test

Question 1

single celled organisms

Answer 1

The need for specialised exchange surfaces arises as the size of the organism, and its surface area to volume ratio increases.

Question 2

multicellular organisms

Answer 2

that distance is much larger due to a higher surface area to volume ratio. As a result of that, multicellular organisms required specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen.

Question 3

Features of an efficient exchange surface

Answer 3

large surface area
thin
good blood supply/ventilation

Question 4

Fish

Answer 4

mall surface area to volume ratio
Bony fish have four pairs of gills, each gill supported by an arch.
multiple projections called gill filaments
lamellae
Blood and water flow across the lamellae in a counter current direction meaning they flow in the opposite direction to one another. This ensures that a steep diffusion gradient
maximum amount of oxygen is diffusing into the deoxygenated blood from the water
Ventilation is required to maintain a continuous unidirectional flow

Question 5

Ventilation in fish

Answer 5

maintain a continuous unidirectional flow.
ish opening its mouth followed by lowering the floor of buccal cavity.
fish closes its mouth, causing the buccal cavity floor to raise, thus increasing the pressure. The water is forced over the gill filaments by the difference in pressure between the mouth cavity and opercular cavity. The operculum acts as a valve and pump and lets water out and pumps it in

Question 6

Plants

Answer 6

stomata which allow gases to enter and exit the leaves. The large number of these means no cell is far from the stomata, reducing the diffusion distance. Leaves also possess air spaces to allow gases to move around the leaf and easily come into contact with photosynthesising mesophyll cells.

Question 7

Structures of mammalian gaseous exchange system

Answer 7

Cartilage
Ciliated epithelium
Goblet cell
Smooth muscle
Elastic fibres

Question 8

Cartilage

Answer 8

involved in supporting the trachea and bronchi, plays an important role in preventing the lungs from collapsing in the event of pressure drop during exhalation.

Question 9

Ciliated epithelium

Answer 9

present in bronchi, bronchioles and trachea, involved in moving mucus along to prevent lung infection by moving it towards the throat where it can be swallowed.

Question 10

Goblet cell

Answer 10

cells present in the trachea, bronchi and bronchioles involved in mucus secretion to trap bacteria and dust to reduce the risk of infection with the help of lysozymes which digest bacteria.

Question 11

Smooth muscle

Answer 11

heir ability to contract enables them to play a role in constricting the airway, thus controlling its diameter as a result and thus controlling the flow of air to and from the alveoli.

Question 12

Elastic fibres

Answer 12

stretch when we exhale and recoil when we inhale thus controlling the flow of air.

Question 13

inspiration

Answer 13

xternal intercostal muscles contract whereas the internal muscles relax, as a result this causes the ribs to raise upwards. The diaphragm contracts and flattens. In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, thus lowering 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 14

Expiration

Answer 14

During expiration, the internal intercostal muscles contract whereas the external muscles relax therefore lowering the rib cage. The diaphragm relaxes and raises upwards. This action in combination decrease the volume inside the thorax, therefore increasing the pressure, forcing the air out of the lungs.

Question 15

Spirometer

Answer 15

used to measure lung volume.
breathes in and out of the airtight chamber, thus causing it to move up and down, leaving a trace on a graph which can then be interpreted.

Question 16

Vital capacity

Answer 16

the maximum volume of air that can be inhaled or exhaled in a single breath. Varies depending on gender, age, size as well as height.

Question 17

Tidal volum

Answer 17

– the volume of air we breathe in and out at each breath at rest

Question 18

Breathing rate

Answer 18

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

Question 19

Digestion

Answer 19

hydrolysis of large biological molecules into smaller molecules which can be absorbed across cell membranes.

Question 20

how carbohydrates are digested

Answer 20

by many different enzymes. Amylases in the mouth digest larger polymers, maltases in the ileum break down monosaccharides, and sucrases and lactases break down the dissacharides sucrose and lactose respectively.

Question 21

lipids digested

Answer 21

lipases which hydrolyse the ester bond between the monoglycerides and fatty acid. Before being broken down in the ileum, lipids are emulsified into micelles by bile salts released by the liver. Emulsification increases the surface area and speeds up the chemical reaction.

Question 22

how proteins digested

Answer 22

by enzymes called peptidases of which they are divided into 3 main groups:
endopeptidases
exopeptidases
dipeptidases

Question 23

endopeptidase

Answer 23

hydrolyse peptide bonds between specific amino acids in the middle of a polypeptid

Question 24

exopeptidases

Answer 24

hydrolyse bonds at ends of a polypeptides

Question 25

dipeptidases

Answer 25

break dipeptides into individual amino acids

Question 26

amino acids are absorbed by facilitated diffusion

Answer 26

through specific carrier molecule in the surface membrane of epithelial cells. With each amino acid, one Na+ is also taken up, therefore amino acid absorption occurs via a process known as co-transport. A diffusion gradient for Na+ is maintained by their active transport through the base of epithelial cells where amino acids pass by facilitated diffusion.

Question 27

why monoglycerises can diffuse easily across cell membrane

Answer 27

polar
diffuse across the cell membrane into the epithelial cells lining the epithelium. Once inside they are transported to the endoplasmic reticulum where they are reformed into triglycerides again. After this they move out of the cells by vesicles into the lymph system.

Question 28

ringing experimnets

Answer 28

n order to investigate if the phloem is responsible for mass flow a ringing experiment can be used. In this the bark and phloem of a tree are removed leaving just the xylem in the centre. Overtime the tissues above the missing ring swell with sucrose solution and the tissue below dies. This shows that sucrose is transported in the phloem.

Question 29

tracer Experiments

Answer 29

Tracer experiments can also be used to investigate the transport of sucrose in plants. Plants are grown in a environment that contains radioactivity labelled carbon dioxide (14CO2). The presence of this means that they are incorporated into the sugar produced in photosynthesis.
The movement of these sugars can now be traced through the plant using autoradiography. Those areas that have been exposed to the radiation produced by the 14C in the sugars will appear black. It follows that these regions correspond to the area where the phloem is and therefore suggest that this is where the sugars are transported.

Question 30

haemoglobin structure

Answer 30

water soluble globular protein
two polypeptide chains and two alpha helix
haem group
carries oxygem
each molecule carries 4 oxygen

Question 31

what affinity of oxygen depends on

Answer 31

partial pressure of oxygen
as partial pressure increases, the affinity of haemoglobin for oxygen increases, that is, oxygen binds to haemoglobin tightly. This occurs in the lungs in the process known as loading.

Question 32

partial pressure during respiration

Answer 32

oxygen is used up and therefore the partial pressure decreases, thus decreasing the affinity of oxygen for haemoglobin. As a result of that, oxygen is released in respiring tissues where it is needed. After the unloading process, the haemoglobin returns to the lungs where it binds to oxygen again.

Question 33

what dissociation curve shows

Answer 33

Initially the curve is shallow because it is hard for the first oxygen molecule to bind. Once it has bound though it changes the shape making it easier for oxygen molecules two and three to bind, hence the steep increase. This is called positive cooperativity. Finally the gradient begins to flatten out because the likelihood of the fourth oxygen finding a binding site is low.

Question 34

fetal haemoglobin

Answer 34

different affinity for oxygen compared to adult haemoglobin, as in needs to be better at absorbing oxygen because by the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased. Therefore, fetal haemoglobin must have a higher affinity for oxygen in order for the foetus to survive at low partial pressure.

Question 35

carbon dioxide on affinity of oxygen

Answer 35

Carbon dioxide is released by respiring cells which require oxygen for the process to occur. Therefore, in the presence of carbon dioxide, the affinity of haemoglobin for oxygen decreases, thus causing it to be released. This is known as the Bohr effect. It does this because carbon dioxide creates slightly acidic conditions which change the shape of the haemoglobin protein, thus making it easier for the oxygen to be released.

Question 36

atrium

Answer 36

• an atrium - thin walled and elastic, the atrium can stretch when filled with blood

Question 37

ventricle

Answer 37

thick muscular wall to pump blood around the body or to the lungs.

Question 38

why two seperaate pumps needed

Answer 38

maintain blood pressure around the whole body. One pump would not be able to do this as the slow down of the blood as it passes the lungs would cause it to lose all pressure.

Question 39

Aorta

Answer 39

connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.

Question 40

Pulmonary Artery

Answer 40

connected to the right ventricle and carries deoxygenated blood to the lungs where it is oxygenated and the carbon dioxide is removed.

Question 41

Pulmonary Vein

Answer 41

connected to the left atrium and brings oxygenated blood back from the lungs.

Question 42

.Vena Cava

Answer 42

connected to the right atrium and brings deoxygenated blood back from the tissues except the lungs.

Question 43

myogenic.

Answer 43

heart’s ability to initiate its own contraction

Question 44

3 stages of the cardiac cycle:

Answer 44

Cardiac diastole
Atrial systole
Ventricular systole

Question 45

Cardiac diastole

Answer 45

atria and ventricles relax, elastic recoil of the heart lowers the pressure inside the heart chambers and blood returns to the heart from the vena cava and the pulmonary vein and fill the atria. Pressure increases in the atria until the atrioventricular valves open and blood flows into the ventricles. The relaxed aria and ventricles means that the semi-lunar valves are closed.

Question 46

Atrial systole –

Answer 46

The atria then contract forcing any remaining blood into the ventricles.

Question 47

Ventricular systole

Answer 47

contraction of the ventricles causes the atrioventricular valves to close and semi-lunar valves to open thus allowing blood to leave the left ventricle through the aorta and right ventricle through the pulmonary artery.

Question 48

Arteries

Answer 48

adapted to carrying blood away from the heart to the rest of the body, thick walled to withstand high blood pressure, contain elastic tissue which allows them to stretch and recoil thus smoothing blood flow. They also contain smooth muscle which enables them to vary blood flow, lined with smooth endothelium to reduce friction and ease the flow of blood.

Question 49

Arterioles

Answer 49

branch off arteries, have thinner and less muscular walls, their role is to feed blood into capillaries.

Question 50

Capillaries

Answer 50

smallest blood vessels, site of metabolic exchange, only one cell thick for fast exchange of substances

Question 51

Venules

Answer 51

larger than capillaries but smaller than veins.

Question 52

Veins

Answer 52

carry blood from the body to the heart, contain a wide lumen to maximise the volume of blood carried to the heart. They are thin walled as blood is under low pressure and contain valves to prevent the back-flow of blood. A weak pulse of blood means there is little elastic tissue or smooth muscle as there is no need for stretching and recoiling.

Question 53

what tisssue fluid contains

Answer 53

dissolved oxygen and nutrients which serves as a means of supplying the tissues with the essential solutes in exchange for waste products such as carbon dioxide.

Question 54

hydrostatic pressure and tissue fluid

Answer 54

s created when blood is pumped along the arteries, into arterioles and then capillaries. This pressure forces blood fluid out of the capillaries. Only substances which are small enough to escape through the gap in a capillary are components of the tissue fluid – this includes dissolved nutrients such as amino acids, fatty acids, ions in solution, glucose and oxygen. The fluid is referred to as tissue fluid, as described above.
The fluid is also acted on by hydrostatic pressure which pushes some of the fluid back into the capillaries. As both the tissue fluid and blood contain solutes, they have a negative water potential. Although the water potential of the tissue fluid is negative, it is less negative in comparison to the blood (the blood contains more solutes). Therefore, the tissue fluid is positive in comparison to the blood. This causes water to move down the water potential gradient from the tissue fluid to the blood by osmosis.

Question 55

xylem featurees

Answer 55

They transport water and minerals, and also serve to provide structural support.
They are long cylinders made of dead tissue with open ends, therefore they can form a continuous column.
Xylem vessels also contain pits which enable water to move sideways between the vessels.
They are thickened with a tough substance called lignin, which is deposited in spiral patterns to enable the plant to remain flexible.

Question 56

what is tarsnpiration

Answer 56

the process where plants absorb water through the roots, which then moves up through the plant and is released into the atmosphere as water vapour through pores in the leaves. Carbon dioxide enters, while water and oxygen exit through a leaf’s stomata.

Question 57

transpiration stream

Answer 57

which is the movement of water up the stem, enables processes such as photosynthesis, growth and elongation as it supplies the plant with water which is necessary for all of these processes. Apart from this, the transpiration stream supplies the plant with the required minerals, whilst enabling it to control its temperature via evaporation of water.

Question 58

trasnpiration and osmosis

Answer 58

Transpiration involves osmosis, where water moves from the xylem to the mesophyll cells.

Question 59

evapouration

Answer 59

from the surface of mesophyll cells into intercellular spaces and the diffusion of water vapour down a water vapour potential gradient out of the stomata.

Question 60

trasnpiration and potometer

Answer 60

water lost by the leaf is replaced by water in a capillary tube. Therefore, measuring the movement of the meniscus or a bubble can be used to determine the rate of transpiration.

Question 61

Factors which affect

Answer 61

number of leaves, number/size or position of stomata, presence of waxy cuticle, the amount of light present, the temperature, humidity of the air, air movement and water availability.

Question 62

how xerophytes adapted to dry conditions

Answer 62

smaller leaves to reduce the surface area for water loss. Both densely packed mesophyll and thick waxy cuticle prevent water loss via evaporation. Moreover, xerophytes respond to low water availability by closing the stomata to prevent water loss. Apart from this, they also contain hairs and pits which serve as a means of trapping moist air, thus reducing the water vapour potential gradient. Xerophytes also roll their leaves in order to reduce the exposure of the lower epidermis to the atmosphere, thus trapping air that is moist.

Question 63

movement of water in the root

Answer 63

Water enters through root hair cells and moves into the xylem tissue located in the centre of the root. This movement occurs as a result of a water potential gradient, as the water potential is higher inside the soil than inside the root hair cells, due to the dissolved substances in the cell sap. Therefore, the purpose of root hair cells it to provide a large surface area for the movement of water to occur. Minerals are also absorbed through the root hair cells by active transport, as they need to be pumped against the concentration gradient.

Question 64

two ways water is taken up by root hair cells and moves across the cortex of the root into the xylem

Answer 64

symplast pathway
apoplast pathway

Question 65

symplast pathway

Answer 65

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

Question 66

apoplast pathway

Answer 66

where the 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 67

Casparian strip,

Answer 67

When the water reaches a part of the root called the endodermis, it encounters a layer of suberin which is known as the Casparian strip, which cannot be penetrated by water.

in order for the water to cross the endodermis, the water that has been moving through the cell walls must now enter the symplast pathway to reach xylem

Question 68

water moving up the stem

Answer 68

from the top of the xylem vessels into the mesophyll cells down the water potential gradient. The push of water upwards is aided by the root pressure which is where the action of the endodermis moving minerals into the xylem by active transport drives water into the xylem by osmosis, thus pushing it upwards.
The flow of water is also maintained with the help of surface tension of water and the attractive forces between water molecules known as cohesion. The action of these two forces in combination is known as the cohesion-tension theory, which is further supported by capillary action where the forces involved in cohesion cause the water molecule to adhere to the walls of xylem, thus pulling water up.

Question 69

transloaction

Answer 69

an energy requiring process which serves as a means of transporting assimilates such as sucrose in the phloem between sources which release sucrose such as leaves and sinks e.g. roots and meristem which remove sucrose from the phloem.

Question 70

phloem vessels which have the following features:

Answer 70

tubes made of living cells involved in translocation of nutrients to storage organs and growing parts of the plant.
Consist of sieve tube elements and companion cells.
Sieve tube elements form a tube to transport sugars such as sucrose, in the dissolved form of sap.
Companion cells are involved in ATP production for active processes such as loading sucrose into sieve tubes.
The cytoplasm of the sieve tube elements and companion cells is linked through structures known as plasmodesmata which are gaps between cell walls which allow communication and flow of substances such as minerals between the cells.

Question 71

process of translocation occurs as follows:

Answer 71

1.Sucrose enters the phloem in a process known as active loading where companion cells use ATP to transport hydrogen ions into the surrounding tissue, thus creating a diffusion gradient, which causes the H+ ions to diffuse back into the companion cells.
2.Facilitated diffusion involving co-transporter proteins allows the returning H+ ions to bring sucrose molecules into the companion cells, thus causing the concentration of sucrose in the companion cells to increase.
3.As a result the sucrose diffuses out of the companion cells down the concentration gradient into the sieve tube elements through links known as plasmodesmata.
4. As sucrose enters the sieve tube elements, the water potential inside the tube is reduced, therefore causing water to enter via osmosis from the xylem, increasing the hydrostatic pressure of the sieve tube element.
5. As a result water moves down the sieve tube from an area of high hydrostatic pressure to an area of low hydrostatic pressure.
6. Eventually, sucrose is removed from the sieve tube elements by diffusion or active transport into the surrounding cells, thus increasing the water potential in the sieve tube. This in turn means that water leaves the sieve tube by osmosis back into the xylem, and as a result reduces the pressure in the phloem at the sink.

Question 72

Evidence for mass transport

Answer 72

pressure in the sieve tube elements, as shown by sap being released when the stem of a plant is cut.
- The concentration of sucrose is higher in the leaves (source) of plants than in roots (sink).
- Increases in sucrose levels in the leaves are followed by a similar increase in sucrose concentration in the phloem.
- Metabolic poisons/a lack of oxygen inhibit translocation of sucrose in the phloem.

Question 73

Evidence against mass transport

Answer 73

The function of the sieve plates is unclear as they would appear to hinder mass flow (some suggest though they have a structural function to help prevent bursting under pressure).
- Not all solutes move at the same speed, they should do if it is mass flow.
- Sucrose is delivered at more or less the same rate to all regions, rather than going more quickly to the ones with the lowest sucrose concentration, which the mass flow theory would suggest.