Topic 7 Flashcards Preview

A Level Biology (Edexcel Salters-Nuffield) > Topic 7 > Flashcards

Flashcards in Topic 7 Deck (76):

Where does movement (caused by muscles) occur?

At joints


How many muscles are needed to move a bone and why?

At least 2

Muscles can only pull so need to work in pairs (or more)


What are antagonistic muscles?

Pairs of muscles that work together to move a bone


How does the knee move?

When bent, the hamstrings at the back contracts.
At the same time, the quadriceps relax so they can be stretched.

When straightened, the quads contract whilst the hamstrings relax so can be stretched


What is an extensor?

A muscle that contracts to cause the extension of a joint

(e.g. quadriceps)


What is a flexor?

A muscle that contracts to reverse joint movement/the action of an extensor

'Pulls' e.g. the hamstrings


What are synovial joints?

Give examples

Joints in which the bones that move (articulate) are seperated by a cavity filled with synovial fluid

This enables them to move freely

E.g. hips, knee, ankle joint

They all have the same basic structure...


Draw and label the structure of a synovial joint

See image


What is the function of tendons?

Attach bones to muscles

This enables joint movement


What property do tendons have and how does this relate to their function?

Non-elastic so when uscle contracts bones moves

Otherwise tendon would just stretch and bone wouldn't be moved!


What is the function of ligaments?

Connect bones to bones


How does the structure of a ligament relate to its function?

Have a small amount of elasticity, allows them to gradually lengthen, increasing flexibility

Are strong + flexible


Describe the structure of cartilage and how this relates to its function

Absorbs synovial fluid + acts as shock-absorber

Strong but not as tough/brittle as bone

Smooth, prevents bones rubbing


What is the function of the synovial fluid in synovial joints?

Acts as a shock absorber

Is thick + viscous, enabling it to act as a lubricant


Why do the ends of bones in joints sometimes have pads of cartilage on them?

To give additional protection - acts as a shock-absorber + prevents rubbing


What is the function of the synovial membrane in joints?

Secretes synovial fluid


What is the function of the fibrous capsule in joints?

Encloses joints

(Stops the synovial fluid leaking out...)


What are all the types of joints found in humans?

Synovial joints

Ball-and-socket joints

Gliding joints

Hinge joints

Pivot joints


Describe the structure of ball-and-socket joints and what type of movement they enable

Give an example

A round head fits into a cup-shaped socket

Allows movement in many directions

e.g. the hip


Describe the structure of gliding joints and what type of movement they enable

Give an example

Two flat surfaces slide over one another

Allows movement in 1 plane but many combined allows many planes of movement

e.g. the articulating surfaces between vertibrae


Describe the structure of hinge joints and what type of movement they enable

Give an example

A convex surface fits into a concave surface

Allows movement in 2 directions

e.g. the elbow


Describe the structure of pivot joints and what type of movement they enable

Give an example

Part of one bone fits into a ring-shaped structure in

Allows movement in 2 planes/rotation

e.g. joint at the top of the spine (shake/nod head)


Describe the structure of a muscle

Muscle made up of bundles of muscle fibres up to 2cm across. These are bound together with connective tissue that is continuous with tendons

Each fibre is a single muscle cell surrounded by a cell membrane

Within each fibre there are numerous myofibrils, each composed of repreated contractile units called sarcomeres


Why are muscle fibres multinucleate?

What does this mean?

Each fibre/cell contains multiple nuclei

Because 1 nucleus couldn't effectively control metabolism of such a long cell (can be up to 2cm long)

It would take too long to move proteins synthesised from mRNA to further parts of cell


Why are muscles described as striated?

What does this mean?

Means striped

Because the sarcomeres in the myofibrils are made up of actin + myosin

Where they overlap there is a dark band

Where only actin filaments occur there is a light band


(Briefly) describe how a muscle contracts

Within the sarcomere, the actin filaments move towards the centre of the sarcomere so they overlap with the myosin more.

This shortens the sarcomere and hence the muscle (so it contracts)


What is the sarcoplasmic reticulum?

Specialised type of endoplasmic reticulum

System of membrane-bound sacs around the myofibrils containing store of Ca2+ needed for muscle contraction

Ca2+ only released when SR recieves nerve impulse via neuromuscular junction


What is the sarcoplasm?

The name given to the cytoplasm in a muscle cell (fibre)


Describe the process of muscle contraction using the sliding filament theorem

  • A nerve impulse arrives at the neuromuscluar junction in the muscle fibre. This triggers the release of Ca2+ from the sarcoplasmic reticulum
  • The Ca2+ ions then diffuse through the sarcoplasm and attach to troponin molecules, causing then to move
  • This exposes the myosin binding sites on the actin filaments
  • The myosin 'heads' bind with the binding sites on the actin, forming cross-bridges
  • The myosin changes shape, causing the myosin 'head' to 'nod' forward. This results in the movement of the filaments as the attached actin moves over the myosin
  • An ATP molecule binds to the myosin, causing it to detach from the actin
  • An ATPase on the myosin hydrolyses ATP to ADP + Pi causing the myosin 'head' to return to the upright position, thus allowing the cycle to begin again
  • The collective bending of many myosin heads moves the actin filament in relation to the myosin filament, thus the muscle contracts


What causes a muscle to relax and what happens when it does?

A muscle relaxes when it is no longer stimulated by nerve impulses

Ca2+ ions are actively pumped out of sarcoplasm using ATP

The troponin + tropomyosin move back, blocking myosin-binding sites on actin again


What happens when there is a lack of both nerve stimulation and ATP in a muscle fibre?

The muscle stops contracting/relaxes

The lack of ATP means actin-myosin cross-bridges remain, hence the muscle remains contracted/unmoves

This is what happens in rigor mortis


What are T tubulues?

What does the T stand for?

Transverse tubules

Used to transport/bathe muscle in Ca2+ 

This results in the spread the nervous impulse throughout the muscle fibre + allows the muscle to contract


What is BMR?

Basal metabolic rate

The minimum energy requirement of the body at rest to fuel basic metabolic processes

Measured in kJg-1h-1


How is BMR measured?

By recording oxygen consumption under strict conditions:

No food consumed 12hrs before

Body is totally at rest in a thermostatically controlled room


What factors affect BMR?

It's roughly proportional to the body's surface area

Varies depending on age + gender

Body fat seems to be important in accounting for these differences


What must happen to phosphate ions before they can be combines with ADP to make ATP?

They must be dehydrated - must be seperated from the water molecules bound to them when they are in solution

This requires energy


How can ATP stored in water be used as a way of storing chemical potential energy in the body?

ATP in water is higher in energy than ADP + Pi in water

ATP keeps the Pi seperated from water, however when one is removed by hydrolysis, the Pi is hydrated, releasing a lot of energy

This is because the energy released by the bonds formed between H2O + Pi is greater than the small amound needed to hydrolyse the Pi

ADP is also formed as a result of the hydrolysis of ATP


What is the overall equation for the hydrolysis of ATP?


ATP in water → ADP in water + hydrated Pi + energy transfered


Why are glucose and oxygen not brought together directly during respiration?

Because this would release large amounts of energy quickly which would damage the cell

Releasing the energy quickly would mean some would be wasted/unused


How is the energy used to generate ATP produced?

What is the main/principle reaction underpinning aerobic respiration?

The H stored in glucose is brought together with oxgen to form water

The bonds between O + H in water are stronger than those between C + H in glucose

Therefore the output of energy is greater than the input needed to break bonds


What happens to glucose during aerobic respiration?

What controls this?

What is released as a waste product?

Glucose is split apart (oxidised) in a series of smaller steps

Each of these is controlled by a specific intracellular enzyme

CO2 is released as a waste product


What is the first step of respiration (aerobic and anaerobic)?



What is glycolysis?

What does it literally mean?

The 'splitting of sugar'

The 1st stage of respiration - glucose is broken down into pyruvate


What must happen before glycolysis can take place?

Stores of glycogen in muscle/liver cells must be converted into glucose

To do this they are hydrolysed


Where does glycolysis occur?

In the cytoplasm/sarcoplasm of the cell


What type of molecule is coenzyme NAD?

What does NAD stand for?

A non-protein organic molecule (and coenzyme!)

Nicotinamide adenine dinucleotide


Describe the process of glycolysis

  1. 2 Pi groups are added to glucose from 2ATP to increase its reactivity
  2. It's then split into 2 molecules of phosphorylated 3C compounds
  3. Each intermediate 3C compound oxidised, producing 3C pyruvate
    During this reaction 2H atoms removed + taken up by coenzyme NAD to form NADH
  4. Glucose is at a higher energy level than pyruvate so energy is released
  5. This is used to transfer Pi from the intermediate phosphorylated compounds to ADP to form 2ATP


What are the overall products of glycolysis?


2 pairs of H atoms (4H total)

2 pyruvate (3C)


What does the fate of pyruvate depend upon?

The availability of oxygen


What happens to pyruvate if oxygen is present?

What happens if it is not?

If oxygen present undergoes the link reaction to form acetyl coenzyme A which is used in Krebs cycle

If not it is converted into lactate by the addition of 2H from NADH


Describe the steps of the link reaction

Pyruvate is:

decarboxylated - CO2 released as waste product

dehydrogenated - 2H taken up by 2x coenzyme NAD

Acetyl coenzyme A is formed as a result

This carries the 2C acetyl groups to Krebs cycle


What are the four important types of reaction that occur in Krebs cycle?

Phosphorylation - when Pi added e.g. ADP + Pi → ATP

Deecarboxylation - which break off CO2 e.g. pyruvate → acetyl CoA + CO2

Reduction - H added e.g. oxidied NAD + 2H → NADH

Oxidation - dehydration/H removed e.g. pyruvate → acteyl CoA + 2H


Describe the stages of Krebs cycle

  1. Each 2C acetyl CoA combines with a 4C compound to create a 6C compound
  2. The 6C compound is decarboxylated to remove a CO2 and produce a 5C compound.
    It is also oxidised, removing 2H. These reduce NAD
  3. The 5C compound is then decaroxylated to a 4C compound, allowing the cycle to start again
    It is also oxidised 3x to removes 3x 2H. These reduce 2x NAD and 1x FAD
    Substarate-level phosphorylation also occurs, producing 1 ATP


Where does Krebs cycle take place?

What is also located here/Why does it occur here?

In the mitochondrial matrix

The enzymes that catalyse each stage of the reaction are also located here


What are the overall products of Krebs cycle?

4x 2H which are used to produce:
1x FADH (reduced FAD)
3x NADH (reduced NAD)

2x CO2

1x ATP



What is substrate-level phosphorylation?

The formation of ATP using energy from the substrates in a reaction (e.g. the intermediates in glycolysis)


When does substrate-level phosphorylation occur?

Duing glycolysis

During Krebs cycle


What is FAD and what does it stand for?

A coenzyme (like NAD)

Flavin adenine dinucleotide


Describe the stages of the electron transport chain

  1. Reduced coenzyme (NADH/FADH) carries 2x H+ and e- to the electron transport chain on inner mitochondrial membrane
  2. e- pass from one electron carrier to the next in a series of redox reactions - the carrier is reduced when it recieves e- and oxidised when it passes them on
  3. Protons (H+) move across the inner mitochondrial membrane creating a high H+ conc in the intermembrane space
  4. H+ diffuse back into the matrix down an electrochemical gradient
  5. H+ diffusion allows ATP synthase to catalyse ATP synthesis
  6. e- and H+ recombine to form H atoms when then combine with O to make H2O. If the supply of O stops, the e- transport chain + ATP synthesis stop


What is the name of the reaction that produces ATP in the electron transport chain?

Oxidative phosphorylation


(as opposed to substrate-level phosphorylation during glycolysis + Krebs cycle)


What is a conformational change?

A change in the shape on an enzyme's active site


Can enable the enzyme to catalyse a reaction, for example

e.g. H+ ions cause conformational change in ATP synthase, enabling ADP + Pi to bind


Describe how ATP is produced by chemiosmosis

What is the theory of chemiosmosis?

The theory that explains why the e- transport chain works

  • Energy released as e- pass along chain. This is used to move H+ from matrix across inner mitochondrial membrane into intermembrane space
  • This creates an electrochemical gradient across inner membrane as there is a large difference in H+ conc + large electrical difference - intermembrane space more positive than matrix
  • The H+ then diffuse down this gradient back through hollow protein channels with ATP synthase embedded in. As they do so, they cause a conformational change in ATP synthase
  • This results in the synthesis of ATP being catylsed
  • The H+ then enter the matrix, where they recombine with e- to form H. These combine with O to make water


Draw a diagram to summarise all the steps of aerobic respiraton


How many ATP molecules are produced throught the entire process of aerobic respiration according to simple calculations?

Where do they come from?

38 total

2 from substrate-level phosphorylation during glycolysis

2 from substrate-level phosphorylation during Krebs Cycle

34 from oxidative-phosphorylation during the electron transport chain
(2 from reoxidation of each FAD = 2x2 = 4)
(3 from reoxidation of each NAD = 10x3 = 30)


Why is the theoretical/simple calculation for the total amount of ATP produced during aerobic respiration probably wrong?

What is the total more likely to be?

Total more likely to be 30 ATP from 1 glucose

Because some H+ used to exchange ADP + ATP between matrix + cytoplasm and across the mitochondrial membrane

Some H+ also used to move other ions/molecules across the membrane


How much of the total chemical potential energy from glucose is released via ATP?

What happens to the remainder of the energy/what is it used to do?

Assuming 38 molecules of ATP made, only 40% total chem. potential of glucose released

Assuming 30 molecules of ATP made, only 32% chem. potential of glucose released!

Remainder raises temp of cell. This increases rate of metabolic reacts + in birds & mammals maintains core body temp.


What happens when the demand for oxygen in the cell outstrips supply? Why?

The electron transport chain stops

Because there is no O to accept H+ + e-

This means the NADH formed during glycolysis, the link reaction, + Krebs Cycle aren't reoxidised

Without a supply of (oxidised) NAD ANY respiration reactions can't continue

So body switches to anaerobic respiration...


Describe the process of anaerobic respiration

  1. Glycolysis occurs as normal - glucose decarboxylated to pyruvate.
    Substrate-level phosphorylation occurs producing 2ATP
    Dehydration occurs producing 2x 2H
  2. The 2x 2H reduce 2NAD
  3. Pyruvate is reduced to lactate using the 2x 2H from the 2NADH
  4. This regenerates the (oxidised) NAD


What is the net yield of ATP from anaerobic respiration?

What is is effeciency?

Only 2 ATP per molecule of glucose!

2% efficiency!


If lactate wasn't a limiting factor (or the amount of glucose etc.) why would anaerobic respiration be able to carry on indefinitely?

Because NAD is regenerated from reduced NAD by the oxidation of pyruvate to lactate


Explain why anaerobic respiration cannot continue indefinitely unlike aerboic respiration

Because lactate is produced

Lactate forms lactic acid in solution

As lactate accumulates, so does lactic acid, so the pH of the cell falls

This inhibits the enzymes that catalyse the glycolysis reactions

Therefore the glycolysis reactions and the physical activity depending on them cannot continue


Explain why the build of of H+ ions in the cytoplasm causes enzymes/proteins to denature.

(Why do enzymes function over a narrow pH range?)

Where might the H+ ions come from?

H+ ions may be donated by lactic acid

Many of the amino acids that make up enzymes have positively/negatively charged groups

As H+ ions build up in the cytoplasm, they neutralise any negatively charged groups in the active site

This affects the attraction between the charged groups on the substrate and the active site

Therefore the substrate may no longer be able to bind to the active site and the reaction will be inhibited/stopped


What happens after a period of anaerobic respiration/exercise?


(How does the body get rid of lactate?)

The accumulated lactate is converted back into pyruvate

This is then oxidised directly to CO2 and H2O via Krebs Cycle

Energy is released to synthesis ATP

This requires oxygen, hence O consumption higher after exercise (oxygen debt)

Some lactate may also be converted back into glycogen + stored in the liver/muscles


Give the alternate name for oxygen debt

Post-exercise oxygen consumption


What is oxygen debt?

The excess oxygen required after exercise to oxidise lactate


Outline an experiment that could be used to investigate the rate of respiration

  1. Put some KOH solution/sode lime in the bottom of a test tube. This will absorb the CO2 produced by the organism
  2. Place some gauze above the KOH and place several maggots/organism of choice onto it
  3. Place a bung in the end of the test tube with 2 holes - 1 to allow oxygen in and one connected to a manometer tube/glass tube with a drop of coloured liquid in
  4. If using a manometer tube (in pic), attach this to a 2nd test tube with a double-bung. In the other hole attach a syringe. This compensates for any changes in volume due to variation in gas pressure/temp inside apparatus
  5. Record the starting position of the fluid, then set a timer for 5 mins. Record the position of the fluid every min.
  6. Calculate the vol O2 used using vol=πr2 x dist. moved where r= radius of tube attached to manometer