CSS Compulsory Papers General Science and Ability Syllabus

What are the three subatomic particles, their charges, and locations in an atom?

Protons (positive) and neutrons (neutral) are in the nucleus; electrons (negative) orbit the nucleus in shells.

Distinguish between atomic number and mass number.

Atomic number is the number of protons in an atom (defines the element); mass number is the total number of protons plus neutrons in the nucleus.

What is the difference between an ionic bond and a covalent bond?

An ionic bond forms by the transfer of electrons between atoms, creating charged ions (e.g., NaCl); a covalent bond forms by the sharing of electron pairs between atoms (e.g., H₂O).

What does the pH scale measure, and what values indicate acids, bases, and neutrality?

pH measures the acidity or alkalinity of a solution on a scale of 0–14. Below 7 is acidic, exactly 7 is neutral, and above 7 is basic (alkaline).

Distinguish between a physical change and a chemical change, with an example of each.

A physical change alters form but not composition and is often reversible (e.g., melting ice); a chemical change produces a new substance and is usually not easily reversible (e.g., burning wood, rusting iron).

Who is regarded as the founder of the cell theory, and what are its main points?

The cell theory was developed by Schleiden, Schwann, and Virchow. Its main points: all living things are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

What is the key structural difference between prokaryotic and eukaryotic cells?

Prokaryotic cells (e.g., bacteria) lack a true membrane-bound nucleus and membrane-bound organelles; eukaryotic cells (e.g., plant and animal cells) have a true nucleus and membrane-bound organelles.

Why is the mitochondrion called the 'powerhouse of the cell'?

Because it carries out cellular respiration, producing most of the cell's energy in the form of ATP (adenosine triphosphate).

List three structures found in plant cells but not in animal cells.

A cell wall (cellulose), chloroplasts (for photosynthesis), and a large central vacuole.

What is the function of ribosomes in a cell?

Ribosomes are the sites of protein synthesis, where amino acids are assembled into proteins according to instructions from messenger RNA.

Name the main organs and primary function of the human digestive system.

Mouth, oesophagus, stomach, small intestine, and large intestine (with liver and pancreas as accessory organs). Its function is to break down food, absorb nutrients, and eliminate waste.

What are the four chambers of the human heart?

Two upper chambers called atria (right and left) and two lower chambers called ventricles (right and left).

Trace the path of blood through the heart and lungs (pulmonary circulation).

Deoxygenated blood enters the right atrium, passes to the right ventricle, is pumped to the lungs to be oxygenated, returns to the left atrium, passes to the left ventricle, and is pumped to the body via the aorta.

What is the basic functional unit of the kidney, and what does it do?

The nephron is the basic functional unit of the kidney; it filters blood, reabsorbs useful substances, and excretes waste as urine.

What are the three main parts of the human nervous system?

The central nervous system (brain and spinal cord), the peripheral nervous system (nerves outside the CNS), and the autonomic nervous system (controls involuntary functions).

What gas do we inhale and what gas do we exhale during respiration, and where does gas exchange occur in the lungs?

We inhale oxygen and exhale carbon dioxide; gas exchange occurs in tiny air sacs called alveoli.

Name the six main classes of nutrients required by the human body.

Carbohydrates, proteins, fats (lipids), vitamins, minerals, and water.

What are macronutrients and micronutrients? Give examples.

Macronutrients are needed in large amounts and provide energy: carbohydrates, proteins, and fats. Micronutrients are needed in small amounts: vitamins and minerals.

Which vitamin deficiencies cause scurvy, rickets, and night blindness?

Scurvy is caused by lack of vitamin C; rickets by lack of vitamin D; and night blindness by lack of vitamin A.

What is a balanced diet?

A diet that provides all the essential nutrients—carbohydrates, proteins, fats, vitamins, minerals, water, and fibre—in the correct proportions to maintain good health and meet the body's energy needs.

What is the deficiency disease caused by lack of iron, and what is its main symptom?

Lack of iron causes anaemia, whose main symptom is reduced red blood cells/haemoglobin leading to fatigue, weakness, and pale skin.

Distinguish between communicable and non-communicable diseases, with an example of each.

Communicable (infectious) diseases spread from person to person via pathogens (e.g., tuberculosis, malaria); non-communicable diseases do not spread by contact and are often lifestyle- or genetics-related (e.g., diabetes, hypertension).

Name the pathogens responsible for malaria, tuberculosis, and dengue.

Malaria is caused by the Plasmodium protozoan (spread by the female Anopheles mosquito); tuberculosis by the bacterium Mycobacterium tuberculosis; and dengue by a virus (spread by the Aedes mosquito).

What is the difference between bacteria and viruses as disease-causing agents?

Bacteria are living single-celled organisms that can reproduce on their own and are treated with antibiotics; viruses are non-living particles that can only reproduce inside a host cell and are not affected by antibiotics.

Write the overall word and chemical equation for photosynthesis.

Carbon dioxide + water → (sunlight, chlorophyll) glucose + oxygen. Chemically: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

What is chlorophyll and why is it essential for photosynthesis?

Chlorophyll is the green pigment found in chloroplasts that absorbs light energy (mainly red and blue wavelengths) and uses it to drive the conversion of carbon dioxide and water into glucose.

What is transpiration in plants?

Transpiration is the loss of water vapour from a plant's surface, mainly through tiny pores called stomata on the leaves; it helps in water uptake and cooling the plant.

Define an ecosystem and distinguish between producers, consumers, and decomposers.

An ecosystem is a community of living organisms interacting with their non-living environment. Producers (plants) make their own food; consumers eat other organisms; decomposers (bacteria, fungi) break down dead matter into nutrients.

What is biodiversity, and why is it important?

Biodiversity is the variety of all living organisms—genetic, species, and ecosystem diversity. It is important because it maintains ecosystem stability, provides food, medicine, and resources, and supports ecological balance.

What are the main types of environmental pollution?

Air pollution, water pollution, soil (land) pollution, noise pollution, and (sometimes listed) radioactive, thermal, and light pollution.

What is the greenhouse effect, and name the main greenhouse gases.

The greenhouse effect is the trapping of the Sun's heat in the atmosphere by gases that absorb and re-radiate infrared radiation. Main greenhouse gases: carbon dioxide (CO₂), methane (CH₄), water vapour, and nitrous oxide (N₂O).

What is global warming, and what is its chief human cause?

Global warming is the long-term rise in Earth's average surface temperature, driven chiefly by human emission of greenhouse gases—especially carbon dioxide from burning fossil fuels and deforestation.