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A Level Biology > Exchange of Substances > Flashcards

Exchange of Substances Flashcards

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1
Q

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

A

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

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2
Q

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

A

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

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3
Q

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

A

Changes that increase surface area e.g. folding;body parts become larger; elongating shape;developing a specialised gas exchange surface

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4
Q

Why do multicellular organisms require specialised gas exchange surfaces?

A

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 a single-celled organism

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5
Q

Name 3 features of an efficient gas exchange surface

A
  1. Large surface area e.g folded membranes in mitochondria
  2. Thin/short distance e.g walls of capillaries
  3. Steep concentration gradient, maintained by blood supply or ventilation e.g alveoli
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6
Q

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

A

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

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7
Q

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

A

•Spiracles:holes on the body’s surface which may be open/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

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8
Q

Explain the process of gas exchange in insects

A

•Gases move in and out of 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

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9
Q

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

A

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

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10
Q

Name and describe the 2 main features of a fish’s gas transport system

A

Gills:located within body,supported by arches, along which are multiple projections of gill filaments
Lamellae:at right angles to gill filaments,increases surface area. Blood&water flow opposite directions

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11
Q

Explain the process of gas exchange in fish

A

•Fish opens it mouth to enable water to flow in,then closes its mouth to increase pressure
•Water passes over lamellae & oxygen diffuses into bloodstream
•Waste CO2 diffuses into water and flows back out of gills

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12
Q

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

A

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

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13
Q

Name and describe 3 adaptations of a leaf that allow efficient gas exhange

A

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

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14
Q

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

A

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

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15
Q

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

A

Nasal cavity —> trachea —> bronchi —> bronchioles —> alveoli

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16
Q

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

A

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

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17
Q

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

A

•Wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes
•Lined by ciliated epithelium cells that move mucus towards the throat to be swallowed,preventing lung infections
•Carries air to the bronchi

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18
Q

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

A

•Supported by rings of cartilage that are lined by ciliated epithelium cells
•Narrow than in trachea and there are 2 of them, 1 for each lung
•Allow passage of air into the bronchioles

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19
Q

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

A

•Narrower than the bronchi
•Don’t need to be kept open by cartilage, so mostly have only muscle and elastic fibres so that they can contract&relax easily during ventilation
•Allow passage of air into alveoli

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20
Q

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

A

•Mini air sacs, lined with epithelium cells, site of gas exchange
•Walls only 1 cell thick,covered with a network of capillaries,300 million in each lung all of which facilitates gas diffusion

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21
Q

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

A

•External intercostal muscles contract (Internal relax),pulling ribs up and out
•Diaphragm contracts and flattens
•Volume if thorax increases
•Air pressure outside lungs is higher than outside so air moves in to rebalance

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22
Q

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

A

•External intercostal muscles relax (internal contract),bringing ribs down and in
•Diaphragm relaxes & domes upwards
•Volume of the thorax decreases
•Air pressure inside the lungs is higher than outside so air moves out to rebalance

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23
Q

What is tidal volume?

A

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

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24
Q

What is breathing rate?

A

The number of breaths we take per minute

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25
Q

How do you calculate pulmonary ventilation rate?

A

Tidal volume x breathing rate
Can be measured using a spirometer

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26
Q

Define digestion

A

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

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27
Q

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

A

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

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28
Q

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

A

•Amylase —> starch into smaller polysaccharides
•Maltase —> maltose into 2x glucose
•Sucrase —> sucrose into glucose and fructose
•Lactase —> lactose into glucose and galactose

29
Q

Where are lipids digested?

A

The small intestine

30
Q

What needs to happen before lipids can be digested?

A

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

31
Q

How are lipids digested?

A

Lipase hydrolyses the ester bond between the monoglycerides and fatty acids

32
Q

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

A

•Endopeptidases:break between specific amino acids in middle of a polypeptide
•Exopeptidases:break between specific aminos acids at the end of a polypeptide
•Dipeptidases:break dipeptides into amino acids

33
Q

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

A

Through co-transport

34
Q

Which molecules require co-transport?

A

Amino acids and monosaccharides

35
Q

Explain how sodium ions are involved in co-transport

A

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

36
Q

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

A

The molecules are non-polar, meaning they can easily diffuse across the membrane of the epithelial cells

37
Q

Describe the structure of haemoglobin

A

Globular, water soluble
Consists of 4 polypeptide chains, each carrying a haem group (quaternary structure)

38
Q

Describe the role of haemoglobin

A

Presents 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

39
Q

Name 3 factors affecting oxygen-haemoglobin binding

A

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

40
Q

How does partial pressure of oxygen affect oxygen-haemoglobin binding?

A

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

41
Q

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

A

As partial pressure of carbon dioxide increases, the condition’s become acidic causing haemoglobin to change shape. The affinity of haemoglobin for oxygen therefore decreases, so oxygen is released from haemoglobin. Known as Bohr effecf

42
Q

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

A

It’s hard for the first oxygen molecule to bind. Once it does, it changes the shape to make it easier for the 2nd and 3rd molecules to bind, known as positive cooperativity. Its then slightly harder for the 4th oxygen molecule to bind as there’s a low chance of finding a binding site

43
Q

Explain why oxygen binds to haemoglobin in the lungs

A

•Partial pressure of of oxygen is high
•Low concentration of carbon dioxide in the lungs, so affinity is high
•Positive cooperativity (after the 1st oxygen molecule binds, binding of subsequent molecules is easier)

44
Q

Explain why oxygen is released from haemoglobin in respiring tissues

A

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

45
Q

What do oxyhaemoglobin dissociation curves show?

A

Saturation of haemoglobin with oxygen (in %), plotted against partial pressure of oxygen (in kPa)
Curves further to the left show the haemoglobin has a higher affinity for oxygen

46
Q

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

A

Curve shifts to the right because haemoglobin’s affinity for oxygen has decreased

47
Q

Name 3 common features of a mammalian circulatory system

A

1.Suitable medium for transport,water -based to allow substances to dissolve
2.Means of moving the medium and maintaining pressure throughout the body, such as the heart
3.Means of controlling flow so it remains unidirectional, such as valves

48
Q

Relate the structure of the chambers to their function

A

•Atria:thin-walled and elastic,so they can stretch when filled with blood
•Ventricles:thick muscular walls pump blood under high pressure. Left is thicker than right as has to pump blood all the way around the body

49
Q

Relate the structure of the vessels to their function

A

•Arteries:thick walls to handle high pressure without tearing and are muscular&elastic to control blood flow
•Veins:thin walls due to lower pressure, therefore requiring valves to prevent backflow of blood. Have less muscular&elastic tissue as dont have to control blood flow

50
Q

Why are 2 pumps (left and right) needed instead of 1?

A

To maintain blood pressure around the whole body. When blood passes through the narrow capillaries of the lungs, pressure drops sharply and so wouldnt be flowing strongly enough to continue around whole body.So its returned to heart to increase pressure

51
Q

Describe what happens during cardiac diastole

A

Heart is relaxed.Blood enters the atria increasing pressure and pushing open the atrioventricular valves. This allows blood to flow into the ventricles. Pressure in the heart is lower than in arteries, so semilunar valves remain closed

52
Q

Describe what happens during atrial systole

A

The atria contract, pushing any remaining blood into the ventricles

53
Q

Describe what happens during ventricular systole

A

Ventricles contract. Pressure increases closing the atrioventricular valves to prevent backflow and opening the semi lunar valves. Blood flows into the arteries

54
Q

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

A

•Sinoatrial node (SAN)=wall of right atrium
•Atrioventricular node (AVN)=in between the 2 atria

55
Q

What does myogenic mean?

A

The hearts contraction is initiated from within the muscle itself, rather than by nerve impulses

56
Q

How is the structure of capillaries suited to their function?

A

•Walls are only 1 cell thick,short diffusion pathway
•Very narrow,so they 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

57
Q

What is tissue fluid?

A

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

58
Q

How is tissue fluid formed?

A

As blood is pumped through increasingly small vessels,this creates hydrostatic pressure which forces fluid out of capillaries.It bathes the cells&then returns to the capillaries when the hydrostatic pressure is low enough

59
Q

How is water transported in plants?

A

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

60
Q

Explain the cohesion-tension theory?

A

Water molecules from hydrogen bonds with each other,causing them to ‘stick’ together (cohesion).The surface tension of water creates sticking effect too. So as water is lost through transpiration, more can be drawn up the stem

61
Q

What are the 3 components of phloem vessels?

A

•Sieve-tube elements=form a tube to transport sucrose in the dissolved formed of sap
•Companion cells=involved in ATP production for active loading of sucrose into sieve tubes
•Plasmodesmata=gaps between cell wall where cytoplasm links,allowing substances to flow

62
Q

Name the process whereby organic materials are transported around the plant

A

Translocation

63
Q

How does sucrose in the leaf move into the phloem?

A

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

64
Q

How do phloem vessels transport sucrose around the plant?

A

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

65
Q

Give evidence for the mass flow hypothesis of translocation

A

•Sap is released when a stems cut, so there must be pressure in the phloem
•There’s a higher sucrose concentration in the leaves than the roots
•Increasing sucrose levels in the leaves results in increased sucroses in the phloem

66
Q

Give evidence against the mass flow hypothesis of translocation

A

•The structure of sieve tubes seems 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 the lowest sucrose concentration first

67
Q

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

A

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

68
Q

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

A

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

A Level Biology (7 decks)

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