Exchange ( Year 12 content )

Question 1

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

Answer 1

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

Question 2

How does an organism 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 it small surface area to volume ratio?

Answer 3

Changes that increase surface area such as folding and body parts become larger, e.g., elephant ears; elongating shape

Question 4

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 4

Their smaller surface area to volume ratio Means the distance that needs to be crossed is larger, as substances can not easily enter the cells as in single-celled organism

Question 5

Name three features of an efficient gas exchange surface

Answer 5

1) Large surface area
2) thin/ short diffusion distance
3) steep concentration gradient

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 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 and out of the trachea through the spiracales
● A diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out
● contraction of muscles in the trachea 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, gives an increased surface area. Blood and water flow across in opposite directions(counter current flow)

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

Question 12

How does the counter current exchange system maximise oxygen absorbed by the fish?

Answer 12

Maintains a steep concentration gradient along the gills, as water is always next to blood of a lower oxygen concentration. Keeps the rate of diffusion constant along the whole length of the Gill, enabling 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 diffuses pathway and large surface area to volume ratio
2) Many stomata 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

Guard cells control the opening and closing of the stomata. Most stay closed to prevent water loss while some open to let oxygen in

Question 15

Explain the process of inspiration

Answer 15

●External intercostal muscles contract
●Internal intercostal muscles relax
●The ribs are pulled upwards and outwards
●the diaphragm muscles contracts, causing it to flatten
●increases the volume of the thorax
●reduces pressure
●atmospheric pressure is greater than pulmonary pressure, so air is forced into the lungs

Question 16

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

Answer 16

●external intercostal muscles relax
●internal intercostal muscles contract
●the ribs are pulled downwards and inwards
●the diaphragm muscles relax, causing it to become dome shaped
●decreases the volume in the thorax
●increases pressure
●atmospheric pressure is less than pulmonary pressure, so air is forced out of the lungs

Question 17

Whats tidal volume?

Answer 17

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

Question 18

What is breathing rate?

Answer 18

The number of breaths we take per minute

Question 19

How do you calculate the pulmonary ventilation rate?

Answer 19

Tidal volume X breathing rate

Question 20

Define digestion

Answer 20

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

Question 21

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

Answer 21

●amylase in mouth
● maltase,sucrase, lactase in small intestine

Question 22

What are the substrates and products of carbohydrates digestive enzymes?

Answer 22

●Amylase—> starch into smaller polysaccharides
● Maltase—> maltose into 2 alpha glucose
● sucrase—> sucrose into glucose and fructose
● Lactase—> lactose into glucose and galactose

Question 23

Where are lipids digested?

Answer 23

Small intestine

Question 24

What needs to happen before lipids can be digested?

Answer 24

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 25

How are lipids digested?

Answer 25

Lipase hydrates the ester bond between monoglycerides and fatty acids

Question 26

Which enzymes are involved in protein digestion?

Answer 26

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

Question 27

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

Answer 27

Through Co-transport

Question 28

Which molecules require co-transport?

Answer 28

Amino acids and glucose

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 non-polar, meaning they can easily digguse across the membrane of the epithelial cells

Question 31

Describe the structure of haemoglobin

Answer 31

Protein consisting of 4 polypeptide chains, each carrying a haem group(quaternary structure)

Question 32

Describe the role of haemoglobin

Answer 32

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

Question 33

Name three factors affecting oxygen-haemoglobin binding

Answer 33

1) concentration of oxygen
2) concentration of carbon dioxide
3) saturation of haemoglobin with oxygen

Question 34

How does the concentration of oxygen affect oxygen-haemoglobin binding?

Answer 34

As the concentration of oxygen increases, the affinity of haemoglobin for oxygen increases, so oxygen binds tightly to haemoglobin. When oxygen concentration is low, oxygen is released from haemoglobin

Question 35

How does concentration of carbon dioxide affect oxygen-haemoglobin binding?

Answer 35

As the concentration of carbon dioxide increases, the conditions become acidic, causing haemoglobin to change shape. The affinity of haemoglobin for oxygen decreases, so oxygen is released from haemoglobin

Question 36

How does saturation of haemoglobin with oxygen affect oxygen-haemoglobin binding?

Answer 36

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 molecule to bind, known as positive cooperativity.

Question 37

Explain why oxygen binds to haemoglobin in the lungs?

Answer 37

● concentration of oxygen is high
● low concentration of carbon dioxide in the lungs, so affinity is high
● positive cooperativity

Question 38

Explain why oxygen is released from haemoglobin in respiring tissues

Answer 38

● concentration of oxygen is low
● High concentration of carbon dioxide In respiring tissues, affinity decreases

Question 39

How does carbon dioxide affect the position of an oxhaemogloboin dissociation curve?

Answer 39

Curve shifts to the right because haemoglobins affinity for oxygen has decreased

Question 40

Relate the structures of the Chambers to their functions

Answer 40

●atria: thin-walled and elastic, so they can stretch when filled with blood
●Ventricles: thick muscular walls pump blood under high pressure. The left ventricle is thicker than right because it has to pump blood all the way around the body

Question 41

Relate the structure of the vessels to their functions

Answer 41

●Arteries have thick walls to handle high pressure without tearing, and are muscular and elastic to control blood flow
● Veins have thin walls due to lower pressure, therefore requiring valves to ensure blood doesn’t flow backwards. Have less muscular and elastic layer

Question 42

Why are there two pumps(left and right) needed instead of one?

Answer 42

To maintain blood pressure around the whole body. When blood passes through the narrow capillaries of the lungs, the pressure drops sharply and, therefore, would not be flowing strongly enough to continue around the whole body. Therefore, it is returned to the heart to increase the pressure

Question 43

Describe what happens during cardiac diastole

Answer 43

The heart is relaxed. Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles.

Question 44

What happens during atrial systole

Answer 44

The atria contract, pushing any remaining blood into the ventricles

Question 45

What happens during ventricular systole

Answer 45

The ventricles contract. The pressure increases, closing the AV valves to prevent the back flow of blood. And opening the semi-lunar valves. Blood flows into the arteries

Question 46

How is the structure of capillaries suited to their function?

Answer 46

●walls are only one cell thick; short diffusion pathway
●very narrow, so can permeate tissues and red blood cells can lie flat against the wall, effectively delivering oxygen to tissues
●Numerous and highly branched,providing a large surface area

Question 47

What is tissue fluid?

Answer 47

A watery substance containing glucose, amino acids, oxygen, and other nutrients. It supplies these to the cells while also removing any waste material

Question 48

How is tissue fluid formed?

Answer 48

As blood is pumped through increasingly small vessels, this creates hydrostatic pressure, which forces fluid out of the capillaries

Question 49

How is water transported in plants?

Answer 49

Through the xylem vessels; long, continuous columns that also provide structural support to the stem

Question 50

Explain the cohesion-tension theory

Answer 50

Water molecules form hydrogen bonds with each other, causing them to ‘stick’ together(cohesion). Additionally, water molecules form hydrogen bond between the xylem, which causes it to be pulled in increasing surface tension. Therefore, as water is lost through transpiration, more can be drawn up the stem.

Question 51

What are the three components of phloem vessels?

Answer 51

●Sieve tube elements = from a tube to transport sucrose in the dissolved form of sap
●Companion cells= involved in ATP production for active loading of sucrose into sieve tubes

Question 52

Name the process whereby organic materials are transported around the plant

Answer 52

Translocation

Question 53

How do phloem vessels transport sucrose around the plant?

Answer 53

●sucrose is made in the leaf and is transported into the phloem via companion cells through Co-transport
●This lowers the water potential in the phloem
●This causes water to enter from the xylem via osmosis
●This increases the hydrostatic pressure
●mass flow of sucrose to the sink end

Question 54

Give evidence for the mass flow hypothesis of translocation

Answer 54

●Sap is released when a stem is cut. Therefore, there must be pressure in the phloem
●There is a higher sucrose concentration in the leaves than the roots
●Increasing sucrose levels in the leaves results in increased sucrose in the phloem

Question 55

Give evidence against the mass flow hypothesis of translocation

Answer 55

●The structure sieve tubes seem to hinder mass flow
●Not all solutes move at the same speed, as they would in mass flow
●Sucrose is delivered at the same rate throughout the plant, rather than to areas with lowest sucrose concentration first

Question 56

How can ringing experiments be used to investigate transport in plants?

Answer 56

The bark and phloem of a tree are removed in a ring, leaving behind the xylem. Eventually, the tissues above the missing ring swell due to accumulation of sucrose as the tissue below begins to die. Therefore, sucrose must be transported in the phloem

Question 57

How can tracing experiments be used to investigate transport in plants?

Answer 57

Plants are grown in the presence of radioactive CO2, which will be incorporated into the plants’ sugars. Using autoradiography,we can see that areas exposed to radiation correspond to where the phloem is