B4.2 Organisation

State the levels of organisation in a multicellular organism.

Cells → tissues → organs → organ systems → organism.

Define a tissue.

A group of similar cells working together to carry out a particular function.

Define an organ.

A group of different tissues working together to perform a function.

Define an organ system.

A group of organs working together to carry out a particular function.

What is digestion?

The breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood.

What is the function of digestive enzymes?

They catalyse the breakdown of large food molecules into smaller, soluble molecules.

What is the lock-and-key model of enzyme action?

A substrate with a complementary shape fits into the enzyme's active site, allowing a reaction to occur.

Explain how high temperatures can denature an enzyme.

High temperatures change the shape of the active site, so the substrate no longer fits.

How does pH affect enzyme activity?

Each enzyme has an optimum pH; changes away from it can alter the active site and reduce activity or denature the enzyme.

What does amylase do?

It catalyses the breakdown of starch into sugars.

What do proteases do?

They catalyse the breakdown of proteins into amino acids.

What do lipases do?

They catalyse the breakdown of lipids into glycerol and fatty acids.

Where is amylase produced?

The salivary glands and pancreas.

Where are proteases produced?

The stomach, pancreas and small intestine.

Where are lipases produced?

The pancreas and small intestine.

Where is bile produced and stored?

Bile is produced by the liver and stored in the gall bladder.

State the two functions of bile.

It neutralises stomach acid and emulsifies fats into small droplets.

Explain how emulsification helps fat digestion.

It increases the surface area of fat, allowing lipase to act faster.

How do you test for starch?

Add iodine solution; orange-brown turns blue-black if starch is present.

How do you test for reducing sugars?

Add Benedict's solution and heat in a hot water bath; a positive result changes from blue towards green, yellow, orange or brick-red.

How do you test for protein?

Add Biuret reagent; a positive result changes from blue to lilac or purple.

How do you test for lipids using the emulsion test?

Shake the sample with ethanol, then add water; a cloudy white emulsion indicates lipids.

What is the independent variable in an investigation of pH and amylase activity?

The pH of the reaction mixture.

What is the dependent variable in an investigation of pH and amylase activity?

The time taken for starch to be digested, or the reaction rate calculated from that time.

How can iodine be used to test whether starch remains?

Add samples of the reaction mixture to iodine at regular intervals; iodine turns blue-black if starch remains.

How can reaction rate be estimated from the time taken for starch digestion?

Rate is proportional to 1 ÷ time taken; a shorter time indicates a faster reaction.

Name three variables to control in an investigation of pH and amylase activity.

Temperature, volumes and concentrations of amylase and starch, and the sampling interval.

Why should temperature be controlled in the amylase practical?

Temperature affects enzyme activity, so it must be kept constant to investigate the effect of pH fairly.

What is the function of the heart?

It pumps blood through the lungs and the rest of the body.

What is double circulation?

Blood passes through the heart twice during one complete circuit: once through the lungs and once through the body.

Describe the route of blood from the vena cava to the aorta.

Vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary vein → left atrium → left ventricle → aorta.

What does the pulmonary artery carry?

Deoxygenated blood from the right ventricle to the lungs.

What does the pulmonary vein carry?

Oxygenated blood from the lungs to the left atrium.

Why is the wall of the left ventricle thicker than the right ventricle?

The left ventricle must generate higher pressure to pump blood around the whole body.

What is the role of valves in the heart?

They prevent the backflow of blood.

What is the role of the coronary arteries?

They supply oxygenated blood to the heart muscle.

How is the resting heart rate controlled?

A group of cells in the right atrium acts as a pacemaker, sending electrical impulses that regulate heart contractions.

How are arteries adapted to their function?

They have thick muscular and elastic walls to withstand high pressure.

How are veins adapted to their function?

They have a large lumen and valves to prevent backflow; blood flows towards the heart at low pressure.

How are capillaries adapted for exchange?

Their walls are one cell thick, providing a short diffusion distance, and they form extensive networks near cells.

How are alveoli adapted for gas exchange?

They have a large surface area, thin moist walls and a good blood supply, enabling rapid diffusion.

Name the four main components of blood.

Red blood cells, white blood cells, platelets and plasma.

How are red blood cells adapted to transport oxygen?

They contain haemoglobin, have a biconcave shape and lack a nucleus, leaving more room for haemoglobin.

How do white blood cells defend the body?

They can engulf pathogens, produce antibodies or produce antitoxins.

What is the function of platelets?

They help blood clot, reducing blood loss and preventing pathogen entry.

What is the function of plasma?

It transports dissolved substances, including carbon dioxide, digested food, urea and hormones, around the body.

What causes coronary heart disease (CHD)?

Fatty deposits build up in the coronary arteries, narrowing them and reducing oxygen supply to the heart muscle.

How do stents treat CHD?

They hold narrowed coronary arteries open, improving blood flow to the heart muscle.

How do statins reduce the risk of CHD?

They lower blood cholesterol, slowing the formation of fatty deposits in arteries.

Give one advantage and one disadvantage of stents.

They can quickly improve blood flow, but complications such as blood clots or artery damage can occur.

Give one advantage and one disadvantage of statins.

They reduce cardiovascular risk over time, but can cause side effects and must be taken regularly.

What is health?

A state of physical and mental well-being.

What is a communicable disease?

A disease caused by a pathogen that can be transmitted between organisms.

What is a non-communicable disease?

A disease that is not transmissible between organisms.

What is a risk factor?

A factor associated with an increased likelihood of developing a disease.

How can smoking increase the risk of cardiovascular disease?

It damages blood vessels and increases the risk of atherosclerosis and blood clots.

How can obesity increase the risk of Type 2 diabetes?

Obesity is associated with increased insulin resistance, making blood glucose harder to regulate.

How can alcohol misuse affect health?

It can damage the liver and affect brain function.

What is a carcinogen?

An agent that can cause cancer, such as certain chemicals or ionising radiation.

What is the difference between benign and malignant tumours?

Benign tumours remain in one place; malignant tumours invade surrounding tissues and can spread to other parts of the body.

How can diseases interact?

One disease can weaken the immune system and increase susceptibility to another; some viruses can also trigger cancers.

Application: An amylase reaction takes 40 seconds at pH 7 and 100 seconds at pH 3. Compare the rates using 1/time.

At pH 7: 1/40 = 0.025 s⁻¹. At pH 3: 1/100 = 0.010 s⁻¹. The reaction is faster at pH 7.

Application: A student tests starch with iodine and obtains a blue-black colour. What does this show?

Starch is still present in the sample.

Application: A student tests a food sample with Benedict's solution and it remains blue after heating. What can they conclude?

No reducing sugar was detected by this test.

Application: Explain why the amylase practical should be repeated at each pH.

Repeats help identify anomalous results and allow a mean time to be calculated, increasing reliability.

Application: A patient has a narrowed coronary artery. Explain how this can affect heart muscle cells.

Reduced blood flow means less oxygen reaches the heart muscle, reducing aerobic respiration and potentially causing chest pain or a heart attack.

Application: Explain why a stent is placed in a coronary artery rather than the pulmonary artery to treat CHD.

CHD is caused by narrowing of the coronary arteries that supply the heart muscle; a stent restores blood flow through the affected artery.

Application: A patient is prescribed statins. Explain why the benefits may take time.

Statins lower blood cholesterol and slow the formation of fatty deposits; they do not immediately widen an already narrowed artery.

Application: During exercise, the heart rate increases. Explain why.

Muscle cells need more energy for contraction, so they require more oxygen and glucose for increased aerobic respiration; the heart pumps blood faster to supply them.

Application: Explain why the left ventricle needs a thicker muscular wall than the right ventricle.

It must generate higher pressure to pump blood around the whole body, whereas the right ventricle only pumps blood to the lungs.

Application: A person's red blood cell count is very low. Explain one likely effect.

Less oxygen can be transported to cells, so aerobic respiration may decrease and the person may feel tired.

Application: A study finds that people who smoke have higher rates of CHD. Why does this not by itself prove smoking caused every case?

Other variables may affect the results; the association supports a link but does not prove that smoking caused every individual case.

Application: A tumour invades nearby tissues and cells spread through the blood to another organ. Is it benign or malignant? Explain.

Malignant, because it invades surrounding tissues and can spread to form secondary tumours.