AS-Organisms exchange substances with their environment

Question 1

What factors effect the rate an organism can exchange substances? (actively or passively)

Answer 1

-Volume - the space it occupies
-Surface area - how much is exposed to the environment

Question 2

How does an organism’s size relate to their SA:V ration?

Answer 2

Larger the organism the lower the SA:V ratio

Question 3

How does an organism’s surface area to volume relate to their metabolic rate?

Answer 3

The smaller the SA:V ratio the higher the metabolic rate

Question 4

How might a large organism adapt to compensate for it’s small SA:V ratio?

Answer 4

-create changes to increase surface area e.g.
-body parts getting bigger (e.g. elephant ears
-elongating shape
-specialised gas exchange surface

Question 5

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 5

-Their small SA:V ratio means that their length of diffusion pathway is larger
-substances cannot easily enter the cells

Question 6

Name 3 features of efficient gas exchange

Answer 6

-Large Surface area e.g. folded membranes
-short diffusion pathway e.g thin capillary walls
-Steep concentration gradient e.g alveoli

Question 7

Recall Fick’s Law

Answer 7

rate of diffusion (is proportionate to) surface area X concentration difference (divided by) length of diffusion pathway

Question 8

How do single cell organisms exchange gases/substances?

Answer 8

Diffusion

Question 9

Why can’t insects use their body as an exchange surface

Answer 9

• they have a waterproof chitin exoskeleton
  -they have a reduced SA:V

(ALL TO CONSERVE WATER)

Question 10

Name the 3 main features of the insect’s gas transport system

Answer 10

-spiracles
-tracheae
-tracheoles

Question 11

describe the spiracles

Answer 11

holes in the body’s surface which may be opened or closed by valve for gas or water exchange

Question 12

Describe the Tracheae

Answer 12

large tubes extending through all body tissues, supported by rings to prevent collapse

Question 13

Describe the tracheoles

Answer 13

smaller branches dividing off the trcgeae

Question 14

Explain the process of gas exchange in insects

Answer 14

-gases move in and out of the tracheae through the spiracles

-a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out

-contraction of muscles in the tracheae allows mass movement of air in and out

Question 15

How is the insect gas exchange system efficient

Answer 15

-all body cells are close to tracheole end
(diffusion pathway shortened)

-oxygen concentration is low near respiring tissues
(large concentration difference)

Question 16

What are the problems with the insect gas exchange system?

Answer 16

• relys on passive transport
  (limiting the size of insects)

-waterloss
(when spiracles open water is lost through evaporation)
(closing spiracles completely limits oxygen supply)

Question 17

Why can’t fish use their bodies as an exchange surface?

Answer 17

-they have a waterproof, impermeable outer membrane

-they have a small surface area to volume ratio

Question 18

Name the two main features of a fish’s gas transport system

Answer 18

-Gills
-Lamellae

Question 19

Describe of the Gills

Answer 19

• have gill filaments that are stacks on top of each other

Question 20

Describe the Gill Lamellae

Answer 20

-Right angles to the gill filaments
-give an increases surface area
- blood and water flow in opposite direction
(counter current flow)

Question 21

How does the counter current flow system lead to efficient gas exchange across the gills of a fish

Answer 21

-water and blood flows in opposite directions
-this increases oxygen and CO2 exchange
-this means there is a constant concentration different all throughout gill

Question 22

How are plants adapted to allow efficient gas exchange

Answer 22

-Thin and flat leaves = short diffusion pathway and large SA:V ratio

-lots of stomata = gases can easily enter

-air spaces = allow gases to exchnage to all cells

Question 23

What are the limitations with the plants gas exchange system

Answer 23

water loss through transpiration

Question 24

How do plants limit their water loss while still allowing gas exchange

Answer 24

-stomata regulated by guard cells
-most stay closed to prevent water loss while some open to let oxygen in

Question 25

What are Xerophytes

Answer 25

-plants that live & are adapted to live in arid/dry conditions

Question 26

Name some features of xerophytes

Answer 26

• they have hairs (increases water vapour conc.)

-sunken stomata (increased LODP making it hard for water to escape)

-Leaves curled (increased water vapour outside leaves- conc grad created

-thick stems (reduce water loss)

-water store