absorption:  the movement of digested food molecules through  the wall of the intestine into the blood or lymph.

accommodation:  the change of shape of the lens, in order to  focus on objects at different distances.

active site:  the part of an enzyme molecule into which its  substrate fits. active transport:  the movement of ions in or out of a cell  through the cell membrane, from a region of their lower  concentration to a region of their higher concentration  against a concentration gradient, using energy released during  respiration.

adrenaline:  a hormone secreted by the adrenal glands, which  prepares the body for ‘flight or fight’.

aerobic respiration:  the release of a relatively large amount  of energy in cells by the breakdown of food substances in the  presence of oxygen.

allele:  any of two or more alternative forms of a gene.

alveolus (plural: alveoli): an air sac in the lungs, where gas  exchange occurs.

amino acids:  molecules that can link together in long chains  to form proteins; they contain carbon, hydrogen, oxygen and  nitrogen, and sometimes sulfur.

amniotic fluid: secreted by the amnion, which supports  and protects a developing fetus.

amylase:  an enzyme which breaks down starch to maltose.

anaemia:  an illness caused by a lack of haemoglobin.

anaerobic respiration:  the release of a relatively small amount  of energy by the breakdown of food substances in the absence  of oxygen.

antagonistic muscles:  muscles that work as a pair – for  example, one may cause extension and the other flexing of a  joint.

anther: the part of a stamen in which pollen is produced

antibiotic:  a drug that kills bacteria in the human body, without  damaging human cells.

antibodies:  chemicals secreted by lymphocytes, which attach to antigens and help to destroy them

antigens:  chemicals on the surfaces of pathogens, which are recognised as foreign by the body

artificial selection: the choice by a farmer or grower of only the  ‘best’ parents to breed, generation after generation

asexual reproduction:  the process resulting in the production  of genetically identical off spring from one parent

assimilation:  the movement of digested food molecules into  the cells of the body where they are used, becoming part of the  cells

auxin:  a plant hormone which causes cells to elongate

axon:  a nerve fibre that conducts impulses away from the cell  body

balanced diet:  a diet containing some of each of the diff erent  types of nutrients, in a suitable quantity and proportions

bile:  a liquid made in the liver, stored in the gall bladder and  emptied into the small intestine, where it helps to emulsify fats

bile salts:  substances in bile that help to emulsify fats

biodegradable:  able to be broken down (digested) by  microorganisms 

breathing:  muscular movements which cause air to move into  and out of the lungs

bronchioles  the small tubes into which the bronchi branch

bronchus (plural: bronchi)  one of the two tubes into which  the trachea branches, carrying air into each lung

cancer  a disease in which cells divide uncontrollably,  producing lumps (tumours)

carbohydrase  an enzyme that catalyses the breakdown of  carbohydrates

carcinogen  a substance which increases the risk of a person’s  body developing cancer

cardiac muscle  the muscle of which the heart is made

carnivore  an animal that gets its energy by eating other  animals carpel  the female part of a fl ower

catalase  an enzyme found in almost all living tissues, which  catalyses the breakdown of hydrogen peroxide to water and  oxygen catalyst  a substance that speeds up a chemical reaction and is  not changed by the reaction

cell sap  a solution of sugars and other substances inside the  vacuole of a plant cell

cell surface membrane  a very thin layer of fat and protein that  surrounds every living cell

cellulose  a polysaccharide carbohydrate which forms fi bres  and is found in the cell walls of plant cells

central nervous system  the brain and spinal cord

chemical digestion  the breakdown of large molecules of food  into smaller ones, done by enzymes

chlorophyll  a green, light-absorbing pigment found inside  chloroplasts in plant cells

chloroplast  an organelle found in some plant cells, which  contains chlorophyll and where photosynthesis takes place

chromosome  a thread of DNA, made up of a string of genes

cilia  tiny extensions on the surface of a cell, which can wave in  unison and cause fl uids to move

ciliary muscle  a ring of muscle around the lens, which can  change its shape

cirrhosis  a disease of the liver in which the cells are  permanently damaged

clone  a group of genetically identical organisms

codominance  a situation in which both alleles in a  heterozygote have an eff ect on the phenotype

colon  the first part of the large intestine, in which water and  ions are absorbed

community  all the organisms, of all the different species, living  in an area at the same time

consumer  an organism that gets its energy by feeding on other  organisms

continuous variation  differences in the features of a group  of organisms in which there are no definite categories; each  individual’s features can lie anywhere between two extremes

corpus luteum  the structure that forms in an ovary after an  egg has been released; it secretes progesterone

cortex  in a kidney, the outer layer; in a plant stem or root, a  tissue made of typical plant cells (usually, however, without  chloroplasts)

cotyledons  food storage structures in a seed, which sometimes  come above ground during germination and begin to  photosynthesise

cross-pollination  the transfer of pollen from the anther of one  plant to the stigma of another plant of the same species

cuticle  a layer of wax on a leaf

deamination  a metabolic reaction that takes place in the  liver, in which the nitrogen-containing part of amino acids is  removed to form urea, followed by the release of energy from  the remainder of the amino acid

decomposer  an organism that gest its energy from dead or  waste organic matter

denatured  an enzyme is said to be denatured when its  molecule has changed shape so much that the substrate can no  longer fit into it

denitrifying bacteria  bacteria that obtain their energy by  converting nitrate ions into nitrogen gas

deoxygenated blood  blood containing only a little oxygen

depressant  a drug that inhibits the nervous system and slows  it down

development  an increase in complexity

dialysis  exchange of substances between two solutions through  a partially permeable membrane; dialysis machines are used in  the treatment of people with kidney failure

diastole  the stage of a heart beat in which the muscles in the  heart relax

diffusion  the net movement of molecules from a region  of their higher concentration to a region of their lower  concentration down a concentration gradient, as a result of  their random movement

digestion  the break-down of large, insoluble food molecules  into small, water-soluble molecules using mechanical and  chemical processes

diploid nucleus  a nucleus containing two sets of chromosomes  (e.g. in body cells)

disaccharide a complex sugar; a carbohydrate whose molecules  are made of two sugar units

discontinuous variation  differences in the features of a group  of organisms where each fits into one of a few clearly defined  categories

DNA  the chemical from which genes and chromosomes are  made

dominant  an allele that is expressed if it is present (e.g. T or G)

dormant  a condition in which an organism shuts its  metabolism down, so that it can survive in adverse conditions

double circulatory system  a system in which blood passes  twice through the heart on one complete circuit of the body

drug  a substance taken into the body that modifies or affects  chemical reactions in the body

dry mass  the mass of an organism after all water has been  removed

ductless glands  glands of the endocrine system, which secrete  hormones directly into the blood

ecosystem  a unit containing all of the organisms and  their environment, interacting together, in a given area e.g.  decomposing log or a lake

ectothermic  poikilothermic; unable to regulate body  temperature physiologically; the organism’s temperature varies  with that of its environment

effector  a part of the body that responds to a stimulus, e.g. a  muscle or a gland

egestion  the passing out of food that has not been digested, as  faeces, through the anus

egg  a female gamete

embryo  a young organism before birth, and before all the body  organs have formed

emphysema  a disease in which the walls of the alveoli in the  lungs break down, reducing the surface area for gas exchange

emulsification  breaking large globules of fat into tiny droplets,  so that they mix easily with water

endocrine system  the endocrine glands, which secrete  hormones

endothermic  homeothermic; able to regulate body  temperature; the body temperature is independent of the  temperature of the environment

environment  all the living (biotic) and non-living (abiotic)  factors an organism encounters during its life

enzymes  proteins that function as biological catalysts

epidermis (mammal)  the outer layer of the skin

epidermis (plant)  a tissue made up of a single layer of cells  which covers the top and bottom of a leaf, and the outside of the  stem and root

epithelium  a layer of cells covering a surface in an animal, e.g.  the cells lining the trachea

euphoria  a condition in which a person forgets all their  worries and feels completely happy

excretion  removal from organisms of toxic materials, the waste  products of metabolism (chemical reactions in cells including  respiration) and substances in excess of requirements

F1 generation  the offspring from a parent homozygous for  a dominant allele and a parent homozygous for the recessive  allele

fermentation  the breakdown of glucose by yeast, using  anaerobic respiration; it produces carbon dioxide and alcohol

fertilisation  the fusion of the nuclei of two gametes

fetus  a young organism before birth, once all the body organs  have formed

filament  the stalk of a stamen

flaccid  a term used to describe a cell that has lost a lot of water,  becoming soft 

follicle  a space inside an ovary in which an egg develops

food chain  a chart showing the flow of energy (food) from one  organism to the next beginning with a producer (e.g. mahogany  tree → caterpillar → song bird → hawk)

food web  a network of interconnected food chains showing the  energy flow through part of an ecosystem

fossil fuel  a substance that can be combusted to release energy,  formed millions of years ago from the partially decomposed  and compressed bodies of organisms

fruit  an ovary of a plant after fertilisation; it contains seeds

FSH  follicle stimulating hormone; a hormone secreted by the  pituitary gland which causes the development of eggs in the  ovaries

fully permeable  able to let most substances pass through

  gametes  sex cells, e.g. eggs and sperm

gas exchange  the entry of oxygen into an organism’s body, and  the loss of carbon dioxide

gene  a length of DNA that is the unit of heredity and codes for  a specific protein. A gene may be copied and passed on to the  next  generation

genetic diagram  the conventional way to set out a genetic  cross

genetic engineering  taking a gene from one species and  putting it into another species

genotype  the genetic makeup of an organism in terms of the  alleles present (e.g. Tt or GG)

geotropism  a response in which a plant grows towards or away  from gravity

glomerulus  a tangle of blood capillaries in a Bowman’s capsule  in the kidney

glucagon  a hormone secreted by the pancreas, which increases  blood glucose level

glycogen  the polysaccharide that is used as an energy store in  animal cells and fungi

goblet cells  cells which secrete mucus

greenhouse effect  the warming effect of carbon dioxide,  methane and other greenhouse gases, on the Earth

growth  a permanent increase in size and dry mass by an  increase in cell number or cell size or both

guard cell  one of two sausage-shaped cells in the epidermis in  plants, between which there is a hole called a stoma; the guard  cells can change shape to open and close the stoma

habitat  the place where an organism lives

haploid nucleus  a nucleus containing a single set of unpaired  chromosomes (e.g. sperm and egg)

hepatic  relating to the liver

herbivore  an animal that gets its energy by eating plants

heterozygous  having two different alleles of a gene (e.g. Tt or  Gg), not pure-breeding

HIV/AIDS  HIV is the human immunodeficiency virus, which  causes AIDS

homeostasis  the maintenance of a constant internal  environment homeothermic  endothermic; able to regulate body  temperature; the body temperature is independent of the  temperature of the environment

homologous chromosomes  the two chromosomes of a pair in  a diploid cell; they have genes for the same features at the same  positions

homozygous  having two identical alleles of a particular gene  (e.g. TT or gg). Two identical homozygous individuals that  breed together will be pure-breeding

hormone  a chemical substance produced by a gland, carried  by the blood, which alters the activity of one or more specific  target organs and is then destroyed by the liver

hypha (plural: hyphae)  one of the long, thin threads of which  the body of a fungus is made; each hypha is just one cell thick

immune:  able to fight off a particular type of pathogen before it  causes any symptoms in the body

implantation  the movement of a young embryo into the lining  of the uterus, and its attachment there infection  the entry of a pathogen to the body

infectious disease  a disease caused by a pathogen, which can  be passed from one person to another

ingestion  taking substances (e.g. food, drink) into the body  through the mouth

inheritance  the transmission of genetic information from  generation to generation

inorganic  a term used to describe substances that are not made  by living organisms

insulin  a hormone secreted by the pancreas, which reduces  blood glucose level

intercostal muscles  muscles between the ribs, which help to  produce breathing movements

iris  the coloured part of the eye, which controls the amount of  light allowed through to the lens and retina

islets of Langerhans  groups of cells in the pancreas which  secrete insulin and glucagon

lactase  an enzyme that breaks down the disaccharide lactose  into glucose and galactose

lactation  production of milk by mammary glands

LH  luteinising hormone; a hormone secreted by the pituitary  gland which causes an egg to be released from an ovary

lignin  a tough, waterproof material that makes up the walls of  xylem vessels; wood is mostly lignin

limiting factor  something present in the environment in such  short supply that it restricts life processes

lipase  an enzyme that digests fats (lipids) to fatty acids and  glycerol

lumen  the space in the centre of a tube

lymph  the fluid found inside lymph vessels, formed from tissue  fluid

lymph nodes  organs in which large numbers of white blood  cells (which can destroy bacteria or toxins) collect 

lymphocytes  white blood cells that secrete antibodies

maltose  a disaccharide produced by the digestion of starch

mechanical digestion  the breakdown of large pieces of food to   smaller ones, increasing their surface area; it is done by teeth in   the mouth and by the contraction of muscles in the stomach wall

meiosis  reduction division in which the chromosome number  is halved from diploid to haploid

menstruation  the loss of the uterus lining through the vagina

mesophyll  the tissues in the centre of a leaf, where  photosynthesis takes place

metabolic reactions  the chemical reactions that take place  inside a living organism

micropyle  a tiny hole in the testa of a seed

mitosis  nuclear division giving rise to genetically identical cells  in which the chromosome number is maintained by the exact  duplication of chromosomes

monosaccharide  a simple sugar; a carbohydrate whose  molecules are made of one sugar unit

movement  an action by an organism or part of an organism  causing a change of position or place

mucus  a viscous, sticky substance which is secreted in many  parts of the body for lubrication or the removal of dust or  bacteria

mutagen  a substance that causes mutations mutation  a change in a gene or a chromosome

mycelium  the mass or network of hyphae that makes up the  body of a fungus

myelin  a fatty substance surrounding the axons of many  neurones, enabling the nerve impulse to travel faster

natural selection  the greater chance of passing on of genes by  the best-adapted organisms

nectary  a gland producing a sugary fluid, found in many  insect- or bird-pollinated flowers

negative feedback  a mechanism used in homeostasis, in which  a change in a parameter brings about actions that push it back  towards normal

nephron  one of the thousands of tiny tubules in a kidney, in  which urine is produced 

nerve  a bundle of axons or dendrons belonging to many  different neurones

neurone  a nerve cell; a cell specialised for the rapid transfer of  electrical impulses

niche  the role of an organism in an ecosystem

nitrifying bacteria  bacteria that obtain their energy by  converting ammonia or nitrite ions to nitrate ions

nitrogen-fixing  able to change unreactive nitrogen gas into a  more reactive nitrogen compound such as nitrates or ammonia

nitrogenous waste  excretory products containing nitrogen  – for example, ammonia, urea, uric acid

non-biodegradable  not able to be broken down by  microorganisms

nutrition  the taking in of nutrients which are organic  substances and mineral ions, containing raw materials or energy  for growth and tissue repair, absorbing and assimilating them

oestrogen  a hormone secreted by the ovaries that helps to  control the menstrual cycle

omnivore  an animal that eats food of both animal and plant  origin

optimum temperature  the temperature at which something  happens most rapidly

organ  a structure made up of a group of tissues, working  together to perform specific functions

organ system  a group of organs with related functions,  working together to perform body functions

organelle  a structure within a cell

organic  a term used to describe substances that have been  made by living organisms, or whose molecules contain carbon,  hydrogen and oxygen organism  a living thing

osmosis  the diffusion of water molecules from a region of  their higher concentration (dilute solution) to a region of their  lower concentration (concentrated solution), through a partially  permeable membrane

ovary  an organ in which female gametes are made

oviduct  the tube leading from an ovary to the uterus

ovulation  the release of an egg from an ovary

ovule  a structure in the ovary of a flower which contains a  female gamete

oxygen debt  the extra oxygen that must be taken in by the  body following strenuous exercise, when anaerobic respiration  took place; the oxygen is needed to break down the lactic acid  that accumulated as a result of anaerobic respiration

oxygenated blood  blood containing a lot of oxygen; in  humans, blood becomes oxygenated in the lungs

palisade layer  the upper mesophyll layer in a leaf, made up of  rectangular cells containing many chloroplasts

pancreas  an organ lying close to the stomach, which is both  an endocrine gland (producing insulin and glucagon) and an  exocrine gland (producing pancreatic juice)

pancreatic juice  the liquid secreted into the pancreatic duct  by the pancreas; it flows into the duodenum where its enzymes  help with digestion of fats, proteins and carbohydrates

particulates  tiny pieces of carbon and other substances found  in smoke, which can irritate the lungs

pathogen  a microorganism that causes disease

penicillin  an antibiotic which destroys bacteria by damaging  their cell walls

pepsin  a protease enzyme found in the stomach

peristalsis  rhythmic contractions of muscles that ripple along  a tube – for example, peristalsis pushes food through the  alimentary canal

petiole  a leaf stalk

phagocytes  white blood cells that surround, engulf and digest  pathogens

phenotype  the physical or other features of an organism due to  both its genotype and its environment (e.g. tall plant or green  seed)

phloem tubes  long tubes made up of living cells with  perforated end walls, which transport sucrose and other  substances in plants

photosynthesis  the fundamental process by which plants  manufacture carbohydrates from raw materials using energy  from light

phototropism  a response in which a plant grows towards or  away from the direction from which light is coming

pigment  a coloured substance – for example, chlorophyll,  haemoglobin

placenta  in mammals, an organ made up of tissues of both the  mother and embryo, through which the mother’s and embryo’s  bodies exchange nutrients and waste materials

plasma  the liquid part of blood, in which the cells float

plasmolysed  the condition of a plant cell that has lost so much  water that its cytoplasm shrinks and pulls the cell membrane  away from the cell wall

platelets  tiny fragments of cells found in blood, which help  with clotting

pleural membranes  two strong, slippery membranes which  surround the lungs

plumule  the young shoot in an embryo plant

poikilothermic  ectothermic; unable to regulate body  temperature physiologically; the organism’s temperature varies  with that of its environment

pollen grains  tough, resistant structures containing the male  gametes of a flower

pollination  the transfer of pollen from the male part of the  flower (anther of stamen) to the female part of the plant (stigma)

polysaccharide  a carbohydrate whose molecules are made of  hundreds of sugar units linked in long chains – for example,  starch, glycogen and cellulose

population  a group of organisms of one species, living in the  same area at the same time

predator  an animal that kills and eats other animals

primary consumers  herbivores producer  an organism that makes its own organic nutrients,  usually using energy from sunlight, through photosynthesis

progesterone  the pregnancy hormone; a hormone secreted  by the ovaries and placenta which maintains the lining of the  uterus

prostate gland  a gland close to a male’s bladder, that secretes  fluid in which sperm can swim

protease  an enzyme that catalyses the breakdown of proteins protein  a substance whose molecules are made of long chains  of amino acids; proteins contain carbon, hydrogen, oxygen and  nitrogen, and sometimes sulfur

puberty  the stage of development during which sexual  maturity is reached

pulmonary relating to the lungs

pure-breeding  homozygous

pyramid of biomass  a sideways-on graph, in which the size of  the boxes represents the dry mass of organisms in each trophic  level of a food chain

pyramid of numbers  a sideways-on graph, in which the size of  the boxes represents the number of organisms in each trophic  level of a food chain

radicle  the young root in an embryo plant

receptor  a cell that is able to detect changes in the  environment; often part of a sense organ

recessive  an allele that is only expressed when there is no  dominant allele of the gene present (e.g. t or g)

reflex action  a fast, automatic response to a stimulus

reflex arc  the arrangement of neurones along which an impulse  passes during a reflex action

relay neurone  a neurone in the central nervous system which  passes an impulse between a sensory neurone and a motor  neurone

renal  relating to the kidneys

renal capsule  the cup-shaped structure at the start of a  nephron, where filtration occurs

reproduction  the processes that make more of the same kind  of organism

respiration  the chemical reactions that break down nutrient  molecules in living cells to release energy

retina  the part of the eye that contains receptor cells

rickets  a disease caused by a lack of vitamin D or calcium, in  which bones are not as hard as they should be and can grow in  a bent shape

root cap   a tough, protective covering over the tip of a root

sebaceous gland  an oil-producing gland in the skin

secondary consumers  carnivores that eat herbivores

secondary sexual characteristics  features of the body that  develop at puberty, as a result of the increased secretion of sex  hormones

seed  an ovule after fertilisation; it contains an embryo plant

selection pressure  an environmental factor that causes  organisms with certain characteristics to have a better chance of  survival than others

self-pollination  the transfer of pollen from the anther to the  stigma on the same plant (but not necessarily the same flower)

semen  a mixture of sperm and fluids from the prostate gland  and seminal vesicles seminal vesicles glands that secrete fluid in which sperm can  swim

sense organs  groups of receptor cells responding to specific  stimuli: light, sound, touch, temperature and chemicals

sensitivity  the ability to detect or sense changes in the  environment (stimuli) and to make responses

sexual reproduction  the process involving the fusion of  haploid nuclei to form a diploid zygote and the production of  genetically dissimilar offspring

sickle cell anaemia  a condition caused by a codominant allele  of the gene that codes for haemoglobin, in which a person has  two copies of the gene and suffers serious health problems

simple sugar  a monosaccharide; a carbohydrate whose  molecules are made of one sugar unit

species  a group of organisms with similar characteristics,  which can interbreed with each other to produce fertile  offspring

sperm  a male gamete

sphincter muscle  a muscle surrounding a tube, which can  contract to close the tube

spongy layer  the tissue beneath the palisade layer in a  leaf; it is made up of cells that contain chloroplasts and can  photosynthesise, with many air spaces between them

stamen  the male parts of a flower

starch  the polysaccharide that is used as an energy store in  plant cells

stem tuber  a swollen part of a stem, which stores food

stigma  the part of a flower that receives pollen

stimulant  a drug that makes the nervous system work faster

stimulus  a change in an organism’s surroundings that can be  detected by its sense organs

stoma (plural: stomata)  a gap between two guard cells, usually  in the epidermis on the lower surface of a leaf

stroke  damage caused to the brain by an interruption in blood  supply, caused either by a blood vessel bursting or a blood vessel  becoming blocked by a blood clot

style  the connection between the stigma and ovary of a flower

substrate  the substance on which an enzyme acts

succulent  a plant with swollen stems or leaves, in which water  is stored

sucrase  a carbohydrase found in the small intestine, which  breaks down sucrose to glucose and fructose

sucrose  a disaccharide, non-reducing sugar, made of a glucose  molecule and a fructose molecule linked together; the form in  which carbohydrates are transported in the phloem of plants

suspensory ligaments  a ring of ligaments linking the ciliary  muscles to the lens

systole  the stage of a heart beat in which the muscles in the  walls of the heart chambers contract

target organ  an organ that is affected by a hormone

tertiary consumers  organisms that feed at the fourth stage in a  food chain; they eat carnivores

test cross  breeding an offspring with the dominant phenotype  with an organism with the recessive phenotype; the offspring of  the cross can help to determine the genotype of the parent with  the dominant phenotype

testa  the tough waterproof covering of a seed

testis (plural: testes)  an organ in which sperm are made

testosterone  a hormone secreted by the testes, which causes  male characteristics

tissue  a group of cells with similar structures, working together  to perform specific functions

tissue fluid  the fluid that surrounds all the cells in the body,  formed from blood plasma that leaks out of capillaries

trachea  the tube that carries air from the nose and mouth  down to the lungs

translocation  the movement of sucrose and amino acids in  phloem, from regions of production to regions of storage, or to  regions of utilisation in respiration or growth

transpiration  evaporation of water at the surfaces of the  mesophyll cells followed by loss of water vapour from plant  leaves, through the stomata

transpiration stream  the pathway of water from the root hairs  of a plant, up the root and stem and out of the leaves into the  atmosphere

triceps muscle  a muscle in the upper arm which causes the  arm to straighten when it contracts

trophic level  the position of an organism in a food chain, food  web or pyramid of biomass, numbers or energy

tropism  a plant growth response to a stimulus, in which the  direction of growth is related to the direction of the stimulus

trypsin  a protease enzyme found in pancreatic juice

turgid cell  a plant cell that has absorbed water and has  cytoplasm that is pressing outwards on the cell wall

umbilical cord  an organ linking an embryo to the placenta,  containing blood vessels

urea  the main nitrogenous excretory product of mammals,  produced in the liver from excess amino acids

ureter  a tube that leads from a kidney to the bladder

urethra  a tube that leads from the bladder to the outside

urine  a solution of urea and other excretory products in water,  produced by the kidneys

uterus  the organ in a mammal in which the embryo develops

vaccination  the introduction to the body of dead or weakened  pathogens, to make a person immune to an infectious disease

vascular bundle  a vein in a plant, containing xylem vessels and  phloem tubes

vasoconstriction  narrowing of blood vessels

vasodilation  widening of blood vessels

villus (plural: villi)  a tiny, finger-like process on the inner wall  of the small intestine; villi increase the surface area for digestion  and absorption

water potential gradient  a difference in the concentration of  water molecules; a dilute solution has a high water potential,  and water tends to move from this, down a water potential  gradient, into a concentrated solution

xerophyte  a plant adapted to live in dry conditions

xylem vessels  long hollow tubes made up of dead, empty cells  with lignified walls, which transport water in plants and help to  support them

zygote  the diploid cell produced when two gametes fuse

Reproduction ——————— Sexual —>is a process involving the fusion of two gametes(sex cells) to form a zygote and the production of offspring that are genetically 

          |                                                        different from each other 

          |

          | 

     Asexual —> is the process resulting in the production of genetically identical offspring from one parent 

Asexual reproduction 

• It does not involve sex (or the production of gametes or a zygote)
• eg, bacteria reproduce by cell fission where they simply divided into two and each daughter cell becomes an independent bacterium 
• In unicellular organisms, the organism just divides into 2 whereas in complex organisms or multicellular organisms a part of the body grows and develops into a separate individual 

Asexual reproduction in Fungi 

Fungi have sexual and asexual methods of reproduction 

In asexual methods they form single celled, haploid spores that are dispersed into the air. Here, upon achieving suitable conditions, the grow new hyphae which develops into a mycelium 

Asexual reproduction in flowering plants 

Asexual methods for plant reproductions knows a s vegetative propagation 

Stolons and rhizomes 

• Eg of stolons , strawberry and buttercup 
• These plants have very short shoots and most of their shoot is below the ground 
• These stems o these short shoots are called rootstocks 
• The rootstock can give rise to leaves and flowers 
• Once the main shoot grows, the lateral buds produce long shoots that grow horizontally over the ground. 
• These shoots are called stolons and have only small leaves at their nodes and very long internodes 
• At each node isa bud that is capable of producing shoots as well as roots. 
• Thus a complete plant may develop at the node 
• The plant may be nourished initially by it’s parent by food send through the stolon 
• This changes however and the plant is able to fend for itself once the stolon dries up and withers. 
• In may plats, horizontal shoots arise from lateral buds near the stem base and grow under the ground. 
• Such underground horizontal stems are called rhizomes 
• At the nods of the rhizomes are buds which may develop to produce shoots above the ground. 
• The shoots become independent plants when the connecting rhizome dies 
• Eg of rhizomes – cough crass, bracken 

Bulbs and corms 

• Eg of bulbs, daffodil and snowdrop 
• They have very short shoots 
• Their stem is only a few mm long and they they have leaves which encircle the stem that are thick and fleshy with stored food 
• the food stored in the leaves is used up by a rapidly growing bud in spring and this produces a flowering stalk and a number of small leaves 
• During the growing season, food made is sent to the leaf bases and stored 
• These leaf bases swell and and form a new bulb ready for growth in the following year 
• Vegetative reproduction occurs when some of the food is sent to a lateral bud as well as the leaf bases. The lateral bud grows inside the parent bulb and is all produce a new, independent plant in the following year. 
• corms have a life cycle similar to that of bulbs, except that instead of the leaf bases, the stem swells up with stored food
• Vegetative reproduction takes place when a lateral bud on the short, fat stem grows into an independent plant 

Potatoes are stem tubers. lateral buds as the base of the potato shoot produce underground shoots(rhizomes)

These rhizomes sweet u with stored stretch and form tubers. Since the tubers are stems, they have buds 

If left in the ground, the tubers ca produce shoots, using food stored. Thus, potato can propagate vegetatively

Artificial Propagation 

This is method to exploit vegetative reproduction in order to produce fresh stocks of plants 

It does not occur naturally 

There are 2 methods involved – cuttings and tissue culture 

Cuttings 

• This a method of producing new individuals from certain plants by inserting a cut end of a hoot into water or moist earth
• Roots grow the base of the stem and the shoot continues to grow and produce leaves. 
• The cut end of the stem may be treated with rooting hormones to promote root growth 
• Evaporation from the shoot may also be reduced by covering it with a polythene or glass jar 
• Eg of plants produced by cuttings – carnations, germaniums and chrysanthemum 

Tissue culture 

• One a cell has become part of a tissue, it loss its ability to divide
• However the nucleus of the cell holds all the instructions for making a complete plant 
• In lab conditions, a single cell is cultivated and induced to divide and grow not an independent plant 
• One method is to take small pieces of the plant tissue from a root or stem and treat it with enzymes to separate it into individual checks 
• The cells are provided with plant hormones to induce ceel division 
• This eventually leads to the formation of roots, stems and leaves 
• Another method is place a small piece of tissue on a nutrient jelly. This causes the cells in the tissue to start dividing to produce many cells, forming a shapeless mass called a callus. 
• This callus is then provided with the appropriate hormones to cater for good growth of the plant. 
• Tissue cultures are an advantage as large number of plants can be produced from a small amount of tissue. 
• These plants also have the advantage that of being free from fungal or bacterial infections. 
• The plants produced in this way are called clones of each other as they have been produced by the same parent 

Asexual reproduction in animals 

Eg – hydra 

1. A group of cells on the column of the hydra start dividing and form bulge 
2. The bulge develops tentacles 
3. The daughter hydra pulls itself off the parent 
4. The daughter becomes an independent animal 

Advantages and disadvantages of asexual reproduction 

Advantages                                                                                                                                                              Disadvantages                                                                                       

 No mate is needed                                                                                                                                                    There is little variation created so adaptation to any environment is unlikely.                                                                                                                               

 No gametes are needed                                                                                                                                            The offspring is susceptible to diseases that parents might have 

 All the good characteristics are passed on from the parent to the offspring                                                           lack of dispersal can lead to competition for resources like water light and nutrients 

 When there is no dispersal, the offspring will grow                                                                             

 in the same favourable environment as the parent                                                                             

The plants tore large amounts of food that allow rapid growth under suitable conditions               

Sexual reproduction 

Fertilisation is the fusion of gametes 

Sexual reproduction involves the production of sex cells or gametes. The male and female gametes fuse together to form a zygote which eventually grows into a new individual 

In flowering plants, the male gametes are found in pollen grains and the female gametes, called egg cells, in the ovules 

In animals, male gametes are sperm and female gametes are eggs. 

in both plants and animals, the male gamete is microscopic and mobile whereas the female gametes are larger than the male gametes and ar immobile 

Pollination in plants and mating in ms animals causes the male and female to come close together 

Chromosome numbers 

Diploid number – somatic cell – 46 chromosomes 

Haploid number – gametes – 3 chromosomes 

The haploid chromosomes in the gametes fuse together to give a diploid number of chromosomes 

Advantages                                                                                                                                                                        Disadvantages 

There is variation in the offspring, making adaptation feasible                                                                                      Two parents  are usually needed                                                                                                             

New varieties can be created(with disease resistance for example)                                                                              The growth of a new plant from a seed is slow 

Seeds are produced in plants, allowing dispersal which educes the risk of competition for resources 

Sexual reproduction in plants 

Male organs – Stamens 

Female organs – Carpels 

After fertilisation, the carpel modifies itself and some part of it becomes the fruit and contains the seeds. 

In the flowers of most plants there are both stamens and carpels. Side they contain both male and female parts, they are known to be hermaphrodite or bisexual. 

The process that brings the male and female gametes close in plants is known as pollination 

Flower structure 

Petals 

• Brightly coloured and scented sometimes to attract insects for pollination 
• Usually arranged in a circle or cylinder 
• Have about 4 to 10 petals 
• Flowers of grasses and many tress don’t have flowers but have small, leaf-like structures that enclose the reproductive organs 

Sepals 

• Present outside petals in the form of a ring 
• They are often green 
• Much smaller than the petal 
• Protects the flower in its bud stage 

Stamens 

• Male reproductive organs
• Consists of a stalk called the filament along with an anther on the end 
• Plants may have many or a few stamens 
• Each anther consists of 4 pollen sacs in which pollen grains are produced by cell division 
• When the pollen grains are ripe, the pollen sac bursts and release the pollen 

Pollen 

• Insect pollinated flowers  produce smaller amounts pf pollen grain which are often round and sticky, or covered in tiny spikes to attach to the bodies of insects 
• Wind pollinated flowers tend to produce larger amounts of pollen grains which are smooth and light so it may easily carried away by the wind; large amounts sea needed as they have a great chance of being lost 

Carpels 

• Female reproductive organs 
• Plants may have many carpels or just one 
• Consists of an ovary, bearing a style and stigma
• Inside the ovary are one or more ovules 
• After fertilisation, the ovary becomes the fruit ad he ovules become the seeds 
• The style and stigma project out from the top of the ovary 
• The stigma has a stick surface and pollen grains stick to it during pollination
• The style need not be long 

Receptacle 

• All of the above flower structures are attached to the expanded end of a flower stalk. This is called the receptacle 
• In some cases, after fertilisation , the receptacle becomes fleshy and edible 

Pollination 

Pollination is the transfer of pollen grains from the anther to the stigma

Insect pollination  

• the plants are adapted to be able to become insect pollinated 
• They have bright petals and a nice scent which attract a variety of insects 
• Some flowers also produce nectar 
• Some of them are adapted to be pollinated by one one type of insect(honeysuckle ad foxglove)

Drugs 

A drug is any substance taken into the body that modifies or affects chemical reactions in the body. 

There are two types of drugs: Medicinal Drugs(to reduce symptoms like headaches, bacterial infections) and Misused Drugs(taken to provide stimulation, induce sleep and create hallucinations(recreational drugs), often illegally)

Medicinal drugs:

Antibiotics-

This has to be a chemical that destroys the pathogen without harming the tissues of the host. 

Eg: Penicillin, produced by mould fungus Penicillium 

How do antibiotics act on the pathogen without harming the host cell?

• They act by destroying the cell wall. Since animal/human cells do not contain a cell wall, the hosts cells are not affect and the pathogens are targeted and removed. 
• They can also act on 70S ribosomes, since human/animal cells produce 80S ribosomes. Thus, they do not affect the host cell. 

ANTIBIOTICS DO NOT ACT ON VIRUSES

This is because they viruses make use if the host cell to survive. 

It is also important not to use antibiotics in a diluted form, for too short a period or for a trivial complaints. It is also crucial to finish the course of the antibiotic as some of the bacteria that is being used to destroy will not be killed, but will become resistant to the antibiotic. This causes the antibiotic to become less effective. Eg:- MRSA(methicillin-resistant Staphylococcus aureus)

Misused Drugs 

Narcotics 

Heroin, morphine(depressants), codeine- made from Opium 

Once gotten addicted to, it gives temporary “high” feelings. When tried to give up, these drugs cause severe withdrawal symptoms. 

Alcohol

Alcohol acts as a depressant of The Central Nervous system. Small amounts give a sense of well being and release from anxiety. However, it causes a fall-down in any activity requiring skill 

It also gives a misleading sense of confidence(drunken drivers think they are driving extremely well)

Even a small amount in our blood increases our reaction time(the interval between receiving  a stimulus and making a response)(DON’T DRINK AND DRIVE)

It causes vasodilation in the skin, giving a sensation of warmth but in fact leading to a greater loss in body heat. 

Different amounts can lead to unconsciousness and even to death. 

The liver treats alcohol as a toxin and 90% of the alcohol is detoxified in the liver———— the oxidation of alcohol to carbon dioxide and water. Only 10% is excreted by the kidneys 

When the level of alcohol in the blood builds up to toxic proportions, it is called intoxication 

Some ppl build up a tolerance and dependence to alcohol, called alcoholism. 

High doses of alcohol can cause the liver cells to form too many fat droplets, leading to the disease cirrhosis.(A cirrhotic liver is less able to stop poisonous substances in the intestinal blood from reaching the general circulation. 

Pregnancy 

Drinking alcohol during pregnancy can present a major risk to the developing fetus(Fetal Alcohol Syndrome(FAS))

Behaviour 

Alcohol reduces inhibitions because it depresses the part of the brain that causes shyness. It can lead to being outroverted but can also lead to irresponsible behaviour like vandalism and aggression. 

Moderate Drinking 

A moderate intake of alcohol is ok 

Upper limits of alcohol for men: 21-28 units ——————over a one week period       

                                                                                                                |

Upper limits of alcohol for women: 14-21 units ——————————

Pregnant women should avoid alcohol together 

Smoking 

The short- term effects of smoking cause the bronchioles to constrict and the cilia lining the air passages  to stop beating 

The smoke also makes the lining to produce more mucus 

Nicotine, the addictive component of tobacco smoke, produces an increase in the rate of the heartbeat and a rise in blood pressure 

It may, in some cases cause an erratic or irregular heartbeat and a rise in blood pressure. 

Tar in cigarettes causes lung cancer. 

Carbon monoxide permanency binds with haemoglobin in RBC , reducing the smokers ability to provide oxygen to respiring cells. This results in the smoker getting out of breath easily and reduces physical fitness 

The long term effects can be severe, disabling and often lethal 

Lung Cancer 

Cancer is a term used for diseases in which cells become abnormal and divide out of control. Tar , a carcinogen(cancer causing substance, increases the risk of the lungs becoming cancerous. 

This causes tumours to develop(balls of abnormal cells which do not allow gaseous exchange like normal cells)

The higher the no o cigarettes soaked, the greater the risk of cancer. 

Chronic Obstructive Pulmonary Disorder(COPD)

Eg:- Chronic Bronchitis, Emphysema and Chronic Obstructive Airways Disease. 

Symptoms are breathing difficulties (because of the narrowing of the airways(bronchi and bronchioles)), breathlessness when active, frequent chest infections and a persistent cough with phlegm 

Emphysema 

Emphysema is a breakdown of the alveoli. The action of one or more substances in tobacco smoke weakens the walls of the alveoli. This results in smoker’s cough which may burst some of the  weakend alveoli. In time, the absorbing surface of the lungs is greatly reduced. Then the smoker cannot oxygenate his or her blood properly and the least exertion makes one breathless and exhausted. 

Chronic Bronchitis 

The smoke stops the cilia from beating in the air passages and so the irritant substances in the smoke and excess mucus collect in the bronchi. This leads to an inflammation called bronchitis

Heart Diseases 

Coronary Heart disease is the leading cause of death in most developed countries. It results from the blockage of the  coronary artery by fatty deposits. This reduces the supply of oxygenated blood to the hear and may lead to heart failures. High BP, diets with too much animal fat and lack of exercise also may cause it, but mostly it is caused by smoking. 

The nicotine and carbon monoxide from cigarette smoke increase the tendency for the blood to clot and so block the coronary arteries, already partially blocked by the fatty deposits. The carbon monoxide increases the rate at which the fatty material is deposited at the arteries. 

Other risks 

Leg amputations

Strokes

Cancer of the bladder

Babies born to smokers are smaller in average 

Twice the frequency of miscarriages

50% higher still- birth rate for babies

26% higher death rate for babies 

Passive Smoking 

It is not only the smokers who re affected but even the non- smokers in the same room are affected 

Reducing the Risks 

By giving up smoking, a person who smokes unto 20 cigarettes a day will, after 10 years, be at no greater risk than a non- smoker of he same age. A pipe or cigar smoker, provided he or she doesn’t inhale, is at a less risk than a cigarette smoker but greater risk than a non- smoker 

Chapter 1 : CHARACTERISTICS AND CLASSIFICATION OF LIVING ORGANISMS 

Characteristics of living organisms:

• All organisms, whether they are unicellular or multicolour have certain common characteristics. They can be shown by the acronym MRS GREN 

• M-movement-action by an organism causing a change of position or place.
• R-respiration- describes the chemical reactions in cells that break down nutrient molecules to release energy
• S-sensitivity-the ability to detect and respond to changes in the environment(stimulus)
• G-growth-permanent increase in size 
• R-reproduction-process of making more of the same type of organism
• E- excretion -removal from organisms of toxic materials and other substances in excess of requirements 
• N- nutrition- taking in of materials for energy, growth and development 
•  

Concept and use of a classification system 

• There are two types of classification- Artificial and Natural
• The Artificial system involves classifying organisms according to their colour, habitat, etc . This however, is an inefficient method and therefore organisms cannot be classified correctly in this method
• The Natural system of classification involves classifying organisms on the basis of shared features. This is a much more efficient method than Artificial classification 
• Species: A group of organisms that can reproduce to produce fertile offspring 
• Closely related species are grouped into a genus 

Binomial nomenclature 

• This is a way of grouping organisms in two names- the genus name and the species name 
• The binomial system of naming organisms is an internationally agreed system of classification where organisms are given Latin names for universal recognition 
• Eg: the stoat is Mustella erminea and the the weasel is Mustella nivalis. Both these organisms belong to the same genus(Mustella) but are of different species(erminea and nivalis respectively)
• The first letter of the generic name is always given in capital and the the specific name always starts with a small letter. Both the names are in italics 

Types of classification

• Morphology is the study of the form, or outward appearances of organisms 
• Anatomy is the study of the internal structure of the organism, as revealed by dissection 
• Cladistics is the classification of organisms based on whether or it they have one or more shared unique characteristics derived from the group’s last common ancestor, which are not present in more distant ancestors. Organisms which share a more recent ancestor(and are, therefore, more closely related) have DNA base sequences that are more similar than those that share only a distant ancestor 

The Five Kingdom Classification 

• Animals 
• Plants 
• Fungi 
• Prokaryotes 
• Protoctists 

The Animal Kingdom 

• Animals are classified into two groups: the arthropods and the vertebrates 

Arthropods 

• There are four classes of Arthropods
• They have a segmented body with a waterproof exoskeleton and are invertebrates(they have no backbone or spinal cord). They have jointed legs as their exoskeleton prevents movement 
• Insects 

Insects are the class of Arthropods that have their body divided into three parts, mainly the head, thorax and abdomen. The breathe through trachea, they have 1 or 2 pairs of wings and 3 pairs of jointed legs. They also have 1 pair of antenna and compound eyes 

Eg: cockroach, other insects

• Crustaceans 

They breathe through gills and live in very wet places, hence many of them are aquatic. 

Eg: crabs, woodlice 

• Myriapods

They are the centipedes and millipedes. They have a long, thin body with many segments and their bodies are not obviously divided into a thorax and abdomen. They have simple eyes and one pair of antennae. 

• Arachnides

These are land dwelling organisms. They have four pairs of legs and their body is divided  into a cephalothorax and abdomen. They have no wings and several pairs of simple eyes. They all have piercing jaws and chelicerae(poison fangs). They also have pedipalps to aid in reproduction.

Eg: Spiders and Scorpions 

Vertebrates: 

• This is the class of beings with a backbone 
• They are either poikilothermic (they have a variable body temperature) or homeothermic ( they have a constant body temperature) 
• They are divided into five classes:
• Fish 

They are poikilothermic organisms. They have eyes. They have external fertilisation and they produce jelly covered eggs in water. They have scales and a lateral line on their body to detect vibrations in the water. They breathe  through gills.

• Reptiles

They are poikilothermic organisms. They lay soft shelled eggs on land and have internal fertilisation. They have dry skin and scales and have four limbs( except for snakes). They breathe through lungs. they have eyes and ears 

• Amphibians 

They are poikilothermic organisms. They lay jelly covered eggs in water. They have eyes and ears and have four limbs. They go through external fertilisation and 

• Birds 
• Mammals