Science Basic Facts

,

• Publisher: Collins
• Year: 2013
• Print ISBN: 9780007144976
• eBook ISBN: 9780007554911
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

A completely new full-colour edition of the popular guide to scienceA completely new full-colour edition of the popular guide to scienceFirst published in 1989, this is the third edition of the popular Gem Basic Facts Science. The Basic Facts series is a series of illustrated gem dictionaries in important school subjects. First published in 1989, this is the third edition of the popular Gem Basic Facts Science. The Basic Facts series is a series of illustrated gem dictionaries in important school subjects.

S

saliva Fluid secreted by the salivary glands into the mouths of many animals. Its function is to moisten and lubricate food so that it can be swallowed more easily. In some mammals, including humans, saliva contains the enzyme salivary amylase (sometimes called ptyalin) which digests starch into maltose.

salt This is a compound formed when the hydrogen of an acid is totally or partially replaced by a metal. When an acid reacts with a metal the result is a salt and hydrogen gas, e.g.

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

When an acid reacts with a base the result is a salt and water, e.g.

NaOH(aq) + HNO3(aq) → NaNO₃(aq) + H₂O(l)

Salts may sometimes also be made by the direct combination of two elements, e.g.

2Na(s) + Cl₂(g) → 2NaCl(s)

If only one hydrogen atom of a dibasic acid is replaced the result is an acid salt, e.g. sodium hydrogen carbonate NaHCO3. The name of the salt is derived from the metal and the acid used.

sulphuric acid → sulphates
nitric acid → nitrates
hydrochloric acid → chlorides

For example, the name of the salt formed by the reaction of copper(II) oxide and dilute sulphuric acid is copper(II) sulphate.

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

secondary sexual characteristics The features which distinguish between adult male and female animals (excluding the reproductive organs). For example, the lion’s mane and the antlers on a stag. In humans, secondary sexual characteristics include breast development in females and facial hair in males. The development of these features is usually controlled by hormones. Compare primary sexual characteristics.

sedimentary rocks Rocks which are formed in layers at the earth’s surface. The layers may be formed:

(a) From fragments of rock produced by weathering and erosion.

(b) By chemical precipitation of dissolved substances.

(c) From the remains of plants and animals.

Sedimentary rocks are classified in terms of their composition.

Rock	Main minerals present
Limestone	Carbonate minerals calcite and dolomite
Sandstone	Quartz

They may also be classified in terms of their grain size. The following rocks may have similar composition but differ in grain size.

Rock	Diameter of grains in mm
Conglomerate	more than 2
Sandstone	1/16–2
Siltstone	1/256–1/16
Mudstone	less than 1/256

seed This develops from an ovule after fertilization in flowering plants. The seeds of a plant are enclosed in a fruit (which develops from the ovary).

Within the seed, the embryo becomes differentiated into an embryonic shoot bud (plumule) and root (radicle) and either one or two seed leaves (cotyledons). Given the right conditions, germination will occur and the seed will grow into a new plant. See fruit and seed dispersal.

seed The structure of a seed: (a) broad bean (b) maize grain.

selective breeding The breeding of animals or plants in order to enhance particular desirable features in their offspring. For example, by breeding only from the cows in a dairy herd which give the highest milk yields, the average milk yield of the whole herd might be expected to increase in time.

sensitivity The ability of plants and animals to respond to stimuli, such as heat, light, sound, etc., resulting from changes in their environment. Sensitivity makes organisms aware of changes in their environment, thus they can make appropriate responses to any changes which occur. Certain parts of animals, such as the eyes, ears and skin, are specialized in sensing particular environmental stimuli. They are called sense organs or receptors. Similarly, plant tissues such as shoot tips are receptors and are important in tropisms.

Stimuli from the environment cause responses to be initiated in specialized structures called effectors. The muscles in our bodies are examples of effectors. The responses which an organism makes constitute its behaviour.

sensitivity Organisms respond to changes in their environment.

sexual reproduction A form of reproduction which involves the fusing of two sex cells (gametes), one from a male parent and the other from a female parent, to form a zygote. The fusing process is called fertilization. The gametes are haploid; however, the resulting zygote has a diploid number of chromosomes. After fertilization the zygote divides repeatedly, ultimately resulting in a new organism.

Unlike asexual reproduction, the offspring of sexual reproduction are genetically unique (with the exception of identical twins) because they have obtained half of their chromosomes from their male parent and half from their female parent. Thus each fertilization produces a new combination of chromosomes unique to the new organism formed.

shadow A dark shape cast on a surface by an object through which light, a form of radiation, cannot pass, as radiation travels in a straight line through a given medium. If the source of radiation is small, and the object large, a sharp shadow is formed.

...

Table of contents

• Title Page
• Contents
• Introduction
• A
• B
• C
• D
• E
• F
• G
• H
• I
• J
• K
• L
• M
• N
• O
• P
• R
• S
• T
• U
• V
• W
• X-Y
• Appendix A: Abbreviations and Symbols
• Appendix B: Circuit Symbols
• Appendix C: Characteristics of living things
• Appendix D: The Differences between Plants and Animals
• Appendix E: The Major Groups of Living Organisms
• Appendix F: The Solar System
• Keep Reading
• Copyright
• About the Publisher