

Answer 30

• ventricles are relaxed and atria contracts which decreases volume of chambers, increasing pressure inside the chambers
• this pushes blood into ventricles through the atrioventricular valves
• there’s a slight increase in ventricular pressure and chamber column as the ventricles receive the ejected blood from the contracting atria

Question 31

What happens in stage 2 of the cardiac cycle?

Answer 31

• atria relax and ventricles contract which decreases volume and increases pressure
• pressure becomes higher in ventricles than the atria, which forces the AV valves to shut to prevent backflow
• the pressure in the ventricles is also higher than then in the aorta and pulmonary artery, which forces open the SL valves and blood is forced out into these arteries

Question 32

What happens in stage 3 of the cardiac cycle?

Answer 32

• ventricles and atria both relax
• higher pressure in pulmonary artery and aorta closes the SL valves to prevent backflow into the ventricles
• blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein
• this starts to increase pressure in the atria
• as ventricles continue to relax, their pressure falls bellow the pressure of atria and so AV valves open
• this allows blood to flow passively (without being pushed by atrial contraction) into the ventricles from the atria
• the atria contract and stage 1 starts again

Question 33

What is cardiac output?

Answer 33

Volume of blood pumped by the heart per minute (cm3 min-1)

Question 34

How do you calculate cardiac output?

Answer 34

Heart Rate x Stroke Volume