surface area to volume ration q/a

Question 1

The adult damselfly uses a tracheal system for gas exchange.
Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange.

Answer 1

1) Tracheoles have thin walls so short diffusion distance to cells

2) highly branched - short diffusion distance

3)Tracheae provide tubes full of air so fast diffusion (into insect tissues)

4) Fluid in the end of the tracheoles that moves out (into tissues) during
exercise so faster diffusion through the air to the gas exchange surface

Question 2

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water.

Explain how the presence of gills adapts the damselfly to its way of life.

Answer 2

higher respiratory rate
uses more oxygen

Question 3

Many different substances enter and leave a cell by crossing its cell surface membrane. Describe how substances can cross a cell surface membrane.

Answer 3

• simple diffusion from high to low concentration down concentration gradient
• water moves into cells by osmosis from high water concentration to low water concentration
• active transport against conc gradient - requires ATP
• sodium potassium pump
• facilitated diffusion - carrier and channel proteins

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Question 4

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

Answer 4

• many folded alveoli walls providing large surface area
• many capillaries providing large surface area and fast diffusion
• thin capillary walls, short diffusion distance between alveoli and blood

Question 5

Name the process by which oxygen passes from an alveolus in the lungs into the blood.

Answer 5

Diffusion

Question 6

Describe two adaptations of the structure of alveoli for efficient gas exchange.

Answer 6

1) folded alveoli that provide large surface area
2) thin capillary walls for short diffusion distance /pathway

Question 7

Chlamydomonas lives in fresh water ponds. Use your knowledge of osmosis to suggest

an advantage of using starch as a carbohydrate store

Answer 7

Starch is insoluble so reduces osmosis and does not affect water potential

Question 8

he body of a flatworm is adapted for efficient gas exchange between the water and
the cells inside the body.
Using the diagram, explain how two features of the flatworm’s body allow efficient
gas exchange.

Answer 8

• thin body allows for short diffusion distance and provides large surface area

Question 9

What is an organ.

Answer 9

, a group of tissues.

Question 10

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside
the leaf.

Answer 10

1) CO2 enters via stomata which are opened by the guard cell
2) CO2 then diffuses through airspace’s down diffusion gradient