CSS General Science and Ability Biological Sciences Syllabus

What is an enzyme, and what is its chemical nature?

An enzyme is a biological catalyst that speeds up the rate of a biochemical reaction without being consumed. Most enzymes are proteins (some are RNA, called ribozymes).

What is the 'lock and key' model of enzyme action?

The lock and key model proposes that an enzyme's active site has a specific shape that fits exactly with its substrate (like a key fits a lock), allowing the enzyme to act only on a specific substrate.

How do temperature and pH affect enzyme activity?

Each enzyme has an optimum temperature and pH at which it works best. Beyond these, the enzyme denatures (loses its shape) and activity decreases. High temperature and extreme pH cause irreversible denaturation.

How do enzymes speed up reactions?

Enzymes lower the activation energy required for a reaction to proceed, allowing the reaction to occur faster and at lower temperatures than it would otherwise.

What is the basis of the five-kingdom classification system, and who proposed it?

The five-kingdom system, proposed by R.H. Whittaker (1969), classifies organisms into Monera, Protista, Fungi, Plantae, and Animalia based on cell type, body organization, and mode of nutrition.

How are plants classified into non-vascular and vascular groups?

Non-vascular plants (bryophytes, e.g. mosses) lack true vascular tissue (xylem and phloem). Vascular plants have xylem and phloem and include pteridophytes (ferns), gymnosperms (conifers), and angiosperms (flowering plants).

What is the difference between gymnosperms and angiosperms?

Gymnosperms produce naked (uncovered) seeds, usually in cones, and have no flowers or fruits (e.g. pine). Angiosperms are flowering plants that produce seeds enclosed within fruits (e.g. mango, wheat).

What is the difference between monocots and dicots?

Monocots have one cotyledon, parallel leaf venation, fibrous roots, and floral parts in multiples of three. Dicots have two cotyledons, net (reticulate) leaf venation, taproots, and floral parts in multiples of four or five.

What distinguishes vertebrates from invertebrates?

Vertebrates have a backbone (vertebral column) and an internal bony or cartilaginous skeleton (e.g. fish, amphibians, reptiles, birds, mammals). Invertebrates lack a backbone (e.g. insects, worms, mollusks) and make up about 95% of animal species.

Name the five classes of vertebrates with one distinguishing feature each.

Fish (gills, fins, scales); Amphibians (moist skin, live on land and water, e.g. frog); Reptiles (dry scaly skin, lay shelled eggs); Birds (feathers, wings, lay eggs); Mammals (hair/fur, mammary glands, mostly give live birth).

What is the main function of the digestive system, and where does most absorption occur?

The digestive system breaks down food into smaller molecules that can be absorbed for energy and nutrition. Most absorption of digested food occurs in the small intestine through finger-like projections called villi.

Name three digestive enzymes and the substances they break down.

Amylase breaks down starch into sugars; protease (e.g. pepsin, trypsin) breaks down proteins into amino acids; lipase breaks down fats into fatty acids and glycerol.

Trace the pathway of air during respiration in humans.

Air passes through the nose/mouth, pharynx, larynx, trachea, bronchi, bronchioles, and finally to the alveoli, where gas exchange (O2 in, CO2 out) occurs by diffusion.

Where does gas exchange occur in the lungs, and how is it adapted for it?

Gas exchange occurs in the alveoli (air sacs). They are adapted by having thin walls, a large surface area, a moist surface, and a rich blood capillary supply for efficient diffusion of gases.

What are the four chambers of the human heart and the type of blood each handles?

Right atrium and right ventricle handle deoxygenated blood (pumped to lungs); left atrium and left ventricle handle oxygenated blood (pumped to the body).

What is the difference between arteries, veins, and capillaries?

Arteries carry blood away from the heart (usually oxygenated) at high pressure with thick walls. Veins carry blood toward the heart (usually deoxygenated) and have valves. Capillaries are tiny thin-walled vessels where exchange of materials occurs.

What are the main components of blood and their functions?

Plasma (transports nutrients, wastes, hormones); red blood cells (carry oxygen via hemoglobin); white blood cells (fight infection/immunity); platelets (help in blood clotting).

What are the two main divisions of the nervous system?

The central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of the nerves connecting the CNS to the rest of the body.

What is a neuron, and what are its main parts?

A neuron is the basic functional unit of the nervous system that transmits nerve impulses. Its main parts are the cell body (soma), dendrites (receive impulses), and the axon (carries impulses away).

What is the function of the kidney in the excretory system?

The kidneys filter the blood to remove nitrogenous wastes (mainly urea), excess water, and salts, forming urine. They also regulate water balance, salt balance, and blood pressure (osmoregulation).

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

The nephron is the functional unit of the kidney. It filters blood (in the glomerulus), reabsorbs useful substances, and secretes wastes to produce urine.

Name the main male and female reproductive organs in humans and the gametes they produce.

The male organ is the testis, which produces sperm. The female organ is the ovary, which produces eggs (ova). Fertilization of egg by sperm produces a zygote.

What is a virus, and why is it considered on the borderline between living and non-living?

A virus is a non-cellular infectious particle made of genetic material (DNA or RNA) enclosed in a protein coat (capsid). It is borderline because it can reproduce only inside a host cell but is inert outside it.

Name three common viral diseases in humans.

Common viral diseases include influenza (flu), measles, polio, hepatitis, AIDS (caused by HIV), COVID-19, dengue, and chickenpox.

What causes AIDS, and how is it transmitted?

AIDS is caused by the Human Immunodeficiency Virus (HIV), which attacks the immune system (CD4 helper T-cells). It spreads through unprotected sex, infected blood/needles, and from mother to child.

Name two diseases caused by protozoan parasites and their causative agents.

Malaria is caused by Plasmodium (transmitted by the Anopheles mosquito), and amoebic dysentery is caused by Entamoeba histolytica.

Name three common bacterial diseases in humans.

Common bacterial diseases include tuberculosis (TB), typhoid, cholera, tetanus, pneumonia, and diphtheria.

What are vectors, and how can vector-borne diseases be prevented and controlled?

Vectors are organisms (e.g. mosquitoes, flies) that transmit pathogens from one host to another. Control measures include eliminating breeding sites, using insecticides and bed nets, ensuring clean water and sanitation, and vaccination.

What is biotechnology, and name two of its major applications.

Biotechnology is the use of living organisms or their products to make useful products or improve processes. Applications include genetic engineering, production of medicines (e.g. insulin), vaccines, GM crops, and biofuels.

What is a biofuel, and name two common types and their sources.

A biofuel is a renewable fuel produced from biological material (biomass). Bioethanol is produced by fermentation of sugars/starch from crops like sugarcane and corn; biodiesel is produced from vegetable oils and animal fats. Biogas (mainly methane) is produced by anaerobic digestion of organic waste.