Science - Exemplar Problems

The most important difference between a plant cell and an animal cell is that the former has a cell wall. A cell wall gives mechanical support to a plant cell. Animal cells do not have cell walls.

Plants have both a cell wall that is made up of cell membrane (plasma membrane) and cellulose. The cell wall is a rigid membrane matrix found on the surface of all plant cells whose primary role is to protect the cell and its content. Hence statement 1 is correct and statement 2 is not correct.

Plant cells have a large central vacuole that can occupy up to 90% of the cell’s volume. Animal cells may have many small vacuoles, a lot smaller than the plant cell. Hence statement 3 is correct.

Source: NCERT

The only thing absolute in this universe according to Einstein is the speed of light, rest everything is relative. Light travels at the speed of about 300,000 km per second and it is always the same throughout the universe. A light-year is the distance light travels in one Earth year.

On the scale of the universe, measuring distances in miles or kilometers doesn't cut it; therefore, astronomers measure the distances of stars and other astronomical distances in the time it takes for light to travel to us. Hence, option (d) is the correct option.

Source: Class 11th NCERT

Option 1 is right because viruses do not have the chemical machinery needed to survive on their own.

Option 2 is wrong because they seek out host cells in which they can multiply. Viruses can't be grown on synthetic media (e.g. agar [a type of gelatin]) but they can be grown on cultures of bacteria. Bacteria reproduce and live like any other living organism would; they take in nutrients and reproduce using binary fission (like mitosis).

Viruses, on the other hand, are like little aliens. They really aren't living since they don't absorb nutrients or produce waste. Rather, they hook onto another cell (e.g. a bacterium) and inject the cell with its own viral genetic code. This code then causes the cell to produce multiple copies of the virus, essentially doing the reproduction for the virus at the cost of its own resources. The virus can't reproduce itself without another cell to build its copies. Therefore, we can't grow a virus on synthetic media.

Option 3 is also wrong because viruses enter the body from the environment or other individuals from soil to water to air via nose, mouth, or any breaks in the skin and seek a cell to infect.

Source Citation: NCERT: Class X Science

The most important difference between a plant cell and an animal cell is that the former has a cell wall. A cell wall gives mechanical support to a plant cell. Animal cells do not have cell walls.

Plants have both a cell wall that is made up of cell membrane (plasma membrane) and cellulose. The cell wall is a rigid membrane matrix found on the surface of all plant cells whose primary role is to protect the cell and its content. Hence statement 1 is correct and statement 2 is not correct.

Plant cells have a large central vacuole that can occupy up to 90% of the cell’s volume. Animal cells may have many small vacuoles, a lot smaller than the plant cell. Hence statement 3 is correct.

Source: NCERT

Option 1: Each individual droplet of water acts as a tiny prism that both disperses the light and reflects it back to our eye.

Option 2: Since water is more dense than air, light is refracted as it enters the drop.

Option 3: Some of the light will reflect off the back of the drop if the angle is larger than the critical angle (48° for water).

Source: NCERT: Class X Science