Class 8 Biology — Important Questions with Answers

What it is

Plant cells have a cell wall, a big vacuole and chloroplasts; animal cells have none of these.

Answer

A plant cell has a rigid cell wall outside its cell membrane and usually contains a large central vacuole and green chloroplasts for photosynthesis. An animal cell has no cell wall (only a cell membrane), has small or no vacuoles and lacks chloroplasts. This is why plants can make their own food while animals cannot.

What it is

Microbes are tiny living things that can help us (curd, bread, medicine) or harm us (disease).

Answer

Useful: yeast is used to make bread and in brewing (fermentation), and Lactobacillus bacteria turn milk into curd. Harmful: the bacterium that causes tuberculosis, and the Plasmodium protozoan that causes malaria. So micro-organisms can help or harm us depending on the type.

What it is

Manure is natural and releases nutrients slowly; fertiliser is a chemical that acts fast.

Answer

Manure is a natural substance made by decomposing animal dung and plant waste; it adds humus, improves soil texture and releases nutrients slowly. A fertiliser is a chemical made in factories that is rich in a specific nutrient (like nitrogen, phosphorus or potassium) and acts fast, but its overuse can harm the soil and water. Manure is eco-friendly; fertilisers give a quick nutrient boost.

What it is

At puberty, hormones bring body changes that mark a child becoming an adult.

Answer

Secondary sexual characters are the physical features that appear at puberty and distinguish males from females - such as growth of facial hair and deepening of the voice in boys, and development of breasts in girls. They are controlled by hormones released by the endocrine glands: testosterone from the testes in boys and oestrogen from the ovaries in girls.

What it is

Animals either lay eggs (oviparous) or give birth to live young (viviparous).

Answer

Oviparous animals lay eggs that develop and hatch outside the mother's body, for example a hen or a frog. Viviparous animals give birth to live young that develop inside the mother's body, for example a human or a cow.

What it is

Biodiversity is the variety of all living things - plants, animals and microbes - in an area.

Answer

Biodiversity is the variety of living organisms - plants, animals and micro-organisms - found in a particular area. It should be conserved because every species has a role in keeping the ecosystem balanced, and the loss of one can affect many others. Biodiversity gives us food, medicines, and clean air and water, and losing it through deforestation and pollution can push species to extinction.