Exchange And Transport

Question 1

What materials need to be exchanged between organisms and the environment?

Answer 1

• respiratory gases
• excretory products
• heat

Question 2

Give examples of passive exchange processes

Answer 2

Osmosis, diffusion, facilitated diffusion

Question 3

Give features of an exchange surface

Answer 3

• large SA to volume ratio
• short pathway for diffusion
• movement of internal and external medium to maintain gradient
• partially permeable

Question 4

What is the equation for rate of diffusion?

Answer 4

SA x diff in conc

Length of pathway

Question 5

Describe gas exchange in single-called organisms

Answer 5

They are small, so have a large SA to volume ratio. Gases can be exchanged across body surface, which is just a cell-surface membrane (is partially permeable)

Question 6

What adaptations to insects have to limit water loss?

Answer 6

• waterproof covering

- small surface area to volume ratio

Question 7

Describe route of gases within an insect

Answer 7

Gases enter and leave through spiracles on body surface,then enter internal network of tracheae. Tracheae branch into trachioles that penetrate into tissues.

Question 8

How do gases move in and out of an insect?

Answer 8

• along a diffusion gradient; at end of trachioles there is high conc of CO2 and low conc of O2, gases diffuse
• ventilation; movement of air is accelerated by compression and expansion of abdominal muscles

Question 9

Explain why a fish’s body surface is not suitable for direct gas exchange

Answer 9

Fish have a waterproof, gas-tight outer covering, and a small SA;volume ratio. Therefore a specialised internal exchange surface is required; the gills.

Question 10

What is the purpose of lamellae on gill filaments?

Answer 10

Increase SA

Question 11

What is countercurrent exchange?

Answer 11

Describes how blood flow in gills is in opposite direction to flow of water; this way there is always more O2 in water, so equilibrium is never reached and diffusion is constant

Question 12

How are leaves adapted for rapid diffusion of gases?

Answer 12

• thin and flat; large SA to volume ratio
• many stomata (especially on underside)
• numerous air spaces throughout mesophyll

Question 13

How do plants control the rate of gaseous exchange in leaves?

Answer 13

Guard cells open and close stoma; water loss is balanced with need of gases

Question 14

Why do large organisms need a transport system for gas exchange?

Answer 14

SA to volume decreases with increasing size, needs cannot be fulfilled by body surface alone. Exchange system is needed to absorb nutrients and gases, transport system is required to move materials to cells and back to exchange surface.

Question 15

Give some features of transport systems

Answer 15

• suitable medium in which to carry materials
• closed system of vessels
• mechanism for moving materials (animals use muscular contraction or heart, plants rely on transpiration pull)
• mechanism to maintain flow in 1 direction (valves)
• way of controlling flow

Question 16

Why is the transport system in mammals referred to as ‘double circulatory system’?

Answer 16

Blood passes through the heart twice for each complete circuit of the body

Question 17

What are the 5 layers of arteries, arterioles and veins?

Answer 17

• tough outer layer; resists pressure changes
• muscle layer; contracts and controls flow
• elastic layer; maintains pressure by stretching and recoiling
• thin inner lining; prevents friction
• lumen; central cavity

Question 18

Why is the elastic layer of arteries relatively thick compared to veins?

Answer 18

Blood pressure has to remain high for blood to reach extremities; elastic stretches with each beat of heart and springs back in diastole, maintaining high pressure

Question 19

Which has a thicker muscle layer and why; arteries or arterioles?

Answer 19

Arterioles; contraction of muscle layer allows constriction of lumen, and therefore controls blood flow into capillaries

Question 20

What is the function of valves in veins?

Answer 20

To prevent backflow and pooling

Question 21

How are capillaries adapted for their function?

Answer 21

• walls are 1 cell thick; short diffusion pathway
• narrow lumen; red blood cells are squeezed flat, reduces diff pathway
• numerous and highly branched; large SA
• permeate tissues

Question 22

What is tissue fluid?

Answer 22

A watery liquid containing glucose, amino acids, fatty acids, salts and oxygen. Bathes all cells, giving nutrients to cells and receiving CO2 and waste materials in return.

Question 23

Describe how tissue fluid is removed and returned to blood

Answer 23

• at arteriol end of capillaries, hydrostatic pressure is produced by pressure of blood moving through narrower vessels. Pressure only pushes out tissue fluid-ultrafiltration
• at venule end, hydrostatic pressure is higher in tissue fluid outside of blood, tissue fluid is returned. Osmotic forces pull water back in.

Question 24

How are the contents of the lymphatic system moved?

Answer 24

• hydrostatic pressure of tissue fluid that has left capillaries
• muscle contraction