Paper 2 Questions

Question 1

Why does the layer of spongy mesophyll have gaps between its cells? [2]

Answer 1

• gas exchange [1]
• so carbon dioxide can enter cells/ so oxygen can leave the cells [1]

Question 2

Describe how stomata open [3]

Answer 2

• guard cells [1]
• take in water [1]
• through osmosis [1]
• (guard cells) become turgid/ change shape/swell [1]

Question 3

A leaf peel from the upper surface of a leaf showed no stomata, whereas a leaf peel from the lower surface did.
Explain why it is an advantage to have this distribution of stomata in the upper and lower surfaces of the leaf [2]

Answer 3

• no stomata (in upper surface) to reduce water loss [1]
• water loss during transpiration/ evaporation [1]
  OR
• stomata (on lower surface) allow gas exchange [1]
• gas exchange is required for photosynthesis [1]

Question 4

Iguanas are lizards.
Some species of iguana live on hot islands in the pacific ocean and use the environment to regulate their body temperature.
As their body temperature increases, so does their oxygen consumption. Explain why the body temperature of the iguana affects its oxygen consumption. [3]

Answer 4

• {chemical/metabolic/enzyme} reactions are increased at higher temperatures [1]
• (more) respiration occurs [1]
• (more respiration) requires more oxygen [1]

Question 5

Iguanas do not have sweat glands.
When an iguana is too hot, it pants by opening its mouth to cool it down.
Explain why this behaviour helps to cool the iguana down. [2]

Answer 5

• (panting) causes water loss [1]
• causing evaporation [1]

Question 6

Where in the human brain is the thermoregulartory centre? [1]

Answer 6

Hypothalamus

Question 7

Explain the role of vasodilation in thermoregulation [4]

Answer 7

• vasodilation helps to cool the body down [1]
• more blood flows near the skin surface [1]
• less blood flows through the shunt valve [1]
• causing increased thermal energy loss [1]

Question 8

Explain why reducing the water content of a food item, such as strawberry jam, can help in its preservation [2]

Answer 8

• reduces the number of microorganisms that can reproduce [1]
• reduces the decay processes

Question 9

Some respirometers read the movement of a bubble along a capillary tubing
Carbon dioxide can affect the measurement of oxygen used in this type of respirometer.
State a chemical that could be placed in a respirometer that would stop carbon dioxide from affecting the experiment. [1]

Answer 9

• soda lime [1]
• cotton wool soaked with potassium hydroxide [1]

Question 10

Explain why cellular respiration is essential for living organisms. [2]

Answer 10

An explanation linking:
* to release energy (1)
* for metabolic processes / chemical reactions (1)

Question 11

Describe how a student could test a sample of urine for the presence of protein. [2]

Answer 11

• add Biuret {reagent / solution} /do the biuret test (1)
• colour change (from blue) to purple protein is present (1)

Question 12

Urine contains urea.
State how urea is formed in the human body. [2]

Answer 12

• (breakdown of) amino acids (1)
• in the liver (1)

Question 13

During clomifene therapy, a woman takes a clomifene tablet each day for the first five days
of her menstrual cycle.
Describe the changes that would happen inside the ovaries during the first five days of this treatment. [2]

Answer 13

• one or more ova will start to mature (1)
• (inside the) follicles (1)
• oestrogen is released (1)

Question 14

During clomifene therapy, the woman has a blood test on day 20 of the menstrual cycle.
The blood test shows a high level of progesterone.
Explain the cause of this high level of progesterone on day 20 of the menstrual cycle. [2]

Answer 14

• (day 20) is after ovulation / after the egg has been released (1)
• so the corpus luteum produces progesterone (1)
• to maintain the lining of the uterus (1)

Question 15

Nitrogen is cycled through the environment.
Describe the roles of bacteria in the nitrogen cycle. [4]

Answer 15

• decomposers break down waste matter (into ammonia) (1)
• nitrifying bacteria convert ammonia / nitrifying bacteria make {nitrites / nitrates} (1)
• nitrogen fixing bacteria convert nitrogen into nitrates (1)
• denitrifying bacteria {convert nitrates / release nitrogen} (1)

Question 16

Describe two ways in which the human small intestine is adapted for dissolving small food molecules [2]

Answer 16

• Highly folded surface / microvilli / villi to increase surface area to volume ratio; [1 mark]
• Thin wall between small intestine (lumen) and capillaries/blood supply to make diffusion distance as short as possible; [1 mark]
• an efficient blood supply to remove absorbed substances / maintain concentration gradients; [1 mark]

Question 17

Describe the features that make a gas exchange surface efficient [3]

Answer 17

• Large surface area; [1 mark]
• Thin membrane/barrier to reduce the diffusion distance; [1 mark]
• Large concentration gradient; [1 mark]
• Adequate supply of gas; [1 mark]
• Efficient removal of waste gases (e.g CO2); [1 mark]

Question 18

Describe how starch is broken down into glucose. [2]

Answer 18

Any two from:
* enzyme / amylase / carbohydrase (1)
* starch fits into the active site (1)
* bonds (between glucose molecules in starch) broken (1)

Question 19

Which food group is digested by trypsin? [1]

Answer 19

Protein

Question 20

Explain how phototropism is controlled in plant shoots. [3]

Answer 20

An explanation linking three of the
following:
* phototropism is controlled by the hormone auxin (1)
* auxins move to the shaded side of the shoot (1)
* causing cell elongation (1)
* causing the shoot to bend towards the light (1)

Question 21

The scientist selects an area near the edge of the woodland where many stinging nettles are growing.
This area is partly shaded by the trees.
Describe how the scientist should use a belt transect to investigate how light intensity affects the growth of stinging nettles. [3]

Answer 21

A description including three from:
* place a quadrat along a {rope / tape} measure (1)
* tape measure to measure along the transect (1)
* measure light intensity at different distances (from the wood) (1)
* measure the stinging nettles {along the transect / at different light intensities} (1)
* way of measuring growth of stinging nettles (in the quadrats) (1)

Question 22

Describe how to test for glucose in the dialysis fluid. [3]

Answer 22

• add Benedict’s solution (to some dialysis fluid) (1)
• {heat / boil / put in water bath} (1)
• see if it turns {green /yellow / orange / red} (1)

Question 23

Decomposers in the soil convert… [1]

Answer 23

urea into ammonia

Question 24

What does blackspot fungus indicate about the air quality? [1]

Answer 24

• clean air/ low sulfur dioxide

Question 25

Explain how crop rotation increases nitrate levels in the soil. [3]

Answer 25

• leguminous crops planted (1)
• that have nitrogen-fixing bacteria (1)
• in root (nodules) (1)
• which fix nitrogen (gas) (1)

Question 26

Explain why increased nitrate levels in the soil improve crop yield. [2]

Answer 26

• nitrates are needed to make {protein / amino acids} (1)
• which are needed for growth (1)

Question 27

Explain how high levels of amino acids in the blood cause a high concentration of urea in urine. [4]

Answer 27

• because excess amino acids are broken down into urea (1)
• amino acids broken down in the liver (1)
• it is then transported in the blood to the kidney (1)
• enter the nephron (1)
• during ultrafiltration (1)
• pass through the nephron / not reabsorbed back into the blood (1)
• (so urine with a high concentration of urea) forms in the collecting duct (1)

Question 28

Outline how nitrogen in the air is converted into nitrates for plants to use [2]

Answer 28

• Nitrogen fixing bacteria (in the root nodules) convert atmospheric nitrogen to nitrates; [1 mark]
• (The heat and pressure of) lightning combines oxygen and nitrogen in the atmosphere; [1 mark]

Question 29

As earthworms move through the soil, they create air pockets between the soil particles. Suggest why this may lead to an increase in nutrients in the soil. [4]

Answer 29

• There is more oxygen available (due to air pockets); [1 mark]
• This increases aerobic respiration; [1 mark]
• Of bacteria, fungi, decomposers, microorganisms; [1 mark]
• (Therefore) there is an increased rate of decay / decomposition of dead plant and animal material / organic material OR more nutrients are released from dead organic material through decomposition; [1 mark]

Question 30

Describe the role of bacteria in the nitrogen cycle [4]

Answer 30

• Decomposers break down waste matter/dead organisms (into ammonia); [1 mark]
• Nitrifying bacteria convert ammonia / nitrifying bacteria make nitrites/nitrates; [1 mark]
• Nitrogen fixing bacteria convert nitrogen into nitrates; [1 mark]
• Denitrifying bacteria convert nitrates/release nitrogen; [1 mark]
  Accept nitrification for nitrifying bacteria
  Accept ammonia/nitrogen compounds for nitrates

Question 31

State 3 ways in which the concentration of nitrates in the soil can be increased [3]

Answer 31

• (Add) artificial fertilisers / nitrates / named nitrate compound; [1 mark]
• (Add) manure / slurry / faeces / compost / decomposing matter / (use) green manuring; [1 mark]
• Use crop rotation; [1 mark]
• Nitrogen fixing bacteria; [1 mark]
• Nitrifying bacteria / nitrification; [1 mark]