Chapter 3- Exchange of substances

Question 1

Why do multicellular organisms need a specialised gas exchange system

Answer 1

The surface area to volume ratio increases

Question 2

What are features of an efficient gas exchange

Answer 2

1. Large surface area
2. Good blood supply/ventilation to maintain a steep gradient
3. Thin for a short diffusion distance

Question 3

Do fish have a small surface area to volume ratio

Answer 3

Yes

Question 4

Describe the gas exchange structure of a fish

Answer 4

-Gills that are supported by arches
-On arches there are multiple gill filaments, with lamellae on them which participate in gas exchange

Question 5

Describe gas exchange for a fish

Answer 5

Fish need a supply of oxygen for cells, they do this with the counter current system
1. When water flows over the gills, blood and water flow in opposite directions- this creates a diffusion gradient (which allows oxygen from the water to diffuse into an area of low oxygen concentration, the blood)

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 three main features of an insects gas exchange 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 supported by cartilage rings, to prevent collapse extending through the body
Tracheoles- Smaller branches dividing off tracheae

Question 8

Explain the process of gas exchange in insects

Answer 8

1. Gases move in and out of the tracheae through the opening of the spiracles
2. A concentration gradient is created as respiring tissues use oxygen, which allows more oxygen to diffuse in
3. Carbon dioxide is produced by respiring cells

Question 9

How is water loss minimised in terrestrial insects

Answer 9

-They have a waterproof exoskeleton
- They have the ability to close spiracles
-Hairs around the spiracles reduces diffusion of water vapour

Question 10

How is water loss minimised in xerophytic plants

Answer 10

-Few stomata
-Stomata are in pits
-Hairs surrounding stomata
-Needle shaped leaves which reduce surface area
-A thickened waxy cuticle

Question 11

Name parts of the mammalian gas exchange system

Answer 11

1. Trachea: The airway that leads from the mouth and nose to the bronchi. It is lined with mucus-secreting goblet cells and cilia. The cilia sweep microorganisms and dust away from the lungs
2. Humans have two lungs, both which are central parts of the respiratory system
3. Bronchi: The bronchi lead to smaller bronchioles
4. Bronchioles: These are narrow tubes, which carry air from the bronchi to the alveoli. They have no supporting cartilage
5. Alveoli: Tiny sacs of air with many structural adaptations to enable efficient gas exchange

Question 12

What are goblet cells

Answer 12

Goblet cells are mucus producing cells, which traps dusts, bacteria and other microorganisms

Question 13

Describe adaptations of alveoli in gas exchange system

Answer 13

1. The alveoli are very thin, around one cell thick, which allows for a short diffusion distance
2. Constant blood supply by the capillaries means that there is a steep concentration gradient that is maintained
3. Large number of alveoli in the lungs, which collectively give it a large surface area for more gas exchange to occur

Question 14

Describe breathing in mechanism

Answer 14

Breathing in causes the volume inside the chest to increase, and air pressure in the lungs to decrease, until slightly low
1. External intercostal muscles contract, internal intercostal muscles relax.
2. Ribcage moves up and out
3. Diaphragm moves down and flattens
3. Volume of thorax increases
4. Pressure inside thorax decreases
5. Air is drawn in

Question 15

Describe breathing out mechanism

Answer 15

Breathing out causes the volume inside the chest to decrease and pressure increases
1. External intercostal muscles relax, internal intercostal muscles contract
2. Ribcage moves down and out
3. Diaphragm relaxes and moves up
4. Volume of thorax decreases
5. Pressure inside thorax increases
6. Air is forced out

Question 16

Describe the structure and functions of the mammalian gas exchange system

Answer 16

1. Cartilage: Rings of cartilage in the trachea and bronchi prevent the lungs from collapsing due to pressure drop.
2. Ciliated epithelium: Present in bronchi, bronchioles, and trachea, which is involved in moving mucus along to prevent lung infection by moving it towards the throat.
3. Smooth muscle- Their ability to contract enables them to play a role in constricting the airway
4. Elastic fibres: Stretch when we exhale and recoil when we inhale, which controls the flow of air

Question 17

Describe inspiration

Answer 17

External intercostal muscles contract and internal intercostal muscles relax, where the ribs raise upwards.
The diaphragm contracts and flattens. The thorax volume increases, which lowers the pressure
The difference between the
pressure inside the lungs and atmospheric
pressure creates a gradient, thus causing the
air to be forced into the lungs.

Question 18

Describe expiration

Answer 18

Internal intercostal muscles contract, external intercostal muscles relax, which lowers the ribcage.
The diaphragm relaxes and raises upwards, which decreases the volume inside the thorax. Thus the pressure is increased, which forces air outside the lungs

Question 19

What is a spirometer

Answer 19

A spirometer is a device used to measure lung volume. A person using this device, breathes in and out the airtight chamber, which causes it to move up and down, leaving a trace on the graph which can be interpreted.

Question 20

Define vital capacity

Answer 20

The maximum volume of air that can be inhaled or exhaled in a single breath and varies depending on gender, size, age and height

Question 21

Define tidal volume

Answer 21

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

Question 22

Define breathing rate

Answer 22

The number of breaths per minute, can be calculated from the spirometer trace by counting the peaks or troughs in a minute

Question 23

Define the residual volume

Answer 23

The volume of air which is always present in the lungs is known as the residual volume

Question 24

Define digestion

Answer 24

Digestion is the hydrolysis of large biological molecules into smaller molecules, which can be absorbed across cell membranes

Question 25

Describe the mouth and its function in digestion

Answer 25

Carbohydrate digestion begins here, with the release of amylase from salivary glands

Question 26

Describe carbohydrates in relation to digestion

Answer 26

The digestion of carbohydrates begin in the mouth and the small intestine 1. Amylase (produced in the salivary, the pancreas, and small intestine) is a carbohydrase that hydrolyses starch into maltose 2. Maltose is then hydrolysed into glucose by the enzyme maltase, which then diffuses into epithelial cells of small intestine

Question 27

Describe protein digestion

Answer 27

Protein digestion begins in the lumen of the stomach by protease enzymes - Endopeptidases hydrolyse peptide bonds to produce dipeptides -Exopeptidases hydrolyse peptide bonds at the ends of the chain to produce dipeptides -Dipeptidase enzymes hydrolyse the peptide bond between the two amino acids, which are released into the cytoplasm in the cell

Question 28

Describe the digestion of lipids

Question 29

What are the substrates and products of carbohydrate digestive enzymes

Answer 29

- Starch into smaller polysaccharides - Maltase into 2 glucose molecules - Sucrase, sucrose into glucose and fructose, - Lactase, lactose into glucose and galactose

Question 30

Where are lipids digested

Answer 30

The small intestine

Question 31

What needs to happen to lipids before they can be digested

Answer 31

They must be emulsified by bile salts produced by the liver. This breaks down large fat molecules into smaller, soluble molecules called micelles, which increase its surface area for the enzyme's

Question 32

How are lipids digested

Answer 32

Lipase hydrolyses the ester bond between the monoglycerides and fatty acids

Question 33

What is haemoglobin

Answer 33

Haemoglobin is a water soluble globular protein which consists of 2 beta polypeptide chains and 2 alpha helices, each molecule forms a complex containing a haem group.

Question 34

Where does loading of oxygen occur

Answer 34

In the lungs

Question 35

Describe the role of haemoglobin

Answer 35

It is present in red blood cells. Oxygen molecules bind to the haem groups and are carried around the body to respiring tissues

Question 36

Name three factors that impact the oxygen-haemoglobin binding

Answer 36

1. Partial pressure/concentration of oxygen 2. Partial pressure/concentration of carbon dioxide 3. Saturation of haemoglobin with oxygen

Question 37

How does partial pressure of oxygen affect oxygen-haemoglobin binding

Answer 37

As partial pressure of oxygen increases, the affinity of oxygen also increases, so oxygen binds tightly to haemoglobin. When partial pressure is low, oxygen is released from haemoglobin.

Question 38

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

Answer 38

As partial pressure of carbon dioxide increases, the conditions become acidic which causes haemoglobin to change shape. Therefore the affinity of haemoglobin for oxygen decreases, so oxygen is released. This is known as the Bohr affect

Question 39

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

Answer 39

1. It is hard for the first oxygen molecule to bind 2. Once it does, it changes shape which makes it easier for the second and third oxygen molecule to bind 3. It is slightly harder for the fourth oxygen molecule to bind as there is a low chance of it finding a binding site

Question 40

Explain why oxygen binds to haemoglobin in the lungs

Answer 40

Partial pressure of oxygen is high Low concentration of carbon dioxide in the lungs so affinity is high Positive cooperativity (after the first oxygen molecule binds, binding of other oxygen molecules is easier)

Question 41

Explain why haemoglobin is released in respiring tissues

Answer 41

- The partial pressure of oxygen is low -High concentration of carbon dioxide in respiring tissues, so affinity decreases

Question 42

What do oxyhaemoglobin dissociation curves show

Answer 42

The saturation of haemoglobin with oxygen, plotted against partial pressure of oxygen. Curves further to the left show the haemoglobin has a higher affinity for oxygen

Question 42

How does carbon dioxide concentration affect the position of an oxyhaemoglobin dissociation curve

Answer 42

The curve shifts to the right as the haemoglobin's affinity for oxygen has decreased

Question 43

Name some common features of a mammalian's circulatory system

Answer 43

-Suitable medium for transport (blood is water based so allows substances to dissolve) -Means of moving the medium and maintaining pressure around the body, such as the heart - Means of controlling flow so it remains unidirectional, such as valves -

Question 44

Draw a diagram of the human heart, including names of chambers, vessels and valves

Answer 44

Drawing must include named chambers, valves, and vessels

Question 45

Relate the structure of the chambers to their function

Answer 45

-Atria: Thin walled so they can stretch when filled with blood -Ventricles: Thick muscular walls to pump blood under high pressure. The left ventricle is thicker than the right because it has to pump blood around the body

Question 46

Relate the structure of the vessels in relation to their function

Answer 46

-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, which requires valves to prevent the backflow of blood. They have less muscular and elastic tissue as they dont have to control blood flow

Question 47

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

Answer 47

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

Question 48

Describe what happens at cardiac diastole

Answer 48

The heart is relaxed. Blood enters the atria, which increases the pressure inside the atria. This forces open the atrioventricular valves and blood pours into the ventricles. Pressure in the heart is lower than in the arteries, so semi-lunar valves remain closed.

Question 49

Describe what happens at atrial systole

Answer 49

The atria contract, pushing any remaining blood into the ventricles

Question 50

Describe what happens during ventricular systole

Answer 50

The ventricles contract. The pressure increases, closing the atrioventricular valves to prevent backflow, and opening the semi-lunar valves. Blood flows into the arteries

Question 51

Name the nodes involved in heart contraction and where they are situated

Answer 51

Sinoatrial node (SAN)- wall of right atrium Atrioventricular node (AVN)- In between the two atria

Question 52

What does myogenic mean

Answer 52

The heart's contraction is initiated from within the muscle itself, rather than by nerve impulses

Question 53

Explain how the heart contracts

Answer 53

-SAN initiates and spreads the impulse across the atria, so they contract -AVN receives, delays, and then conveys the impulse down the bundle of His -Impulse travels into the Purkinje fibres which branch across the ventricles, so they contract from the bottom up

Question 54

Why does the impulse need to be delayed

Answer 54

If the impulse spread straught from the atria to the ventricles, there would not be enough time for all the blood to pass through and the valves to close

Question 55

How is the structure of the capillaries suited for their function

Answer 55

-Walls are one cell thick, which means that there is a short diffusion pathway -Very narrow so can permeate tissues and red blood cells can lie flat against the wall, which effectively brings oxygen to tissues - Numerous and highly branched, providing a large surface area

Question 56

What is tissue fluid

Answer 56

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

Question 57

Describe how tissue fluid is formed

Answer 57

1. When blood is at the arteriole end of a capillary, the hydrostatic pressure is high enough to push out molecules out of the capillary 2. Proteins remain in the blood, 3. At the venule end of the capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced 4. The water potential gradient between the capillary and the tissue fluid remains the same as at the arteriole end, so water begins to flow back into the capillary from the tissue fluid 5. Overall, more fluid leaves the capillary then returns, leaving tissue fluid behind to bathe cells

Question 58

Describe the formation of lymph

Answer 58

1. Some tissue fluid re-enters the capillaries while some enter lymph capillaries 2. Larger molecules that are not able to pass through the capillaries walls enter the lymphatic system 3. The liquid moves along the larger vessels of this system by compression caused by body movement. Any backflow is prevented by valves 4. The lymph eventually reenters the bloodstream through veins located close to the heart 5. Any plasma proteins that have escaped from the blood are returned to the blood via the lymph capillaries

Question 59

How is water transported in plants

Answer 59

Through xylem vessels

Question 60

Describe features of the xylem

Answer 60

- They are long cylinders made of dead tissue with open ends, therefore they can form a continuous volume - Xylem vessels also contain pits which enable the water to move sideways between the vessels - They are thickened with a tough substance such as lignin

Question 61

Describe the transpiration process

Answer 61

1. Water vapour diffuses from air spaces through a stoma by a process called transpiration, which lowers the water potential 2. Water evaporates from a mesophyll cell, which creates a transpiration pull 3. Water moves through the mesophyll cell

Question 62

Explain the cohesion tension theory

Answer 62

- Water molecules form hydrogen bonds with each other, causing them to stick together (cohesion) - The surface tension of the water also creates a sticking affect and the xylem walls bend inwards as water is pulled up the xylem

Question 63

Movement of water in the root

Answer 63

1. Water enters through root hair cells and moves into the xylem tissue located at the centre of the root 2. This movement occurs as a result of a water potential gradient, as the water potential in the soil is higher than in the root. Therefore water moves by osmosis into the root. 3. Minerals are also absorbed through root hair cells by active transport, as they need to be pumped against a concentration gradient.

Question 64

Describe the symplast pathway

Answer 64

Water enters the cytoplasm through the plasma membrane and passes from one cell to the next by plasmodesmata, the channels which connect the cytoplasm of one cell to the next.

Question 65

Apoplast pathway

Answer 65

Water moves through the water filled spaces between cellulose molecules in the cell walls. In this pathway, water doesn't pass through any plasma membranes therefore it can carry dissolved mineral ions and salts

Question 66

What are three components of phloem cells vessels

Answer 66

Sieve tube elements= Form 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 Plasmodesmata= Gaps between cell walls where the cytoplasm links, allowing substances to flow

Question 67

Name the process whereby organic materials are transported around the plant

Answer 67

Translocation

Question 68

How does sucrose in the leaf move into the phloem

Answer 68

Sucrose enters companion cells of the phloem vessels by active loading, which uses ATP and a diffusion gradient of hydrogen ions. Sucrose then diffuses from companion cells into sieve tube elements through the plasmodesmata

Question 69

How do phloem vessels transport sucrose around the plant

Answer 69

1. As sucrose moves into the tube elements from the companion cells, the water potential inside the phloem is reduced. 2. This causes water to enter from the xylem via osmosis, which increases hydrostatic pressure inside the phloem 3. Water moves along the sieve tube towards areas of lower hydrostatic pressure 4. Sucrose diffuses into surrounding cells where it is needed

Question 70

Give evidence for the mass flow hypothesis of translocation

Answer 70

1. Sap is released when a stem is cut, therefore there must be pressure inside the phloem 2. There is a higher sucrose concentration in the leaves than the roots 3. Increasing sucrose levels in the leaves results in increased sucroses in the phloem

Question 71

Give evidence against the mass flow hypothesis of translocation

Answer 71

1. The structure of sieve tubes seems to hinder mass flow. 2. Not all solutes move at the same speed, as they would in mass flow 3. Sucrose is delivered at the same rate throughout the plant, rather than to areas with the lowest sucrose concentration first

Question 72

How can ringing experiments be used to investigate transport in plants

Answer 72

1. The bark and phloem of a tree are removed in a ring, leaving behind the xylem 2. Eventually, the tissues above the missing ring swells due to the accumulation of sucrose as the tissue below begins to die. Therefore sucrose must be transported in the phloem

Question 73

How can tracing experiments be used to investigate transport in plants

Answer 73

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