Category: chemistry FAQ’s

An atom is the smallest recognised division of a chemical element and is made up of three particles: the proton, neutron and electron.

99% of the mass of the atom is held in the central nucleus, comprising the protons and neutrons. The negatively charged electrons whip around the nucleus in orbital shells of different energies.

• The number of protons in a nucleus is called its atomic number.
• The number of electrons in an atom is equal to the number of protons – this means that atoms have no overall charge.
• If an atom gains or loses electrons, it is called an ion.

Fast Fact: The word Atom comes from the Greek word for ‘indivisible’ – ironic, seeing as we know atoms are made of even smaller subatomic particles.

Atomic Structure

Particle	Relative Charge	Relative Mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836

Put simply, an acid is any substance that has pH of less than 7. The pH scale is used to measure how acid or alkali a substance is:

• 0-3 = strong acid (UI turns red)
• 4-6 = weak acid (UI turns orange/yellow)
• 7 = neutral (UI turns green)
• 8-10 = weak alkali (UI turns blue)
• 11-14 = strong alkali (UI turns purple)

The pH of an acid is determined by the concentration of Hydrogen ions (H⁺) the substance has when in solution. All acids contain hydrogen ions when in solution; the higher the concentration of H⁺ ions, the lower the pH.

Fast Fact: Bee stings are acidic. They can be neutralised using baking powder which contains sodium hydrogen carbonate – a base.

Common Acids

Name	Formula
Hydrochloric Acid	HCl
Sulphuric Acid	H2SO4
Nitric Acid	HNO3
Phosphoric Acid	H3PO4
Ethanoic Acid (Vinegar)	CH3COOH

The plant life cycle is known as the alternation of generations because, in this cycle, there are two different forms of living organisms that alternate with each other, one of which is haploid and the other of which is diploid. The alternation of generations is also called the diplobiontic cycle or metagenesis, and it does not just occur in plants. Other living organisms, such as cnidarians, go through this cycle.

Zygotic meiosis occurs in the haplontic haplobiontic life cycle. Gametes from adult haploid individuals unite to form the diploid zygote. The zygote undergoes meiosis and generates four haploid cells that develop into adult individuals via mitosis. Therefore, in zygotic meiosis, the cell that undergoes meiosis is the zygote and the gametes are formed by mitosis.

Gametic meiosis is when meiosis produces gametes, or rather, haploid cells which can each unite with another gamete to form the zygote. It occurs in the diplontic haplobiontic life cycle (in humans, for example), in which the individual is diploid and meiosis forms gametes.

Sporic meiosis happens in metagenesis (the alternation of generations, or diplobiontic life cycle). In this life cycle, cells from the diploid individual (called a sporophyte) undergo meiosis, producing haploid spores that do not unite with others but instead develop by mitosis into haploid individuals (called gametophytes). In this life cycle, the gametes are produced via mitosis from cells of the gametophyte.

Sexual reproduction may take place through three different types of life cycles: the haplontic haplobiontic cycle (the organism is haploid, a single type of organism) ; the diplontic haplobiontic cycle (the organism is diploid , a single type of organism); and the diplobiontic cycle (two types of organisms, one haploid and the other diploid). The diplobiontic cycle is known as the alternation of generations, or metagenesis. In humans, the cycle is diplontic haplobiontic (a single diploid organism).

Cryptogamic (hidden sex organs) plants do not present flowers or seeds. They include the bryophytes and pteridophytes.

Phanerogamic plants have seeds. They include the gymnosperms and angiosperms.

Bryophytes are nonvascular plants (mosses, liverworts, hornworts), meaning that they do not have a conducting system for the transport of sugar, water and nutrients. Tracheophyte plants are vascular plants, meaning that they have conducting structures.

The kingdom Plantae is divided into two large subkingdoms: bryophytes and tracheophytes (pteridophytes, gymnosperms and angiosperms). The criterion for the division is the presence or not of conducting (vascular) tissue.

While plant cells are eukaryotic, autotrophic, photosynthetic and have chloroplasts and a cell wall, animal cells are eukaryotic, heterotrophic and do not have  chloroplasts nor a cell wall.

Typical plant cells are eukaryotic (they have a nucleus), autotrophic (they produce their own food) and photosynthetic (they use light to make food). Plant cells also have chloroplasts and a cell wall (a structure exterior to the plasma membrane) made of cellulose.