Unit 3- Gas Exchange in fish, dicotyledonous plants and insects

Question 1

Define a gas exchange surface

Answer 1

A boundary between the outside environment and the internal environment of an organisms

Question 2

Which two gases do organisms need to be able to diffuse across gas exchange surfaces as quickly as possible?

Answer 2

Carbon dioxide and oxygen

Question 3

What are the two main factors which increase the rate of diffusion across exchange surfaces

Answer 3

-A large surface area
-Thin so they have a short diffusion pathway across the gas exchange surface

Question 4

Does the organism maintaining a steep concentration gradient of gases across the exchange surface increase or decrease the rate of diffusion?

Answer 4

Increase

Question 5

How do single-celled organisms absorb and release gases?

Answer 5

Diffusion through their cell surface membranes

Question 6

Why do single-celled organisms not need a specialised gas exchange system?

Answer 6

-Relatively large surface area
-Thin surface
-Short diffusion pathway
(oxygen can take part in biochemical reactions as soon as it diffuses into the cell)

Question 7

Is there a lower concentration of oxygen in water than in air?

Answer 7

Yes

Question 8

How does oxygen enter the fish?

Answer 8

Water (containing oxygen) enters the mouth and passes through the gills

Question 9

How is each gill adapted for gas exchange?

Answer 9

-Gill filaments- thin plates which give a large surface area for exchange of gases, increased rate of diffusion
-Gill filaments are covered in lamellae which further increase the SA

Question 10

How do lamellae speed up diffusion?

Answer 10

-Have a lot of blood capillaries
-Thin surface layer of cells between the water and blood

Question 11

What is the counter-current system?

Answer 11

-Blood flows through the lmelllae in one direction
-Water flows in the opposite direction

Question 12

How is a steep concentration gradient maintained between water and blood over the whole length of the gill?

Answer 12

-Water with a relatively high oxygen concentration flows next to blood with a lower concentration of oxygen
-Means as much oxygen as possible diffuses from the water into the blood

Question 13

Plants need CO2 for photosynthesis which is the waste gas produced?

Answer 13

O2

Question 14

What do plants need for respiration that leaves CO2 as a waste gas?

Answer 14

O2

Question 15

What is the main exchange surface in the leaf?

Answer 15

Mesophyll cells

Question 16

What adaptions do mesophyll cells have?

Answer 16

-Large SA
-Stomata- pores in the epidermis which allow gases to move in and out

Question 17

Why are guard cells (control the opening and closing of the stomata) important?

Answer 17

-Stomata opens to allow the exchange of gases
-Close if the plant is losing too much water

Question 18

What do terrestrial insects use for gas exchange?

Answer 18

-Trachae

Question 19

What are spiracles?

Answer 19

-Pores on the surface of the trachea

Question 20

Does oxygen travel up or down the concentration gradient?

Answer 20

Down

Question 21

What are tracheoles?

Answer 21

-Branches of the trachea

Question 22

How does oxygen diffuse directly into respiring cells? (insects circulatory system does not transport O2

Answer 22

-Tracheoles have thin, permeable walls and go to individual cells

Question 23

How is carbon dioxide released into the atmosphere?

Answer 23

-Moves down its own concentration gradient towards the spiracles

Question 24

How is air moved in and out of the spiracles?

Answer 24

Rythmic abdominal movements

Question 25

how do insects control water loss during gas exchange?

Answer 25

-Close their spiracles using muscles
-Have a waterproof waxy cuticle all over their body
-Tiny hairs around their spiracles

Question 26

How do guard cells control water loss?

Answer 26

-Water enters = turgid (opens the pore)
-Loss of water flaccid (closes the pore)

Question 27

Give some examples of adaptions of xerophytes

Answer 27

-Stomata sunk in pits to trap water vapour- reduces concentration gradient between leaf air, reduces evaporation
-Hairs on the epidermis- traps water vapour around the stomata
-Curled leaf with stomata inside- protects from wind (increases the rate of diffusion and evaporation
-Reduced number of stomata- fewer places for water to escape
-Thick waxy cuticle- waterproof, reduces evaporation