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Responding to Change

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Biology

Living things sense and respond to change to ensure survival and optimum functioning. No environment is perfect for sustaining life without the organism itself adapting to it.

What are the changes in our ecosystem?

Our environment is in a state of constant change. One day might bring you a heatwave, making you sweat and hyperventilate, another day might bring you a broken thermostat in the middle of the winter. While some animals in the desert are in a state of constant water deficit, others could be struggling to keep themselves dry. Taller plants in the rainforest get an abundance of light, while the lower branches get fractured bits of sunlight.

While adaptations assist organisms to successfully respond to long-term environmental conditions, organisms have to prepare for sudden, emergent changes that the environment can surprise them with. These changes require an instant response for the organism to protect itself. This is where the concept of homeostasis comes in.

Cells maintain homeostasis by responding to change

Homeostasis is the maintenance of the internal conditions of the cells to the optimum levels, despite the external environment and the changes that occur within it.

The five facets that constitute the internal conditions of the cell include:

  • The water content.

  • Temperature.

  • pH level of the cell contents.

  • The nutrition level – mainly the concentration of glucose in the cell.

  • Pressure levels in comparison to the environment.

Changes in any of these parameters act as a trigger for cells. These changes are known as stimuli.

Response to stimuli

Internal and external changes in the organism’s environment that interfere with the organism’s ability to carry out reactions efficiently require a response. It is vital that a response is given. Let’s take a closer look at the process.

The role of stimuli in responding to change

Stimuli are sudden environmental changes that stimulate a cascade of organised chemical reactions in various organ systems. This leads to adapting and responding to change to protect the organism.

Cells detect changes through a specialised monitoring and security system called receptors.

What are receptors?

Receptors are molecules sensitive to changes in the cells’ internal and external environment.

When the receptors detect changes, they send signals to the control centres to remedy the changes.

What is a response?

What happens next? As discussed, receptors send chemical or electrical impulses to the organism’s control centre. The control centre, in turn, sends signals to the relevant systems that can identify and respond positively to change. These target organs are called effectors, and the reaction to the stimuli is called a response.

Responding to Change [+] stimulus receptor response [+] StudySmarter

Figure 1. Response to change. StudySmarter Originals.

Let’s look at glucose control in the body as an example of a cell responding to its environment.

Example of cells responding to their environment

Meet X, a healthy person with no history of disease. Let's follow a scenario:

  1. X eats a doughnut.
  2. A few hours later, glucose is absorbed through the intestines into the bloodstream, causing an increase in blood glucose concentration. Some of the glucose is absorbed by the cells through simple diffusion, but not enough. The amount left in the bloodstream remains higher than normal.
  3. High blood glucose level stimulates the receptors in the pancreas, which in turn cause the production and release of a hormone called insulin. Insulin enters the bloodstream and stimulates the uptake of glucose molecules into the cells, thus providing them with the nutrition they require to carry out their functions.

However, what happens if X doesn’t eat anything else that day and there is no glucose in their bloodstream? Luckily, earlier, when X had just eaten, some of the glucose molecules were stored by the liver cells and packed away in the form of glycogen. When the blood glucose concentration is dangerously low, a hormone called glucagon is released. Glucagon stimulates the conversion of glycogen into glucose and its release into the bloodstream. This ensures the maintenance of the homeostasis of blood glucose.

When presented with a complicated question loaded with a lot of information, first break it down into broad categories, as demonstrated below. It will make the question’s intentions clearer.

Responding to Change [+] cells respond to changes in their environment [+] StudySmarter

Figure 2. Example of cells responding to their environment in the human body. StudySmarter Originals.

Responding to change in plants

While animals have more dramatic responses to stimuli, plants have to modify their growth patterns according to the changes in the environment. This is due to their inability to move around. Plants need adequate sunlight and water for optimum survival. They grow towards or away from the stimuli through patterns of growth called tropism.

Tropisms are predominantly regulated by the hormone auxin, present in the plant’s roots and shoots. Auxin promotes cell division, and its concentration in various areas of the stem or root determines the direction of growth. Plant stems grow towards the light as they contain chloroplasts which are the site of photosynthesis reactions. The auxins are distributed towards the area of the plant, which receives light and stimulates growth.

The plant identifies ways to respond positively to change and lean towards the stimulus – this is positive phototropism. Roots demonstrate negative phototropisms by growing away from the well-lit into the shaded areas (usually underground, as deeper soil has higher water concentration).

Another hormone called ethylene causes the fruits of the plant to ripen.

Responding to Change [+] positive and negative phototropism [+] StudySmarter

Figure 3. Phototropism in roots and shoots of plants. StudySmarter Originals.

Nervous coordination in responding to change

In animals, the response to change involves a more complex mechanism of action, which includes various groups of cells. The receptors flag the stimulus, which converts it into electrical and chemical signals, further transmitting these signals to the brain via nerve cells called neurons. Signals are transmitted amongst cells via action potential – changes in the potential of the cell membranes. All these changes occur in the nervous system, which consists of the brain, the spinal cord, nerves, and neurons.

Muscle contraction in responding to change

Some stimuli require the organism to move to respond to the stimulus. This involves the limbs and other muscle groups which are responsible for mobility. There is a synchronised contraction and relaxation of the various skeletal muscle groups, overseen by the brain and the spinal cord and transmitted through neurons. The movement of the sliding filaments and the consequent contraction and relaxation of the muscles are controlled by electric and chemical signals and can be voluntary or involuntary.

Responding to Change - Key Takeaways

  • When there is a change in the organism’s environment, it needs to react and protect itself to survive. This involves a cascade of reactions which are called a response to change.

  • Homeostasis is the internal environment of the cell and is a careful balance of five parameters: the water content, temperature, the pH level of the cell contents, the nutrition level – mainly the concentration of glucose in the cell, and pressure levels in comparison to the environment.

  • A stimulus is a change in the ecosystem that can affect the organism’s homeostasis and requires a response for the organism to survive. A receptor is a structure that notices the stimulus and signals the organism’s control centre to organise and carry out a response to the environment.

  • Plants respond to environmental stimuli through patterns of growth called tropisms. These are regulated by a hormone called auxin, which is present in the roots and shoots of the plant. Ethylene is a plant hormone that is responsible for the blooming of flowers and the ripening of fruits.

  • Animals respond to changes in the internal environment through predominantly hormones and enzymes. They respond to changes in the external environment through neuro-muscular coordination.

Frequently Asked Questions about Responding to Change

Plants require an optimum level of sunlight to survive and grow. Most plants thrive during spring and summer as the conditions are nearly perfect for survival, growth, and reproduction. This is when the majority of the plant hormones are released. However, as the duration of daylight and the temperature decreases during autumn, most plants tend to shed their leaves and enter a state of dormancy to survive the harsh winters.

Changes in the environment or stimuli trigger the receptors present in cells. These receptors signal the presence of these changes to the organism’s control centre through chemical or electrical signals.  This stimulates responses conducted by the control centre (the nucleus of the cell or the brain) and the target organelles. This ensures the maintenance of homeostasis.

There are two major reasons why organisms change. The first one is to adapt to long-term changes in the environment and ensure the optimal functioning of the organism. The second reason is to protect themselves from sudden, endangering stimuli. Broadly, the reason for the change is to maintain homeostasis.

When an organism is placed in a cold environment, the body has to compensate to maintain the optimal body temperature of 37.5 C. It responds to the cold stimulus by rapidly contracting the skeletal muscles, what we call shivering, by constricting capillaries on the surface of the skin, which causes a reduction in heat loss, and by constricting the hair follicle, causing the hair to stand up and form an insulating layer of air above the skin.

Communities respond to change by adapting to change as a cohesive unit by establishing specific roles amongst members of the community. A community responds to change by adaptation, interdependence, and sometimes competing for resources with other communities. Competition can be for resources in the environment and can occur between communities or between other organisms in the environment.

Final Responding to Change Quiz

Question

Define response to change.

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Answer

Response to change is the mechanism through which the organism responds to changes in the environment that can threaten the homeostasis of the cell.

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Question

What is the term used to describe the organelles or organ systems that respond to a stimulus?

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Answer

Effectors

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Question

Select a plant hormone from the list below:

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Answer

Auxin

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Question

You are a farmer, and you get an emergency order of bananas from a client you cannot lose. But none of your bananas is ripe. What hormone can you administer to ripen fruits quickly?

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Answer

Ethylene helps fruits ripen quickly.

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Question

Your younger sibling has type 1 diabetes and regularly takes insulin to manage her blood sugar levels. One day she accidentally takes two doses of insulin instead of one. Now she is feeling quite unwell. What do you think she should do to rectify the situation?


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Answer

Her blood sugar concentration is low due to increased insulin in the bloodstream. She needs to have something sweet, such as chocolate, to normalise her blood sugar.

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Question

A plant has been growing beside a huge tree which completely shadows the new plant. The sunlight predominantly hits the area from the west due to neighbouring structures looming over the area. Considering all the other variables to be constant, in which direction will the plant’s roots and shoots grow?

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Answer

Stems will grow towards the west; the roots will grow underground towards the east.

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Question

 ________ converts glucose into __________ molecules which are stored in the liver cells. 

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Answer

Glucagon, Glycogen

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Question

Patterns of growth in plants that are dependent on stimuli are _______.


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Answer

Tropisms

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Question

Arrange in the correct order:
A. response B. receptor C. effector D. stimulus

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Answer

D, B, C, A.

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Question

What are the five parameters that need to be controlled to maintain homeostasis?

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Answer

The five parameters are: 

  • The water content.
  • Temperature.
  • pH level of the cell contents. 
  • The nutrition level – mainly the concentration of glucose in the cell
  • Pressure levels in comparison to the environment.

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Question

Name the three types of muscle in the body and give one example of each.

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Answer

1. Cardiac muscle found exclusively in the heart (myocardium)

2. Smooth muscle, found in the walls of blood vessels and the gut. 

3. Skeletal muscle, Biceps brachii

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Question

What is the role of myoglobin in striated muscles?

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Answer

Myoglobin has a higher affinity for oxygen than haemoglobin. Therefore, it assists in unloading oxygen from haemoglobin and delivering it to muscles during intense activity.

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Question

Define the terms isometric and isotonic contraction.


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Answer

Isometric contraction: Generation of tension in the muscle while its length remains constant. 

Isotonic contraction: Tension remains constant, but muscle length changes. 

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Question

Name the three types of muscle contraction.

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Answer

Isometric, concentric isotonic, and eccentric isotonic contractions

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Question

Why do sarcomeres shorten in length during muscle contraction? 

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Answer

Due to actin and myosin filaments sliding over one another.

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Question

What is the source of energy for muscle contraction? 

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Answer

ATP hydrolysis by the myosin head.

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Question

What is the source of energy for muscle contraction? 

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Answer

ATP hydrolysis by the myosin head.

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Question

What does the term ‘antagonistic pair of muscles’ mean?


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Answer

Muscle can only pull and cannot push. Therefore, they need to work in pairs to move bones in different directions at the joints. Antagonistic pairs pull in different directions. When the agonist muscle contracts, its antagonist is relaxed.

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Question

How do antagonistic muscles maintain posture?


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Answer

When they undergo isometric contraction simultaneously at a joint to keep the joint angle constant.

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Question

Define the term ‘Concentric isotonic contraction’ and give an example.


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Answer

Concentric isotonic contraction is a type of muscle contraction during which the length of the muscle shortens and, as a result, brings the origin and insertion of the muscle closer. An example would be the contraction of the biceps muscle while lifting a dumbbell.

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Question

In __________ contraction, the force generated than the resisting force, and the muscle shortens as it contracts.


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Answer

Concentric

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Question

In __________ contraction, the force generated is smaller than the opposing force on the muscle. Hence, the sarcomeres lengthen as they contract. This type of contraction is used for decelerating a body part or gently lowering a load.


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Answer

Eccentric

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Question

In __________ contraction, the force generated equals the resisting force, and the muscle length remains constant. An example would be holding an object without any movement. 


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Answer

Isometric

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Question

Define negative feedback.

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Answer

A mechanism of homeostasis that acts to stop the stimulus that triggered it.

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Question

Define positive feedback.

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Answer

A mechanism that acts to increase the original stimulus.

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Question

What are the five components of a homeostatic mechanism?


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Answer

Having an optimum point, a sensor, an effector, a control centre, and a feedback mechanism.

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Question

What is a sensor?


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Answer

A cell or group of cells that monitor conditions in the internal or external environment and relay it to the control centres.

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Question

What is a control centre? 


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Answer

Clusters of cells that receive information from the sensors. Ater processing the information, they send signals to the effectors.

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What are effectors?


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Answer

Usually muscles or glands that receive impulses from the control centres and generate a response that re-establishes the optimum value.

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Question

Give examples of homeostasis against hot temperatures.


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Answer

Vasodilation, increased sweating and lowering of skin hair.

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Question

Give examples of homeostasis against cold temperatures?

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Answer

Vasoconstriction, shivering, increased metabolism, and huddling together.

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Question

Give examples of negative feedback.


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Answer

Calcium regulation, thermoregulation, and osmoregulation.

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Give an example of positive feedback.


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Answer

Oxytocin and uterus contraction during childbirth.

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Question

What is the definition of muscle?

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Answer

It refers to a number of muscle fibres bundled together in layers of connective tissue.

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Question

What is a myofiber?

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Answer

An individual muscle cell.

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Question

A muscle fibre contains multiple _______?


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Answer

Nuclei.

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Question

Can an injured muscle fibre be replaced by dividing existing skeletal muscle fibre? 


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Answer

No. Muscle fibres cannot divide.

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Question

How do muscle fibres get bigger? 


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Answer

By hypertrophy.

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Question

_____ filament is composed of 2 intertwined helical chains. Each of which contains a binding site for _____.


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Answer

Actin, myosin.

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Question

There are two I bands per sarcomere, one at each end. One end of the I bands is free. To what is the other end bound?

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Answer

Z line.

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Question

The portion of the thin filaments that does NOT overlap the thick filaments is called _____.


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Answer

I band.

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Question

What do we call a narrow dark band in the centre of the H zone that corresponds to proteins linking together the central region of adjacent myosin filaments?


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Answer

M line.

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Question

What is the section between two Z lines called?


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Answer

A sarcomere.

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Question

Name a series of tubular sleeve-like segments surrounding each individual myofibril. Their main role is to store calcium ions.


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Answer

Sarcoplasmic reticulum.

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Question

Name three common causes of muscle spasms.


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Answer

  1. Overuse and muscle fatigue.
  2. Dehydration.
  3. Electrolyte abnormalities.

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Question

The sliding filament theory involves the act of five different molecules + calcium ions. Name them.

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Answer

1.Myosin 

2.Actin

3.Tropomyosin

4.Troponin, 

5.ATP

 + 6.Calcium ions

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Question

What are the six steps of the cross-bridge formation cycle?

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Answer

1. The influx of calcium ions 🡺 triggers the unblocking of the actin-binding sites.

2. Myosin head binds to actin. 

3. The power stroke of the myosin head causes the sliding of the thin actin filaments.

4. The binding of ATP to myosin head resulting in the cross-bridge detachment.  

5. The hydrolysis of ATP, which re-energizes the myosin head and makes it ready for the next cycle. 

6. The transport of calcium ions back to the SR.

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Question

An ___brings about the release of calcium ions from the _______.


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Answer

  • Action potential
  • SR

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Question

Calcium ions flood into the sarcoplasm and _____, causing a ________of the troponin-tropomyosin complex.

This conformation change ____the binding sites on ____.

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Answer

  • Bind to the troponin c
  • Conformational change
  • Unblocks
  •  Actin filaments

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Question

The binding of myosin to actin brings about a _____ of the cross bride, resulting in the release of ___and___.

At the same time, the cross-bridge ___, pulling the ____inward toward the _____. This movement is called the "_____."

The _____has been transformed into the ____of contraction.

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Answer

  • conformational change
  • ADP 
  • phosphate ion
  • flexes
  • actin filament
  • M line
  • Power Stroke
  • chemical energy of ATP hydrolysis
  • mechanical energy

Show question

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