Systems in the Human Body (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

False.

As an organism gets larger, its surface area to volume ratio decreases. This means large, multicellular organisms cannot rely on diffusion alone to meet their needs.

The order is:

1. Cells → specialised to carry out specific functions

2. Tissues → groups of similar cells

3. Organs → groups of tissues working together

4. Organ systems → groups of organs performing a function

A tissue is made up of cells with a similar structure and function. Several of these combine to form an organ, and groups of organs form an organ system.

True.

Single-celled organisms have a large surface area to volume ratio, which means diffusion, osmosis, and active transport across their cell membrane are sufficient to exchange all the substances they need without a specialised transport system.

Give four features that increase the effectiveness of an exchange surface in a multicellular animal.

1. Large surface area: allows more particles to diffuse at once

2. Thin membrane: provides a short diffusion distance

3. Efficient blood supply: maintains a steep concentration gradient

4. Ventilation (for gas exchange): keeps oxygen levels high and carbon dioxide levels low

The alveoli in the lungs, the villi in the small intestine, and root hair cells in plant roots are all examples of specialised exchange surfaces.

Large multicellular organisms have a small surface area to volume ratio, so diffusion alone is too slow to supply all cells with what they need. Specialised exchange surfaces and transport systems (such as the circulatory system) ensure materials reach every cell efficiently.

The human circulatory system is a double circulatory system because blood passes through the heart twice for each full circuit of the body — once to the lungs and once to the rest of the body.

Deoxygenated blood enters the right atrium via the vena cava, is pumped to the lungs via the pulmonary artery, and returns to the left atrium via the pulmonary vein.

True.

The left ventricle has the thickest wall because it must pump oxygenated blood at high pressure around the entire body. The right ventricle only pumps blood to the nearby lungs.

The pacemaker is a group of cells located in the right atrium that controls the natural resting heart rate by sending out electrical impulses that cause the heart muscle to contract.

An artificial pacemaker is an electrical device implanted under the skin that delivers electrical impulses to the heart muscle to correct irregularities in the heart rate, such as when the natural pacemaker stops functioning correctly.

1. Arteries have thick walls with elastic fibres and a narrow lumen; veins have thinner walls and a wider lumen.

2. Veins contain valves to prevent the backflow of blood; arteries do not.

True.

Capillary walls are just one cell thick (a single layer of endothelial cells), which minimises the diffusion distance for oxygen, carbon dioxide, and other substances between the blood and body cells.

In the lungs, oxygen diffuses from the air in the alveoli into the blood, while carbon dioxide diffuses from the blood into the alveoli.

Air travels through:

1. Trachea

2. Bronchi (one per lung)

3. Bronchioles

4. Alveoli

Haemoglobin is the protein found in red blood cells that binds reversibly with oxygen to form oxyhaemoglobin, allowing red blood cells to transport oxygen around the body.

Give two structural adaptations of a red blood cell and explain how each helps it carry oxygen.

1. Biconcave disc shape: gives a large surface area to volume ratio, maximising the rate of diffusion of oxygen into and out of the cell.

2. No nucleus: leaves more space for haemoglobin, increasing the amount of oxygen each cell can carry.

False.

Platelets are fragments of cells — they contain cytoplasm but no nucleus. Their role is to help form blood clots when a blood vessel is damaged.

Blood is a tissue consisting of plasma, in which red blood cells, white blood cells and platelets are suspended.

1. Phagocytes engulf and digest pathogens.

2. Lymphocytes produce specific antibodies that clump pathogens together or disable them.

3. Some lymphocytes produce antitoxins that neutralise toxic substances produced by pathogens.

True.

Oxygen combines reversibly with haemoglobin in red blood cells to form oxyhaemoglobin. This is reversed in body tissues, releasing oxygen to the cells.

Phagocytes engulf and digest pathogens, while lymphocytes produce antibodies and antitoxins as part of the immune response.

Plasma is the liquid part of blood (mainly water with dissolved substances). It transports dissolved food molecules, carbon dioxide, urea, hormones, and heat around the body.

Digestion is the process of breaking down large, insoluble molecules in food into small, soluble molecules that can be absorbed into the bloodstream and transported to body cells.

Enzymes are biological catalysts that speed up the breakdown of large food molecules. The three main types are carbohydrases (break down carbohydrates), proteases (break down proteins) and lipases (break down lipids).

Starch is broken down by carbohydrase enzymes into glucose. Glucose is then absorbed into the blood and used by cells during respiration to release energy.

True.

Amylase is a carbohydrase that breaks down starch into maltose. It is produced in the salivary glands and the pancreas.

Excess amino acids cannot be stored. The liver breaks them down to form urea, which is then transported in the blood to the kidneys, which excrete it in urine.

Protease enzymes break down proteins into amino acids in the stomach and small intestine. Cells then use these to make new proteins for growth and repair.

False.

Lipase enzymes break down lipids into glycerol and fatty acids (not glucose and water). These can be reformed into fats and stored as an energy reserve.

Lipids (fats and oils) are stored as an energy reserve because cells can break them down and use them in respiration when needed. Lipase enzymes digest lipids into glycerol and fatty acids.

Lipase enzymes are produced in the pancreas and are secreted into the duodenum (the first part of the small intestine), where they break down lipids.

A qualitative food test is a test that indicates whether a substance is present or absent in a sample. It is identified by a colour change but does not tell you how much of the substance is present.

The Benedict's test is used to detect reducing sugars. A positive result shows a colour change from blue to brick-red (orange-red).

True.

When iodine solution is added to a starch-containing sample, it turns from yellow-brown to blue-black, indicating the presence of starch.

A positive Biuret test produces a colour change from blue to purple. The Biuret reagent contains sodium hydroxide and copper(II) sulfate solution.

To test for lipids, the emulsion test is used. The sample is mixed with ethanol, which is then added to water. A positive result is a cloudy white emulsion.

True.

Ethanol is highly flammable and must be kept away from the Bunsen burner used in the Benedict's test. The Bunsen should be turned off completely before ethanol is used.

Goggles should be worn because:

1. Biuret solution contains copper(II) sulfate and sodium hydroxide, which are harmful, especially to the eyes.

2. Iodine solution is also an irritant to the eyes.

1. Grind the food using a pestle and mortar.

2. Transfer to a test tube and add distilled water.

3. Stir with a glass rod to mix.

4. Filter the mixture using a funnel and filter paper.

5. Use the collected solution for the food tests.

The central nervous system (CNS) is the coordinator of the body, made up of the brain and the spinal cord.

The correct order is:

stimulus → receptor → coordinator → effector → response

True.

Information travels through the nervous system as electrical impulses that pass along nerve cells called neurones.

Neurones are insulated by a fatty myelin sheath which speeds up the transmission of electrical impulses.

A reflex action is an automatic and rapid response to a stimulus that does not involve the conscious part of the brain.

A relay neurone carries electrical impulses within the CNS (spinal cord or brain), connecting the sensory neurone to the motor neurone.

False.

Neurones never touch. They are separated by tiny gaps called synapses. Neurotransmitters are released to carry signals across these gaps.

In a reflex arc, the sensory neurone carries impulses from the receptor to the spinal cord, while the motor neurone carries impulses from the CNS to the effector.

Reflex actions are automatic and rapid, which means they help to minimise damage to the body without waiting for the brain to consciously process the stimulus.

Reaction time is the time taken for a person to respond to a stimulus. It typically takes less than a second and can range from around 0.3 s to 0.9 s.

A ruler is dropped and the participant catches it. The further down the ruler is caught, the slower the reaction time, because the ruler has fallen further before being caught.

True.

The shorter the distance the ruler falls before being caught, the faster the reaction time.

Reaction time can be affected by factors such as age, stress or the use of drugs such as caffeine.

Repeating the test allows a mean average to be calculated, which reduces the effect of random error and makes the results more reliable.

False.

To produce valid results, you must use the same ruler and the participant's dominant hand every time. Only the independent variable should be changed.

If the effect of caffeine on reaction time is being investigated, participants should not consume any caffeine before the experiment begins.

A computer is more precise because it removes human error from measurements, and reaction times can be recorded in milliseconds rather than seconds.

A hormone is a chemical messenger secreted by a gland directly into the bloodstream, which carries it to a target organ where it produces an effect.

Hormones act more slowly than nerve impulses but their effects last longer. Nerve impulses are fast but short-lived.

Complete the table of endocrine glands and their hormones.

True.

The pituitary gland produces hormones such as FSH and LH, and plays a key role in controlling other glands in the endocrine system.

Negative feedback is a mechanism where a change away from the normal level triggers a response that reverses the change, helping to maintain conditions within a narrow optimal range.

False.

Negative feedback does the opposite — it reverses a change and brings conditions back to normal. It stabilises the system rather than amplifying changes.

Adrenaline is produced by the adrenal glands (located above the kidneys) in response to fear or stress, preparing the body for 'flight or fight'.

Adrenaline increases heart rate and boosts the delivery of oxygen and glucose to the brain and muscles.

Thyroxine stimulates the basal metabolic rate (BMR), controlling the speed of chemical reactions at rest. It also plays an important role in growth and development.

False.

When thyroxine levels are too high, the release of TSH from the pituitary gland is inhibited, so less thyroxine is released. This is an example of negative feedback.