Module 3: Exchange and Transport

Question 1

Mass flow hypothesis/ Translocation?

Answer 1

– Solutes are actively loaded into the sieve tube element of the ploem at the source.
– This lowers the water potential inside the sieve tube so water enters the tubes by osmosis from the xylem and companion cells.
– This creates a high pressure inside the sieve tube at the source end.
– At the sink, solutes are removed fro the the phloem to be used up.
– This increases the water potential inside the sieve tube so water leaves the ubes by osmosis.
– This lowers the pressure
– This results in a pressure gradient form thes ource end to the sink end.

Question 2

What is the term given to a muscle that contracts without an external stimulus?

Answer 2

Myogenic

Question 3

From which part of the heart is the heartbeat initiated?

Answer 3

Sino-atrial node

Question 4

Which blood vessel bring blood to the lungs?

Answer 4

Pulmonary artery

Question 5

What type of epithelial tissue is found in the alveoli?

Answer 5

Squamous

Question 6

The walls of the alveoli contains elastic fibres. What are these fibres for?

Answer 6

The walls allow the alveoli to recoil after expanding

Question 7

What is the term given to plants that are adapted for dry ocnditions?

Answer 7

– Xerophytic

Question 8

In which part of the heart is the heartbeat initiated?

Answer 8

Sinoatrial node

Question 9

Explain the term “biological catalyst”

Answer 9

Biologial catalyst speed up the rate of a reaction without being used up in the process.

Question 10

In multicellular animals, diffusion across the membrane is too slow. Why is this?

Answer 10

– Some cells are deep within body so there is a big distance between the cells an dthe environment.
– Some animals have a low surface area to volume ratio so it is difficult to excahnge substancesthrough a relatively small surface area.
– Multi-cellular organisms have a higher metabolic rate so they use up glucose and oxygen quite uickly.

Question 11

What is the surface area of alveoli cells made out of?

Answer 11

– Squamous cells

Question 12

How are plants specialised to make surface exhange efficient?

Answer 12

– Plants have root hair cells.
– Each root hair cell has millions of microscopic ahirs on it. This means that ther’s more surface area.
– This in turn increases the rate at which water is absorbed into the cell by osmosis and mineral ions by active transport.

Question 13

Alveoli are tiny air sacs present in the lungs that aid in the transport and exchange of gases.
How are they adapted for gas exchange?

Answer 13

Adaptation of alveoli:

The alveoli present in the lungs have thin walls composed only of a single layer of cells(squamus cell). They are one cell thuck so there is a short diffusion distance.

They have a large capillary network giving each alveolus its’s own blood supply.

It maintains a high diffusion gradient to aid the incorporation of oxygen into blood and simultaneously remove carbon dioxide.

Question 14

How is each alveolus adapted to make gas exchange as efficient as possible?

Answer 14

Large surface area: there are approximately 700 million alveoli in our lungs with a combined surface area of 70 square meters.

Good blood supply: lots of capillaries surround each alveolus

Short diffusion distance: the walls of both the alveoli and capillaries are just one cell thick

Moist surfaces: the liquid on the surface of alveoli dissolves gases and facilitates diffusion

Inhalation and exhalation: breathing in and out replaces the air in the alveoli, maintaining a steep concentration gradient.

Location in the centre of the body: the lungs are right in the middle of our body, inside our thorax. The core of our body is the warmest, giving the gas molecules more heat energy and making them move around faster (so quicker diffusion).

Question 15

What are the functions of the structures in the human respiratory system?

Answer 15

Goblet cells – secrete mucus which traps dust and microorganisms to prevent infection. Found in the trachea, bronchi and larger bronchioles.

Cilia – beat to move mucus up towards the throat when it’s swallowed and destroyed by stomach acid. Found in the trachea, bronchi and bronchioles.

Elastic fibres – found in the walls of the trachea, bronchi, bronchioles and alveoli. The fibres stretch when we breathe in and recoil when we breathe out.

Smooth muscle – found in the trachea, bronchi and bronchioles. They control and relax to expand or narrow the airways.

Cartilage – found in rings in the walls of the trachea and bronchi. It’s strength and flexibility provides support and prevent the airways from collapsing when pressure drops during inhalation.

Question 16

What happens during inhalation?

Answer 16

During inhalation, the diaphragm contracts and flattens, while the rib cage moves up and out. This increases the volume of the thorax, resulting in a drop in pressure. The reduced pressure causes air to be sucked into our lungs.

Question 17

What happens during exhalation?

Answer 17

During exhalation, the diaphragm relaxes and forms a dome shape, while the rib cage moves down and in. This reduces the volume of the thorax and increases the pressure, pushing air out of our lungs.

Question 18

How are fishes adapted for efficient gas excahnge?

Answer 18

– Each gill is made up of several gill filaments stacked up on top of each other. The gill filaments are covered in lamellae to further increase their surface area.
– The lamellae have very thin walls to reduce the diffusion distance and are filled with capillaries.

Question 19

How are fishes ventilated?

Answer 19

When the fish opens its mouth, the buccal cavity lowers, increasing the mouth’s volume.

Pressure drops inside the mouth, forcing water into the mouth and the buccal cavity.

When the fish closes its mouth, the floor of the buccal cavity moves up, reducing its volume.

Pressure increases, forcing water out of the cavity and across the gill filaments.

Each gill is covered by a protective bony flap called the operculum. When water moves over the gill filaments, it increases the pressure and forces the operculum on each side of the head to open. This allows water to leave the gills.

Question 20

What is the structure of the artery?

Answer 20

Carry blood away from the heart to the various organs of the body.

They need to cope with the high pressure generated from the heart forcing out blood with each heartbeat. This is why they have a really thick muscular wall containing lots of elastic tissue.

The inner lining of the arteries, called the endothelium, is folded which allows the artery to expand (elastic recoil) which also helps it to withstand the high pressure.

The small lumen ensures a high pressure is maintained.

Question 21

What is the structure of the vein?

Answer 21

Carry blood from the organs of the body towards the heart.

Blood is flowing at a much lower pressure so veins have a large lumen and much thinner walls containing little elastic fibres or muscle tissue.

Valves prevent the slow-moving blood from flowing backwards.

The contraction of nearby body muscles helps blood to flow through veins.

Question 22

what is the structure of the vein?

Answer 22

Connect arteries and veins.

Substances move out of the blood to the body tissues - things like oxygen, glucose and mineral ions. Any waste products, such as carbon dioxide and water, will move out of the body tissues and into the capillaries.

Small holes (pores) enable the exchange of substances.

Walls are just one cell thick which reduces the diffusion distance for these substances.

Question 23

How is tissue fluid formed?

Answer 23

At the arterial end

When blood is at the arterial end of a capillary thehydrostatic pressureis great enough toforce fluid outof the capillary
Proteins remain in the blood as they are too large to pass through the pores in the capillary wall
Theincreased protein contentcreates awater potentialgradient(osmotic pressure) between the capillary and the tissue fluid
At the arterial end thehydrostatic pressure is greater than the osmotic pressureso the net movement of water isout of the capillariesinto the tissue fluid

At the venous end
At the venous end of the capillary the hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries
Thewater potential gradientbetween the capillary and the tissue fluid remains thesameas at the arterial end
At the venous end theosmotic pressure is greater than the hydrostatic pressureand water begins to flow back into the capillary from the tissue fluid

Question 24

How is tissue fluid formed from plasma?

Answer 24

Plasmais a straw-coloured liquid that constitutes around 55 % of the blood
Plasma is largely composed of water (95 %) and becausewateris a goodsolventmany substances can dissolve in it, allowing them to be transported around the body
As blood passes throughcapillariessome plasma leaks out through gaps in the walls of the capillary to surround the cells of the body
This results in the formation of tissue fluid
The composition of plasma and tissue fluid are very similar, althoughtissue fluidcontains farfewer proteins
Proteins aretoo large to fit through gaps in the capillary wallsand so remain in the blood