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GCSE Biology > B2 - Organisation > Flashcards

B2 - Organisation Flashcards

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1
Q

Where is lipase produced in the body (2 areas)?

A
  • Small intestine

- Pancreas

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2
Q

Where is protease produced in the body (2 areas)?

A
  • Stomach
  • Pancreas
  • Small intestine
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3
Q

Where is amylase produced in the body (3 areas)?

A
  • Small intestine
  • Mouth
  • Pancreas
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4
Q

What is the role of bile?

A
  • Emulsifies lipids

- Neutralises stomach acid

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5
Q

What chemical is used for a test to find protein?

A

Biuret reagent

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6
Q

What chemical is used for a test to find stach?

A

Iodine

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7
Q

What chemical is used for a test to find sugar?

A

Benedict’s solution

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8
Q

What chemical is used for a test to find lipids?

A

Sudan III / ethanol

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9
Q

What food uses biuret reagent to find it?

A

Protein

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10
Q

What food uses iodine to find it?

A

Starch

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11
Q

What food uses Benedict’s solution to find it?

A

Sugar

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12
Q

What food uses sudan III or ethanol to find it?

A

Lipids

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13
Q

What colour does biuret reagent turn when mixed with protein?

A

Pink / purple

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14
Q

What colour does iodine turn when mixed with starch?

A

Black / blue

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15
Q

What colour does Benedict’s solution turn when mixed with sugar?

A

Orange / red

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16
Q

What colour does sudan III / ethanol turn when mixed with lipids?

A

Red layer / cloudy

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17
Q

What is the role of the mouth?

A

Chew food into small pieces

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18
Q

What is the role of the stomach?

A

Churn / break down food

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19
Q

What is the role of the small intestine?

A

Absorb nutrients

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20
Q

What is the role of the large intestine?

A

Absorb water

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21
Q

What is the main function of the heart?

A

It’s responsible for pumping oxygenated and deoxygenated blood to different areas of the body

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22
Q

Which side of the heart sends deoxygenated blood to the lungs?

A

The right side

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23
Q

Which side of the heart sends oxygenated blood to the body?

A

The left side

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24
Q

What route does deoxygenated blood take through the heart?

A

Vena cava > right atrium > right ventricle > pulmonary artery > lungs

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25
Q

What route does oxygenated blood take through the heart?

A

Pulmonary vein > left atrium > left ventricle > aorta > body

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26
Q

Where is our natural pacemaker?

A

In the right atrium

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27
Q

What can be used to regulate an irregular heartbeat?

A

Artificial pacemaker

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28
Q

Our double circulatory system is made up of two circuits. What are they called?

A 
- Pulmonary circuit 
  (between the heart and 
  lungs)
- Systemic circuit (between 
  the heart and the other 
  organs)
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29
Q

What do red blood cells do?

A

Carry oxygen

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30
Q

What do white blood cells do?

A

Fight infection

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31
Q

What does plasma do?

A

Carry waste

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32
Q

What do platelets do?

A

Clot blood

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33
Q

What does CVD stand for?

A

Cardiovascular disease

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34
Q

What does CHD stand for?

A

Coronary heart disease

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35
Q

What are some treatments for CHD?

A
  • Statins
  • Stents
  • Replacement heart valves
  • Artificial blood
  • Heart transplant
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36
Q

What do statins do?

A

They are drugs to lower your cholesterol levels

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37
Q

How do stents work?

A

Catheter inserted, with stent inside, into coronary artery > balloon inflated > catheter removed

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38
Q

What is a replacement valve?

A

A metal or animal valve to replace a faulty valve

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39
Q

What is a heart transplant?

A

Transplanting / replacing your heart (needed in case of heart failure)

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40
Q

What happens in CHD?

A 
- Fatty deposits build up in 
  the arteries
- Narrows the lumen
- Reduces blood flow
- Heart gets a lack of 
  oxygen
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41
Q

What is a tissue?

A

A group of similar cells that work together to perform a specific function

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42
Q

What is the function of muscle tissue?

A

To contract to move what it’s attached to

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43
Q

What is the function of glandular tissue?

A

It makes and secretes chemicals like enzymes or hormones

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44
Q

Where is epithelial tissue found?

A

It covers some parts of the body, e.g. the inside of the gut

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45
Q

What is the role of muscular tissue in the stomach?

A

Moves the stomach wall to churn up food.

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46
Q

What is the role of epithelial tissue in the stomach?

A

Covers the inside and outside of the stomach.

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47
Q

Explain what is meant by the term “organ system”.

A

A group of organs working together to perform a specific function.

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48
Q

What does the digestive system do?

A

Breaks down and absorbs food.

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49
Q

What is the role of glands in the digestive system? Give 2 examples.

A

They produce digestive juices.

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50
Q

What is the role of the liver in the digestive system?

A

Produces bile

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51
Q

What is the role of the stomach and small intestine in the digestive system?

A
  • They both digest food

- Small intestine absorbs soluble food molecules

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52
Q

What is the role of the large intestine in the digestive system?

A

Absorbs water from undigested food (leaving faeces)

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53
Q

What are enzymes?

A

They are large proteins which break down large molecules into smaller, soluble ones

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54
Q

What are enzymes made out of?

A

Proteins are made of chains of amino acids.

These are folded into unique shapes (i.e. active sites).

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55
Q

Why can enzymes be described as biological catalysts?

A
  • The body needs to speed up chemical reactions
  • Raising body temperature isn’t a good way of doing this, because this accelerates unwanted reactions and harms cells
  • So we have enzymes which speed up reactions instead
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56
Q

What is a catalyst?

A

A substance which increases the speed of a reaction without being altered or used up in the reaction.

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57
Q

The substance that an enzyme acts on is called the ______

A

Substrate

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58
Q

Why do enzymes usually only catalyse one reaction?

A

For enzymes to work, the substrate has to fit into its active site. If it doesn’t, the reaction won’t be catalysed

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59
Q

Why is the lock and key model of enzymes slightly inaccurate?

A
  • The model shows the enzyme remaining the same after a reaction.
  • The active site actually changes shape a little as the substrate binds to it (to fit tighter).
  • This is referred to as the induced fit model.
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60
Q

Enzymes have an optimum ___ and ___, which is often ___

A

1) Temperature
2) pH
3) Neutral

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61
Q

What is meant by an enzyme being “denatured”? Describe how this happens and what leads up to it.

A
  • An increase in temperature will increase the rate of reaction until the enzyme reaches its optimum temperature.
  • At a certain temperature, bonds in an enzyme are broken.
  • This changes the shape of the active site- substrate doesn’t fit.
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62
Q

The enzyme amylase catalyses the breakdown of starch to maltose. Iodine can be used to detect starch- if starch is present, iodine solution will change from browny-orange to blue-black.

Describe how you could investigate the effect of pH on the rate of amylase activity.

A

1) Put a drop of iodine solution into every well of a spotting tile.
2) Place a bunsen burner on a heatproof mat and a tripod and gauze over the bunsen burner.
3) Put a beaker of water on top of the gauze and heat it until it reacher 35°C (measure using a thermometer). Try to keep the water temperature constant throughout the experiment.
4) Put a boiling tube in the beaker. Use a syringe to add 1cm3 of amylase solution and 1cm3 of a buffer solution (pH 5) to the boiling tube.
5) Use a different syringe to add 5cm3 of a starch solution to the boiling tube. Immediately mix the contents and start a stopwatch.
6) Use continuous sampling to record how long it takes for the amylase to break down all of the starch. Do this by using a pipette to take a sample from the boiling tube every 30 seconds and putting a drop into different wells of the spotting tile. When the iodine solution remains browny-orange, starch is no longer present.
7) Repeat the experiment with buffer solutions of different pH values to see how pH affects the time taken for the starch to be broken down.

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63
Q

The enzymes used in digestion are produced by ___ and then released into the ___ to mix with food.

A

1) Specialised cells in glands and in the gut lining

2) Gut

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64
Q

What do enzymes do to starch, proteins and fats, and why?

A

They are molecules too big to pass through the walls of the digestive system- they can’t be absorbed into the bloodstream. Enzymes break them down into smaller, soluble molecules.

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65
Q

Give 4 examples of smaller molecules that result from enzymes breaking down starches, proteins and fats.

A

Sugars (e.g. glucose and maltose), amino acids, glycerol and fatty acids

66
Q

What is starch?

A

A carbohydrate

67
Q

In what three places is amylase made?

A
  • The salivary glands
  • The pancreas
  • The small intestine
68
Q

What is amylase and what does it do?

A

It is a carbohydrase and it catalyses the breakdown of starch- a carbohydrate- into maltose and other sugars like dextrins.

69
Q

What do proteases do?

A

Convert proteins into amino acids

70
Q

What do lipases do?

A

Convert lipids into glycerol and fatty acids

71
Q

What does the body do with the products of digestion?

A

Make them into new carbohydrates, proteins and lipids

Some glucose is used in respiration

72
Q

Where is bile produced?

A

Liver

73
Q

Where is bile stored before it’s released into the small intestine?

A

Gall bladder

74
Q

What does bile do?

A
  • Neutralises stomach acid: hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline so it neutralises the acid and makes conditions alkaline, which is best for enzymes in the small intestine.
  • Emulsifies fats: breaks fats into tiny droplets, giving fats a bigger surface area for the enzyme lipase to work on. This makes its digestion faster.
75
Q

An enzyme controlled reaction was carried out at pH 4. After 60 seconds, 33cm3 of product had been released. Calculate the rate of reaction in cm3 s-1.

A

33/60 = 0.55cm3 s-1

76
Q

What is the formula used to calculate the rate of reaction for a certain pH?

A

Amount of product formed = change

change/time(s)

(units: cm3 s-1 or cm3/s)

77
Q

What is the formula for mean rate of reaction?

A

mean rate of reaction = quantity of reactant used ÷ time taken

mean rate of reaction = quantity of product formed ÷ time taken

78
Q

What enzyme do the salivary glands produce?

A

Amylase

79
Q

What digestive enzyme does the stomach produce? What other substance is produced by the stomach and why?

A
  • Pepsin (a type of protease).

- Hydrochloric acid, to kill bacteria, and to give the right pH (2) for pepsin to function.

80
Q

What is the function of the stomach?

A
  • Pummels food with its muscular walls.
  • Produces pepsin.
  • Produces HCl - to kill bacteria, and to give the right pH (2) for pepsin to function
81
Q

What is the function of the liver?

A

Produce bile

82
Q

What is stored in the gall bladder?

A

Bile

83
Q

What is the function of the pancreas?

A

Produces the enzymes protease, amylase and lipase and releases these into the small intestine

84
Q

What is the function of the small intestine?

A
  • Produces the enzymes protease, amylase and lipase to complete digestion.
  • Here, nutrients from digested food are absorbed into the blood.
85
Q

What is the function of the large intestine?

A

This is where excess water is absorbed from food.

86
Q

What is the function of the rectum?

A

This is where faeces is stored before it is excreted through the anus.

87
Q

Describe the pathway of ingested food as it travels through the digestive system. (6 marks)

A

1) When the food is chewed in the mouth, it is digested by the enzyme amylase in saliva (produced by the salivary glands).
2) It travels town the oesophagus to the stomach, which pummels the food with its muscular walls. The stomach also produces pepsin, to digest the food, and hydrochloric acid, to kill bacteria and provide the optimal pH for pepsin to function.
3) When the food reaches the small intestine, it is neutralised by bile (produced in the liver and stored in the gall bladder).
4) It is digested by the enzymes protease, amylase and lipase (produced mostly by the pancreas and a little by the small intestine).
5) Nutrients from the digested food are then absorbed into the bloodstream.
6) In the large intestine, excess water is absorbed from the food, leaving faeces.
7) The faeces is stored in the rectum before being excreted through the anus

88
Q

Before doing a food test, how would you prepare a food sample?

A
  • Break a piece of food up with a mortar and pestle.
  • Transfer it to a beaker and stir in some distilled water.
  • Filter out any solid bits of food
89
Q

How would you test for reducing sugars?

A

Using the Benedict’s test

90
Q

How would you test for starch?

A

Using iodine solution

91
Q

How would you test proteins?

A

Using the biuret test

92
Q

How would you test for lipids?

A

Using the Sudan III / ethanol test

93
Q

What would be a positive result for the Benedict’s test?

A

Testing for reducing sugars

The solution starts off blue, then can change to green, to yellow and to brick-red, depending on the concentration of sugar.

94
Q

What would be a positive result for the iodine solution test?

A

Testing for starch.

The solution will change from browny-orange to blue-black.

95
Q

What would be a positive result for the Biuret test?

A

Testing for proteins.

The solution will change from blue to pink to purple.

96
Q

What would be a positive result for the Sudan III test?

A

Testing for lipids.

The mixture will separate into 2 layers, the top one (containing the lipids) bright red.

97
Q

What is the thorax?

A

The top part of your body (bottom of neck downwards), separated from the lower part by the diaphragm.

98
Q

What surrounds the lungs?

A
  • Pleural membranes.
  • Intercostal muscles.
  • Protected by the ribcage.
99
Q

The air you breathe in travels through the __, which splits into 2 tubes called the __ (each one is a __), one going to each lung.

Each of these splits into progressively smaller tubes called __, which finally end at small bags called __.

A

1) Trachea
2) Bronchi
3) Bronchus
4) Bronchioles
5) Alveoli

100
Q

Where does gas exchange happen?

A

The lungs contain millions of tiny air sacs, called alveoli, surrounded by a network of blood capillaries. Gas exchange happens between the alveoli and capillaries

101
Q

Describe what happens during gas exchange.

A

Blood passing through capillaries by the alveoli has just returned to the lungs from the body, so it contains lots of carbon dioxide and very little oxygen.

An alveolus contains air just breathed in, so the concentrations of these gases are the other way around.

Oxygen diffuses out of the alveolus into the blood; carbon dioxide diffuses out of the blood into the alveolus, to be breathed out

102
Q

Describe how gas is exchanged between body cells and capillaries.

A

When blood reaches body cells, oxygen is released from red blood cells and diffuses into body cells.

Carbon dioxide diffuses out of body cells and into the blood.

The blood is then carried to the lungs.

103
Q

Through which vein does blood flow into the right atrium?

A

Vena cava

104
Q

Through which vein does blood flow into the left atrium?

A

Pulmonary vein

105
Q

Through which artery does blood flow out of the left ventricle?

A

Aorta

106
Q

Why does the heart have valves?

A

To assure that blood flows in the right direction - to prevent it flowing backwards.

107
Q

Humans have a double circulatory system. Describe the flow of blood through each circuit and how they fit together.

A

1) In the first one, the right ventricle pumps deoxygenated blood to the lungs, to take in oxygen; the blood then returns to the heart.
2) In the second one, the left ventricle pumps oxygenated blood to all our organs; deoxygenated blood returns to the heart to be pumped out to the lungs again.

108
Q

Where in the heart is the natural pacemaker?

A

In the wall of the right atrium.

109
Q

How does the heart’s natural pacemaker work?

A

It is a group of cells which produce a small electric impulse which spreads to the surrounding muscle cells, causing them to contract. This causes the heart to beat regularly.

110
Q

Arteries carry blood __ the heart; veins carry blood __ the heart.

A

1) Away from

2) Towards

111
Q

Describe the structure of arteries and how this relates to their function.

A
  • Strong, thick and elastic walls to carry blood pumped out by the heart at high pressure. There is a thick muscular layer and elastic fibres.
  • Small lumen (doesn’t need to be big as the blood is at high pressure).
112
Q

Describe the structure of veins and how this relates to their function.

A

1) Walls thinner than arteries’ as blood is at lower pressure in veins.
2) Elastic fibres.
3) Big lumen to help the blood to flow despite the low pressure.
4) Valves keep blood flowing in the right direction.

113
Q

Describe the structure of capillaries and how this relates to their function.

A

Thin and permeable (1 cell thick) walls allow the diffusion of substances at a high rate.

Capillaries carry blood close to cells to allow food and gases to be exchanged.

114
Q

What are platelets and what is their function?

A

They are small fragments of cells (no nucleus) which help blood to clot at wounds. This prevents excessive bleeding, bruising and infection.

115
Q

Plasma is the liquid that carries the contents of the blood. Name at least 3 substances carried by plasma (there are 7).

A

1) Red blood cells, white blood cells, platelets.
2) Nutrients/soluble products of digestion - e.g. glucose.
3) Carbon dioxide, oxygen.
4) Urea.
5) Hormones.
6) Proteins.
7) Antibodies, antitoxins.

116
Q

What is coronary heart disease?

A

Where the coronary arteries (which supply blood to the muscles of the heart) become blocked by buildup of fatty deposits.

This narrows the arteries, restricting blood flow so that there is a lack of oxygen to the heart muscle, risking a heart attack.

117
Q

Give 3 advantages of stents

A

1) Lower the risk of cardiac arrest
2) Effective for a long time
3) Recovery time from surgery is relatively quick

118
Q

Give 3 disadvantages of stents.

A

1) Risk of complications during operation, e.g. heart attack
2) Risk of infection from surgery
3) Risk of thrombosis (patients developing a blood clot near the stent)

119
Q

How can cholesterol lead to coronary heart disease?

A

Cholesterol is an essential lipid that the body needs to function properly, but producing too much LDL cholesterol causes fatty deposits to form inside arteries.

120
Q

How do statins work?

A

The body producing too much LDL cholesterol causes fatty deposits to form inside arteries. Statins are drugs which reduce the amount of LDL present in the bloodstream, slowing the rate of fatty deposits forming.

121
Q

Give 3 advantages of statins.

A

1) Reduce risk of strokes, coronary heart disease and heart attacks.
2) As well as reducing LDL cholesterol, statins increase the amount of HDL cholesterol produced, a beneficial type that removes LDL cholesterol from the blood.
3) Studies suggest statins may prevent some other diseases.

122
Q

Give 3 disadvantages of statins.

A

1) There is a risk that someone forgets to take the drug.
2) Can cause negative side effects, e.g. headaches, kidney failure, liver damage or memory loss.
3) The effect of the drug is not instant.

123
Q

Give 3 disadvantages of heart transplants.

A

1) Donor organs aren’t always available straight away.
2) A donor heart may be rejected by the receiver’s immune system.
3) Transplant surgery can lead to bleeding and/or infection.

124
Q

Give 2 advantages of artificial hearts.

A

1) They can be sourced straight away (compared to donor organs) so keep people alive in emergencies.
2) They’re less likely to be rejected by someone’s immune system than donor hearts.

125
Q

Give 3 disadvantages of artificial hearts.

A

1) Surgery can lead to bleeding and/or infection.
2) They don’t work as well as real hearts - parts could wear out, or the motor could fail.
3) Blood doesn’t flow smoothly through them, causing clots and leading to strokes. (The patient has to take drugs to thin their blood to prevent this.)

126
Q

How can heart valves become damaged?

A
  • Can be damaged/weakened by heart attacks, infection or age.
  • This can cause stiffening of tissue, so that it won’t open properly.
  • Or a valve could become leaky, allowing blood to flow in both directions.
127
Q

How does artificial blood keep people alive in emergencies?

A
  • When someone loses a lot of blood, their heart can still pump the remaining red blood cells to their organs, provided that they have a high enough volume of blood.
  • Artificial blood is a saline solution which is used as a substitute for this lost volume.
  • It keeps people alive, and may give someone enough time to produce new red blood cells (or they’ll need a transfusion).
128
Q

What is health?

A

The state of physical and mental wellbeing.

129
Q

Give 4 examples of how different diseases can interact.

A

1) Defects of the immune system make people more vulnerable to communicable diseases.
2) Viruses living in cells can trigger cancers.
3) Immune reactions caused by pathogens can trigger allergic reactions or rashes, or worsen athsma symptoms.
4) Severely ill physical health can trigger mental illnesses.

130
Q

Discuss the human cost of non-communicable (non infectious) diseases.

A
  • Death
  • Lower quality of life
  • Shorter lifespan
  • Affects loved ones around those suffering
131
Q

Discuss the financial cost of non-communicable (non infectious) diseases.

A
  • Research and treatment is very expensive for health organisations.
  • Families have to accomodate for someone with a disease (which is costly), e.g. moving house or adapting their home.
  • If someone with a disease has to stop working or dies, their income stops, affecting their family and the economy.
132
Q

What are the 3 main types of risk factor for non-communicable diseases?

A
  • Lifestyle choices
  • Substance’s in someone’s body or environment
  • Genetics
133
Q

Give at least 3 (there are 6 in total) examples of causual mechanisms (things which are proven to directly cause) for non-communicable diseases.

A

1) Diet, smoking and exercise risk cardiovascular disease.
2) Smoking risks lung disease and lung (and some other types of) cancer.
3) Obesity risks Type 2 diabetes and cancer.
4) Alcohol risks damaging liver and brain function.
5) Smoking and alcohol affect the health of unborn babies.
6) Carcinogens, including ionising radiation, are risk factors of cancer.
7) UV exposure risks skin cancer.
8) Certain viruses increase the chances of developing certain cancers.

Many diseases are caused by the interaction of a number of factors.

134
Q

What is cancer?

A

Uncontrolled cell division leads to the formation of a tumour. But not all tumours are cancerous - only malignant ones.

135
Q

What are the 2 types of tumour?

A
  • Benign

- Malignant

136
Q

What are benign tumours?

A

Growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body.

137
Q

What are malignant tumours?

A

Cancerous growths of abnormal cells which invade neighbouring tissues. Malignant cells can break off and spread to different parts of the body, through the blood, where they form secondary tumours.

138
Q

Name 5 risk factors of cancer.

A

1) Smoking risks lung (and some other types of) cancer.
2) Obesity/diet.
3) Carcinogens (substances capable of causing cancer) e.g. ionising radiation, alcohol, UV exposure (causes skin cancer)
4) Certain viruses increase the chances of developing certain cancers.
5) There are genetic risk factors for some cancers.

139
Q

Where is plant epidermal tissue found?

A

It covers the whole plant.

140
Q

Where are xylem and phloem tissues found?

A

Through the roots, stems and leaves of plants.

141
Q

Where is meristem tissue found? What is its function?

A
  • Found at the growing tips of shoots and roots.

- It’s able to differentiate into many different types of plant cell, allowing the plant to grow.

142
Q

Name the 4 types of tissue found in leaves.

A
  • Upper epidermis
  • Palisade mesophyll tissue
  • Spongy mesophyll tissue
  • Lower epidermis
143
Q

How is the structure of plant epidermal tissue related to its function?

A

It is covered with a waxy cuticle, which reduces water lost by evaporation

144
Q

How is the structure of the upper epidermis related to its function?

A

It is transparent so that light can pass through to the palisade layer.

145
Q

How is the structure of the palisade mesophyll tissue related to its function?

A

It has lots of chloroplasts; most photosynthesis happens here. It is near the top of the leaf, where it can get the most light

146
Q

How is the structure of spongy mesophyll tissue related to its function?

A

It contains many air spaces, which increase the rate of diffusion of gases in + out of cells

147
Q

How is the structure of the lower epidermis (at the bottom of the leaf) releated to its function?

A

It’s an exchange surface, covered in holes, called stomata, which allow the direct diffusion of carbon dioxide into the leaf (and oxygen + water vapour out).

The opening + closing of stomata is controlled by guard cells in response to environmental conditions

148
Q

How is the structure of xylem and phloem tissue releated to its function?

A

These cells form a network of vascular bundles which deliver water and other nutrients to the entire leaf, and take away the glucose produced by photosynthesis. They also help support the leaf’s structure.

149
Q

What is the role of phloem tubes?

A

They transport food substances (mainly dissolved sugars), made in the leaves, to the rest of the plant for immediate use (like growth) or for storage.

This process is called translocation and transport goes in both directions.

150
Q

What is the structure of phloem tissue?

A

It’s made of columns of elongated living cells, with small pores in the end walls that allow cell sap to flow through.

151
Q

What is the process of phloem tubes transporting food called?

A

Translocation

152
Q

What is the function of xylem tissue?

A

The tubes carry water and mineral ions from the roots to the stem and leaves. Xylem tubes only transport things upwards.

This is called the transpiration stream

153
Q

The movement of water from the roots, through the xylem tubes and out of the leaves is called what?

A

The transpiration stream

154
Q

What is transpiration?

A

The evaporation of water from the surface of plants. Most transpiration happens at the leaves.

155
Q

Why is there a constant transpiration stream of water through plants?

A

1) Leaves have to have stomata for gas exchange and photosynthesis.
2) This, however, means that water is lost through diffusion out of the stomata.
3) So more water has to be soaked up from the roots.
4) This creates a constant stream of water through the plant.

156
Q

What are the 4 main factors that affect the rate of transpiration?

A

1) Light intensity: the brighter the light, the greater the transpiration rate (photosynthesis can’t happen in the dark, so stomata aren’t opened, so no water is lost).
2) Temperature: the warmer it is, the greater the transpiration rate.
3) Air flow: the more wind around a plant, the greater the transpiration rate (water vapour is constantly blown away, maintaining a high concentration gradient for diffusion).
4) Humidity: the drier the air, the greater the transpiration rate (concentration gradient higher).

157
Q

How can the rate of transpiration be measured?

A

Measuring the rate of uptake of water by a plant (because you can assume this is directly related to water loss). This can be recorded with a potometer.

158
Q

How are guard cells adapted to open and close stomata?

A

Their kidney shape opens and closes the stoma (singular for stomata) in the middle.

It has thin outer walls and thickened inner walls to make the opening and closing work

159
Q

How are guard cells adapted for gas exchange and controlling water loss from leaves?

A

1) When the plant has a lot of water, the guard cell becomes turgid, opening the stoma for gas exchange (for photosynthesis).
2) When the plant is transpiring faster than water is being taken up by the roots, the guard cell becomes flaccid, closing the stoma to limit water loss and wilting.
3) They are sensitive to light and close at night (when photosynthesis can’t happen) to prevent water loss.
4) There are more guard cells on the underside of a leaf, which is cool and shaded, compared to the upper side. These conditions reduce the rate of transpiration

160
Q

How is a leaf’s structure adapted to maximise the rate of diffusion and gas exchange needed for photosynthesis? (6 marks)

A

1) The lower epidermis is an exchange surface, covered in stomata, through which carbon dioxide diffuses directly into the leaf, and oxygen and water vapour diffuse out.
2) The flattened shape of the leaf increases the area of this exchange surface, so that diffusion happens at a faster rate.
3) Air spaces between the walls of cells in the spongy mesophyll layer increase the surface area, increasing the rate of diffusion of gases, and therefore of gas exchange.
4) Therefore, the rate of gas exchange is maximised, so the rate of photosynthesis is also maximised

GCSE Biology (7 decks)

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