IGCSE Biology - Pearson Edexcel - GLOSSARY DEFINITIONS ONLY - COMPLETED Flashcards
FLASHCARDS MADE MYSELF WITH AID OF SOURCE BOOK: BIOLOGY PEARSON EDEXCEL INTERNATIONAL GCSE (9-1) STUDENT BOOK BY PHIL BRADFIELD AND STEVE POTTER
1
Q
What is an abiotic factor?
A
A physical or chemical factor affecting an ecosystem (e.g. light intensity or temperature).
2
Q
Name 2 examples of abiotic factors:
A
- Light intensity
- Temperature
3
Q
What is accommodation?
A
Accommodation refers to the changes taking place in the eye which allow it to focus on objects at different distances.
4
Q
What is the ACCURACY of experimental results?
A
The closeness of an experimental result to its true value.
5
Q
What is acid rain?
A
Rain with a pH of less than 5.5, caused by pollutant gases such as sulphur dioxide and nitrogen oxides.
6
Q
What is the active site?
A
The area on the surface of an enzyme where the substrate attaches and products are formed.
7
Q
What is active transport?
A
The net movement of molecules or ions against a concentration gradient (from an area of low concentration to an area of high concentration), using energy from respiration.
8
Q
What is an adaptation (of an organism)?
A
Feature of an organism that suits its structure to its function.
9
Q
What does ATP stand for?
A
Adenosine Triphosphate
10
Q
What is adenosine triphosphate (ATP)?
A
A chemical present in all cells which acts as an energy ‘currency’. ATP is made by respiration and used up by any process that needs a supply of energy.
11
Q
What are the adrenal glands?
A
A pair of endocrine glands situated above the kidneys which secrete adrenaline.
12
Q
What is adrenaline?
A
Adrenaline is a hormone secreted by the adrenal glands. It stimulates several organs in the ‘fight or flight’ response.
13
Q
What is aerobic respiration?
A
A reaction that releases energy from food. It uses oxygen and produces carbon dioxide and water.
14
Q
What is agar?
A
A jelly-like substance used as a culture medium for growing microorganisms.
15
Q
What are algae?
A
Photosynthetic protocists. Mostly unicellular, some multicellular lifeforms (such as seaweed).
16
Q
What is algal bloom?
A
A rapid increase in numbers of algal cells in an aquatic habitat. It is often caused by eutrophication.
17
Q
What are alleles?
A
Alleles are different forms of a gene.
18
Q
What is the singular form of alveoli?
A
Alveolus
19
Q
What is the plural form of alveolus?
A
Alveoli
20
Q
What is an amino acid?
A
One of about 20 different molecules that form the building blocks of proteins.
21
Q
What is the amnion?
A
The membrane enclosing the embryo during pregnancy.
22
Q
What is amniotic fluid?
A
Fluid secreted by the amnion that protects the embryo by acting as a shock absorber.
23
Q
What is amylase?
A
An enzyme that digests starch into maltose.
24
Q
What is anaerobic respiration?
A
A reaction that releases energy from food, without using oxygen. It produces lactate in mammals, and produces carbon dioxide and ethanol in yeast.
25
What is the anther?
The part of the stamen where pollen grains are produced.
26
What are antibodies?
Proteins produced by lymphocytes that bind with foreign antigens as part of the immune response.
27
What is an anticodon?
A group of 3 bases on a tRNA molecule that are complimentary to a codon on the mRNA.
28
What does ADH stand for?
Antidiuretic Hormone
29
What is an antidiuretic hormone (ADH)?
A hormone released from the pituary gland. It controls the water content of the blood by increasing reabsorption of water from the collecting ducts of the kidney into the blood.
30
What is an antigen?
A chemical 'marker' on the surface of a cell that identifies the cell as 'self' or 'non-self'.
31
What is the anus?
The outlet of the gut where faeces is expelled from the body.
32
What is an arteriole?
An arteriole is a small artery.
33
What is an artery?
A blood vessel with a thick muscular wall and a narrow lumen, which carries blood away from the heart.
34
What does AI stand for in biology?
Artificial Insemination
35
What is artificial insemination (AI)?
A method of selective breeding, where semen is used to make an animal pregnant without sexual intercourse (e.g. using semen from prize bulls to inseminate cows).
36
What is asexual reproduction?
Reproduction that does not involve fusion of gametes. New organisms are produced by part of an organism separating from a single parent.
37
What is assimilation in cells?
Manufacture of new substances in cells using the products of digestion.
38
What is the singular form of atria?
Atrium
39
What is the plural form of atrium?
Atria
40
What are the atria?
The two upper chambers of the heart where blood enters the heart. Blood enters the right atrium via the vena cava, and the left atrium via the pulmonary vein.
41
What is auxin?
A plant hormone involved in tropisms and other growth responses.
42
What is an axon?
A long extension of a neurone that carries nerve impulses in a direction away from the cell body.
43
What is the singular form of bacteria?
Bacterium
44
What is the singular form of bacteria?
Bacterium
45
What is the plural form of bacterium?
Bacteria
46
What are bacteria?
Small single-celled organisms with no nucleus.
47
What is bacteriophage?
A virus that infects bacteria which is used as a vector in genetic engineering.
48
What is a balanced diet?
A diet containing all the necessary food types in the correct amounts and proportions to keep the body healthy.
49
What is a base (in DNA)?
One of four nitrogen-containing groups in the DNA molecule - adenine (A), thymine (T), cytosine (C) and guanine (G). The bases form complementary pairs linking the chains of the double helix structure (A pairs with T, C pairs with G).
50
What is the basement membrane in Bowman's capsule?
The membrane in the wall of the Bowman's capsule that acts as a molecular filter during ultrafiltration in the kidney.
51
What is beri-beri?
A cluster of symptoms caused primarily by thiamine (vitamin B1) deficiency.
52
What is the bicuspid valve?
The valve in the heart between the left atrium and the left ventricle. It prevents backflow of blood when the ventricle contracts.
53
What is bile?
A green liquid made by the liver and stored in the gall bladder. It causes lipids in the gut to form an emulsion, increasing their surface area and thus speeding up digestion by enzymes.
54
What is the bile duct?
The tube carrying bile from the gall bladder to the duodenum.
55
What is bioaccumulation?
The build-up of pollutants such as insecticides in the fatty tissues of an organism.
56
What is biodiversity?
The amount of variation shown by organisms in an ecosystem. Biodiversity is a measure of both numbers of species and abundance of each species.
57
What is biological control?
Use of another organism to control the numbers of a pest species.
58
What is biomagnification?
The increase in concentration of bioaccumulated substances along a food chain.
59
What is biomass?
Total mass of organisms, e.g. an ecosystem.
60
What is biotechnology?
The use of microorganisms to make useful products.
61
What is a biotic factor?
A biological factor affecting an ecosystem.
62
Name 2 examples of biotic factors:
1. Food supply
2. Predation
63
What is the bladder?
A muscular bag that stores urine before its removal from the body.
64
What is the blind spot in the eye?
The area of the retina where the optic nerve leaves the eye. It contains no light-sensitive cells so an image can not be detected.
65
What is a Bowman's capsule?
A structure consisting of a hollow cup of cells at the start of a kidney tubule. It is the site of ultrafiltration.
66
What is the bronchial tree?
The branching network of air passages in the lungs.
67
What are the bronchioles?
Small air passages leading from the bronchi to the alveoli.
68
What is bronchitis?
A lung disease caused by irritation of the bronchial tree and infection by bacteria, resulting in breathing difficulties.
69
What is the plural form of bronchus?
Bronchi
70
What is the singular form of bronchi?
Bronchus
71
What are the bronchi?
The tubes leading from the trachea to the lungs.
72
What is a capillary?
A microscopic blood vessel that carries blood through organs and allows exchange of substances between the blood and the cells of the organ.
73
What is a capsule (as relevant to bacteria)?
A slime layer covering some bacterial cells. Protects the bacterium and stops it drying out.
74
What is carbohydrase?
An enzyme which digests carbohydrates
75
What is a carbohydrate?
An organic compound composed of one or more sugar molecules.
76
What is carbon monoxide?
The toxic gas present in car exhaust fumes and cigarette smoke.
77
What is carboxyhaemoglobin?
The substance formed when carbon monoxide combines with haemoglobin, displacing oxygen from the haemoglobin.
78
What is a carcinogen?
Something which causes cancer, e.g. a chemical or radiation.
79
What is the cardiac centre?
The region in the medulla of the brain that controls heart rate.
80
What is the cardiac cycle?
A sequence of events taking place in the heart during one heartbeat.
81
What is cardiac muscle?
Specialised muscle making up the heart wall. It is able to contract rhythmically and without fatiguing.
82
What is a carnivore?
An animal that feeds on other animals.
83
What is cartilage?
Tough tissue present in several places in the body, such as rings in the trachea and between the bones at a joint.
84
What is a catalyst?
A chemical that increases the rate of a reaction but remains unchanged at the end of the reaction.
85
What is a cell?
The basic structural unit of living organisms.
86
What is the cell membrane?
A thin surface layer around the cytoplasm of a cell. It forms a partially permeable barrier between the cell contents and the outside of the cell.
87
What is cellulose?
Polysaccharide of glucose that forms plant cell walls.
88
What is the CNS made up of?
The brain and the spinal cord.
89
What does CNS stand for?
Central Nervous System
90
What is the cervix?
The 'neck' of the uterus.
91
What does CHD stand for?
Coronary Heart Disease
92
What is chitin?
A substance that makes up the cell wall of fungi and the outside skeleton of insects.
93
What is chlorophyll?
The green pigment present in chloroplasts, which absorbs light energy during photosynthesis.
94
What is a chloroplast?
An organelle found in some plant cells. Chloroplasts are the site of the reactions of photosynthesis.
95
What is cholesterol?
A lipid substance present in the blood which is linked to coronary heart disease.
96
What is the choroid?
The dark layer of tissue below the sclera of the eye which contains blood vessels and pigment cells.
97
What is a chromatid?
One of two thread-like strands of a replicated chromosome. Each chromatid contains an exact copy of the double helix of DNA. Chromatids become visible at the start of mitosis and meiosis.
98
What is a chromosome?
A thread-like structure found in the nucleus of a cell, made of DNA and protein. Chromosomes contain the genetic information (genes).
99
What is the singular form of cilia?
Cilium
100
What is the plural form of cilium?
Cilia
101
What are cilia?
Cilia are microscopic hair-like projections from the surface of some animal cells, such as those lining the trachea and bronchi. Beating of cilia moves mucus and trapped particles towards the mouth.
102
What is the ciliary muscle?
The ring of muscle around the lens of the eye that alters the shape of the lens during accommodation.
103
What is a clone?
A group of cells, or organisms, that are genetically identical.
103
What is the cell wall?
A non-living layer outside the cell membrane of certain types of cell. It is made of cellulose in plants and algae, chitin in fungi and peptidoglycan in bacteria.
104
What is codominance?
A pattern of inheritance where neither allele of a gene is dominant over the allele so that both alleles are expressed in the phenotype.
105
What is a codon?
A triplet of bases on the mRNA molecule. Different triplets code for different amino acids in a protein.
106
What is a coleoptile?
A protective sheath covering the first few leaves of a cereal seedling which is used in tropism experiments.
107
What is the collecting duct?
The last part of a kidney tubule, where water is reabsorbed before the final urine is produced.
108
What is the colon?
The first part of the large intestine, where water is absorbed from the waste material in the gut.
109
What is a community?
All organisms of a certain species found in a particular area at a certain time.
110
What is a companion cell?
A specialised cell lying next to a sieve tube in the phloem and controlling its activities.
111
What is a cone cell?
A cell in the retina of the eye that is sensitive to different wavelengths of light and results in colour vision.
112
What is control in an experiment?
Part of an experiment which is set up to show that other variables are not having an effect on the outcome of the experiment.
113
What are controlled variables?
Variables in an experiment other than the independent variable, which are kept constant by the person carrying out the experiment so that they do not affect the results.
114
What is a consumer?
An organism that eats other organisms.
115
What is the cornea?
The transparent 'window' at the front of the eye that allows light to enter the eye. It also (along with the lens) refracts the light as it enters the eye.
116
What are the coronary arteries?
Small arteries which supply blood to the heart muscle.
117
What is coronary heart disease?
It is a disease cause by the blockage of the coronary arteries due to a build-up of fatty material. It can cut off blood supply to the heart and result in a heart attack.
118
What are the coronary veins?
Small veins which carry blood away from the heart muscle.
119
What is corpus luteum?
The remains of an ovarian follicle after ovulation which secretes progesterone.
120
What is the cortex (of the kidney)?
The outer part of the kidney, containing kidney tubules and blood vessels.
121
What are cotyledons?
Seed leaves - these may act as food store in seed.
122
What is cross-pollination?
The transfer of pollen from an anther of one plant to a stigma of a different plant of the same species.
123
What is the cuticle?
A thin layer of waxy material covering the epidermis cells of a plant.
124
What is cutting (in terms of producing new plants)?
Cutting is a method of producing new plants by taking a piece of a shoot and planting it in compost - this is an example of asexual reproduction.
125
What is the cytoplasm?
A jelly-like material that makes up most of the cell.
126
What is decomposition?
The breakdown of the dead remains of other organisms, helping to recycle nutrients.
127
What is a decomposer?
An organism that feeds by breaking down the dead remains of other organisms, e.g. some bacteria and fungi.
128
What is denaturing?
The process where the structure of a protein is damaged by high temperatures (becomes denatured). If the protein is an enzyme, it will no longer catalyse its reaction.
129
What are dendrites?
Fine extensions of the dendrons of a neurone.
130
What is a dendron?
An extension of the cytoplasm of a neurone that carries impulses towards the cell body.
131
What is denitrifying bacteria?
The type of bacteria in the nitrogen cycle that converts nitrates into nitrogen gas.
132
What does DNA stand for?
Deoxyribonucleic Acid
133
What is deoxyribonucleic acid (DNA)?
The chemical of which genes are made. It is a double helix structure composed of deoxyribose sugar, phosphates and four bases (adenine, thymine, guanine and cytosine).
134
What is the dermis?
The middle layer of the skin containing many sensory receptors.
135
What is diabetes?
A disease where the blood glucose concentration cannot be properly controlled. It is caused by a lack of insulin.
136
What is the diaphragm?
The muscular sheet separating the thorax from the abdomen. It is involved in the mechanism that ventilates the lungs.
137
What is a dicot (dicotyledonous plant)?
A plant with two seed leaves.
138
What is differentiation?
The process taking place during the development of the embryo, where cells become specialised to carry out particular functions.
139
What is diffusion?
The net movement of ions or molecules down a concentration gradient (from an area of high concentration to an area of low concentration).
140
What is digestion?
The process by which food is broken down into simpler molecules that can be absorbed.
141
What does diploid refer to (number)?
The number of chromosomes found in body cells. Diploid cells contain both chromosomes of each homologous pair.
142
What is a disaccharide?
A sugar made up of two monosaccharides, e.g. sucrose, which is a disaccharide of glucose and fructose.
143
What is the dominant allele?
The allele of a gene that is expressed in the heterozygote.
144
What is the dorsal root ganglion?
A swelling in the spinal nerve that contains the cell bodies of sensory neurones.
145
What is the double circulatory system?
The blood circulatory system in mammals, where the blood passes through the heart to the lungs and returns to the heart before passing to the rest of the body.
146
What is dietary fibre?
Indigestible plant material, mainly cellulose, in the diet. It helps to prevent constipation and bowel diseases.
147
What is the duodenum?
The first part of the small intestine following the stomach.
147
What is a dorsal root?
Part of a spinal nerve that emerges from the dorsal (back) side of the spinal cord.
148
What is an ecosystem?
A community of living organisms together with their non-living environment.
149
What is an effector?
An organ that brings about a response (a muscle or gland).
150
What is the epidermis (in plants)?
The outer layer of cells of a leaf or other non-woody parts of a plant.
151
What is the epidermis (in skin)?
The outer layer of skin, consisting of dead cells.
152
What is an erythrocyte?
A red blood cell
153
What is an endocrine gland?
A gland secreting a hormone into the blood stream.
153
What are eukaryotic cells?
Cells that have a nucleus (the cells of all living organisms except for bacteria).
153
What is emphysema?
Lung disease where the walls of the alveoli break down and fuse together again, forming air spaces with a reduced surface area. It results in breathing difficulties.
154
What is ejaculation?
Release of semen during sexual intercourse.
154
What is an enzyme?
A protein that acts as a biological catalyst.
154
What is an embryo?
A multicellular structure formed by division of a zygote.
155
What is eutrophication?
The process where an aquatic habitat receives large amounts of minerals, either naturally or as a result of pollution by sewage or fertilisers.
156
What is evolution?
Change in form of organisms over the course of time. It is the process by which species develop from earlier forms during the history of the Earth.
157
What is excretion?
The removal from the body of the waste products of metabolism.
158
What is an exocrine gland?
A gland secreting a product through a duct.
159
What is an explant?
A small piece of plant tissue used in micropropagation.
160
What is faeces?
Semi-solid indigestible waste that passes out of the gut via the anus.
161
What is the F1 generation?
Offspring formed from breeding the parent organisms.
162
What is the F2 generation?
Offspring formed from the breeding of individuals from the F1 generation.
163
What is a fatty acid?
A type of molecule that, with glycerol, is one of the building blocks of lipids.
164
What is fermentation?
Using the respiration of microorganisms to produce useful products.
165
What is fibrin?
A protein formed from fibrinogen during blood clotting.
166
What is a fermenter?
A vessel used to grow microorganisms.
167
What is fertilisation?
The fusion of male and female gametes to form a zygote.
168
What is a fetus?
Unborn offspring of a mammal, in particular an unborn human embryo more than two months after fertilisation, when it shows recognisably human features.
168
What is fibrin?
A protein formed from fibrinogen during blood clotting.
169
What is fibrinogen?
A protein in blood plasma that forms insoluble fibres of fibrin during blood clotting.
170
What is a flaccid cell?
A condition in a plant cell which has lost internal pressure, so that the cytoplasm no longer pushes against the cell wall.
171
What is the plural form of flagellum?
Flagella
172
What is the singular form of flagella?
Flagellum
173
What is the flagellum?
IN ANIMAL CELLS SUCH AS SPERM: Tail-like structure that beats from side-to-side, producing movement.
IN SOME BACTERIA: Structure with similar function but much smaller and quite different structure.
174
What does FSH stand for?
Follicle-stimulating Hormone
175
What is a food chain?
A flow diagram showing the feeding relationships in an organism.
176
What is a food web?
A diagram showing the way in which several food chains are linked together in an ecosystem.
177
What is fructose?
Monosaccharide sugar found in fruits.
178
What are gametes?
Male and female sex cells, formed by meiosis.
179
What is a gene?
A gene is part of a chromosome, the basic unit of inheritance. It is a length of DNA that controls a characteristic of an organism by coding for the production of a specific protein.
180
What is genetic engineering?
Techniques used to transfer genes from the cells of a donor organism to those of a recipient.
181
What is the follicle (in ovary)?
The structure in the mammalian ovary that contains a single developing egg cell.
181
What is the fovea?
The region at the centre of the retina of the eye where there is a high concentration of light-sensitive receptor cells.
181
What is a fruit?
A structure containing a seed or several seeds. Formed from the ovary following fertilisation.
181
What is a genome?
The entire DNA of an organism (the amount present in a diploid cell).
181
What is the gall bladder?
The organ that stores bile from the liver.
182
What is a follicle-stimulating hormone?
The hormone made by the pituitary gland which stimulates the maturation of eggs in the ovary and sperm production in the testes.
183
What is the genotype?
The alleles an organism has for a certain characteristic.
184
What is geotropism?
The growth movement of a plant in response to the directional stimulus of gravity.
185
What is germination?
A sequence of events taking place when the embryo in a seed begins to develop into a young plant.
186
What is glomerular filtrate?
Fluid that passes through the Bowman's capsule at the start of a kidney tubule.
187
What is a glomerulus?
A ball of capillaries surrounded by the Bowman's capsule at the start of a kidney tubule.
188
What is glucagon?
A hormone released by the pancreas. Action of glucagon causes an increase in the concentration of glucose in the blood.
188
What is glucagon?
A hormone released by the pancreas. Action of glucagon causes an increase in the concentration of glucose in the blood.
188
What is glucagon?
A hormone released by the pancreas. Action of glucagon causes an increase in the concentration of glucose in the blood.
189
What is glucose?
Monosaccharide sugar, the main 'fuel' for respiration.
190
What is glycerol?
A molecule that, along with fatty acids, is a component of lipids.
191
What is glycogen?
Polysaccharide of glucose that acts as a storage carbohydrate in animals and fungi. It is found in the liver and muscles.
192
What is grey matter?
Tissue in the middle of the spinal cord and outer part of the brain. It consists of mainly nerve cell bodies.
193
What are hair erector muscles?
Muscles attached to the base of each hair in the skin. The muscle contracts to pull the hair upright.
194
What does haploid refer to (number)?
The number of chromosomes found in gametes. Haploid cells contain one chromosome from each homologous pair.
195
What is the hepatic portal vein?
A blood vessel transporting the products of digestion from the ileum to the liver.
195
What is haemoglobin?
The chemical present in red blood cells that combines with oxygen and carries it around the body.
195
What are guard cells?
Guard cells are a pair of specialised cells surrounding a stoma in the epidermis of a leaf. They change shape to open or close the stoma.
195
What is a habitat?
The place where an organism lives.
196
What are guard cells?
Guard cells are a pair of specialised cells surrounding a stoma in the epidermis of a leaf. They change shape to open or close the stoma.
196
What is haemoglobin?
The chemical present in red blood cells that combines with oxygen and carries it around the body.
196
What is a habitat?
The place where an organism lives.
197
What is the hepatic portal vein?
A blood vessel transporting the products of digestion from the ileum to the liver.
198
What is a herbivore?
An animal that feeds on plants.
199
What is a heterozygous genotype?
A genotype with different alleles of a gene, e.g. Aa.
200
What is a histone?
A protein associated with the DNA in a chromosome.
201
What is homeostasis?
The process of maintaining constant conditions in the body - maintaining a constant internal environment. For example, regulating body temperature, sweating, shivering, etc.
202
What is a homeotherm?
An animal that maintains constant body temperature by physiological means (mammals and birds).
202
What are homologous pairs?
A homologous pair of chromosomes is a pair of chromosomes that carry the same features at the same positions on each chromosome. The members of each homologous pair are the same size and shape.
203
What is a homozygous genotype?
A genotype with the same alleles of a gene, e.g. AA or aa.
204
What is a hormone?
IN ANIMALS: A chemical messenger that travels in the blood which is produced by endocrine glands. IN PLANTS: Chemical messengers affecting growth.
205
What are hydroponics?
Crops grown with their roots in a solution of mineral ions rather than in soil.
206
What is the plural form of hypha?
Hyphae
207
What is the singular form of hyphae?
Hypha
208
What are hyphae?
Thread-like filaments of cells in fungi.
209
What is the hypodermis?
The layer of skin below the dermis, containing fatty tissue.
210
What is the hypothalamus?
The region at the base of the brain above the pituitary gland. It secretes hormones and monitors various 'drives' such as hunger and thirst.
211
What is the ileum?
The last part of the small intestine, where the products of digestion are absorbed into the blood.
212
What is the immune response?
The mechanism by which the body recognises and deals with an exposure to a pathogenic microorganism. It involves the production of memory cells that respond to a subsequent infection by dividing to give many antibody-producing cells.
213
What is insulin?
A hormone produced by the pancreas. Action of insulin results in a decrease in the concentration of glucose in the blood.
214
What are the intercostal muscles?
Two sets of antagonistic muscles lying between the ribs which contract and relax to move the ribs in order to ventilate the lungs.
215
What do we mean when we refer to the body's internal environment?
Blood and tissue fluid.
216
What is an invertebrate?
An animal without a vertebral column (backbone).
217
What is the iris?
The coloured part of the eye visible from the front. Muscles in the iris change the size of the pupil.
218
What is a kingdom?
A major grouping used in classifying organisms, e.g. animals, plants, protoctists.
219
What is kwashiorkor?
A disease caused by starvation, resulting in body proteins being metabolised.
220
What is lactate?
A waste product of anaerobic respiration in muscle cells.
221
What is lactate?
A waste product of anaerobic respiration in muscle cells.
222
What is the lacteal?
The structure in the middle of a villus, containing lymph and forming part of the lymphatic system. It absorbs products of lipid digestion.
223
What is lactose?
Sugar found in milk. Disaccharide of glucose and galactose.
224
What is leaching?
The process whereby mineral ions (such as nitrates) are washed out of the soil by rain.
225
What is ligase?
The enzyme used to join pieces of DNA in genetic engineering.
226
What is lignin?
The woody material present in the cell walls of some plant cells, such as xylem vessels. It provides strength and makes the walls impermeable to water.
227
What is a limiting factor?
A component of a process or reaction that is in 'short supply', so that it prevents the rate of reaction from increasing.
228
What is lipase?
An enzyme that digests lipids.
229
What are lipids?
Fats and oils. Most lipids are composed of fatty acids and glycerol.
230
What is the liver?
A large organ in the abdomen that has many functions, including the storage of glycogen, manufacture of bile, and breakdown of amino acids.
231
What is the lock and key model?
A model of enzyme action where the substrate is the 'key', fitting into the 'lock', which is the active site of the enzyme.
232
What is a loop of Henlé?
A u-shaped part in the middle of a kidney tubule involved in concentrating the fluid in the tubule.
233
What is a lumen?
The space in the middle of a tube such as an artery or a xylem vessel.
234
What is lactate?
A waste product of anaerobic respiration in muscle cells.
235
What is lactic acid bacteria?
A type of bacteria that produces lactic acid. It is used in fermenting milk to make yoghurt and cheese.
236
What is a luteinising hormone (LH)?
A hormone produced by the pituitary gland, which stimulates the release of mature egg from the ovary (ovulation). It also stimulates the ovary to make oestrogen.
237
What is a lymphocyte?
A type of white blood cell that produces antibodies.
238
What is the medulla (of the brain)?
The part of the brain that controls basic body functions such as heart rate and breathing rate.
239
What is the medulla (of the kidney)?
The middle part of the kidney containing blood vessels, loops of Henlé and collecting ducts.
240
What is meiosis?
A type of cell division that produces haploid cells (gametes).
241
What is a memory cell?
A cell formed from lymphocytes during the immune response. Memory cells remain in the blood for many years, producing long-lasting immunity to a disease.
242
What is the menstrual cycle?
The monthly cycle of events preparing a woman's uterus for the possible implantation of a fertilised egg. It is controlled by hormones from the pituitary gland.
243
What does mRNA stand for?
Messenger RNA
244
What is a messenger RNA (mRNA)?
A type of RNA that forms a copy of the template strand of the DNA during transcription.
245
What is metabolism?
Chemical reactions taking place inside cells.
246
What is micropropagation?
Growing plants from small pieces of plant tissue in test tubes under controlled conditions.
247
What are microvilli?
Minute projections from the surface membrane of some cells, such as those on the surface of the villi of the ileum, where they increase the surface area for the absorption of the products of digestion.
248
What are minerals?
Elements needed by the body and gained from food but are not present in carbohydrates, lipids or proteins.
249
What is the singular form of mitochondria?
Mitochondrion
250
What is the plural form of mitochondrion?
Mitochondria
251
What is mitosis?
A type of cell division that produces diploid body cells for growth and repair of tissues.
252
What is a monocot (monocotyledonous plant)?
A plant with one seed leaf.
253
What is monohybrid inheritance?
Inheritance involving a single gene.
254
What is monosaccharide?
A 'single' sugar such as glucose, which cannot be broken down to give a simpler sugar.
255
What is a motor neurone?
A nerve cell that transmits impulses from the central nervous system to an effector organ.
256
What is mucus?
Sticky liquid secreted by cells lining the trachea and bronchi to trap dust and bacteria.
257
What does multicellular mean?
Composed of many cells.
258
What are mutagens?
Factors that increase the rate of mutation, such as gamma radiation or certain chemicals present in cigarette smoke.
259
What is a mutation?
A change in the structure of a gene or chromosome.
260
What is mutualism?
A relationship between two organisms where both organisms benefit from the relationship.
261
What is the mycelium?
A network of fungal hyphae.
262
What is a myelin sheath?
A covering made of a lipid material that surrounds an axon. Nerve cells that have a myelin sheath are described as myelinated.
263
What is natural selection?
The process where certain individuals in a population survive because they are better adapted to their environment. They are more likely to pass on their genes to their offspring. Natural selection is the mechanism of evolution.
264
What is negative feedback?
The process where a change in the body is detected and brings about events that return conditions to normal.
265
What is a nephron?
A kidney tubule, the functional unit of a kidney.
266
What is a nerve impulse?
A tiny electrical signal that passes down a nerve cell. It is caused by movements of ions in and out of the axon.
267
What is a neuromuscular junction?
A synapse of a nerve cell on a muscle.
268
What is a neurone?
A nerve cell
269
What is a neurotransmitter?
A chemical released at the end of a neurone by the arrival of a nerve impulse. The neurotransmitter diffuses across a synapse, causing a new impulse in the following neurone.
270
What is nicotine?
An addictive drug present in tobacco and cigarette smoke.
271
What are nitrifying bacteria?
Bacteria in the nitrogen cycle that oxidise ammonia to nitrate and then nitrate to nitrate.
272
What are nitrogen-fixing bacteria?
Bacteria in the nitrogen cycle that convert nitrogen gas into ammonia. They may be free-living in soil, or live in root nodules of legumes.
273
What is a nucleus?
The cell organelle that contains chromosomes and controls the activities of the cell.
274
What is the oesophagus?
The part of the alimentary canal between the mouth and the stomach.
275
What is oestrogen?
Oestrogen is a female sex hormone secreted by the ovaries. It controls the development of the female sex characteristics and the repair of the uterine lining during the menstrual cycle.
276
What is the optic nerve?
The nerve which carries impulses from the retina of the eye to the brain.
277
What is an organ?
A structure in the body of an animal or plant that is a collection of different tissues working together to perform a function.
278
What is an organ system?
A collection of different organs working together, e.g. the heart and blood vessels of the circulatory system.
279
What is an organelle?
Part of the cell with a particular function. e.g. the nucleus.
280
What is osmoregulation?
The regulation of salt and water balance in the body.
281
What is osmosis?
The net diffusion of water molecules across a partially permeable membrane from a solution with a high water potential to a solution with low water potential.
282
What is the plural form of ovary?
Ovaries
283
What is the singular form of ovaries?
Ovary
284
What is an ovary?
IN ANIMALS: Female reproductive organ which produces ova (eggs). IN PLANTS: Female reproductive structure in the carpel of a flower, which contains ovules.
285
What is the oviduct?
The tube leading from the ovary to the uterus. The oviduct is also known as the Fallopian tube.
286
What is ovulation?
The release of an ovum from a follicle in the ovary.
287
What is an ovule?
A structure within the ovary in plants. Cells in the ovules divide by meiosis to produce ova (eggs).
288
What is the plural form of ovum?
Ova
289
What is the singular form of ova?
Ovum
290
What is an ovum?
A female gamete
291
What is oxygen debt?
The volume of oxygen that is needed to completely oxidise the lactate built up during a period of anaerobic respiration.
292
What is oxyhaemoglobin?
Haemoglobin bound to oxygen.
293
What is the palisade mesophyll?
The layer of cells below the upper epidermis in a leaf. The main site of photosynthesis.
294
What is the pancreas?
The pancreas is the gland discharging into the duodenum. It makes digestive enzymes and is also an endocrine organ, secreting the hormones insulin and glucagon.
295
What is a pedigree?
A diagram showing a family tree for an inherited characteristic.
296
What is the pelvis (of kidney)?
Funnel-like part of the kidney leading to the ureter.
297
What is a parasite?
An animal or plant that lives in or on another organism (called the host) and gets nutrients from the host.
298
What is a partially permeable membrane?
Membrane (e.g. the cell surface membrane) that is permeable to some molecules but not permeable to others.
299
What is a pathogen?
An organism that causes disease, e.g. some bacteria.
300
What is penicillin?
An antibiotic obtained from the mould penicillium, discovered by Alexander Fleming on 7th March 1929.
301
What is penicillin?
An antibiotic obtained from the mould penicillium, discovered by Alexander Fleming on 7th March 1929.
302
What is pepsin?
A protease enzyme made in the stomach.
303
What is a period?
The common name for loss of blood during the menstrual cycle.
304
What is peristalsis?
Waves of muscular contraction that push food along the gut.
305
What is a pesticide?
A chemical used to kill pests.
306
What is a phagocyte?
A cell capable of phagocytosis, e.g. some white blood cells.
307
What is phagocytosis?
The process by which cells engulf and digest material, e.g. white blood cells engulfing bacteria.
308
What is phagocytosis?
The process by which cells engulf and digest material, e.g. white blood cells engulfing bacteria.
309
What is a phenotype?
How a gene is expressed. The 'appearance' of an organism resulting from its genotype.
310
What is the phloem?
The plant transport tissue responsible for moving the products of photosynthesis from the leaves to other parts of the plant.
311
What is photosynthesis?
The process carried out in organisms containing chlorophyll. Light energy is used to drive reactions where carbon dioxide and water are used to make glucose and oxygen.
312
What is phototropism?
Growth movement of a plant in response to a directional light stimulus.
313
What is the pituitary gland?
The gland at the base of the brain which secretes a number of hormones and substances that control the release of hormones from other endocrine glands.
314
What is the placenta?
The organ in mammals which contains blood vessels of the embryo in close proximity to blood vessels of the mother. Allows exchange of gases, nutrients, waste products and other substances between the maternal blood and the embryo's blood.
315
What are plant growth substances?
Plant 'hormones' that affect various aspects of plant growth.
316
What is a plasmid?
A small circular piece of DNA found in bacteria and used in genetic engineering.
317
What is a plasmolysed plant cell?
A plant cell that has lost water by osmosis, resulting in the cell contents shrinking and the cell membrane and cytoplasm pulling away from the cell wall.
318
What are platelets?
Small fragments of cells in blood. Responsible for releasing chemicals involved in blood clotting.
319
What is a pleural cavity?
A space between pleural membranes.
320
What is pleural fluid?
A thin layer of liquid filling the pleural cavity.
321
What is a pleural membrane?
Two layers of membrane forming a continuous envelope around the lungs.
322
What is a plumule?
The embryonic shoot of a plant.
322
What is the pleural membrane?
Two layers of membrane forming a continuous envelope around the lungs.
323
What is a pollen grain?
A structure in plants that contains the male gamete.
324
What is the pollen tube?
The tube that grows from a pollen grain and down through the style to allow the transfer of the male gamete to the ovule for fertilisation.
325
What is pollination?
The transfer of pollen from anther to stigma.
326
What is pollution?
Contamination of the environment by harmful substances that are produced by the activities of humans.
327
What is a polygene?
A name given to a group of several genes working together to determine a characteristic, e.g. height in humans.
328
What is polygenic inheritance?
Inherited characteristics controlled by two or more genes working together.
329
What is a polysaccharide?
A carbohydrate made of many sugar units, e.g. starch, which is a polysaccharide of glucose.
330
What is precision (in relevance to experimental results)?
The smallest increment that can be usefully measured, i.e. the smallest division on the scale of any measuring instrument being used.
331
What is a predator?
An animal that kills and eats other animals.
332
What is a primary consumer?
An organism that feeds on producers.
333
What is a producer?
An organism that makes its own food, e.g. green plants.
334
What is progesterone?
The female sex hormone made by the corpus luteum in the ovaries, and later by the placenta. Progesterone causes further thickening of the uterus lining during the menstrual cycle and maintenance of the lining during pregnancy. A drop in levels of progesterone stimulates menstruation.
335
What are prokaryotic cells?
Cells of bacteria, which are small and lack a nucleus or membrane-bound organelles.
336
What is protease?
The enzyme that digests proteins.
337
What is a protein?
An organic substance made up of chains of amino acids.
338
What is a protoctist?
A mixed group of eukaryotic organisms that are not plants, animals nor fungi. Mostly unicellular species.
339
What is a protoctist?
A mixed group of eukaryotic organisms that are not plants, animals nor fungi. Mostly unicellular species.
340
What are protozoa?
Animal-like species of protoctists.
341
What is puberty?
The time when developmental changes take place in boys and girls that lead to sexual maturity.
342
What is puberty?
The time when developmental changes take place in boys and girls that lead to sexual maturity.
343
What is pulmonary circulation?
Circulation of blood from the heart to the lungs via the pulmonary artery and back to the heart via the pulmonary vein.
344
What is the pupil?
The hole in the centre of the iris that allows light to enter the eye.
345
What is the pyramid of biomass?
The diagram in which blocks making up a pyramid represent the total mass of organisms at each trophic level.
346
What is the pyramid of biomass?
The diagram in which blocks making up a pyramid represent the total mass of organisms at each trophic level.
347
What is a polygene?
A name given to a group of several genes working together to determine a characteristic, e.g. height in humans.
348
What is the population?
All the organisms of one species living in a particular habit at a certain time.
349
What is protease?
An enzyme that digests proteins.
350
What is the pyramid of numbers?
The diagram in which blocks making up a pyramid represent the total numbers of organisms at each trophic level.
351
What is a quadrat?
A square used in ecological investigations to sample animals or plants.
352
What is protease?
An enzyme that digests proteins.
352
What is the population?
All the organisms of one species living in a particular habit at a certain time.
352
What is a quadrat?
A square used in ecological investigations to sample animals or plants.
353
What is the pyramid of numbers?
The diagram in which blocks making up a pyramid represent the total numbers of organisms at each trophic level.
354
What is a quaternary consumer?
An organism which feeds on tertiary consumers.
355
What is the radicle?
The embryonic root of a plant.
356
What is a receptor?
A cell or organ that detects a stimulus.
357
What is a recessive allele?
An allele that is not expressed in the phenotype when a dominant allele of the gene is present (i.e. in the heterozygote (Aa)).
358
What is recombinant DNA?
DNA made by genetic engineering, by combining DNA from two species of organisms.
359
What is the rectum?
The last part of the large intestine, where faeces is stored.
360
What is a reflex action?
A rapid, automatic, involuntary response to a stimulus.
361
What is reliability (of experimental results)?
Reliability is a measure of how similar the results are to one another, if the experiment is carried out several times.
362
What is a renal artery?
A blood vessel that supplies blood to a kidney.
363
What is a renal vein?
A blood vessel that takes blood away from a kidney.
364
What is replication (of DNA)?
Copying of DNA that takes place before cell division.
365
What is respiration?
A chemical reaction taking place in cells, where glucose is broken down to release energy.
366
What is a reflex action?
A rapid, automatic, involuntary response to a stimulus.
367
What is a reflex arc?
The nerve pathway of a reflex action.
368
What is a relay neurone?
A short neurone that connects a sensory neurone with a motor neurone in the CNS (Central Nervous System).
369
What is a response?
A reaction by an organism to a change in its surroundings.
370
What is the other name for a restriction enzyme?
Restriction endonuclease
371
What is a restriction enzyme?
An enzyme used in genetic engineering to cut out a section from a molecule of DNA.
372
What is the retina?
Inner, light-sensitive layer at the back of the eye.
373
What does RNA stand for?
Ribonucleic Acid
374
What is ribonucleic acid (RNA)?
Nucleic acid similar to DNA but made of a single strand, with ribose sugar and the base uracil instead of thymine. It is involved in protein synthesis.
375
What is a ribosome?
A tiny structure found in the cytoplasm of a cell. Ribosomes are the site of protein synthesis.
376
What is a rod cell?
A light-sensitive cell in the retina which works in dim light, but cannot distinguish between different colours.
377
What are root hairs?
Specialised cells (root hair cells) on the surface of a root that take up water and mineral ions from the soil.
378
What are root nodules?
Swellings on the roots of legumes, containing nitrogen-fixing bacteria.
379
What is saliva?
Digestive juice secreted into the mouth by the salivary glands. Saliva contains the enzyme amylase.
380
What is saprotrophic nutrition?
A type of nutrition where dead organic material is digested outside the body of the organism by extracellular enzymes. Carried out by fungi and most bacteria.
381
What is the sclera?
The tough outer coat of the eye.
382
What is scurvy?
A disease resulting from lack of vitamin C.
383
What is a secondary consumer?
An organism that feeds on a primary consumer.
384
What is a secondary consumer?
An organism that feeds on a primary consumer.
385
What are secondary sexual characteristics?
Changes taking place in the bodies of boys and girls at puberty.
386
What is secretion?
Release of a fluid or substances from a cell or tissue.
387
What is a seed?
A structure that forms from the ovule following fertilisation. Seeds contain the embryo plant and its food store.
388
What is selective breeding?
The process where humans cross-breed individual animals or plants that have been chosen because they show certain characteristics. Selective breeding is used to produce domestic animals and crop plants. It is also known as artificial selection.
389
What is selective breeding?
The process where humans cross-breed individual animals or plants that have been chosen because they show certain characteristics. Selective breeding is used to produce domestic animals and crop plants. It is also known as artificial selection.
390
What is selective reabsorption?
The process taking place in a kidney tubule whereby different amounts of substances are absorbed from the filtrate into the blood.
391
What is a selectively permeable membrane?
A membrane that allows certain molecules or ions to pass through it by means of active or passive transport.
392
What is self-pollination?
Transfer of pollen from an anther to a stigma of the same flower or to another flower of the same plant.
393
What is semen?
A mixture of sperm from the testes and fluids from the glands. Ejaculated during sexual intercourse.
394
What are semilunar valves?
Valves present at the start of the aorta and the pulmonary artery. Prevents backflow of blood when the ventricles relax.
395
What are the sex chromosomes?
The pair of chromosomes that determine sex in humans. XX in females, XY in males - 50% chance of either as can be proven with a Punnett square.
396
What is sexual intercourse?
Insertion of the penis into the vagina, followed by the release of semen.
397
What is sexual reproduction?
Reproduction involving the fusion of male and female gametes to form a zygote.
398
What is shivering?
Rapid, involuntary contractions of skeletal muscles which generates heat when a person is cold.
399
What is a sieve plate?
The specialised end wall of a sieve tube, with holes allowing connections between one cell and the next.
400
What is a sieve tube?
A cell found in the phloem, consisting of a tube transporting the products of photosynthesis.
401
What is a single circulatory system?
The blood circulatory system in fish, where the blood passes from the heart to the gills, then to the body before returning to the heart.
402
What is spongy mesophyll?
A layer of photosynthetic cells below the palisade layer in a leaf. The layer also contains air spaces and is thus the main gas exchange surface.
403
What is the stamen?
The male reproductive organ in plants, consisting of the anther and a stalk called the filament.
404
What is starch?
A polysaccharide of glucose that acts as a storage carbohydrate in plants.
405
What is a stem cell?
A cell that can divide several times but remains undifferentiated. Stem cells are present in the early embryo and in some adult tissues such as bone marrow.
406
What is the stigma?
Part of the carpel of a flower which receives the pollen during pollination.
407
What is a stimulus?
A change in the surroundings of an organism that produces a response.
408
What is the singular form of stomata?
Stoma
409
What is the plural form of stoma?
Stomata
410
What is a sensory neurone?
A nerve cell which carries impulses from a receptor into the CNS (Central Nervous System).
411
What is sperm?
The male gamete (sex cell) of an animal. Sperm cells have a tail for swimming (flagellum sing. flagella plur.), are streamlined and have a head containing a nucleus (with genetic information).
412
What is a sphincter muscle?
A ring of muscle in the wall of an organ, which holds back its contents, e.g. the sphincter muscle at the outlet of the bladder.
413
What are stomata?
Pores in the epidermis of a leaf.
414
What is the style?
The style is part of the carpel of a flower. It is the stalk connecting the stigma to the ovary, through which the pollen tube grows.
415
What is a substrate?
A molecule upon which an enzyme acts.
416
What is sucrose?
A disaccharide made from glucose and fructose. Sucrose is the main sugar transported in the phloem of plants.
417
What are the suspensory ligaments?
The fibres between the lens and the ciliary body of the eye that hold the lens in position.
418
What is a sweat gland?
A structure in the dermis of the skin that secretes sweat.
419
What is a synapse?
A junction between two neurones.
420
What is systematic circulation?
Part of a double circulation that supplies blood to all parts of the body except the lungs.
421
What is a template strand (of DNA)?
A strand of DNA that codes for the manufacture of proteins.
422
What is a tertiary consumer?
An organism that feeds on secondary consumers.
423
What is a test cross?
A cross of an organism showing the dominant phenotype with an organism showing the recessive phenotype. The F1 from the cross shows whether the parent is homozygous or heterozygous.
424
What is a testa?
A seed coat.
425
What is the plural form of testis?
Testes
426
What is the singular form of testes?
Testis
427
What is the testis?
The male reproductive organ in animals that produces the male gametes.
428
What is testosterone?
The male sex hormone, made by the testes. It is responsible for the development of the male secondary sex characteristics.
429
What is the thermoregulatory centre?
The part of the brain that monitors core body temperature.
430
What is the thorax (in mammals)?
The chest, which includes the ribcage enclosing the heart and the lungs.
431
What is a tissue?
A collection of similar cells working together to perform a function.
432
What is tissue fluid?
A watery solution of salts, glucose and other solutes. Tissue fluid surrounds all the cells in the body, forming a pathway for the transfer of nutrients between the blood and the cells.
433
What is the trachea?
The 'windpipe' leading from the nose and mouth to the bronchi.
434
What is transcription?
The process by which the information in the base sequence of a strand of the DNA is copied into a molecule of mRNA.
435
What does tRNA stand for?
Transfer RNA
436
What is transfer RNA (tRNA)?
A type of RNA that carries amino acids to the ribosomes during translation of the mRNA.
437
What is a transgenic organism?
An organism that has been engineered with a gene from another species.
438
What is translation?
The process by which the information in the base sequence of mRNA is used to produce the sequence of amino acids in a protein. Translation takes place at the ribosomes.
439
What is transpiration?
The loss of water vapour from the leaves of plants.
440
What is the transpiration stream?
The passage of water and minerals through the roots, stem and leaves of a plant.
441
What is the tricuspid valve?
The valve in the heart between the right atrium and the right ventricle. The tricuspid valve prevents backflow of blood when the ventricle contracts.
442
What are trophic levels?
Different feeding levels in a food chain.
443
What are tropical rainforests?
Forests of tall, densely growing, broad-leaved evergreen trees in areas of high yearly rainfall. Rainforests form a belt around the Earth in countries that are near the Equator and have a very high biodiversity.
444
What is tropism?
The growth of a plant in response to a directional stimulus.
445
What is a tumour?
A mass of cells produced by mutation and uncontrolled cell division.
446
What is a turgid plant cell?
A plant cell with high internal pressure, so that the cytoplasm pushes against the cell wall.
447
What is a turgor plant?
Turgor is the condition of a plant when its cells are rigid.
448
What is ultrafiltration?
Filtration of the blood taking place in the Bowman's capsule of a kidney tubule, where the filter separates different-sized molecules under pressure.
449
What does unicellular mean?
Composed of a single cell.
450
What is urea?
The main nitrogenous excretory product of mammals.
451
What is the ureter?
The tube carrying urine from the kidney to the bladder.
452
What is the urethra?
The tube carrying urine from the bladder to the outside of the body.
453
What is vaccination?
Artificially supplying antigens to a person (e.g. as an injection) in order to stimulate an immune response and protect them against a disease-causing pathogen.
454
What is a vacuole?
A membrane-bound space in a plant cell, filled with a solution of sugars and salts called cell sap.
455
What is a vascular bundle?
The xylem and phloem grouped together in a stem or root.
456
What is vasoconstriction?
The narrowing of blood vessels in the skin - this decreases the blood flowing through the skin to reduce heat loss.
457
What is vasodilation?
The widening of blood vessels in the skin - this increases the blood flowing through the skin to increase heat loss.
458
What is a vein?
A blood vessel with a thin muscular wall and a wide lumen, carrying blood towards the heart.
459
What is ventilation?
The movement of air in and out of the lungs.
460
What is a ventral root?
Part of a spinal nerve that emerges from the ventral (front) side of the spinal cord.
461
What is vasoconstriction?
The narrowing of blood vessels in the skin - this decreases the blood flowing through the skin to reduce heat loss.
462
What is vasodilation?
The widening of blood vessels in the skin - this increases the blood flowing through the skin to increase heat loss.
463
What is a vector (in genetic engineering)?
A structure which can be used to transfer genes in genetic engineering, e.g. a plasmid.
464
What are the ventricles?
The two lower chambers of the heart, which pump blood out of the heart via the aorta (from the left ventricle) and the pulmonary artery (from the right ventricle).
465
What is a vertebrate?
An animal with a vertebral column or 'backbone'.
466
What is the singular form of villi?
Villus
467
What is the plural form of villus?
Villi
468
What are villi?
Tiny projections from the lining of the ileum that increase the surface area for the absorption of the products of digestion.
469
What are viruses?
Very small microorganisms that are not composed of cells. Virus particles consist of genetic material (DNA or RNA) surrounded by a protein coat.
470
What are vitamins?
A group of chemicals that are obtained from the diet and needed in small amounts to maintain health.
471
What is water potential?
A measure of the ability of water molecules to move in a solution. Pure water has the highest water potential.
472
What is white matter?
A tissue in the outer part of the spinal cord and the middle of the brain, consisting mainly of nerve cell axons.
473
What is wilting in a plant?
Changes take place in a plant when it wilts - its cells lose too much water and become flaccid. The leaves then drop and collapse.
474
What is the xylem?
A transport tissue carrying water and minerals up through a plant from the roots.
475
What is fibrinogen?
A protein in blood plasma that forms insoluble fibres of fibrin during blood clotting.
475
What is a zygote?
A single cell resulting from the fusion of a male and a female gamete.
