Exchange surfaces and Transport in animals

Question 1

NEED FOR EXCHANGE SYSTEM: size

Answer 1

-in very small organisms, such as singled celled organisms, cytoplasm very close to environment in which they live
-diffusion supply enough oxygen and nutrients to keep cells alive
-multicellular organisms may have several layers of cells
-any oxygen or nutrients diffusing in from outside have longer diffusion pathway therefore insufficient

Question 2

NEED FOR EXCHANGE SYSTEM: surface area to volume ratio

Answer 2

-small organisms have small surface area and small volume -meaning their surface area to volume ratio large and all cells can be supplied with sufficient oxygen
-larger organisms have larger surface area but also larger volume - they have smaller surface area to volume ratio therefore need an exchange system

Question 3

NEED FOR EXCHANGE SYSTEM: level of activity

Answer 3

-some organisms are more active than others
-metabolic activity uses energy from food and requires energy released from oxygen in aerobic respiration
-cells of an active organism need good supplies of nutrients and oxygen to supply energy for movement
-this needs for energy is increased in those animals such as mammals, that keep themselves warm

Question 4

Features of a good exchange system

Answer 4

-large surface area to provide more space for molecules to pass though
-thin barrier to reduce diffusion pathway - must be permeable to substances being exchanged
-good blood supply to maintain steep concentration gradient so diffusion can occur rapidly

Question 5

How is gas exchanged in the lungs

Answer 5

-gases pass by diffusion through thin walls of alveoli
-oxygen passes from air in alveoli to blood in capillaries
-carbon dioxide passes from blood to air in alveoli
-lungs must maintain steep concentration gradient to ensure diffusion continues
-alveoli provide a very large surface area and are lined by thin layer of moisture which evaporates and is lost as we breathe out
-alveoli also produce surfactant that coats internal surface of alveoli to reduce cohesive forces between water molecules as these forces tend to make alveoli collapse