Biology 2018 Jamb Examination

Double fertilisation is a distinctive process in angiosperms where one sperm fertilizes the egg forming a zygote, while another sperm fuses with two polar nuclei to form the endosperm. This ensures simultaneous formation of embryo and nutritive tissue.

The thyroid gland is located near the trachea in the neck. It produces hormones such as thyroxine and triiodothyronine, which regulate metabolism, growth, and development. Its position close to the trachea ensures efficient hormone distribution via the blood.

Hair is a key characteristic that distinguishes mammals from other vertebrates. It provides insulation, aids in sensory perception, and plays roles in camouflage and communication. All mammals, including humans, have hair at some stage of life.

Micronutrients are essential nutrients required in small amounts, such as vitamins and minerals. Carbon is a macronutrient and a basic element of organic compounds, so it does not fall under the category of micronutrients.

Etiolation occurs when plants grow in partial or complete absence of light. It results in pale, elongated stems and underdeveloped leaves. Light influences chlorophyll production and normal plant development, so absence of light triggers etiolation.

Botany, the scientific study of plants, is also called phytology. It covers plant physiology, structure, growth, reproduction, and classification. This term originates from the Greek 'phyton' meaning plant and 'logia' meaning study.

Blood platelets (thrombocytes) lack a nucleus. They are small cell fragments involved in clotting and wound repair. Unlike white blood cells or red blood cells in some species, platelets carry out their functions without a nucleus.

Chlorofluorocarbons (CFCs) are chemical compounds that cause depletion of the stratospheric ozone layer. They release chlorine atoms upon exposure to ultraviolet light, which catalyze the breakdown of ozone molecules, increasing UV radiation at Earth's surface.

The long neck of a giraffe is often cited as an example of Lamarck’s theory of use and disuse, where the frequent stretching to reach leaves supposedly lengthened the neck over generations. Though modern biology attributes it to natural selection, the question references Lamarckian theory.

A species is defined as a group of closely related organisms capable of interbreeding and producing fertile offspring. This is the fundamental unit of biological classification, distinct from higher taxonomic levels such as family, class, or kingdom.