CBSE Class 8 Science - Flashcards: Microorganisms, Metals & Non-Metals, Conservation, Reproduction, and Force & Heating

Practice flashcards covering key concepts from the notes on microorganisms, metals/non-metals, conservation, reproduction, and force & heating.

What happens when vegetables are sun-dried for pickling?

Water is removed; microbes cannot grow, preventing spoilage and extending shelf life.

Why is a puffed juice packet considered unsafe?

Gas produced by microbes indicates spoilage; the juice is unsafe to drink.

Why do doctors give Vitamin B with antibiotics?

Antibiotics kill beneficial gut bacteria that produce Vitamin B; supplementation prevents deficiency.

What is a colony in microbiology?

A cluster of similar unicellular organisms.

What is Spirogyra?

A filamentous alga.

Can viruses be seen with a light microscope?

No. Viruses are visible only under an electron microscope.

Name the five main types of microorganisms.

Bacteria, Fungi, Protozoa, Algae, and Viruses.

What is vaccination?

Introducing a weakened or dead microbe to provoke immunity.

How do microbes help in maintaining a clean environment?

They decompose dead plants, animals and waste into simpler substances.

How do microbes help increase soil fertility?

Some bacteria fix nitrogen (Rhizobium) and blue-green algae fix nitrogen.

Name two chemical preservatives.

Sodium benzoate and Sodium metabisulphite.

Name the common shapes of bacteria.

Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral), Vibrio (comma-shaped).

What is a bacteriophage?

A virus that infects bacteria.

What is the bread mould mentioned?

Rhizopus.

List methods to preserve food.

Drying, Salting, Refrigeration, Pasteurization, Chemical preservatives.

Metal oxides vs non-metal oxides: basic vs acidic.

Metal oxides are basic and turn red litmus blue; non-metal oxides are acidic and turn blue litmus red.

What happens when zinc is placed in copper sulfate solution?

Zinc displaces copper; blue solution becomes colourless and copper is deposited.

Why does silver tarnish on exposure to air?

Silver reacts with sulfur compounds to form black silver sulfide.

Why is aluminium foil used for packaging?

Aluminium is malleable, non-toxic, light, and resistant to corrosion.

What is an alloy?

A mixture of two or more elements (usually metals) with improved properties; e.g., brass, steel.

Compare the general properties of metals and non-metals.

Metals form basic oxides, conduct electricity, are malleable and ductile; non-metals form acidic oxides, poor conductors, brittle.

Name four uses of metals and four uses of non-metals.

Metals: jewellery, wires, machinery/buildings, foils. Non-metals: oxygen for respiration, nitrogen fertilizers, sulfur vulcanisation of rubber, chlorine for water purification.

What is the Red Data Book?

A record of endangered and extinct species to raise awareness and protection.

What is biodiversity?

Variety of plants, animals, and microorganisms in an area.

What is an ecosystem?

A system formed by interaction of living organisms with each other and their surroundings.

What are major threats to biodiversity?

Deforestation, pollution, hunting, habitat loss, climate change.

What is a biosphere reserve vs a national park?

Biosphere reserve is larger and protects whole ecosystem including humans; national park is smaller and protects wildlife habitats.

What information is in the Red Data Book?

List endangered, extinct, and vulnerable species to raise awareness and protection.

What is desertification?

Fertile land turning into desert due to erosion; prevented by afforestation and soil conservation.

Why is biodiversity important?

Maintains balance, provides food, medicine, oxygen, raw materials, and ecosystem resilience.

What is metamorphosis? Give examples.

A major change in body form; examples: frog (t tadpole to frog), butterfly, housefly.

What are identical and non-identical twins?

Identical: one zygote splits into two; Non-identical: two eggs fertilised by two sperms.

Where does fertilization occur in humans?

Fallopian tube.

What is IVF?

In vitro fertilisation; egg and sperm fertilised outside the body; embryo placed in uterus.

What is zygote vs embryo?

Zygote is the single cell after fertilisation; embryo is the multicellular stage formed after divisions.

Name the main parts of the male reproductive system mentioned.

Testes, Vas deferens, Urethra, Penis.

Where does embryo implant in humans?

Uterus.

What is external vs internal fertilisation?

External fertilisation: outside the body (e.g., frogs); Internal fertilisation: inside the body (e.g., humans).

Who are hermaphrodites? Examples.

Organisms with both male and female reproductive organs; e.g., earthworm, leech.

What makes sperm mobile? Structure.

Tail (flagellum) enables movement; middle piece contains mitochondria for energy; head carries DNA.

What is the SI unit of current?

Ampere.

What is the function of a Miniature Circuit Breaker (MCB)?

A safety device that automatically cuts off excess current.

In heating effect, what are the three factors?

Current, resistance, time.

Why does a sharp edge increase pressure?

Smaller contact area concentrates force, increasing pressure.

Why do camels walk easily on sand?

Broad feet increase contact area, reducing pressure.

What does balanced forces imply about motion?

Net force is zero; the body remains at rest or continues moving at constant speed.