Exchange

Question 1

How does an organisms size relate to their surface area to volume ratio?

Answer 1

The larger the organism the lower the surface area to volume ratio

Question 2

How does an organisms surface area to volume ratio relate to their metabolic rate?

Answer 2

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

Question 3

How might a large organism adapt to compensate for its small surface area to volume ratio?

Answer 3

Changes that increase surface area e.g folding; body parts become larger e.g elephants ears; elongating shape

Question 4

Why do multicellular organisms require specialised gas exchange?

Answer 4

Their smaller surface area to volume ratio means the distance that needs to be crossed is larger and substances cannot easily enter the cells as in a single celled organism

Question 5

Name three features of an efficient gas exchange system

Answer 5

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

Question 6

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

Answer 6

They have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water

Question 7

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

Answer 7

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 8

Explain the process of gas exchange in insects

Answer 8

Gases move in an 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?

Answer 9

They have a waterproof, impermeable outer membrane and a small surface area to volume ratio

Question 10

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

Answer 10

Gills = located within the body supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles

Lamellae = at right angles to the gill filaments, give an increased surface area. Blood and water flow across them in the opposite directions

Question 11

Explain the process of gas exchange in fish

Answer 11

The fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure

The water passes over the lamellae and the oxygen diffuses into the bloodstream

Waster carbon dioxide diffuses into the water and flows back out of the gills

Question 12

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

Answer 12

Maintains a steep concentration gradient, as water is always next to blood or a lower oxygen concentration. Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed

Question 13

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

Answer 13

1. Thin and flat to provide short diffusion pathway and large surface area to volume ratio
2. Many minute pores in the underside of the leaf 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?

Answer 14

Stomata regulated by guard cells which allows them to open and close as needed. Most stay closed to prevent water loss while some open to let oxygen in

Question 15

Describe the pathway taken by air as it enters the mammalian gaseous exchange system

Answer 15

Nasal cavity - trachea - bronchi - bronchioles - alveoli

Question 16

Describe the function of the nasal cavity in the mammalian gaseous exchange system

Answer 16

A good blood supply warms and moistens the air entering the lungs. Goblet cells in the membrane secrete mucus which traps dust and bacteria

Question 17

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

Answer 17

Wide tube supported by C shaped cartilage to keep the air passage open during pressure changes

Lined by ciliated epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections

Carries air to the bronchi

Question 18

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

Answer 18

They are supported by rings of cartilage and are lined by ciliated epithelium cells

They are narrower and there are two of them, one for each lung

Allow passage of air into the bronchioles

Question 19

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

Answer 19

Narrower than the bronchi

Do not need to be kept open by cartilage, therefore mostly have only muscle and elastic fibres so that they can contract and relax easily during ventilation

Allow passage of air into the alveoli

Question 20

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

Answer 20

Mini air sacs, lined with epithelium cells, site of gas exchange

Walls only one cell thick, covered with a network of capillaries, 300 million in each lung, all of which facilitates gas diffusion

Question 21

Explain the process of inspiration and the changes that occur throughout the thorax

Answer 21

External intercostal muscles contract, pulling the ribs up and out

Diaphragm contracts and flattens

Volume of thorax increases

Air pressure outside the lungs is therefore higher than the air pressure inside so air moves in

Question 22

Explain the process of expiration and the changes that occur throughout the thorax

Answer 22

External intercostal muscles relax bringing the ribs down and in

Diaphragm relaxes and domes upwards

Volume of the thorax decreases

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

Question 23

What is tidal volume?

Answer 23

The volume of air we breathe in and out during each breathe at rest

Question 24

What is breathing rate?

Answer 24

The number of breaths we take per minute

Question 25

How do we calculate pulmonary ventilation rate?

Answer 25

Tidal volume x breathing rate

Question 26

Define digestion

Answer 26

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

Question 27

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

Answer 27

Amylase in the mouth

Maltase, sucrase, lactase in membrane of small intestine

Question 28

What are the substrates and products of the carbohydrate digestive enzymes?

Answer 28

Amylase - starch into smaller polysaccharides

Maltase - maltose into 2x glucose

Sucrase - sucrose into glucose and fructose

Lactase - lactose into glucose and galactose

Question 29

Where are lipids digested?

Answer 29

The small intestine

Question 30

What needs to happen before lipids can be digested?

Answer 30

They must be emulsified by bile salts produced by the liver. This breaks down large fat molecules into smaller, soluble molecules called micelles, increasing surface area

Question 31

How are lipids digested?

Answer 31

Lipase hydrolyses the ester bond between the monoglycerides and fatty acids

Question 32

Which enzymes are involved in protein digestion? What are their roles?

Answer 32

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 33

How are certain molecules absorbed into the ileum despite a negative concentration gradient?

Answer 33

Co-transport

Question 34

Which molecules require co-transport?

Answer 34

Amino acids and monosaccharides

Question 35

Explain how sodium ions are involved in co-transport

Answer 35

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

Question 36

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

Answer 36

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