TGT and PGT (English previous year questions) (Part-V)

Your heart beats around 60 times a minute, delivering nutrients and removing waste from every cell in your body. It has been doing this since you were in the womb-the heart forms 18 days into foetal development and begins to pump blood about three days later.

But for all we know about this vital organ, researchers are still learning new things about it. The heart is made of cardiac muscle. Unlike some muscles in the body, we can't control it, instead, the hearts speed is controlled by the autonomic nervous system.

The nerves that relay input about our required heart rate connect to a specialised centre in the wall of the right atrium (one of the heart's four chambers), known as the sinoatrial (SA) node. The SA node is composed of specialised pacemaker cells, which send out an electrical impulse throughout the cardiomyocytes (cardiac cells), ensuring the heart beats properly. But the (SA) node can be dysfunctional.

These faults can be acquired or inherited. Acquired dysfunction is more common, often caused by age, certain medications and lifestyle factors such as increased BMI, diabetes and hypertension.

Many people who have a dysfunction may not have symptoms. One of the most common symptoms of a dysfunctional (SA) node, experienced by about two million people a year in the UK, is arrhythmia.

This is where the heart beats too fast, too slow or irregularly. There are a variety of treatment options for arrhythmia including cardoversion, pacemakers and cardiac ablation.

In how many days, heart starts to pump blood after its development in our body

I. The symptoms of dysfunctional (SA) node are not same for every person.
II. We can control all the muscles in our body except heart.

Mars is known for its thin atmosphere, where CO, dominates and provides most of the atmospheric mass and pressure. Water on Mars is currently found on the surface as a layer of ice-several kilometres thickat the north pole.

It also appears as seasonal frost at the coldest times of the year, and in the atmosphere as vapour and ice. Nevertheless, the Martian atmosphere is extremely dry compared to Earth's, with about 100 times less water.

While precipitation on Earth results in water layers several centimetes thick, water that would precipitate on Mars would only form a thin film of less than a milimetre.

The evidence suggests that Mars was not always the cold, arid planet we observe today. There is plenty of evidence of water on Mars' surface in the distant past-about four billion years ago. At that time, liquid water flowed in great streams and stagnated in the form of pools or lakes.

For liquid water to circulate and reside on the surface long enough to leave these marks, there must have been a (A) different climate than the one we see today.

Mars, Earth and Venus probably formed from the gradual accumulation of the same basic materials, which means that they must have had great similarities early in their history. But while Earth and Venus have retained most of their thick atmosphere, Mars, because of its small size and low gravity, has lost most of its atmosphere.

Choose the word that means the same as the word 'plenty' as used in the passage