B3 Examination Hints and Tips ANSWERS

B3 Examination Hints and Tips ANSWERS

B3 Examination ‘hints and tips’ ANSWERS

Candidates should:

B3.1 Movement of molecules in and out of cells
B3.1.1 Dissolved substances
Define the term ‘diffusion’. Random movement of particles in a liquid of gas, from an area of high concentration to a low concentration.
Define the term ‘osmosis’ and explain what a partially permeable membrane is.
Osmosis is the diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane.
A partially permeable membrane allows the passage of some small molecules (like water, oxygen and carbon dioxide) whilst preventing the passage of larger molecules (like starch).
Be able to explain why a long distance runner may choose an isotonic drink.
Isotonic drinks contain water, electrolytes (like sodium and potassium ions) and sugar (often glucose). The water helps athletes to rehydrate (water moves by osmosis into cells). The mineral ions replace lost electrolytes (mineral ions lost in sweat) and the glucose helps to replace lost energy.
Define the term active transport.
The movement of particles from a low concentration to a high concentration, through a partially permeable membrane using energy from respiration (and carrier proteins).
Explain why active transport requires energy.
Energy is required to move the particles against the concentration gradient (from low to high). In this way cells can absorb ions from very dilute solutions.
Label diagrams to show where active transport occurs in humans and plants and what is transported.

Be able to describe two adaptations of the villi which help the small intestine to function.
Villi have a good blood supply to quickly transport away absorbed products of digestion (maintaining the diffusion gradient)
Cells of the villi have microvilli (folds in the membrane to increase the surface area for absorption)

Explain why some food molecules are absorbed by diffusion (often after fasting) and others by active transport.
Molecules are absorbed by diffusion when there is a favourable concentration gradient (eg high outside cell, low inside cell).
Molecules are absorbed by active transport when there is a unfavourable concentration gradient (eg low outside cell, high inside cell).
B3.1.2 Gaseous exchange
Be able to identify the main parts of the breathing system on a diagram. For example, add labels to a diagram for alveolus, diaphragm, rib and trachea.
Breathing
Explain the changes that occur to bring about ventilation of the lungs in terms of relaxation and contraction of muscles, movement of the ribcage and diaphragm, changes in volume and pressure in the thorax. (use diagram above right to help)
Inhalation: intercostal muscles contract and move the ribs up and outwards. Diaphragm muscle contracts and flattens. Both movements increase the volume of the thorax (chest cavity), lowering the pressure, forcing air to enter and inflate the lungs.
Exhalation: intercostal muscles relax and move the ribs down and inwards. Diaphragm muscle relaxes and becomes dome-shaped. Both movements decrease the volume of the thorax (chest cavity), increasing the pressure, forcing air out of the lungs which deflate.
Evaluate the development and use of artificial aids for breathing:
Iron lung: negative pressure system. An air pump removes air from the cylinder around the patient creating a vacuum. This lowers the pressure outside the body which expands the chest, lowering pressure inside the lungs, so causing air to move in from outside. When the pump is switched off external pressure returns, the chest falls down, reducing the volume, increasing the pressure, forcing air to be squeezed out. Disadvantage: Patient movements are restricted.
Positive pressure system: Ventilator forces air into lungs (similar to inflating a balloon!). When the pressure stops ribs fall down , reducing volume, forcing air out of lungs. Advantages: patients do not need to be inside system, can move about. Patients can have some control over system. Keep people alive after surgery or if paralysed.

B3.1.3 Exchange systems in plants
Be able to suggest how having more stomata on the lower surface (rather than upper side) of the leaf helps the plant to survive better.
Having stomata on the lower side of leaves reduces water loss by transpiration, as the underside of the leaf will be cooler as it is less exposed to the sun.
Define the term transpiration. Loss of water by evaporation from the surface of a plant (mainly leaves).
Write a method to explain how a potometer can be used to measure the rate of water uptake by a shoot.
Fill syringe and capillary tube with water. Attach leafy shoot ensuring air tight seal. Measure distance moved by air bubble each minute as water evaporates from leaves. Reset the air bubble using the syringe to allow repeat readings.

Explain why warm + windy conditions increase water loss.
In warm conditions water molecules have more kinetic energy and evaporate faster from leaves. If it is windy the water molecules are blown away from the leaf surface helping to maintain a steep diffusion gradient.
B3.2 Transport systems in plants and animals
B3.2.1 The blood system
Label a diagram of the heart showing 4 chambers, vena cava (main vein), pulmonary artery, pulmonary vein and aorta (main artery).

Describe the flow of blood from the body, through the heart and lungs and back to the body.
Blood leaves the heart via the aorta (main artery) → body → returns to heart via vena cava (main vein)→right atrium→ right ventricle → pulmonary artery → lungs→ pulmonary vein→ left atrium → left ventricle→ aorta
Evaluate the use of heart valves.
Heart valves prevent backflow of blood. Faulty/leaky valves can be replaced, a major operation. Mechanical valves made from polymers or titanium are long lasting, but patients need drugs for rest of lifetime to stop blood clotting. Biological valves use valves from humans, pigs or cattle. Patients do not need drugs after, but they only last about 15 years.
Evaluate the use of artificial hearts.
Temporary solution to keep patients alive whilst they wait for a suitable heart donor.
Need lots of machinery to keep working, patients with them often have to stay in hospital.
Higher risk of blood clotting
Be able to recognise veins and arteries from diagrams of blood vessels.

Describe what a stent is and what it is used for.

Evaluate the use of stents.
Stents are used to widen coronary arteries that have narrowed or been blocked by fatty deposits like cholesterol. This increases blood flow to heart muscle helping to prevent heart attacks.
Can be done with just a local anaesthetic for a low cost.
But will not open the most severely blocked arteries.
B3.2.2 The blood
Draw diagrams of red blood cells, white blood cells and platelets.

Explain the structure and function of red blood cells, white blood cells and platelets.
Red blood cells have a biconcave disc shape creating a large surface area to volume ratio for rapid diffusion of oxygen.
No nucleus inside allows more space for haemoglobin which carries oxygen.
White blood cells have a nucleus. They defend us against pathogens by making antibodies and antitoxins. Some engulf pathogens.
Platelets are cell fragments that help the blood to clot. They do not have a nucleus.
Explain why the reversible reaction between oxygen and haemoglobin is important.
Haemoglobin + oxygen → oxyhaemoglobin. This reaction occurs inside red blood cells at the lungs where there is a high concentration of oxygen, allowing red blood cells to collect oxygen.
Oxyhaemoglobin → haemoglobin + oxygen. This reaction occurs inside red blood cells at actively respiring cells (like muscles) where there is a low concentration of oxygen, allowing red blood cells to give up oxygen which then diffuses into respiring cells.
Evaluate the use of artificial blood products.
Plasma / saline (salt water):
Used in emergencies to replace lost blood volume, helping to keep blood pressure normal.
Can give time for body to make own blood or while awaiting blood transfusion.
Plasma has a little dissolved oxygen.
PFCs (Perfluorocarbons)
A more sophisticated artificial blood. Perfluorocarbons carry oxygen.
As they have no blood cells can get oxygen to swollen/damaged tissues.
Long storage life.
No danger of disease.
Disadv’: breakdown quickly, side effects, difficult to dissolve in blood.
Haemoglobin only (no rbc)
Haemoglobin taken from human or animal red blood cells, made synthetically or made using GM bacteria.
Carries more oxygen than normal blood, BUT its broken down quickly inside the body
NOTE: NONE of the artificial bloods can clot or fight disease.
B3.2.3 Transport systems in plants
Explain the function of xylem and phloem.
Xylem is dead and hollow. It transports water and minerals
Phloem is living. It transports sugars in the plant.
Name the process by which water vapour is lost from a leaf. Transpiration
B3.3 Homeostasis
B3.3.1 Give examples of waste products that have to be removed and explain where they are excreted from the body.
Carbon dioxide – lungs
Urea - kidneys
Name where urea is made (and what it is made from) and where it is excreted from the blood.
Urea is made in the liver from excess protein (amino acids). It is excreted by the kidneys.
Name the organ which stores urine. Bladder
Be able to name two substances which will pass through the filter from blood plasma into the filtrate. Glucose (sugar), water, urea, mineral ions
Be able to explain why protein is not found in the urine of a healthy person. Protein molecules are too big to get filtered from the blood.
State which substances are reabsorbed back into the blood and explain how this happens.
Glucose (sugar) and mineral ions are selectively reabsorbed by kidney tubules. Reabsorption uses active transport and requires energy from respiration because the sugar and ions are moved against a concentration gradient.
Explain how a kidney machine works in terms of the partially permeable membrane and composition of the dialysis fluid.

Be able to give two advantages of a kidney transplant rather than dialysis treatment.
No routine dialysis needed, so a more independent better quality of life.
Fewer dietary restrictions.
Be able to give one disadvantage of having a kidney transplant.
Need to be on immunosuppressant drugs for the rest of your life to avoid rejection.
(May be difficult to find a suitable donor/tissue match)
B3.3.2 Temperature control
State how body temperature is monitored: Thermoregulatory centre in brain monitors core body temperature as blood flows through it.
Describe how body temperature is controlled on a hot day.
Sweat more. Heat energy needed to make sweat evaporate is taken from skin cooling it.
Vasodilation increases blood flow to skin surface so more heat is lost by radiation
Hairs lie flat to trap less air.
Describe how body temperature is controlled on a cold day.
No sweat
Vasoconstriction reduces blood flow near skin surface reducing heat lost by radiation.
Shivering. Muscle contractions involved need more respiration which releases more heat energy, raising body temperature.
B3.3.3 Sugar control
Be able to give one way other than using insulin of treating diabetes.
Controlled diet especially carbohydrate intake.
Be able to state which organ controls blood glucose concentration. Pancreas
Be able to describe how insulin reduces the concentration of glucose in the blood.
Insulin from the pancreas travels in the blood to liver and muscles. Their cells absorb sugar and convert it into glycogen (a storage carbohydrate).
Be able to describe how the body increases the concentration of glucose in the blood.
The pancreas releases the hormone glucagon. This makes the liver breakdown glycogen into sugar.
Compare and contrast Type 1 and Type 2 diabetes.
In both types patients are unable to control blood glucose.
Type 1: no insulin made. Young people. Control with insulin injections and careful diet and exercise.
Type 2: make some insulin, but body does not respond to insulin. Older people, often obese and needing exercise.
Evaluate modern methods of treating diabetes.
Pancreatic organ or cell transplants = high risk, expensive. Need immunosuppressant to stop rejection.
Genetically engineering patients own cells to contain working insulin gene would avoid rejection issues.
Using embryonic stem cells to become pancreatic cells ethically not acceptable for some.
B3.4 Humans and their environment
B3.4.1 Waste from human activity
List the problems associated with an increasing human population.
More waste, more pollution, more land needed for agriculture, houses etc
Describe how water can be polluted
Sewage and fertilisers wash into river/stream. Algae grow fast. Algae underneath die (lack of light). Bacteria decay dead algae suing oxygen in respiration. Fish die due to low oxygen in water. Whole process is eutrophication.
Give examples of air pollutants and where they come from:
Sulphur dioxide, nitrogen oxides and smoke particles. Burning fossil fuels.
Describe how acid rain is formed.
Sulphur dioxide released from burning fossil fuels (eg coal). Sulphur dioxide dissolves in water in clouds forming sulphuric acid. This falls as acid rain. Acid rain kills leaves on trees and makes ponds acidic.
B3.4.2 Deforestation and the destruction of areas of peat
Be able to explain why peat free composts are of increasing importance.
Peat-free compost reduces the demand for peat, helping to conserve peat bogs. Peat bogs are a carbon store.
Be able to give two reasons why deforestation increases the amount of carbon dioxide in the atmosphere.
Less trees means less carbon dioxide is removed from the air by photosynthesis
Burning trees releases carbon dioxide.
Explain how deforestation could lead to an increase in methane in the atmosphere.
Deforested land is often used for agriculture. Cattle on this land produce methane in their gut. Some land is used to grow rice. Microbes in paddy fields produce methane.
B3.4.3 Biofuels
Be able to give some effects of global warming
Increasing the Earth’s temperature may: change earth’s climate; melt ice caps, making sea levels rise; reduce biodiversity; change migration patterns; change the distribution of species.
Be able to explain the greenhouse effect using the words or phrases “absorb” and “re-radiate heat”.
Heat energy from the Sun is absorbed by the Earth. The Earth re-radiates this heat (as infra-red) back into the atmosphere where greenhouse gases (carbon dioxide + methane) absorb/trap it, warming the Earth.
Be able to explain the link between carbon dioxide emissions and the greenhouse effect.
Carbon dioxide is a greenhouse gas. As levels increase more heat is trapped warming the Earth.
Define the term ‘biofuel’. Biofuels are renewable fuels made from natural products by fermentation using bacteria or yeast.
Write the equation for the production of ethanol using yeast. Glucose → ethanol + carbon dioxide + water
Explain the advantages and disadvantages of growing crops for biofuels.
Advantages: carbon neutral (CO2 absorbed during crops photosynthesis = CO2 released when biofuel burns).
Less pollution when fuel burns.
Disadvantages:
Uses mainly edible parts of plants, leaving waste/unused plant material
Less land for food crops
Cars need to be adapted to run on ethanol
Define the term ‘biogas’. Mixture of gases (mainly methane) made when bacteria breakdown plant or animal waste in anaerobic conditions.

Be prepared to evaluate the use of gas generators.
Be able to explain how the output from a biogas generator is affected by climatic conditions, such as India and the UK.
Bacteria need temperature near 30 C. Generators are often insulated to prevent heat energy loss in the UK and may be sunk in the ground for the same reason. In warmer countries output can be higher as decay occurs faster.
Be able to state the main useful gas in biogas. Methane
B3.4.4 Food production
Be able to suggest one reason why calves raised indoors grow faster than those raised outdoors.
Muscles waste less energy as there is less movement, so more energy is available for growth. OR
They use less energy keep their body temperature constant as it is warmer in doors. More energy available for growth.
Be able to suggest one reason why some people prefer to buy meat from animals that have been kept outdoors.
Some object to animals having unnatural, restricted lives.
Explain why some fish stocks are declining and why this is a problem.
Overfishing. Removal of too many breeding stock fish, so that reproduction rates are too low to replace caught fish.
Describe ways that fish stocks can be conserved.
Fishing quotas - restrict the amount of fish caught each year.
Controlling the size of holes in fishing nets - only larger fish are caught, leaving younger ones to grow and reproduce.
(Ban on fishing during breeding season).
Describe how Fusarium is grown to produce mycoprotein that can be eaten.
The fungus Fusarium is grown on glucose syrup in aerobic conditions inside a fermenter. The fungus reproduces rapidly. Respiration by the fungus releases heat energy, so a cooling water jacket helps keep the fermenter at the optimum temperature. The fungal biomass is harvested and then purified.
Evaluate the use of mycoprotein as a food.
Mycoprotein is a healthy food high in protein and low in fat, a suitable meat substitute.
It is a sustainable food source which uses glucose syrup made from waste starch.
Some consumers dislike the texture and flavour or the idea of eating fungus.