Paper 1 PPQ

Question 1

The student tried to look at cells using a microscope. Suggest one reason why the student could not see any cells when looking.

Answer 1

any 1 of the following:
- no cells in the field of view
- slide / mirror not in correct position
- (objective) lens not clicked into place or (objective) lens dirty
- microscope not focussed

Question 2

A student prepared some animal cells to view using a microscope. Name two pieces of laboratory equipment the student could have used to prepare cells to view using a microscope.

Answer 2

any 2 of the following:
- (microscope) slide
- cover slip
- dye / stain
- (mounted) needle
- pipette / dropper
- scalpel
- forceps / tweezers

Question 3

Red blood cells are specialised animal cells. Compare the structure of a red blood cell with the structure of a plant cell. [6 marks]

Answer 3

• red blood cell has no nucleus and plant cell has a nucleus
• red blood cell has no cell wall and plant cell has a cell wall
• red blood cell is a biconcave disc
• red blood cell contains haemoglobin and and plant cell has chloroplasts
• red blood cell has no (permanent) vacuole and plant cell has (permanent) vacuole
• red blood cells are (much) smaller than plant cells
• both have: cytoplasm and cell membrane

Question 4

When placed into a beaker of water: a red blood cell bursts and a plant cell does not burst. Explain why the red blood cell bursts but the plant cell does not burst.

Answer 4

water enters the cells by osmosis but plant cell has a cell wall which prevents it from bursting

Question 5

The number of people who are obese in the UK is increasing. Explain the financial impact on the UK economy of an increasing number of people who are obese.

Answer 5

costs the NHS more money because:
- need to pay for additional surgery / medication / hospital stay to treat stroke / diabetes
- more time off work so Government have to give financial support

Question 6

Arthritis is a condition that damages joints. Suggest how arthritis could affect a person’s lifestyle.

Answer 6

• movement issues
• loss of job / income
• mental health impact of lack of movement or mental health impact of pain
• may need surgery

Question 7

Energy is released in respiration. Give 4 uses of the energy released in respiration

Answer 7

• movement / muscle contraction
• keeping warm
• active transport
• building larger molecules

Question 8

Describe 5 differences between aerobic and anaerobic respiration in humans. Do not refer to oxygen in your answer

Answer 8

• anaerobic produces lactic acid and aerobic does not
• aerobic produces carbon dioxide and anaerobic does not
• aerobic produces water and anaerobic does not
• aerobic occurs (mainly) in the mitochondria and anaerobic does not
• anaerobic releases less energy than aerobic

Question 9

What are the two products of anaerobic respiration in plant cells?

Answer 9

carbon dioxide and ethanol

Question 10

Explain how amylase breaks down starch.

Answer 10

• starch substrate binds to active site of enzyme because shape of active site and substrate are complementary
• a chemical reaction occurs to produce smaller molecules or bonds between the starch molecules are broken to produce smaller molecules

Question 11

Name the cells in a leaf that control the rate of water loss.

Answer 11

guard cells

Question 12

Compare the structure and function of xylem tissue and phloem tissue. [6 marks]

Answer 12

• xylem is made of dead cells and phloem is made of living cells
• phloem cells have pores in their end walls and xylem cells do not have pores in their end walls
• xylem is hollow and phloem contains cytoplasm
• xylem contains lignin and phloem does not (
• both made of cells
• both tubular
• xylem transports water / mineral ions and phloem transports (dissolved) sugars
• xylem is involved in transpiration and phloem is involved in translocation
• xylem transports unidirectionally and phloem transports bidirectionally
• both transport liquids / substances throughout the stem / leaves / roots / plant

Question 13

A person with cancer may experience symptoms such as: tiredness, frequent infections, bleeding that will not stop after the skin is cut. Explain how a very low number of blood components in the body can cause these symptoms. [6 marks]

Answer 13

• Tiredness:
  
  • fewer RBC so less haemoglobin so less oxygen transported around the body so less aerobic respiration can take place so more anaerobic respiration takes place
  • less energy released for metabolic processes and lactic acid produced causes muscle fatigue
• Frequent infections:
  
  • fewer WBC cells so fewer antibodies produced and less phagocytosis so fewer pathogens killed
• Bleeding
  
  • fewer platelets so blood does not clot as easily

Question 14

A person has a tumour blocking the tube leading from the gall bladder to the small intestine. Explain why this person would have difficulty digesting fat.

Answer 14

• less bile reaches the small intestine
• less emulsification of fat so smaller surface area for lipase to break down fat
• pH of small intestine is not neutralised so lipase is not at its optimum pH to break down fat

Question 15

explain how electron microscopy has helped to develop an increased knowledge and understanding of cells.

Answer 15

• increased detail because there is a high magnification and high resolution
• can see structures in 3D
• can see sub-cellular structures

Question 16

why does calculating percentage change in mass give more accurate results?

Answer 16

It accounts for the initial mass and allows for comparison between different starting points.

Question 17

explain how the ventricle is adapted to its function.

Answer 17

it has to generate enough pressure to send blood around the body so has thick muscular walls

Question 18

describe how scientists could find out if a sample of chicken broth contained salmonella bacteria.

Answer 18

• pass an inoculating loop through a flame to sterilise it
• when it has cooled, dip it into the broth then spread onto agar in a petri dish
• pass the loop through the flame a second time
• seal the petri dish with tape and incubate it at a suitable temperature

Question 19

suggest one possible risk of using stem cells.

Answer 19

transfer of pathogens - risk of infection

Question 20

describe 2 ways someone’s breathing will change as exercise intensity increases

Answer 20

• breathing rate will increase
• depth of breathing increases

Question 21

what happens to lactic acid, when it builds up in muscle cells?

Answer 21

taken to the liver by the bloodstream where it is converted to glucose

Question 22

what are 5 ways the glucose produced in photosynthesis may be used.

Answer 22

• stored as starch
• respiration
• to produce fat/oil
• to produce cellulose
• to produce amino acids

Question 23

Explain how the leaf is adapted for photosynthesis

Answer 23

• the upper epidermis is thin and transparent so light can easily pass through
• palisade cells full of chloroplasts for photosynthesis and are near the upper surface of the leaf to catch the light
• spongy mesophyll had many air spaces to allow rapid diffusion of gases
• leaf contains veins to supply the plant with water for photosynthesis

Question 24

what illness or disease is a person who had HPV more at risk from?

Answer 24

cervical cancer

Question 25

when comparing water loss rates in 2 different plants, what are some variables the students would need to control?

Answer 25

• size/mass of plants
• length of roots
• number/size of leaves
• conditions they were in eg temp

Question 26

explain how guard cells control the opening and closing of stomata

Answer 26

• in light conditions, guard cells photosynthesise and produce glucose
• this increases the concentration inside the guard cells so they take in water from surrounding cells by osmosis
• cells become turgid
• thin outer wall bends more than thick inner wall so stomata open
• when photosynthesis stops, guard cells lose water and inner walls move closer together, closing stomata

Question 27

explain how lamellae increase the efficiency of gas exchange in fish.

Answer 27

• lots of lamellae cover each gill filament to increase the sa for gas exchange
• lamellae have lots of blood capillaries to speed up diffusion
• lamellae have a thin surface layer to minimise diffusion distances

Question 28

explain how the structure of a leaf allows gases to diffuse in and out of cells

Answer 28

• the underneath is covered in lots of stomata, through which co2 diffuses into the leaf and o2 and water vapour diffuse out
• the leaf has a flattened shape to increase the area of the exchange surface
• the walls of the cells inside the leaf form another exchange surface and air spaces inside the spongy mesophyll increase the area of this surface, increasing the chance of co2 getting into cells

Question 29

give 3 ways in which WBC are adapted to perform their function.

Answer 29

• some WBC can change shape and engulf pathogens in the blood and carry out phagocytosis
• some WBC produce antibodies
• some WBC produce antitoxins
• WBC have a large multi-lobed nucleus which allows for a high degree of control within the cell

Question 30

Some athletes train in locations high above sea level for several weeks before a race. This increases the no. RBC the athletes have. Suggest why this might improve an athlete’s performance in a race [4 marks]

Answer 30

• having more RBC means that more oxygen can be carried to the muscles
• this may improve an athlete’s performance during a race as it means there is more oxygen available for aerobic respiration
• this means more energy can be transferred for muscle contraction allowing the athlete to run faster/longer

Question 31

compare how foxgloves and garden roses defend themselves against:
- infection from pathogens
- damage from herbivores [6 marks]

Answer 31

• both GR and F have similar methods for protecting themselves against infection by pathogens
• both plants have a waxy cuticle which provides a barrier to stop pathogens entering
• the cells of both plants will have cell walls that contain cellulose. these will form a physical barrier against pathogens that make it past the waxy cuticle.
• the GR produces antibacterial compounds to kill bacteria on its surfaces, whereas it is not known whether the F is able to do this
• GR and F have different methods for protecting themselves against damage from herbivores. GR have thorns and F have poisonous stems/leaves. Both thorns and poisonous chemicals will deter herbivores from eating a plant and causing damage.

Question 32

Explain how statins can reduce the risk of developing CHD.

Answer 32

statins are used to reduce blood cholesterol levels which slows down the rate at which fatty deposits form in coronary arteries.

Question 33

Explain why clinical trials are always carried out on healthy volunteers before patients.

Answer 33

To make sure the drug does not have any harmful effects on the body when it is working normally

Question 34

Suggest 1 reason why it may sometimes be unethical to prescribe a placebo to patients in a control group.

Answer 34

Patients taking a placebo could become very ill without proper treatment.

Question 35

Cystic fibrosis results in the body producing thick sticky mucus in the air passages and alveoli. Explain what effect cystic fibrosis is likely to have on gas exchange.

Answer 35

Gas exchange would be less efficient because the mucus would block parts of the alveoli, reducing their SA

Question 36

Use your knowledge of digestive enzymes to explain how a dog may digest and absorb a meal containing proteins.

Answer 36

• proteases are digestive enzymes
• they are likely to be produced by the dog’s stomach, pancreas and small intestine
• proteases from these locations break down large, insoluble proteins in the dog’s food into small, soluble amino acids
• the amino acids will then be absorbed into the bloodstream from the small intestine

Question 37

Explain how malaria is spread from person to person.

Answer 37

The protist that causes malaria is carried by a mosquito which acts as a vector. The mosquito passes the protist between people when it bites them.

Question 38

Describe how MAbs are made against a particular pathogen.

Answer 38

• a mouse is injected with an antigen from the pathogen
• B-lymphocytes that produce antibodies against the antigen are then taken from the mouse and fused with myeloma cells to produce hybridoma cells
• the hybridoma cells are cloned to produce lots of identical cells which all produce MAbs against the pathogen
• these antibodies are collected and purified

Question 39

Explain what impact an anti-malaria vaccine might have on the number of cases of malaria in affected regions. [4 marks]

Answer 39

• the vaccine should help to reduce the number of cases in affected regions
• this is because the vaccine should create immunity to malaria in the people who receive it
• the vaccine will work by exposing the person to the malaria pathogen, which will stimulate the WBC to produce antibodies against the malaria pathogen.
• if the person who has received the vaccine comes into contact with the malaria pathogen at a later date, their WBC should be able to respond quickly to produce the anti-malaria antibodies to stop them from getting malaria.
• if a large % of the population is vaccinated against malaria, it should help to prevent the spread of the disease because there will be fewer people to pass it on.