Edexcel A Level Biology Topic 7 Exam Questions

Explain why it is necessary for the cardiac output of marathon runners to increase during a race. (3)

• M1: Increase supply of oxygenated blood to muscles

• M2: To allow aerobic respiration

• M3: To provide more energy (to meet the increased demands)

Adrenaline acts on the heart to cause changes in heart rate. Deduce how adrenaline can cause a change in heart rate. (4)

• M1: Adrenaline carried in the blood

• M2: Acts on the sinoatrial node

• M3: Increasing the frequency of impulses {produced by SAN/ that spread across the heart}

• M4: Increasing the rate at which heart contracts

At the start of exercise, breathing rate increases.

Explain how starting to exercise causes an increase in breathing rate. (3)

• M1: Exercise initiates impulses from the {motor cortex/ stretch receptors in muscles/ proprioceptors}

• M2: Impulses sent from the {ventilation centre/ respiratory control centre/ medulla oblongata}

• M3: Leading to increased impulses to {intercostal muscles/ diaphragm}

The demand for oxygen changes during exercise.

The change in demand affects the breathing rate.

Explain the effect of exercise on the changes in oxygen consumption. (4)

• M1: Exercise will increase oxygen consumption

• M2: Because there is increased aerobic respiration

• M3: Because more {energy/ ATP} is needed by muscles

• M4: Oxygen required to convert {lactate/ lactic acid} into {glucose/ pyruvate}

• M5: Oxygen consumption begins to decrease after exercise

Describe how a spirometer trace can be used to calculate the respiratory minute ventilation and the oxygen consumption per minute. (4)

Respiratory Minute Ventilation

• M1: Find the difference in peak to trough volume (to give the tidal volume)

• M2: Find Ventilation rate (count the no. of peaks in a stated time)

• M3: Multiply the tidal volume by ventilation rate

Oxygen Consumption

• M1: Difference in volume of one {peak/ trough} compared to a subsequent one

• M2: Divide by time between the two peaks/ trough and multiply by 60

Describe how the sinoatrial node (SAN) is involved in bringing about a change in heart rate as the level of activity increases. (2)

• M1: More {stimulation/ depolarisation} of the SAN from the sympatric nervous system/ more impulses to the SAN

• M2: Causing more frequent waves of depolarisation from the SAN to the atria

• M3: Leading to more frequent {contraction of atria/ stimulation of AVN}

Heat stress occurs when the core body temperature rises above 40 °C. Describe how thermoregulatory mechanisms are controlled to help marathon runners avoid heat stress. (4)

• M1: Thermoreceptors in the hypothalamus/ skin detect increase in temperature

• M2: {heat loss/ thermoregulatory} centre in the hypothalamus stimulated

• M3: Hypothalamus sends impulses to sweat glands

• M4: Increased blood flow to the surface of the skin by {vasodilation/ constriction of shunt vessels}

• M5: Decreased metabolic rate

Explain the role of the brain in reducing the student's heart rate after the exercise. (2)

• M1: Chemoreceptors detect change in {carbon dioxide/ pH}

• M2: The cardiovascular control centre receives impulses from the {chemoreceptors/ sends impulses to the heart}

• M3: Therefore, impulses are transmitted along the parasympathetic {nerve/ nervous system/ nerve pathway} to the SAN reducing heart rate

Describe how the brain reduces the activity of the sweat glands after the exercise. (2)

• M1: Thermoreceptors detect a decrease in temperature

• M2: {hypothalamus/ thermoregulatory centre} sends fewer impulses to sweat glands

Explain why too much exercise could be harmful to the human body. (3)

• M1: increased exercise results in wear and tear of {joints/ cartilage/ tendons/ ligaments}

• M2: Therefore leading to joint damage

• M3: Suppression of immune system

• M4: Therefore leading to increased risk of infection

Explain how transcription factors could activate insulin gene expression in beta cells. (3)

• M1: Interaction between transcription factor and promoter region on gene

• M2: RNA polymerase binds to promoter region

• M3: {transcription/ mRNA} produced for insulin gene

Extracellular enzymes are produced by specialised cells. Explain how groups of cells can produce the same enzyme. (3)

• M1: Genes can be activated or deactivated

• M2: These cells receive the same stimulus

• M3: All of these cells have the gene for the enzyme {activated/ switched on}

• M4: Resulting in production of mRNA for the enzyme

Describe the changes caused when calcium ions bind to the molecules shown in the diagram (troponin, tropomyosin). (2)

• M1: Tropomyosin is moved by troponin

• M2: Myosin binding sites on actin are exposed

Explain how changes to troponin/tropomyosin cause muscles to contract. (4)

• M1: Myosin heads can bind to binding sites

• M2: Bound myosin changes shape

• M3: Actin filaments {slide/ pull} over the myosin

• M4: Therefore {muscle fibres/ myofibril sarcomeres} shorten

• M5: ATP hydrolysed/ ADP and {inorganic phosphate} released

Describe how the concentration of calcium ions around the myofibrils is controlled. (3))

• M1: Calcium ions released from sarcoplasmic reticulum

• M2: In response to {nerve impulse/ action potential/ depolarisaiton} at neuromuscular junction

• M3: Calcium channels open to allow calcium ions to cross the membrane/ enter the sarcoplasm

• M4: Calcium ions taken back up into the sarcoplasmic reticulum by active transport

Calcium ions are required for muscle contraction. Describe the role of calcium ions in the contraction of muscle fibres. (3)

• M1: Calcium ions {bind/ attach} to the troponin

• M2: Causing tropomyosin to be {displaced/ shape altered}

• M3: Exposing myosin binding sites on actin

Describe two structural differences between fast twitch muscle fibres and slow twitch muscle fibres. (2)

• M1: Fast twitch fibres have {no/ few} mitochondria present/ slow twitch fibres have many mitochondria

• M2: Fast twitch fibres have {no/ few} capillaries present/ slow twitch fibres have many capillaries present

A muscle fibre is a specialised body cell. Explain how the structure of a muscle fibre is related to its specialised function. (3)

• M1: {cell surface membrane/ sarcolemma} contain voltage gated channels to allow depolarisation of muscle fibres

• M2: Many mitochondria for {aerobic respiration/ to supply ATP}

• M3: Presence of {myofibrils/ actin and myosin}

• M4: Myofibrils allow contraction of muscles

The outer mitochondrial membrane is not permeable to hydrogen ions (H⁺ ). Explain the importance of this feature of the membrane. (4)

• M1: To stop H⁺ diffusing out of mitochondrion/ into cytoplasm

• M2: Therefore maintaining high concentration of H⁺ in the intermembrane space

• M3: So {H⁺/ protons} can move down {concentration/ electrochemical gradient}

• M4: By chemiosmosis

• M5: to sythesise ATP

Explain why some ATP is broken down during glycolysis. (2)

• M1: because breakdown of ATP {donates phosphate to/ phosphorylates} glucose

• M2: ATP supplies energy to break down the glucose

• M3: To produce phosphorylated 3-carbon compounds

The electron transport chain occurs in the cristae of mitochondria.

The electron transport chain involves a number of carrier molecules. Explain the role of these carrier molecules in the electron transport chain. (3)

• M1: Receives hydrogen from reduced {NAD/ FAD}/ to allow reduced {NAD/ FAD} to be oxidised

• M2: Break down into {protons/ hydrogen ions} and electrons

• M3: Electrons transferred by a series of redox reactions

• M4: Energy released is used to pump {hydrogen ions/ protons} into intermembranal space

Explain the need for reduced NAD to be oxidised in a mitochondrion.

• M1: So that hydrogen can be delivered to electron transport chain (allow: supply of {hydrogen ions/ protons})

• M2: To allow {ATP synthesis/ chemiosmosis}

• M3: To regenerate NAD

Devise a valid investigation, using a spirometer, to compare the breathing rate and tidal volume of people with larger thorax vs smaller thorax. (4)

• M1: Select people with different thorax sizes/ large thorax and small thorax

• M2: Select people who are similar in other respects (e.g. same age, same fitness level, same sex)

• M3: One relevant variable controlled (e.g. temperature, same level of previous activity, data collected when subjects were at rest)

• M4: Measurement of tidal volume from spirometer trace (difference in peak to trough volume gives tidal volume)

• M5: Measure breathing rate as number of {peaks / troughs} in a set time

Explain why there is a greater ratio of wound infections in open surgery compared with keyhole surgery. (2)

• M1: Larger opening / slower recovery time

• M2: Access for (more) {pathogens / bacteria} / (therefore) more time for { pathogen entry / bacteria entry / infection }

Explain how the production of sweat is controlled during exercise in humans. (4)

• M1: By {homeostasis / a negative feedback response}

• M2: Thermoreceptors {in the skin / hypothalamus} detect a rise in temperature

• M3: Send impulses to the {heat loss centre / thermoregulatory centre / hypothalamus}

• M4: {heat loss centre / thermoregulatory centre / hypothalamus} sends impulses to the sweat glands

• M5: to increase sweat production