Transport in Animals

Question 1

What happens to an organisms SA:V ratio as they increase in size?

Answer 1

It decreases

Question 2

If an organism has a smaller SA:V ratio then…

Answer 2

There is less surface area for the absorption of gases and nutrients, and the secretion of waste products.

Question 3

If there are more cells, then there is a higher level of metabolic activity, so…

Answer 3

The demand for oxygen and nutrients is greater, and more waste is produced.

Question 4

Why do we need a circulatory system?

Answer 4

Because all living organisms need a constant supply of reactants for metabolism (e.g., oxygen & glucose).

Question 5

What are circulatory systems?

Answer 5

They are systems that transport fluids containing oxygen, nutrients & waste.

Question 6

What is the difference between a single and a double circulatory system?

Answer 6

A single circulatory system is where the blood passes through the heart once during one complete circuit of the body, whereas a double circulatory system is where the blood passes through the heart twice during one complete circuit of the body.

Question 7

Explain the single circulatory system in fish.

Answer 7

deoxygenated blood is pumped into the gills from the heart. The gills are the exchange site where oxygen and carbon dioxide are exchanged with the atmosphere and the blood. The oxygenated blood flows from the gills to the rest of the body (travels through the capillaries in organs). The blood returns to the heart. The heart only has one atrium and one ventricle.

Question 8

Explain the double circulatory system in mammals.

Answer 8

The deoxygenated blood in the right side of the heart leaves and travels to the lungs. The blood returns to the left side of the heart before being pumped around the rest of the body. Once the blood has passed through all the other organs and tissues it returns to the right side of the heart.

Question 9

What are venules and arterioles?

Answer 9

Arterioles are small arteries that branch from larger ones to connect to capillaries, and venules are small veins that branch from larger ones to connect to capillaries.

Question 10

What is a closed circulatory system?

Answer 10

It is where blood is pumped around the body and is always contained within a network of blood vessels.

Question 11

What is an open circulatory system?

Answer 11

It is where blood is not contained within blood vessels but is pumped directly into body cavities.

Question 12

Explain the circulatory system of an insect.

Answer 12

Insects have one main blood vessel - the dorsal vessel. The tubular heart in the abdomen pumps haemolymph (insect blood) into the dorsal vessel. The dorsal vessel delivers the haemolymph into the haemocoel (body cavity). Haemolymph surrounds the organs and eventually renters the heart via one-way valves called ostia.

Question 13

Describe the structure of an artery.

Answer 13

Tunica intima — made of endothelial layer (one cell think, lines lumen, very smooth, reduces friction), connective tissue layer, elastic fibres layer.
Tunica media — smooth muscle cells (strengthens arteries so they can withstand high pressures, enables them to contract and narrow lumen for reduced blood flow), think layer of elastic tissue (helps maintain blood pressure, stretches and recoils to even out pressure fluctuations).
Tunica adventitia — covers exterior, mainly made of collagen (strong protein, protects from damage of over-stretching).
Narrow lumen helps maintain blood pressure.
A pulse is present.

Question 14

Describe the structure of an arteriole.

Answer 14

Muscular layer — contract and partially cut off blood flow to specific organs.
Lower proportion of elastic fibres and a higher proportion of muscle cells (allows them to contract and close lumen to stop and regulate blood flow).

Question 15

Describe the structure of veins.

Answer 15

Tunica media is much thinner than in arteries — no need for thick muscular layer (do not need to withstand high pressures).
Lumen is much larger than in arteries — ensures that blood flow returns to the heart at an adequate speed (reduces friction between blood and endothelial layer).
Veins contain valves — prevent back flow of blood.
Pulse is absent.

Question 16

Describe the structure of venules.

Answer 16

Few or no elastic fibres.
Large lumen.
No need for muscular layer (as blood is at low pressure).

Question 17

Describe the structure of capillaries.

Answer 17

Very small diameter — forces blood to travel slowly, provides more opportunity for diffusion.
Large number of capillaries branch between cells — substances can diffuse between the blood and cells quickly as there is a short diffusion distance.
One-cell thick wall — reduces diffusion distance for oxygen and carbon dioxide.
Gaps in wall called pores — allow blood plasma to leak out and form tissue fluid.
WBC can combat infection in affected tissues — squeezing through the intercellular junction in the capillary walls.

Question 18

What is plasma?

Answer 18

It is a straw-coloured liquid that constitutes around 55% of the blood.
It is largely composed of water (95%), and because water is a good solvent, many substances can dissolve in it.

Question 19

What is tissue fluid?

Answer 19

It is very similar in composition to plasma, however it contains far fewer proteins, as they are too large to fit through the gaps in the capillary walls, therefore they remain in the blood.
Tissue fluid bathes almost all of the cells in the body outside of the circulatory system.
Exchange of substances between cells and the blood occurs via tissue fluid.

Question 20

What is hydrostatic pressure?

Answer 20

The pressure exerted by a fluid, e.g. blood.

Question 21

What is oncotic pressure?

Answer 21

The osmotic pressure exerted by plasma proteins within a blood vessel - it usually pulls water into the circulatory system.

Question 22

(In terms of tissue fluid formation) What happens at the arterial end of the capillary?

Answer 22

Hydrostatic pressure is great enough to force fluid out of capillary.
Proteins remain in the blood as they are too big to leave.
Increased protein content creates a water potential gradient (oncotic pressure) between capillary and tissue fluid.
High hydrostatic pressure is greater than oncotic pressure so net movement of water is out of the capillaries into the tissue fluid.

Question 23

(In terms of tissue fluid formation) What happens at the venous end of the capillaries?

Answer 23

Hydrostatic pressure within the capillary is reduced.
Water potential gradient between capillary and tissue fluid remains the same as at the arterial end - water begins to flow back into capillary from tissue fluid.

Question 24

What are lymph capillaries?

Answer 24

They are separate to the circulatory system - have closed ends and large pores that allow large molecules to pass through.
Some tissue fluid reenters capillaries through these lymph capillaries.

Question 25

How does the lymphatic system work?

Answer 25

Larger molecules can’t pass through capillary wall, so enter the lymphatic system as lymph - small valves in the vessel walls are the entry point to the lymphatic system.
The liquid moves along the larger vessels of this system by compression caused by body movement (back flow is prevented by valves).
Lymph reenters the bloodstream through veins located close to the heart.
Any plasma proteins that have escaped form the blood are returned via the lymph capillaries.
After digestion, lipids are transported from intestines to bloodstream by the lymph system.

Question 26

How is the heart protected?

Answer 26

In the chest cavity by the pericardium - tough & fibrous sac

Question 27

Which side of the heart pumps deoxygenated blood?

Answer 27

Right side - into vena cava, out of pulmonary artery

Question 28

Which side of the heart pumps oxygenated blood?

Answer 28

Left side - into pulmonary vein, out of aorta