Unit 3

Question 1

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

Answer 1

The smaller the surface area to volume
ratio, the higher the metabolic rate

Question 2

Name three features of an efficient gas exchange
surface

Answer 2

1. Large surface area, e.g. folded membranes
   in mitochondria.
2. Thin/short distance, e.g. wall of capillaries.
3. Steep concentration gradient, maintained
   by blood supply or ventilation, e.g. alveoli

Question 3

what is Fiks law

Answer 3

Rate of diffusion is proportional to:

(short)length of diffusion pathway

Question 4

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

Answer 4

-waterproof chitin exoskeleton
-small surface area to volume ratio in order to conserve water.

Question 5

Name and describe the three main features of an
insect’s gas transport system. 3

Answer 5

● Spiracles= holes on the body’s surface which may be
opened or closed by a valve for gas or water exchange.

● Tracheae= large tubes extending through all body
tissues, supported by rings to prevent collapse.

● Tracheoles= smaller branches dividing off the tracheae

Question 6

describe how the trachea and tracheoles lead to efficient gas exchange 2

Answer 6

-wall of tracheole 1 cell thick ; short diffusion path between surrounding tissue

-trachea divide into smaller branches (tracheoles) : highly branched to prevent the tube from collapsing, large S.A, short diffusion path

Question 7

describe how abdominal pumping leads to efficient gas exchange 2

Answer 7

muscle contraction, mass movement of air in and out of the trachea and tracheoles so conc. gradient of CO2/ O2 maintained, so more oxygen diffuses into the tissues

Question 8

Explain the process of gas exchange in insects. 3

Answer 8

● 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 9

Why can’t fish use their bodies as an
exchange surface? 2

Answer 9

-waterproof, impermeable outer membrane
- small surface area to volume ratio.

Question 10

Structure of gills 4

Answer 10

-fillaments =stacked, lamellae 90*; provide large surface area

-large number of capillaries to remove oxygen/ maintain gradient

-thin epithelium= short diffusion pathway

-pressure changes to bring in more water

Question 11

Explain the process of gas exchange in
fish 4-6

Answer 11

1. mouth opens, operculum valve shuts;
2. floor of mouth lowered;
3. water enters due to decreased pressure / increased volume
4. mouth closes, operculum valve opens
5. floor raised results in increased pressure / decreased volume
6. increased pressure pushes water over gills;

Question 12

How does the countercurrent exchange system maximise oxygen absorbed by the fish?

Answer 12

-Maintains a steep concentration gradient so more oxygen diffuses in (steep) along the whole length of the gill
-Amount of oxygen in water is always higher in the blood

Question 13

Name and describe three adaptations of a leaf that
allow efficient gas exchange. 3

Answer 13

1. Thin and flat to provide short diffusion pathway, large S.A: V ratio
2. Many minute pores in the underside of the leaf (stomata)
   allow gases to easily enter.
3. Air spaces in the mesophyll allow gases to move around the leaf, facilitating photosynthesis.

Question 14

How do plants limit their water loss while still allowing gases to be exchanged?
2

Answer 14

-Stomata regulated by guard cells which allows them to open and close as needed ( reduce water loss through evaporation)

Question 15

plant adaptations 4

Answer 15

-thick waxy cuticle
-rolled hairy leaves to trap H20
-sunken stomata to decrease the water potential gradient
-small leaves reduces surface area ( less water loss)

Question 16

Gas exchange in a plant4

Answer 16

1. Carbon dioxide enters via stomata;
2. Stomata opened by guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 17

Describe the trachea and its function in the mammalian gaseous exchange system 2

Answer 17

-supported by rings of cartilage to prevent it from collapsing during pressure surges

-lined with ciliated epithelium cells to move mucus to throat to be swallowed (traps dirt)

-carriers air to bronchi

Question 18

Describe the bronchi and their function in
the mammalian gaseous exchange
system 2

Answer 18

• lined by ciliated epithelium cells
• Allow passage of air into the bronchioles.

Question 19

Describe the bronchioles and their
function in the mammalian gaseous
exchange system 2

Answer 19

● Narrower than the bronchi.
-walls made of muscle and lined with epithelial cells that constrict so they allow passage of air into alveoli

Question 20

Describe the alveoli and their function in the mammalian gaseous exchange system 4

Answer 20

-Mini air sacs, lined with epithelium cells, site of gas exchange
-Walls only one cell thick
-Covered in many blood capillaries provide large surface area
-thin capillary walls provide large SA, short diffusion pathway

Question 21

inspiration 4

Answer 21

● External intercostal muscles contract (while internal
relax), pulling the ribs up and out.
● Diaphragm contracts and flattens.
● Volume of the thorax increases
-Air flows down a pressure gradient

● Air pressure outside the lungs is therefore higher than
the air pressure inside, so air moves in to rebalance

Question 22

expiration 4

Answer 22

● External intercostal muscles relax (while internal contract), bringing the ribs down and in.
● Diaphragm relaxes and moves upwards.
● Volume of the thorax decreases.
-Air moves down a pressure gradient out of the lungs

● Air pressure inside the lungs is therefore higher than the
air pressure outside, so air moves out to rebalance.

Question 23

pulmonary ventilation rate
pvr

Answer 23

Tidal volume x breathing rate.

tv=volume of air we breathe in and out
during each breath at rest.

br= breaths per minute

Question 24

Define digestion

Answer 24

The hydrolysis of large, insoluble molecules into smaller molecules that can be absorbed across cell membranes.

Question 25

Which enzymes are involved in carbohydrate
digestion? Where are they found? 3

Answer 25

● Amylase in mouth
● Maltase, sucrase, lactase in
membrane of small intestine

Question 26

Where are lipids digested? and what happens before they are digested 3

Answer 26

-digested in the small intestine
-emulsified by bile salts produced by the liver
this breaks down large fat soluble molecules into smaller, soluble
molecules called micelles, increasing surface area.

Question 27

How are lipids digested?

Answer 27

Lipase hydrolyses the ester bond between the monoglycerides and fatty
acids.

Question 28

Which enzymes are involved in protein digestion?
What is their role? 3

Answer 28

● Endopeptidases= break between specific amino acids in the middle of a polypeptide.
● Exopeptidases= break between specific amino acids at the end of a polypeptide.
● Dipeptidases= break dipeptides into amino acids.

Question 29

Explain how sodium ions are involved in
co-transport.

Answer 29

Sodium ions (Na+) are actively transported out of the cell into the lumen, creating a diffusion gradient.
Nutrients are then taken up into the cells along with Na+ ions

Question 30

Why do fatty acids and monoglycerides not require
co-transport?

Answer 30

The molecules are nonpolar, meaning
they can easily diffuse across the membrane of the epithelial cells.

Question 31

Describe the structure of haemoglobin

Answer 31

• Globular, water soluble protein
• quaternary structure with 4 polypeptide chains carrying a haem (Fe) group

Question 32

Describe the role of haemoglobin.

Answer 32

Present in red blood cells. Oxygen molecules bind to the haem groups and
are carried around the body to where they are needed in respiring tissues.

Question 33

How does partial pressure of oxygen (PP02 )affect oxygen-haemoglobin binding?

Answer 33

as the pp02 of oxygen increases, the affinity of Hb for oxygen also
increases, so oxygen binds tightly to Hb.

When partial pressure is low, oxygen is released from Hb

Question 34

How does partial pressure of carbon dioxide affect oxygen-haemoglobin
binding? 3

Answer 34

as ppC02 increases, the conditions become acidic causing Hb to change shape.

*CO2 dissolves in the blood forming carbonic acid decreasing the pH

*Hb has a lower affinity for oxygen so more oxygen is released (unloaded)
from Hb to respiring tissuses. This is known as the Bohr effect

Question 35

How does saturation of Hb with oxygen affect oxygen-Hb binding 3

Answer 35

-It is hard for the first oxygen molecule to bind.

-Once it does, it changes the shape to make it easier for the second and third molecules to bind, known as cooperative binding

-Slightly harder for the fourth oxygen molecule to bind because there is
a low chance of finding a binding site

Question 36

Explain why oxygen binds to haemoglobin in the lungs 3

Answer 36

● Partial pressure of oxygen is high.
● Low concentration of carbon dioxide in the lungs, so affinity is high.
● Cooperative binding = (after the first oxygen molecule binds binding of subsequent molecules is easier)

Question 37

Explain why oxygen is released from haemoglobin in respiring tissues. 2

Answer 37

● Partial pressure of oxygen is low
● High concentration of carbon dioxide in respiring tissues, so affinity
decreases

Question 38

1. What do oxyhaemoglobin dissociation curves show?

2.How does carbon dioxide affect the position of an oxyhaemoglobin
dissociation curve?

Answer 38

1. Curves further to the left show the Hb has a higher affinity for oxygen.
2. Curve shifts to the right because Hb affinity for oxygen has decreased