Micro-Organisms: Friends and Foe — Science STD 8 — Question

John saw full moon on a particular day. After how many days, he will be able to see the full moon again?

Differentiate the terms atoms, molecules, and ions.

State any two physical properties for believing that aluminium is a metal.

Tashu saw her mother keeping the wheat grains on the terrace in a sunny day before storing them. She was confused to see this as she thought the grains will get dirty if kept in open and approached her mother for clearing her doubts.
Her mother explained Tashu the reason behind her act. Tashu then helped her mother to carry the grains to the terrace happily.
(i) The grains were kept on the terrace. Can you suggest a reason ?
(ii) Is it necessary to keep the grains in the Sun? Why or why not ?

Write the importance of petrochemicals.

What variables increase or decrease the heating effect of electric current?

When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.

Paddy is a major cereal crop in our country.
(i) In which season is paddy cultivated ?
(ii) Discuss the method of sowing
(iii) What measures must be taken to prevent spollage and insect attack of harvested grains ?

Cartilage is present in the joints of our body, which helps in their smooth movement. With advancing age, this cartilage wears off. How would this affect the movement of joints?

List some points about the discovery of cell.