GCSE Biology 4 & 6 markers

Explain how a very low number of blood components in the body can cause:

- tiredness

- frequent infections

- bleeding that will not stop after the skin is cut

[6 marks]

Tiredness

- Fewer red blood cells

- 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 or less energy released so organs cannot function as well

- lactic acid produced (during anaerobic respiration) causes muscle fatigue

Frequent infections

- fewer white blood cells / phagocytes / lymphocytes

- so fewer antibodies produced or less phagocytosis

- so fewer pathogens

- so fewer pathogens / bacteria / viruses killed

Bleeding

- fewer platelets

- so blood does not clot as easily

Explain the body's response to exercise

[6 marks]

Heart rate increases

- to increase blood flowing to muscles / lungs

- to provide more oxygen (to muscles)

- to provide more glucose (to muscles)

- to remove carbon dioxide more quickly (from the muscles / blood)

- to remove lactic acid more quickly (from the muscles)

Breathing rate increases

- supplies more oxygen / air to lungs

- so more oxygen to blood

- for muscle contraction

More oxygen to muscles

- needed to (increased) respiration

- which causes a build-up of lactic acid

- oxygen debt

- muscle fatigue / pain

Explain how the human lungs are adapted for efficient exchange of gases by diffusion

[6 marks]

- (many) alveoli

- provide a large(r) surface area (:volume)

- capillaries are thin or alveoli / capillary walls are thin or one cell thick or capillaries are close to the alveoli

- which provides short diffusion path (for oxygen / carbon dioxide)

- breathing (mechanism) moves air in and out or lungs are ventilated

- to bring in (fresh) oxygen

- to remove carbon dioxide

- to maintain a concentration / diffusion gradient

- large capillary network (around alveoli) or good blood supply

- to remove oxygen(ated blood) quickly

- to bring carbon dioxide to the lungs quickly

- to maintain a concentration / diffusion gradient

Describe the effects of liver failure on the human body

[4 marks]

- no bile made (in the liver)

- fats / lipids are not emulsified

- surface of fats / lipids not increased

- pH of small intestine will not be alkaline / neutralised

- enzymes (in small intestine) will not work effectively or (named) food not digested / absorbed

- so may lose weight

- lactic acid not broken down / oxidised

- accumulation of lactic acid in blood / body

- lactic acid i toxic or body will be poisoned

- oxygen debt higher / prolonged

- so muscle pain / fatigue

- proteins / amino acids will not be broken down (in liver)

- (amino acids) not deaminated

- amino acids not made into urea or will not form ammonia

- (however) any ammonia formed is toxic

- so accumulation of amino acids in blood / body

- liver does not break down / remove other toxins (like alcohol)

- toxins accumulate in blood / body

- body will be poisoned

- so pain or jaundice or swollen liver or portal hypertension occurs

- glycogen store will not be formed

- cannot control blood glucose

- so hyperglycemia / hypoglycemia / diabetes / coma may occur

Explain why a person with a leaking heart valve has difficulty exercising

[4 marks]

- backflow may occur or some blood flows backwards

- less blood leaves the heart or less blood is pumped around the body or some blood stays in the heart (instead of being pumped out) or reduced blood pressure or reduced flow rate

- less oxygen supplied to muscles / cells

- (so) less aerobic respiration

- (so) less energy released

- (so) less efficient muscle contraction

- anaerobic respiration takes place

- less (efficient) removal of lactic acid or lactic acid builds up or oxygen debt occurs

- (lactic acid building up) causes muscle fatigue

- less (efficient) removal of carbon dioxide (from blood)

Evaluate the use of mechanical replacement heart valves and biological replacement heart valves

[6 marks]

Mechanical valves

- longer lasting or more durable or don't wear out as easily or less likely to need replacing (within 6 years)

- blood clots (on the brain) are more likely (after surgery)

- patient has to take anti-clotting medication (for the rest of their lives)

- if medication not taken (correctly), clots can lead to blood clots on brain / heart attack

- some patients say they can hear the valves opening and closing

- survival rate at 5 years is significantly higher for mechanical valve

- lower percentage of deaths due to heart-related problems

Biological valve

- no additional medication required

- ethical issues surrounding use of animal tissue

- valve may harden

- more likely to need further operation or another new valve

- more likely to be rejected

- more likely to need (immuno-suppressant) medication

Both valves

- both are readily available

- little wait time

Response should contain comparisons of both valves and some reference to won knowledge

One symptom of pancreatic cancer is weight loss

Explain how pancreatic cancer may cause a person to lose weight

Do not refer to hormones in your answer

[4 marks]

- reduced / no enzyme production / release (from pancreas)

- food is not broken down fully or food is not digested fully

- plus any one of the following routes for max 2 marks (marked as pairs)

- less glucose / sugar absorbed or less glucose / sugar passes into the blood(stream)

- (so) less glucose / sugar absorbed or less glucose available for respiration so more (body / stored) fat used up in metabolism / respiration

or

- fewer amino acids absorbed or fewer amino acids pass into the blood(stream)

- (so) fewer amino acids are available for making new protein for repair / replacement

or

- fewer fatty acids absorbed or fewer fatty acids pass into the blood(stream)

- fewer fatty acids available so less fat is stored in the body

or

- chemotherapy / radiotherapy causes nausea / loss of appetite

- (so) less intake of food

Describe how you would test a sample of food to show it contained protein

Give the reason for any safety precautions you would take

[4 marks]

- grinding up the food

- add Biuret reagent (CuSo4 and NaOH allowed) to food (sample)

- protein turns solution (from blue) to purple / lilac

- wear goggles to protect eyes

- clean up spills immediately

- Biuret / NaOH is an irritant / corrosive / poisonous

Describe how a student could test cow's milk to show whether it contains protein and different types of carbohydrate

[6 marks]

- Biuret reagent (CuSO4 and NaOH allowed) tests for protein

- add Biuret reagent to milk

- solution will turn (from blue) to lilac if positive

- iodine solution tests for starch (ignore iodine unqualified)

- add iodine solution to milk

- solution will turn (from orange / brown) to blue / black if positive

- Benedict's reagent tests for sugars

- add Benedict's reagent to milk and boil heat (allow any temperatures above 60 degrees Celsius)

- solution will turn (from blue) to (brick) red / brown / orange / yellow / green if positive

Response should include references to all 3 tests

Describe the route taken by oxygenated blood from the lungs to the body cells

[4 marks]

- (blood) travels through (the) pulmonary vein

- (blood) enters left atrium

- (blood) enters (the) left ventricle

- (blood) leaves the heart via / through (the) aorta

Explain how the villi and the alveoli are adapted to absorb molecules into the bloodstream

[6 marks]

- both have a large surface area

- villi have many microvilli

- alveolar walls are not flat / folded

- to maximise diffusion (of gases) / absorption of (food) molecules

- both have many capillaries / good blood supply / capillaries near the surface

- to provide a short diffusion distance (for molecules to travel)

- villi have many mitochondria

- to provide energy for active transport (of food molecules)

- cells of the villi have microvilli / more projections

- to further increase the surface area / increase the number of proteins in the membrane / to allow active transport to take place

Describe how a student could investigate the effect of the pH on the breakdown of starch by amylase

[4 marks]

- range of at least 3 pH values / use of buffer solutions

- control variables / keep amount or concentration of starch and amylase the same

- keep temperature the same using water bath / electric heater

- use iodine test to make qualitative observations

- observe colour changes at different temperatures

- do repeats at each pH

Explain how the circulatory system is adapted to:

- supply oxygen to the tissues

- remove waste products from tissues

- dual / double circulatory system which means that it has higher blood pressure and a greater flow of blood to the tissues

- heart made of specialised (cardiac) muscle cells which have long protein filaments that can slide past each other to shorten the cell to bring about contraction for pumping blood

- heart pumps blood to lungs in pulmonary artery so that oxygen can diffuse into blood from air in alveoli

- blood returns to the heart via pulmonary vein where muscles pump blood to the body via aorta

- oxygen carries by specialised cells / RBCs which contain haemoglobin to bind oxygen and have no nucleus so there is more space available to carry oxygen

- arteries carry oxygenated blood to tissues where capillaries deliver oxygen to cells for respiration and energy release

- thin walls allow for easy diffusion to cells

- large surface area of capillaries to maximise exchange

- waste products removed eg CO2 diffuse from cells into the blood plasma

- blood goes back to the heart in veins which have valves to prevent backflow

- cardiac output can vary according to demand / is affected by adrenaline

Compare the structure and function of xylem tissue and phloem tissue

[6 marks]

Structure

- 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 or xylem does not contain cytoplasm

and

- phloem contains cytoplasm

- xylem contains lignin

and

phloem does not (contain lignin)

- both made of cells

- both tubular

Function

- xylem transports water / mineral ions

and

- phloem transports (dissolved) sugars

- xylem is involves 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

Describe the transport of water through a plant from the soil to the atmosphere

[4 marks]

- (water is) absorbed though the root hair cells by osmosis

- (water is) transported in xylem

- water evaporates (from leaves)

- through the stomata

When light intensity is high potassium ions are moved into the guard cells

Describe how the movement of potassium ions into the guard cells causes the stoma to open

[4 marks]

- (potassium) ions increase the concentration of the solution (inside guard cells)

or

- (potassium) ions make the cell more concentrated / less dilute

- water moves in the (guard) cells by osmosis

- cell swells unevenly (so stomata opens)

- as inner wall is less flexible than the outer wall or thick part of the wall is less flexible than the thin part (of the wall)

Explain why root hair cells contain mitochondria

[4 marks]

- (aerobic) respiration occurs in mitochondria

- (mitochondria / respiration) release energy

- (energy used for) active transport

- to transport ions, against concentration gradient

or

- from a low concentration to high concentration

Describe how ions, water and sugar are obtained and transported through plants

[6 marks]

Ions

- taken up by diffusion or active transport

- from an area of high to low concentration (diffusion) or an area of low to high concentration (active transport)

- travel in the xylem

- to the leaves or the roots / soil

Water

- taken up by osmosis

- from an area of low to high concentration (high concentration of water to low concentration of water allowed)

- travels in the xylem

- to the leaves or the roots / xylem

- transpiration stream

- movement replaces water as it evaporates from the leaves in the xylem

Sugar

- made during photosynthesis

- travels in the phloem

- to other parts of the plant or to storage organs or travels up and down

Describe how the human body:

- prevents pathogens from entering

- defends itself against pathogens inside the body

[6 marks]

Skin

- tough / dry / dead outer layer

- skin acts as a barrier

- sebum / oil on (surface of) skin

- sebum / oil repels pathogens

- scabs form over cuts or scabs from a barrier

- platelets are involved in forming clots / scab

Stomach

- contains (hydrochloric) acid

- (HCl) kills bacteria

- in food or in swallowed mucus

Eyes

- produce tears

- contain enzymes to kill bacteria

- tears are antiseptic

Breathing system

- trachea / bronchi / nose produce mucus

- mucus is sticky

- (mucus) traps bacteria

- (mucus) carried away by cillia

Defends itself against pathogens inside the body

- immune system / white blood cells (WBCs)

- WBCc engulf pathogens

- antitoxins are produced

- (antitoxins) neutralise toxins / poisons (produced by pathogen)

- antibodies are produced

- (antibodies) help destroy pathogens

- memory cells are formed

- (memory cells give a) more rapid response if pathogen re-enters

Vaccination can be used to prevent an illness in a person

Explain how a vaccination can prevent an illness

[4 marks]

- dead / inactive pathogen

- introduced to the body

- white blood cells respond

- produce antibodies

- antibodies are specific to pathogen

- antibodies produced quickly (on reinfection) / rapid response

- in larger quantities

- killing the pathogen

Explain how different types of organism defend themselves against microorganisms

[6 marks]

Animals

- skin

- sebum / oils to kill microbes

- dead layer difficult to penetrate

- nose

- hairs keep out dust and microbes

- trachea / brochi

- mucus traps microbes

- cillia move mucus

- stomach

- (hydrochloric) acid kills bacteria

- white blood cells

- produce antibodies

- produces antitoxins

- engulf microbes / phagocytosis

Plants

- cell wall

- tough / difficult to penetrate

- waxy cuticle

- tough / difficult to penetrate

- dead cells / bark

- fall off, taking pathogens with them

- production of antibacterial chemicals

- kills bacteria

Fungi

- antibiotic production

- kill bacteria

Describe the steps in the procedure to produce monoclonal antibodies for a virus

[6 marks]

- inject the virus into a mouse

- stimulate (mouse) lymphocytes to produce antibody

- combine (mouse) lymphocyte with tumour cell or (create a) hybridoma

- clone (hybridoma) cell

- (hybridoma) divides rapidly and produces the antibody

Explain what testing must be done before a new drug can be used to treat people

[6 marks]

- pre-clinical trials of the new drug on cells / tissue / live animals

- to test toxicity, dosage and efficacy

- clinical trials / test on healthy volunteers and patients at very low doses

- so that you can monitor for safety / side effects

- and only then do trials to find the optimum dosage and test for efficacy

- double blind trial / use of placebo

- which does not contain the new drug

- random allocation of patients to groups

- so no one knows who has the placebo / the new drug

- peer review of data

- to help prevent false claims

It has been shown that this mAbs treatment is effective in the laboratory using both:

- infected tissue culture cells

- infected live animals

Describe how clinical trials should now be carried out

[6 marks]

- given first to healthy volunteers

- at (very) lose dose

- to test it is safe or to test for toxicity or to check for any side effects

- then to some patients (with the disease) or people with the disease

- to test for the correct / optimum dose

- to check for any side effects

- to test for efficacy or to test if it works

- in a double blind trial

- where neither the patients nor doctors know who has the mAbs and who has the placebo (or alternative treatment)

- reference to large trial or long duration or control variables

A pregnancy test strip will show a positive test result when a women is pregnant

Explain how the pregnancy test strip works to show a positive result

[6 marks]

- (as) urine passes through the reaction zone

- HCG hormone binds to the mobile HCG antibody (in the reaction zone)

- (passes up the stick) HCG hormone binds to the immobilised HCG antibodies in the results zone

- (the other) antibodies which do not attach to HCG

- bind to antibodies in the control zone

- blue dye appears in both control and results zones (to show positive result)

A gorse plant has an area of yellow leaves and stunted growth

One reason for yellow leaves and stunted growth is a deficiency of nitrate ions in the soil

Explain two other reasons for yellow leaves and stunted growth

Do not refer to nitrate ions in your answer

[6 marks]

- lack of magnesium (ions)

- (so) not enough chlorophyll for (efficient) photosynthesis

- (so not enough glucose to make proteins for growth or not enough glucose to release energy for growth

- infection by pathogen / bacteria / virus / fungus

- (so) leaves become discoloured /yellow so less photosynthesis

- (so) not enough glucose to make proteins for growth or not enough glucose to release energy for growth

- infected by aphids

- (which) remove sugars from phloem

- (so) not enough glucose to make proteins for growth or not enough glucose to release energy for growth

- lack of (available) light

- (so) chlorophyll breaks down

- (so) not enough glucose to make proteins for growth or not enough proteins to release energy for growth

TMV can cause plants to produce less chlorophyll

This causes leaf discolouration

Explain why plants with TMV have stunted growth

[4 marks]

- less photosynthesis

- therefore less glucose made

so

- less energy released for growth

- because glucose is needed for respiration

and / or

- therefore less amino acids / proteins / cellulose for growth

- because glucose is needed for making amino acids / proteins / cellulose

Describe an investigation of the effect of light intensity on the rate of photosynthesis

Include details of

- how to set up the apparatus and the materials you would use

- the measurements you would make

- how you could make this a fair test

[6 marks]

- weed in water beaker

- light shining in water beaker

- method of varying the light-intensity e.g. changing distance of lamp from plant

- use same pond weed or same length of pond weed

- temperature: water bath or heat screen

- CO2 concentration kept constant

- leave sufficient time at each new light intensity before measurements taken

- method of measuring photosynthesis e.g. counting bubbles of gas released or collecting gas and measuring volume in a syringe

- measuring rate of photosynthesis by counting bubbles for set period of time

- repetitions

Explain the ways the body responds to excercise

Include details of

- heart rate

- breathing rate

[6 marks]

Heart rate increased

- to increase blood flowing to muscles / lungs

- to provide more oxygen (to muscles)

- to provide more glucose (to muscles)

- to remove carbon dioxide more quickly (from the muscles / blood)

- to remove lactic acid more quickly (from the muscles)

Breathing rate increased

- supplies more oxygen / air to lungs

- so more oxygen to blood

- more carbon dioxide removed

More oxygen to muscles

- needed for (increased) respiration

- to release / provide energy

- for muscle contraction

Anaerobic respiration occurs

- due to lack of oxygen

- which causes a build-up of lactic acid

- oxygen debt

- muscle fatigue / pain

"During exercise, the heart rate of smokers increases more than the heart rate of non-smokers."

Design an investigation that would allow you to test this hypothesis

[6 marks]

- two groups of people - non-smokers and smokers

- have at least five people in each group or large groups

- get each person to do (named) exercise

- controlled variables

- same number of people in each group or large groups

- same gender

- same level of activity / exercise

- same age

- no health issues / illnesses

- same type of exercise

- same time for exercise

- record heart rate for each person before and after exercise

- calculate increase in heart rate for each person after exercise

- compare results for each group

Explain how the change in blood flow to an athlete's muscles helps them to run

[4 marks]

- supplies (more) oxygen

- supplies (more) glucose

- for (more) respiration

- releases (more) energy (for muscle contraction)

Describe the advantages and disadvantages of having a kidney transplant instead of having dialysis

[4 marks]

Advantages

- no need for regular / long hospital visits or is a long-term solution

- flexible lifestyle, such as can go on holidays

- may not live near a hospital or reference to transport costs

- no risk of infection from frequent needles / treatment

- less / no need to control diet

- maintains correct concentration of substances in blood / body

- cheaper long term for NHS / hospital

Disadvantages

- may be rejected

- have to keep taking anti-rejection drugs or immunosuppressants

- (suitable) donor may not be available or need for tissue matching

- risk from surgery (e.g. anaesthesia or infection)

Describe how the body responds when a decrease in core body temperature is detected

[6 marks]

- blood vessels supplying skin

- constrict

- less blood flow (to / through capillaries / to skin)

- so less energy is lost (to the surroundings)

- "shivering" by muscle (contraction)

- releasing energy or respiring (more)

A woman's hand accidentally touches a hot object

The woman mover her hand away rapidly

Describe how the woman's nervous system coordinates the reflex action

[6 marks]

- receptor (in skin of finger / hand) detects stimulus / temperature change

- (electrical) impulses pass along neurones

- (impulses pass from) sensory to relay to motor neurones

- synapse between neurons where chemical crosses gap

- (synapses) in spinal cord / CNS

- muscle contraction (to pull hand away) or effector is a muscle

Describe how hormones control the menstrual cycle

[5 marks]

- FSH (release from pituitary) stimulates maturation of egg / ovum / follicle

- oestrogen (release from ovary) inhibits FSH production and stimulates LH production

- LH (release from pituitary) stimulates ovulation

- progesterone (release from ovary) inhibits FSH and LH production

- oestrogen and progesterone maintain the uterus lining

The eyes of some birds contain cells that detect ultraviolet (UV) light

UV light is reflected by some fruits and the urine of small mammals

Explain how birds that detect UV light have evolved from birds that could not detect UV light

[6 marks]

- mutation (in gene / DNA)

- randomly or due to chance

- causes new / different protein / (visual) pigment to be made in the retina of bird

- (so more) variation in the wavelengths of light birds retinas could detect

- birds with the mutation or birds able to detect UV are more likely to see fruits (that reflect UV)

- birds with the mutation or birds able to detect UV are more likely to see where small mammals are or have been

- therefore get more food (small mammals or fruit)

- avoid being eaten (by small mammals)

- out competing those birds without the mutation or birds not able to see UV

- so more likely to survive and reproduce or have offspring

- by natural selection

- passing on allele / gene / mutation to offspring

- repeated over many generations

Explain how a person's eye could adjust to form a clear image of a nearer object

[6 marks]

- ciliary muscles contract

- (so ciliary muscles have a) smaller diameter

- (so) suspensory ligaments loosen / slacken

- (so) lens thickens or lens becomes more curves / rounded

- (thicker) lens is more convergent

- light rays / image focused on retina

Describe how a reflex action is coordinated

[6 marks]

- receptor detects stimulus

- e.g. receptor detects pressure

- receptor generates impulses / electrical signals

- neurones conduct impulses / electrical signals

- sensory neurone conducts impulses to spinal cord

- synapse between neurones

- chemical (/neurotransmitter) crosses synapse

- chemical stimulates impulse(s) in relay neurone

- and then to motor neurone

- effector carries out response

- e.g. muscles of arm / leg contract

- muscles contract or gland secretes chemicals

Describe the changes in the pupil and iris in low light levels

Explain how these changes occur

Refer to changes in the light level in your answer

[4 marks]

- pupils dilated

- in dim light / low light levels

- because circular muscles (in iris) relax

- (and) radial muscles contract

Describe the difference between the function of a receptor and the function of an effector

In your answer you should give one example of a receptor and one example of an effector

[4 marks]

- receptors detect / sense stimuli / change in surroundings or convert stimulus into an impulse

- example of a receptor

- effectors allow / make response or convert an impulse to an action

- (effector) muscle / gland

Explain how the pituitary gland and the kidneys reduce water loss

[3 marks]

- high(er) concentration of blood causes (more) ADH / hormone release

- (and hormone / ADH causes) increased permeability of kidney tubules (to water)

- (so) increased water reabsorption

Explain two biological reasons why most doctors think that a kidney transplant is a better method of treatment than dialysis

Do not refer to cost or convenience

[4 marks]

- changes in concentrations / levels of substances / urea are mimimised

- (so) less / no chance of causing damage to body cells / tissues

- not repeatedly puncturing skin or blood not in contact with machine

- (so) less / no chance of infection or less / no chance of blood clots or no need to take anti-clotting drugs

Explain how the hormones insulin and glucagon control a person's blood glucose concentration after a meal

[5 marks]

- (blood glucose increases after meal causing) insulin secretion

- insulin causes glucose to enter cells / liver / muscles

- (insulin causes) glucose conversion to glycogen

- (so) blood glucose decreases causing glucagon secretion

- glucagon causes glycogen to be converted to glucose

Explain how negative feedback controls the blood glucose concentration in the hours after eating a meal

[4 marks]

- glucose from meal enters blood or increase in blood glucose

- glucose detected by pancreas

- pancreas secretes insulin

- (insulin causes) glucose to move (out of blood) into cells / liver

- liver converts glucose to glycogen

- causing a fall in blood glucose

- low blood glucose detected by pancreas

- pancreas releases glucagon

- liver converts glycogen to glucose (which enters blood)

- blood glucose rises

Explain how blood glucose levels are controlled in the body of someone who does not have diabetes

[4 marks]

- if too high insulin released from pancreas

- so glucose is moved into cells

- if too low, glucagon is released (from pancreas)

- causes glycogen to be converted to glucose and released into the blood

Compare how each type of diabetes is caused

Suggest how each type of diabetes can be treated

[4 marks]

- type 1 not enough / no insulin produced

- whereas type 2 cells do not respond to insulin

- type 1 is treated with injections of insulin

- whereas type 2 is treated with diet and exercise or loss of weight or drugs

Suggest what would happen in the body of a person with hyperthyroidism

[3 marks]

- too much thyroxine is released into the blood

- which raised BMR

- causing increase in formation of glycogen / lipids / proteins or increase in rate of respiration or increase in breakdown of excess proteins

Explain why missing a dose of the mini-pill would reduce the success rate of the mini-pill

[4 marks]

(missing a dose causes a) dip / drop in progesterone levels

- (therefore) FSH is not inhibited anymore

- (therefore) LH is not inhibited anymore

- (and consequently) an egg is matured and released

Explain why a transplanted organ may be rejected

[3 marks]

- immune system

- produces antibodies

- (which) attack the antigens on the transplanted organ

Plan an investigation to show the effect of light from one direction on the growth of plant seedlings

[6 marks]

- several seedlings in each batch or one pot of seedlings in each batch

- measure heights of shoots

- leave some in dark with light from one side / direction in box with hole

- control(s) with all-round light or rotating on clinostat or in dark

- control variable(s) e.g. same temperature / water / soil type

- after suitable time (at least several hours)

- record appearance of seedlings re. light direction

- re-measure heights of shoots

- detail of how bent shoots were measured - e.g. use thread or straighten them out

- calculate mean height increase for each group

- use ruler / protractor to estimate angle of bending